Title of Invention

"A PROCESS OF MAKINGYITTRIUM ALUMINIUM PEROVSITE POWDER"

Abstract

The patent describes the making of yttrium aluminium perovskite 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 perovskite powder. Here the principle of intermediate polynuclear complexing affect the formation of homogeneous yttrium aluminium perovskite powder at a temperature as low as 800°C. 13

Full Text

The present invention relates to a process of making yttrium aluminium perovskite powder. The yttrium aluminium perovskite powder is used as a precursor material to produce sintered components for engineering applications. The yttrium aluminium perovskite powder precursor is also used as an additive for sintering non-oxide materials like SiC, Si3N4 and SiAlON. Yttrium aluminium perovskite powder in also used as a compositing material with oxide and non-oxide compounds like Al2O3, SiC, Si3N4 and MgO and as a laser material. The present day method of making yttrium aluminium psrovskite powder for which reference may be made to Donald R. Messier and George £. Gazza in Ceramic Bulletin, vol. 51, No. 9, 1972; wherein oxide powder e.g. Y2O3 and A12O3 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. Laine in J. Am. 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 perovskite. The perovskite 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 perovskite 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 reactants volume ratio resulting very low yield. The main object of the present invention is to provide a process of making yttrium aluminium perovskite 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 perovskite powder. 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 increase the solid volume : reactant volume ratio in comparison to sol-gel processing. Still 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 aluminium perovskite powder which comprises: mixing aqueous solution of yttrium salt and aluminium salt containing 0.5 M to 3.5 M yttrium salt and 0.5 M to 4 M aluminium salt respectively, mixing the solution with aqueous ammonia in the range of 1:1 to 1:5 or by passing gaseous ammonia, stirring the mixture for 2 to 3 hours, keeping the mixture for 24 hours to 36 hours, filtering and washing the solid product formed by water, heat treating the washed solid product formed at a temperature in the range of 350 - 650°C for 2-6 hours, grinding the heat treated mass to pass through 100 mesh B.S., compacting the powder materials by known processes, firing the compacted shapes at a temperature in the range of 800 -1600°C for 1 -6 hrs, grinding and milling the fired shapes by conventional methods to obtain yttrium aluminium perovskite powder. In an embodiment of the present invention yttrium and aluminium salts may be used such as 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 O.S to 4 (M) b) Solutions of yttrium salts are prepared in distilled water in the range of 0.5 to 3.5 (M) c) The two solutions prepared in step 'a' and 'b' are mixed in 12.5 to 88.9 vol% yttrium salt solutions with 11.1 to 87.5 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' under constant stirring. e) Gaseous ammonia is passed into the mixed solution prepared in step 'c' with constant stirring. f) The entire mass converts to a gel like semi-solid which is allowed to age for 24-36 hrs. g) The product formed in step 'f' is filtered and washed by water. h) Heat treating the material obtained in step 'g' is heat tieated at 350-650°C for 2-6 hrs. i) The heat treated product is ground and sieved through 100 mesh B.S. j) The sieved powder obtained in step 'i' 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°Cfor 1-6 hours. YzO3 and A12O3 combine to form different solid solutions containing Y, Al and O in different proportion giving approximate formulae Y3Al5O13 , YA1O2 and Y4Al2O9 which are properly known as yttrium aluminium garnet ( YAG ), yttrium aluminium perovskite ( YAP) and yttrium aluminate 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 perovskite 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 60.9 ml 1(M) A1(NO3)3, 9H2O and 61 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 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 pheses are identified as YAP along with YAG. Example - 2 121.9 ml 0.5 (M) A1(NO3)3, 9H2O and 122 ml 0.5(M) YC13, 6I12O 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 for 24 hours. The gel mass is filtered, washed with distilled water and heat treated at 600°C for 4 hours. The heat treated material is ground and pelletised at 250 MPa pressure. The pressed specimen is fired at 16GO°C in air for 2 hours.The phases are identified YAP as major phase along with YAG and A12O3. Example - 3 40.6 ml 1.5 (M) AKNO3)3 9H2O and 17.4 ml 3.5 (M) YC13, 6H2O 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 3 hours and then allowed the whole set-up for 48 hours. The gel mass is filtered, washed with distilled water and heat treated at 550°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 air for 4 hours. The phases are identified YAP as major phase along with YAG and A12O3. Example - 4 30.49 ml 1(M) Al2(SO4)3,16H2O and 61 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 things 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 14()0°C in air for 2 hours. The phases are identified YAP as major phase along with YAG Example - 5 60.9 ml 0.5 (M) Al2(SO4)3, 16H2O and 30.5 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 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 1600°C in air for 1 hours.The phases are identified YAP as major phase along with YAG as minor phase. Example - 6 60.9 ml 1(M) A1(NO3)3, 9H2O and 61 ml 1(M) YCl3, 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 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 are identified YAP as major phase along with YAG and A12O3. Example - 7 60.9 ml 0.5 (M) Al2SO4)3, 16H2O and 30.5 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 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 1600°C in air for 1 hours. The phases are identified YAP as major phase along YAG as minor phase. Example -8 121.9 ml 0.5 (M) A1(NO3)3, 9H2O and 61 ml 1(M) YC13, 6H2O solutions aro 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 for 24 hours. The gel mass is filtered, washed with distilled water and heat treated at 600°C for 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 are identified YAP as major phase along YAG as minor phase. The main advantages of the present invention are 1. The formation temperature of yttrium aluminium perovskite phase is reduced. 2. The homogeneity of mixed reactants in comparison to solid-mixing process is increased. 3. The reactivity of the reactants in comparison to solid-state mixing process is increased. 4. The volume ratio of solid to reactants is increased in comparison to sol-gel processing. We Claim: 1. A process of making yttrium aluminium perovskite powder which comprises: mixing of aqueous solution of yttrium salt and aluminium salt containing 0.5 M to 3.5 M yttrium salt and 0.5 M to 4 M aluminium salt respectively, mixing the solution with aqueous ammonia in the range of 1:1 to 1: 5 or by passing gaseous ammonia, stirring the mixture for 2 to 3 hours, keeping the mixture for 24 hours to 36 hours, filtering and washing the solid product formed by water, heat treating the washed solid product formed at a temperature in the range of 350 - 650°C for 2-6 hours, grinding the heat treated mass to pass through 100 mesh B.S., compacting the powder materials by known processes, firing the compacted shapes at a temperature in the range of 800 - 1600°C for 1-6 hrs, grinding and milling the fired shapes by conventional methods to obtain yttrium aluminium perovskite powder. 2. A process as claimed in claim 1 wherein yttrium and aluminium salts are selected from nitrate, chloride, sulphate. 3. A process of making yttrium aluminium perovskite powder substantially as herein described with reference to the examples.

Documents:

164-del-2000-abstract.pdf

164-del-2000-claims.pdf

164-del-2000-correspondence-others.pdf

164-del-2000-correspondence-po.pdf

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

164-del-2000-form-1.pdf

164-del-2000-form-19.pdf

164-del-2000-form-2.pdf