Title of Invention

A COMPOSITION FOR CONSOLIDATION OF DENSE CERAMICS AND METAL COMPACTS

Abstract

THE PRESENT INVENTION RELATES TO A COMPOSITION OFRCONSOLIDATION OF PARTICULATE SLURRIES OF DENSE OZXIDE, NON-OXIDE CERAMIC OR METAL COMPACTSCOMOPRISING CERAMI8C OR METAL POWDER; ONE OR MORE SACCHARIDS USED AS DISPERSING AGENT AND AT LEAST ONE WATER SOLUBLE POLYMERIZABLE, ORGNIC BINDER. THE INVENTION FURTHER RELATES TO A DENSE CERAMIC OR A METAL COMPACT MANUFACTURED FROM SUCH COMPOSITIONS AND A PROCESS FOR MAKNG THE SAME.

Full Text

FIELD OF THE INVENTION The present invention relates to a composition for consolidation of particulate slurries including dense oxide, non-oxide ceramic and metal compacts. In particular, the invention relates to consolidation of ceramic or metallic materials involving saccharides selectively monosaccharides, disaccharides, oligosaccharides and polysaccharides in combination with one or more of water-soluble polymerizable, other organic binders and gel forming materials. BACKGROUND ART Advanced ceramic or metallic materials have a large number of existing as well as emerging applications in areas that span a wide range including chemical, structural, electrical, electronic, wear resistant, thermal. Fabrication of advanced ceramic or metallic components from powders requires preparation of dense green compacts of various shapes. There are a number of well-known processes of fabrication of dense ceramic or metallic bodies that are based on use of aqueous slurries. The most common ones being slip casting [Ratan K. Govila, "Strength of Slip-cast, Sintered Silicone Nitride", J. Am. Ceram. Soc, 73 [6] 1744-51 (1990) ; Andrew J. Ruys and Charles C. Sorrell, "Slip Casting Alumina with Na-CMC", Am. Ceram. Soc. Bull., 75 [11] 66-69 (1996)], gelcasting [O. O. Omatete, M.A. Janney and R.A. Strehlow, "Gel casting - A new ceramic forming process", Am. Ceram. Soc. Bull., 70 [10] 1641-49 (1991); M. A. Janney, S. D. Nunn, C. A. Walls, O. O. Omatete, R. B. Ogle, G. H. Kirby and A. D. McMillan, "Gelcasting" in "The Hand Book of Ceramic Engineering, Mohamed N. Rahaman", Editor, Marcel Dekker, 1998; M. A. Janney and O. O. Omatete, "Method for Molding Ceramic Powders Using a Water-Based Gelcasting," U. S. Pat. No. 5,028,362, July 2, 1991; M. A. Janney and O. O. Omatete, "Method for Molding Ceramic Powders Using a Water-Based Gelcasting Process," U. S. Pat. No. 5,145,908, Sept. 8, 1992; M. A. Janney, "Method for Molding Ceramic Powders, " U. S. Pat. No. 4,894,194, Jan. 16, 1990] and the recently invented direct coagulation casting [Wenjie Si, Thomas J. Graule, Felix H. Baader and Ludwig J. Gauckler, "Direct Coagulation Casting of Silicon Carbide Components", J. Am. Ceram. Soc, 82 [5] 1129-36 (1999); F. Filser, P. Kocher, L. J. Gauckler, H. Luthy, P. Sharer, "Aggregation and Gelation of Concentrated Colloidal Suspensions", A patent application for this method was filed with the Swiss Institute of Intellectual Property on 27 February 2000 under number 200 0335/00 ; T. J. Graule, J. Gauckler, F. H. Badder, "Direct Coagulation Casting-A New Green Shaping Technique Part I: Processing Principles ", Industrial Ceramics, 16 [1] 31-35 (1996)]. Slip casting has been used for a long time and has many limitations including the constraint of using porous molds, results in low green strength and non-uniform shrinkage. While gelcasting has many advantages over most of the well-known ceramic fabrications processes there are a number of aspects, which make the process unfavourable for large-scale use. Gelcasting depends on in-situ polymerization of the water-soluble monomer-crosslinker, which requires homogeneous mixing of small amount of initiator and catalyst into large volume of slurries. Also the free radical polymerization is significantly inhibited in presence of air (oxygen) thus requiring the use of inert environment. If inert environment is not used, gelation (polymerization) remains incomplete and the unreacted monomer migrates during drying and crystallizes on the exposed surface. The crystals of the unreacted monomer can be a source of defects in sintered samples. It must be noted that specifically the surface of the gelcast parts does not undergo complete gelation as it is directly exposed to air. This incomplete gelation of the surface leads to surface spallation and associated defects [J. Ma, Z. Xie, H. Miao, L. Zhou and Y. Huang, "Elimination of surface Spallation of Alumina Green Bodies Prepared by Acrylamide-Based Gelcasting via Poly(vinylpyrrolidone)", J. Am. Ceram. Soc, 86 [2] 266-72 (2003)]. The sample surface often does not thus have a good finish. The gelcast parts are very sensitive to drying conditions. Thus, the use of closed molds becomes almost essential. When open molds are used, during gelation non-uniform drying is unavoidable leading to defects. Unless extreme care is taken, the gelcast parts often develop curvature and/or cracks during drying. When casting large parts the restraint to shrinkage due to weight of the samples itself leads to cracking. Casting of complex shapes that involve use of a core or otherwise where the mold feature restrain the drying shrinkage, cracking of gelcast parts occurs easily. Direct coagulation casting is a recently invented process, which is based on developing a green body by uniform coagulation of particles through manipulation of the ionic or changing pH. The green body produced by manipulation of ionic strength hits plasticity im.1 YP but involves shrinkage during drying. While the green body produced by attaining change in pH has no plasticity but has zero shrinkage. Though the above processes of direct coagulation casting have some advantages but they do not involve the use of binder, which makes the green bodies/weaker. The change in ionic strength or pH is achieved by heating the slurry after having been poured in the molds. Thus, the use of the above process is restricted to use of the molds that are stable during heating. Another known process involves use of aqueous ceramic slurries based on use of proteins to make dense ceramic compacts [O. Lyckfeldt, J. Brandt, S. Lesca, "Protein Forming - a Novel Shaping Technique for Ceramics" J. Eur. Ceram. Soc. 20 [14-15] 2551-2559 (2000); Patent EP767154 Al]. A study of similar process based on use of ovalbumin in fabrication of dense ceramic components has shown several limitations with the process. The ceramic loading in the slurries has to be limited to 45 — 50 volume % due to increase in viscosity in presence of ovalbumin. The poor fluidity due to polymeric nature of ovalbumin when the slurry is kept at rest makes elimination of air bubbles difficult. The constraint of maintaining low solids loading results in large shrinkage during drying. The samples are sensitive to the drying rate and have to be dried under controlled humidity conditions. During drying, the samples suffer from migration of binder to the exposed surface, which sometimes leads to lamination cracks [S. Dhara, P. Bhargava, "Egg White as an Environment Friendly Low-Cost Binder for Gelcasting of Ceramics", J. Am. Ceram. Soc, 84 [12] 3048-50 (2001)]. For all of the above processes, the cast samples do not possess sufficient strength and thus may pose problems during unmolding. In case of some specific commercially important ceramics, like silicon carbide, the preparation of aqueous suspension involves dispersion of particles under basic pH conditions created by use of a base like tetra methyl ammonium hydroxide (TMAH). Under basic pH conditions, the free silicon often present with the silicon carbide powder reacts to produce hydrogen gas, which causes defects in the green body. Also, during gelcasting of the above aqueous silicon carbide suspensions, the initiator ammonium persulphate (APS) also react with free silicon to produce nitrogen gas, which may again result into defects in green bodies. OBJECTS OF THE INVENTION It is thus the basic object of the present invention to provide composition for consolidation of participate slurries such as dense oxide, non-oxide ceramic and metal compacts which would avoid the prior art limitations of providing such dense ceramic/metal compacts. Another object of the present invention is to make the cast bodies significantly less sensitive to drying conditions. Another object of the present invention is to induce plasticity in cast samples such that the samples are less prone to cracking. Another object of the present invention is to improve the surface finish of the as cast ceramic or metal compacts. Another object of the present invention is to increase the green strength of the ceramic or metal compacts utilizing the synergistic effect of the organic binders and the saccharides. Yet another object of the present invention is to provide a simple environment friendly process for fabrication of dense ceramic and metal compacts, which obviates the drawbacks of presently known process of fabrication of dense ceramic/metal compacts as detailed above. Another object is to make selective use of saccharides including monosaccharides, disaccharides (e.g., sucrose), oligosaccharides and polysaccharides in combination with water-soluble polymerizable, other organic binders and gel forming materials not limited to but inclusive of methacrylamide (MAM)-methylenebisacrylamide (MBAM), phenol- formaldehyde resin, water soluble proteins such as egg white (ovalbumin), bovine serum albumin, gelatin, whey protein concentrate, collagen etc. Another object of the present invention is directed to improvement in processes involving casting of aqueous suspensions. Another object of the present invention is to selectively provide monosaccharides (glucose, fructose), disaccharides (especially sucrose) and oligosaccharides as the dispersing agent for ceramic and metal powder particles. Another object of the present invention is to provide aqueous slurries with reduced viscosity and yield stress to enable easy pouring and easy removal of air bubbles. Another object of the present invention is to enable preparation of highly loaded aqueous slurries that have low viscosity and yield stress. Another object of the present invention is to make possible gelling and drying as a single step and carry out drying of the samples while still contained in the molds. Another object of the present invention is to reduce drying shrinkage of cast body such that even very large components can be fabricated free of defects such as cracks, curvature etc. Another object of the present invention is to minimize binder migration during drying of cast samples. SUMMARY OF THE INVENTION Thus according to one aspect of the present invention there is provided composition for consolidation of particulate slurries such as dense oxide, non-oxide ceramic, metal compacts comprising a selective/synergistic combination of one or more saccharides including monosaccharide, disaccharide, oligosaccharide and polysaccharide and atleast one of water soluble polymerizable, organic binders and gel forming materials. According to another aspect of the present invention there is provided dense ceramic/metal compacts from aqueous particulate slurries involving anyone or more of monosaccharide, disaccharide, oligosaccharide and polysaccharide in combination with water soluble polymerizable, other organic binders and gel forming materials. According to yet another aspect of the present invention there is provided improvement in process of manufacture of dense ceramic/metal compacts from aqueous particulate slurries involving one or more saccharides including monosaccharide, disaccharide, oligosaccharide and polysaccharide in combination with one or more of water soluble polymerizable, organic binders and gel forming materials. Importantly, the invention disclosed above is directed to offer tremendous unprecedented advantages in ceramic processing by way of advantageous selective application of ability of sucrose to hold water. These benefits by use of sucrose are almost impossible to achieve by most other known methods or compositions. DESCRIPTION OF THE INVENTION The present inventors have surprisingly found that addition of monosaccharides, disaccharides, oligosaccharides or polysaccharides, preferably sucrose, to the composition for consolidation of particulate slurries offers many advantages including, but not limited to: • Shrinkage in ceramic compacts derived from such aqueous slurries can be controlled. • Gelation and drying can be effected simultaneously without any risk of cracking the samples. Samples prepared from sucrose containing slurries experienced significantly reduced drying shrinkage consequently making the samples less sensitive to drying conditions. Since sucrose has inherent property of retaining moisture, the drying rate was naturally slowed down, making the sample less sensitive to drying conditions in turn. • The migration of binder can be minimized which helps in obtaining homogenous samples. Comparison of the interrupted binder burnout runs of sample without and with sucrose indicated significantly reduced binder migration in latter samples. The reduced binder migration was clear form the almost uniform color attributed to the binder in the interrupted binder burnout samples. • The saccharides added reduce the viscosity of the aqueous slurry. • The said reduction in viscosity due to saccharide addition has a latent beneficial effect on control of entrapped air bubble population in the aqueous slurry. • Induced plasticity: Samples containing sucrose were not only resistant to cracking but the induced plasticity enabled shaping of sucrose containing foams simply by deformation without leading to any cracking. • Homogenous microstructure and High strength: Addition of sucrose resulted in lowering of viscosity indicative of greater steric hindrance, which resulted in slurries with little or no entrapped air bubbles. The samples thus obtained had higher strength and elastic modulus. The invention therefore provides for a saccharide-based composition for consolidation of particulate slurries including non-oxide ceramic, metal compacts and the non-oxide ceramic, metal compacts obtained involving the same. It was further seen that addition of sucrose or polysaccharides had beneficial effects on particularly egg white based alumina slurries and also on the compacts obtained form such slurries. Further experiments were conducted with increasing amount of polysaccharides or sucrose in the 55% by volume alumina slurries and also for 15% by volume alumina slurries. It was seen that there existed an optimum amount of sucrose for both low and high solids loading slurries. This optimum amount of sucrose yielded the highest green, sintered strength and the best surface finish, the amount of sucrose on the higher side being limited by sample deformation, due to melting of sucrose during heating and due to the difficulties during binder burn out for either of the low or high solids loading. The amount of sucrose added was limited on the lower side by only a marginal decrease in viscosity. Thus, the composition described above is not a mere admixture and would not be an obvious derivative to a person skilled in the art in terms of the known use of saccharides and its purpose in the composition. According to a preferred embodiment of the invention, the saccharide used is preferably sucrose. Sucrose is unique among saccharides as it is the most easily available naturally occurring polyhydroxyl aldehyde. Sucrose results in the lowest yield stress as compared o other saccharides like mono, di, oligo and poly saccharides etc. the drastic influence of sucrose addition for ovalbumin based slurries is clearly visible from the fact that in absence of sucrose, it becomes difficult to obtain high ceramic loading. The addition of even a small amount of sucrose to the slurries makes it easier to obtain high solids loading. The consolidation composition described above can be further made storage stable by addition of commercially available biocides or by keeping the slurries under slight agitation. The storage stable composition thus obtained can be used directly when required for obtaining the compact. The compacts of the proposed compositions could be consolidated by any of the casting routes that involve pouring or injecting the slurries in open or closed molds followed by gelation of the ceramic slurries simply by heating. Thin sheets of ceramic could be obtained by tape casting. With manipulation of composition such that a paste like mixture is obtained, dense ceramic compacts could be produced through extrusion also. It would be evident to a person skilled in the art that many such other variations of the composition described herein are possible, which are hereby intended to be within the scope and ambit of the present invention. The process for forming of dense ceramic components from aqueous particulate slurries is, therefore, based on water-soluble polymerizable, other organic binders and gel forming materials in combination with one or all of the saccharides including monosaccharides, disaccharides, oligosaccharides and polysaccharides, the water-soluble polymerizable organic binder and gel forming material being preferably selected from Acrylamides, methacrylamide/methylenebis acrylamide, Carrageenan, Starch, Urea-formaldehyde resin, Phenol formaldehyde resin, Phenol urea resin, Hydroxymethacrylamide, any protein and gelatin etc. Urea and formaldehyde are soluble in water and phenol is partly soluble. Accordingly, the components used may be individually soluble in water, if the resin becomes insoluble, it may still be used in the present invention. The proposed process is capable of forming simple to complex ceramic or metallic components with wide range of sizes. The aqueous ceramic slurries containing ovalbumin-sucrose may be used to obtain bullet proof grade dense alumina tile, various types of ceramic nozzles for high speed water jets, pouring of molten metals etc., threaded bolts, specialized ceramic crucibles, ceramic knife, ceramic tubes and large area ceramic compacts such as SiC space mirror etc. . The proposed process involves addition of controlled amount of the saccharides to the above-mentioned organic binder containing aqueous ceramic or metal particulate slurries. Ceramic or metal powder, dispersant, water, any of the above mentioned organic binders and one of the saccharides are mixed/milled in a ball mill in presence of hard ceramic milling media. A typical slurry composition may consist of 15 - 80 volume % ceramic or metal powders, a prior optimized amount of dispersant, and the rest is water, any of the above mentioned binders and any one of the saccharides. The organic binder-water ratio could be adjusted to obtain the desired viscosity. The saccharides could be added upto about 85-wt % of the ceramic or metal powder. With increasing amount of sucrose the shrinkage of the dense body reduced eventually approaching zero. While a much broader composition range could be used in forming dense ceramic/metal compacts as previously described, the preferred slurry composition could be in the following range — Ceramic loading 45 — 60 volume %, ovalbumin 1-100 volume % and 1 - 80% sucrose on a dry powder weight basis. In the most preferred embodiment, the ceramic solid loading can be varied from 10 — 60 volume %, the binder, which may be preferably ovalbumin, amount may range from 10 - 30 volume % based on amount of premix used and saccharide, which is preferably sucrose, may be varied from 1-5 weight % on dry powder weight basis. Importantly, selective additions of saccharides specifically sucrose resulted in lowering of the yield stress thus enabling easy pouring of the highly loaded slurries. Also, the use of saccharides prevented binder migration in the cast parts. Presence of polyhydroxy groups in saccharides was responsible for holding water molecules, which made the drying rate slower as well as induced plasticity in the cast parts. The reduced shrinkage due to presence of saccharides made the parts significantly less sensitive to drying rate and conditions. Also the reduced shrinkage was a great advantage when casting complex components particularly with curvature, thin-thick sections or the ones that involved use of cores. Heavy sections which typically cracked due to resistance to drying shrinkage under the weight of the part can be made easily due to minimal shrinkage. Gelation and drying could be done in a single step. The parts are not likely to crack regardless of the drying rate or conditions. For the above process aqueous slurries were also made without using the dispersant where sucrose also served the purpose of dispersing the ceramic or metal powder particles. The plasticity of the parts due to presence of saccharid the mold removal easy and also resulted in improved surface finish. EXAMPLES The invention, its objects and advantages are explained in greater detail in relation to following non-limiting exemplary illustrations. Example 1 An improved process for forming of dense ceramic components from ovalbumin-based slurries is proposed. The proposed process is capable of forming simple to complex ceramic components with wide range of size. The proposed improved proce.ss involves addition of controlled amount of sucrose to ovalbumin based aqueous slurries. Ceramic powder, water, ovalbumin and sucrose are mixed/milled in a ball mill in presence of hard ceramic milling media and antifoaming agent with or without addition of dispersants. A typical slurry composition may consist of 15-80 volume % ceramics or metal powder or combination of both, a prior optimized amount of dispersant and the rest is water, ovalbumin and sucrose. The ovalbumin-water ratio could be adjusted to obtain the desired viscosity. Sucrose could be added upto 65-wt % of ceramic powder. With increasing amount of sucrose, the shrinkage of the dense body reduced eventually approaching zero. The resulted slurry is cast in desired mold followed by temperature-induced gelation and drying to form green compacts. The green compacts formed are subjected to binder burnout and sintering to get the final components. The reduced shrinkage made the parts significantly less sensitive to drying rate and conditions. Also the reduced shrinkage has a great advantage when casting complex components particularly with curvature, thin-thick sections or the ones that involved use of cores. Heavy sections, which typically cracked due to resistance to drying shrinkage under the weight of the part, can be made easily due to minimal shrinkage. Gelation and drying can be done in a single step. The parts are not likely to crack regardless of the drying rate or conditions. The beneficial role of sucrose in lowering slurry viscosity could also be utilized is highly loaded alumina slurries. Without the addition of sucrose, it would not have been possible to prepare ceramic compacts samples from some of the highly loaded alumina slurries. A slurry composition containing 55-volume % alumina (d50 =7 micrometer, surface area 7m2/gm), with 20-volumes % ovalbumin in ovalbumin-water mix, could not even be prepared easily due to very high viscosity. All of the above problems were addressed by replacing part of the ovalbumin with sucrose. Addition of 1.7-wt % sucrose to the above slurry resulted in lowering of viscosity. Example 2 An improved process for forming of dense ceramic, metal compacts using any of the polymerizable materials (such as MAM-MBAM, phenol-formaldehyde or phenol-urea) based slurries is proposed. The proposed process is capable of forming ceramic simple to complex components with wide range of size. The proposed improved process involves addition of controlled amount of sucrose to any of the polymerizable materials based aqueous slurries. Ceramic powder, water, polymerizable binders (such as MAM-MBAM, phenol-formaldehyde or phenol-urea) and sucrose are mixed/milled in a ball mill in presence of hard ceramic milling media and antifoaming agent with or without addition of dispersants. A typical slurry composition may consist of 15 - 80 volume % ceramic or metal powder or combination of both, a prior optimized amount of dispersant and the rest is water, polymerizable binders monomer and sucrose. Sucrose could be added upto 65-wt % of ceramic powder. With increasing amount of sucrose the shrinkage of the dense body reduced eventually approaching zero. The resulted slurry is cast in desired mold followed by temperature-induced gelation and drying to form green compacts. The green compact formed are subjected to binder burnout and sintering to get the final components. The reduced shrinkage made the parts significantly less sensitive to drying rate and conditions. Also the reduced shrinkage has a great advantage when casting complex components particularly with curvature, thin-thick sections or the ones that involved use of cores. Heavy sections, which typically cracked due to resistance to drying shrinkage under the weight of the part, can be made easily due to minimal shrinkage. Gelation and drying can be done in a single step. The parts are not likely to crack regardless of the drying rate or conditions. The beneficial role of sucrose in lowering slurry viscosity could also be utilized in highly loaded alumina slurries. Without the addition of sucrose, it would not have been possible to prepare ceramic or metal compacts samples from some of the highly loaded slurries. Controlled addition of sucrose increase moisture holding tendency resulted in plasticity of the samples thus green compacts are less prone to crack during drying. The compacts are relatively stronger due to use of this combination of the binders. Association of the sucrose molecules with polymerizable binder materials reduces binder migration and inhibits crystal growth of the ungelled monomer. Example 3 An improved process for forming of dense silicon carbide and silicon nitride components from ovalbumin-based slurries is proposed. The proposed process is capable of forming simple to complex ceramic components with wide range of sizes. The proposed improved process involves addition of controlled amount of sucrose to ovalbumin based aqueous slurries. Silicon carbide powder, water, ovalbumin and sucrose are mixed/milled in a ball mill in presence of hard ceramic milling media and antifoaming agent with or without addition of dispersants. A typical slurry composition may consist of 15 - 80 volume % silicon carbide or silicon nitride powder without use of any dispersant and the rest is water, ovalbumin and sucrose. The ovalbumin-water ratio could be adjusted to obtain the desired viscosity. Sucrose could be added upto 65-wt % of ceramic powder. With increasing amount of sucrose, the shrinkage of the dense body reduced eventually approaching zero. The resulted slurry is cast in desired mold followed by temperature-induced gelation and drying to form green compacts. The green compact formed are subjected to binder burnout and sintering to get the final components. As sucrose act as dispersant, the reaction of free silicon present in the ceramic powder surface with basic medium is prevented. Thus green compacts of the SiC, Si3N4 can be produced without much of defects. More over, the sucrose helps in dispersion of the SiC, Si3N4 and SiO2 powders. The reduced shrinkage made the parts significantly less sensitive to drying rate and conditions. Also the reduced shrinkage has a great advantage when casting complex components particularly with curvature, thin-thick sections or the ones that involved use of cores. Heavy sections, which typically cracked due to resistance to drying shrinkage under the weight of the part, can be made easily due to minimal shrinkage. Gelation and drying can be done in a single step. The parts are not likely to crack regardless of the drying rate or conditions. The beneficial role of sucrose in lowering slurry viscosity could also be utilized in highly loaded slurries. Example 4 An improved process for forming of dense metal compacts using any of the polymerizable materials (such as MAM-MBAM, phenol-formaldehyde or phenol-urea) or water-soluble protein based slurries is proposed. The proposed process is capable of forming ceramic simple to complex components with wide range of size. It is difficult to make stable dispersed slurry using metal powder owing to high specific gravity. Use of sucrose with combination of water-soluble protein and/ any other poymerizable binders (monomer-cross linker) resulted in increase in specific gravity of the liquid mix. Preparation of slurry using metal powders and sucrose-binders mix (such as ovalbumin, MAM-MBAM) resulted in stable suspensions due to decrease in difference specific gravity of both powder and mix of binder-saccharides. The slurry is prepared using different amount of metal powders, water, binders and sucrose with dispersant. The resulted slurry is cast in desired mold followed by temperature-induced gelation and drying to form green compacts. The green compact formed are subjected to binder burnout and sintering to get the final components. It is thus possible by way of the above invention to achieve significantly reduced shrinkage with appropriate amount of addition of sucrose. Moreover, the reduced drying shrinkage coupled with pseudoplasticity and binding properties of sucrose ensure crack free samples each and every time. For the above reasons it is possible by way of the above invention to achieve layered ceramics as the drying rate is reduced thus minimizing any mismatches between sequentially cast layers. Also, the samples can be dried without controlling humidity. If required gelation and drying could be done in a single step or the samples could be dried at above ambient temperature (about 50°C) soon after casting. Slurries could be dried by stirring under low vacuum without fearing for loss of significant amount of water which would raise the viscosity of the slurries. It would also be possible, due to the present invention, to use open molds. Importantly, large sized parts can be made without defects during post- processing. Importantly, casting and drying defects can be minimized following the teachings of the present invention. Addition of sucrose to MAM-MBAM or other polymerizable binders can achieve reduced drying rate and shrinkage, which helps in minimization of defects. The above mentioned use of the combination of sucrose and the binders is also directed to increase in green strength and inhibit the binder migration due to association of sucrose with the binders. The other further advantages in the selective combination of ovalbumin and sucrose include the possibility of the use of high molecular weight binder (ovalbumin) with high ceramic loading and yet maintaining high flowability of the slurries. Selective use of sucrose is found to reduce the slurry viscosity and yield stress. The association of sucrose with protein (ovalbumin) inhibits binder migration. A homogeneous green body with high green strength is produced. Besides the large number of advantages, the combination of sucrose and ovalbumin is a commonly available, naturally occurring, low cost, environment friendly alternative for ceramic processing. WE CLAIM: 1. A composition for consolidation of particulate slurries of dense oxide, non-oxide ceramic or metal compacts comprising ceramic or metal powder; one or more saccharides used as dispersing agent and at least one water soluble polymerizable, organic binder. 2. A composition as claimed in claim 1, wherein the saccharide is selected from monosaccharides, disaccharides, oligosaccharides and polysaccharides. 3. A composition as claimed in claim 2, wherein the disaccharide is sucrose. 4. A composition as claimed 2, wherein the monosaccharide is glucose or fructose. 5. A composition as claimed in claim 1, wherein the water soluble polymerizable organic binder is selected from acrylamides such as methacrylamide, methylenebisacrylamide and hydroxymethacrylamide; phenol-formaldehyde resin; water soluble proteins such as egg white (ovalbumin); bovine serum albumin; gelatin; whey protein concentrate; collagen; starch and urea-formaldehyde resin and mixtures thereof. 6. A composition as claimed in claim 5, wherein the organic binder used is egg white (ovalbumin). 7. A composition as claimed in anyone of claims 1 to 6, wherein the ceramic or metal powder is present in an amount 15-80 volume % of the composition, ovalbumin is present in an amount 1 — 100 volume % of total liquid volume and saccharides is present upto 85 weight % of the ceramic or metal powder. 8. A composition as claimed in claim 7, wherein the ceramic or metal powder is present in an amount 45 — 60% volume % of the composition, ovalbumin is present in an amount 1-100 volume % of total liquid volume and saccharides is present in amount 1-80 weight % of the ceramic or metal powder. 9. A composition as claimed in claim 8, wherein the ceramic or metal powder is present in an amount 10-60 volume %of the composition, ovalbumin is present in an amount 10-30 volume % and saccharides is present in an amount 1-5 weight % of the ceramic or metal powder. 10. A composition as claimed in anyone of claims 1 to 8, further comprising biocides. 11. A dense ceramic or metal compact manufactured from the composition as claimed in anyone of claims 1 to 10. 12. A process for the manufacture of dense ceramic or metal compacts from the composition as claimed in anyone of claims 1 to 10 comprising: (a) mixing and milling ceramic or metal powder, water, ovalbumin and sucrose in a ball mill in the presence of hard ceramic milling media and antifoaming agent with or without addition of dispersants; (b) casting the resultant slurry in desired mold followed by temperature induced gelation and drying to form green compacts, and (c) subjecting the green compacts thus formed to binder burnout and sintering to get the final dense ceramic or metal compact. characterized in that the gelation and drying in step (b) are effected in a single step. 13. A composition substantially as described herein and illustrated by the accompanying examples. The present invention relates to a composition for consolidation of particulate slurries of dense oxide, non-oxide ceramic or metal compacts comprising ceramic or metal powder; one or more saccharides used as dispersing agent and at least one water soluble polymerizable, organic binder. The invention further relates to a dense ceramic or a metal compact manufactured from such compositions and a process for making the same.

Documents:

479-KOL-2003-FORM-27.pdf

479-kol-2003-granted-abstract.pdf

479-kol-2003-granted-claims.pdf

479-kol-2003-granted-correspondence.pdf

479-kol-2003-granted-description (complete).pdf

479-kol-2003-granted-form 1.pdf

479-kol-2003-granted-form 18.pdf

479-kol-2003-granted-form 2.pdf

479-kol-2003-granted-form 3.pdf

479-kol-2003-granted-form 5.pdf

479-kol-2003-granted-letter patent.pdf

479-kol-2003-granted-pa.pdf

479-kol-2003-granted-reply to examination report.pdf

479-kol-2003-granted-specification.pdf