Composition useful for making in-situ silicon carbide...

Details Composition useful for making in-situ silicon carbide... Composition useful for making in-situ silicon carbide...

2001-02-22

2003-04-15

Cain, Edward J. (Department: 1714)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

At least one aryl ring which is part of a fused or bridged...

C423S324000, C423S345000, C501S088000

Reexamination Certificate

active

06548586

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a composition useful for making in-situ Silicon Carbide in the form of particulate, whiskers and fibers in an inorganic composite matrix and a process thereof.
The process of the present invention particularly relates to the use of wide variety of natural fibers such as jute, hem, sisal or any other natural fibre having cellulosic or hemicellulosic fibre as its backbone as raw materials for providing useful carbon for the formation of silicon carbide in the form of particulate, whiskers and fibers in an inorganic composite matrix selected from Silicon Carbide-carbon and carbon matrix.
The main usage of the silicon carbide particulate, whiskers, fibre in Silicon Carbide-carbon or carbon composite matrix is in the field of engineering materials in any shape as may be deemed fit.
BACKGROUND OF THE INVENTION
The present day method of making Silicon Carbide particulate, whisker and fibre reinforced composite in Silicon Carbide-carbon matrix or carbon matrix 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 Characterization of VLS—Derived SiC whiskers” of P. D. Shalek in Conf. Whisker and Fiber 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, pp979-991 (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 fibers 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. DKG74 (5), 1997. The fibers and whiskers produced by the above processes are mixed mechanically with the matrix material 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 Al
2
O
3
/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 fibers by melt-spinning or solvent—assisted dry spinning, stabilising the fibers to prevent remelting followed by thermally decomposing into fibers, 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 um 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); U.S. Pat. No. 3,808,015 (1974); U.S. Pat. No. 4,753,904 (1988), Mitsul Mihie Co. Ltd. Japanese P 217182 (1986); European P. 0,206,868-A2 (1988), U.S. Pat. No. 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 fibers require special arrangements.
3. It is difficult to disperse whiskers and short fibers 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 fibers inman inorganic composite matrix selected from Silicon Carbide-carbon and carbon matrix composite.
Another object of the present invention is to provide a process for making in-situ silicon carbide in the form of particulate, whiskers and fibers in an inorganic composite matrix selected from Silicon Carbide carbon and carbon matrix composite which obviates the drawbacks as detailed above.
Yet another object of the present invention is to utilise natural fibers 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 fibers in situ during processing to eliminate totally the possibility of health hazard.
DETAILED DESCRIPTION OF THE INVENTION
Accordingly the present invention provide a composition useful for making in-situ silicon carbide in the form of particulate, whiskers and fibers in an inorganic composite matrix selected from silicon carbide carbon and carbon composite matrix, wherein the said composition comprising:
Natural Fibre
1.6-6.5
Wt %
TetraEthyl Orthosilicate
10.4-42
Wt %
Phenolic Resin
38-73.5
Wt %
Curing agent
4.2-11
Wt %
Silicon Carbide (optional)
9.4-12
Wt %
Organic Solvent
requisite amount
to dissolve
Phenolic resin
In an embodiment of the present invention the inorganic composite matrix such as a silicon carbide-carbon composite matrix further comprising:
Natural Fibre
1.6-6.4
Wt %
TetraEthyl Orthosilicate
10.4-42
Wt %
Phenolic Resin
38-46
Wt %
Curing agent
4.2-6.6
Wt %
Silicon Carbide
9.4-12.4
Wt %
Organic Solvent
requisite amount
of dissolve
Phenolic resin
In yet another embodiment the inorganic composite matrix such as a carbon composite matrix further comprising:
Natural Fibre
2.5-6.5
Wt %
TetraEthyl Orthosilicate
13.4-40
Wt %
Phenolic Resin
46-73.5
Wt %
Curing agent
7.5-11
Wt %
Organic Solvent
requisite amount
to dissolve
Phenolic resin
In yet another embodiment the fibre used is a natural fibre selected from the group consisting of jute, sisal, hem and any other natural fibre having cellulosic or hemicellulosic constituent at its backbone.
In yet another embodiment the curing agent used is selected from hexamine, para toluenesulphonic acid and para formaldehyde most preferably hexamine.
In yet another embodiment the molecular weight of phenolic Fresin used is in the range of 450-700.
In still another embodiment the organic solvent used is selected from methanol, toluene and benzene.
In an another embodiment of the present invention provides a process for making in-situ carbide in the form of particulate, whiskers and fibers in an inorganic composite matrix, which comprises, dissolving 38 to 73.5 Wt % of phenolic resin in an organic solvent to obtain a phenolic resing solution, adding 4.2-11.0 Wt % of a curing agent optionally adding 9.4-12 Wt % of silicon carbide powder to obtain a resin mix followed by impregnating 1.6-6.5 Wt % of natural fibre with the said resin mix dried at 60°-70° C. for a period in the range of 1-5 hrs. to obtain a dough in the form of a composite plate sheet, drying the said composite plate or sheet at a temperature in the range of 70°-90° C. for a time period in the range of 1-2 hrs., drying the composite plate or sheet, heat treating the dried composite plate or 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 or sheet with 10.4-42 Wt % tetraethyl orthosilicate in vacuum, subjecting the impregnated composite plate/sheet to heat treatment in absence of air 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° C.-1850° C., maintaining the final temperature for a period in the range of 0.5-2 hrs.
In yet another embodiment the natural fibre introduced in the body in desired alignment is selected from unidirectional, multidirectional, woven, and randomly oriented structure.
In yet

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