Title of Invention

"A PROCESS OF MAKING YTTRIUM ALUMINIUM GARNET POWDER"

Abstract

The patent describes the making of yttrium aluminium garnet powder useful a precursor materials for making sintered components for engineering application. The solutions of yttrium salt as well as aluminium salt were mixed with the addition of aqueous ammonia in the form of aqueous solution while stirring or gaseous ammonia is passed through the mixed salt solution to obtain a semi-solid gel mass and heat treated to produce yttrium aluminium garnet powder. The intermediate polynuclear complexing affect the formation of homogeneous yttrium aluminium garnet powder at a temperature as low as 800°C.

Full Text

The present invention relates to a process of making yttrium aluminium garnet powder. The yttrium aluminium garnet powder is used as a precursor material to produce sintered components for engineering applications. The yttrium aluminium garnet powder precursor is also used as a sintering additive for sintering non-oxide materials like SiC, Si3N4 and SiAlON. Yttrium aluminium garnet powder is also used as-a compositing material with oxide and non-oxide compounds like A12O3, SiC, Si3N4 and MgO and as a laser material. The present day method of making yttrium aluminium garnet powder for which reference may be made to Donald R. Messier and George E. Gazza in Ceramic Bulletin, vol. 51, No. 9, 1972; wherein oxide powder e.g. Y2O3 and Al2O3.are mixed intimately, subsequently compacted and fired at a temperature in the range of 1500°C to 1600°C. In another method, coprecipitated yttrium hydroxide and aluminium hydroxide powders from their respective salt solutions are heat treated for the details of which reference may be made to J. W. G. A. Vrolijk, J. W. M. M. Willems and R. Metselaar in J. Euro. Ceram. Soc., 6, 1990, 47-51; Kyoung R. Han, Hee Jin Koo and Chang Sup Lim in J. Am. Ceram. Soc. 82 (6) 1598-1600,1999; Lin Liu, Zhi-Fan Zhang, Bruce King, Jhon Halloran and Richard M. Laine in J. Am. Ceram. Soc., 79(2) 385-394, 1996; Yin Liu, Zhi-Fan Zhang, Jhon Halloran and K. M. Lainc in J. Ani. Ceram. Soc., 81(3) 629-645, 1998. References may also be made to G. Gowda in J. Mater. Sci. Lett. 5 (1986) 1029- 1032, wherein sol-gel processing for making hydroxide precursors are effected which were subsequently heat treated at a temperature in the range of 800° to 1600°C for making yttrium aluminium garnet. The garnet prepared by above processes were ground by conventional processing to obtain the precursor powder. The draw back of the above processes are listed below : i) Attainment of homogeneity in mixing is difficult with solid materials. ii) Temperature of formation of yttrium aluminium garnet powder is high. iii) Co-precipitation increases the reactivity but only to a small extent. iv) Sol-gel processing leads to homogeneous products but with low solid to reactant volume ratio resulting very low yield. The main object of the present invention is to provide a process of making yttrium aluminium garnet powder which obviates the draw backs as detailed above. Another object of the present invention is to use inorganic salt solutions like nitrate, chloride, sulphate. Still another object of the present invention is to increase homogeneity of mixed reactants in comparison to solid-mixing process. Yet another object of the present invention is to lowering the formation temperature of yttrium aluminium garnet powder. Still another object of the present invention is to increase the solid volume: reactant volume ratio in comparison to sol-gel processing. Yet another object of the present invention is to increase the reactivity of the reactants in comparison to solid-state mixing process. Accordingly the present invention provides a process of making yttrium aluminum garnet powder which comprises: a) preparing 0.5 M to 3.5M yttrium salt solutions, b) preparing 0.5M to 4M aluminum salt solutions, c) characterised in that mixing solutions prepared in steps a) and b) under stirring at room temperature in 8 to 91 vol % yttrium salt solution and 9 to 92 vol % aluminum salt solutions, d) stirring the mixture for a period of 0.2 - 8 hrs, e) passing ammonia solution containing 10 to 50% ammonia or gaseous ammonia in the said mixture obtained in step d), f) stirring the mixture as obtained in step e) for 1 to 3 hrs to obtain gel like semi- solid, g) allowing to age the said semi-solid mass for 24-36 hrs, h) filtering and washing by water the semi-solid mass, i) heat treating the material obtained in step h) at 350-650°C for 2-6 hrs, j) grinding the heat treated product obtained in step i) and sieving through 100 mesh B.S., k) compacting the sieved powder obtained in step j) by cold isostatic pressing, 1) firing the compacted product at a temperature in the range of 800 to 1600°C for 1- 6 hrs, m) grinding and milling the fired product obtained in step 1) by conventional methods to obtain yttrium aluminum garnet powder. In an embodiment of the present invention yttrium and aluminium salts may be used in the form of nitrate, chloride, sulphate. In another embodiment of the present invention reaction with ammonia may be effected by passing gaseous ammonia through the solution. The details of the process of the present invention are given below : a) Solutions of aluminium salts are prepared in distilled water in the range of 0.5 to 4 M b) Solutions of yttrium salts are prepared in distilled water in the range of 0.5 to 3. c) The two solutions prepared in step 'a' and 'b' are mixed in 8 to 9i vol % yttrium salt solution and 9 to 92 vol % aluminium salt solutions. d) Aqueous ammonia ( 1:1, 1:2, 1:4 and 1:5) is passed into the mixed solution prepared in step 'c' with constant stirring. e) Gaseous ammonia is passed into the mixed solution prepared in step V under constant stirring. f) The entire mass converts to a gel like semi-solid which is allowed to age for 24-36 hours. g) The product formed in step 'f is filtered and washed by water. h) Heat treating the material obtained in step 'g' at 350 - 650°C for 2-6 hours. i) The heat treated product obtained in step 'h' is ground and sieved through 100 mesh B.S. j) The sieved powder obtained in step V is formed into green shape by cold isostatic pressing. k) The green pressed product obtained in step "j' is fired in the temperature range of 800 -1600°C for 1-6 hours. Y2O3 and Al2O3 combine to form different solid solutions containing Y, Al and O in different proportion giving approximate formulae Y3Al5O1:2, YA1O2 and Y4Al2O9 which are properly known as yttrium aluminium garnet ( YAG ),yttrium aluminium perovskite ( YAP) and yttrium alummate monoclinic ( YAM ). The normal formation temperature of those compounds are well above 1200°C and the different forms i.e. YAP and YAM decomposes at different temperatures. Since the formation temperature, decomposition temperature and sintering temperature are very close to each other it is difficult to obtain the desired phases in the sintered compacts. To avoid this problem sol - gel or co-precipitation techniques are normally adopted in which the formation temperature of different phases are much lower. However, the above two methods have their inherent . short comings. A new processing route involving intermediate hydrogel formation may yield such powder precursors that may be converted to different Y, Al and O compounds at comparatively lower temperature with greater homogeneity and higher reactivity. The technique involves intermediate hydrogel formation based on principles of polynuclear complexing. The novelty of the present invention lies in preparing yttrium aluminium garnet powder by using inorganic salts through the intermediate polycondensed hydroxy aquo complexes by the inventive steps of adding the salt solutions into concentrated ammonia solution. 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 84.2 ml 1(M) Al(NO3)3 9H2O and 50.55 ml 1(M) YCl3 6H2O solutions are mixed. Ammonium hydroxide ( 1:1) is added to this mixed solution with constant stirring. The stirring is continued with the formation of gel mass for 2 hours and then allowed to age the whole set-up to settle for 24 hours. The gel mass is filtered, washed with distilled water and heat treated at 650°C for 2 hours. The heat treated material is ground and pelletised at 200 MPa pressure. The pressed specimen is fired at 1400°C in air for 2 hours. The phases was identified as YAG only. Example - 2 ' 168.4 ml 0.5 (M) A1(NO3)3, 9H2O and 50.55 ml 1(M) YC13, 6H2O solutions are mixed. Ammonium hydroxide ( 1:2) is added to this mixed solution with constant stirring. The stirring is continued with the formation of gel mass for 2 hours and then allowed to age the whole set-up to settle for 24 hours. The gel mass is filtered, washed with distilled water and heat treated at 600°C tor 4 hours. The heat treated material is ground and pelletised at 250 MPa pressure. The pressed specimen is fired at 1600°C in air for 2 hours. The phases was identified as YAG only. Example - 3 42.1 ml 2 (M) A1(NO3)3, 9H2O and 14.44 ml 3.5 (M) YCl3 6H2O solutions are mixed. Ammonium hydroxide (1:4) is added to this mixed solution with constant string. The stirring is continued with the formation of gel mass for 3 hours and then allowed to age the whole set-up to settle for 48 hours. The gel mass is filtered, washed with distilled water and heat treated at 600°C for 3 hours. The heat treated material is ground and pelletised at 200 MPa pressure. The pressed specimen is fired at 1200°C in nir for 4 hours. The phases was identified as YAG only. Example - 4 42.1 ml 1(M) Al2(SO4)3,16H2O and 50.5 ml 1(M) Y(NO3)3, 5H2O solutions are mixed. Ammonium hydroxide ( 1:1) is added to this mixed solution with constant stirring. The stirring is continued with the formation of gel mass for 2 hours and then allowed to age the whole set-up to settle for 24 hours. The gel mass is iiltered, washed with distilled water and heat treated at 650°C for 2 hours. The heat treated material is ground and pelletised at 200 MPa pressure. The pressed specimen is fired at 800°C in air for 2 hours. The phases were identified YAG as major phase along with A12O3 and Y2O3 as minor phases. Example - 5 84.2 ml 0.5 (M) Al2(SO4)3,16H2O and 25.2 ml 2(M) Y(NO3)3, 5H2O solutions are mixed. Ammonium hydroxide (1:4) is added to this mixed solution with constant stirring. The stirring is continued with the formation of gel mass for 2 hours and then allowed to age the whole set-up to settle for 24 hours. The gel mass is filtered, washed with distilled water and heat treated at 550°C for 2 hours. The heat treated material is ground and pelletised at 200 MPa pressure. The pressed specimen is fired at 900°C in air for 1 hours. The phases were identified YAG as major phase along with A12O3 and Y2O3 as minor phases. Example - 6 84.2 ml 1(M) Al(NO3)3 9H2O and 50.55 ml 1(M) YC13, 6H2O solutions are mixed. Gaseous ammonia is passed to this mixed solution with constant stirring. The stirring is continued with the formation of gel mass for 2 hours and then allowed to age the whole set-up to settle for 24 hours. The gel mass is filtered, washed with distilled water and heat treated at 650°C for 2 hours. The heat treated material is ground and pelletised at 200 MPa pressure. The pressed specimen is fired at 1200°C in air for 2 hours. The phases were identified YAG as major phase along with trace of A12O3. Example - 7 84.2 ml 0.5 (M) Al2(SO4), 16H2O and 25.2 ml 2(M) Y(NO3)3. 5H2O solutions are mixed. Gaseous ammonia is added to this mixed solution with constant stirring. The stirring is continued with the formation of gel mass for 2 hours and then allowed to age the whole set-up to settle for 24 hours. The gel mass is filtered, washed with distilled water and heat treated at 600°C for 2 hours. The heat treated material is ground and pelletised at 200 MPa pressure. The pressed specimen is fired at 1000°C in air for 1 hours. The phases were identified YAG as major phase along with A12O3 and Y2O3 as minor phases. Example -8 168.4 ml 0.5 (M) A1(NO3)3, 9H2O and 50.55 ml 1(M) YC13, 6H2O solutioiis_arejnixed. Gaseous ammonia is added to this mixed solution with constant stirring. The stirring is continued with the formation of gel mass for 2 hours and then allowed to age the whole set-up to settle for 24 hours. The gel mass is filtered, washed with distilled water and heat treated at 550°C for 4 hours. The heat treated material is ground and peiletised at 250 MPa pressure. The pressed specimen is fired at 1600°C in air for 2 hours. The main advantages of the present invention are : 1. The inorganic salt solutions are used. 2. The formation temperature of yttrium aluminium garnet phase is reduced. 3. The homogeneity of mixed reactants in comparison to solid-mixing process is increased. 4. The reactivity of the reactants in comparison to solid-state mixing process is increased. 5. The volume ratio of solid to reactants is increased in comparison to sol-gel processing. We Claim: 1. A process of making yttrium aluminum garnet powder which comprises: a) preparing 0.5 M to 3.5M yttrium salt solutions, b) preparing 0.5M to 4M aluminum salt solutions, c) characterised in that mixing solutions prepared in steps a) and b) under stirring at room temperature in 8 to 91 vol% yttrium salt solution and 9 to 92 vol% aluminum salt solutions, d) stirring the mixture for a period of 0.2 - 8 hrs, e) passing ammonia solution containing 10 to 50% ammonia or gaseous ammonia in the said mixture obtained in step d), f) stirring the mixture as obtained in step e) for 1 to 3 hrs to obtain gel like semi- solid, g) allowing to age the said semi-solid mass for 24-36 hrs, h) filtering and washing by water the semi-solid mass, i) heat treating the material obtained in step h) at 350-650°C for 2-6 hrs, j) grinding the heat treated product obtained in step i) and sieving through 100 mesh B.S., k) compacting the sieved powder obtained in step j) by cold isostatic pressing, 1) firing the compacted product at a temperature in the range of 800 to 1600°C for 1- 6 hrs, m) grinding and milling the fired product obtained in step 1) by conventional methods to obtain yttrium aluminum garnet powder 2. A process of making yttrium aluminum garnet powder as claimed in claim 1, wherein yttrium and aluminum salts used are nitrate, chloride, sulphate. 3. A process of making yttrium aluminum garnet powder substantially as herein described with reference to the examples.

Documents:

149-del-2000-abstract.pdf

149-del-2000-claims.pdf

149-del-2000-comlete specification (granted).pdf

149-del-2000-correspondence-others.pdf

149-del-2000-correspondence-po.pdf

149-del-2000-description (complete).pdf

149-del-2000-form-1.pdf

149-del-2000-form-19.pdf

149-del-2000-form-2.pdf