Title of Invention

A PROCESS FOR THE MANUFACTURE OF ZINC ALUMINATE POWDER

Abstract

A process for the manufacture of zinc aluminate is provided by synthesizing a powder precursor and calcining the same at low temperature. The process is an improvement on co precipitation technique where a specific buffer was used for stoichiometric precipitation of the reactive ingredients thus producing a reactive powder precursor. Heat treatment of this powder precursor produced zinc aluminate. Zinc aluminate powder thus manufactured may be used as catalytic reaction such as cracking, hydrogenation, dehydrogenation, dehydration. This material is also used as sintering aid or bonding material for sintering of various inorganic materials. This is also used as coating material, high temperature stain or as sensor in some electronic devices.

Full Text

The present invention relates to a process for the manufacture of Zinc Aluminate powder. Zinc aluminate is used for catalytic reaction such as cracking, hydrogenation, dehydrogenation, dehydration. This material is also used as sintering aid or bonding material for sintering of various inorganic materials. This is also used as coating material, high temperature stain or as sensor in some electronic devices. The material is presently made by two broad processes such as solid state reaction of oxide raw materials and solution phases reaction using metal salts in polyvinyl alcohol media. References may be made to D.L. Branson, Kinetics and mechanism of the reaction between zinc oxide and aluminium oxide", J. Am. Ceram. Soc., 48, 1965, p. 591-595;T. Tsuchida, M. Kondo, R. Furuichi and T. Ishii, "Transformation of n-AbOa prepared by thermal dcomposition of Al2(SO4)3.18H20 and AI(NO3)3.(H20) to a-AI203 and ZnAI204 formation", J. Chem. Soc. Japan, 8(8), 1974,p. 1443-1450;T. Tsuchida, R. Furuichi and T. Ishii,"Effect of chlorine or its compounds on the reaction of rV aluminium oxide with zinc oxide", Chem. Lett, 11.1975, p.1191-1194;T. Tsuchida, R. Furuichi and T. Ishii, "Reactivity of 6-and 6-aluminium oxide for zinc aluminate (ZnAI2O4) formation", Z.Anorg.Allg.Chem.,423(2),1976,p.180-184;K. Nakaymay, M. Hasiba, E. Mura, Y. Nurishi and T. Hibino, "Effect of weak mixing method on the formation of ZnAI204", J. Chem. Soc Japan,88(7),1980,p.394-400; H. Kawakami, H. Okada, M. Hashiba, E. Mura, Y. Nurishi and T. Hibino," Effect of dispersion of reactants mixture on the kinetics of formaton of ZnAI204", J. Chem. Soc. Japan, 90(11), 1982, p.642-648, wherein in most cases metal oxide such as zinc oxide, aluminium oxide was mixed which on heat treatment produced zinc aluminate. In some cases metal salts such as aluminium sulphate, aluminium nitrate, zinc nitrate were also used as oxide precursors. Reference may also be made to A.K.Adak, A. Pathak and P. Paramanik, "Characterisation of ZnAI204 nanocrystals prepared by the polyvinyl alcohol evaporation route", J. Mat. Sci. Lett., 17,1998,p.559-561 wherein mixed salt solution was treated with PVA solution, heat treated to obtain a powder which on calcination and pulverization yielded zinc aluminate. Main drawbacks of the above processes are : 1. For solid state route : a) High purity fine oxide powder were mechanically mixed, as a result of which it was difficult to maintain proper homogeneity for maintaining actual stoichiometric ratio for the preparation of zinc aluminate. b) Crystalline size increased. c) Reactivity decreased. d) Surface area decreased. e) Particle size increased. f) High formation temperature was required. 2. For poly vinyl alcohol evaporation route : a) Difficulty in stirring after sometime due to increase in viscosity. b) Voluminous fluffy mass, occupies huge space. c) Sticks to reacting vessel. As a result it is difficult to get it out. d) Large amount of poisionous /toxic NC>2 fumes were released. The main object of the present invention is to provide a process for the manufacture of zinc aluminate powder, which obviates the above noted drawbacks. Another object of the present invention is to increase the homogeneity of the powder precursor prepared for manufacturing zinc aluminate. Still another object of the present invention is to increase the reactivity of the produced zinc aluminate by increasing surface area of the manufactured zinc aluminate powder. Yet another object of the present invention is to reduce the reaction temperature for the production of zinc aluminate. A further object of the present invention is to avoid / reduce the evolution of toxic nitrogen dioxide gas during calcinations. Zinc aluminate is formed by direct combination of zinc oxide and aluminium oxide. Since this is a solid state reaction, intimate mixing of individual oxides is an essential part but it is difficult to achieve. This problem of mixing has been solved in the present invention by taking the reactants in soluble form in which AI3+ and Zn2+ are intimately mixed in solution. From this mixed solution of cations, it is possible to precipitate mixed hydroxide by incorporating OH" anion in the reaction system. However, it is difficult to precipitate both aluminium and zinc stoichiometrically by simply adding an alkali. In the present invention the stoichiometric precipitation of the mixed phase has been made possible by maintaining the pH between 7.5 to 8.0, by providing a basic media consisting of a specified mixture of either Tri ethanol amine and ammonium hydroxide or Hexamethylene tetra amine and ammonium hydroxide. The novelty of the present invention is in obtaining zinc aluminate powder of higher reactivity by an hitherto unknown and non-obvious inventive step of providing the basic media, to control the pH between 7.5 to 8.0, in the form of Triethanolamine(TEA)-ammoniaum hydroxide solution or Hexamethylene tetra amine (HMT)- ammonium hydroxide solution. Accordingly the present invention provides a process for the manufacture of zinc aluminate powder, which comprises preparing mixed salt solution by mixing soluble salts of zinc and aluminium in 1:1 molar proportion with water in such amount that the concentration of mixed salt solution obtained lies in the range of 0.05 to 0.15 molar, maintaining the pH of the mixed salt solution in the range of 7.5 to 8.0 by adding a basic media into the mix solution under stirring till the gelation is completed with the formation of gel, ageing the gel for a period in the range of 24-30 hours, filtering the aged gel to obtain a solid mass, washing the solid mass with water, drying the washed solid mass at a temperature in the range of 80°-110°C to obtain a dried solid mass, calcining the said dried solid mass at a temperature in the range of 500°-800°C, pulverizing the calcined mass by conventional methods to obtain zinc aluminate powder. In an embodiment of the present invention the soluble salts of zinc and aluminium are any soluble salts of zinc and aluminium such as nitrate, chloride, sulphate. In another embodiment of the present invention the basic media is prepared by mixing organic amines such as Triethanolamine (TEA), Hexamethylene tetra amine (HMT) with ammonium hydroxide solution maintaining the concentration of amine in the range of 0.01 to 0.02 moles per litre and pH of the solution in the range of 7.5-8.5. The following examples are given by way of illustrations and therefore should not be construed to limit the scope of the present invention. Example-1 Triethanolamine (0.01M) is mixed with diluted ammonium(1:20) in such a way that the pH becomes 7.9 to prepare the basic media. Preparation of co precipitated gel: 18.90 gm zinc nitrate and 42.70 gm aluminium nitrate is mixed with 1000 ml water to make a solution of 0.1 (M), and is taken in a beaker. Basic media is added drop by drop with simultaneous stirring until the gelation is completed. After completion of the gelation the gel was allowed to age for 29 hrs followed by filtration and washing with distilled water. The gels were dried at 110°C. The dried mass was agated in an agate morter. The powders were compacted and heat treated at 500°C with a soaking period of 1 hr. Finally the compacted mass was pulverized to make fine powder. The powder was characterized by XRD and was found to contain zinc aluminate. Example-2 Hexamethylene tetra amine(HMT) (0.01M) is mixed with diluted ammonium(1:20) in such a way that the pH becomes 7.5. Preparation of co precipitated gel: 18.90 gm zinc nitrate and 42.70 gm aluminium nitrate is mixed with 1000 ml water to make a solution of 0.1 (M), and is taken in a beaker. Basic media is added drop by drop with simultaneous stirring until the gelation is completed. After completion of the gelation the gel was allowed to age for 25 hrs followed by filtration and washing with distilled water. The gels were dried at 90°C. The dried mass was agated in an agate rnorter. The powders were compacted and heat treated at 600°C with a soaking period of 1 hr. Finally the compacted mass was pulverized to make fine powder. The powder was characterized by XRD and was found to contain zinc aluminate. Example-3 Triethanolamine (0.015M) is mixed with diluted ammonium(1:15) in such a way that the pH becomes 8.0 to prepare the basic media. Preparation of co precipitated gel: 28.80 gm zinc sulphate and 51.30 gm aluminium sulphate is mixed with 1000 ml water to make a solution of 0.15(M), and is taken in a beaker. Basic media is added drop by drop with simultaneous stirring until the gelation is completed. After completion of the gelation the gel was allowed to age for 27 hrs followed by filtration and washing with distilled water. The gels were dried at 110°C. The dried mass was agated in an agate morter. The powders were compacted and heat treated at 500°C with a soaking period of 1 hr. Finally the compacted mass was pulverized to make fine powder. The powder was characterized by XRD and was found to contain zinc aluminate. Example-4 Hexamethylene tetra amine(HMT) (0.015M) is mixed with diluted ammoniurn(1:15) in such a way that the pH becomes 8.0. Preparation of co precipitated gel: 28.80 gm zinc sulphate and 51.30 gm aluminium sulphate is mixed with 1000 ml water to make a solution of 0.1 (M), and is taken in a beaker. Basic media is added drop by drop with simultaneous stirring until the gelation is completed. After completion of the gelation the gel was allowed to age for 24 hrs followed by filtration and washing with distilled water. The gels were dried at 110°C. The dried mass was agated in an agate morter. The powders were compacted and heat treated at 500°C with a soaking period of 1 hr. Finally the compacted mass was pulverized to make fine powder. The powder was characterized by XRD and was found to contain zinc aluminate. Example-5 Triethanolamine (0.02M) is mixed with diluted ammonium(1:10) in such a way that the pH becomes 8.5 to prepare the basic media. Preparation of co precipitated gel: 6.80 gm zinc chloride and 6.675 gm aluminium chloride is mixed with 1000 ml water to make a solution of 0.05(M), and is taken in a beaker. Basic media is added drop by drop with simultaneous stirring until the gelation is completed. After completion of the gelation the gel was allowed to age for 24 hrs followed by filtration and washing with distilled water. The gels were dried at 100°C. The dried mass was agated in an agate morter. The powders were compacted and heat treated at 600°C with a soaking period of 1 hr. Finally the compacted mass was pulverized to make fine powder. The powder was characterized by XRD and was found to contain zinc aluminate. Example-6 Hexamethylene tetra amine(HMT) (0.02M) is mixed with diluted ammonium(1:10) in such a way that the pH becomes 8.5. Preparation of co precipitated gel: 6.80 gm zinc chloride and 6.675 gm aluminium chloride is mixed with 1000 ml water to make a solution of 0.05(M), and is taken in a beaker. Basic media is added drop by drop with simultaneous stirring until the gelation is completed. After completion of the gelation the gel was allowed to age for 24 hrs followed by filtration and washing with distilled water. The gels were dried at 100°C. The dried mass was agated in an agate morter. The powders were compacted and heat treated at 600°C with a soaking period of 1 hr. Finally the compacted mass was pulverized to make fine powder. The powder was characterized by XRD and was found to contain zinc aluminate. Example-7 Triethanolamine (0.01M) is mixed with diluted ammonium(1:20) in such a way that the pH becomes 7.5 to prepare the basic media. Preparation of co precipitated gel: 18.90 gm zinc nitrate and 42.70 gm aluminium nitrate is mixed with 1000 ml water to make a solution of 0.1 (M), and is taken in a beaker. Basic media is added drop by drop with simultaneous stirring until the gelation is completed. After completion of the gelation the gel was allowed to age for 26 hrs followed by filtration and washing with distilled water. The gels were dried at 110°C. The dried mass was agated in an agate morter. The powders were compacted and heat treated at 700°C with a soaking period of 1 hr. Finally the compacted mass was pulverized to make fine powder. The powder was characterized by XRD and was found to contain zinc aluminate. Example-8 Hexamethylene tetra amine(HMT) (0.01M) is mixed with diluted ammonium(1:20) in such a way that the pH becomes 7.5. Preparation of co precipitated gel: 18.90 gm zinc nitrate and 42.70 gm aluminium nitrate is mixed with 1000 ml water to make a solution of 0.1 (M), and is taken in a beaker. Basic media is added drop by drop with simultaneous stirring until the gelation is completed. After completion of the gelation the gel was allowed to age for 26 hrs followed by filtration and washing with distilled water. The gels were dried at 110°C. The dried mass was agated in an agate morter. The powders were compacted and heat treated at 700°C with a soaking period of 1 hr. Finally the compacted mass was pulverized to make fine powder. The powder was characterized by XRD and was found to contain zinc alurninate. Example-9 Triethanolamine (0.018M) is mixed with diluted ammonium(1:20) in such a way that the pH becomes 7.8 to prepare the basic media. Preparation of co precipitated gel: 18.90 gm zinc nitrate and 42.70 gm aluminium nitrate is mixed with 1000 ml water to make a solution of 0.1 (M), and is taken in a beaker. Basic media is added drop by drop with simultaneous stirring until the gelation is completed. After completion of the gelation the gel was allowed to age for 28 hrs followed by filtration and washing with distilled water. The gels were dried at 90°C. The dried mass was agated in an agate morter. The powders were compacted and heat treated at 600°C with a soaking period of 1 hr. Finally the compacted mass was pulverized to make fine powder. The powder was characterized by XRD and was found to contain zinc aluminate. Example-10 Hexamethylene tetra amine(HMT) (0.018M) is mixed with diluted ammonium(1:20) in such a way that the pH becomes 7.8. Preparation of co precipitated gel: 18.90 gm zinc nitrate and 42.70 gm aluminium nitrate is mixed with 1000 ml water to make a solution of 0.1 (M), and is taken in a beaker. Basic media is added drop by drop with simultaneous stirring until the gelation is completed. After completion of the gelation the gel was allowed to age for 28 hrs followed by filtration and washing with distilled water. The gels were dried at 90°C. The dried mass was agated in an agate morter. The powders were compacted and heat treated at 600°C with a soaking period of 1 hr. Finally the compacted mass was pulverized to make fine powder. The powder was characterized by XRD and was found to contain zinc aluminate. Example-11 Triethanolamine (0.01M) is mixed with diluted ammonium(1:20) in such a way that the pH becomes 7.5 to prepare the basic media. Preparation of co precipitated gel: 37.80 gm zinc nitrate and 85.40 gm aluminium nitrate is mixed with 1000 ml water to make a solution of 0.2(M), and is taken in a beaker. Basic media is added drop by drop with simultaneous stirring until the gelation is completed. After completion of the gelation the gel was allowed to age for 30 hrs followed by filtration and washing with distilled water. The gels were dried at 100°C. The dried mass was agated in an agate morter. The powders were compacted and heat treated at 800°C with a soaking period of 1 hr. Finally the compacted mass was pulverized to make fine powder. The powder was characterized by XRD and was found to contain zinc aluminate. Example-12 Hexamethylene tetra amine(HMT) (0.01M) is mixed with diluted ammonium(1:20) in such a way that the pH becomes 7.5. Preparation of co precipitated gel: 37.80 gm zinc nitrate and 85.40 gm aluminium nitrate is mixed with 1000 ml water to make a solution of 0.2(M), and is taken in a beaker. Basic media is added drop by drop with simultaneous stirring until the gelation is completed. After completion of the gelation the gel was allowed to age for 30 hrs followed by filtration and washing with distilled water. The gels were dried at 110°C. The dried mass was agated in an agate morter. The powders were compacted and heat treated at 600°C with a soaking period of 1 hr. Finally the compacted mass was pulverized to make fine powder. The powder was characterized by XRD and was found to contain zinc aluminate. Example-13 Triethanolamine (0.01M) is mixed with diluted ammonium(1:20) in such a way that the pH becomes 7.5 to prepare the basic media. Preparation of co precipitated gel: 13.60 gm zinc chloride and 13.35 gm aluminium nitrate is mixed with 1000 ml water to make a solution of 0.1 (M), and is taken in a beaker. Basic media is added drop by drop with simultaneous stirring until the gelation is completed. After completion of the gelation the gel was allowed to age for 27 hrs followed by filtration and washing with distilled water. The gels were dried at 110°C. The dried mass was agated in an agate morter. The powders were compacted and heat treated at 800°C with a soaking period of 1 hr. Finally the compacted mass was pulverized to make fine powder. The powder was characterized by XRD and was found to contain zinc aluminate. Example-14 Hexamethylene tetra amine(HMT) (0.01M) is mixed with diluted ammonium(1:20) in such a way that the pH becomes 7.5. Preparation of co precipitated gel: 19.20 gm zinc sulphate and 34.20 gm aluminium sulphate is mixed with 1000 ml water to make a solution of 0.1 (M), and is taken in a beaker. Basic media is added drop by drop with simultaneous stirring until the gelation is completed. After completion of the gelation the gel was allowed to age for 25 hrs followed by filtration and washing with distilled water. The gels were dried at 90°C. The dried mass was agated in an agate morter.The powders were compacted and heat treated at 500°C with a soaking period of 1 hr. Finally the compacted mass was pulverized to make fine powder. The powder was characterized by XRD and was found to contain zinc aluminate. Example-15 Triethanolamine (0.01M) is mixed with diluted ammonium(1:20) in such a way that the pH becomes 7.5 to prepare the basic media. Preparation of co precipitated gel: 28.35 gm zinc nitrate and 64.05 gm aluminium nitrate is mixed with 1000 ml water to make a solution of 0.15(M), and is taken in a beaker. Basic media is added drop by drop with simultaneous stirring until the gelation is completed. After completion of the gelation the gel was allowed to age for 29 hrs followed by filtration and washing with distilled water. The gels were dried at 100°C. The dried mass was agated in an agate morter. The powders were compacted and heat treated at 700°C with a soaking period of 1 hr. Finally the compacted mass was pulverized to make fine powder. The powder was characterized by XRD and was found to contain zinc aluminate. Example-16 Hexamethylene tetra amine(HMT) (0.01M) is mixed with diluted ammonium(1:20) in such a way that the pH becomes 7.9. Preparation of co precipitated gel: 13.60 gm zinc chloride and 13.35 gm aluminium chloride is mixed with 1000 ml water to make a solution of 0.1 (M), and is taken in a beaker. Basic media is added drop by drop with simultaneous stirring until the gelation is completed. After completion of the gelation the gel was allowed to age for 30 hrs followed by filtration and washing with distilled water. The gels were dried at 90°C. The dried mass was agated in an agate morter. The powders were compacted and heat treated at 500°C with a soaking period of 1 hr. Finally the compacted mass was pulverized to make fine powder. The powder was characterized by XRD and was found to contain zinc aluminate. Example-17 Triethanolamine (0.01M) is mixed with diluted ammonium(1:20) in such a way that the pH becomes 8.4 to prepare the basic media. Preparation of co precipitated gel: 18.90 gm zinc nitrate and 42.70 gm aluminium nitrate is mixed with 1000 ml water to make a solution of 0.1 (M), and is taken in a beaker. Basic media is added drop by drop with simultaneous stirring until the gelation is completed. After completion of the gelation the gel was allowed to age for 27 hrs followed by filtration and washing with distilled water. The gels were dried at 110°C. The dried mass was agated in an agate morter. The powders were compacted and heat treated at 600°C with a soaking period of 1 hr. Finally the compacted mass was pulverized to make fine powder. The powder was characterized by XRD and was found to contain zinc aluminate. Example-18 Hexamethylene tetra amine(HMT) (0.01M) is mixed with diluted ammonium(1:20) in such a way that the pH becomes 7.5. Preparation of co precipitated gel: 19.20 gm zinc sulphate and 34.20 gm aluminium sulphate is mixed with 1000 ml water to make a solution of 0.1 (M), and is taken in a beaker. Basic media is added drop by drop with simultaneous stirring until the gelation is completed. After completion of the gelation the gel was allowed to age for 29 hrs followed by filtration and washing with distilled water. The gels were dried at 100°C. The dried mass was agated in an agate morter. The powders were compacted and heat treated at 800°C with a soaking period of 1 hr. Finally the compacted mass was pulverized to make fine powder. The powder was characterized by XRD and was found to contain zinc aluminate. In the process of the present invention zinc aluminate spinel is manufactured at low temperature(500°C) using zinc-aluminium hydroxy compounds which are synthesized from mix salt solutions of Zn2+ and AI3+. Triethanolamine(TEA)-ammonium hydroxide and Hexamethylene tetra amine(HMT)-ammonium hydroxide are used as basic media for gelation. It has been found that spinel formation was very much influenced by the mixed hydroxide precursors obtained by using different basic media. Heat treatment of the precursor zinc-aluminium based hydroxy compounds produced pure spinel at relatively low temperature. The main advantages of the present invention are: 1. All the raw materials are easily available. 2. Hydroxy precursor can be prepared at room temperature. 3. There is no evolution of any toxic fumes such as nitrogen dioxide, sulphur dioxide or chlorine. 4. Precursor itself can be used as bonding material/sintering aid 5. Highly reactive amorphous material can be obtained by heat treatment (300°-350°C) of mixed hydroxide for application as high temperature stain, coating material. 6. Temperature for the formation of zinc aluminate is low, of the order of 500°C. We Claim: 1. A process for the manufacture of zinc aluminate powder comprises; preparing mixed salt solution by mixing soluble salts of zinc and aluminum in 1:1 molar proportion with water so that the concentration of mixed salt solution obtained lies in the range of 0.05 to 0.15 molar, characterized in that maintaining the pH of the mixed salt solution in the range of 7.5 to 8.0 by adding a basic media into the mix solution under stirring till the gelation is completed with the formation of gel, ageing the gel for a period in the range of 24-30 hours, filtering the aged gel to obtain a solid mass, washing the solid mass with water, drying the washed solid mass at a temperature in the range of 80-110°C to obtain a dried solid mass, calcining the said dried solid mass at a temperature in the range of 500-800°C, pulverizing the calcined mass by conventional methods to obtain zinc aluminate powder. 2. A process as claimed in claim 1, wherein the soluble salts of zinc and aluminum are any soluble salts of zinc and aluminum nitrate, chloride, sulphate. 3. A oprocess s claimed in claim 1-2, wherein the basic media is prepared by mixing organic amines Triethanolamine (TEA), Hexamethylene tetra amine (HMT) with ammonium hydroxide solution maintaining the concentration of amine in the range of 0.01 to 0.02 moles per liter and pH of the solution in the range of 7.5-8.5. 4. A process for the manufacture of zinc aluminate powder substantially as herein described with reference to the examples.

Documents:

699-DEL-2002-Abstract-(11-03-2008).pdf

699-del-2002-abstract.pdf

699-DEL-2002-Claims-(08-09-2008).pdf

699-DEL-2002-Claims-(11-03-2008).pdf

699-del-2002-claims.pdf

699-DEL-2002-Correspondence-Others-(08-09-2008).pdf

699-DEL-2002-Correspondence-Others-(11-03-2008).pdf

699-del-2002-correspondence-others.pdf

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699-DEL-2002-Description (Complete)-(11-03-2008).pdf

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