Title of Invention	"A PROCESS FOR MAKING ALUMINATE SPINEL USEFUL AS REFRACTORIES AND ENGINEERING CERAMICS IN THE WIDE RANGE OF MAGNESIA CONTENT"
Abstract	A process for making Magnesium Acuminate spinal useful as refractories and engineering ceramics in the wide range of Magnesia content which comprises preparing aluminum oxide suspension in a solution of magnesium salt with dispersants such as herein described, adding to the said suspension a soluble hydroxide such as herein described, maintaining the pH in the range of 9.4 to 12.4 to obtain a gel-like mass, allowing the gel-like mass to age for a period in the range of 8 to 48 hours, filtering and washing the aged gel-like mass, drying the gel-like mass at a temperature in the range of 110-200°C, grinding and palletizing the dried material, firing the palletized material at a temperature in the range of 1200-1400°C, grinding the pellets by known methods.

Title of Invention

"A PROCESS FOR MAKING ALUMINATE SPINEL USEFUL AS REFRACTORIES AND ENGINEERING CERAMICS IN THE WIDE RANGE OF MAGNESIA CONTENT"

Abstract

A process for making Magnesium Acuminate spinal useful as refractories and engineering ceramics in the wide range of Magnesia content which comprises preparing aluminum oxide suspension in a solution of magnesium salt with dispersants such as herein described, adding to the said suspension a soluble hydroxide such as herein described, maintaining the pH in the range of 9.4 to 12.4 to obtain a gel-like mass, allowing the gel-like mass to age for a period in the range of 8 to 48 hours, filtering and washing the aged gel-like mass, drying the gel-like mass at a temperature in the range of 110-200°C, grinding and palletizing the dried material, firing the palletized material at a temperature in the range of 1200-1400°C, grinding the pellets by known methods.

Full Text	The present invention relates to an improved process for making magnesium aluminate spinel useful as refractory and engineering ceramics. The present invention particularly relates to an improved process for making magnesium aluminate spinel in the wide range of magnesia content useful for refractory and engineering ceramics and a process for making articles thereof. The process of the present invention particularly relates to the use of gel derived magnesia additive for makinIg magnesia-alumina-spinel material. The main usage of the magnesium aluminate spinel are in the field of refractories as bricks and monolithic castables and also in engineering ceramics like automobile engine, pump etc. as sintering aid for silicon carbide etc. due to its superior thermo-mechanical properties and chemical stability and in various other industrial applications where magnesium aluminate spinel is required for its different physicochemical properties. The present day method of making magnesium aluminate essentially consists of using powdered magnesium oxide and aluminium oxide for which reference may be made to Eugene Ryskhewitch "Oxide Ceramics" Academic Press, New York & London, 1960 leading to a product formed at much higher temperature and considerable inhomogeneity and to R. J. Bratton as referred in J. of American Ceramic Society Bulletin, Vol. 48, No. 8, pp. 759 wherein submicron reactants were used to reduce formation temperature and also to Bother. R and co-workers "Modelling Chemical Composition and microstructure of Mg-Al hydroxide coprecipitation for Mg-aluminate spinel formation" in Euro Ceramics Vol. 1: Processing of Ceramics, edited by G. de With, R. A. Terpstra & R. Metselaar, Elsevier Applied Science, London, 1989, 1.82-88, wherein a solution containing magnesium and aluminium nitrate as precursor for co-precipitation at pH = 10 and temperature of 60°C and also separately precipitated hydroxide prepared from magnesium and aluminium nitrate, having the similar disadvantages or it may also be referred to J. F. Pasquier, S. Komarneni and R. Roy "Synthesis of MgAl2O4 spinel : Seeding effect on formation temperature" in J. Mat. Sci. Vol. 26, pp 3797, 1991 who have used sol-gel technique by using either a boehmite sol and a solution of Mg(NO3)2 or a boehmite sol and a solid MgO or using two nitrates or aluminium isopropoxide and magnesium ethoxide with or withot seeding crystals, where maintaining homogeneous stoichiometry throughout the bulk of the precipitate is difficult. Main drawbacks in the above processes may be listed below : 1. Mixing of solids very often leads to inhomogeneous products. 2. Due to inhomogeneity of the powder mix, Magnesia-Alumina ratio does not remain constant throughout the bulk of the material. 3. Magnesium aluminate formation generally requires at least 1400-1700°C. 4. To avoid deleterious effect of volume expansion during formation of magnesium aluminate preforming of magnesium aluminate separate process is resorted to. 5. Remixing of preformed magnesium aluminate with rest of the ingredients in solid state reintroduces the possibility of inhomogeneity in the formed articles resulting into degradation of properties. The main object of the -present invetion is to provide a process for aluminate spinel useful as refractories and engineering ceramics, which obviates the drawbacks as detailed above. Another object of the present invention is to use gel-derived magnesium oxide for making magnesium aluminate spinal keeping aluminum oxide as solid. Still another object of the present invention is to reduce the firing temperature of magnesium aluminate formation. Yet another object of the present invention is to ensure homogeneity or of composition throughout the body of other fired articles. Still another object of the present invention is to make magnesium aluminate spinel containing articles by single firing. Yet another object of the present invention is to eliminate intermediate grinding operations like attrition or ball milling during making of magnesium aluminate spinel containing articles. Still another object of the present invention is to provide a process for making articles using the magnesium aluminate spinel prepared by the process of the present invention. Accordingly, the present invention provide a process for making magnesium aluminate spinel useful as refractories and engineering ceramics in the wide range of Magnesia content characterized by preparing aluminum oxide suspension in a solution of magnesium salt with dispersants such as herein described, adding to the said suspension a soluble hydroxide such as herein described, maintaining the pH in the range of 9.4 to 12.4 to obtain a gel-like mass, allowing the gel-like mass to age for a period in the range of 8 to 48 hours, filtering and washing the aged gel-like mass, drying the gel-like mass at a temperature in the range of 110-200° C, grinding and pelletising the dried material, firing the pelletised material at a temperature in the range of 1200-1400° C, grinding the pellets by known methods. In an embodiment of the present invention the ratio of alumina to magnesium salt may be such that the MgO:Al2O3 weight ratio in the fired product is in the range of 0.04 to 1.58. In another embodiment of the present invention the dispersants used may be such as triporyphosphate, hexametaphosphate, poryacrylate. In still another embodiment of the present invention soluble hydroxide used may be such as known soluble hydroxide, calcined dolomite and calcite. The details of the process of the present invention are given below: a) Aluminium oxide is mixed with dispersing agents and magnesium chloride solution by constant stirring to prepare a suspension. b) Soluble hydroxide like ammonia solution is added in the suspension prepared in step 'a' with stirring to reach the pH of the solution above 9.4. c) The pH of the suspension is further raised to 12.4 for completion of reaction. d) Gel-like mass formed in step 'c' is kept for ageing for 8 - 48 hours. e) Aged gel-like mass formed in step 'd' is washed and filtered. f) Washed gel-like mass formed in step 'e' is dried at 100-200°C for 6-48 hours. g) Dried gel-like mass produced in step 'f is heat treated at 1200-1400°C for 2-5 hours. The process of the present invention can be used to produce magnesium aluminate for use as raw material or sintered body of different shapes and sizes for direct application as refractory and engineering ceramics. MgO and A12O3 forms a series of solid solution in an wide range of composition. MgO : Al2O3 mole ratio varies continuously in the magnesium aluminate with their ratio in the starting raw material. Physicochemical properties of magnesium aluminate depends on the molar ratio of MgO : A12O3 . This require precision control of MgO: A12O3 ratio for tailoring the properties of magnesium aluminate spinel. Solid state mixing of powders are not only a difficult process but also leads to inhomogeneity often resulting into a product of erotic property profile. The alternative is co-precipitation from solution of their salts. Leaving aside the cost parameter, which is prohibitive for most of the industrial items, the process is difficult to control particularly in a scaled-up operation. The process is extremely pH sensitive as the precipitation of A1(OH)3 starts at 3.3 whereas the corresponding figure for Mg(OH)2 is 9.4. Again dissolution of Al(OH)3 precipitates starts at pH of 7.8 and complete dissolution of A1(OH)3 occurs at 10.8 whereas for complete precipitation of Mg(OH)2, pH is to be increased to 12.4. So, it is obvious that there is a complete mismatch concerning precipitation of hydroxides of aluminium and magnesium in relation to pH of the medium and an extremely narrow zone of pH may be fixed for co-precipitation of both the ions, that too in an incomplete way. This difficulty is completely eliminated by fixing one solid component, precipitating the other over it. This process may further be improved by bringing the solid component, A12O3 in the present case, in suspension and forming the hydroxide of Mg in the form of a gel-like structure in which A12O3 particles will be embedded. Since the particles will be embedded, as the solid is in colloidal suspension, homogeneity in composition throughout the bulk of the material is anticipated. Moreover, volume expansion due to the formation of magnesium aluminate is anticipated to be compensated by the volume shrinkage accompanying dehydroxylation of gel-structure eliminating the additional process of preforming magnesium aluminate before use and the phenomenon may be utilised to formulate batch composition in such a way that volume of specimens remain unchanged before and after firing. The following examples are given by way of illustration and should not be construed to limit the scope of the present invention. Example -1 95.80 gm of A12O3 was mixed with 31.10 ml of MgCl2 solution containing 0.064 g. MgCl2 per ml and 0.05 g poryacrylate was mixed and stirred for 2 hours. In the suspension so produced 45 ml concentrated ammonia solution was added with stirring for 15 minutes. The entire volume of mixture turned into a semi-solid gel-like mass. The entire material was left for 24 hours for ageing. Aged material was filtered followed by washing with hot water. After complete washing, till free from chloride, the material was dried at 200°C for 3 hours. Dried material was ground to pass through 200 mesh B.S. and was pressed uniaxialry at 250 MPa. Pressed body was fired at 1400°C. Example - 2 91.01 gm of A12O3 was mixed with 66.57 ml of MgCl2 solution containing 0.064 g. MgCl2 per ml and 0.05 g triporyphosphate was mixed and stirred for 2 hours. In the suspension so produced 45 ml concentrated ammonia solution was added with stirring for 15 minutes. The entire volume of mixture turned into a semi-solid gel-like mass. The entire material was left for 24 hours for ageing. Aged material was filtered followed by washing with hot water. After complete washing, till free from chloride, the material was dried at 200°C for 3 hours. Dried material was ground to pass through 200 mesh B.S. and was pressed uniaxialry at 250 MPa. Pressed body was fired at 1400°C. Example - 3 85.82 gm of A12O3 was mixed with 107.23 ml of MgCl2 solution containing 0.064 g. MgCl2 per ml and 0.05 g hexametaphosphate was mixed and stirred for 2 hours. In the suspension so produced 45 ml concentrated ammonia solution was added with stirring for 15 minutes. The entire volume of mixture turned into a semi-solid gel-like mass. The entire material was left for 24 hours for ageing. Aged material was filtered followed by washing with hot water. After complete washing, till free from chloride, the material was dried at 200°C for 3 hours. Dried material was ground to pass through 200 mesh B.S. and was pressed uniaxialry at 250 MPa. Pressed body was fired at 1400°C. Example - 4 79.15 gm of A12O3 was mixed with 154.40 ml of MgCl2 solution containing 0.064 g. MgCl2 per ml and 0.05 g polyacrylate was mixed and stirred for 2 hours. In the suspension so produced 45 ml concentrated ammonia solution was added with stirring for 15 minutes. The entire volume of mixture turned into a semi-solid gel-like mass. The entire material was left for 24 hours for ageing. Aged material was filtered followed by washing with hot water. After complete washing, till free from chloride, the material was dried at 200°C for 3 hours. Dried material was ground to pass through 200 mesh B.S. and was pressed uniaxially at 250 MPa. Pressed body was fired at 1400°C. Example - 5 62.79 gm of A12O3 was mixed with 176.60 ml of MgCl2 solution containing 0.064 g. MgCl2 per ml and 0.05 g tripolyphosphate was mixed and stirred for 2 hours. In the suspension so produced 45 ml concentrated ammonia solution was added with stirring for 15 minutes. The entire volume of mixture turned into a semi-solid gel-like mass. The entire material was left for 24 hours for ageing. Aged material was filtered followed by washing with hot water. After complete washing, till free from chloride, the material was dried at 200°C for 3 hours. Dried material was ground to pass through 200 mesh B.S. and was pressed uniaxially at 250 MPa. Pressed body was fired at 1400°C. Example - 6 38.75 gm of Al2O3 was mixed with 290.72 ml of MgCl2 solution containing 0.064 g. MgCl2 per ml and 0.05 g hexametaphosphate was mixed and stirred for 2 hours. In the suspension so produced 45 ml concentrated ammonia solution was added with stirring for 15 minutes. The entire volume of mixture turned into a semi-solid gel-like mass. The entire material was left for 24 hours for ageing. Aged material was filtered followed by washing with hot water. After complete washing, till free from chloride, the material was dried at 200°C for 3 hours. Dried material was ground to pass through 200 mesh B.S. and was pressed uniaxially at 250 MPa. Pressed body was fired at 1400°C. The results obtained by the process of present intention are given in Table -1 by way of illustration. (Table Removed) From the Table above it may be inferred that specimens contain Magnesium Aluminate spinel of different MgO : A12O3 molar ratio without any noticeable dimensional changes. The main advantages of the present invention are : (1) It's usability to produce Magnesium Aluminate based material of various shapes and sizes for application as refractory and engineering materials, (2) Simpler processing technique is sufficient for the production of homogeneous products, (3) Temperature of formation may be reduced to 1200-1400°C depending upon composition, (4) Sintering of larger shapes without any deleterious dimensional deformities, (5) Tailoring of composition is possible with more accuracy, (6) Flexibility of the process to accommodate any composition in the system within the same technological parameters. 1. A process for making magnesium aluminate spinel useful as refractories and engineering ceramics in the wide range of Magnesia content chracterised by preparing aluminum oxide suspension in a solution of magnesium salt with dispersants such as herein described, adding to the said suspension a soluble hydroxide such as herein described, maintaining the pH in the range of 9.4 to 12.4 to obtain a gel-like mass, allowing the gel-like mass to age for a period in the range of 8 to 48 hours, filtering and washing the aged gel-like mass, drying the gel-like mass at a temperature in the range of 110-200°C, grinding and pelletizing the dried material, firing the pelletized material at a temperature in the range of 1200-1400°C, grinding the pellets by known methods. 2. A process as claimed in claim -1 wherein the ratio of alumina to magnesium salts such that the MgO: AI203 weight ratio in the fired product are in the range of 0.04 to 1.58. 3. A process as claimed in claims 1 & 2 wherein the dispersants used is selected from tripolyphosphate, hexametaphosphate, polyacrylate. 4. A process as claimed in claims 1-3 wherein'soluble hydroxide used is selected from soluble hydroxide, dolomite and calcite. 5. A process for making magnesium aluminate spinel substantially as herein described with reference to the examples.

Full Text

The present invention relates to an improved process for making magnesium aluminate spinel useful as refractory and engineering ceramics.
The present invention particularly relates to an improved process for making magnesium aluminate spinel in the wide range of magnesia content useful for refractory and engineering ceramics and a process for making articles thereof.
The process of the present invention particularly relates to the use of gel derived magnesia additive for makinIg magnesia-alumina-spinel material.
The main usage of the magnesium aluminate spinel are in the field of refractories as bricks and monolithic castables and also in engineering ceramics like automobile engine, pump etc. as sintering aid for silicon carbide etc. due to its superior thermo-mechanical properties and chemical stability and in various other industrial applications where magnesium aluminate spinel is required for its different physicochemical properties.
The present day method of making magnesium aluminate essentially consists of using powdered magnesium oxide and aluminium oxide for which reference may be made to Eugene Ryskhewitch "Oxide Ceramics" Academic Press, New York & London, 1960 leading to a product formed at much higher temperature and considerable inhomogeneity and to R. J. Bratton as referred in J. of American Ceramic Society Bulletin, Vol. 48, No. 8, pp. 759 wherein submicron reactants were used to reduce formation temperature and also to Bother. R and co-workers "Modelling Chemical Composition and microstructure of Mg-Al hydroxide coprecipitation for Mg-aluminate spinel formation" in Euro Ceramics

Vol. 1: Processing of Ceramics, edited by G. de With, R. A. Terpstra & R. Metselaar, Elsevier Applied Science, London, 1989, 1.82-88, wherein a solution containing magnesium and aluminium nitrate as precursor for co-precipitation at pH = 10 and temperature of 60°C and also separately precipitated hydroxide prepared from magnesium and aluminium nitrate, having the similar disadvantages or it may also be referred to J. F. Pasquier, S. Komarneni and R. Roy "Synthesis of MgAl2O4 spinel : Seeding effect on formation temperature" in J. Mat. Sci. Vol. 26, pp 3797, 1991 who have used sol-gel technique by using either a boehmite sol and a solution of Mg(NO3)2 or a boehmite sol and a solid MgO or using two nitrates or aluminium isopropoxide and magnesium ethoxide with or withot seeding crystals, where maintaining homogeneous stoichiometry throughout the bulk of the precipitate is difficult. Main drawbacks in the above processes may be listed below :
1. Mixing of solids very often leads to inhomogeneous products.
2. Due to inhomogeneity of the powder mix, Magnesia-Alumina ratio does not remain
constant throughout the bulk of the material.
3. Magnesium aluminate formation generally requires at least 1400-1700°C.
4. To avoid deleterious effect of volume expansion during formation of magnesium
aluminate preforming of magnesium aluminate separate process is resorted to.
5. Remixing of preformed magnesium aluminate with rest of the ingredients in solid state
reintroduces the possibility of inhomogeneity in the formed articles resulting into
degradation of properties.
The main object of the -present invetion is to provide a process for
aluminate spinel useful as refractories and engineering ceramics, which obviates the
drawbacks as detailed above.
Another object of the present invention is to use gel-derived magnesium oxide for making magnesium aluminate spinal keeping aluminum oxide as solid.
Still another object of the present invention is to reduce the firing temperature of magnesium aluminate formation.
Yet another object of the present invention is to ensure homogeneity or of composition throughout the body of other fired articles.
Still another object of the present invention is to make magnesium aluminate spinel containing articles by single firing.
Yet another object of the present invention is to eliminate intermediate grinding operations like attrition or ball milling during making of magnesium aluminate spinel containing articles.
Still another object of the present invention is to provide a process for making articles using the magnesium aluminate spinel prepared by the process of the present invention.
Accordingly, the present invention provide a process for making magnesium aluminate spinel useful as refractories and engineering ceramics in the wide range of Magnesia content characterized by preparing aluminum oxide suspension in a solution of magnesium salt with dispersants such as herein described, adding to the said suspension a soluble hydroxide such as herein described, maintaining the pH in the range of 9.4 to 12.4 to obtain a gel-like mass, allowing the gel-like mass to age for a period in the range of 8 to 48 hours, filtering and washing the aged gel-like mass, drying the gel-like mass at a
temperature in the range of 110-200° C, grinding and pelletising the dried material, firing
the pelletised material at a temperature in the range of 1200-1400° C, grinding the pellets
by known methods.
In an embodiment of the present invention the ratio of alumina to magnesium salt may be
such that the MgO:Al2O3 weight ratio in the fired product is in the range of 0.04 to 1.58.
In another embodiment of the present invention the dispersants used may be such as
triporyphosphate, hexametaphosphate, poryacrylate.
In still another embodiment of the present invention soluble hydroxide used may be such as
known soluble hydroxide, calcined dolomite and calcite.
The details of the process of the present invention are given below:
a) Aluminium oxide is mixed with dispersing agents and magnesium chloride solution by
constant stirring to prepare a suspension.
b) Soluble hydroxide like ammonia solution is added in the suspension prepared in step 'a'
with stirring to reach the pH of the solution above 9.4.
c) The pH of the suspension is further raised to 12.4 for completion of reaction.
d) Gel-like mass formed in step 'c' is kept for ageing for 8 - 48 hours.
e) Aged gel-like mass formed in step 'd' is washed and filtered.
f) Washed gel-like mass formed in step 'e' is dried at 100-200°C for 6-48 hours.
g) Dried gel-like mass produced in step 'f is heat treated at 1200-1400°C for 2-5 hours.
The process of the present invention can be used to produce magnesium aluminate for use as raw material or sintered body of different shapes and sizes for direct application as refractory and engineering ceramics.
MgO and A12O3 forms a series of solid solution in an wide range of composition. MgO : Al2O3 mole ratio varies continuously in the magnesium aluminate with their ratio in the starting raw material. Physicochemical properties of magnesium aluminate depends on the molar ratio of MgO : A12O3 . This require precision control of MgO: A12O3 ratio for tailoring the properties of magnesium aluminate spinel. Solid state mixing of powders are not only a difficult process but also leads to inhomogeneity often resulting into a product of erotic property profile. The alternative is co-precipitation from solution of their salts. Leaving aside the cost parameter, which is prohibitive for most of the industrial items, the process is difficult to control particularly in a scaled-up operation. The process is extremely pH sensitive as the precipitation of A1(OH)3 starts at 3.3 whereas the corresponding figure for Mg(OH)2 is 9.4. Again dissolution of Al(OH)3 precipitates starts at pH of 7.8 and complete dissolution of A1(OH)3 occurs at 10.8 whereas for complete precipitation of Mg(OH)2, pH is to be increased to 12.4. So, it is obvious that there is a complete mismatch concerning precipitation of hydroxides of aluminium and magnesium in relation to pH of the medium and an extremely narrow zone of pH may be fixed for co-precipitation of both the ions, that too in an incomplete way.
This difficulty is completely eliminated by fixing one solid component, precipitating the other over it. This process may further be improved by bringing the solid component, A12O3 in the present case, in suspension and forming the hydroxide of Mg in the form of a gel-like structure in which A12O3 particles will be embedded. Since the particles will be embedded, as the solid is in colloidal suspension, homogeneity in composition throughout the bulk of the material is anticipated. Moreover, volume expansion due to the formation of
magnesium aluminate is anticipated to be compensated by the volume shrinkage accompanying dehydroxylation of gel-structure eliminating the additional process of preforming magnesium aluminate before use and the phenomenon may be utilised to formulate batch composition in such a way that volume of specimens remain unchanged before and after firing.
The following examples are given by way of illustration and should not be construed to limit the scope of the present invention.
Example -1
95.80 gm of A12O3 was mixed with 31.10 ml of MgCl2 solution containing 0.064 g. MgCl2 per ml and 0.05 g poryacrylate was mixed and stirred for 2 hours. In the suspension so produced 45 ml concentrated ammonia solution was added with stirring for 15 minutes. The entire volume of mixture turned into a semi-solid gel-like mass. The entire material was left for 24 hours for ageing. Aged material was filtered followed by washing with hot water. After complete washing, till free from chloride, the material was dried at 200°C for 3 hours.
Dried material was ground to pass through 200 mesh B.S. and was pressed uniaxialry at 250 MPa. Pressed body was fired at 1400°C.
Example - 2
91.01 gm of A12O3 was mixed with 66.57 ml of MgCl2 solution containing 0.064 g. MgCl2 per ml and 0.05 g triporyphosphate was mixed and stirred for 2 hours. In the suspension so produced 45 ml concentrated ammonia solution was added with stirring for
15 minutes. The entire volume of mixture turned into a semi-solid gel-like mass. The entire material was left for 24 hours for ageing. Aged material was filtered followed by washing with hot water. After complete washing, till free from chloride, the material was dried at 200°C for 3 hours.
Dried material was ground to pass through 200 mesh B.S. and was pressed uniaxialry at 250 MPa. Pressed body was fired at 1400°C.
Example - 3
85.82 gm of A12O3 was mixed with 107.23 ml of MgCl2 solution containing 0.064 g. MgCl2 per ml and 0.05 g hexametaphosphate was mixed and stirred for 2 hours. In the suspension so produced 45 ml concentrated ammonia solution was added with stirring for 15 minutes. The entire volume of mixture turned into a semi-solid gel-like mass. The entire material was left for 24 hours for ageing. Aged material was filtered followed by washing with hot water. After complete washing, till free from chloride, the material was dried at 200°C for 3 hours.
Dried material was ground to pass through 200 mesh B.S. and was pressed uniaxialry at 250 MPa. Pressed body was fired at 1400°C.
Example - 4
79.15 gm of A12O3 was mixed with 154.40 ml of MgCl2 solution containing 0.064 g. MgCl2 per ml and 0.05 g polyacrylate was mixed and stirred for 2 hours. In the suspension so produced 45 ml concentrated ammonia solution was added with stirring for 15 minutes. The entire volume of mixture turned into a semi-solid gel-like mass. The
entire material was left for 24 hours for ageing. Aged material was filtered followed by washing with hot water. After complete washing, till free from chloride, the material was dried at 200°C for 3 hours.
Dried material was ground to pass through 200 mesh B.S. and was pressed uniaxially at 250 MPa. Pressed body was fired at 1400°C.
Example - 5
62.79 gm of A12O3 was mixed with 176.60 ml of MgCl2 solution containing 0.064 g. MgCl2 per ml and 0.05 g tripolyphosphate was mixed and stirred for 2 hours. In the suspension so produced 45 ml concentrated ammonia solution was added with stirring for 15 minutes. The entire volume of mixture turned into a semi-solid gel-like mass. The entire material was left for 24 hours for ageing. Aged material was filtered followed by washing with hot water. After complete washing, till free from chloride, the material was dried at 200°C for 3 hours.
Dried material was ground to pass through 200 mesh B.S. and was pressed uniaxially at 250 MPa. Pressed body was fired at 1400°C.
Example - 6
38.75 gm of Al2O3 was mixed with 290.72 ml of MgCl2 solution containing 0.064 g. MgCl2 per ml and 0.05 g hexametaphosphate was mixed and stirred for 2 hours. In the suspension so produced 45 ml concentrated ammonia solution was added with stirring for 15 minutes. The entire volume of mixture turned into a semi-solid gel-like mass. The entire material was left for 24 hours for ageing. Aged material was filtered followed by
washing with hot water. After complete washing, till free from chloride, the material was
dried at 200°C for 3 hours.
Dried material was ground to pass through 200 mesh B.S. and was pressed uniaxially at
250 MPa. Pressed body was fired at 1400°C.
The results obtained by the process of present intention are given in Table -1 by way of
illustration.

(Table Removed)
From the Table above it may be inferred that specimens contain Magnesium Aluminate spinel of different MgO : A12O3 molar ratio without any noticeable dimensional changes. The main advantages of the present invention are :
(1) It's usability to produce Magnesium Aluminate based material of various shapes and
sizes for application as refractory and engineering materials,
(2) Simpler processing technique is sufficient for the production of homogeneous
products,
(3) Temperature of formation may be reduced to 1200-1400°C depending upon
composition,
(4) Sintering of larger shapes without any deleterious dimensional deformities,
(5) Tailoring of composition is possible with more accuracy,
(6) Flexibility of the process to accommodate any composition in the system within the
same technological parameters.

1. A process for making magnesium aluminate spinel useful as refractories and
engineering ceramics in the wide range of Magnesia content chracterised by
preparing aluminum oxide suspension in a solution of magnesium salt with
dispersants such as herein described, adding to the said suspension a soluble
hydroxide such as herein described, maintaining the pH in the range of 9.4 to
12.4 to obtain a gel-like mass, allowing the gel-like mass to age for a period in
the range of 8 to 48 hours, filtering and washing the aged gel-like mass, drying
the gel-like mass at a temperature in the range of 110-200°C, grinding and
pelletizing the dried material, firing the pelletized material at a temperature in
the range of 1200-1400°C, grinding the pellets by known methods.
2. A process as claimed in claim -1 wherein the ratio of alumina to magnesium salts
such that the MgO: AI203 weight ratio in the fired product are in the range of
0.04 to 1.58.
3. A process as claimed in claims 1 & 2 wherein the dispersants used is selected
from tripolyphosphate, hexametaphosphate, polyacrylate.
4. A process as claimed in claims 1-3 wherein'soluble hydroxide used is selected
from soluble hydroxide, dolomite and calcite.
5. A process for making magnesium aluminate spinel substantially as herein
described with reference to the examples.

Documents:

288-del-1999-abstract.pdf

288-del-1999-claims.pdf

288-del-1999-correspondence-others.pdf

288-del-1999-correspondence-po.pdf

288-del-1999-description (complete).pdf

288-del-1999-form-1.pdf

288-del-1999-form-19.pdf

288-del-1999-form-2.pdf

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Patent Number

216807

Indian Patent Application Number

288/DEL/1999

PG Journal Number

13/2008

Publication Date

31-Mar-2008

Grant Date

19-Mar-2008

Date of Filing

19-Feb-1999

Name of Patentee

COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH ''

Applicant Address

RAFI MARG, NEW DELHI-110001, INDIA,

Inventors:

#	Inventor's Name	Inventor's Address
1	SANTANU MANDAL	CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, CALCUTTA 700 032,
2	GUTAM BANERJEE,	CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, CALCUTTA 700 032,
3	SANKAR GHATAK	CENTRAL GLASS & CEEAMIC RESEARCH INSTITUTE, CALCUTTA 700 032,
4	ARUP KUMAR SA,MANTA,	CENTRAL GLASS & CERAMIC RESEARCH INSTITUE CALCUTTA 700 032,

PCT International Classification Number

C04B 35/19

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA