Title of Invention	A METHOD AND APPARATUS FOR PRODUCING TITANIUM-ALUMINIUM COMPOUNDS
Abstract	The present invention relates to a method and apparatus for the production of titanium alloys and titanium-aluminium inter-metallic compounds and alloys. Starting from a precursor material including titanium subchloride (titanium trichloride or titanium dichloride), the precursor material is reduced by aluminium tc produce titanium-aluminium intermetallic complexes or alloys and aluminium chloride which is driven away from the reaction zone so as to favour the forward reaction and the production of the titanium-aluminium compounds. Starting from a precursor material of titanium subchloride avoids the problems associated with starting from titanium metal (which is expensive to produce) or titanium tetrachloride (a reaction very difficult to 0control), and results in the production of powdered forms of titanium-aluminium compounds with controllable composition.

Title of Invention

A METHOD AND APPARATUS FOR PRODUCING TITANIUM-ALUMINIUM COMPOUNDS

Abstract

The present invention relates to a method and apparatus for the production of titanium alloys and titanium-aluminium inter-metallic compounds and alloys. Starting from a precursor material including titanium subchloride (titanium trichloride or titanium dichloride), the precursor material is reduced by aluminium tc produce titanium-aluminium intermetallic complexes or alloys and aluminium chloride which is driven away from the reaction zone so as to favour the forward reaction and the production of the titanium-aluminium compounds. Starting from a precursor material of titanium subchloride avoids the problems associated with starting from titanium metal (which is expensive to produce) or titanium tetrachloride (a reaction very difficult to 0control), and results in the production of powdered forms of titanium-aluminium compounds with controllable composition.

Full Text	Field of the Invention The present invention relates to a method and apparatus for the production of metal and metal compounds and, particularly, but not exclusively, to a method and apparatus for production of titanium-based alloys and intermetallic complexes, and more particularly, but not exclusively, to a method and apparatus for the production of titanium-aluminium based alloys and intermetallic complexes, and more particularly, but not exclusively, to a method and apparatus for the production of titanium- aluminium based alloys and intermetallic complexes in a powder form. Background of the Invention Titanium-aluminium alloys and inter-metallic compounds (generically termed herein "titanium-aluminium compounds") are very valuable materials. However, they are difficult and expensive to prepare, particularly in the preferred powder form. This expense of preparation limits wide use of these materials, even though they have highly desirable properties for use in automotive, aerospace and other industries. Titanium minerals are found in nature in the form of a very stable oxide (TiO2) . Common processes for the production of ' titanium are the Kroll process and the Hunter process. The Kroll process requires the use of magnesium as a reducing agent to reduce TiCl4 (prepared from the oxide by a pre-process of chlorination) to produce the Ti metal. The Hunter process requires the use of sodium as the reducing agent. Because TiCl4 is still thermodynamically stable, highly reactive reducing agents such as magnesium or sodium are required to produce titanium metal out of TiCl4. Such highly reactive reducing agents are difficult and expensive to handle. As the magnesium chlorides in the case of the Kroll process are stable up to temperatures in excess of 130OK, the product is often in the form of a Ti sponge mixed with MgCl2 and remnants of Mg and TiCl2. To obtain pure Ti, the product requires extensive post-processing, including washing and melting in a vacuum arc furnace to remove all impurities. This contributes to the present high cost of the production of titanium. In the known technologies for production of titanium alloys such as Ti-Al-V, and intermetallic compounds such as Ti3Al, TiAl, TiAl3, Ti-Al- (Cr, Hb, Mo, etc) and alloys based on these compounds, appropriate amounts of sponges, ingots or powders of the metals which comprise these alloys are milled or melted together and annealed, hence adding to the production cost, particularly as it is necessary to obtain the metals first which, as discussed, in the case of titanium, involves considerable expense. For production of a powder of these titanium alloys and intermetallic compounds, further processing is usually required, adding to the already high production cost. Prior Al-based processes for manufacturing of Ti-Al compounds include starting from Al powder and Ti powder (references: (I.Lu, M.O. Lai and F.H. Froes, Journal of Metals, February 2002, p62) and (N. Bertolino et al.. Intermetallies, Vol 11, 2003, p 41} and reduction of TiCl4 with A1C1 {US patent application US2002/0184 971 Al). For the first process, the starting materials are Al and Ti powders, the powders usually being mechanically milled to make a uniform mixture followed by heating in a furnace. The resulting materials are at best in the form of solid lumps and this process is usually unable to produce fine powder. Furthermore, the resulting compounds often require heat treatment to produce the required material properties. For the second process, Al metal is heated in the presence of chlorine at temperature around 1200C to produce gaseous AlCl that is then reacted with TiCl4 in the gas phase to produce powders of titanium aluminides. Both these processes are quite complex and costly to operate. It is also known to perform direct reduction of TiCl4 with aluminium. However, this results in the production of an uncontrollable composition of compounds and production of a single phase material such as TiAl has not been achieved (see in particular S J Gerdemann & D E Alman, page 3341 in Gamma Titanium Alumini 1999, edited by- Kim, Dimiduk & Loretto, The Minerals Metals and Materials Society USA) - Over the past several decades, there have been extensive attempts made to replace the existing Kroll and Hunter technologies using techniques such as electrowinning, plasma-hydrogen and also aluminothermic reduction. The use of hydrogen plasma for the reduction of titanium chloride in a plasma atmosphere is difficult due to unfavourable thermodynatnic characteristics, since chlorine preferably reacts with titanium in the reverse reaction to produce titanium chlorides, hence degrading the quality of the produced Ti powder and.limiting the efficiency of the method. In a process disclosed in US Patent 5,935,293, a fast quench reactor was used to cool down the plasma in order to prevent recombination processes leading to formation of titanium chlorides. According to the description in US Patent 5,935,293, the process is highly energy expensive relative to the existing Kroll technology. In another process (G.Z. Chen, D.J. Fray and T.Vf. Farthing, Nature, Vol 407, (2000), 361), Chen et al. made titanium sponge directly from the oxide by reduction in a molten calcium chloride salt. Oxygen from the titanium oxide recombines with carbon at an anode to form CO2. However, the composition of the resulting sponge-like titanium product produced corresponds to the composition of the starting minerals. The process is still under development and is yet to be demonstrated on an industrial scale. Attempts have been made to uBe aluminium as a reducing agent for TiCl4 in plasma systems. For reduction of TiCl* using aluminium, the products are in the form of solid phase titanium-aluminium intermetallic compounds mixed with aluminium chloride and some residual titanium dichloride. A description of various attempts using aluminium together with a description of the thermodynamics of the process are given by Murphy and Bing {High Temp. Chem. Processes, Vol 3, 365-374, 1994). Because of difficulties associated with gas phase reactions it has not been possible to produce titanium and/or titanium-aluminium compounds by direct aluminothermic reduction of titanium chlorides. Summary of the Invention In accordance with a first aspect, the present invention provides a etepwise method of producing titanium-aluminium compounds, comprising a first step oft - reducing an amount of titanium chloride (TiCl) with an amount of aluminium at a temperature to trigger reactions to form titanium subchloride(s) and aluminium chloride (AlCl3) products; and then a second step of: - mixing said products, with the addition of more aluminium if required, and heating the mixture in a reaction zone to a temperature above 3 00C to form AICI3 in a gas phase, and to produce an end product in the reaction zone of the titanium- altmiinium compounds. When the term titanium subchloride is used, it can. refer to titanium trichloride TiCl3 and/or titanium dichloride TiClj or other combinations of titanium and chloride excluding. TiCl4 which is referred to herein as titanium chloride. When the term titanium compound is used, it can refer to titanium alloyB and/or titanium/metal intermetallic compounds. In one preferred form which is referred to herein, the titanium compounds include titanium-aluminium alloys and/or titanium-aluminium intermetallic compounds. In one embodiment, the method can also comprises the step of driving the removal of A1C13 away from the reaction zone to favour a forward reaction in the second step. In one form, the step of removing the A1C13 from the reaction zone is continuous- In one embodiment, the first step can be conducted at a temperature above the boiling point of AlCla. In another embodiment, the first step can be conducted at a temperature above 200C, In one embodiment of the method, the first step can be conducted with an excess amount of aluminium present to reduce all of the titanium chloride (TICI4) to form said titanium subchloride(s) and aluminium chloride (AICI3) products. In one embodiment, TMCI3 is prepared by the reduction of T1C1.4, although this reaction may also form titanium dichloride TiCla. In one embodiment of the method, the second step can be conducted at a temperature in the range 300C to 1000C. One embodiment of the method can comprise the further step of recycling at least some o£ the aluminium chloride formed, and utilising the aluminium chloride to produce Tid.4. The aluminium chloride can be used to reduce titanium oxide to produce TiCl4. In any of the embodiments of the method mentioned, aluminium oxide can be produced by the reduction of titanium oxide and the aluminium oxide electrolysed to produce aluminium raw material for use in the steps of said method. 1 In one embodiment of the method, the aluminium chlorides can be condensed away from the reaction zone at a temperature lower than that in the reaction zone. In one embodiment of the method, if titanium subchloride escapee the reaction zone it can be condensed at a temperature different to that in the reaction zone. Furthermore the condensed titanium subchloride can optionally be returned to the reaction zone. In further embodiments of the method, the precursor material can include a source of one or more elements selected from the group comprising chromium (cr), niobium (Nb), vanadium (V), zirconium (Zr), silicon (SiJ, boron (B), molybdenum (Mo), tantalum {Ta) and carbon (C), and products of said method can include titanium-aluminium compounds which include one or more of these elements. The source of the element(s) can be a metal halide, a subhalide, a pure element or another compound which includes the element. The products can also include one or more of an interrnetallic compound/ a titanium- (selected element)-alloy, and intermediate compounds. The source may also include a source of other precursors containing a required alloy additive, depending upon the required end product. In one form of the method, the source can include vanadium subchloride, auch as vanadium trichloride and/or vanadium dichloride, and a product of said method is an alloy or intermetallic complex including titanium, aluminium and vanadium. This method can comprise the steps of adding the source in appropriate .proportions, and carrying out the method to produce T1-6A1-4V. In a further form of the method, the source can include zirconium subchloride, and a product of the method is an alloy or intermetallic complex including titanium, aluminium, zirconium and vanadium. In one form of the method, the source can include niobium halide and chromium halide, and a product of said method is an alloy or intermetallic complex including titanium, aluminium, niobium and chromium. This method can also comprise the step of adding the source in appropriate proportions, and carrying out the method to produce Ti-48Al-2Nb-2Cr. In one embodiment of the method/ the aluminium can be added in the form of a powdei having an approximate upper grain size of less than about 50 micrometres. In an alternative form of the method, the aluminium can be in the form of a powder of an approximate upper grain size of greater than about 50 micrometres, and the method comprises the step of milling the aluminium powder and titanium subchloride to reduce the grain size of the aluminium powder in at least one dimension, in yet another alternative form of the method, the aluminium can be in the form of flakes having a thickness in one dimension of less than about 50 micrometres. Using a fine aluminium powder is preferred, although the relatively coarser aluminium powder or flakes is a cheaper raw material. In an embodiment, the method is conducted in an inert gas atmosphere or in a vacuum. In any of the embodiments described, the method can also include a pre-processing step of forming the titanium subchloride as precursor material. The inventor has found that using a precursor material which includes titanium subchloride (preferably titanium trichloride) gives a number of advantages. There are not the problems of different; uncontrollable phases which are involved in starting from titanium tetrachloride as a precursor. The composition of the end product is relatively controllable and depends on the ratios of the starting materials. The correct ratios of starting materials are incorporated in the precursor materials to produce the appropriate proportions of components in the product. The inventor believes that the new method enables a cheaper and more controllable process for the production of titanium-aluminium compounds. It is not necessary to convert the raw titanium minerals to titanium metal, as in some of the prior art processes discussed earlier. In one ¦embodiment of the present process, titanium oxide can be chlorinated using conventional technology to give titanium tetrachloride. This can then be reduced using aluminium or hydrogen to give titanium subchlorides (mainly titanium trichloride); which can then be used as the precursor material for the formation of the titanium-aluminium compounds. It is possible to form TA-6A1-4V using this process, which is one of the major titanium alloys used. It is also possible to form Ti-48Al-2Nb-2Cr. It is also possible to form other alloys such as Ti-Al-Nb-C, and Ti3Al based alloys. A process in accordance with embodiments, of the present invention described has the advantage that alloy powder is produced directly, with no further physical processing. In accordance with a second aspect, the present invention provides a method for production of a powder of titanium-aluminium intermetallic compounds including at least one of Ti3Al, TiAl and TiAl3, and alloys based on titanium-aluminium intermetallics, as defined in the first aspect, and wherein starting materials for the method include aluminium powder and titanium chloride. In accordance with a third aspect, the present invention provides a method of producing titanium- aluminium compounds, comprising a first step of-; - heating an amount of titanium chloride (TiCl4) in a plasma of an inert gas and hydrogen mixture, to produce titanium subchloride(s); and then a second step of: - mixing aluminium with said titanium subchloride(s), and heating the resultant mixture to produce titanium-aluminium compounds and A1C13. In one embodiment, the method of the third aspect can be otherwise as defined in the first aspect. In accordance with a fourth aspect, the present invention provides a stepwise method of producing titanium-aluminium compounds, comprising a first step of: - reducing an amount of titanium chloride (TiCl with hydrogen in an inert gas atmosphere or in a vacuum, and at a temperature to trigger reactions to form titanium subchloride(s) and aluminium chloride (A1C13) products; and then a second step of: - mixing said products with aluminium, and heating the mixture in a reaction zone to a temperature above 300C to form A1C13 in a gas phase, and to produce an end product in the reaction zone of the titanium-aluminium compounds. In one embodiment, the method of the fourth aspect can be otherwise as defined in the first aspect. In accordance with a fifth aspect, the present invention provides a stepwise method of producing titanium-aluminium compounds, comprising a first step of: - heating' a mixture of Ticl* and aluminium to form products TiCl3 and A1C13, at a temperature leas than 300C; and then a second step of: - mixing said products, with the addition of more aluminium if required, and heating the mixture to a reaction zone temperature above 300C to cause AICI3 to be evaporated from the reaction zone and to form titanium-aluminium compounds. In one embodiment, the method of the fifth aspect can be otherwise as defined'in the first aspect. In accordance with a sixth aspect, the present invention provides a stepwise method of producing a metal- aluminium compound, comprising the first step of: - adding a reducing agent to reduce an amount of a metal halide to form metal subhalide(s); and the second step of: - mixing said metal subhalide(e) with aluminium, and heating the mixture in a reaction zone to a temperature above 300C to form aluminium halides in a gaa phase, and to produce an end product in the reaction zone comprising a metal compound containing a percentage of aluminium. In one embodiment of this method, the reducing agent can be selected from the group comprising zinc, magnesium, sodium, aluminium or other like metals. In one embodiment the metal halide can be a titanium subhalide such as titanium trichloride, and a product of the reaction can include titanium compounds. In one embodiment, the method of the sixth aspect can be otherwise as defined in the first aspect. In any of the embodiments described, the method can also comprise the further step of adding a reagent to a product of the method, to produce a further product. In accordance with a seventh aspect, the present invention provides a method for the production of vanadium and/or vanadium compounds, comprising the Bteps of mixing aluminium with a precursor material including vanadium subhalide, and heating the mixture, to form aluminium halides and vanadium and/or vanadium compounds. In one embodiment, the vanadium compounds may include vanadium-aluminium alloys and/or vanadium aluminium intermetallic complexes. In accordance with an eighth aspect, the present invention provides a method for the production of zirconium and/or zirconium compounds, comprising the steps of mixing aluminium with a precursor material including zirconium subhalide, and heating the mixture, to form aluminium halides and zirconium and/or zirconium compounds. In one embodiment, the zirconium compounds may include zirconium-aluminium alloys and/or zirconium- aluminium intermetallic complexes. In accordance with a ninth aspect, the present invention provides an apparatus for the production of a metal compound, comprising: - a reaction vessel arranged in use for the mixing of aluminium with a metal halide or subhalide; the vessel also adapted in use for the resultant mixture to be heated to a temperature sufficient for the metal halide or subhalide to react with the aluminium to form the metal compound and an aluminium halide; - one condensation zone arranged in use to operate at a temperature such that any metal halide or subhalide escaping the reaction mixture condenses in that condensation zone; and - another condensation zone arranged in use to operate at a temperature such that the. aluminium halide condenses in the another condensation zone. In one embodiment, the apparatus also can comprise a third condensation zone arranged to condense metal halide that is produced by dieproportionation from escaping the reaction mixture. In a further embodiment, the one condensation zone can be arranged to return condensed metal halide or subhalide to the reaction zone. In one embodiment, the reaction zone operates at a temperature Tl and the first condensation zone at a temperature T2 which is lower than the temperature Tl. In one form, the second condensation zone operates at a temperature T3 which is between Tl and T2. In one example, the precursor material may be a material containing titanium as a component, such as titanium trichloride and/or titanium dichloride. Where the precursor material includes titanium trichloride and where the apparatus includes a first condensation zone that operates at temperature T2, T2 is preferably below 200C, wherein gaseous aluminium trichloride emanating from the reaction zone is condensed. When the apparatus includes a second condensation zone, T3 is below 500C and titanium trichloride which escapes from the reaction zone is recondensed at the second condensation zone. In one embodiment, the second condensation zone is located between the reaction zone and the first condensation zone. Typically the apparatus includes a heating arrangement for heating the precursor material, In some embodiments, openings are provided for the introduction of further gases. Openings may also be provided to evacuate the vessel to a low pressure. In still further embodiments, the reaction vessel may be a number of discrete vessels, each vessel providing a different reaction or condensation zone. Preferably, the apparatus of this aspect of the invention ie suitable for implementing the method of any of the foregoing or following aspecte of the invention described herein. in accordance with a tenth, aspect, th& present invention provides an apparatus for the production of at least one of a titanium compound, another metal compound or a product, wh«n the apparatus is used with the method as defined in any one of the first to the eighth aspects. In accordance with an eleventh aspect, the present invention provides at least one of a titanium compound/ a metal compound or a product produced by either the apparatus or the method as defined in any one of the first to the ninth aspects. Brief Description of the Accompanying Drawings Features and advantages of the present invention will become apparent from the following description of embodiments thereof, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows the Gibbs energy of formation of AlCl3:gi/ TiCl3 and TiClj + Ti-Al; Figure 2 shows the total Gibbs free energy for reactions leading to formation of Ti-metal based compounds; Figure 3 illustrates the equilibrium composition of TiCl4 - Hydrogen plasma at temperatures of between 300K and 5000K; Figure 4 is a schematic diagram of an apparatus for implementing a process in accordance with an embodiment of the present invention; Figure 5 is a schematic diagram of a further embodiment of an apparatus for implementing a process in accordance with an embodiment of the present invention; Figure 6 is a schematic diagram illustrating a process for production of titanium based compounds in accordance with an embodiment of the present invention; Figure 7 illustrates the Gibbs free energy for half reactions leading to the formation of titanium- tetrachloride; Figure 8 is a schematic diagram illustrating a process for production of titanium based compounds in accordance with a further embodiment of the invention; Figure 9 is an XRD spectrum for a T1-6A1-4V powder produced by an embodiment of the present invention; and Figure 10 is an XRD spectrum for a Gamma TiAl compound produced by an embodiment of the present invention. Description of Preferred Embodiments The following description is of preferred embodiments of processes for producing metal compounds, including fine powder and ingots with specific compositions. The processes are useful for production of forms of metals such as titanium, vanadium and zirconium together with alloys and intermetallic compounds of these metals with a controllable amount of aluminium. For example, Ti-Al, Ti3Al, TiAl3, Ti-Al-Cr and Ti-V- Al can be made with accuracy by varying the aluminium content. The relative amounts of titanium chlorides and aluminium are determined by the required composition of end product. In one embodiment the process comprises the steps of preparing solid metal halides, mixing the halides with aluminium metal and heating the mixture to a temperature Tl to trigger reactions leading to formation of aluminium chloride at a temperature (Tl) above the boiling temperature of aluminium chlorides, and condensing the aluminium chlorides away from the reaction zone at a temperature T2, where T2 is less than Tl. The driving of the aluminium chloride away from the reaction zone moves the equilibrium of reaction in the forward direction i.e. to formation of aluminium chloride and metal (and other products depending upon reaction conditions and components). For titanium compounds, titanium subchlorides, (preferably titanium trichloride TiCl3) can be produced from a precursor material of TiCl4. The TiCl3 is mixed with aluminium and then heated to a temperature above 300C so that AICI3 is formed in the gas phase and the AlCl3 is condensed away from the reaction zone at a temperature below 200C, leaving a powder of Ti in the reaction zone containing a percentage of aluminium, as required for the end product. In one embodiment, the process comprises the steps of heating TiCl4 in a plasma of an argon-hydrogen mixture to produce TiCl.3, and then mixing the resulting TiCl3 powder with aluminium and then heating the mixture to trigger the reaction. The reaction vessel used is arranged to ailow for aluminium chloride to be continuously removed and condensed in a region away from the reaction zone of the titanium chloride and aluminium mixture. The T1CI3, and aluminium in a powder or a lump form (but preferably in a powder form) are mixed together under inert gas or in a vacuum. The mixture is then heated to a temperature of several hundred degrees to trigger reaction between the two compounds, leading to formation of AlCl3(gj. The A1C13 is then condensed elsewhere in the vessel at a temperature below 200C- In a further embodiment, the process comprises the steps of heating predetermined amounts of TiCl4 and aluminium to form TiCl3 and A1C13, heating the product mixture to a temperature above 3O0C and providing foor A1C13 to be evaporated from the reaction zone. The Ald3 was driven away from the reaction and condensed away from the reaction zone at a temperature below 2 00C. Further aluminium material was then added to the product in an amount depending on the required composition, and then the mixture was heated under the same physical conditions to a temperature above 300C to trigger chemical reactions leading to formation of AlCl3(g) whilst providing for the AlCl^g) to be condensed elsewhere in the vessel at a temperature below 200C. The overall reactions between titanium subchlorides TiCl3 and Al occur in the following form-. TiCl3 + Al «* Ti where Al is present in the solid or liquid phase. The presence of Ti and Al may lead formation of Ti-Al intermetallic compounds such as TiAl3(S), TiAl TisAlte). Then TiCl3 may react with aluminium according to the following simplified reactions: TiCl3{g) + TiAl3(s> ** 2 TiAly + AlCl3{g> (2) TiCl3(g) + TiAl(S) * 2 TixAly + AlCl3(g, (3) TiCl3{g) + Ti3Al(a, ? 2 TixAly + AlCl3(gj (4) Reactions 1-4 are driven in the forward direction by continuous removal of A1C13 from the reaction zone. As a result, equilibrium is moved to the right and the reaction proceeds "until completion. The inventor has found that the reaction proceeds slowly at temperatures slightly above 200C under an argon atmosphere at 1 atmosphere. The reaction becomes very rapid at temperatures above 500C as the Gibbs free energy of the total reaction becomes negative as seen in Figures 1 and 2. Figure 1 shows the Gibbs energy for AICI3, TiCl3 and TiCl3+Ti-Al. Figure 2 shows the total Gibbs energy for Reactions 1-4 leading to formation of solid titanium. Because of the strong affinity between titanium and aluminium, the presence of Al and Ti may result in formation of titanium-aluminium alloys and/or intermetallic compounds TixAly. For these compounds, the Gibbs energy of formation AGf is generally less than 32kJ.mole~1 for aluminium concentrations up to 80% of the alloys (R.G.Reddy et al. J. Alloys and Compounds, vol 321 (2001) 223) - Figure 2 shows the variation with temperature of the total Gibbs energy for reactions leading to formation of AlCl3(g) and Ti(S), starting from TiCl3 and Al. Also shown in Figure 2 is the total Gibbs energy for reaction leading to formation of Ti{S) and AlCl3(g), starting from TiCl3 and Ti-Al compounds. The total Gibbs free energy for Ti-Al is taken to be ~32kJ.roole~1. It is usually considered that chemical reactions proceed rapidly for negative values of the total Gibbs energy of the reaction. It is seen in Figure 2 that AG is negative at temperatures above 800K (525C) for Reaction 1. This is in excellent agreement with the experimental observations which show rapid reaction between TiCl3 and Al at a temperature of SOOC in an argon atmosphere at 1 atmosphere pressure. The inventor found that as the temperature of the mixture TiCl3-Al increased above 3 00C, a cloud of white fume moved from the reaction zone towards the cold region of the vessel where it recondensed to form solid AlCl3. At temperatures above 500C, the reaction became almost spontaneous, which is in agreement with the results shown in Figure 2. For reactions involving Ti-Al compounds, the inventor found that in argon at 1 atmosphere pressure, reactions leading to formation of Ti(S) and TixAly (Reactions 2, 3 and 4} seem to proceed rapidly at temperatures above 850C. Titanium chlorides may escape from the reaction zone, or disproportionate during heating. Gaseous TiCl3 that may evaporate during the heating process reacts more readily with Al and further enhances formation of Ti compounds. For a mixture of TiCl3 and Al powder, with the ratio of [Al]/[TiCl3] > 1, the inventor found that only small quantities of less than a few percent of TiCl3 escape the reaction 2one, and are recondensed in a region of the vessel at a temperature around 50 OK and introduced back into the reaction sone, or alternatively collected for reprocessing. Any TiCl2 that is produced due to disproportionation, reacts with Al compounds faster than TiCl3 and enhances reactions, leading to formation of Ti compounds. The inventor found no evidence of major losses due to escape of TiCL. The inventor has made experimental observations which suggest that, for production of titanium with a high aluminium content, disproportionation reactions have little or no significant impact on the efficiency of the process, since most of the Ti in the feedstock materials was able to be accounted for. For production of titanium with a low aluminium content, the initial amount of aluminium used is less than the stoichiometric amount needed to remove all of the chlorine from the TiCl3 materials. Excess titanium chloride remaining after depletion of available aluminium, is evaporated from the product and condensed, elsewhere for reprocessing. Production of TiCl3 can be carried out from TiCl4 using a hydrogen plasma route or through reduction with aluminium. Production of TiCl3 in a hydrogen plasma, known as the Huel process, has been used in industry for several decades. Figure 3 shows the composition of TiCl4-Hydrogen plasma at temperature between 30OK and 500OK. It is seen that TiCl4 can be converted into solid TiCl3 by reacting it with hydrogen in a plasma. It is also seen that the conversion rate is almost 100%. The energy cost for synthesis of solid TiCl3 is very low as the overall reaction leading to TiCl3: TiCl4£3) + (1/2)H2 e* TiCl3(s) + HCl with AH=50 KJ/mole. For reduction of TiCl4 with aluminium, the process is usually carried out in closed vessel containing appropriate amounts of TiCl4 and Al at a temperature above 2Q0C, leading to formation of a mixture of TiCl3 and A.lCl3. Pure TiCl3 is obtained from the mixture by distillation at temperature above 200C and. allowing AlCl3 to condense elsewhere. For the process disclosed herein, production of titanium-aluminium compounds is made by mixing titanium subchlorides, preferably TiCl3/ with aluminium in a powder form, placing the materials in a vessel under vacuum or in an inert atmosphere, and heating the mixture. For processing under flowing inert gas or under vacuum, A1C13 formed due to reactions described above is driven into a different part of the vessel at a temperature below 200C. This favours the forward reaction formation of the aluminium halide. ' The heating continues until the reactions proceed to completion, or until complete depletion of available titanium subchlorides and/or aluminium occurs. Figure 4 shows a simple system used to make Ti-Al compounds with different Al contents and compositions. For this configuration, a mixture of TiCla and Al, fl) , is placed into a vessel (2) and heated to a temperature higher than 3 00C (typically up to a temperature of the order of 1000C depending on the composition of the mixture) . Reactions between TiCl3 and Al in the vessel (2) lead to formation of gaseous A1C13. A stream of argon gas (10) that is introduced in the vessel (2) carries the gaseous AlCl3 together with any titanium chlorides that may escape from the reaction zone and drives them through a second vessel (3) which is held at a temperature between 3 00C and S00C, so that TiCl3 is recondensed while AlCl3 remains in. the gas phase. Alternatively, TiCl^ may be recondensed on the upper walls of the vessel (2) if it is held at an appropriate temperature. The remaining AlCl3 together with any TiCl4 that may have formed in the reaction zone due to disproportionation is driven through a vessel (4) at a temperature higher than 136C and lower than 200C so that A1C13 is recondensed, and the remaining TiCl4 is driven into a vessel (5) which is held at room temperature. The remaining argon gas is discharged out of the system or recycled. Typically the gaseous atmosphere in the vessel is an inert gas, such as argon, helium, neon, xenon. Reactive gases such as methane or oxygen are undesirable as they can chemically react with the mixture resulting in other products. It is noted that the reactions can also be conducted in the absence of a gaseous atmosphere (eg under vacuum). The TiCl3 and an aluminium powder, the relative mass of which compared to the mass of TiCl3 depends on the composition of the required product, are introduced into a vessel as described above and then heated until the reaction is complete. For these processes described above, the product is typically in the form of a fine powder. The powder may be discharged from the vessel, at the completion of chemical reactions in the reaction zone, for further processing. Alternatively, the powder may be further processed in-situ for production of other materials. Alternatively the powder may be heated in-situ to make coarse grain powder. In a further embodiment, the powder may be compacted and/or heated in-situ and then melted to produce ingot. It is highly advantageous to have titanium-aluminium compounds produced in powder form. As discussed in the preamble this is something that prior art processes cannot do directly. The powder form is much more versatile in manufacture of titanium aluminium alloy products, eg shaped fan blades that may be used in the aerospace industry. The aluminium to be mixed with the titanium subchloride in these processes is, in one ¦ embodiment, in fine powder form, usually having an approximate grain topsize of less than 5Q micrometres in diameter. Fine aluminium powder is usually less than 50 micrometres in diameter. A problem with using fine aluminium powder is that it is quite expensive to produce and therefore increases the cost of the process, although the inventor still believes that the cost will still be far less than prior art processes. In an alternative embodiment, coarse aluminium powder is used, the powder having an approximate grain topsiae of greater than SO micrometres in diameter. The coarse aluminium powder is added to the titanium subchloride and the mixture is mechanically milled to reduce the dimensions of the aluminium powder in at least one dimension. This can result in the production of "flakes" of aluminium which have a size in at least one dimension which is less than 50 micrometres and which is sufficient to facilitate a satisfactory reaction between the titanium subchlorides and the aluminium. Flakes provide a higher reaction surface area and the small thickness of the flakes results in a more uniform composition of product. In a further alternative embodiment, the aluminium raw material may be obtained in the form of flakes (±e already pre-milled) and mixed with the titanium subchlorides before reaction commences. A further embodiment of an. apparatus which can be used to prepare titanium-aluminium compounds in accordance -with the present invention is illustrated in Figure 5. The apparatus in this case is a simple vessel (60) having relatively long (tall) side walls (20) . An upper pozrtion • (40) of the side walls (20) forms a first condensation zone at temperature T2, for condensation of A1C13. A middle portion (50) of the side walls (2 0) forms a second condensation zone at temperature T3 allowing for condensation of TiCi3. Titanium-aluminium compounds (11) are formed at the bottom of the vessel (60). Parameters influencing reactions in the reaction zone, include the pressure in the reaction vessel, the temperature of the reaction zone and the grain size of the Al powder. The inventor has found that, for operation under low pressure, a lower temperature is required in order to drive the reaction, as A1C13 is removed faster from the reaction zone and TiCl3 species become more volatile and more active, thus triggering reactions with aluminium. However, this also results in a lower yield, escape of some volatile titanium chloride, and possibly to the production of a two phase product due to disproportionate on. Also, the inventor found that the reaction between TiCl3 and Al depends strongly on the size of the Al powder grains. The reaction is much faster for smaller grains and also the yield is higher. Very fine aluminium powder results in the formation of a product of Ti-Al compounds with very fine grains, having irregular shapes. The inventor also found that with cheaper, less fine powders, the production yield of titanium aluminium compounds was still satisfactorily high and the resultant grain size comparable to that achieved with finer aluminium powders. As discussed above, relatively coarse titanium powders can also be used, and the mixture can be milled to produce flakes, or the aluminium starting material can be provided in the form of flakes. As discussed above, TiCl4 can be used to produce the titanium subchlorides to be used as the precursor material for the production of the titanium aluminium compounds. Thus, titanium tetrachloride can be used as a feedstock material. The production of TiCl4 from titanium ore (titanium oxide) is a well known process, usually as a precursor step for preparation of Ti metal by processes such as the Kroll and Hunter process. Methods in accordance with the present invention can also use TiCl4 as a feedstock material. Instead of preparing the metal directly from TiCl4, however, TiCl4 is reduced to produce the precursor material TiCl3. As briefly described above, this embodiment utilises two methods for the production of TiCl3: Reduction of TiCl4 using Aluminium: TiCl4 and aluminium metal (coarse or fine powder) in appropriate amounts are introduced into a closed vessel under an inert gas atmosphere (such as argon) . The vessel is then heated to a temperature above 200C to form a mixture of TiCl3 and A1C13. .The TiCl3 powder is then extracted from the mixture by distillation as described before. The TiCl3 powder is then mixed with more aluminium if required and processed utilising an apparatus such as described above in relation to Figure 4. Reduction of TiCl4 using hydrogen: TiCl4 may be fed into a plasma-processing unit operating with argon and hydrogen gas to produce TiCl3. Products exiting from the plasma processing system may travel through a filter to separate TiCl3 from the gas stream and the resulting TiCl3 powder can then be moved into a processing chamber where it is mixed with an appropriate amount of aluminium, depending on the required composition of the end product. The mixture is then processed utilising an apparatus such as that described earlier in relation to Figure 4 or Figure 5. At the completion of the reaction/ the materials can be discharged from the reaction vessel for use in manufacturing. Alternatively, the powder can be consolidated in-situ, and then melted to produce ingots. Gases from the plasma system may be re-used after separation and cleaning. In the above-described processes, it is possible to include other precursor materials in addition to the aluminium and titanium subchlorides, to obtain products of desired composition. For example, the precursor materials may include vanadium subchlorides, such as vanadium trichloride and/or vanadium dichloride and the products may include titanium-aluminium-vanadium compounds. The precursor material may include chromium halides and the products may include titanium-aluminium-chromium compounds. Kiobium. halide may be added as a starter material to produce titanium-aluminium-niobium-chromium compounds. The precursor materials may also include one or more halides of elements such as chromium., niobium, vanadium, zirconium, silicon, boron, molybdenum and carbon. Figure 6 is a schematic diagram of a process for the production of titanium-aluminium compound powder from titanium tetrachloride starting materials, in accordance with an embodiment of the present invention. The process discloses how aluminium trichloride can be recycled to produce raw materials. TiGl4 is reduced using hydrogen, as discussed above, to result in TiCl3 (Step 1) . TiCl3 is then mixed with aluminium powder and any other precursors that are required are added (Step 2) and then the mixture is processed at temperatures of up to 1000C (temperature will depend upon the precursor mix and products required). Any titanium trichloride given off is put back into the reaction mixture (Step 4) and any titanium tetrachloride which is given off is fed back into the process (Step 5) for the production of titanium trichloride (Step 1) . From the processing of Step 3, alloy powder products are also obtained (Step 6). Any aluminium trichloride produced as a by-product (Step 7) can be used for other purposes. For example, such by-products can be electrolysed to produce aluminium and chlorine (the aluminium may be fed back into Step 2) . Advantageously, in accordance with an embodiment of the present invention, the aluminium trichloride can be recycled to produce titanium tetrachloride by reacting the A1C13 with the titanium ore (rutile or titanium oxide, Step 8; producing titanium tetrachlorides, Step 9; and aluminium oxide, Step 10) . The aluminium oxide produced by this process can be sold or electrolysed to produce aluminium raw material, which can be added to the precursor material in this process. Figure 7 shows the Gibbs free energy for the half reaction leading to aluminium oxide and titanium tetrachloride. The total Gibbs free energy for reaction leading to the formation of titanium tetrachloride is negative at all temperatures higher than 30OK, suggesting the reaction is exothermic. Figure 8 is a schematic diagram of a further production process for the production of titanium aluminium compound powder which involves the step of reduction of titanium tetrachloride with aluminium in order to obtain the required titanium trichloride precursor material. All the other process steps in the Figure 8 production process are the same as the process illustrated in Figure 6 with the exception of Step 1A which is the reduction of titanium tetrachloride by aluminium. Note that Step 1A also may produce some aluminium trichloride by-products which can be recycled via Step 7. The following are examples of preparation of titanium aluminium compounds in accordance with an embodiment of the present invention. Example 1: TJ-6A1-4V TiCl3 is prepared by reducing TiCl4 with Al powder. The starting materials were 20g of TxCl3 + lg of Al powder {grain size materials were mixed together very thoroughly and then introduced into a Ta crucible and heated in a quartz tube under flowing argon (100 cc/minute) . The temperature is taken to 1000C over 30 minutes and kept there for 1 hour. Materials left in the crucible are 1.65g of metallic powder. The powder is washed in distilled water to remove any residual chlorine (at ppm level) and then dried under argon. XRT> analysis of the powder (Figure 9) shows peaks that can. be indexed on the T1-6A.1-4V composition, EDX analysis of the powder shows a weight % composition of Ti: 90.1%; Al: 5.8%; V: 4.1%. It was noted that the chlorine and oxygen level were either non existant or below the detection limits of the instrument. Example 2: Gamma Titanium aluminides lOg of TiCl3 was mixed with 3. 5g of Al powder {grain size crucible and heated in a quartz tube under flowing argon (100 cc/tninute) . The temperature is taken to 10 00C over 30 minutes and kept there for 1 hour. The crucible is then left to cool down and opened. Materials left in the crucible consisted of 4.72 g of grey metallic powder. The powder was washed in distilled water and then dried under argon. XRD analysis (Figure 10) is consistent with the gamma TiAl composition. EDX analysis of the powder suggests the composition of 49.4% (atomic)Ti and 50.6% (atomic)Al. Example 3: Ti-48Al-2Cr-2Nb lOg of TiCl3, 3.52g of Al powder, 0.34g of CrCl2 and 0 .78g of HbCl5 were mixed thoroughly and then placed in a Ta crucible in a quartz tube and then heated under flowing argon (100 cc/minute) . The temperature was taken to 1000C over a period of 30 minutes and then left at 1000C for 1 hour. 4.4g of metallic powder were left in the crucible. An EDX analysis of the powder suggests a composition of Ti-47Al-2.3Cr-2.3Wb (atomic percent). The methods described herein may also be used for production of metals and metal alloys hy mixing metal halide or a mixture of metal halides (chlorides, bromides, iodides and fluorides) and carrying out the process as described above for the TiCl4 zirconium alloys may be produced using the same procedures described above for Ti and Ti-alloys respectively. For zirconium-based products, the starting material is zirconium chloride. Other examples of metals that can be produced using the present process include vanadium and its alloys and intermetallic compounds. Titanium metal can be produced by the above process following extensive recycling of titanium chlorides. Titanium intermetallic compounds which can be produced include Ti3Al, TiAl and TiAl3. In still further embodiments, reducing agents other than aluminium which may be able to be used with a metal subhalide to produce a metal compound can include zinc, magnesium, sodium, aluminium or other like metals. The present method may be used for production of powders with a controlled particle size of various compositions including compounds of pure metal, oxides, nitrides of elements such as vanadium and zirconium, as described above for titanium. Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention. WE CLAIM : 1. A stepwise method of producing titanium-aluminium compounds, comprising a first step of: - reducing an amount of titanium chloride (TiCl4) with an amount, of aluminium at a temperature to trigger reactions to form titanium subchloride(s) and aluminium chloride (A1C13) products; and then a second step of: - mixing said products, with the addition of more aluminium if required, and heating the mixture in a reaction zone to a temperature above 300C tc form A1CI? in a gas phase, and no produce an end product in the reaction zone of the titanium- aluminium compounds. 2. A method as claimed in claim 1, wherein the method also provides for driving the removal of A1C1» from the reaction zone to favour a forward reaction ir. the second step. 3. A method as claimed in claim 2, wherein the removal of A1C13 from the reaction zone is continuous. 4. A method as claimed in any one of the preceding claims, wherein the first step is conducted at a temperature above the boiling point of A1C13. 5. A method as claimed in any one of the preceding claims, wherein the first step is conducted at a temperature above 200C. 6. A method as claimed in any one of the preceding claims, wherein the first step is conducted with an excess amount cf aluminium present to reduce all of the titanium chloride (TiCl) to form said titanium subchloride(s) and aluminium chloride v'A1CI3) products. 7. A method as claimed in any one of the preceding claims, wherein the second step is conducted at a temperature in the range 300C to 1000C. 8. A method as claimed in any one of the preceding claims, comprising the further step of recycling at least some of che aluminium chloride formed, and utilising the aluminium chloride to produce TiClj. 9. A method as claimed in claim 8, wherein the aluminium, chloride is used tc reduce titanium oxide to produce TiClj. 10. A method as claimed in claim 9, wherein aluminium oxide is produced by reduction of titanium oxide, and the aluminium oxide is electrolysed to produce aluminium raw material for use in the method of any one of the preceding claims. 11. A method as claimed in any one of the preceding claims, wherein the aluminium chloride is condensed away from the reaction zone at a temperature lower than that in the reaction zone. 12. A method as claimed in any one of the preceding claims, wherein titanium subchloride which escapes the reaction zone is condensed at a temperature different to that in the reaction zone. 13. A method as claimed in claim 12, comprising the further step of returning the condensed titanium subchloride tc the reaction zone. 14. A method as claimed in any one of the preceding claims, also comprising the step of introducing a source of one or mere elements selected from the group comprising chromium, niobium, vanadium, zirconium, silicon, boron, molybdenum, tantalum and carbon, and products of said method include titanium- aluminium compounds which include one or more of these elements. 15. A method as claimed in claim 14, wherein the source of the element{3) can be a metal halide, a subhalide, a pure element or another compound which includes the element. 16. A method as claimed in claim 14 or claim 15, wherein the products also include one or more of an intermetallic compound, a titanium-(selected element)-alloy, and intermediate compounds. 17. A method as claimed in any one of claim 14 to claim 16, wherein the source includes vanadium subchloride, and a produce of said method is an alloy cr intermetallic complex including titanium, aluminium and vanadium. 18. A method as claimed in claim 17, comprising the steps of adding the source in appropriate proportions, and carrying out the method to produce Ti-6A1-4V. 19. A method as claimed in claim 14, wherein the source includes zirconium subchloride, and a product of the method is an alloy or intermetallic complex including titanium, aluminium and zirconium. 20. A method as claimed in any one of claims 14 to 16, wherein the source includes niobium haiide and chromium halide, and a product of said method is an alloy or intermetallic complex including titanium, aluminium, niobium and chromium. 21. A method as claimed in claim 20, comprising the step ot adding the source in appropriate proportions, and carrying cut the method to produce Ti-48Al-2Nb-2Cr. 22. A method as claimed in any cne cf the preceding claims, wherein the aluminium is added in the form of a powder having an approximate upper grain size of less than about 50 micrometres. 23. A method as claimed in any one of claims 1 tc 21, wherein the aluminium is in the form of a powder of an approximate upper grain size cf greater than about 5C micrometres, and the method comprises the step of milling the aluminium powder and titanium subchloride to reduce the grain size of the aluminium powder in at least one dimension. 24. A method as claimed in any one cf claims 1 to 21, wherein the aluminium is in the form of flakes having a thickness in one dimension of less than about 50 micrometres. 25. A method as claimed in any one of the preceding claims, wherein the method is conducted in ar. inert gas atmosphere or in a vacuum. 26. A method for production of a powder of titanium- aluminium intermetallic compounds including at least one of Ti2Al, TiAl and TiAl3/ and alloys based on titanium-aluminium intermetailics as claimed in any one of claims 1 to 25, wherein starting materials for the method include aluminium powder and titanium chloride. 27. A method of producing titanium-aluminium compounds, comprising a first step of: - heating an amount of titanium chloride (TiClJ in a plasma of an inert gas and hydrogen mixture, to produce titanium subchloride(s); and then a second step of: - nixing aluminium with said titanium subchloride{s), and heating the resultant mixture to produce titanium-aluminium compounds and A1C1. 28. A method as claimed in claim 27 which is otherwise as claimed in any one of claims 2 to 25. 29. A stepwise method of producing titanium-aluminium compounds, comprising a first step of: - reducing an amount of titanium chloride (TiCl with hydrogen in an inert gas atmosphere or in a vacuum, and at a temperature to trigger reactions to form titanium subchloride{s) and aluminium chloride (AICI2) products; and then a second step of: - mixing said products with aluminium, and heating the mixture in a reaction zone to a temperature above 30CC tc form AlClj- in a gas phase, and to produce an end product ir. the reaction zone of the titanium-aluminium compounds. 30. A method as claimed in claim 29 which is otherwise as claimed in any one of claims 2 to 25. 31. A stepwise method of producing titanium-aluminium compounds, comprising a first step of: - heating a mixture of TiClj and aluminium to form products TiCl3 and AlClj, at a temperature less than 300C; and then a second step of: - mixing said products, with the addition of more aluminium if required, and heating the mixture to a reaction zone temperature above 300C to cause AICI3 tc be evaporated from the reaction zone and to form titanium-aluminium compounds. 32. An apparatus for the production of a titanium- aluminium compound, comprising: - a reaction vessel arranged in use for the mixing of aluminium with a titanium haiide or subhalide; - the vessel also adapted in use for the resultant mixture to ba heated to a temperature sufficient for the titanium haiide or subhalide to react with the aluminium to form the titanium-aluminium compound and an aluminium haiide; - one condensation zone arranged in use to operate at a temperature such that any titanium haiide or subhalide escaping the reaction mixture condenses in. that condensation zone; and - another condensation zone arranged in use to operate at a temperature such that the aluminium haiide condenses in the another condensation zone. 33. An apparatus as claimed in claim 32, also comprising a third condensation zone arranged to condense titanium haiide that is produced by disproportior.ation fron escaping the reaction mixture. 34. An apparatus as claimed in claim 32 or claim 33, wherein the one condensation zone is arranged to return condensed titanium haiide or subhalide to the reaction, zone. The present invention relates to a method and apparatus for the production of titanium alloys and titanium-aluminium inter-metallic compounds and alloys. Starting from a precursor material including titanium subchloride (titanium trichloride or titanium dichloride), the precursor material is reduced by aluminium tc produce titanium-aluminium intermetallic complexes or alloys and aluminium chloride which is driven away from the reaction zone so as to favour the forward reaction and the production of the titanium-aluminium compounds. Starting from a precursor material of titanium subchloride avoids the problems associated with starting from titanium metal (which is expensive to produce) or titanium tetrachloride (a reaction very difficult to 0control), and results in the production of powdered forms of titanium-aluminium compounds with controllable composition.

Full Text

Field of the Invention
The present invention relates to a method and
apparatus for the production of metal and metal compounds
and, particularly, but not exclusively, to a method and
apparatus for production of titanium-based alloys and
intermetallic complexes, and more particularly, but not
exclusively, to a method and apparatus for the production
of titanium-aluminium based alloys and intermetallic
complexes, and more particularly, but not exclusively, to
a method and apparatus for the production of titanium-
aluminium based alloys and intermetallic complexes in a
powder form.
Background of the Invention
Titanium-aluminium alloys and inter-metallic
compounds (generically termed herein "titanium-aluminium
compounds") are very valuable materials. However, they
are difficult and expensive to prepare, particularly in
the preferred powder form. This expense of preparation
limits wide use of these materials, even though they have
highly desirable properties for use in automotive,
aerospace and other industries.
Titanium minerals are found in nature in the form of
a very stable oxide (TiO2) . Common processes for the
production of ' titanium are the Kroll process and the
Hunter process. The Kroll process requires the use of
magnesium as a reducing agent to reduce TiCl4 (prepared
from the oxide by a pre-process of chlorination) to
produce the Ti metal. The Hunter process requires the use
of sodium as the reducing agent. Because TiCl4 is still
thermodynamically stable, highly reactive reducing agents
such as magnesium or sodium are required to produce
titanium metal out of TiCl4. Such highly reactive reducing
agents are difficult and expensive to handle. As the
magnesium chlorides in the case of the Kroll process are
stable up to temperatures in excess of 130OK, the product
is often in the form of a Ti sponge mixed with MgCl2 and
remnants of Mg and TiCl2. To obtain pure Ti, the product
requires extensive post-processing, including washing and
melting in a vacuum arc furnace to remove all impurities.
This contributes to the present high cost of the
production of titanium.
In the known technologies for production of titanium
alloys such as Ti-Al-V, and intermetallic compounds such
as Ti3Al, TiAl, TiAl3, Ti-Al- (Cr, Hb, Mo, etc) and alloys
based on these compounds, appropriate amounts of sponges,
ingots or powders of the metals which comprise these
alloys are milled or melted together and annealed, hence
adding to the production cost, particularly as it is
necessary to obtain the metals first which, as discussed,
in the case of titanium, involves considerable expense.
For production of a powder of these titanium alloys and
intermetallic compounds, further processing is usually
required, adding to the already high production cost.
Prior Al-based processes for manufacturing of Ti-Al
compounds include starting from Al powder and Ti powder
(references: (I.Lu, M.O. Lai and F.H. Froes, Journal of
Metals, February 2002, p62) and (N. Bertolino et al..
Intermetallies, Vol 11, 2003, p 41} and reduction of TiCl4
with A1C1 {US patent application US2002/0184 971 Al). For
the first process, the starting materials are Al and Ti
powders, the powders usually being mechanically milled to
make a uniform mixture followed by heating in a furnace.
The resulting materials are at best in the form of solid
lumps and this process is usually unable to produce fine
powder. Furthermore, the resulting compounds often
require heat treatment to produce the required material
properties. For the second process, Al metal is heated in
the presence of chlorine at temperature around 1200C to
produce gaseous AlCl that is then reacted with TiCl4 in the
gas phase to produce powders of titanium aluminides. Both
these processes are quite complex and costly to operate.
It is also known to perform direct reduction of TiCl4
with aluminium. However, this results in the production
of an uncontrollable composition of compounds and
production of a single phase material such as TiAl has not
been achieved (see in particular S J Gerdemann & D E
Alman, page 3341 in Gamma Titanium Alumini 1999, edited by-
Kim, Dimiduk & Loretto, The Minerals Metals and Materials
Society USA) -
Over the past several decades, there have been
extensive attempts made to replace the existing Kroll and
Hunter technologies using techniques such as
electrowinning, plasma-hydrogen and also aluminothermic
reduction.
The use of hydrogen plasma for the reduction of
titanium chloride in a plasma atmosphere is difficult due
to unfavourable thermodynatnic characteristics, since
chlorine preferably reacts with titanium in the reverse
reaction to produce titanium chlorides, hence degrading
the quality of the produced Ti powder and.limiting the
efficiency of the method. In a process disclosed in US
Patent 5,935,293, a fast quench reactor was used to cool
down the plasma in order to prevent recombination
processes leading to formation of titanium chlorides.
According to the description in US Patent 5,935,293, the
process is highly energy expensive relative to the
existing Kroll technology.
In another process (G.Z. Chen, D.J. Fray and T.Vf.
Farthing, Nature, Vol 407, (2000), 361), Chen et al. made
titanium sponge directly from the oxide by reduction in a
molten calcium chloride salt. Oxygen from the titanium
oxide recombines with carbon at an anode to form CO2.
However, the composition of the resulting sponge-like
titanium product produced corresponds to the composition
of the starting minerals. The process is still under
development and is yet to be demonstrated on an industrial
scale.
Attempts have been made to uBe aluminium as a
reducing agent for TiCl4 in plasma systems. For reduction
of TiCl* using aluminium, the products are in the form of
solid phase titanium-aluminium intermetallic compounds
mixed with aluminium chloride and some residual titanium
dichloride. A description of various attempts using
aluminium together with a description of the
thermodynamics of the process are given by Murphy and Bing
{High Temp. Chem. Processes, Vol 3, 365-374, 1994).
Because of difficulties associated with gas phase
reactions it has not been possible to produce titanium
and/or titanium-aluminium compounds by direct
aluminothermic reduction of titanium chlorides.
Summary of the Invention
In accordance with a first aspect, the present
invention provides a etepwise method of producing
titanium-aluminium compounds, comprising a first step oft
- reducing an amount of titanium chloride (TiCl*)
with an amount of aluminium at a temperature to
trigger reactions to form titanium subchloride(s)
and aluminium chloride (AlCl3) products;
and then a second step of:
- mixing said products, with the addition of more
aluminium if required, and heating the mixture in
a reaction zone to a temperature above 3 00C to
form AICI3 in a gas phase, and to produce an end
product in the reaction zone of the titanium-
altmiinium compounds.
When the term titanium subchloride is used, it can.
refer to titanium trichloride TiCl3 and/or titanium
dichloride TiClj or other combinations of titanium and
chloride excluding. TiCl4 which is referred to herein as
titanium chloride.
When the term titanium compound is used, it can refer
to titanium alloyB and/or titanium/metal intermetallic
compounds. In one preferred form which is referred to
herein, the titanium compounds include titanium-aluminium
alloys and/or titanium-aluminium intermetallic compounds.
In one embodiment, the method can also comprises the
step of driving the removal of A1C13 away from the reaction
zone to favour a forward reaction in the second step. In
one form, the step of removing the A1C13 from the reaction
zone is continuous-
In one embodiment, the first step can be conducted at
a temperature above the boiling point of AlCla. In
another embodiment, the first step can be conducted at a
temperature above 200C,
In one embodiment of the method, the first step can
be conducted with an excess amount of aluminium present to
reduce all of the titanium chloride (TICI4) to form said
titanium subchloride(s) and aluminium chloride (AICI3)
products. In one embodiment, TMCI3 is prepared by the
reduction of T1C1.4, although this reaction may also form
titanium dichloride TiCla.
In one embodiment of the method, the second step can
be conducted at a temperature in the range 300C to 1000C.
One embodiment of the method can comprise the further
step of recycling at least some o£ the aluminium chloride
formed, and utilising the aluminium chloride to produce
Tid.4. The aluminium chloride can be used to reduce
titanium oxide to produce TiCl4.
In any of the embodiments of the method mentioned,
aluminium oxide can be produced by the reduction of
titanium oxide and the aluminium oxide electrolysed to
produce aluminium raw material for use in the steps of
said method.
1
In one embodiment of the method, the aluminium
chlorides can be condensed away from the reaction zone at
a temperature lower than that in the reaction zone. In
one embodiment of the method, if titanium subchloride
escapee the reaction zone it can be condensed at a
temperature different to that in the reaction zone.
Furthermore the condensed titanium subchloride can
optionally be returned to the reaction zone.
In further embodiments of the method, the precursor
material can include a source of one or more elements
selected from the group comprising chromium (cr), niobium
(Nb), vanadium (V), zirconium (Zr), silicon (SiJ, boron
(B), molybdenum (Mo), tantalum {Ta) and carbon (C), and
products of said method can include titanium-aluminium
compounds which include one or more of these elements.
The source of the element(s) can be a metal halide, a
subhalide, a pure element or another compound which
includes the element. The products can also include one
or more of an interrnetallic compound/ a titanium- (selected
element)-alloy, and intermediate compounds. The source
may also include a source of other precursors containing a
required alloy additive, depending upon the required end
product.
In one form of the method, the source can include
vanadium subchloride, auch as vanadium trichloride and/or
vanadium dichloride, and a product of said method is an
alloy or intermetallic complex including titanium,
aluminium and vanadium. This method can comprise the
steps of adding the source in appropriate .proportions, and
carrying out the method to produce T1-6A1-4V.
In a further form of the method, the source can
include zirconium subchloride, and a product of the method
is an alloy or intermetallic complex including titanium,
aluminium, zirconium and vanadium.
In one form of the method, the source can include
niobium halide and chromium halide, and a product of said
method is an alloy or intermetallic complex including
titanium, aluminium, niobium and chromium. This method
can also comprise the step of adding the source in
appropriate proportions, and carrying out the method to
produce Ti-48Al-2Nb-2Cr.
In one embodiment of the method/ the aluminium can be
added in the form of a powdei* having an approximate upper
grain size of less than about 50 micrometres. In an
alternative form of the method, the aluminium can be in
the form of a powder of an approximate upper grain size of
greater than about 50 micrometres, and the method
comprises the step of milling the aluminium powder and
titanium subchloride to reduce the grain size of the
aluminium powder in at least one dimension, in yet
another alternative form of the method, the aluminium can
be in the form of flakes having a thickness in one
dimension of less than about 50 micrometres. Using a fine
aluminium powder is preferred, although the relatively
coarser aluminium powder or flakes is a cheaper raw
material.
In an embodiment, the method is conducted in an inert
gas atmosphere or in a vacuum.
In any of the embodiments described, the method can
also include a pre-processing step of forming the titanium
subchloride as precursor material. The inventor has found
that using a precursor material which includes titanium
subchloride (preferably titanium trichloride) gives a
number of advantages. There are not the problems of
different; uncontrollable phases which are involved in
starting from titanium tetrachloride as a precursor. The
composition of the end product is relatively controllable
and depends on the ratios of the starting materials. The
correct ratios of starting materials are incorporated in
the precursor materials to produce the appropriate
proportions of components in the product.
The inventor believes that the new method enables a
cheaper and more controllable process for the production
of titanium-aluminium compounds. It is not necessary to
convert the raw titanium minerals to titanium metal, as in
some of the prior art processes discussed earlier. In one
¦embodiment of the present process, titanium oxide can be
chlorinated using conventional technology to give titanium
tetrachloride. This can then be reduced using aluminium
or hydrogen to give titanium subchlorides (mainly titanium
trichloride); which can then be used as the precursor
material for the formation of the titanium-aluminium
compounds.
It is possible to form TA-6A1-4V using this process,
which is one of the major titanium alloys used. It is
also possible to form Ti-48Al-2Nb-2Cr. It is also
possible to form other alloys such as Ti-Al-Nb-C, and Ti3Al
based alloys.
A process in accordance with embodiments, of the
present invention described has the advantage that alloy
powder is produced directly, with no further physical
processing.
In accordance with a second aspect, the present
invention provides a method for production of a powder of
titanium-aluminium intermetallic compounds including at
least one of Ti3Al, TiAl and TiAl3, and alloys based on
titanium-aluminium intermetallics, as defined in the first
aspect, and wherein starting materials for the method
include aluminium powder and titanium chloride.
In accordance with a third aspect, the present
invention provides a method of producing titanium-
aluminium compounds, comprising a first step of-;
- heating an amount of titanium chloride (TiCl4) in
a plasma of an inert gas and hydrogen mixture, to
produce titanium subchloride(s);
and then a second step of:
- mixing aluminium with said titanium
subchloride(s), and heating the resultant mixture
to produce titanium-aluminium compounds and A1C13.
In one embodiment, the method of the third aspect can
be otherwise as defined in the first aspect.
In accordance with a fourth aspect, the present
invention provides a stepwise method of producing
titanium-aluminium compounds, comprising a first step of:
- reducing an amount of titanium chloride (TiCl with hydrogen in an inert gas atmosphere or in a
vacuum, and at a temperature to trigger reactions
to form titanium subchloride(s) and aluminium
chloride (A1C13) products;
and then a second step of:
- mixing said products with aluminium, and heating
the mixture in a reaction zone to a temperature
above 300C to form A1C13 in a gas phase, and to
produce an end product in the reaction zone of the
titanium-aluminium compounds.
In one embodiment, the method of the fourth aspect
can be otherwise as defined in the first aspect.
In accordance with a fifth aspect, the present
invention provides a stepwise method of producing
titanium-aluminium compounds, comprising a first step of:
- heating' a mixture of Ticl* and aluminium to form
products TiCl3 and A1C13, at a temperature leas
than 300C;
and then a second step of:
- mixing said products, with the addition of more
aluminium if required, and heating the mixture to
a reaction zone temperature above 300C to cause
AICI3 to be evaporated from the reaction zone and
to form titanium-aluminium compounds.
In one embodiment, the method of the fifth aspect can
be otherwise as defined'in the first aspect.
In accordance with a sixth aspect, the present
invention provides a stepwise method of producing a metal-
aluminium compound, comprising the first step of:
- adding a reducing agent to reduce an amount of a
metal halide to form metal subhalide(s);
and the second step of:
- mixing said metal subhalide(e) with aluminium, and
heating the mixture in a reaction zone to a
temperature above 300C to form aluminium halides
in a gaa phase, and to produce an end product in
the reaction zone comprising a metal compound
containing a percentage of aluminium.
In one embodiment of this method, the reducing agent
can be selected from the group comprising zinc, magnesium,
sodium, aluminium or other like metals. In one embodiment
the metal halide can be a titanium subhalide such as
titanium trichloride, and a product of the reaction can
include titanium compounds.
In one embodiment, the method of the sixth aspect can
be otherwise as defined in the first aspect.
In any of the embodiments described, the method can
also comprise the further step of adding a reagent to a
product of the method, to produce a further product.
In accordance with a seventh aspect, the present
invention provides a method for the production of vanadium
and/or vanadium compounds, comprising the Bteps of mixing
aluminium with a precursor material including vanadium
subhalide, and heating the mixture, to form aluminium
halides and vanadium and/or vanadium compounds.
In one embodiment, the vanadium compounds may include
vanadium-aluminium alloys and/or vanadium aluminium
intermetallic complexes.
In accordance with an eighth aspect, the present
invention provides a method for the production of
zirconium and/or zirconium compounds, comprising the steps
of mixing aluminium with a precursor material including
zirconium subhalide, and heating the mixture, to form
aluminium halides and zirconium and/or zirconium
compounds.
In one embodiment, the zirconium compounds may
include zirconium-aluminium alloys and/or zirconium-
aluminium intermetallic complexes.
In accordance with a ninth aspect, the present
invention provides an apparatus for the production of a
metal compound, comprising:
- a reaction vessel arranged in use for the mixing
of aluminium with a metal halide or subhalide;
the vessel also adapted in use for the resultant
mixture to be heated to a temperature sufficient
for the metal halide or subhalide to react with
the aluminium to form the metal compound and an
aluminium halide;
- one condensation zone arranged in use to operate
at a temperature such that any metal halide or
subhalide escaping the reaction mixture condenses
in that condensation zone; and
- another condensation zone arranged in use to
operate at a temperature such that the. aluminium
halide condenses in the another condensation zone.
In one embodiment, the apparatus also can comprise a
third condensation zone arranged to condense metal halide
that is produced by dieproportionation from escaping the
reaction mixture. In a further embodiment, the one
condensation zone can be arranged to return condensed
metal halide or subhalide to the reaction zone.
In one embodiment, the reaction zone operates at a
temperature Tl and the first condensation zone at a
temperature T2 which is lower than the temperature Tl. In
one form, the second condensation zone operates at a
temperature T3 which is between Tl and T2.
In one example, the precursor material may be a
material containing titanium as a component, such as
titanium trichloride and/or titanium dichloride. Where
the precursor material includes titanium trichloride and
where the apparatus includes a first condensation zone
that operates at temperature T2, T2 is preferably below
200C, wherein gaseous aluminium trichloride emanating from
the reaction zone is condensed.
When the apparatus includes a second condensation
zone, T3 is below 500C and titanium trichloride which
escapes from the reaction zone is recondensed at the
second condensation zone. In one embodiment, the second
condensation zone is located between the reaction zone and
the first condensation zone.
Typically the apparatus includes a heating
arrangement for heating the precursor material, In some
embodiments, openings are provided for the introduction of
further gases. Openings may also be provided to evacuate
the vessel to a low pressure. In still further
embodiments, the reaction vessel may be a number of
discrete vessels, each vessel providing a different
reaction or condensation zone.
Preferably, the apparatus of this aspect of the
invention ie suitable for implementing the method of any
of the foregoing or following aspecte of the invention
described herein.
in accordance with a tenth, aspect, th& present
invention provides an apparatus for the production of at
least one of a titanium compound, another metal compound
or a product, wh«n the apparatus is used with the method
as defined in any one of the first to the eighth aspects.
In accordance with an eleventh aspect, the present
invention provides at least one of a titanium compound/ a
metal compound or a product produced by either the
apparatus or the method as defined in any one of the first
to the ninth aspects.
Brief Description of the Accompanying Drawings
Features and advantages of the present invention will
become apparent from the following description of
embodiments thereof, by way of example only, with
reference to the accompanying drawings, in which:
Figure 1 shows the Gibbs energy of formation of
AlCl3:gi/ TiCl3 and TiClj + Ti-Al;
Figure 2 shows the total Gibbs free energy for
reactions leading to formation of Ti-metal based
compounds;
Figure 3 illustrates the equilibrium composition of
TiCl4 - Hydrogen plasma at temperatures of between 300K and
5000K;
Figure 4 is a schematic diagram of an apparatus for
implementing a process in accordance with an embodiment of
the present invention;
Figure 5 is a schematic diagram of a further
embodiment of an apparatus for implementing a process in
accordance with an embodiment of the present invention;
Figure 6 is a schematic diagram illustrating a
process for production of titanium based compounds in
accordance with an embodiment of the present invention;
Figure 7 illustrates the Gibbs free energy for half
reactions leading to the formation of titanium-
tetrachloride;
Figure 8 is a schematic diagram illustrating a
process for production of titanium based compounds in
accordance with a further embodiment of the invention;
Figure 9 is an XRD spectrum for a T1-6A1-4V powder
produced by an embodiment of the present invention; and
Figure 10 is an XRD spectrum for a Gamma TiAl
compound produced by an embodiment of the present
invention.
Description of Preferred Embodiments
The following description is of preferred embodiments
of processes for producing metal compounds, including fine
powder and ingots with specific compositions. The
processes are useful for production of forms of metals
such as titanium, vanadium and zirconium together with
alloys and intermetallic compounds of these metals with a
controllable amount of aluminium.
For example, Ti-Al, Ti3Al, TiAl3, Ti-Al-Cr and Ti-V-
Al can be made with accuracy by varying the aluminium
content. The relative amounts of titanium chlorides and
aluminium are determined by the required composition of
end product. In one embodiment the process comprises the
steps of preparing solid metal halides, mixing the halides
with aluminium metal and heating the mixture to a
temperature Tl to trigger reactions leading to formation
of aluminium chloride at a temperature (Tl) above the
boiling temperature of aluminium chlorides, and condensing
the aluminium chlorides away from the reaction zone at a
temperature T2, where T2 is less than Tl. The driving of
the aluminium chloride away from the reaction zone moves
the equilibrium of reaction in the forward direction i.e.
to formation of aluminium chloride and metal (and other
products depending upon reaction conditions and
components).
For titanium compounds, titanium subchlorides,
(preferably titanium trichloride TiCl3) can be produced
from a precursor material of TiCl4. The TiCl3 is mixed
with aluminium and then heated to a temperature above 300C
so that AICI3 is formed in the gas phase and the AlCl3 is
condensed away from the reaction zone at a temperature
below 200C, leaving a powder of Ti in the reaction zone
containing a percentage of aluminium, as required for the
end product.
In one embodiment, the process comprises the steps of
heating TiCl4 in a plasma of an argon-hydrogen mixture to
produce TiCl.3, and then mixing the resulting TiCl3 powder
with aluminium and then heating the mixture to trigger the
reaction. The reaction vessel used is arranged to ailow
for aluminium chloride to be continuously removed and
condensed in a region away from the reaction zone of the
titanium chloride and aluminium mixture. The T1CI3, and
aluminium in a powder or a lump form (but preferably in a
powder form) are mixed together under inert gas or in a
vacuum. The mixture is then heated to a temperature of
several hundred degrees to trigger reaction between the
two compounds, leading to formation of AlCl3(gj. The A1C13
is then condensed elsewhere in the vessel at a temperature
below 200C-
In a further embodiment, the process comprises the
steps of heating predetermined amounts of TiCl4 and
aluminium to form TiCl3 and A1C13, heating the product
mixture to a temperature above 3O0C and providing foor A1C13
to be evaporated from the reaction zone. The Ald3 was
driven away from the reaction and condensed away from the
reaction zone at a temperature below 2 00C. Further
aluminium material was then added to the product in an
amount depending on the required composition, and then the
mixture was heated under the same physical conditions to a
temperature above 300C to trigger chemical reactions
leading to formation of AlCl3(g) whilst providing for the
AlCl^g) to be condensed elsewhere in the vessel at a
temperature below 200C.
The overall reactions between titanium subchlorides
TiCl3 and Al occur in the following form-.
TiCl3 + Al «* Ti where Al is present in the solid or liquid phase.
The presence of Ti and Al may lead formation of Ti-Al
intermetallic compounds such as TiAl3(S), TiAl TisAlte). Then TiCl3 may react with aluminium according to
the following simplified reactions:
TiCl3{g) + TiAl3(s> ** 2 Ti*Aly + AlCl3{g> (2)
TiCl3(g) + TiAl(S) ** 2 TixAly + AlCl3(g, (3)
TiCl3{g) + Ti3Al(a, *? 2 TixAly + AlCl3(gj (4)
Reactions 1-4 are driven in the forward direction by
continuous removal of A1C13 from the reaction zone. As a
result, equilibrium is moved to the right and the reaction
proceeds "until completion. The inventor has found that
the reaction proceeds slowly at temperatures slightly
above 200C under an argon atmosphere at 1 atmosphere. The
reaction becomes very rapid at temperatures above 500C as
the Gibbs free energy of the total reaction becomes
negative as seen in Figures 1 and 2. Figure 1 shows the
Gibbs energy for AICI3, TiCl3 and TiCl3+Ti-Al. Figure 2
shows the total Gibbs energy for Reactions 1-4 leading to
formation of solid titanium.
Because of the strong affinity between titanium and
aluminium, the presence of Al and Ti may result in
formation of titanium-aluminium alloys and/or
intermetallic compounds TixAly. For these compounds, the
Gibbs energy of formation AGf is generally less than
32kJ.mole~1 for aluminium concentrations up to 80% of the
alloys (R.G.Reddy et al. J. Alloys and Compounds, vol 321
(2001) 223) -
Figure 2 shows the variation with temperature of the
total Gibbs energy for reactions leading to formation of
AlCl3(g) and Ti(S), starting from TiCl3 and Al. Also shown
in Figure 2 is the total Gibbs energy for reaction leading
to formation of Ti{S) and AlCl3(g), starting from TiCl3 and
Ti-Al compounds. The total Gibbs free energy for Ti-Al is
taken to be ~32kJ.roole~1.
It is usually considered that chemical reactions
proceed rapidly for negative values of the total Gibbs
energy of the reaction. It is seen in Figure 2 that AG is
negative at temperatures above 800K (525C) for Reaction 1.
This is in excellent agreement with the experimental
observations which show rapid reaction between TiCl3 and Al
at a temperature of SOOC in an argon atmosphere at 1
atmosphere pressure. The inventor found that as the
temperature of the mixture TiCl3-Al increased above 3 00C, a
cloud of white fume moved from the reaction zone towards
the cold region of the vessel where it recondensed to form
solid AlCl3. At temperatures above 500C, the reaction
became almost spontaneous, which is in agreement with the
results shown in Figure 2. For reactions involving Ti-Al
compounds, the inventor found that in argon at 1
atmosphere pressure, reactions leading to formation of
Ti(S) and TixAly (Reactions 2, 3 and 4} seem to proceed
rapidly at temperatures above 850C.
Titanium chlorides may escape from the reaction zone,
or disproportionate during heating. Gaseous TiCl3 that may
evaporate during the heating process reacts more readily
with Al and further enhances formation of Ti compounds.
For a mixture of TiCl3 and Al powder, with the ratio of
[Al]/[TiCl3] > 1, the inventor found that only small
quantities of less than a few percent of TiCl3 escape the
reaction 2one, and are recondensed in a region of the
vessel at a temperature around 50 OK and introduced back
into the reaction sone, or alternatively collected for
reprocessing. Any TiCl2 that is produced due to
disproportionation, reacts with Al compounds faster than
TiCl3 and enhances reactions, leading to formation of Ti
compounds. The inventor found no evidence of major losses
due to escape of TiCL*. The inventor has made experimental
observations which suggest that, for production of
titanium with a high aluminium content, disproportionation
reactions have little or no significant impact on the
efficiency of the process, since most of the Ti in the
feedstock materials was able to be accounted for. For
production of titanium with a low aluminium content, the
initial amount of aluminium used is less than the
stoichiometric amount needed to remove all of the chlorine
from the TiCl3 materials. Excess titanium chloride
remaining after depletion of available aluminium, is
evaporated from the product and condensed, elsewhere for
reprocessing.
Production of TiCl3 can be carried out from TiCl4
using a hydrogen plasma route or through reduction with
aluminium. Production of TiCl3 in a hydrogen plasma, known
as the Huel process, has been used in industry for several
decades. Figure 3 shows the composition of TiCl4-Hydrogen
plasma at temperature between 30OK and 500OK. It is seen
that TiCl4 can be converted into solid TiCl3 by reacting it
with hydrogen in a plasma. It is also seen that the
conversion rate is almost 100%. The energy cost for
synthesis of solid TiCl3 is very low as the overall
reaction leading to TiCl3:
TiCl4£3) + (1/2)H2 e* TiCl3(s) + HCl with AH=50 KJ/mole.
For reduction of TiCl4 with aluminium, the process is
usually carried out in closed vessel containing
appropriate amounts of TiCl4 and Al at a temperature above
2Q0C, leading to formation of a mixture of TiCl3 and A.lCl3.
Pure TiCl3 is obtained from the mixture by distillation at
temperature above 200C and. allowing AlCl3 to condense
elsewhere.
For the process disclosed herein, production of
titanium-aluminium compounds is made by mixing titanium
subchlorides, preferably TiCl3/ with aluminium in a powder
form, placing the materials in a vessel under vacuum or in
an inert atmosphere, and heating the mixture. For
processing under flowing inert gas or under vacuum, A1C13
formed due to reactions described above is driven into a
different part of the vessel at a temperature below 200C.
This favours the forward reaction formation of the
aluminium halide. ' The heating continues until the
reactions proceed to completion, or until complete
depletion of available titanium subchlorides and/or
aluminium occurs.
Figure 4 shows a simple system used to make Ti-Al
compounds with different Al contents and compositions.
For this configuration, a mixture of TiCla and Al, fl) , is
placed into a vessel (2) and heated to a temperature
higher than 3 00C (typically up to a temperature of the
order of 1000C depending on the composition of the
mixture) . Reactions between TiCl3 and Al in the vessel (2)
lead to formation of gaseous A1C13. A stream of argon gas
(10) that is introduced in the vessel (2) carries the
gaseous AlCl3 together with any titanium chlorides that may
escape from the reaction zone and drives them through a
second vessel (3) which is held at a temperature between
3 00C and S00C, so that TiCl3 is recondensed while AlCl3
remains in. the gas phase. Alternatively, TiCl^ may be
recondensed on the upper walls of the vessel (2) if it is
held at an appropriate temperature. The remaining AlCl3
together with any TiCl4 that may have formed in the
reaction zone due to disproportionation is driven through
a vessel (4) at a temperature higher than 136C and lower
than 200C so that A1C13 is recondensed, and the remaining
TiCl4 is driven into a vessel (5) which is held at room
temperature. The remaining argon gas is discharged out of
the system or recycled.
Typically the gaseous atmosphere in the vessel is an
inert gas, such as argon, helium, neon, xenon. Reactive
gases such as methane or oxygen are undesirable as they
can chemically react with the mixture resulting in other
products. It is noted that the reactions can also be
conducted in the absence of a gaseous atmosphere (eg under
vacuum).
The TiCl3 and an aluminium powder, the relative mass
of which compared to the mass of TiCl3 depends on the
composition of the required product, are introduced into a
vessel as described above and then heated until the
reaction is complete.
For these processes described above, the product is
typically in the form of a fine powder. The powder may be
discharged from the vessel, at the completion of chemical
reactions in the reaction zone, for further processing.
Alternatively, the powder may be further processed in-situ
for production of other materials. Alternatively the
powder may be heated in-situ to make coarse grain powder.
In a further embodiment, the powder may be compacted
and/or heated in-situ and then melted to produce ingot.
It is highly advantageous to have titanium-aluminium
compounds produced in powder form. As discussed in the
preamble this is something that prior art processes cannot
do directly. The powder form is much more versatile in
manufacture of titanium aluminium alloy products, eg
shaped fan blades that may be used in the aerospace
industry.
The aluminium to be mixed with the titanium
subchloride in these processes is, in one ¦ embodiment, in
fine powder form, usually having an approximate grain
topsize of less than 5Q micrometres in diameter. Fine
aluminium powder is usually less than 50 micrometres in
diameter. A problem with using fine aluminium powder is
that it is quite expensive to produce and therefore
increases the cost of the process, although the inventor
still believes that the cost will still be far less than
prior art processes.
In an alternative embodiment, coarse aluminium powder
is used, the powder having an approximate grain topsiae of
greater than SO micrometres in diameter. The coarse
aluminium powder is added to the titanium subchloride and
the mixture is mechanically milled to reduce the
dimensions of the aluminium powder in at least one
dimension. This can result in the production of "flakes"
of aluminium which have a size in at least one dimension
which is less than 50 micrometres and which is sufficient
to facilitate a satisfactory reaction between the titanium
subchlorides and the aluminium. Flakes provide a higher
reaction surface area and the small thickness of the
flakes results in a more uniform composition of product.
In a further alternative embodiment, the aluminium
raw material may be obtained in the form of flakes (±e
already pre-milled) and mixed with the titanium
subchlorides before reaction commences.
A further embodiment of an. apparatus which can be
used to prepare titanium-aluminium compounds in accordance
-with the present invention is illustrated in Figure 5.
The apparatus in this case is a simple vessel (60) having
relatively long (tall) side walls (20) . An upper pozrtion
• (40) of the side walls (20) forms a first condensation
zone at temperature T2, for condensation of A1C13. A
middle portion (50) of the side walls (2 0) forms a second
condensation zone at temperature T3 allowing for
condensation of TiCi3. Titanium-aluminium compounds (11)
are formed at the bottom of the vessel (60).
Parameters influencing reactions in the reaction zone,
include the pressure in the reaction vessel, the
temperature of the reaction zone and the grain size of the
Al powder. The inventor has found that, for operation
under low pressure, a lower temperature is required in
order to drive the reaction, as A1C13 is removed faster
from the reaction zone and TiCl3 species become more
volatile and more active, thus triggering reactions with
aluminium. However, this also results in a lower yield,
escape of some volatile titanium chloride, and possibly to
the production of a two phase product due to
disproportionate on.
Also, the inventor found that the reaction between
TiCl3 and Al depends strongly on the size of the Al powder
grains. The reaction is much faster for smaller grains
and also the yield is higher. Very fine aluminium powder
results in the formation of a product of Ti-Al compounds
with very fine grains, having irregular shapes. The
inventor also found that with cheaper, less fine powders,
the production yield of titanium aluminium compounds was
still satisfactorily high and the resultant grain size
comparable to that achieved with finer aluminium powders.
As discussed above, relatively coarse titanium
powders can also be used, and the mixture can be milled to
produce flakes, or the aluminium starting material can be
provided in the form of flakes.
As discussed above, TiCl4 can be used to produce the
titanium subchlorides to be used as the precursor material
for the production of the titanium aluminium compounds.
Thus, titanium tetrachloride can be used as a feedstock
material. The production of TiCl4 from titanium ore
(titanium oxide) is a well known process, usually as a
precursor step for preparation of Ti metal by processes
such as the Kroll and Hunter process. Methods in
accordance with the present invention can also use TiCl4 as
a feedstock material. Instead of preparing the metal
directly from TiCl4, however, TiCl4 is reduced to produce
the precursor material TiCl3. As briefly described above,
this embodiment utilises two methods for the production of
TiCl3:
Reduction of TiCl4 using Aluminium:
TiCl4 and aluminium metal (coarse or fine powder) in
appropriate amounts are introduced into a closed vessel
under an inert gas atmosphere (such as argon) . The vessel
is then heated to a temperature above 200C to form a
mixture of TiCl3 and A1C13. .The TiCl3 powder is then
extracted from the mixture by distillation as described
before. The TiCl3 powder is then mixed with more aluminium
if required and processed utilising an apparatus such as
described above in relation to Figure 4.
Reduction of TiCl4 using hydrogen:
TiCl4 may be fed into a plasma-processing unit
operating with argon and hydrogen gas to produce TiCl3.
Products exiting from the plasma processing system may
travel through a filter to separate TiCl3 from the gas
stream and the resulting TiCl3 powder can then be moved
into a processing chamber where it is mixed with an
appropriate amount of aluminium, depending on the required
composition of the end product. The mixture is then
processed utilising an apparatus such as that described
earlier in relation to Figure 4 or Figure 5. At the
completion of the reaction/ the materials can be
discharged from the reaction vessel for use in
manufacturing. Alternatively, the powder can be
consolidated in-situ, and then melted to produce ingots.
Gases from the plasma system may be re-used after
separation and cleaning.
In the above-described processes, it is possible to
include other precursor materials in addition to the
aluminium and titanium subchlorides, to obtain products of
desired composition. For example, the precursor materials
may include vanadium subchlorides, such as vanadium
trichloride and/or vanadium dichloride and the products
may include titanium-aluminium-vanadium compounds. The
precursor material may include chromium halides and the
products may include titanium-aluminium-chromium
compounds. Kiobium. halide may be added as a starter
material to produce titanium-aluminium-niobium-chromium
compounds. The precursor materials may also include one
or more halides of elements such as chromium., niobium,
vanadium, zirconium, silicon, boron, molybdenum and
carbon.
Figure 6 is a schematic diagram of a process for the
production of titanium-aluminium compound powder from
titanium tetrachloride starting materials, in accordance
with an embodiment of the present invention. The process
discloses how aluminium trichloride can be recycled to
produce raw materials.
TiGl4 is reduced using hydrogen, as discussed above,
to result in TiCl3 (Step 1) . TiCl3 is then mixed with
aluminium powder and any other precursors that are
required are added (Step 2) and then the mixture is
processed at temperatures of up to 1000C (temperature will
depend upon the precursor mix and products required). Any
titanium trichloride given off is put back into the
reaction mixture (Step 4) and any titanium tetrachloride
which is given off is fed back into the process (Step 5)
for the production of titanium trichloride (Step 1) . From
the processing of Step 3, alloy powder products are also
obtained (Step 6).
Any aluminium trichloride produced as a by-product
(Step 7) can be used for other purposes. For example,
such by-products can be electrolysed to produce aluminium
and chlorine (the aluminium may be fed back into Step 2) .
Advantageously, in accordance with an embodiment of the
present invention, the aluminium trichloride can be
recycled to produce titanium tetrachloride by reacting the
A1C13 with the titanium ore (rutile or titanium oxide, Step
8; producing titanium tetrachlorides, Step 9; and
aluminium oxide, Step 10) . The aluminium oxide produced
by this process can be sold or electrolysed to produce
aluminium raw material, which can be added to the
precursor material in this process.
Figure 7 shows the Gibbs free energy for the half
reaction leading to aluminium oxide and titanium
tetrachloride. The total Gibbs free energy for reaction
leading to the formation of titanium tetrachloride is
negative at all temperatures higher than 30OK, suggesting
the reaction is exothermic.
Figure 8 is a schematic diagram of a further
production process for the production of titanium
aluminium compound powder which involves the step of
reduction of titanium tetrachloride with aluminium in
order to obtain the required titanium trichloride
precursor material. All the other process steps in the
Figure 8 production process are the same as the process
illustrated in Figure 6 with the exception of Step 1A
which is the reduction of titanium tetrachloride by
aluminium. Note that Step 1A also may produce some
aluminium trichloride by-products which can be recycled
via Step 7.
The following are examples of preparation of titanium
aluminium compounds in accordance with an embodiment of
the present invention.
Example 1: TJ-6A1-4V
TiCl3 is prepared by reducing TiCl4 with Al powder. The
starting materials were 20g of TxCl3 + lg of Al powder
{grain size materials were mixed together very thoroughly and then
introduced into a Ta crucible and heated in a quartz tube
under flowing argon (100 cc/minute) . The temperature is
taken to 1000C over 30 minutes and kept there for 1 hour.
Materials left in the crucible are 1.65g of metallic
powder. The powder is washed in distilled water to remove
any residual chlorine (at ppm level) and then dried under
argon. XRT> analysis of the powder (Figure 9) shows peaks
that can. be indexed on the T1-6A.1-4V composition, EDX
analysis of the powder shows a weight % composition of
Ti: 90.1%; Al: 5.8%; V: 4.1%. It was noted that the
chlorine and oxygen level were either non existant or
below the detection limits of the instrument.
Example 2: Gamma Titanium aluminides
lOg of TiCl3 was mixed with 3. 5g of Al powder {grain size
crucible and heated in a quartz tube under flowing argon
(100 cc/tninute) . The temperature is taken to 10 00C over
30 minutes and kept there for 1 hour. The crucible is
then left to cool down and opened. Materials left in the
crucible consisted of 4.72 g of grey metallic powder. The
powder was washed in distilled water and then dried under
argon. XRD analysis (Figure 10) is consistent with the
gamma TiAl composition. EDX analysis of the powder
suggests the composition of 49.4% (atomic)Ti and 50.6%
(atomic)Al.
Example 3: Ti-48Al-2Cr-2Nb
lOg of TiCl3, 3.52g of Al powder, 0.34g of CrCl2 and 0 .78g
of HbCl5 were mixed thoroughly and then placed in a Ta
crucible in a quartz tube and then heated under flowing
argon (100 cc/minute) . The temperature was taken to 1000C
over a period of 30 minutes and then left at 1000C for 1
hour. 4.4g of metallic powder were left in the crucible.
An EDX analysis of the powder suggests a composition of
Ti-47Al-2.3Cr-2.3Wb (atomic percent).
The methods described herein may also be used for
production of metals and metal alloys hy mixing metal
halide or a mixture of metal halides (chlorides, bromides,
iodides and fluorides) and carrying out the process as
described above for the TiCl4 zirconium alloys may be produced using the same procedures
described above for Ti and Ti-alloys respectively. For
zirconium-based products, the starting material is
zirconium chloride. Other examples of metals that can be
produced using the present process include vanadium and
its alloys and intermetallic compounds. Titanium metal
can be produced by the above process following extensive
recycling of titanium chlorides. Titanium intermetallic
compounds which can be produced include Ti3Al, TiAl and
TiAl3. In still further embodiments, reducing agents other
than aluminium which may be able to be used with a metal
subhalide to produce a metal compound can include zinc,
magnesium, sodium, aluminium or other like metals.
The present method may be used for production of
powders with a controlled particle size of various
compositions including compounds of pure metal, oxides,
nitrides of elements such as vanadium and zirconium, as
described above for titanium.
Modifications and variations as would be apparent to
a skilled addressee are deemed to be within the scope of
the present invention.
WE CLAIM :
1. A stepwise method of producing titanium-aluminium
compounds, comprising a first step of:
- reducing an amount of titanium chloride (TiCl4)
with an amount, of aluminium at a temperature to
trigger reactions to form titanium subchloride(s)
and aluminium chloride (A1C13) products;
and then a second step of:
- mixing said products, with the addition of more
aluminium if required, and heating the mixture in
a reaction zone to a temperature above 300C tc
form A1CI? in a gas phase, and no produce an end
product in the reaction zone of the titanium-
aluminium compounds.
2. A method as claimed in claim 1, wherein the method
also provides for driving the removal of A1C1» from
the reaction zone to favour a forward reaction ir. the
second step.
3. A method as claimed in claim 2, wherein the removal
of A1C13 from the reaction zone is continuous.
4. A method as claimed in any one of the preceding
claims, wherein the first step is conducted at a
temperature above the boiling point of A1C13.
5. A method as claimed in any one of the preceding
claims, wherein the first step is conducted at a
temperature above 200C.
6. A method as claimed in any one of the preceding
claims, wherein the first step is conducted with an
excess amount cf aluminium present to reduce all of
the titanium chloride (TiCl*) to form said titanium
subchloride(s) and aluminium chloride v'A1CI3)
products.
7. A method as claimed in any one of the preceding
claims, wherein the second step is conducted at a
temperature in the range 300C to 1000C.
8. A method as claimed in any one of the preceding
claims, comprising the further step of recycling at
least some of che aluminium chloride formed, and
utilising the aluminium chloride to produce TiClj.
9. A method as claimed in claim 8, wherein the aluminium,
chloride is used tc reduce titanium oxide to produce
TiClj.
10. A method as claimed in claim 9, wherein aluminium
oxide is produced by reduction of titanium oxide, and
the aluminium oxide is electrolysed to produce
aluminium raw material for use in the method of any
one of the preceding claims.
11. A method as claimed in any one of the preceding
claims, wherein the aluminium chloride is condensed
away from the reaction zone at a temperature lower
than that in the reaction zone.
12. A method as claimed in any one of the preceding
claims, wherein titanium subchloride which escapes
the reaction zone is condensed at a temperature
different to that in the reaction zone.
13. A method as claimed in claim 12, comprising the
further step of returning the condensed titanium
subchloride tc the reaction zone.
14. A method as claimed in any one of the preceding
claims, also comprising the step of introducing a
source of one or mere elements selected from the
group comprising chromium, niobium, vanadium,
zirconium, silicon, boron, molybdenum, tantalum and
carbon, and products of said method include titanium-
aluminium compounds which include one or more of
these elements.
15. A method as claimed in claim 14, wherein the source
of the element{3) can be a metal halide, a subhalide,
a pure element or another compound which includes the
element.
16. A method as claimed in claim 14 or claim 15, wherein
the products also include one or more of an
intermetallic compound, a titanium-(selected
element)-alloy, and intermediate compounds.
17. A method as claimed in any one of claim 14 to claim
16, wherein the source includes vanadium subchloride,
and a produce of said method is an alloy cr
intermetallic complex including titanium, aluminium
and vanadium.
18. A method as claimed in claim 17, comprising the steps
of adding the source in appropriate proportions, and
carrying out the method to produce Ti-6A1-4V.
19. A method as claimed in claim 14, wherein the source
includes zirconium subchloride, and a product of the
method is an alloy or intermetallic complex including
titanium, aluminium and zirconium.
20. A method as claimed in any one of claims 14 to 16,
wherein the source includes niobium haiide and
chromium halide, and a product of said method is an
alloy or intermetallic complex including titanium,
aluminium, niobium and chromium.
21. A method as claimed in claim 20, comprising the step
ot adding the source in appropriate proportions, and
carrying cut the method to produce Ti-48Al-2Nb-2Cr.
22. A method as claimed in any cne cf the preceding
claims, wherein the aluminium is added in the form of
a powder having an approximate upper grain size of
less than about 50 micrometres.
23. A method as claimed in any one of claims 1 tc 21,
wherein the aluminium is in the form of a powder of
an approximate upper grain size cf greater than about
5C micrometres, and the method comprises the step of
milling the aluminium powder and titanium subchloride
to reduce the grain size of the aluminium powder in
at least one dimension.
24. A method as claimed in any one cf claims 1 to 21,
wherein the aluminium is in the form of flakes having
a thickness in one dimension of less than about 50
micrometres.
25. A method as claimed in any one of the preceding
claims, wherein the method is conducted in ar. inert
gas atmosphere or in a vacuum.
26. A method for production of a powder of titanium-
aluminium intermetallic compounds including at least
one of Ti2Al, TiAl and TiAl3/ and alloys based on
titanium-aluminium intermetailics as claimed in any
one of claims 1 to 25, wherein starting materials for
the method include aluminium powder and titanium
chloride.
27. A method of producing titanium-aluminium compounds,
comprising a first step of:
- heating an amount of titanium chloride (TiClJ in
a plasma of an inert gas and hydrogen mixture, to
produce titanium subchloride(s);
and then a second step of:
- nixing aluminium with said titanium
subchloride{s), and heating the resultant mixture
to produce titanium-aluminium compounds and A1C1*.
28. A method as claimed in claim 27 which is otherwise as
claimed in any one of claims 2 to 25.
29. A stepwise method of producing titanium-aluminium
compounds, comprising a first step of:
- reducing an amount of titanium chloride (TiCl with hydrogen in an inert gas atmosphere or in a
vacuum, and at a temperature to trigger reactions
to form titanium subchloride{s) and aluminium
chloride (AICI2) products;
and then a second step of:
- mixing said products with aluminium, and heating
the mixture in a reaction zone to a temperature
above 30CC tc form AlClj- in a gas phase, and to
produce an end product ir. the reaction zone of the
titanium-aluminium compounds.
30. A method as claimed in claim 29 which is otherwise as
claimed in any one of claims 2 to 25.
31. A stepwise method of producing titanium-aluminium
compounds, comprising a first step of:
- heating a mixture of TiClj and aluminium to form
products TiCl3 and AlClj, at a temperature less
than 300C;
and then a second step of:
- mixing said products, with the addition of more
aluminium if required, and heating the mixture to
a reaction zone temperature above 300C to cause
AICI3 tc be evaporated from the reaction zone and
to form titanium-aluminium compounds.
32. An apparatus for the production of a titanium-
aluminium compound, comprising:
- a reaction vessel arranged in use for the mixing
of aluminium with a titanium haiide or subhalide;
- the vessel also adapted in use for the resultant
mixture to ba heated to a temperature sufficient
for the titanium haiide or subhalide to react with
the aluminium to form the titanium-aluminium
compound and an aluminium haiide;
- one condensation zone arranged in use to operate
at a temperature such that any titanium haiide or
subhalide escaping the reaction mixture condenses
in. that condensation zone; and
- another condensation zone arranged in use to
operate at a temperature such that the aluminium
haiide condenses in the another condensation zone.
33. An apparatus as claimed in claim 32, also comprising
a third condensation zone arranged to condense
titanium haiide that is produced by
disproportior.ation fron escaping the reaction
mixture.
34. An apparatus as claimed in claim 32 or claim 33,
wherein the one condensation zone is arranged to
return condensed titanium haiide or subhalide to the
reaction, zone.

The present invention relates to a method and
apparatus for the production of titanium alloys and
titanium-aluminium inter-metallic compounds and alloys.
Starting from a precursor material including titanium
subchloride (titanium trichloride or titanium dichloride),
the precursor material is reduced by aluminium tc produce
titanium-aluminium intermetallic complexes or alloys and
aluminium chloride which is driven away from the reaction
zone so as to favour the forward reaction and the
production of the titanium-aluminium compounds.
Starting from a precursor material of titanium
subchloride avoids the problems associated with starting
from titanium metal (which is expensive to produce) or
titanium tetrachloride (a reaction very difficult to
0control), and results in the production of powdered forms
of titanium-aluminium compounds with controllable
composition.

A METHOD AND APPARATUS FOR PRODUCING TITANIUM-ALUMINIUM COMPOUNDS

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