Title of Invention

"A PROCESS FOR MAKING ADVANCED CERAMIC MATERIAL"

Abstract A process for making advance ceramic materials: The invention broadly consists of making alkali glycolato silicates by reaction of silica containing raw materials with alkali/alkaline earth oxides/hydroxides and alcohols/glycols in the temperature range 198° to 250°C for a period of 2 to 48 hours to obtain alkali or alkaline earth alkoxy silicates, the said silicates being dissolved in water and reacted with ammonium salt under continuous stirring followed by repeated washing with water and drying to obtain the silicon precursors, reacting the said precursors with complementary reactants selected from carbon black, sucrose, petroleum pitch, phenolic resin, aluminium containing compounds, nitrogen or ammonia at a temperature ranging between 1300° to 1600°C for a period ranging between 1 to 6 hours to obtain the desired advanced ceramic materials.
Full Text This invention relates to an improved process for the preparation of advanced ceramic materials based on substantially alkali free, amorphous silicon precursors.
This invention also relates to a low temperature process for making substantially alkali free, high surface area, amorphous silicon precursor useful in making advanced ceramic materials such as silicon carbide, mullite, silicon nitride and sialon.
In the prior art, different types of silicon containing precursors are prepared by carbo-thermal reduction of silica to silicon at high temperature (1800 to 2000°C) followed by halogenation and subsequent hydroxylation or reaction with alcohols/glycols (Encyclopaedia of Science and Technology; McGraw-Hill, New York, 1982, 5th edition, 408-10). The alkali free silicon precursors obtained by this method have been used for making silicon carbide (C.W. George, C.R. Kennedy and L.A. Harris, Ceramic Bulletin 63(8) (1984) 1054-61), silicon oxynitride (Clint R. Bickmore and Richard M. Laine, J. Am Ceram. Soc. 79 (11) (1996) 2865-77), ceramic-polymer composite (L. Mascia and A Kioul, J. Mater. Sci. Lett. 13 (1994) 641-3). While this method results in alkali free organo-silane precursors useful for making advanced ceramic materials such as silicon carbide or mullite, it is cumbersome and requires high temperature processing during carbo-thermal preparation of silicon metal, thus making it energy intensive.
Another method of preparing silicon containing precursors in the prior art is by fusion of silica/silica containing raw materials with alkali carbonates, in the temperature range of 980 to 1050°C to obtain water glass followed by its hydrolysis and subsequent precipitation with acids (disclosed in Encyclopaedia of Chemical Technology, Kirk-Othmer (ed.) John Wiley and Sons, 3rd edition, Vol. 20, pp 864-5, 877). The silicon precursors obtained by this method and the method disclosed in the preceding paragraph have been used for making mullite (N.N. Ghosh and P. Pramanik, Bull Mater. Sci. Vol. 20 (2) (1997) 283-6). The method also requires fairly high temperature during the process of fusion and yields precursor with relatively low surface area of 50 to 270 m2/g.
The prior art also discloses the reaction of silica with alkali and alcohol/glycols to obtain hexa- or penta- co-ordinated silicon containing precursors (Richard M. Laine, K.Y. Blohowiak, T.R. Robinson, M.L. Hoppe, Paola Narul, J. Kampf and Jackie Uhm; Nature 353 (1991) 642-4; Pallavi Kansal and Richard M. Laine J. Am. Ceram. Soc. 77(4) (1994) 875-82., P. Kansal and Richard M. Laine, J. Am. Ceram. Soc. 76, 100 (1993) 2571-82). The precursors obtained by this method have been used for making silicate glasses due to presence of high alkali content in them. However, this
been used for making silicate glasses due to presence of high alkali content in them. However, this method yields precursor of silicon with high alkali content (about 10 to 12%) and can thus, be used tor making glasses but not for making materials requiring high temperature processing (e.g., SiC), mullite etc. Another drawback of this method is that the precursor obtained is poor in silicon content (it has only about 14% silicon content).
It is an object of the invention to provide a process for the preparation of substantially alkali free high surface area, amorphous silicon precursors useful in the preparation of advanced ceramic materials which obviates the drawbacks listed above.
The substantially alkali free, high surface area, amorphous silicon precursor obtained by the low temperature process of present invention may also be used for the preparation of ceramic materials such as silicon carbide, mullite, silicon oxynitride and ceramic-polymer composites, adsorbents, catalytic supports and insulating material for micro-electronic packaging.
It is an object of the invention to provide a process for the preparation of advanced ceramic materials from substantially alkali free, high surface area amorphous silicon precursors which obviates the drawbacks stated above.
It is another object of the invention to provide a process which is not energy intensive.
It is another object of the invention to provide a process for the preparation of amorphous silicon precursors useful in the preparation of advanced ceramic materials which are substantially alkali free and of high surface area.
It is another object of the invention to provide a low temperature process for the preparation of the substantially alkali free high surface area amorphous silicon precursors.
It is yet another object of the present invention to develop a low temperature process, operating at temperatures of about 200 to 250°C, for making substantially alkali free, high surface area, amorphous silicon precursor and its application in making advanced ceramic materials such as silicon carbide and mullite.
Figure 1 is an X-ray pattern of precursor recorded using X-ray diffraction method. The diffractogram obtained shows characteristics typical of amorphous materials.
Figure 2 is an X-ray diffraction pattern of X-ray powder diffraction analysis of the prepared silicon carbide. The analysis confirmed it to be p-silicon carbide as evidenced from the X-ray diffraction pattern.
power. The analysis confirmed the presence of mullite as evidenced from the X-ray diffraction pattern.
