Title of Invention

A PROCESS FOR MAKING IN-SITU SILICON CARBIDE IN THE FORM OF PARTICULATE, WHISKERS AND CARBON MATRIX COMPOSITES.

Abstract A process for making in-situ silicon carbide in the form of particulate, whiskers and carbon matrix composites: The process of present invention provides silicon carbide using wide variety of natural fibre such as jute , sisal, sunhamp or any nature fibre having cellulosic and hemicellulosic constituent at its back bone for providing useful carbon for the formation of silicon carbide in the form of particulate , whikers and fibres in the matrix of the 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 carbon matrix composite and a process for making in-situ Silicon Carbide in the form of particulate, whiskers and fibres in 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 carbon. The main usage of the silicon carbide in the form of particulate, whiskers and fibres in 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 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 J.J.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 Al203/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.2,618150; 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 µm to control shrinkage - the references for which may be made to E.I. du Pont de Nemovrs and 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 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
carbon matrix composites which obviates the drawbacks as detailed above.
Yet another object of the present invention is to utilise 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 composition useful for making
in-situ silicon carbide in the form of particulate, whiskers and fibres in
Silicon Carbide-carbon matrix composites which comprises:

Natural fibre 1.6- 6.4 wt%
Tetraethyl orthosilicate 33 - 50.2 wt.%
Phenolic resin 42 - 52 wt%
Curing agent 6.2 - 8.6 wt%
Organic solvent requisite amount to dissolve
phenolic resin
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 process for making in-situ silicon carbide in the form of particulate, whiskers and carbon matrix composites which comprises dissolving 42-52% of phenolic resin in an organic solvent such as herein described, to obtain a phenolic resin solution, adding 6.2-8.6 wt% of curing agent such as herein described to obtain a resin mix , to the obtained mix impregnating by conventional manner 1.6-6.4 wt% of natural fibre dried at 60° -70 ° C for a period in the range of 1-5 h , to the obtained mix by conventional manner to obtain a dough in the form of composite ,drying the said composite at a temperature in the range of 70 ° - 90 °C for a period in the range of 1 -2 h , drying and heat treating the dried composite at a temperature ranging 150° -200° C for a period of 1-2-5 h , impregnating the resultant composite with 33 - 50.2 wt % of tetraethyl orthosilicate in vacuum , subjecting the impregnated composite to further heat treatment in absence of air at a rate of 2° -5° C per minute upto a temperature in the range of 200° - 400 °C followed by at a rate 10° - 15° C per minute upto temperature range of 1400° - 1850° C , maintaining the final temperature for a period in the range of 0.5 -2 h to get the desired silicon carbide.
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° to 70°C for a
period in the range of 1 to 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) 42 - 52 wt % of phenolic resin is dissolved in organic solvent.
b) 6.2 -8.6 wt % of curing agent is mixed with the solution prepared in
step (a).
c) Natural fibre is dried at 60° - 70°C for 1 to 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° to 90°C for 1 -2 hrs.
f) The dried composite plate/sheet is heat treated at 150°-200°C for 1 -2.5hrs.
g) The dried composite plate/sheet is impregnated with 33 -50.2 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 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 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
42 gms. of phenolic resin of molecular weight 450 is dissolved in 100 ml. of
mathanol. 6.2 gms. of hexamine is added to it and stirred. 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 50.2 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
43 gms. of phenolic resin of molecular weight 600 is dissolved in 102 ml. of
toluene. 6.3 gms. of hexamine is added to it and stirred. 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 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 48.7 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 44 gms. of phenolic resin of molecular weight 700 is dissolved in 102 ml. of methanol. 6.3 gms. of hexamine is added to it and stirred. 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 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 47.2 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 46 gms. of phenolic resin of molecular weight 550 is dissolved in 105 ml. of benzene. 6.5 gms. of hexamine is added to it and stirred. 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 44.5 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
47 gms. of phenolic resin of molecular weight 650 is dissolved in 105 ml. of
toluene. 7 gms. of hexamine is added to it and stirred. 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 42.5 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
48 gms. of phenolic resin of molecular weight 475 is dissolved in 108 ml. of
methanol. 7 gms. of hexamine is added to it and stirred. 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 41 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 49 gms. of phenolic resin of molecular weight 675 is dissolved in 110 ml. of toluene. 7 gms. of hexamine is added to it and stirred. 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 39.5 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 52 gms. of phenolic resin of molecular weight 525 is dissolved in 115 ml. of benzene. 8.6 gms. of hexamine is added to it and stirred. 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 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 33 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.





















claim:
1. A process for making in-situ silicon carbide in the form of particulate, whiskers and carbon matrix composites which comprises dissolving 42-52% of phenolic resin in an organic solvent such as herein described, to obtain a phenolic resin solution, adding 6.2-8.6 wt% of curing agent such as herein described to obtain a resin mix , to the obtained mix impregnating by conventional manner 1.6-6.4 wt% of natural fibre , dried at 60° -70 ° C for a period in the range of 1-5 h to obtain a dough in the form of composite ,drying the said composite at a temperature in the range of 70 ° - 90 °C for a period in the range of 1-2 h , drying and heat treating the dried composite at a temperature ranging 150 -200 C for a period of 1-2-5 h , impregnating the resultant composite with 33 - 50.2 wt % of tetraethyl orthosilicate in vacuum , subjecting the impregnated composite to further heat treatment in absence of air at a rate of 2° -5° C per minute upto a temperature in the range of 200° - 400 °C followed by at a rate 10° - 15° C per minute upto temperature range of 1400° - 1850° C , maintaining the final temperature for a period in the range of 0.5 - 2 h to get the desired silicon carbide.
2. A process as claimed in claim 1 wherein natural fibre used are selected from jute , sisal, sunhamp or any nature fibre having cellulosic and hemicellulosic constituent at its back bone.
3. A process as claimed in claim 1 and 2 wherein phenolic resin used is selected from phenolic resin having molecular wt. in the range of 450-700.
4. A process as claimed in claim 1 -3 wherein curing agent used is selected from hexamine , para toluene sulphonic acid , paraformaldehyde , resorcinol and di -isocyanate prepolymer.
5. A process as claimed in claim 1-4 wherein the organic solvent used is selected from methanol, toluene and benzene.
6. A process for making in-situ silicon carbide in the form of particulate, whiskers and carbon matrix composites substantially as herein described with reference to the examples .

Documents:

1508-del-1999-abstract.pdf

1508-del-1999-claims.pdf

1508-DEL-1999-Correspondence-Others.pdf

1508-del-1999-correspondence-po.pdf

1508-del-1999-description (complete).pdf

1508-del-1999-form-1.pdf

1508-del-1999-form-19.pdf

1508-del-1999-form-2.pdf

1508-del-1999-form-3.pdf

1508-del-1999-petiton-138.pdf

1508-delnp-2003-complete specification (granted).pdf


Patent Number 211364
Indian Patent Application Number 1508/DEL/1999
PG Journal Number 37/2008
Publication Date 12-Sep-2008
Grant Date 26-Oct-2007
Date of Filing 26-Nov-1999
Name of Patentee COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH
Applicant Address RAFI MARG, NEW DELHI-110 001, INDIA.
Inventors:
# Inventor's Name Inventor's Address
1 KALYAN KUMAR PHANI, CENTRAL GLASS & CERAMIC RESEARCH INSTITUTE, CALCUTTA, 700032
2 ASOK KUMAR DE, CENTRAL GLASS& CERAMIC RESEARCH INSTITUTE, CALCUTTA, 700032
3 NRIPATI RANJAN BOSE CENTRAL GLASS& CERAMIC RESEARCH INSTITUTE, CALCUTTA, 700032
4 SANKAR GHATAK, CENTRAL GLASS& CERAMIC RESEARCH INSTITUTE, CALCUTTA, 700032
PCT International Classification Number C08K 3/34
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA