Solid anti-friction devices – materials therefor – lubricant or se – Solid anti-friction device – article or material therefor – Silicon compound
Reexamination Certificate
2001-03-15
2002-04-23
Howard, Jacqueline V. (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Solid anti-friction device, article or material therefor
Silicon compound
C428S367000, C428S408000, C428S446000, C428S698000, C427S228000
Reexamination Certificate
active
06376431
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention includes a carbon/carbon (C/C) composite comprising crystalline silicon carbide which is essentially uniformly distributed on both the internal and external surfaces of the composite, wherein the amount of silicon carbide is in a range of 0.001 to 1.00 weight percent based upon the total weight of the composite, a process for producing said composite and the use of said composite in brake materials for industrial roll goods, automotives, trucks, trains and aircrafts.
BACKGROUND OF THE INVENTION
The art has recognized the advantages of frictional braking elements, such as brake discs, made of carbon. In more advanced production techniques, the carbon materials are made by molding a mixture of carbon fibers and an organic polymer, and pyrolyzing the polymer binder. The carbon materials have the advantage of a high temperature resistance coupled with a low density, which substantially reduces the dead load making them particularly useful for vehicles such as aircrafts.
Yamazaki et al. (U.S. Pat. No. 5,462,800) teach the formation of a silicon carbide layer in a carbon matrix/carbon fiber composite material by introducing SiO (silicon-mono-oxide) gas at the surface of a C/C composite thereby reacting the SiO with the pyrolytic graphite (and in part the carbon fibers) and forming the silicon carbide layer. According to Yamazaki et al., the silicon carbide is formed to a depth of 3000 &mgr;m, and as such, the SiC is essentially present on the external surface of the composite only.
Barnard et al. U.S. Pat. No. 5,665,848, teach a composite comprising carbon containing fibers in a matrix of silicon carbide. An assembly of carbon fibers are impregnated with a organopolysilazane/crosslinker/promoter preceramic mixture to form a “pre-preg”. The pre-preg is then exposed to a series of heating steps to form the final ceramic composite. The final ceramic composite contains a matrix of a char which is noncrystalline.
Kaya et al. U.S. Pat. No. 5,459,114 teach a process for producing a ceramic comprising repeating a step of impregnating a metal fiber or ceramic fiber preform with a mixture of organopolysilazane-type polymers. Optionally, the surface of the metal or ceramic fiber containing woven fabric, can be covered with carbon before impregnating with the organopolysilazane. In addition, Kaya et al. teach a step of chemical vapor deposition of a heat resistant ceramic either before or after the organopolysilazane impregnation step. The final composite contains a noncrystalline matrix of the organopolysilazane char.
The large amounts of silicon carbide created in these patents would result in high friction coefficients and high wear rates. None of the above-described patents address the process of coating a porous preform or final body with a small amount (less than 1 wt %) of thin crystalline silicon carbide distributed throughout the part, i.e., on both the internal and external surfaces to reduce the wear rates with either no change or a slight increase in the friction coefficients.
SUMMARY OF THE INVENTION
The present inventors have found that small amounts of crystalline silicon carbide uniformly distributed throughout the part results in reduced wear with either no change or a slight increase in the friction coefficient. Also, the properties of this material remain constant during use even after wear of the outer surface.
The present invention includes a C/C composite comprising crystalline silicon carbide which is essentially uniformly distributed on both the internal and external surfaces of the composite, wherein the amount of silicon carbide is in a concentration range of 0.001 to 1.00 weight percent based upon the total weight of the composite, a process for producing said composite and the use of said composite in brake materials for industrial roll goods, automotives, trucks, trains and aircrafts.
Advantages of the present invention will become more apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
DETAILED DESCRIPTION OF THE INVENTION
The present invention, in part, relates to a C/C composite comprising crystalline silicon carbide which is essentially uniformly distributed on both the internal and external surfaces of the composite, wherein the silicon carbide is in a concentration range of 0.001 to 1.00 weight percent based upon the total weight of the composite. Preferably, the concentration range of the silicon carbide is 0.01 to 0.5 weight percent.
The present invention, in part, relates to a C/C composite containing silicon carbide, wherein the composite has a wear rate in the range of 0.01 to 0.13 inch/s/s×10
−4
, and a friction coefficient in the range of 0.27 to 0.4. Preferably, the wear rate is in the range of 0.03 to 0.12 inch/s/s×10
−4
, and the friction coefficient is in the range of 0.28 to 0.395.
The present invention, in part, relates to a C/C composite, wherein the SiC in the composite is at least 60 wt % crystalline, preferably at least 90 wt % crystalline, and most preferably about 100 wt % crystalline.
The present invention, in part, relates to a process for preparing a C/C composite comprising crystalline silicon carbide which is essentially uniformly distributed on both the internal and external surfaces of the composite, said process comprising: contacting a C/C composite preform with a solution of a preceramic compound composed of silicon and carbon; and heating the C/C composite to a temperature sufficient to convert the preceramic compound to silicon carbide; wherein the amount of silicon carbide is in a range of 0.001 to 1.0 weight percent based on the weight of the total composite (in the dried state).
The preceramic compound can be either a polymer or a small molecule and is not specifically limited, but is required to form silicon carbide upon heat treatment. The type of preceramic polymer is not specifically limited, but it is required to have silicon-carbon bonds and the amount of silicon in it should not be so high as to produce an excess of silicon, since excess silicon will attack the carbon fibers. The ratio of silicon to carbon can be controlled by adding a carbon containing crosslinking agent. The type of preceramic small molecule is preferably an alkyl orthosilicate such as tetraethyl orthosilicate (TEOS).
It is preferred that the preceramic polymer composed of silicon and carbon is polycarbosilane, organopolysilazane, polycarbosiloxane, or mixtures thereof.
The organopolysilazanes (or silazane polymers) useful in this invention are generally well known in the art. The organopolysilazanes of this invention generally contain units of the type [R
2
SiNH], [RSi(NH)
1.5
] and/or [R
3
Si(NH)
½
] wherein each R is independently selected from the group consisting of hydrogen, alkyl radicals containing 1 to 20 carbon atoms, aryl radicals, and alkenyl radicals. Naturally, the organopolysilazanes useful in this invention may contain other silazane units. Examples of such units include [MeSi(NH)
1.5
], [Me
2
SiNH], [ViSi(NH)
1.5
], [Vi
2
SiNH], [PhMeSiNH], [PhViSiNH], [MeViSiNH], [HSl(NH)
1.5
], [H
2
SiNH], and the like. Mixtures of organopolysilazanes may also be employed in the practice of this invention.
The organopolysilazanes of this invention and their method of preparation can be prepared by techniques well known in the art. Suitable preceramic silazane polymers or organopolysilazanes may be prepared by the methods of Cannady in U.S. Pat. No. 4,540,803 (issued Sep. 10, 1985) and U.S. Pat. No. 4,543,344 (issued Sep. 24, 1985) which are hereby incorporated by reference. Other organopolysilazane
Forsythe George D.
Matsumoto Roger L. K.
Honeywell International , Inc.
Howard Jacqueline V.
Palguta Larry J.
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