Accordingly the present invention provides, a process for making advance ceramic materials based on substantially alkali free, high surface area, amorphous silicon precursors, said process comprising (a) providing alkali or alkaline earth alkoxy silicates by reacting conventional silica containing raw materials with alkali/alkaline earth oxides/hydroxides or mixtures thereof and glycols/alcohols at a temperature ranging between 198° to 250°C for a period ranging between 2 to 48 hours (b) dissolving the silicates obtained in step (a) in distilled water and reacting with an ammonium salt selected from the group consisting of ammonium nitrate, ammonium acetate, ammonium carbonate, tetra alkyl ammonium salts under continuous stirring followed by repeated washing with water and drying to obtain the silicon precursors, (c) reacting the said silicon precursor obtained from step (b) with a conventional complementary reactant such as herein described , at a temperature ranging between 1300° to 1600°C for a period ranging between 1 to 6 hours to obtain the desired advanced ceramic materials.
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In an embodiment of the invention, the silicon containing raw materials are selected from one or more of natural minerals/materials or synthetic compounds such as rice hulls or husk, fumed or amorphous silica, fly ash, sand, quartz and the like.
In another embodiment of the present invention the amorphous silicon precursor prepared has silicon content: 75 to 85%, sodium content: 0.001 to 0.01%, potassium: 0.04 to 0.06%, calcium: 0.05 to 0.07% and magnesium: 0.01 to 0.02% and loss on ignition : 20 to 25%.
In another embodiment of the present invention, the amorphous silicon precursor prepared possesses high surface area of 425 to 475 m2/g.
In yet another embodiment of the present invention, the prepared amorphous silicon precursor is used to make advanced ceramic materials such as silicon carbide, mullite, silicon nitride, sialon and the like.
In another embodiment of the present invention, the conventional complementary reactant is selected from carbon black or any other carbon source/aluminium containing compounds/nitrogen or ammonia.
In yet another embodiment of the invention, the ammonium/tetra alkyl ammonium ion released by ammonium nitrate /ammonium acetate / tetra alkyl ammonium salts reacts with alkali or alkaline earth alkoxy silicates to substitute alkali/alkaline earth ion and the gradual addition of dilute
earth alkoxy silicates to substitute alkali/alkaline earth ions and the gradual addition of dilute solution of ammonium nitrate/ammonium acetate/tetra alkyl ammonium salts, which are weak electrolytes, causes a slow and gradual change in the pH in the vicinity of alkali/alkaline earth alkoxy silicate molecules leading to formation of highly dispersed silicon precursor gel, having large surface area. The alkali/alkaline earth metal ions released by above substitution reaction are present in solution and are removed by filtration and repeated washing with distilled water.
In another embodiment of the invention, the said silicon precursor is dispersed in ammonium hydroxide solution and homogeneously mixed with carbon slurry to obtain silicon carbide.
In a further embodiment of the invention, the said silicon precursor obtained is dispersed in ammonium hydroxide solution and homogeneously mixed with aluminium compounds to obtain mullite.
In yet another embodiment of the invention, the said silicon precursor is heated in nitrogen or ammonia atmosphere to obtain silicon nitride and sialon.
To this end, the invention broadly consists of making alkali glycolato silicates by reaction of silica containing raw materials (5 to 80%) with alkali/alkaline earth oxides/hydroxides (8 to 70%) and alcohols/glycols (10 to 80%) in the temperature range 198 to 250°C (depending on the molecular weight of the glycol selected) for a period of 2 to 48 hours to obtain alkali or alkaline earth alkoxy silicates, the said silicates being dissolved in water and reacted with ammonium nitrate under continuous stirring followed by repeated washing with water and drying to obtain the silicon precursors, reacting the said precursors with complementary reactants selected from carbon black, sucrose, petroleum pitch, phenolic resin or any other carbon source, aluminium containing compounds, nitrogen or ammonia at a temperature ranging between 1300 to 1600 C for a period ranging between 1 to 6 hours to obtain the desired advanced ceramic materials.
The silica containing raw materials consist of one or more of natural minerals/materials or synthetic compounds such as rice hulls or husk, fumed or amorphous silica, fly ash, sand, quartz etc.
The ammonium/tetra alkyl ammonium ion released by ammonium nitrate/ammonium acetate/tetra alkyl ammonium salts reacts with alkali or alkaline earth alkoxy silicates to substitute alkali/alkaline earth ions and the gradual addition of dilute solution of ammonium nitrate/ammonium acetate/tetra alkyl ammonium salts, which are weak electrolytes, causes a slow and gradual change in the pH in the vicinity of alkali/alkaline earth alkoxy silicate molecules leading to formation of highly dispersed silicon precursor gel, having large surface area. The alkali/alkaline earth metal ions released by above substitution reaction are present in solution and are removed by filtration and
repeated washing with distilled water
The silicon precursor obtained by the process of present invention can be co-precipitated with similar precursors of other valve metal elements and thus enabling preparation of composite precursors useful for making ceramic- ceramic composites. The silicon precursor can also be used for making ceramic-polymer composites.
When the silicon precursor obtained is dispersed in ammonium hydroxide solution and then homogeneously mixed with carbon slurry, silicon carbide is obtained. Similarly, mullite can be obtained by homogeneously mixing the silicon precursor dissolved in ammonium hydroxide solution with aluminium compounds. To obtain silicon nitride and sialon, the silicon precursor is heated in nitrogen or ammonia atmosphere.
The high surface area, amorphous silicon precursor with low alkali/alkaline cation content was characterised a) for its elemental silicon content using standard wet chemical analysis method and ion chromatography for alkali/alkaline earth metal contents (b) surface area measurement using B.E.T. method, (c) absence of crystailinity by X-ray diffraction technique.
The silicon precursor prepared using the process of present invention is found to contain 35 to 40% silicon and is substantially alkali free.
The following examples illustrate the method of making alkali free, high surface area, amorphous silicon precursor and its application in making advanced ceramic materials such as silicon carbide and mullite and should not be construed to limit the scope of the present invention.
EXAMPLE -1
15 gm of highly dispersible silicon di-oxide, 10 gm of sodium hydroxide and 250 ml of ethylene glycol, all of extra pure grade and Merck make were reacted under nitrogen atmosphere at 200°C in a round bottom flask for a period of 3 hours.
After cooling under nitrogen atmosphere the product, namely sodium glycolato silicate was dissolved in double distilled water and reacted with 100 ml of 25% ammonium nitrate solution under continuous stirring using magnetic stirrer. This precursor was made substantially free from alkali ( The alkali free, high surface area amorphous silicon precursor and the silicon carbide
prepared therefrom were characterised with following results: Elemental Analysis of the silicon precursor:
Elemental form. Oxide form
1. Silicon content - 37.70%, 80.75%
2. Sodium content - 0.01% 0.0138%
3. Potassium Content - 0.05% 0.0602%
4. Calcium - 0.05% 0.07%
5. Magnesium - 0.01% 0.0165%
37.87% 80.86%
Wt. loss due to removal of structural water 20.85 %
between 110-950° C
Total Analysis 101.71
Surface area measurement of the silicon precursor:
For surface area measurement 0.7977 gms of the vacuum dried precursor was taken in a glass bulb and evacuated under heating at 200°C to remove adsorbed air, where after it was equilibrated with nitrogen and surface area measurement was performed. The surface area of the precursor was found to be 456 M2 /gm. Test for Crystallinity of silicon precursor:
The X-ray pattern of precursor was recorded using X-ray Diffraction method and the
• Diffractogram obtained shows the characteristics typical of amorphous materials as shown in Fig. 1.
Characterisation of Silicon Carbide: The X-Ray powder diffraction analysis of the prepared silicon carbide confirmed it to be p-silicon carbide as evidenced from the X-ray Diffraction pattern shown in Fig. 2.
EXAMPLE - 2
Rice hulls, obtained from local sources was thoroughly washed with distilled water, dried in air oven and decarbonised by heating in an electric muffle furnace at 700° C. The rice hull ash so obtained was treated with hydrochloric acid to remove impurities such as iron. The purified rice hull ash was thoroughly washed with water and dried in an air oven. 15 gm of the rice hull ash was reacted with 10 gm of NaOH and 300 ml of ethylene glycol at 200° C for duration of 4 hours under nitrogen atmosphere. After cooling under nitrogen atmosphere, the product - sodium glycolato silicate was dissolved in water. The solution so obtained was treated with 100 ml of 30% ammonium nitrate solution under continuous stirring using magnetic stirrer to obtain silicon containing amorphous precursor. This precursor was made alkali free by repeated washing with distilled water and dried in
an air oven at 110 °C. For making mullite, 4 765 gm of the precursor was slurred in 500 ml water of pH 9.5 (adjusted by the addition of ammonium hydroxide). To this solution, a solution of 26.43 gm of A1(NO3)3.9 H:0 dissolved in 200 ml water was added drop by drop under continuous stirring. After boiling for 5 minutes, the contents were cooled and filtered. The solid mass was heat treated in an electrical muffle furnace at 1300° C for six hours to obtain mullite powder.
The alkali free, high surface area amorphous silicon precursor and the mullite prepared therefrom were characterised with following results: Elemental Analysis of silicon precursor:
Elemental Form Oxide Form
1. Silicon content - 36.80% 78.80 %
2. Sodium content - 0.01% 0.013 %
3. Potassium Content - 0.04% 0.048 %
+ 4. Calcium - 0.05% 0.070 %
5. Magnesium - 0.01% 0.016 %
78.947 %
Weight loss due to loss of structural water 21.063 %
in the temperature range 110 - 950 °C
100.01 % Surface area measurement of the silicon precursor:
For surface area measurement 0.8200 gm of the vacuum dried precursor was taken in a glass bulb and evacuated under heating at 200°C to remove adsorbed air, where after it was equilibrated with nitrogen and surface area measurement was performed. The surface area of the precursor was found to be 430 m2 /gm. Characterisation of Mullite
The X-ray powder diffraction analysis of the prepared powder confirmed the presence of mullite as evidenced from the X-ray diffraction pattern shown in Fig. 3.
The following are the main advantages of the present invention.
1. The process of present invention for making alkali free, high surface area, amorphous silicon
precursor is carried out at a significantly low temperature in the range of 198 to 250 C.
2. The silicon precursor prepared using the process of present invention is found to contain 35 to
40% silicon.
3. The silicon precursor prepared by the process of present invention possesses a high surface area
(between 425 to 475 m2 /gm).
4. The silicon precursor prepared by the process of the present invention is substantially free from
alkali.
5 The silicon precursor obtained by the process of present invention can he co-precipitated with
similar precursors of other valve metal elements and thus enabling preparation of composite
precursors useful for making ceramic- ceramic composites.
6 The silicon precursor obtained by the process of present invention can be dispersed in ammonium
hydroxide solution and thus enables the homogeneous mixing with carbon slurry for making silicon
carbide.
7. The silicon precursor obtained by the process of present invention can be dispersed in ammonium
hydroxide solution and thus enables the homogeneous mixing with compounds of aluminium for
making mullite.
8. The silicon precursor obtained by the process of present invention can be heated in
nitrogen/ammonia atmosphere to obtain silicon nitride and sialon.
9. The silicon precursor obtained by the process of present invention can be used for making
ceramic-polymer composites.






We Claim:
1. A process for making advance ceramic materials based on
substantially alkali free, high surface area, amorphous silicon
precursors, said process comprising (a) providing alkali or
alkaline earth alkoxy silicates by reacting conventional silica
containing raw materials with alkali/alkaline earth
oxides/hydroxides or mixtures thereof and glycols/alcohols at a
temperature ranging between 198 to 250°C for a period ranging
between 2 to 48 hours (b) dissolving the silicates obtained in
step (a) in distilled water and reacting with an ammonium salt
selected from the group consisting of ammonium nitrate,
ammonium acetate, ammonium carbonate, tetra alkyl
ammonium salts under continuous stirring followed by repeated
washing with water and drying to obtain the silicon precursors,
(c) reacting the said silicon precursor obtained from step (b)
with a conventional complementary reactant such as herein
described, at a temperature ranging between 1300° to 1600°C
for a period ranging between 1 to 6 hours to obtain the desired
advanced ceramic materials.
2. A process as claimed in claim 1 wherein the advanced ceramic
material as prepared is selected from silicon carbide, mullite,
silicon nitride and sialon.
3. A process as claimed in 1 to 2, wherein said conventional silica
containing raw materials used are selected from the group
consisting of one or more of natural minerals/materials or
synthetic compounds selected from quartz, sand, fly ash, rice
hulls or husk or any other agro-waste, fumed or amorphous
silica.
4. A process as claimed in claims 1-3, wherein said alkali or
alkaline earth silicate is a alkali or alkaline earth glycolato
silicate or alkoxy silicate.
5. A process as claimed in claims 1-5, wherein the conventional
complementary reactant used is selected from carbon black ,
aluminium containing compounds, nitrogen , ammonia.
6. A process as claimed in claims 1 - 6 , wherein the
alkali/alkaline earth metal ions released by the substitution
reaction between said ammonium salt and the said alkali or
alkaline earth alkoxy silicates are removed by conventional
filtration and repeated washing with distilled water.
7. A process as claimed in claims 1-7, wherein the said silicon
precursor is dispersed in ammonium hydroxide solution and
homogeneously mixed with carbon slurry to obtain silicon
carbide.
8. A process as claimed in claims 1-8, wherein the said silicon
precursor obtained is dispersed in ammonium hydroxide
solution and homogeneously mixed with aluminium compounds to obtain mullite.
9. A process as claimed in claims 1-9, wherein the said silicon
precursor is heated in nitrogen or ammonia atmosphere to
obtain silicon nitride and sialon.
10. A process for the preparation of advanced ceramic materials
based on substantially alkali free, high surface area, amorphous
silicon precursors, substantially as described herein before and
with reference to the preceding examples.


Documents:

1247-del-1999-abstract.pdf

1247-del-1999-claims.pdf

1247-del-1999-correspondence-others.pdf

1247-del-1999-correspondence-po.pdf

1247-del-1999-description (complete).pdf

1247-del-1999-drawings.pdf

1247-del-1999-form-1.pdf

1247-del-1999-form-19.pdf

1247-del-1999-form-2.pdf

1247-del-1999-form-3.pdf

1247-del-1999-form-5.pdf

1247-del-1999-petition-138.pdf


Patent Number 242316
Indian Patent Application Number 1247/DEL/1999
PG Journal Number 35/2010
Publication Date 27-Aug-2010
Grant Date 23-Aug-2010
Date of Filing 16-Sep-1999
Name of Patentee COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH
Applicant Address RAFI MARG, NEW DELHI-110001
Inventors:
# Inventor's Name Inventor's Address
1 SUDHIR SITARAM AMRITPHALE INDIAN NATIONAL, REGIANOL RESEARCH LABORATORY, BHOPAL
2 NAVIN CHANDRA INDIAN NATIONAL, REGIANOL RESEARCH LABORATORY, BHOPAL
3 EDWIN KROKE, GERMAN NATIONAL, TECHNISCHE UNIVERSITY DARM STAFF
4 RALF RIEDEL GERMAN NATIONAL, TECHNISCHE UNIVERSITY DARM STAFF
PCT International Classification Number C04B 33/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA