Title of Invention	A DEVICE FOR PRODUCING INTERMETALLICS AND A METHOD FOR PRODUCING INTERMETALLICS USING THE DEVICE
Abstract	A device to produce intermetallics and a method for producing intermetallics using the device which comprises of tubular refractory container capable of holding a highly exothermic reaction mixture and the said container being closed at one end by a refractory plate, the closed end of the container being provided with a coaxially fixed tubular refractory capsule having cap/plug capable of holding a reaction mixture of the desired intermetallic, the container housing the capsule said container housing the capsule being characterized in that being enclosed in a metal tube closed at the capsule end with a metal plate , the assembly so obtained being capable of rotation around a external axis .

Title of Invention

A DEVICE FOR PRODUCING INTERMETALLICS AND A METHOD FOR PRODUCING INTERMETALLICS USING THE DEVICE

Abstract

A device to produce intermetallics and a method for producing intermetallics using the device which comprises of tubular refractory container capable of holding a highly exothermic reaction mixture and the said container being closed at one end by a refractory plate, the closed end of the container being provided with a coaxially fixed tubular refractory capsule having cap/plug capable of holding a reaction mixture of the desired intermetallic, the container housing the capsule said container housing the capsule being characterized in that being enclosed in a metal tube closed at the capsule end with a metal plate , the assembly so obtained being capable of rotation around a external axis .

Full Text	The present invention relates to a device for producing intermetallics and a method for producing intermetallics using the device. The present invention provides particularly a device for producing intermetallics by a highly exothermic reaction and a method for producing intermetallics using the novel device. The present invention is also useful to produce many alloys and composites. The materials so produced are useful for many engineering applications. This invention also provides a simple and inexpensive laboratory method for producing new materials. Many intermetallics possess properties such as high melting point, low density, good corrosion resistance and good high temperature strength. These properties have made intermetallics the focus of research for high temperature applications. During the last decade, progress in alloy design and fabrication techniques has brought some of these intermetallics to the threshold of commercial application. Besides intermetallics with good high temperature properties, there are intermetallics with other outstanding properties, which are useful for many important applications. Intermetallics are produced from their constituent elements by various methods. Conventional melting methods, such as arc melting, induction melting and resistance heating have been employed to produce cast intermetallics. Reactive infiltration, where the constituent metal with lower melting point is melted and pressure infiltrated into a porous preform made of the other constituent metal, has also been employed to form these intermetallics. Intermetallics are also produced by Self propagating High temperature Synthesis (SHS). SHS is the term used to describe a process in which reactants, when ignited locally to initiate the reaction, spontaneously transform to products due to the high exothermic heat released by the reaction. Because of the relatively low heats of formation of many intermetallics, particularly many aluminides, the reaction between the constituent elements to produce such an intermetallic can only be initiated after heating the entire mass of the reaction mixture to elevated temperature at a suitable rate using an electric heater. This is referred to as the thermal explosion mode of SHS. Another technique used to carry out such weak exothermic reactions without the help of an electric heater is referred to as the chemical oven method. In this case, the weakly exothermic reaction mixture is encapsulated and placed in a highly exothermic reaction mixture and the later reaction is initiated through * standard methods. Although the formation of the products will be completed, the products produced by SHS will generally have unacceptable levels of porosity. Hence the products produced by SHS require further processing to generate the desired densification and physical form. To overcome this problem, pressure is applied by suitable pressure application devices during or immediately after the reaction to improve the densification of the product. Thus, the disadvantages of the known methods of producing intermetallics from their constituent elements are high consumption of electric power, unacceptable levels of porosity, multiple steps and the requirement of sophisticated equipments. The main object of the present invention is to provide a device for producing intermetallics which obviates the drawbacks as detailed above. Another object of the present invention is to provide a method for producing intermetallics using the device of the present invention. In the drawing accompanying this specification, Fig. 1 represents the schematic illustration of the sectional view of an embodiment of the device of the present invention employed to produce intermetallics according to the present invention. In the present invention, the device to produce intermetallics consists of a refractory container (1) that is closed at one end by a refractory plate (2) and a thin walled refractory capsule (3) containing the mixture of reactants (4) comprising of powders of constituent elements of an Intermetallic. The refractory capsule being closed by a refratory cap (5). The encapsulated mixture of reactants being placed at the end of the refratory container where the refratory container is closed by the refractory plate (2). The refractory container (1) being filled with a highly exothermic reaction mixture (6). The refractory container being enclosed in a metal tube (7) closed near the end housing the encapsulated mixture of reactants by a metal plate (8). The whole assembly being capable of rotation about an external axis (0) by any conventional means. Accordingly, the present invention provides a device for producing intermetallics which comprises a tubular refractory container (1) capable of holding a highly exothermic reaction mixture (6), the said container being closed at one end by a refractory plate (2), the closed end of the container being provided with a coaxially fixed tubular refractory capsule (3) having cap/plug (5) capable of holding a reaction mixture (4) of the desired intermetallic and the said container housing the capsule being characterized in that being enclosed in a metal tube (7) closed at the capsule end with a metal plate (8) and the assembly so obtained being capable of rotation around a external axis (0). In an embodiment of the present invention the capsule used is a thin walled refractory capsule with a removably fixed cap/plug. In another embodiment of the present invention the rotation about an external axis is provided by any conventional means. In yet another embodiment of the present invention a method for producing intermetallics, using the device which comprises. a) filling the thin walled refractory capsule with the homogeneous mixture of reactants, containing powders of the constituent elements of the desired intermetallic in stoichiometric amounts, b) closing the refractory capsule by a refractory cap, c) housing the encapsulated mixture of reactants at the end of the refractory container where the refractory container is closed by a refractory plate, d) filling the hollow space in the refractory container with a highly exothermic reaction mixture capable of self propagating exothermic reaction on ignition, e) rotating the whole assembly about an external axis to provide a centrifugal force of atleast 5G at the base of the capsule, f) igniting the highly exothermic reaction mixture in the refractory container at least at one point on its free or exposed surface to initiate the reaction, g) continuing the rotation for sufficient time to allow the assembly to cool by loosing heat to the surroundings, h) removing the reaction products of the highly exothermic reaction along with the embedded refractory capsule, containing the intermetallic, from the refractory container, i) separating the refractory capsule, containing the intermetallic, from the products of the highly exothermic reaction and j) releasing the intermetallic from the refractory capsule. In an embodiment of the present invention, the mixture of reactants may be compacted and the compact is encapsulated prior to carrying out the said method. In another embodiment of the present invention, the highly exothermic reaction mixture used may be aluminium based thermit mixture. In yet another embodiment the synthesis may be carried out in an inert atmosphere. In still another embodiment of the present invention, the centrifugal force at the base of the capsule may be in the range of 5 to 1500 G. The detailed description of the process steps required to produce intermetallics by the present method is given below. In the present invention, a self propagating exothermic reaction is carried out by igniting a small portion of a highly exothermic reaction mixture held in a refractory container having an encapsulated mixture of reactants, containing powders of the constituent elements of the desired intermetallic, at its closed end while the refractory container is rotated about an external axis so that the heat released by the highly exothermic reaction is transferred to the encapsulated mixture of reactants resulting in the complete conversion of the reactants in the capsule to the desired intermetallic. Any self sustaining exothermic reaction, that can release sufficient quantity of heat to raise the temperature of the encapsulated mixture of reactants, consisting of powders of the constituents elements of the desired intermetallic, to the temperature required for complete conversion of the mixture of reactants to the desired intermetallic is useful in the present method. Many self sustaining exothermic reactions involving solid + solid and solid + gas reactants are useful. Since many self sustaining exothermic reactions involving solid + gas reactants require gas at high pressure, self sustaining exothermic reactions which involve solid + solid reactants and meet the above requirements arc preferred in the present method. Many conventionally used thermit reactions, which involve solid + solid reactants, readily meet these requirements to produce most of the intermetallics by the present method. However, aluminium based thermit reactions are more preferred in the present method due to lower ignition temperature (approx.1200°C), easiness in controlling the reaction and easy availability of the materials at tower costs. Additionally, other elements or compounds can be added to the thermit mixture or combination of thermit mixtures can be employed to generate the required quantity of heat to produce the desired intermetallic by the present method. A few self sustaining thermit reactions useful for the present method and their estimated heats of reaction (AH) and adiabatic temperatures (Tad) are shown in table 1. The values of AH and Tad (i.e. the temperature to which the products of the thermit reaction are raised) were estimated from the principles of thermodynamics assuming that the thermit reactions take place under adiabatic conditions. Table 1. (Table Removed) If the thermit reaction is not self sustaining, prior heating of the thermit mixture to a suitable temperature is required to meet the requirements of the method. A thermit mixture is prepared by uniformly blending the powders of a strongly reductive element, preferably aluminium, and a reducible metal oxide, together with any material if desired, in stoichio metric amounts. This is done by mixing the powders in a mechanical mixer or blender, preferably sealed, for 12 to 24 hours. The powders used are preferably of size -200 mesh or finer and baked at about 120°C for 12 to 24 hours. A homogeneous mixture of reactants is prepared by uniformly mixing or blending the powders of the constituent elements of the required intermetallic. The mixing ratio can be stoichiometric or otherwise as permitted by the phase diagram of the system. The required quantities of powders of other materials can be blended with this mixture for producing an alloy or a composite based on the desired intermetallic. When small quantities of powders are handled, mortar and pestle are useful for producing a homogeneous mixture. When large quantities of powders are involved, mixing or blending for long time in a mechanical mixer or blender is essential to prepare such homogeneous mixture of reactants. The powders of reactants used are preferably of size -100 mesh or finer. In the next step, a thin walled capsule is filled to the required depth with the prepared homogeneous mixture of reactants. The capsufc can be gently tapped and the powder in the capsule can be lightly pressed using a metal plunger to improve packing of the powder mixture in the capsule. This helps in improving the heat transfer between the capsule and the powder mixture and the particles themselves. The mixture of reactants can also be compacted in a mechanical press and the compact can be inserted in the capsule. This helps in improving the heat transfer between particles further. However, the compact should be of size such that it is inserted in the capsule as closely as possible for good heat transfer between the capsule and the compact. It is desirable to make the thin walled capsules from a material that is capable of withstanding high temperature while it is stable, inert and having good thermal conductivity at all temperatures. Depending on the intermetallic to be produced and the thermit reaction employed in the present method, many high temperature refractories and metallic materials, which meet these requirements partly or fully, are useful for making thin walled capsules. Graphite is the preferred capsule material in most cases as it is easily available, low in cost, easily machinable, having good thermal conductivity, having good thermal shock resistance, inert with respect to many metals and products of many thermit reactions at elevated temperatures and easily castable with a suitable binder to produce thin walled shaped capsules. The wall thickness of the capsule should be as small as possible. However, it should be sufficient to withstand the stresses developed while carrying out the method. The wall thickness in the range 0.25 to 4 mm is sufficient in most cases. It is desirable to provide a thin coating of an inert material on the inside surface of the capsule if the capsule material reacts with the contents of the capsule at the operating temperatures. The size and shape of the capsule determines the size and shape of the article being produced from the desired intermetaliic by the present method. The capsule filled with the mixture of reactants is then tightly closed by a cap. The material and wall thickness of the cap can be identical to those used for the capsule. The cap prevents the products of the thermit reaction, being carried out in the refractory container, from entering the capsule. Additionally, the cap allows the gases present in the capsule and produced during the formation of the intermetaliic to escape to the ambient by separating itself from the capsule under the pressure developed inside the capsule during the synthesis of the intermetaliic at elevated temperature. This prevents bursting of the thin walled capsule while carrying out the present method. A simple plug can also be used in place of the cap to close the capsule. The closed capsule containing the mixture of reactants is then placed, as shown in Fig.l, inside a hollow refractory container at the end where the refractory container is closed by a refractory plate. It is desirable to secure the capsule firmly to the refractory plate. The refractory container and plate are made of a material, which can withstand high temperature while it is stable and inert at the temperature attained during the thermit reaction. Graphite is a suitable material for refractory container and plate in most cases. It is preferable to maintain the thickness of the refractory plate and wall thickness of the refractory container as small as possible to prevent the refractory container and plate from absorbing major portion of the heat produced by the thermit reaction. Thickness of * from 1 to 5 mm is adequate in most cases. It is preferable to provide suitable thermal insuktion on the external surfaces of the refractory container and pkte in such cases. These conditions help in the effective utilisation of the heat produced by the thermit reaction to produce the desired intermetallic by the present method. The refractory container, having the encapsulated mixture of reactants, is then filled with the prepared thermit mixture. The size of the refractory container should be such that it can accommodate enough quantity of thermit mixture so that, after the completion of the thermit reaction, the products of the thermit reaction cover approximately the height of the mixture of reactants inside the capsule. Also, the heat released by the thermit reaction in the container should be sufficient to raise the temperature of the encapsulated mixture of reactants to the temperature required for complete conversion of the reactants to the desired intermetallic, after taking into account the heat tosses to the surroundings. The refractory container can be tapped gently for a few times and the thermit mixture inside the container can be packed well using a metal plunger either manually or in a mechanical press. The refractory container, along with the components thus assembled, is then inserted in a supporting metal tube such that the encapsulated mixture of reactants inside the container is at the end of the metal tube where the tube is closed by a metal plate. The wall thickness of the metal tube and thickness of the metal plate should be selected such that the metal tube and plate have sufficient strength to withstand the stresses induced in them by the centrifugal force developed while carrying out the present method. Suitable metals for the tube and plate include iron, nickel, chromium as well as their alloys. The metal tube, along with the components assembled as above, is rotated about an external axis by any conventional means. The speed of rotation should be selected such .' that the encapsulated mixture of reactants experience the desired centrifugal force at the closed end of the refractory container. Centrifugal force of from 5 to 1500 G at the closed end of the refractory container is adequate in most of the cases. While the assembly is rotating, the thermit reaction is initiated by locally heating the thermit mixture in the refractory container at least at one point on the free or exposed surface of the thermit mixture, facing the center of rotation, to or above the ignition temperature. This may be carried out, for example, by bringing an electric arc, struck between two electrodes, in contact with the free surface of the thermit mixture in the refractory container. The thermit reaction, thus initiated, rapidly propagates through the remaining thermit mixture in the refractory container to convert all the thermit mixture to products. The products of thermit reaction collect at the closed end of the refractory container surrounding the encapsulated mixture of reactants. The heat content of the products of the thermit reaction is transferred to the capsule and the mixture of reactants therein by conduction to convert the mixture of reactants to the desired intermetallic. The temperature to which the mixture of reactants is heated can be determined approximately by encapsulating the powders of pure metals or alloys having known melting points and carrying out the method similarly. An intermetallic based on a reactive metal can be produced by the present method by carrying out the method under vacuum or inert atmosphere. After the completion of the reaction, the rotation of the assembly is continued for sufficient time to allow the assembly to cool by loosing heat to the surroundings. The cooling time can be reduced by forced convection. After cooling of the assembly, the rotation is stopped and the refractory container is separated from the metal tube. The products of the thermit reaction, along with the embedded capsule containing the intermetallic, are removed from the refractory container. This can be done using a metal plunger either manually or in a mechanical press. The intermetallic is then separated from the refractory capsule. As is understood from the above description, heat released by a highly exothermic reaction is utilised to produce an intermetallic. Thus the present method requires no expensive furnace to produce an intermetallic, thereby, minimising power consumption. The application of centrifugal force during the synthesis helps in producing dense intermetallics and thus overcomes the use of separate pressure application devices. This also helps in preventing the escape of the products of the thermit reaction from the refractory container and, thereby, utilising the optimum quantity of thermit mixture required for the synthesis. The method is simple and inexpensive as no sophisticated equipments are involved. The method permits the production of shaped articles from the desired intermetallic using shaped refractory capsules. The following examples are given by way of illustration of the present invention and should not be construed to limit the scope of the present invention. Example 1 Iron Oxide (Fe2O3) and aluminium powders, having size of -325 mesh, were dried in an electric oven at 120°C for 12 hours. A thermit mixture was prepared from these powders by mixing 100 g of iron oxide and 33.8 g of aluminium in a sealed double cone blender for 12 hours. The mixing ratio was approximately stoichiometric. A homogeneous mixture of reactants for producing nickel aluminide (NiAl) was prepared by mixing 20g of nickel and 9.19g of aluminium powders of-200 mesh size in a pestle and mortar. The mixing ratio was nearly stoichiometric. A graphite capsule of 6mm internal diameter, 0.5 mm wall thickness and 15 mm length was loaded with l.lg of this mixture of reactants. The capsule was then tightly closed by a graphite cap. The capsule, containing the mixture of reactants, was then placed in upright position inside a graphite container, having 15mm internal diameter, 1.5mm wall thickness and 39.5mm length, at the end where the container was closed by 1 mm thick graphite disc. The external surfaces of the container and disc were provided with thermal insulation using a ceramic of 3mm thickness. The graphite container was then filled with 6.5g of the prepared thermit mixture. The graphite container, along with other components thus assembled, was inserted in a mild steel tube of 25mm inside diameter, 3 mm wall thickness and 50mm length. The end of the mild steel tube, where the capsule was located inside the container, was closed by fixing 12 mm thick circular mild steel plate inside the steel tube. The mild steel tube, along with the components thus assembled, was rotated at 4260 rpm about an external axis so that the closed end of the graphite container experienced a centrifugal force of about 950G. While the assembly was rotating, the thermit reaction was initiated by bringing an electric arc, struck between two mild steel electrodes, in contact with the free surface of the thermit mixture in the graphite container. The reaction, thus initiated, rapidly propagated through the remaining thermit mixture in the graphite container and was completed in about three seconds. The products of the thermit reaction collected at the closed end of the graphite container surrounding the graphite capsule. The rotation of the assembly was continued for 15 more minutes to allow the assembly to cool. The graphite container was then removed from the steel tube. The products of the thermit reaction and the capsule embedded therein were separated from the graphite container. The intermetallic produced was then released from the capsule. X-ray analysis showed that the intermetallie was predominantly NiAl. The density of the produced NiAl was 5.7g/cm3. The average Vickers hardness for 200g load was found to be 336. The EDX analysis in SEM showed that it contained 74% Ni and 26% Al (in wt.%). Example 2 Iron Oxide (Fe2O3) and aluminium powders, having size of -325 mesh, were dried in an electric oven at 120° C for 12 hours. A thermit mixture was prepared from these powders by mixing l00g of iron oxide and 33.8 g of aluminium in a sealed double cone blender for 12 hours. The mixing ratio was approximately stoichiometric. A homogeneous mixture of reactants for producing nickel aluminide (NiAl) was prepared by mixing 20g of nickel and 9.19g of aluminium powders of -200 mesh size in a pestle and mortar. The mixing ratio was nearly stoichiometric. A graphite capsule of 6mm internal diameter, 0.5 mm wall thickness and 15 mm length was loaded with l.lg of this mixture of reactants in argon atmosphere. The capsule was then tightly closed by a graphite cap. The capsule, containing the mixture of reactants, was then placed in upright position inside a graphite container, having 15mm internal diameter, 1.5mm wall thickness and 39.5mm length, at the end where the container was closed by 1mm thick graphite disc. The external surfaces of the container and disc were provided with thermal insulation using a ceramic of 3mm thickness. The graphite container was then filled with 5.7g of the prepared thermit mixture. The graphite container, along with other components thus assembled, was inserted in a mild steel tube of 25mm inside diameter, 3 mm wall thickness and 50mm length. The end of the mild steel tube, where the capsule was located inside the container, was closed by fixing 12 mm thick circular mild steel plate inside the steel tube. The mild steel tube, along with the components thus assembled, was rotated at 2840 rpm about an external axis inside a stainless steel chamber filled with argon gas so that the closed end of the graphite container experienced a centrifugal force of about 425G. While the assembly was rotating, the thermit reaction was initiated by bringing an electric arc, struck between two mild steel electrodes, in contact with the free surface of the thermit mixture in the graphite container. The reaction, thus initiated, rapidly propagated through the remaining thermit mixture in the graphite container and was completed in about three seconds. The products of the thermit reaction collected at the closed end of the graphite container surrounding the graphite capsule. The rotation of the assembly was continued for 15 more minutes to allow the assembly to cool. The graphite container was then removed from the steel tube. The products of the thermit reaction and the capsule embedded therein were separated from the graphite container. The intermetallic produced was then released from the capsule. X-ray analysis showed that the intermetallic was predominantly NiAl. The density of the produced NiAl was 5.82g/cm3. The average Vickers hardness for 200g load was found to be 389. The EDX analysis in SEM showed that it contained 74% Ni and 26% Al (in wt.%). Example 3 Iron Oxide (Fe2O3) and aluminium powders, having size of -325 mesh, were dried in an electric oven at 120° C for 12 hours. A thermit mixture was prepared from these powders by mixing 100 g of iron oxide and 33.8 g of aluminium in a sealed double cone blender for 12 hours. The mixing ratio was approximately stoichiometric. A homogeneous mixture of reactants for producing nickel aluminide (NiAl) was prepared by mixing 20g of nickel and 9.19g of aluminium powders of-200 mesh size in a pestle and mortar. The mixing ratio was nearly stoichiometric. A compact of 6 mm diameter and 9.4mm length was prepared from this mixture in a screw press using stainless steel die and punches. The green density of the compact was 87% of the theoretical density of the mixture. This compact was inserted in a graphite capsule of 6 mm internal diameter, 0.5 mm wall thickness and 15 mm length. The capsule was then tightly closed by a graphite cap. The capsule, containing the compact was then placed in upright position inside a graphite container, having 15mm internal diameter, 1.5mm wall thickness and 39.5mm length, at the end where the container was closed by 1mm thick graphite disc. The external surfaces of the container and disc were provided with thermal insulation using a ceramic of 3mm thickness. The graphite container was then filled with 6.5g of the prepared thermit mixture. The graphite container, along with other components thus assembled, was inserted in a mild steel tube of 25mm inside diameter, 3 mm wall thickness and 50mm length. The end of the mild steel tube, where the capsule was located inside the container, was closed by fixing 12 mm thick circular mild steel plate inside the steel tube. The mild steel tube, along with the components thus assembled, was rotated at 2840 rpm about an external axis so that the closed end of the graphite container experienced a centrifugal force of about 425G. While the assembly was rotating, the thermit reaction was initiated by bringing an electric arc, struck between two mild steel electrodes, in contact with the free surface of the thermit mixture in the graphite container. The reaction, thus initiated, rapidly propagated through the remaining thermit mixture in the graphite container and was completed in about three seconds. The products of the thermit reaction collected at the closed end of the graphite container surrounding the graphite capsule. The rotation of the assembly was continued for 15 more minutes to allow the assembly to cool. The graphite container was then removed from the steel tube. The products of the thermit reaction and the capsule embedded therein were separated from the graphite container. The intermetallic produced was then released from the capsule. X-ray analysis showed that the intermetallic was predominantly NiAl. The density of the produced NiAl was 5.7g/cm3. The average Vickers hardness for 200g load was found to be 356. The EDX analysis in SEM showed that it contained 71% Ni and 29% Al (in wt.%). Example 4 Iron Oxide (T^Ch) and aluminium powders, having size of -325 mesh, were dried in an electric oven at 120°C for 12 hours. A thermit mixture was prepared from these powders by mixing 100 g of iron oxide and 33.8 g of aluminium hi a sealed double cone blender for 12 hours. The mixing ratio was approximately stoichiometric. A homogeneous mixture of reactants for producing nickel aluminide (NiAl) was prepared by mixing 20g of nickel and 9.19g of aluminium powders of-200 mesh size in a pestle and mortar. The mixing ratio was nearly stoichiometric. A compact of 6 mm diameter and 10mm length was prepared from this mixture in a screw press using stainless steel die and punches. The green density of the compact was 79% of the theoretical density of the mixture. This compact was inserted in a graphite capsule of 6 mm internal diameter, 0.5 mm wall thickness and 15 mm length in argon atmosphere. The capsule was then tightly closed by a graphite cap. The capsule, containing the compact was then placed in upright position inside a graphite container, having 15mm internal diameter, 1.5mm wall thickness and 39.5mm length, at the end where the container was closed by 1mm thick graphite disc. The external surfaces of the container and disc were provided with thermal insulation using a ceramic of 3mm thickness. The graphite container was then filled with 5.8g of the prepared thermit mixture. The graphite container, along with other components thus assembled, was inserted in a mild steel tube of 25mm inside diameter, 3 mm wall thickness and 50mm length. The end of the mild steel tube, where the capsule was located inside the container, was closed by fixing 12 mm thick circular mild steel plate inside the steel tube. The mild steel tube, along with the components thus assembled, was rotated at 2840 rpm about an external axis inside a stainless steel chamber filled with argon gas so that the closed end of the graphite container experienced a centrifugal force of about 425G. While the assembly was rotating, the thermit reaction was initiated by bringing an electric arc, struck between two mild steel electrodes, in contact with the free surface of the thermit mixture in the graphite container. The reaction, thus initiated, rapidly propagated through the remaining thermit mixture in the graphite container and was completed in about three seconds. The products of the thermit reaction collected at the closed end of the graphite container surrounding the graphite capsule. The rotation of the assembly was continued for 15 more minutes to allow the assembly to cool. The graphite container was then removed from the steel tube. The products of the thermit reaction and the capsule embedded therein were separated from the graphite container. The intermetallic produced was then released from the capsule. X-ray analysis showed that the intermetallic was predominantly NiAl. The density of the produced NiAl was 5.86g/cm3. The average Vickers hardness for 200g load was found to be 361. The EDX analysis in SEM showed that ft contained 72% Ni and 28% Al (in wt.%). The present method for producing intermetallics has been demonstrated by these examples wherein dense intermetallics were produced without employing an electric furnace or a separate pressure application device. Also, the intermetallics were synthesized and densified in one step. The present method can also be employed to produce other alloys and composites not covered in these examples. The present method permits the production of shaped articles using shaped refractory capsules. The method can be used for batch production by placing the required number of devices, shown in fig.l, radially about a central axis and carrying out the method. The main advantages of the present invention are : 1. simplicity, 2. Shorter processing time, 3. lower energy consumption as no electric heating device is required to produce intermetallics, 4. the material is synthesized and densified in one step, 5. no separate pressure application device is needed for densification of the product, 6. the method permits the production of shaped articles, 7. batch production is possible and 8. the method is useful as a simple and inexpensive laboratory method for producing alloys and composites. WE CLAIM : 1. A device for producing intermetallics which comprises of tubular refractory container(l) capable of holding a highly exothermic reaction mixture (6), the said container being closed at one end by a refractory plate (2), the closed end of the container being provided with a coaxially fixed tubular refractory capsule (3) having cap/plug (5) capable of holding a reaction mixture (4) of the desired intermetallic and the said container housing the capsule being characterized in that being enclosed in a metal tube (7) closed at the capsule end with a metal plate (8) and the assembly so obtained being capable of rotation around a external axis . 2. A device as claimed in claim 1, wherein the capsule used is a thin walled refractory capsule with a removably fixed cap/plug. 3. A device as claimed in claim 1-2, wherein the rotation about an external axis is provided by any conventional means. 4. A method for producing intermetallics, using the device as claimed in claims 1- 3 , which comprise a) filling the thin walled refractory capsule with the homogeneous mixture of reactants, containing powders of the constituent elements of the desired intermetallic in stoichiometric amounts, b) closing the refractory capsule by a refractory cap, c) housing the encapsulated mixture of reactants at the end of the refractory container where the refractory container is closed by a refractory plate, 8. A method as claimed in claims 4-7, wherein the synthesis is carried out in an inert atmosphere. 9. A device for producing intermetallics substantially as herein described with reference to the examples and drawing accompanying this specification.

Full Text

The present invention relates to a device for producing intermetallics and a method for producing intermetallics using the device.
The present invention provides particularly a device for producing intermetallics by a highly exothermic reaction and a method for producing intermetallics using the novel device. The present invention is also useful to produce many alloys and composites. The materials so produced are useful for many engineering applications. This invention also provides a simple and inexpensive laboratory method for producing new materials.
Many intermetallics possess properties such as high melting point, low density, good corrosion resistance and good high temperature strength. These properties have made intermetallics the focus of research for high temperature applications. During the last decade, progress in alloy design and fabrication techniques has brought some of these intermetallics to the threshold of commercial application. Besides intermetallics with good high temperature properties, there are intermetallics with other outstanding properties, which are useful for many important applications. Intermetallics are produced from their constituent elements by various methods. Conventional melting methods, such as arc melting, induction melting and resistance heating have been employed to produce cast intermetallics. Reactive infiltration, where the constituent metal with lower melting point is melted and pressure infiltrated into a porous preform made of the other constituent metal, has also been employed to form these intermetallics. Intermetallics are also produced by Self propagating High temperature Synthesis (SHS). SHS is the term used to describe a process in which reactants, when ignited locally to initiate the reaction,
spontaneously transform to products due to the high exothermic heat released by the reaction. Because of the relatively low heats of formation of many intermetallics, particularly many aluminides, the reaction between the constituent elements to produce such an intermetallic can only be initiated after heating the entire mass of the reaction mixture to elevated temperature at a suitable rate using an electric heater. This is referred to as the thermal explosion mode of SHS. Another technique used to carry out such weak exothermic reactions without the help of an electric heater is referred to as the chemical oven method. In this case, the weakly exothermic reaction mixture is encapsulated and placed in a highly exothermic reaction mixture and the later reaction is initiated through
*
standard methods. Although the formation of the products will be completed, the products produced by SHS will generally have unacceptable levels of porosity. Hence the products produced by SHS require further processing to generate the desired densification and physical form. To overcome this problem, pressure is applied by
suitable pressure application devices during or immediately after the reaction to improve the densification of the product. Thus, the disadvantages of the known methods of producing intermetallics from their constituent elements are high consumption of electric power, unacceptable levels of porosity, multiple steps and the requirement of sophisticated equipments.
The main object of the present invention is to provide a device for producing intermetallics which obviates the drawbacks as detailed above.
Another object of the present invention is to provide a method for producing intermetallics using the device of the present invention.
In the drawing accompanying this specification, Fig. 1 represents the schematic illustration of the sectional view of an embodiment of the device of the present invention employed to produce intermetallics according to the present invention.
In the present invention, the device to produce intermetallics consists of a refractory
container (1) that is closed at one end by a refractory plate (2) and a thin walled
refractory capsule (3) containing the mixture of reactants (4) comprising of powders of constituent elements of an Intermetallic. The refractory capsule being closed by a refratory cap (5). The encapsulated mixture of reactants being placed at the end of the refratory container where the refratory container is closed by the refractory plate (2). The
refractory container (1) being filled with a highly exothermic reaction mixture (6). The refractory container being enclosed in a metal tube (7) closed near the end housing the encapsulated mixture of reactants by a metal plate (8). The whole assembly being capable of rotation about an external axis (0) by any conventional means.
Accordingly, the present invention provides a device for producing intermetallics which comprises a tubular refractory container (1) capable of holding a highly exothermic reaction mixture (6), the said container being closed at one end by a refractory plate (2), the closed end of the container being provided with a coaxially fixed tubular refractory capsule (3) having cap/plug (5) capable of holding a reaction mixture (4) of the desired
intermetallic and the said container housing the capsule being characterized in that being enclosed in a metal tube (7) closed at the capsule end with a metal plate (8) and the assembly so obtained being capable of rotation around a external axis (0).
In an embodiment of the present invention the capsule used is a thin walled
refractory capsule with a removably fixed cap/plug.
In another embodiment of the present invention the rotation about an external axis
is provided by any conventional means.
In yet another embodiment of the present invention a method for producing
intermetallics, using the device which comprises.
a) filling the thin walled refractory capsule with the homogeneous mixture of
reactants, containing powders of the constituent elements of the desired
intermetallic in stoichiometric amounts,
b) closing the refractory capsule by a refractory cap,
c) housing the encapsulated mixture of reactants at the end of the refractory
container where the refractory container is closed by a refractory plate,
d) filling the hollow space in the refractory container with a highly exothermic
reaction mixture capable of self propagating exothermic reaction on
ignition,
e) rotating the whole assembly about an external axis to provide a centrifugal
force of atleast 5G at the base of the capsule,
f) igniting the highly exothermic reaction mixture in the refractory container at least at
one point on its free or exposed surface to initiate the reaction,
g) continuing the rotation for sufficient time to allow the assembly to cool by loosing
heat to the surroundings,
h) removing the reaction products of the highly exothermic reaction along with the embedded refractory capsule, containing the intermetallic, from the refractory container,
i) separating the refractory capsule, containing the intermetallic, from the products of the highly exothermic reaction and
j) releasing the intermetallic from the refractory capsule.
In an embodiment of the present invention, the mixture of reactants may be compacted and the compact is encapsulated prior to carrying out the said method.
In another embodiment of the present invention, the highly exothermic reaction mixture
used may be aluminium based thermit mixture.
In yet another embodiment the synthesis may be carried out in an inert atmosphere.
In still another embodiment of the present invention, the centrifugal force at the base of the capsule may be in the range of 5 to 1500 G.
The detailed description of the process steps required to produce intermetallics by the present method is given below.
In the present invention, a self propagating exothermic reaction is carried out by igniting a small portion of a highly exothermic reaction mixture held in a refractory container having an encapsulated mixture of reactants, containing powders of the constituent elements of the desired intermetallic, at its closed end while the refractory container is rotated about an external axis so that the heat released by the highly exothermic reaction is transferred to the encapsulated mixture of reactants resulting in the complete conversion of the reactants in the capsule to the desired intermetallic.
Any self sustaining exothermic reaction, that can release sufficient quantity of heat to raise the temperature of the encapsulated mixture of reactants, consisting of powders of the constituents elements of the desired intermetallic, to the temperature required for complete conversion of the mixture of reactants to the desired intermetallic is useful in the present method. Many self sustaining exothermic reactions involving solid + solid and solid + gas reactants are useful. Since many self sustaining exothermic reactions involving solid + gas reactants require gas at high pressure, self sustaining exothermic reactions which involve solid + solid reactants and meet the above requirements arc preferred in the present method. Many conventionally used thermit reactions, which involve solid + solid reactants, readily meet these requirements to produce most of the intermetallics by the present method. However, aluminium based thermit reactions are more preferred in the present method due to lower ignition temperature (approx.1200°C), easiness in controlling the reaction and easy availability of the materials at tower costs. Additionally, other elements or compounds can be added to the thermit mixture or combination of thermit mixtures can be employed to generate the required quantity of
heat to produce the desired intermetallic by the present method. A few self sustaining thermit reactions useful for the present method and their estimated heats of reaction (AH) and adiabatic temperatures (Tad) are shown in table 1. The values of AH and Tad (i.e. the temperature to which the products of the thermit reaction are raised) were estimated from the principles of thermodynamics assuming that the thermit reactions take place under adiabatic conditions.
Table 1.
(Table Removed)
If the thermit reaction is not self sustaining, prior heating of the thermit mixture to a suitable temperature is required to meet the requirements of the method.
A thermit mixture is prepared by uniformly blending the powders of a strongly reductive element, preferably aluminium, and a reducible metal oxide, together with any material if desired, in stoichio metric amounts. This is done by mixing the powders in a mechanical mixer or blender, preferably sealed, for 12 to 24 hours. The powders used are preferably of size -200 mesh or finer and baked at about 120°C for 12 to 24 hours.
A homogeneous mixture of reactants is prepared by uniformly mixing or blending the powders of the constituent elements of the required intermetallic. The mixing ratio can
be stoichiometric or otherwise as permitted by the phase diagram of the system. The required quantities of powders of other materials can be blended with this mixture for producing an alloy or a composite based on the desired intermetallic. When small quantities of powders are handled, mortar and pestle are useful for producing a homogeneous mixture. When large quantities of powders are involved, mixing or blending for long time in a mechanical mixer or blender is essential to prepare such homogeneous mixture of reactants. The powders of reactants used are preferably of size -100 mesh or finer.
In the next step, a thin walled capsule is filled to the required depth with the prepared homogeneous mixture of reactants. The capsufc can be gently tapped and the powder in the capsule can be lightly pressed using a metal plunger to improve packing of the powder mixture in the capsule. This helps in improving the heat transfer between the capsule and the powder mixture and the particles themselves. The mixture of reactants can also be compacted in a mechanical press and the compact can be inserted in the capsule. This helps in improving the heat transfer between particles further. However, the compact should be of size such that it is inserted in the capsule as closely as possible for good heat transfer between the capsule and the compact. It is desirable to make the thin walled capsules from a material that is capable of withstanding high temperature while it is stable, inert and having good thermal conductivity at all temperatures. Depending on the intermetallic to be produced and the thermit reaction employed in the present method, many high temperature refractories and metallic
materials, which meet these requirements partly or fully, are useful for making thin walled capsules. Graphite is the preferred capsule material in most cases as it is easily available, low in cost, easily machinable, having good thermal conductivity, having good thermal shock resistance, inert with respect to many metals and products of many thermit reactions at elevated temperatures and easily castable with a suitable binder to produce thin walled shaped capsules. The wall thickness of the capsule should be as small as possible. However, it should be sufficient to withstand the stresses developed while carrying out the method. The wall thickness in the range 0.25 to 4 mm is sufficient in most cases. It is desirable to provide a thin coating of an inert material on the inside surface of the capsule if the capsule material reacts with the contents of the capsule at the operating temperatures. The size and shape of the capsule determines the size and shape of the article being produced from the desired intermetaliic by the present method.
The capsule filled with the mixture of reactants is then tightly closed by a cap. The material and wall thickness of the cap can be identical to those used for the capsule. The cap prevents the products of the thermit reaction, being carried out in the refractory container, from entering the capsule. Additionally, the cap allows the gases present in the capsule and produced during the formation of the intermetaliic to escape to the ambient by separating itself from the capsule under the pressure developed inside the capsule during the synthesis of the intermetaliic at elevated temperature. This prevents bursting of the thin walled capsule while carrying out the present method. A simple plug can also be used in place of the cap to close the capsule.
The closed capsule containing the mixture of reactants is then placed, as shown in Fig.l, inside a hollow refractory container at the end where the refractory container is closed by a refractory plate. It is desirable to secure the capsule firmly to the refractory plate. The refractory container and plate are made of a material, which can withstand high temperature while it is stable and inert at the temperature attained during the thermit reaction. Graphite is a suitable material for refractory container and plate in most cases. It is preferable to maintain the thickness of the refractory plate and wall thickness of the refractory container as small as possible to prevent the refractory container and plate from absorbing major portion of the heat produced by the thermit reaction. Thickness of
*
from 1 to 5 mm is adequate in most cases. It is preferable to provide suitable thermal insuktion on the external surfaces of the refractory container and pkte in such cases. These conditions help in the effective utilisation of the heat produced by the thermit reaction to produce the desired intermetallic by the present method.
The refractory container, having the encapsulated mixture of reactants, is then filled with the prepared thermit mixture. The size of the refractory container should be such that it can accommodate enough quantity of thermit mixture so that, after the completion of the thermit reaction, the products of the thermit reaction cover approximately the height of the mixture of reactants inside the capsule. Also, the heat released by the thermit reaction in the container should be sufficient to raise the temperature of the encapsulated mixture of reactants to the temperature required for complete conversion of the reactants to the
desired intermetallic, after taking into account the heat tosses to the surroundings. The refractory container can be tapped gently for a few times and the thermit mixture inside
the container can be packed well using a metal plunger either manually or in a mechanical press.
The refractory container, along with the components thus assembled, is then inserted in a supporting metal tube such that the encapsulated mixture of reactants inside the container is at the end of the metal tube where the tube is closed by a metal plate. The wall thickness of the metal tube and thickness of the metal plate should be selected such that the metal tube and plate have sufficient strength to withstand the stresses induced in them by the centrifugal force developed while carrying out the present method. Suitable metals for the tube and plate include iron, nickel, chromium as well as their alloys.
The metal tube, along with the components assembled as above, is rotated about an external axis by any conventional means. The speed of rotation should be selected such
.'
that the encapsulated mixture of reactants experience the desired centrifugal force at the closed end of the refractory container. Centrifugal force of from 5 to 1500 G at the closed end of the refractory container is adequate in most of the cases.
While the assembly is rotating, the thermit reaction is initiated by locally heating the thermit mixture in the refractory container at least at one point on the free or exposed surface of the thermit mixture, facing the center of rotation, to or above the ignition temperature. This may be carried out, for example, by bringing an electric arc, struck between two electrodes, in contact with the free surface of the thermit mixture in the refractory container. The thermit reaction, thus initiated, rapidly propagates through the
remaining thermit mixture in the refractory container to convert all the thermit mixture to products. The products of thermit reaction collect at the closed end of the refractory container surrounding the encapsulated mixture of reactants. The heat content of the products of the thermit reaction is transferred to the capsule and the mixture of reactants therein by conduction to convert the mixture of reactants to the desired intermetallic. The temperature to which the mixture of reactants is heated can be determined approximately by encapsulating the powders of pure metals or alloys having known melting points and carrying out the method similarly. An intermetallic based on a reactive metal can be produced by the present method by carrying out the method under vacuum or inert atmosphere.
After the completion of the reaction, the rotation of the assembly is continued for sufficient time to allow the assembly to cool by loosing heat to the surroundings. The
cooling time can be reduced by forced convection.
After cooling of the assembly, the rotation is stopped and the refractory container is separated from the metal tube. The products of the thermit reaction, along with the embedded capsule containing the intermetallic, are removed from the refractory container. This can be done using a metal plunger either manually or in a mechanical press. The intermetallic is then separated from the refractory capsule.
As is understood from the above description, heat released by a highly exothermic reaction is utilised to produce an intermetallic. Thus the present method requires no
expensive furnace to produce an intermetallic, thereby, minimising power consumption. The application of centrifugal force during the synthesis helps in producing dense intermetallics and thus overcomes the use of separate pressure application devices. This also helps in preventing the escape of the products of the thermit reaction from the refractory container and, thereby, utilising the optimum quantity of thermit mixture required for the synthesis. The method is simple and inexpensive as no sophisticated equipments are involved. The method permits the production of shaped articles from the desired intermetallic using shaped refractory capsules.
The following examples are given by way of illustration of the present invention and should not be construed to limit the scope of the present invention.
Example 1
Iron Oxide (Fe2O3) and aluminium powders, having size of -325 mesh, were dried in an electric oven at 120°C for 12 hours. A thermit mixture was prepared from these powders by mixing 100 g of iron oxide and 33.8 g of aluminium in a sealed double cone blender for 12 hours. The mixing ratio was approximately stoichiometric. A homogeneous mixture of reactants for producing nickel aluminide (NiAl) was prepared by mixing 20g of nickel and 9.19g of aluminium powders of-200 mesh size in a pestle and mortar. The mixing ratio was nearly stoichiometric. A graphite capsule of 6mm internal diameter, 0.5 mm wall thickness and 15 mm length was loaded with l.lg of this mixture of reactants. The capsule was then tightly closed by a graphite cap. The capsule, containing the mixture of reactants, was then placed in upright position inside a graphite container,
having 15mm internal diameter, 1.5mm wall thickness and 39.5mm length, at the end where the container was closed by 1 mm thick graphite disc. The external surfaces of the container and disc were provided with thermal insulation using a ceramic of 3mm thickness. The graphite container was then filled with 6.5g of the prepared thermit mixture. The graphite container, along with other components thus assembled, was inserted in a mild steel tube of 25mm inside diameter, 3 mm wall thickness and 50mm length. The end of the mild steel tube, where the capsule was located inside the container, was closed by fixing 12 mm thick circular mild steel plate inside the steel tube. The mild steel tube, along with the components thus assembled, was rotated at 4260 rpm about an external axis so that the closed end of the graphite container experienced a centrifugal force of about 950G. While the assembly was rotating, the thermit reaction was initiated by bringing an electric arc, struck between two mild steel electrodes, in contact with the free surface of the thermit mixture in the graphite container. The reaction, thus initiated, rapidly propagated through the remaining thermit mixture in the graphite container and was completed in about three seconds. The products of the thermit reaction collected at the closed end of the graphite container surrounding the graphite capsule. The rotation of the assembly was continued for 15 more minutes to allow the assembly to cool. The graphite container was then removed from the steel tube. The products of the thermit reaction and the capsule embedded therein were separated from the graphite container. The intermetallic produced was then released from the capsule. X-ray analysis showed that the intermetallie was predominantly NiAl. The density of the produced NiAl was 5.7g/cm3. The average Vickers hardness for 200g
load was found to be 336. The EDX analysis in SEM showed that it contained 74% Ni and 26% Al (in wt.%).
Example 2
Iron Oxide (Fe2O3) and aluminium powders, having size of -325 mesh, were dried in an electric oven at 120° C for 12 hours. A thermit mixture was prepared from these powders by mixing l00g of iron oxide and 33.8 g of aluminium in a sealed double cone blender for 12 hours. The mixing ratio was approximately stoichiometric. A homogeneous mixture of reactants for producing nickel aluminide (NiAl) was prepared by mixing 20g of nickel and 9.19g of aluminium powders of -200 mesh size in a pestle and mortar. The mixing ratio was nearly stoichiometric. A graphite capsule of 6mm internal diameter, 0.5 mm wall thickness and 15 mm length was loaded with l.lg of this mixture of reactants in argon atmosphere. The capsule was then tightly closed by a graphite cap. The capsule, containing the mixture of reactants, was then placed in upright position inside a graphite container, having 15mm internal diameter, 1.5mm wall thickness and 39.5mm length, at the end where the container was closed by 1mm thick graphite disc. The external surfaces of the container and disc were provided with thermal insulation using a ceramic of 3mm thickness. The graphite container was then filled with 5.7g of the prepared thermit mixture. The graphite container, along with other components thus assembled, was inserted in a mild steel tube of 25mm inside diameter, 3 mm wall thickness and 50mm length. The end of the mild steel tube, where the capsule was located inside the container, was closed by fixing 12 mm thick circular mild steel plate inside the steel tube. The mild steel tube, along with the components thus
assembled, was rotated at 2840 rpm about an external axis inside a stainless steel chamber filled with argon gas so that the closed end of the graphite container experienced a centrifugal force of about 425G. While the assembly was rotating, the thermit reaction was initiated by bringing an electric arc, struck between two mild steel electrodes, in contact with the free surface of the thermit mixture in the graphite container. The reaction, thus initiated, rapidly propagated through the remaining thermit mixture in the graphite container and was completed in about three seconds. The products of the thermit reaction collected at the closed end of the graphite container surrounding the graphite capsule. The rotation of the assembly was continued for 15 more minutes to allow the assembly to cool. The graphite container was then removed from the steel tube. The products of the thermit reaction and the capsule embedded therein were separated from the graphite container. The intermetallic produced was then released from the capsule. X-ray analysis showed that the intermetallic was predominantly NiAl. The density of the produced NiAl was 5.82g/cm3. The average Vickers hardness for 200g load was found to be 389. The EDX analysis in SEM showed that it contained 74% Ni and 26% Al (in wt.%).
Example 3
Iron Oxide (Fe2O3) and aluminium powders, having size of -325 mesh, were dried in an electric oven at 120° C for 12 hours. A thermit mixture was prepared from these powders by mixing 100 g of iron oxide and 33.8 g of aluminium in a sealed double cone blender for 12 hours. The mixing ratio was approximately stoichiometric. A homogeneous mixture of reactants for producing nickel aluminide
(NiAl) was prepared by mixing 20g of nickel and 9.19g of aluminium powders of-200 mesh size in a pestle and mortar. The mixing ratio was nearly stoichiometric. A compact of 6 mm diameter and 9.4mm length was prepared from this mixture in a screw press using stainless steel die and punches. The green density of the compact was 87% of the theoretical density of the mixture. This compact was inserted in a graphite capsule of 6 mm internal diameter, 0.5 mm wall thickness and 15 mm length. The capsule was then tightly closed by a graphite cap. The capsule, containing the compact was then placed in upright position inside a graphite container, having 15mm internal diameter, 1.5mm wall thickness and 39.5mm length, at the end where the container was closed by 1mm thick graphite disc. The external surfaces of the container and disc were provided with thermal insulation using a ceramic of 3mm thickness. The graphite container was then filled with 6.5g of the prepared thermit mixture. The graphite container, along with other components thus assembled, was inserted in a mild steel tube of 25mm inside diameter, 3 mm wall thickness and 50mm length. The end of the mild steel tube, where the capsule was located inside the container, was closed by fixing 12 mm thick circular mild steel plate inside the steel tube. The mild steel tube, along with the components thus assembled, was rotated at 2840 rpm about an external axis so that the closed end of the graphite container experienced a centrifugal force of about 425G. While the assembly was rotating, the thermit reaction was initiated by bringing an electric arc, struck between two mild steel electrodes, in contact with the free surface of the thermit mixture in the graphite container. The reaction, thus initiated, rapidly propagated through the remaining thermit mixture in the graphite container and was completed in about three seconds. The products of the thermit reaction collected at the closed end of the graphite container
surrounding the graphite capsule. The rotation of the assembly was continued for 15 more minutes to allow the assembly to cool. The graphite container was then removed from the steel tube. The products of the thermit reaction and the capsule embedded therein were separated from the graphite container. The intermetallic produced was then released from the capsule. X-ray analysis showed that the intermetallic was predominantly NiAl. The density of the produced NiAl was 5.7g/cm3. The average Vickers hardness for 200g load was found to be 356. The EDX analysis in SEM showed that it contained 71% Ni and 29% Al (in wt.%).
Example 4
Iron Oxide (T^Ch) and aluminium powders, having size of -325 mesh, were dried in an electric oven at 120°C for 12 hours. A thermit mixture was prepared from these powders by mixing 100 g of iron oxide and 33.8 g of aluminium hi a sealed double cone blender for 12 hours. The mixing ratio was approximately stoichiometric. A homogeneous mixture of reactants for producing nickel aluminide (NiAl) was prepared by mixing 20g of nickel and 9.19g of aluminium powders of-200 mesh size in a pestle and mortar. The mixing ratio was nearly stoichiometric. A compact of 6 mm diameter and 10mm length was prepared from this mixture in a screw press using stainless steel die and punches. The green density of the compact was 79% of the theoretical density of the mixture. This compact was inserted in a graphite capsule of 6 mm internal diameter, 0.5 mm wall thickness and 15 mm length in argon atmosphere. The capsule was then tightly closed by a graphite cap. The capsule, containing the compact was then placed in upright position inside a graphite container, having 15mm internal diameter, 1.5mm wall thickness and
39.5mm length, at the end where the container was closed by 1mm thick graphite disc. The external surfaces of the container and disc were provided with thermal insulation using a ceramic of 3mm thickness. The graphite container was then filled with 5.8g of the prepared thermit mixture. The graphite container, along with other components thus assembled, was inserted in a mild steel tube of 25mm inside diameter, 3 mm wall thickness and 50mm length. The end of the mild steel tube, where the capsule was located inside the container, was closed by fixing 12 mm thick circular mild steel plate inside the steel tube. The mild steel tube, along with the components thus assembled, was rotated at 2840 rpm about an external axis inside a stainless steel chamber filled with argon gas so that the closed end of the graphite container experienced a centrifugal force of about 425G. While the assembly was rotating, the thermit reaction was initiated by bringing an electric arc, struck between two mild steel electrodes, in contact with the free surface of the thermit mixture in the graphite container. The reaction, thus initiated, rapidly propagated through the remaining thermit mixture in the graphite container and was completed in about three seconds. The products of the thermit reaction collected at the closed end of the graphite container surrounding the graphite capsule. The rotation of the assembly was continued for 15 more minutes to allow the assembly to cool. The graphite container was then removed from the steel tube. The products of the thermit reaction and the capsule embedded therein were separated from the graphite container. The intermetallic produced was then released from the capsule. X-ray analysis showed that the intermetallic was predominantly NiAl. The density of the produced NiAl was 5.86g/cm3. The average Vickers hardness for 200g load was found to be 361. The EDX analysis in SEM showed that ft contained 72% Ni and 28% Al (in wt.%).

The present method for producing intermetallics has been demonstrated by these examples wherein dense intermetallics were produced without employing an electric furnace or a separate pressure application device. Also, the intermetallics were synthesized and densified in one step. The present method can also be employed to produce other alloys and composites not covered in these examples. The present method permits the production of shaped articles using shaped refractory capsules. The method can be used for batch production by placing the required number of devices, shown in fig.l, radially about a central axis and carrying out the method.
The main advantages of the present invention are :
1. simplicity,
2. Shorter processing time,
3. lower energy consumption as no electric heating device is required to produce
intermetallics,
4. the material is synthesized and densified in one step,
5. no separate pressure application device is needed for densification of the product,
6. the method permits the production of shaped articles,
7. batch production is possible and
8. the method is useful as a simple and inexpensive laboratory method for producing
alloys and composites.

WE CLAIM :
1. A device for producing intermetallics which comprises of tubular refractory
container(l) capable of holding a highly exothermic reaction mixture (6), the
said container being closed at one end by a refractory plate (2), the closed end
of the container being provided with a coaxially fixed tubular refractory capsule
(3) having cap/plug (5) capable of holding a reaction mixture (4) of the desired
intermetallic and the said container housing the capsule being characterized
in that being enclosed in a metal tube (7) closed at the capsule end with a
metal plate (8) and the assembly so obtained being capable of rotation around
a external axis .
2. A device as claimed in claim 1, wherein the capsule used is a thin walled
refractory capsule with a removably fixed cap/plug.
3. A device as claimed in claim 1-2, wherein the rotation about an external axis is
provided by any conventional means.
4. A method for producing intermetallics, using the device as claimed in claims 1-
3 , which comprise

a) filling the thin walled refractory capsule with the homogeneous mixture of
reactants, containing powders of the constituent elements of the desired
intermetallic in stoichiometric amounts,
b) closing the refractory capsule by a refractory cap,
c) housing the encapsulated mixture of reactants at the end of the refractory
container where the refractory container is closed by a refractory plate,
8. A method as claimed in claims 4-7, wherein the synthesis is carried out in an
inert atmosphere.
9. A device for producing intermetallics substantially as herein described with
reference to the examples and drawing accompanying this specification.

Documents:

273-del-2001-abstract.pdf

273-del-2001-claims.pdf

273-del-2001-correspondence-others.pdf

273-del-2001-correspondence-po.pdf

273-del-2001-description (complete).pdf

273-del-2001-drawings.pdf

273-del-2001-form-1.pdf

273-del-2001-form-19.pdf

273-del-2001-form-2.pdf

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Patent Number

230783

Indian Patent Application Number

273/DEL/2001

PG Journal Number

13/2009

Publication Date

27-Mar-2009

Grant Date

28-Feb-2009

Date of Filing

12-Mar-2001

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH

Applicant Address

RAFI MARG, NEW DELHI-110001, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	RAJAIYENGAR SESHADRI	NATIONAL AEROSPACE LABORATORIES, POST BAG NO.1779, BANGALOR - 560017, INDIA.

PCT International Classification Number

C30B 25/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA