Title of Invention

"A PROCESS FOR THE MANUFACTURE OF AN ENHANCED CORROSION RESISTANT COMPOSITE MATERIAL WITH ZINC AS METAL MATRIX"

Abstract

In the present invention there is provided a process for the manufacture of an enhanced corrosion resistant composite material with zinc as metal matrix. The process comprises of finely dispersing multiple metal oxides, such as nonconducting, semi-conducting oxides, into molten commercially pure zinc under stirring to obtain a homogenous composite mass. The source of multiple metal oxides is such as flyash, an industrial waste product, or an admixture of multiple metal oxides, essentially consisting of silicon dioxide, aluminum trioxide, iron oxide. The zinc metal matrix composite has enhanced corrosion resistance properties and is thus suitable for industrial applications.

Full Text

The present invention relates to a process for the manufacture of an enhanced corrosion resistant composite material with zinc as metal matrix. The present invention particularly relates to a process for the manufacture of a novel zinc -metal oxides based composite material having enhanced corrosion resistance, wherein the source of multiple metal oxides is such as flyash, an industrial waste material, or an admixture of multiple metal oxides. In the galvanic series of metals in sea water, zinc occupies the most active position next only to magnesium. Since magnesium is highly reactive and is too rapidly consumed, zinc is the most preferred metal for conferring galvanic protection to steel substrates. Compared to two other active metals, namely magnesium and aluminum, zinc is heavier with a density of 7.1 gm/cm3. Reference may be made to Dale CH Nevison, ASM hand book, volume 13 -corrosion, pp 755 - 769, published by ASM international New York, 1996. Zinc ranks 27th in order of abundance of the chemical elements. The major application is galvanizing. Galvanizing zinc is primarily applied to finished parts such as sheets, wires strips and tubes. Historically zinc was one of the very first metals to be used as a galvanic anode. Early in the 19th century Sir Humphray Davy secured pieces of zinc to the copper sheathing in wood hulls of British Navy vessels to prevent severe underwater corrosion of the copper. The automotive industry uses by far the largest number of zinc alloy die castings such as carburetors, bodies for fuel pumps, wind shield wiper parts, speedometer frames. Zinc die castings are also used in washing machines, oil burners, stokers, motor housings, vacuum cleaners, electric clocks, building hard wares and are also used in business machines. However, the inferior corrosion resistance of zinc poses a severe limitation to its wide spread use for industrial applications. Reference may be made to Van No Strand's Scientific Encyclopedia 8th edition edited by Douglas M.Considire and published by Van No Strand Rein How, New York (1995), pp 3375 - 3377, wherein the following drawbacks associated with zinc have been mentioned a) Zinc is readily oxidized in the presence of hydroxide ions e.g. H20. b) In industrial or marine locations, condensed dew is likely to be contaminated with impurities that are corrosive to zinc. Sulphur dioxide being one of the most harmful pollutants. c) Water hardness is an important variable in zinc corrosion. The corrosion rate of zinc in hard water may be 15 urn / year but in soft water it can be 10 times higher. d) When zinc is used in contact with water in a closed system, inhibitors are frequently used to minimize corrosion. e) Zinc is usually not considered to be a useful metal in the acidic or strongly alkaline chemical environment f) Zinc alloy containing aluminum are susceptible to intergranular corrosion at elevated temperatures. Reference may be made to control of pipe line corrosion edited by A.W.Peabody and Published by National Association of Corrosion Engineers, Texas USA (1967) pp 119, wherein it has been stated that zinc used for soil anodes should be high purity zinc such as special high grade classification which is at least 99.99 percent pure zinc. Reference may be made to T.P. Cheng, J.T. Lee, K.L. Lin, and W.T. Tsai, Corrosion Volume 47, No. 6 (1991) pp 436 - 442, wherein it has been stated that 5% Al - Zn and 55% Al - Zn coatings are much inferior to that of galvanized coating in alkaline conditions and that they are not suitable for application in reinforcements. In the hitherto known prior art, either electrochemically active metals such as Aluminum, Magnesium have been used as alloying elements or graphite fibers as reinforcing elements. All these elements are electrically conducting and hence contribute to corrosion of base metal zinc in one wav or other. From the hitherto known prior art it is clear that there is a definite need to overcome the inferior corrosion resistance of zinc which poses a severe limitation to its wide spread use for industrial applications. The main object of the present invention is to provide a process for the manufacture of an enhanced corrosion resistant composite material with zinc as metal matrix, which obviates the drawbacks as detailed above. Another object of the present invention is to provide a process for the manufacture of an enhanced corrosion resistant composite material with zinc as metal mairix, which improves the performance of commercially pure zinc without any metallic alloying elements. Yet another object of the present invention is to provide a process for the manufacture of a novel zinc - metal oxides based composite material which obviates the drawbacks as detailed above. Still another object of the present invention is to provide a process for improved performance of commercially pure zinc by admixing, at the time of casting, a multiple metal oxide system in finest form, so as to form a synergistic metal matrix composite having enhanced corrosion resistance properties. Still yet another object of the present invention is to provide a process for improved performance of commercially pure zinc by admixing, at the time of casting, flyash containing multiple metal oxides, so as to form a synergistic metal matrix composite having enhanced corrosion resistance properties. In the present invention there is provided a process for the manufacture of an enhanced corrosion resistant composite material with zinc as metal matrix. The process comprises of finely dispersing multiple metal oxides, such as nonconducting, semi-conducting oxides, into molten commercially pure zinc under stirring to obtain a homogenous composite mass. The source of multiple metal oxides is such as flyash, an industrial waste product, or an admixture of multiple metal oxides, essentially consisting of silicon dioxide, aluminum trioxide, iron oxide. The zinc metal matrix composite has enhanced corrosion resistance properties and is thus suitable for industrial applications. Accordingly the present invention provides a process for the manufacture of an enhanced corrosion resistant composite material with zinc as metal matrix, which comprises preparing a melt of pure zinc in the presence of flux by known methods, uniformly dispersing into 95 to 99 wt% of the said zinc melt under stirring an admixture of multiple metal oxides such as flyash, an industrial waste product essentially consisting of SiO2 in the range 1 to 3 wt%, Al2O3 in the range 0.5 to 2 wt% and Fe2O3 in the range 0.5 to 2 wt%, to obtain a homogenous corrosion resistant composite material, casting into a mould by known methods. In an embodiment of the present invention, the pure zinc is commercially available pure zinc having 99.9% purity. In another embodiment of the present invention, the flux is commercially available flux based on a mixture of crystals of ammonium chloride. In yet another embodiment of the present invention, the admixture of multiple metal oxides, is such as flyash, an industrial waste product, essentially consisting of SiO2 in the range 1 to 3 wt%, Al2O3 in the range 0.5 to 2 wt% and Fe2O3 in the range 0.5 to 2 wt%. In still another embodiment of the present invention, the multiple metal oxides is such as non-conducting, semi-conducting oxides admixture of metal oxides of pigment grade (95 % pure) silicon dioxide, AR grade aluminium trioxide and AR grade ferric oxide, In hitherto known prior art, alloying elements used are electrochemically active metals such as aluminum, manganese and reinforcing elements used is graphite fibers. All these elements are electrically conducting and hence contribute to corrosion of base metal zinc in one way or other. On the other hand, if nonconducting or semi-conducting oxides are introduced in the metal matrix, they may increase the resistance of the system and thereby reduce the corrosion rate. Such non-conducting or semi-conducting oxides are to be kept within optimum limits so as to retain the functional efficiency of the base metal i.e. zinc. Use of multiple oxides such as silicon dioxide, aluminum trioxide, iron oxide will have a balancing effect on the overall corrosion resistance. Novelty of the present invention resides in providing a process for the manufacture of a novel zinc - metal oxides based composite material having enhanced corrosion resistance, wherein the source of multiple metal oxides is such as flyash, an industrial waste material, or an admixture of multiple metal oxides. Fly ash, an industrial waste product, can serve as an abundant source of multiple oxides. It has been possible to achieve the above noted novelty by the non-obvious inventive step of uniformly dispersing into 95 to 99 wt% of commercial pure zinc melt under stirring flyash or an admixture of multiple metal oxides, essentially consisting of SiO2 in the range 1 to 3 wt%, AI2C>3 in the range 0.5 to 2 wt% and Fe203 in the range 0.5 to 2 wt%, to obtain a homogenous composite mass. The following examples are given by way of illustration and therefore should not be construed to limit the scope of the present invention. EXAMPLE - 1 Casting of composite material based on multiple oxides in flyash: 950 gms of commercially pure zinc (99.9% purity) was weighed and taken in a one litre capacity graphite crucible. The crucible was then kept in an open cupola type furnace and the content was heated. When the zinc metal started melting, 20 gms of a commercially available flux based on a mixture of crystals of ammonium chloride was thrown over the molten metal. Then 25 gms of multiple metal oxides in the form of fly ash containing 15 gms of silicon dioxide 75 gms of aluminum trioxide and 2.5 gms of iron oxide were first added and stirred with a graphite rod. Immediately on addition, there was reduction in temperate and the melt tended to become semisolid. The heating was maintained to reach a temperature of 400°C and remaining 25 gms of multiple metal oxides in the form of fly ash were added and stirred till a homogeneous molten mixture was formed. This molten mixture was simultaneously poured into a plate type graphite die and a cylinder type graphite die so as to have cast plates of size 150x50x3mm and cast rods of size 15mm dia and 120 mm length. These cast plate and rod materials were suitably cut and used in the subsequent evaluation studies. EXAMPLE - 2 Casting of composite material based on admixture of multiple oxides i.e.tri oxides (Si02, AI203and Fe2O3): 980 gms of commercially pure zinc (99.9% purity) was weighed and taken in a 1 litre capacity graphite crucible. The crucible was then kept in an open cupola type furnace and the content was heated. When the zinc metal started melting, 20 gms of a commercially available flux based on crystals of ammonium chloride was thrown over the molten metal. Then 10 gms of pigment grade silicon dioxide (95 % pure) and 5 grams of aluminium trioxide (AR grade) and 5 grams of ferric oxides (AR grade) were added and stirred with a graphite rod, till a homogeneous molten mixture was formed. The molten mixture was simultaneously poured in to a plate type graphite die and cylinder type graphite die so as to have cast plates of size 150 x 50 x 3mm and cast rods of size 15mm dia and 120mm length. These cast plate and rod materials were suitably cut and used in the subsequent evaluation studies. EXAMPLE - 3 Casting of commercial pure zinc metal: 1000 gms of commercially pure zinc (99.99% purity) was weighed and taken in a one litre capacity graphite crucible. The crucible was then kept in an open cupola type furnace and the content was heated. When the zinc metal started melting, 20 gms of a commercially available flux based on a mixture of crystals of ammonium chloride was thrown over the molten metal and stirred with a graphite rod, till a homogeneous molten mixture was formed. The molten mixture was simultaneously poured in to a plate type graphite die and cylinder type graphite die so as to have cast plates of size 150 x 50 x 3mm and cast rods of size 15mm dia and 120mm length. These cast plate and rod materials were suitably cut and used in the subsequent evaluation studies. EXAMPLE - 4 Comparative evaluation of self-corrosion in 1500-ppm chloride solution: 14 mm wide 60 mm long flat specimens were cut from the cast samples. The specimens were heated to 70°C in 5% HNO3, for a period of half an hour, and washed in running water, dried and degreased with trichloroethylene. The specimens were accurately weighed in a Mettler Balance and lacquered at the top 15 mm, so as to expose only 45 mm long portion. Three 500cc capacity glass beakers were taken and each filled with 400 cc of 1500-ppm chloride solution. In one beaker a newly developed composite material as per example I was keot immersed in solution. Simultaneously, in the second beaker newly developed composite material as per example 2 was kept immersed in solution. Similarly in the third beaker the commercially available pure zinc material as per example 3 was kept immersed in solution. The experiments were carried out for a period of 4 hours. At the end of 4 hours, the immersion test was terminated. The specimens were removed, cleaned in 5% HN03, washed in running water, degreased in trichloroethylene and then weighed accurately to determine the weight loss. Similar experiments were carried out for a period of 24 hours. The results are shown in Table 1 below: (Table Remove) it can be seen from the above table that the newly developed composite system based on multiple oxides as per examples 1 and 2 are having lower weight loss, i.e. lower self-corrosion in 1500-ppm chloride medium. EXAMPLE-5 Comparative evaluation of self-corrosion in saturated Ca (OH) 2 solution: 14 mm wide 60 mm long flat specimens were cut from the cast samples. The specimens were heated to 70°C in 5% HMOs and washed in running water, dried and degreased with trichloroethylene. The specimens were accurately weighed in a Mettler Balance and lacquered at the top 15 mm so as to expose only 45 mm long portion. Three 500cc capacity glass beakers were taken and each filled with 450 cc of saturated Ca (OH) 2 solution. In one beaker a newly developed composite material as per example 1 was kept immersed in solution. Simultaneously, in the second beaker newly developed composite material as per example 2 was kept immersed in solution. Similarly in the third beaker the commercially pure zinc as per example 3 was kept immersed in solution. The experiments were carried out for a period of 4 hours. At the end of 4 hours, the immersion test was terminated. The specimens were removed, cleaned in 5% HNO3, washed in running water, dried and degreased with trichloroethylene and then weighed accurately to determine the weight loss. Similar experiments were carried out for a period of 24 hours. The results are shown in Table 2 below. (Table Remove) It can be seen from the above table that the newly developed composite system based on multiple metal oxides as per examples 1 & 2 have lower weight loss, i.e. lower self-corrosion in saturated Ca (OH) 2 solution. EXAMPLE - 6 Comparative evaluation of self-corrosion in saturated Ca (OH) 2 containing 1500 ppm of chloride: 14 mm wide 60 mm long flat specimens were cut from the cast samples. The specimens were heated to 70°C in 5% HNO3 and washed in running water, dried and degreased with trichloroethylene. The specimens were accurately weighed in a Mettler Balance and lacquered at the top 15 mm so as to expose only 45 mm long portion. Three 500cc capacity glass beakers were taken and each filled with 450cc of saturated Ca (OH) 2 solution containing 1500 ppm of chloride solution. In one beaker a newly developed composite material as per example 1 was kept immersed in solution. Simultaneously, in the second beaker newly developed composite material as per example 2 was kept immersed in solution. Similarly in the third beaker the commercially pure zinc as per example 3 was kept immersed in solution. The experiments were carried out for a period of 4 hours. At the end of 4 hours, the immersion test was terminated. The specimens were removed, cleaned in 5% HNO3, washed in running water, dried and degreased with trichloroethylene and then weighed accurately to determine the weight loss. Similar experiments were carried out for a period of 24 hours. The results are shown in Table 3 below: (Table Remove) It can be seen from the above table that the newly developed composite system based on multiple metal oxides as per example 1 & 2 are having a lower weight loss, i.e. lower self-corrosion in saturated Ca (OH) 2 containing 1500 ppm of chloride medium. EXAMPLE-7 Comparative evaluation of galvanic corrosion in 1500 ppm chloride solution: 14 mm wide 60 mm long flat specimens were cut from the cast samples. The specimens were heated to 70°C in 5% HNO3 and washed in running water, dried and degreased with trichloroethylene. The specimens were accurately weighed in a Mettler Balance and lacquered at the top 15 mm so as to expose only 45 mm long portion. 16 mm dia 65 mm long twisted mild steel rods were derusted in pickling acid, washed in running water, dried and degreased with trichloroethylene. Electrical leads were taken from one end, which was sealed with epoxy putty. 55mm long portion was exposed. Three 500cc capacity glass beakers were taken and each filled with 450 cc of aqueous solution containing 1500 ppm of chloride. One mild steel rod and one composite material as per example 1 were kept immersed at the same level in one beaker filled with 450 cc of aqueous solution containing 1500 ppm of chloride. Electrical lead was taken from one end. Individual potentials were measured against a saturated calomel electrode and recorded. Both the terminals were then short circuited to monitor the shift in potential of steel due to galvanic effect. The experiments were carried out for a period of 4 hrs. In the second beaker, similar experiment was simultaneously carried out but with a newly developed composite material as per example 2 as anode. In the third beaker, similar experiment was simultaneously carried out but with a commercially pure zinc as per example 3 as anode. The results are shown in Table 4 below: (Table Remove) It can be seen from the above table that the newly developed system based on multiple oxides (examples 1 & 2) is showing a higher galvanic current as well as higher shift in potential thereby indicating higher anode efficiency. EXAMPLE - 8 Comparative evaluation of galvanic corrosion in saturated Ca (OH)2 solution: 14 mm wide 60 mm long flat specimens were cut from the cast samples. The specimens were heated to 70° C in 5% HN03 and washed in running water, dried and degreased with trichloroethylene. The specimens were accurately weighed in a Mettler balance and lacquered at the top 15 mm so as to expose only 45 mm long portion. 16 mm dia 65 mm long twisted mild steel rods were derusted in pickling acid washed in running water, dried and degreased with trichloroethylene. Electrical leads were taken from one end, which was sealed with epoxy putty. 55mm long portion was exposed. Three SOOcc capacity glass beakers were taken and each filled with 400 cc of aqueous solution containing saturated Ca (OH)2 solution. One mild steel rod and one composite material as per example 1 were kept immersed at the same level. Electrical lead was taken from one end. Individual potentials were measured against a saturated calomel electrode and recorded. Both the terminals were 'hen short circuited to monitor the shift in potential of steel due to galvanic effect. The experiments were carried out for a period of 4 hrs. in the second beaker, similar experiment was simultaneously carried out but with a newly developed composite material as per example 2 as anode. in the third beaker, similar experiment was simultaneously carried out but with a commercially available pure zinc as per example 3 as anode. The results are shown in Table 5 below (Table Remove) It can be seen from the above table that the newly developed system based on multiple oxides (examples 1 & 2) shows a higher galvanic current as well as higher shift in potential thereby indicating higher anode efficiency. EXAMPLE-9 Comparative evaluation of galvanic corrosion in Ca(OH)2 containing 1500 ppm of chloride solution: 14 mm wide 60 mm long flat specimens were cut from the cast samples. The specimens were heated to 70°C in 5% HNO3 and washed in running water, dried and degreased with trichloroethylene. The specimens were accurately weighed in a Mettler Balance and lacquered at the top 15 mm so as to expose only 45 mm long portion. 16 mm dia 65 mm long twisted mild steel rods were derusted in pickling acid, washed in running water, dried and degreased with trichloroethylene. Electrical leads were taken from one end, which was sealed with epoxy putty. 55mm long portion was exposed. Three 500cc capacity glass beakers were taken and each filled with 450 cc of Ca(OH)2 containing 1500 ppm of Chloride solution. In the first beaker one mild steel rod and one composite material as per example 1 were kept immersed at the same level. Electrical lead was taken from one end. Individual potentials were measured against a saturated calomel electrode and recorded. Both the terminals were then short circuited to monitor the shift in potential of steel due to galvanic effect. The experiments were carried out for a period of 4 hrs. In the second beaker, similar experiment was simultaneously carried out but with a newly developed composite material as per example 2 as anode. In the third beaker, similar experiment was simultaneously carried out but with a commercially pure zinc as per example 3 as anode. The results are shown in Table 6 below: (Table Remove) It can be seen from the above table that the newly developed system based on multiple oxides (examples 1 & 2) is showing a higher galvanic current as well as higher shift in potential thereby indicating higher anode efficiency in saturated Ca (OH)2 containing 1500 ppm of chloride medium. EXAMPLE-10 Evaluation of galvanic corrosion in concrete medium: A mild steel reinforcement specimen of size 8mm dia and 10.5 cm long was embedded in concrete prism of size 20x10x1 Ocm with a clear cover of 6 cm from the top surface. A hydroxyl ion reversible electrode (HRE) of size 0.5 cm dia and 4cm long was simultaneously embedded along with mild steel reinforcement at an inter electrode spacing of 0.5 cm. Leads were taken from the steel specimen as well as HRE. The concrete prism was cured for 28 days in tap water and then exposed to ambient condition. A newly developed composite material as per example 1, of size 7cm x 4.5cm was cut from the cast sample, cleaned in 5% HNO3, washed in running water, dried and degreased with trichloro ethylene and weighed accurately in a mettler balance. The open circuit potential of mild steel was measured with respect to HRE and then the newly developed composite material was placed at the top surface of the prism and externally short circuited with rebar terminal. The potential of steel got shifted in the cathodic direction. The experiment was continued for a period of 72 hours and then terminated. The anode specimen was removed, cleaned in 5% HNO3, washed in running water, dried and degreased with trichloroethylene and then weighed accurately to determine the weight loss Subsequently, a newly developed composite material as per example 2, a flat specimen of size 7cm x 4.5 cm was cleaned in 5% HN03, washed in running water, dried and degreased with trichloro ethylene and then weighed accurately in a mettler balance. The open circuit potential of mild steel was measured with respect to HRE and then the commercially pure magnesium was placed at the top surface of the prism and externally short circuited with rebar terminal. The potential of steel got shifted in the cathodic direction. The experiment was continued for a period of 72 hours and then terminated. The anode specimen was removed and cleaned in 5% HNO3 washed in running water, dried and degreased with trichloro ethylene and then weighed accurately to determine the weight loss. Similar, experiment was repeated but with a commercially pure zinc as per example 3 as anode. The results are given in table 7 below: It can be seen from the above table that the newly developed composite materials as per example 1 & 2 having the lowest weight loss compared to commercial pure zinc The main advantages of the present invention are: (i) Fly ash, an abundantly available industrial waste product is utilized in making this composite material. This leads to efficient and eco-friendly consumption of this waste product in the process. (ii) There is no need to specifically control the impurities within critical limits. This makes the process simple. (iii) Enhanced corrosion resistant composite material with zinc as metal matrix, which avoids the use of alloying elements used in the prior art, such as aluminum, manganese, which are electrochemically active metals and hence contribute to corrosion of base metal zinc in one way or other. (iv) There is no need to specifically add the conventional alloying elements such as aluminum, magnesium. This leads to conservation of scarcely available metals. (v) The newly developed composite material has better corrosion resistance in chloride as well as lime media and saturated calcium hydroxide containing 1500 ppm chloride compared to commercially available pure zinc metal. (vi) The newly developed composite material has better galvanic corrosion resistance in chloride as well as lime media and saturated calcium hydroxide containing chloride compared to commercially pure zinc metal. (vii) The newly developed composite material has better anode efficiency in lime media and saturated calcium hydroxide containing chloride compared to commercially pure zinc metal. (viii) The newly developed composite material is having better galvanic corrosion resistance in concrete medium compared to commercially available pure zinc metal. We claim: 1. A process for the manufacture of an enhanced corrosion resistant composite material with zinc as metal matrix, which comprises preparing a melt of pure zinc in the presence of flux by known methods, uniformly dispersing into 95 to 99 wt% of the said zinc melt under stirring an admixture of multiple metal oxides such as flyash, an industrial waste product essentially consisting of SiO2 in the range 1 to 3 wt%, Al2O3 in the range 0.5 to 2 wt% and Fe2O3 in the range 0.5 to 2 wt%, to obtain a homogenous corrosion resistant composite material, casting into a mould by known methods. 2. A process as claimed in claim 1, wherein the pure zinc is commercially available pure zinc having 99.9% purity. 3. A process as claimed in claim 1 - 2, wherein the flux is commercially available flux based on a mixture of crystals of ammonium chloride. 4. A process for the manufacture of an enhanced corrosion resistant composite material with zinc as metal matrix, substantially as herein described with reference to the examples.

Documents:

33-DEL-2003-Abstract-(26-08-2011).pdf

33-del-2003-abstract.pdf

33-DEL-2003-Claims-(26-08-2011).pdf

33-del-2003-claims.pdf

33-DEL-2003-Correspondence Others-(12-09-2011).pdf

33-DEL-2003-Correspondence Others-(26-08-2011).pdf

33-del-2003-correspondence-others.pdf

33-del-2003-correspondence-po.pdf

33-DEL-2003-Description (Complete)-(26-08-2011).pdf

33-del-2003-description (complete).pdf

33-del-2003-form-1.pdf

33-del-2003-form-18.pdf

33-del-2003-form-2.pdf

33-DEL-2003-Form-3-(26-08-2011).pdf

33-del-2003-form-3.pdf