Title of Invention	A SYNERGISTIC COMPOSITION USEFUL FOR MAKING IN-SITU SILICON CARBIDE IN THE FORM OF PARTICULATE, WHISKERS AND FIBRES IN SILICON CARBIDE-CARBON MATRIX COMPOSITE.
Abstract	A composition useful for making in-situ silicon carbide in the form of particulate, whiskers and fibres in Silicon Carbide-carbon matrix composite and a process for making in-situ Silicon Carbide: The present invention provides a composition useful for making in-situ Silicon Carbide in the form of particulate, whiskers and fibres in silicon Carbide-carbon matrix composite and a process for making in-situ Silicon Carbide in the form of particulate, whiskers and fibres in Silicon Carbide-carbon matrix composite. The process of the present invention particularly relates to the use of wide variety of natural fibres such as jute, sunhemp, sisal or any other natural fibres having cellulosic or hemicellusosic constituents at its backbone as raw materials for providing useful carbon for the formation of silicon carbide in the form of particulate, whiskers and fibres in the matrix of Silicon Carbide-carbon.

Title of Invention

A SYNERGISTIC COMPOSITION USEFUL FOR MAKING IN-SITU SILICON CARBIDE IN THE FORM OF PARTICULATE, WHISKERS AND FIBRES IN SILICON CARBIDE-CARBON MATRIX COMPOSITE.

Abstract

A composition useful for making in-situ silicon carbide in the form of particulate, whiskers and fibres in Silicon Carbide-carbon matrix composite and a process for making in-situ Silicon Carbide: The present invention provides a composition useful for making in-situ Silicon Carbide in the form of particulate, whiskers and fibres in silicon Carbide-carbon matrix composite and a process for making in-situ Silicon Carbide in the form of particulate, whiskers and fibres in Silicon Carbide-carbon matrix composite. The process of the present invention particularly relates to the use of wide variety of natural fibres such as jute, sunhemp, sisal or any other natural fibres having cellulosic or hemicellusosic constituents at its backbone as raw materials for providing useful carbon for the formation of silicon carbide in the form of particulate, whiskers and fibres in the matrix of Silicon Carbide-carbon.

Full Text	The present invention relates to a composition useful for making in-situ Silicon Carbide in the form of particulate, whiskers and fibres in Silicon Carbide-carbon matrix composite and a process for making in-situ Silicon Carbide in the form of particulate, whiskers and fibres in Silicon Carbide-carbon matrix composite. The process of the present invention particularly relates to the use of wide variety of natural fibres such as jute, sunhemp, sisal or any other natural fibres having cellulosic or hemicellulosic constituents at its backbone as raw materials for providing useful carbon for the formation of silicon carbide in the form of particulate, whiskers and fibres in the matrix of Silicon Carbide-carbon. The main usage of the silicon carbide in the form of particulate, whiskers and fibres in Silicon Carbide-carbon matrix composites is in the field of engineering materials in any shape as may be deemed fit. The present day method of making Silicon Carbide particulate, whiskers and fibres reinforced composite in Silicon Carbide-carbon matrix composites essentially consists of seeding graphite substrate with metal droplets such as Fe, Co, Cr and Mn as catalyst for the whisker formation. Methane and silicon monoxide supply C and Si respectively - the references for which may be made to "Synthesis and Characterisation of VLS - Derived SiC whiskers" of P.D. Shalek in Conf. Whisker and fibre Toughened Ceramics, Oak Ridge T N (1988) and to "Review of VLS SiC Whisker Growth Technology" by W.E.Holler and JJ.Kim in Ceram. Engg. Sci. Proc., vol. 12, pp 979-991 (1991) or making fibre by melt extrusion and suspension spinning of compositions of ultrafine SiC powders and organic additives such as polyvinyl butyral respectively followed by sintering or making fibre by melt spinning polymers which can be rapidly cured in the solid state and polymerised to ceramic fibres with compositions which are stoichiometric silicon carbide or which are carbon-rich or silicon-rich silicon carbide -the reference for which may be made to "Silicon Carbide: from Acheson's Invention to New Industrial Products" by W. D. G. Boecker in cfi/Ber. DKG 74 (5), 1997. The fibres and whiskers produced by the above processes are mixed mechanically with the matrix materials and are fabricated into different sizes and shapes followed by heat treatment at different temperatures for consolidations - the references for which may be made to "Pressureless Sintering of Al2O3/SiC Materials: Effect of the Reducing Atmosphere" by G. Urretavizcaya, J.M.Porto Lopez & A.L. Cavalieri, J. Eu. Ceram. Soc., 17 1555-63(1997). In a process inorganic polymers that are ceramic precursors are spun into fibres by melt-spinning or solvent-assisted dry spinning, stabilising the fibres to prevent remelting followed by thermally decomposing into fibres - the references for which may be made to German P.2,6181 JO; French P.2,308,590; Japanese P.51 130325, 51 139929, 51 147623 (1976). In slurry spinning a dispersion of crystalline ceramic particulate in a carrier fluid is formed into a fibre, converted to fibre by thermal conversion by several heating stages that may include passing the fibre through a flame. The process generate particulate of not more than 1 ^m to control shrinkage - the references for which may be made to E.I. du Pont de Nemovrs & Co.; B.P. 1,264,973(1972); USP 3,808,015(1974); USP 4,753,904 (1988); Mitsui Mining Co. Ltd.; Japanese P 217182 (1986)p; European P. 0,260,868-A2 (1988); USP 4,812,271 (1989). The overall process has several drawbacks that may be listed below: 1. Number of steps involved in the overall process is higher. 2. Handling of whiskers and short fibres require special arrangements. 3. It is difficult to disperse whiskers and short fibres uniformly in the matrix. 4. Silicon Carbide whiskers particularly of aspect ratio less than 10 cause health hazard. The main object of the present invention is to provide a composition useful for making in-situ silicon carbide in the form of particulate, whiskers and fibres in Silicon Carbide - carbon matrix composites. Another object of the present invention is to provide a process for making in-situ silicon carbide in the form of particulate, whiskers and fibres in Silicon Carbide-carbon matrix composites which obviates the drawbacks as detailed above. Yet another object of the present invention is to utilize natural fibres of plant source. Still another object of the present invention is to reduce the total number of unit processes in the overall operation. Yet another object of the present invention is to form whiskers and fibres in-situ during processing to eliminate totally the possibility of health hazard. Accordingly the present invention provides a synergistic composition useful for making in-situ silicon carbide in the form of particulate, whiskers and fibres in Silicon Carbide-carbon matrix composite which comprises: Natural fibre 1.6 - 6.4 wt% Tetraethyl orthosilicate 28.6 - 46.8 wt.% Phenolic resin 38 - 46 wt% Curing agent 4.2 - 6.6 wt% Silicon carbide 9.4 - 12.4 wt.% In an embodiment of the present invention the fibres used are natural fibres such as jute, sunhemp, sisal or any other natural fibres having cellulosic or hemicellulosic constituents at its backbone. In another embodiment of the present invention the molecular weight of phenolic resin used may be in the range of 450-700. In still another embodiment of the present invention curing agent used may be such as hexamine, para toluene sulphonic acid, para formaldehyde, resorcinol , di-isocyanate prepolymer. In yet another embodiment of the present invention the organic solvent used may be such as methanol, toluene, benzene. There is no chemical reaction in the mixture as such and the composition of the present invention is not a mere admixture but a synergistic mixture having properties which are different and distinct from the mere aggregation of the properties of the individual ingredients. Accordingly the present invention provides a method of making in-situ silicon carbide in the form of particulate, whiskers and fibres in Silicon Carbide-carbon matrix composites whch comprises dissolving 38 - 46 wt % of phenolic resin in organic solvent to obtain a phenolic resin solution, adding 4.2-6.6 wt % of curing agent and 9.4-12.4 wt % of silicon carbide powder to obtain a resin mix, impregnating 1.6 -6.4 wt % of natural fibre dried at 60°-70°C for a period in the range of 1-5 hrs. by known methods to obtain a dough in the form of a composite plate/sheet, drying the said composite plate/sheet at a temperature in the range of 70°- 90° C for a period in the range of 1-2 hrs., heat treating the dried composite plate/sheet at a temperature in the range of 150° -200°C for a period in the range of 1 - 2.5 hrs., impregnating the resultant composite plate/sheet with 28.6-46.8 wt % of tetraethyl orthosilicate in vacuum, subjecting the impregnated composite plate/sheet to heat treatment in argon initially at a heating rate in the range of 2° - 5°C per minute upto a temperature in the range of 200° - 400°C followed by further heating at the rate of 10°- 15°C per minute upto a temperature in the range of 1400° - 1850°C, maintaining the final temperature for a period in the range of 0.5-2 hrs. In an embodiment of the present invention the natural fibres may be introduced in the body in desired alignments such as unidirectional, multidirectional, woven, randomly oriented structure. In another embodiment of the present invention the matrix materials may be of different particle dimension from nano to micron size. In yet another embodiment of the present invention drying of the natural fibre may be effected at a temperature in the range of 60°-70°C for a period in the range of 1 - 5 hrs. In still another embodiment of the present invention impregnation with tetraethylorthosilicate may be carried out in vacuum and repeating if required. In yet another embodiment of the present invention the heat treatment in the absence of air may be done in an inert atmosphere or in vacuum. The details of the present invention are given below: a) 38 - 46 wt % of phenolic resin is dissolved in organic solvent. b) 4.2 - 6.6 wt % of curing agent and 9.4 - 12.4 wt % of Silicon carbide are mixed with the solution prepared in step (a). c) Natural fibre is dried at 60° - 70°C for 1 - 5 hrs. d) 1.6 - 6.4 wt % of dried natural fibre is impregnated with mixture prepared in step (b) to obtain a composite plate/sheet. e) The composite plate/sheet obtained in step (d) is dried at 70° - 90°C for 1- 2 hrs. f) The dried composite plate/sheet is heat treated at 150°-200°C for 1 - 2.5 hrs. g) The dried composite plate/sheet is impregnated with 28.6 - 46.8 wt % of tetraethyl orthosilicate in vacuum. h) The impregnated plate/sheet is initially heat treated in argon at the rate of 2° -5°C/min. upto 200°-400°C followed by further heating at the rate of 10° - 15°C per min. upto 1400°-1850°C maintaining the final temperature for 0.5-2 hrs. The process of the present invention can be used to produce in-situ silicon carbide in the form of particulate, whiskers and fibres in Silicon Carbide-carbon matrix composite of various shapes and sizes required for application as engineering components. Natural fibres of plant origin contain all the ingredients of forming silicon carbide if sufficient amount of silicon is provided. Organo silicon compound such as tetraethyl orthosilicate gives active silica on pyrolysis. This active silica in turn reacts with carbon-formed from cellulosic materials like fibres of plant origin. Silicon carbide thus formed are in molecular dimension and with proper catalyst and seeding crystals, unidirectional grain growth occurs to form long fibres of small diameters or whiskers of different aspect ratios. Isolated silicon carbide grains may grow in the three dimensions resulting into particulate formation. If these complex set of network structure is allowed to grow in Silicon Carbide-carbon matrix - the resulting microstructure consists of randomly orientated fibres and whiskers in a homogeneous matrix leading to enhanced fracture toughness imparting some machinability in otherwise non-machinable material. The following examples are given way of illustration of the present invention and should not be construed to limit the scope of the present invention. Example-1 38 gms.of phenolic resin of molecular weight 525 is dissolved in 95 ml. of mathanol. 4.2 gms. of hexamine is added to it and stirred. 9.4 gms. of silicon carbide powder is then blended in this solution. 1.6 gms. Jute fibre is dried at 60°C for 5 hrs. and is mixed with the above mixture and formed into a composite plate. The composite plate is dried at a temperature of 80°C for 1 hr. followed by curing at a temperature of 160°C for 2 hrs. The plate is then impregnated with 46.8 ml. of tetraethyl orthosilicate under vacuum. The vacuum impregnation step is repeated for 5 cycles. The material so obtained is heat treated in argon at the rate of 2°C per min. upto 400°C followed by heating in argon at 1400°C at the rate of 10°C per min. for 1 hr. Example - 2 39 gms. of phenolic resin of molecular weight 475 is dissolved in 97 ml. of toluene. 4.3 gms. of hexamine is added to it and stirred. 9.6 gms. of silicon carbide powder is then blended in this solution. 2 gms. Jute fibre is dried at 62°C for 4 hrs. and is mixed with the above mixture and formed into a dough. This dough is then pressed into a composite sheet. This composite sheet is dried at a temperature of 75°C for 2 hrs. followed by curing at a temperature of 170°C for 2 hrs. The sheet is then impregnated with 45.1 ml. tetraethyl orthosilicate under vacuum. The vacuum impregnation step is repeated for 5 cycles. The material so obtained is heat treated in argon at the rate of 3°C per min. upto 400°C followed by heating in argon at 1500°C at the rate of 12°C per min. for 1.5 hrs. Example - 3 40 gms. of phenolic resin of molecular weight 550 is dissolved in 100 ml. of methanol. 4.3 gms. of hexamine is added to it and stirred. 9.8. gms. of silicon carbide powder is then blended in this solution. 2.5 gms. Jute fibre is dried at 62°C for 4 hrs. and is mixed with the above mixture and formed into a dough. This dough is then pressed into a composite sheet. This composite sheet is dried at a temperature of 75°C for 2 hrs. followed by curing at a temperature of 170°C for 2 hrs. The sheet is then impregnated with 43.4 ml. tetraethyl orthosilicate under vacuum. The vacuum impregnation step is repeated for 5 cycles. The material so obtained is heat treated in argon at the rate of 3°C per min. upto 400°C followed by heating in argon at 1600°C at the rate of 12°C per min. for 1.5 hrs. Example - 4 41 gins, of phenolic resin of molecular weight 600 is dissolved in 102 ml. of benzene. 4.5 gms. of hexamine is added to it and stirred. 10 gms. of silicon carbide powder is then blended in this solution. 3 gms. Jute fibre is dried at 62°C for 4 hrs. and is mixed with the above mixture and formed into a dough. This dough is then pressed into a composite sheet. This composite sheet is dried at a temperature of 75°C for 2 hrs. followed by curing at a temperature of 170°C for 2 hrs. The sheet is then impregnated with 41.5 ml. tetraethyl orthosilicate under vacuum. The vacuum impregnation step is repeated for 5 cycles. The material so obtained is heat treated in argon at the rate of 3°C per min. upto 400°C followed by heating in argon at 1650°C at the rate of 13°C per min. for 1.5 hrs. Example - 5 42 gms. of phenolic resin of molecular weight 675 is dissolved in 105 ml. of toluene. 5 gms. of hexamine is added to it and stirred. 11 gms. of silicon carbide powder is then blended in this solution. 3.5 gms. Jute fibre is dried at 62°C for 4 hrs. and is mixed with the above mixture and formed into a dough. This dough is then pressed into a composite sheet. This composite sheet is dried at a temperature of 75°C for 2 hrs. followed by curing at a temperature of 170°C for 2 hrs. The sheet is then impregnated with 38.5 ml. tetraethyl orthosilicate under vacuum. The vacuum impregnation step is repeated for 5 cycles. The material so obtained is heat treated in argon at the rate of 4°C per min. upto 400°C followed by heating in argon at 1700°C at the rate of 13°C per min. for 1.5 hrs. Example - 6 43 gms. of phenolic resin of molecular weight 650 is dissolved in 107 ml. of methanol. 5 gms. of hexamine is added to it and stirred. 11.5 gms. of silicon carbide powder is then blended in this solution. 4 gms. Jute fibre is dried at 62°C for 4 hrs. and is mixed with the above mixture and formed into a dough. This dough is then pressed into a composite sheet. This composite sheet is dried at a temperature of 75°C for 2 hrs. followed by curing at a temperature of 170°C for 2 hrs. The sheet is then impregnated with 36.5 ml. tetraethyl orthosilicate under vacuum. The vacuum impregnation step is repeated for 5 cycles. The material so obtained is heat treated in argon at the rate of 4°C per min. upto 400°C followed by heating in argon at 1750°C at the rate of 14°C per min. for 1.5 hrs. Example - 7 44 gms. of phenolic resin of molecular weight 700 is dissolved in 110 ml. of toluene. 5 gms. of hexamine is added to it and stirred. 12 gms. of silicon carbide powder is then blended in this solution. 4.5 gms. Jute fibre is dried at 62°C for 4 hrs. and is mixed with the above mixture and formed into a dough. This dough is then pressed into a composite sheet. This composite sheet is dried at a temperature of 75°C for 2 hrs. followed by curing at a temperature of 170°C for 2 hrs. The sheet is then impregnated with 34.5 ml. tetraethyl orthosilicate under vacuum. The vacuum impregnation step is repeated for 5 cycles. The material so obtained is heat treated in argon at the rate of 4°C per min. upto 400°C followed by heating in argon at 1800°C at the rate of 14°C per min. for 1.5 hrs. Example - 8 46 gms. of phenolic resin of molecular weight 450 is dissolved in 115 ml. of benzene. 6.6 gms. of hexamine is added to it and stirred. 12.4 gms. of silicon carbide powder is then blended in this solution. 6.4 gms. Jute fibre is dried at 62°C for 4 hrs. and is mixed with the above mixture and formed into a dough. This dough is then pressed into a composite plate. This composite plate is dried at a temperature of 75°C for 2 hrs. followed by curing at a temperature of 170°C for 2 hrs. The plate is then impregnated with 28.6 ml. tetraethyl orthosilicate under vacuum. The vacuum impregnation step is repeated for 5 cycles. The material so obtained is heat treated in argon at the rate of 3°C per min. upto 400°C followed by heating in argon at 1850°C at the rate of 15°C per min. for 2 hrs. The main advantages of the present invention are : 1. Processing steps are reduced to a large extent. 2. Natural fibres of plant origin are used that replaces hazardous synthetic raw materials 3. The constituents like silicon carbide whiskers and short fibres are formed in situ during the processing of the composite thereby eliminating the need for handling these components which are potential health hazard. 4. Conventional composite fabricating techniques can be used thereby allowing easy formation of material with different microstructure and properties. We Claim: 1. A synergistic composition useful for making in-situ silicon carbide in the form of particulate, whiskers and fibres in Silicon Carbide- carbon matrix composite which comprises: Natural fibre 1.6 - 6.4 wt% Tetraethyl orthosilicate 28.6 - 46.8 wt.% Phenolic resin 38 - 46 wt% Curing agent 4.2 - 6.6 wt% Silicon carbide 9.4 - 12.4 wt.% 2. A synergistic composition as claimed in claim 1 wherein the fibres used are natural fibres such as jute, sisal, sunhemp and any other natural fibre having cellulosic or hemicellulosic constituent at its backbone. 3. A synergistic composition as claimed in claims 1 & 2 wherein the phenolic resin used is selected from phenolic resin having molecular weight in the range of 450 - 700. 4. A synergistic composition as claimed in claims 1-3 wherein the curing agents used are such as hexamine, para toluene sulphonic acid, paraformaldehyde, resorcinol and di-isocyanate prepolymer. 5. A synergistic composition as claimed in claims 1-4 wherein the organic solvents used are such as methanol, toluene and benzene. 6. A synergistic composition useful for making in-situ silicon carbide in the form of particulate, whiskers and fibres in Silicon Carbide-carbon matrix composite substantially as herein described with reference to the examples.

Full Text

The present invention relates to a composition useful for making in-situ Silicon Carbide in the form of particulate, whiskers and fibres in Silicon Carbide-carbon matrix composite and a process for making in-situ Silicon Carbide in the form of particulate, whiskers and fibres in Silicon Carbide-carbon matrix composite. The process of the present invention particularly relates to the use of wide variety of natural fibres such as jute, sunhemp, sisal or any other natural fibres having cellulosic or hemicellulosic constituents at its backbone as raw materials for providing useful carbon for the formation of silicon carbide in the form of particulate, whiskers and fibres in the matrix of Silicon Carbide-carbon. The main usage of the silicon carbide in the form of particulate, whiskers and fibres in Silicon Carbide-carbon matrix composites is in the field of engineering materials in any shape as may be deemed fit.
The present day method of making Silicon Carbide particulate, whiskers and fibres reinforced composite in Silicon Carbide-carbon matrix composites essentially consists of seeding graphite substrate with metal droplets such as Fe, Co, Cr and Mn as catalyst for the whisker formation. Methane and silicon monoxide supply C and Si respectively - the references for which may be made to "Synthesis and Characterisation of VLS - Derived SiC whiskers" of P.D. Shalek in Conf. Whisker and fibre Toughened Ceramics, Oak Ridge T N (1988) and to "Review of VLS SiC Whisker Growth Technology" by W.E.Holler and JJ.Kim in Ceram. Engg. Sci. Proc., vol. 12, pp 979-991 (1991) or making fibre by melt extrusion and suspension spinning of compositions of ultrafine SiC powders and organic additives such as polyvinyl butyral respectively followed by sintering or making fibre by melt spinning polymers which can be rapidly cured in the solid

state and polymerised to ceramic fibres with compositions which are stoichiometric silicon carbide or which are carbon-rich or silicon-rich silicon carbide -the reference for which may be made to "Silicon Carbide: from Acheson's Invention to New Industrial Products" by W. D. G. Boecker in cfi/Ber. DKG 74 (5), 1997. The fibres and whiskers produced by the above processes are mixed mechanically with the matrix materials and are fabricated into different sizes and shapes followed by heat treatment at different temperatures for consolidations - the references for which may be made to "Pressureless Sintering of Al2O3/SiC Materials: Effect of the Reducing Atmosphere" by G. Urretavizcaya, J.M.Porto Lopez & A.L. Cavalieri, J. Eu. Ceram. Soc., 17 1555-63(1997). In a process inorganic polymers that are ceramic precursors are spun into fibres by melt-spinning or solvent-assisted dry spinning, stabilising the fibres to prevent remelting followed by thermally decomposing into fibres - the references for which may be made to German P.2,6181 JO; French P.2,308,590; Japanese P.51 130325, 51 139929, 51 147623 (1976). In slurry spinning a dispersion of crystalline ceramic particulate in a carrier fluid is formed into a fibre, converted to fibre by thermal conversion by several heating stages that may include passing the fibre through a flame. The process generate particulate of not more than 1 ^m to control shrinkage - the references for which may be made to E.I. du Pont de Nemovrs & Co.; B.P. 1,264,973(1972); USP 3,808,015(1974); USP 4,753,904 (1988); Mitsui Mining Co. Ltd.; Japanese P 217182 (1986)p; European P. 0,260,868-A2 (1988); USP 4,812,271 (1989). The overall process has several drawbacks that may be listed below:
1. Number of steps involved in the overall process is higher.
2. Handling of whiskers and short fibres require special arrangements.

3. It is difficult to disperse whiskers and short fibres uniformly in the matrix.
4. Silicon Carbide whiskers particularly of aspect ratio less than 10 cause health
hazard.
The main object of the present invention is to provide a composition useful for making in-situ silicon carbide in the form of particulate, whiskers and fibres in Silicon Carbide - carbon matrix composites.
Another object of the present invention is to provide a process for making in-situ silicon carbide in the form of particulate, whiskers and fibres in Silicon Carbide-carbon matrix composites which obviates the drawbacks as detailed above. Yet another object of the present invention is to utilize natural fibres of plant source. Still another object of the present invention is to reduce the total number of unit processes in the overall operation.
Yet another object of the present invention is to form whiskers and fibres in-situ
during processing to eliminate totally the possibility of health hazard.
Accordingly the present invention provides a synergistic composition useful for
making in-situ silicon carbide in the form of particulate, whiskers and fibres in Silicon
Carbide-carbon matrix composite which comprises:
Natural fibre 1.6 - 6.4 wt%
Tetraethyl orthosilicate 28.6 - 46.8 wt.%
Phenolic resin 38 - 46 wt%
Curing agent 4.2 - 6.6 wt%
Silicon carbide 9.4 - 12.4 wt.%

In an embodiment of the present invention the fibres used are natural fibres such
as jute, sunhemp, sisal or any other natural fibres having cellulosic or
hemicellulosic constituents at its backbone.
In another embodiment of the present invention the molecular weight of phenolic
resin used may be in the range of 450-700.
In still another embodiment of the present invention curing agent used may be
such as hexamine, para toluene sulphonic acid, para formaldehyde, resorcinol ,
di-isocyanate prepolymer.
In yet another embodiment of the present invention the organic solvent used may
be such as methanol, toluene, benzene.
There is no chemical reaction in the mixture as such and the composition of the
present invention is not a mere admixture but a synergistic mixture having
properties which are different and distinct from the mere aggregation of the
properties of the individual ingredients.
Accordingly the present invention provides a method of making in-situ silicon
carbide in the form of particulate, whiskers and fibres in Silicon Carbide-carbon
matrix composites whch comprises dissolving 38 - 46 wt % of phenolic resin in
organic solvent to obtain a phenolic resin solution, adding 4.2-6.6 wt % of curing
agent and 9.4-12.4 wt % of silicon carbide powder to obtain a resin mix,
impregnating 1.6 -6.4 wt % of natural fibre dried at 60°-70°C for a period in the
range of 1-5 hrs. by known methods to obtain a dough in the form of a composite
plate/sheet, drying the said composite plate/sheet at a temperature in the range of
70°- 90° C for a period in the range of 1-2 hrs., heat treating the dried composite
plate/sheet at a temperature in the range of 150° -200°C for a period in the range of

1 - 2.5 hrs., impregnating the resultant composite plate/sheet with 28.6-46.8 wt %
of tetraethyl orthosilicate in vacuum, subjecting the impregnated composite
plate/sheet to heat treatment in argon initially at a heating rate in the range of 2° -
5°C per minute upto a temperature in the range of 200° - 400°C followed by
further heating at the rate of 10°- 15°C per minute upto a temperature in the range
of 1400° - 1850°C, maintaining the final temperature for a period in the range of
0.5-2 hrs.
In an embodiment of the present invention the natural fibres may be introduced in
the body in desired alignments such as unidirectional, multidirectional, woven,
randomly oriented structure.
In another embodiment of the present invention the matrix materials may be of
different particle dimension from nano to micron size.
In yet another embodiment of the present invention drying of the natural fibre
may be effected at a temperature in the range of 60°-70°C for a period in the range
of 1 - 5 hrs.
In still another embodiment of the present invention impregnation with
tetraethylorthosilicate may be carried out in vacuum and repeating if required.
In yet another embodiment of the present invention the heat treatment in the
absence of air may be done in an inert atmosphere or in vacuum.
The details of the present invention are given below:
a) 38 - 46 wt % of phenolic resin is dissolved in organic solvent.
b) 4.2 - 6.6 wt % of curing agent and 9.4 - 12.4 wt % of Silicon carbide are mixed
with the solution prepared in step (a).
c) Natural fibre is dried at 60° - 70°C for 1 - 5 hrs.

d) 1.6 - 6.4 wt % of dried natural fibre is impregnated with mixture prepared in
step (b) to obtain a composite plate/sheet.
e) The composite plate/sheet obtained in step (d) is dried at 70° - 90°C for 1- 2 hrs.
f) The dried composite plate/sheet is heat treated at 150°-200°C for 1 - 2.5 hrs.
g) The dried composite plate/sheet is impregnated with 28.6 - 46.8 wt % of
tetraethyl orthosilicate in vacuum.
h) The impregnated plate/sheet is initially heat treated in argon at the rate of 2° -5°C/min. upto 200°-400°C followed by further heating at the rate of 10° - 15°C per min. upto 1400°-1850°C maintaining the final temperature for 0.5-2 hrs. The process of the present invention can be used to produce in-situ silicon carbide in the form of particulate, whiskers and fibres in Silicon Carbide-carbon matrix composite of various shapes and sizes required for application as engineering components. Natural fibres of plant origin contain all the ingredients of forming silicon carbide if sufficient amount of silicon is provided. Organo silicon compound such as tetraethyl orthosilicate gives active silica on pyrolysis. This active silica in turn reacts with carbon-formed from cellulosic materials like fibres of plant origin. Silicon carbide thus formed are in molecular dimension and with proper catalyst and seeding crystals, unidirectional grain growth occurs to form long fibres of small diameters or whiskers of different aspect ratios. Isolated silicon carbide grains may grow in the three dimensions resulting into particulate formation. If these complex set of network structure is allowed to grow in Silicon Carbide-carbon matrix - the resulting microstructure consists of randomly orientated fibres and whiskers in a homogeneous matrix leading to enhanced fracture toughness imparting some machinability in otherwise non-machinable material.

The following examples are given way of illustration of the present invention and should not be construed to limit the scope of the present invention.
Example-1
38 gms.of phenolic resin of molecular weight 525 is dissolved in 95 ml. of
mathanol. 4.2 gms. of hexamine is added to it and stirred. 9.4 gms. of silicon
carbide powder is then blended in this solution. 1.6 gms. Jute fibre is dried at 60°C
for 5 hrs. and is mixed with the above mixture and formed into a composite plate.
The composite plate is dried at a temperature of 80°C for 1 hr. followed by curing
at a temperature of 160°C for 2 hrs. The plate is then impregnated with 46.8 ml. of
tetraethyl orthosilicate under vacuum. The vacuum impregnation step is repeated
for 5 cycles. The material so obtained is heat treated in argon at the rate of 2°C
per min. upto 400°C followed by heating in argon at 1400°C at the rate of 10°C per
min. for 1 hr.
Example - 2
39 gms. of phenolic resin of molecular weight 475 is dissolved in 97 ml. of toluene.
4.3 gms. of hexamine is added to it and stirred. 9.6 gms. of silicon carbide powder
is then blended in this solution. 2 gms. Jute fibre is dried at 62°C for 4 hrs. and is
mixed with the above mixture and formed into a dough. This dough is then
pressed into a composite sheet. This composite sheet is dried at a temperature of
75°C for 2 hrs. followed by curing at a temperature of 170°C for 2 hrs. The sheet is
then impregnated with 45.1 ml. tetraethyl orthosilicate under vacuum. The

vacuum impregnation step is repeated for 5 cycles. The material so obtained is heat treated in argon at the rate of 3°C per min. upto 400°C followed by heating in argon at 1500°C at the rate of 12°C per min. for 1.5 hrs.
Example - 3
40 gms. of phenolic resin of molecular weight 550 is dissolved in 100 ml. of
methanol. 4.3 gms. of hexamine is added to it and stirred. 9.8. gms. of silicon
carbide powder is then blended in this solution. 2.5 gms. Jute fibre is dried at 62°C
for 4 hrs. and is mixed with the above mixture and formed into a dough. This
dough is then pressed into a composite sheet. This composite sheet is dried at a
temperature of 75°C for 2 hrs. followed by curing at a temperature of 170°C for 2
hrs. The sheet is then impregnated with 43.4 ml. tetraethyl orthosilicate under
vacuum. The vacuum impregnation step is repeated for 5 cycles. The material so
obtained is heat treated in argon at the rate of 3°C per min. upto 400°C followed
by heating in argon at 1600°C at the rate of 12°C per min. for 1.5 hrs.
Example - 4
41 gins, of phenolic resin of molecular weight 600 is dissolved in 102 ml. of
benzene. 4.5 gms. of hexamine is added to it and stirred. 10 gms. of silicon carbide
powder is then blended in this solution. 3 gms. Jute fibre is dried at 62°C for 4 hrs.
and is mixed with the above mixture and formed into a dough. This dough is then
pressed into a composite sheet. This composite sheet is dried at a temperature of
75°C for 2 hrs. followed by curing at a temperature of 170°C for 2 hrs. The sheet is
then impregnated with 41.5 ml. tetraethyl orthosilicate under vacuum. The
vacuum impregnation step is repeated for 5 cycles. The material so obtained is
heat treated in argon at the rate of 3°C per min. upto 400°C followed by heating in
argon at 1650°C at the rate of 13°C per min. for 1.5 hrs.

Example - 5
42 gms. of phenolic resin of molecular weight 675 is dissolved in 105 ml. of
toluene. 5 gms. of hexamine is added to it and stirred. 11 gms. of silicon carbide
powder is then blended in this solution. 3.5 gms. Jute fibre is dried at 62°C for 4
hrs. and is mixed with the above mixture and formed into a dough. This dough is
then pressed into a composite sheet. This composite sheet is dried at a
temperature of 75°C for 2 hrs. followed by curing at a temperature of 170°C for 2
hrs. The sheet is then impregnated with 38.5 ml. tetraethyl orthosilicate under
vacuum. The vacuum impregnation step is repeated for 5 cycles. The material so
obtained is heat treated in argon at the rate of 4°C per min. upto 400°C followed
by heating in argon at 1700°C at the rate of 13°C per min. for 1.5 hrs.
Example - 6
43 gms. of phenolic resin of molecular weight 650 is dissolved in 107 ml. of
methanol. 5 gms. of hexamine is added to it and stirred. 11.5 gms. of silicon
carbide powder is then blended in this solution. 4 gms. Jute fibre is dried at 62°C
for 4 hrs. and is mixed with the above mixture and formed into a dough. This
dough is then pressed into a composite sheet. This composite sheet is dried at a
temperature of 75°C for 2 hrs. followed by curing at a temperature of 170°C for 2
hrs. The sheet is then impregnated with 36.5 ml. tetraethyl orthosilicate under
vacuum. The vacuum impregnation step is repeated for 5 cycles. The material so
obtained is heat treated in argon at the rate of 4°C per min. upto 400°C followed
by heating in argon at 1750°C at the rate of 14°C per min. for 1.5 hrs.

Example - 7
44 gms. of phenolic resin of molecular weight 700 is dissolved in 110 ml. of toluene. 5 gms. of hexamine is added to it and stirred. 12 gms. of silicon carbide powder is then blended in this solution. 4.5 gms. Jute fibre is dried at 62°C for 4 hrs. and is mixed with the above mixture and formed into a dough. This dough is then pressed into a composite sheet. This composite sheet is dried at a temperature of 75°C for 2 hrs. followed by curing at a temperature of 170°C for 2 hrs. The sheet is then impregnated with 34.5 ml. tetraethyl orthosilicate under vacuum. The vacuum impregnation step is repeated for 5 cycles. The material so obtained is heat treated in argon at the rate of 4°C per min. upto 400°C followed by heating in argon at 1800°C at the rate of 14°C per min. for 1.5 hrs.
Example - 8
46 gms. of phenolic resin of molecular weight 450 is dissolved in 115 ml. of benzene. 6.6 gms. of hexamine is added to it and stirred. 12.4 gms. of silicon carbide powder is then blended in this solution. 6.4 gms. Jute fibre is dried at 62°C for 4 hrs. and is mixed with the above mixture and formed into a dough. This dough is then pressed into a composite plate. This composite plate is dried at a temperature of 75°C for 2 hrs. followed by curing at a temperature of 170°C for 2 hrs. The plate is then impregnated with 28.6 ml. tetraethyl orthosilicate under vacuum. The vacuum impregnation step is repeated for 5 cycles. The material so obtained is heat treated in argon at the rate of 3°C per min. upto 400°C followed by heating in argon at 1850°C at the rate of 15°C per min. for 2 hrs.

The main advantages of the present invention are :
1. Processing steps are reduced to a large extent.
2. Natural fibres of plant origin are used that replaces hazardous synthetic
raw materials
3. The constituents like silicon carbide whiskers and short fibres are formed
in situ during the processing of the composite thereby eliminating the need
for handling these components which are potential health hazard.
4. Conventional composite fabricating techniques can be used thereby
allowing easy formation of material with different microstructure and
properties.

We Claim:
1. A synergistic composition useful for making in-situ silicon carbide
in the form of particulate, whiskers and fibres in Silicon Carbide-
carbon matrix composite which comprises:
Natural fibre 1.6 - 6.4 wt%
Tetraethyl orthosilicate 28.6 - 46.8 wt.%
Phenolic resin 38 - 46 wt%
Curing agent 4.2 - 6.6 wt%
Silicon carbide 9.4 - 12.4 wt.%
2. A synergistic composition as claimed in claim 1 wherein the fibres
used are natural fibres such as jute, sisal, sunhemp and any other
natural fibre having cellulosic or hemicellulosic constituent at its
backbone.
3. A synergistic composition as claimed in claims 1 & 2 wherein the
phenolic resin used is selected from phenolic resin having
molecular weight in the range of 450 - 700.
4. A synergistic composition as claimed in claims 1-3 wherein the
curing agents used are such as hexamine, para toluene sulphonic
acid, paraformaldehyde, resorcinol and di-isocyanate prepolymer.
5. A synergistic composition as claimed in claims 1-4 wherein the
organic solvents used are such as methanol, toluene and benzene.

6. A synergistic composition useful for making in-situ silicon carbide in the form of particulate, whiskers and fibres in Silicon Carbide-carbon matrix composite substantially as herein described with reference to the examples.

Documents:

1509-del-1999-abstract.pdf

1509-del-1999-claims.pdf

1509-del-1999-correspondence-others.pdf

1509-del-1999-correspondence-po.pdf

1509-del-1999-description (complete).pdf

1509-del-1999-form-1.pdf

1509-del-1999-form-19.pdf

1509-del-1999-form-2.pdf

1509-del-1999-form-3.pdf

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Patent Number

232918

Indian Patent Application Number

1509/DEL/1999

PG Journal Number

13/2009

Publication Date

27-Mar-2009

Grant Date

23-Mar-2009

Date of Filing

26-Nov-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	KALYAN KUMAR PHANI	CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, CALCUTTA 700 032, INDIA
2	ASHOK KUMAR DE	CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, CALCUTTA 700 032, INDIA
3	NRIPATI RANJAN BOSE	CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, CALCUTTA 700 032, INDIA
4	SANKAR GHATAK	CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, CALCUTTA 700 032, INDIA

PCT International Classification Number

C01B 33/025

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA