Title of Invention

A PROCESS OF MAKING GLASS-MATRIX CERAMIC COMPOSITES

Abstract

This invention relates to glass matrix-ceramic composite for bonding abrasive materials and a process for preparing the same. Glass matrix ceramic composite according to this invention is prepared by forming a slurry of glass powder in an aqueous solution containing metal salts having Al+3, Si+4, Mg+2 Y+3, Zr+4 ions. pH of this slurry is increased till a gel like mass is formed which is filtered dried and calcined to obtain the composite. This invention also includes abrasive articles produced by admixing known abrasives with the glass matrix ceramic followed by moulding, firing and calcining. Abrasive articles prepared by this method has improved grinding ratio and long life. The glass matrix has the ceramic phase uniformly distributed therein.

Full Text

This invention relates to a process for making glass matrix ceramic composites for manufacturing bonded abrasives and abrasive articles made with them. Glass matrix-ceramic composites are used in bonding electronic components and for preparing bonded abrasive articles. Distribution of ceramic phase uniformly and evenly throughout the glassy matrix is one of the essential requirements of good quality glass matrix-ceramic composites. Grinding ratio and property of bonded abrasive articles are determined by grain holding capability and the rate of fracture of grain from the bond used in bonded abrasive articles. Grinding wheels having alumina abrasives with frit as bonding materials has been disclosed in US patent specification 4898597. Part of the frit has also been replaced with materials such as clay. GB patent no. 572700 discloses the use of borosilicate glass as bonding material. EP 0636457 and the US patent no.5863308 disclose other improvements in the field of bonds for abrasives. Abrasive articles made with the existing composite bonding material show the following drawbacks. When frit is used in the bonding material premature fracture of the grains is noticed which is attributed to the brittle nature of frit. This lowers the grinding ratio and hence the life of the grinding wheel. Addition of clay in the frit improves the bonding strength but formation of crystalline muUite phase is limited at the conventional firing temperature of around 1300°C of the grinding wheel. Though addition of nucleants such as Ti02, ZrO2, and MgO2 enhances the formation of crystalline phase, makes maintenance of nucleation and growth temperature difficult. The main object of the present invention is to provide a novel process of making glass matrix ceramic composite for manufacturing bonded abrasives which obviate the drawbacks described herein above. Yet another object of this invention is directed to the formation of ceramic phase such as mullite, alumina, magnesium-aluminate spinal, yttrium aluminum garnet at considerably lower temperatures in the glassy matrix at the grinding wheel. Glass matrix-composite produced by this process has uniform distribution of the ceramic phase throughout the glass matrix. Grinding ratio and hence the life of the abrasive articles made with the glass matrix-ceramic composite according to this invention are found to be considerably higher than those made with the hitherto known abrasive bonds. Glass matrix composite according to this invention has less thermal expansion coefficient than other glass bonded composites. Glass powder is added to an aqueous solution containing Al+3, Si+4', Mg+2, Y+3 ions either alone or in combination to form a slurry under constant stirring pH of the slurry is raised in the range of 7.5 to 10.5 by passing ammonia gas or by the addition of liquor ammonia, which results in gel formation. This gel is filtered and washed after aging and the filtered mass is ground, sieved and then calcined at a temperature ranging from 600'C to 1450°C. Abrasive articles are prepared by adding known abrasive materials such as alumina to the glass matrix ceramic composite along with any known temporary binder composition. The mixture is moulded in the desired shape, subjected to uniaxial pressing and then dried to obtain the abrasive article. A process for making glass matrix ceramic composite according to this invention comprises the steps of preparing a slurry of glass powder in an aqueous solution of metal salts containing Al+3, Si+4 Mg+2, Y+3, Zr+4 ions either alone or in combination, increasing the pH of said slurry to form a gel, separating the gel from said aqueous mixture, drying, calcining and grinding the same to obtain the glass matrix ceramic composite. This invention also includes a glass matrix ceramic composite when made by the process described herein above. The process for preparing an abrasive article according to this invention comprises the steps of preparing an admixture of a known abrasive material with the glass matrix composite prepared by the process as herein before described along with a known temporary bonding material, shaping and molding said admixture drying said shaped and molded article and subsequently firing the same to obtain said abrasive article. This invention also relates to an abrasive article prepared by a process as described herein above. Water soluble aluminium salts such as aluminum nitrate and aluminum chloride may be used in a concentration ranging from 0.5 to 5.0 (N). Other salts capable of being used are magnesium nitrate, magnesium chloride, yttrium nitrate, yttrium chloride, sodium silicate, silicon chloride and zirconium oxychloride preferably in the concentration ranging from 0.5 to 5.0 (N). Preferably the weight percentage of ceramic phase in the glass matrix may be in the range of 1 to 50%. For the preparation of abrasive articles, any known abrasive such as silicon carbide, aluminum oxide, sol-gel alumina, cubic boron nitride (CBN), diamond, zirconia, silicon nitride, zirconium toughened alumina, and tungston carbide either conventional manner. The abrasive article obtained by this method show better grinding ratio and have longer life span. In a specific embodiment glass powder is mixed with an aqueous solution of the selected metal sah under stirring liquor ammonia is poured into the suspension to raise the pH to the range of 7.5 to 10.5. Gel like mass produced is their aged for about 24 hours and then filtered, washed and calcined at a temperature in the range of 350°C to 950°C. This mass is then ground to the desired mesh size preferably 200 mesh B.S., which is then sieved and heated to a temperature of 600°C to 1450C. The following example combines the steps of preparing glass matrix ceramic composite and abrasive articles such as grinding wheels prepared by bonding abrasive materials with the composite. Example 1 2000 cc of 0.5 (N) aluminum nitrate nona-hydrate solution and 660 cc of 0.5 (N) sodium silicate nona hydrate solution, 640 g of glass powder having composition of 80.5% of SiOj, 3.8% of NajO, 0.4% of KA 12.9% of B2O3 and 2.2% of AliOj are mixed thoroughly. Liquid ammonia is poured into the slurry to reach the pH at 8.5, ammonia gas is purged into the slurry to keep the pH constant while gel like mass is formed. The gel like mass is filtered and the residue is washed thoroughly with water to remove the soluble alkali. The gel like mass is calcined at 800 deg.C. The calcined mass is ground and passed through 200-mesh sieve. 1740 g of white alumina of 60 grit is mixed with the 260 g of sieved powder along with temporary binder is mixed thoroughly and moulded wheel of size 180mm X 15mm X 31.75mm by uniaxial pressing, dried at 120 deg.C. and fired at 1250 deg.C to make the grinding wheel. Example 2 1 litre of 1.0 (N) anhydrous aluminum chloride solution, 67 g of colloidal silica sol having silica content of 30 wt%, 1150 cc of 0.5 (N) zirconium oxychloride solution and 568 g of glass powder having composition of 80.5% of SiO2, 3.8% of Na2O, 0.4% of K2O, 12.9% of B2O3 and 2.2% of AI2O3 are mixed thoroughly. Liquid ammonia is poured into the slurry to reach the pH at 9.0, ammonia gas is purged into the slurry to keep the pH constant while gel like mass is formed. The gel like mass is filtered and the residue is washed thoroughly with water to remove the soluble alkali. The gel like mass is calcined at 800 deg.C. The calcined mass is ground and passed through 200-mesh sieve. 1740 g of white alumina of 60 grit is mixed with the 260 g of sieved powder along with temporary binder is mixed thoroughly and moulded wheel of size 180mm X 15mm X 31.75mm by uniaxial pressing, dried at 120 deg.C. and fired at 1250 deg.C to make the grinding wheel. Example 3 2000 cc of 0.5 (N) anhydrous aluminum chloride solution, 67 g of colloidal silica sol having silica content of 30 wt%, 1420 g of glass powder having composition of 80.5% of Si02, 3.8% of Na2O, 0.4% of K2O, 12.9% of B2O3 and 2.2% of AI2O3 are mixed thoroughly. Liquid ammonia is poured into the sluny to reach the pH at 9.0, ammonia gas is purged into the slurry to keep the pH constant while gel like mass is formed. The gel like mass is filtered and the residue is washed thoroughly with water to remove the soluble alkali. The gel like mass is calcined at 800 deg.C. The calcined mass is ground and passed through 200-mesh sieve, 1740 g of white alumina of 60 grit is mixed with the 260 g of sieved powder along with temporary binder is mixed thoroughly and moulded wheel of size 180mm X 15mm X 31.75mm by uniaxial pressing, dried at 120 deg.C. and fired at 1250 deg.C to make the grinding wheel. Example 4 2000 cc of 0.5 (N) anhydrous aluminum chloride solutiion, 67 g of colloidal silica sol having silica content of 30 wt%, 355 g of glass powder having composition of 80.5% of SiO2, 3.8% of Na2O, 0.4% of K2O, 12.9% of B2O3 and 2.2% of Al2O3 are mixed thoroughly. Liquid ammonia is poured into the slurry to reach the pH at 9.0, ammomia gas is purged into the slurry to keep the pH constant while gel like mass is formed. The ^1 like mass is filtered and the residue is washed thoroughly with water to remove the soluble alkali. The gel like mass is calcined at 800 deg.C. The calcined mass is ground and passed through 200-mesh sieve. 1740 g of white alumina of 60 grit is mixed with the 260 g of sieved powder along with temporary binder is mixed thoroughly and moulded wheel of size 180mm X 15nim X 31.75mm by uniaxial pressing, dried at 120 deg.C. and fired at 1250 deg.€ to make the grinding wheel. The table below shows the comparative performance of grinding wheel prepared by using conventional glass bonding material and the grinding wheel mode using glass matrix composite made according to the invention under identical conditions: Machine used Surface Grinding Machine - M451 Manufactured by Praga Tools Limited, India Grinding wheel Size: 178nim X 13mm X 32mm Grinding Wheel Speed: 2800 rpm Depth of cut: 50µ/pass Shaping of the molded article may altemately be carried out by isostatic pressing, slip casting, and tape casting and injection molding. Firing of the shaped article may be carried out for about one hour. This example is only illustrative as obvious alterations and modificatioms known to persons skilled in the art are within the scope of the appended claims. WE CLAIM: 1. A process for making glass matrix ceramic composite comprising the steps of preparing a slurry of glass powder in an aqueous solution of metal salts containing Al+3, Si+4, Mg+2 Y+3 Zr+4 ions either alone or in combination, increasing the pH of said slurry to form a gel, separating the gel from said aqueous mixture, drying, calcining and grinding the same to obtain the glass matrix ceramic composite. 2. The process as claimed in claim 1 wherein the pH of the aqueous slurry is increased to 7.5 to 10.5 by adding liquor ammonia and thereafter by passing ammonia gas through said slurry to maintain the pH level. 3. The process as claimed in claims 1 and 2 wherein said gel like mass is separated by filtration, and the separated mass washed free of alkali prior to drying, grinding and calcining. 4. The process as claimed in claims 1 and 2 wherein said gel like mass is aged for atleast 24 hours before separation from the aqueous mixture. 5. The process as claimed in claims 1 to 4 wherein calcining is carried out at a temperature ranging from 350°C to 950C. 6. The process as claimed in claims 1 to 5 wherein said calcined mass is ground to a mesh size of 200 BS and then heat treated to a tempreature of 600°C to 1450°C. 7. The process as claimed in claims 1 to 6 wherein said glass matrix ceramic composite consists of 1 to 50 percent of ceramic phase in the glass matrix. 8. The process as claimed in claims 1 to 6 wherein said metal salts are selected from chlorides and nitrates of aluminum, magnesium, yttrium in a concentration ranging from 0.5 (N) to 5.0 (N). 9. The process as claimed in claims 1 to 6 wherein said metal sahs are selected from sodium silicate, sodium chloride, colloidal silica salt and zirconium oxychloride in a concentration of 0.5 (N) to 5.0 (N). 10. A process for preparing an abrasive article such as grinding wheel comprising the steps of preparing an admixture of known abrasive material with the glass matrix composite prepared by the process as claimed in any one of the preceding claims along with a known binder material, shaping said admixliire, drying said shaped article and subsequently firing the same to obtain said abrasive article. 11. A process for making glass mafrix ceramic composite substantially as herein described.

Documents:

0043-che-2003 abstract duplicate.pdf

0043-che-2003 abstract.pdf

0043-che-2003 claims duplicate.pdf

0043-che-2003 claims.pdf

0043-che-2003 correspondence others.pdf

0043-che-2003 correspondence po.pdf

0043-che-2003 description (complete) duplicate.pdf

0043-che-2003 description (complete).pdf

0043-che-2003 form-1.pdf

0043-che-2003 form-19.pdf

0043-che-2003 form-26.pdf

0043-che-2003 form-3.pdf