Plastic and nonmetallic article shaping or treating: processes – Outside of mold sintering or vitrifying of shaped inorganic... – Using organometallic or organosilicon intermediate
Patent
1994-04-29
1998-01-06
Fiorilla, Christopher A.
Plastic and nonmetallic article shaping or treating: processes
Outside of mold sintering or vitrifying of shaped inorganic...
Using organometallic or organosilicon intermediate
264624, 264626, 264627, 264671, C04B 3332
Patent
active
057051224
DESCRIPTION:
BRIEF SUMMARY
This invention relates to ceramic fibres. It is concerned with methods of making such fibres, and with the fibres so made, and with their uses.
Ceramic compositions typically include oxides, carbides and nitrides of metals and non-metals, and extend more generally to simple binary or more complex solid inorganic compounds, excluding salts. Ceramics tend to result from high temperature processing which consolidates the material. Fibres containing ceramic compounds are referred to herein as ceramic fibres. Compounds which yield ceramics after pyrolysis, or firing, are referred to as ceramic precursors, or pre-ceramic materials. Fibres containing ceramic precursors, which after firing will form ceramic fibres, are referred to as pre-ceramic fibres.
This invention is especially concerned with composite or multicomponent ceramic materials that include compounds between metals and non-metals; although ceramics including compounds wholly between non-metals, such as silicon carbide and boron nitride, are also made available by the invention. Glasses may be included among the ceramics, and the invention is applicable to non-glass ceramics and glassy ceramics as distinct classes of product.
References to fibres are intended also to include filaments, ie long or continuous fibres. The fibres are generally manufactured as filaments. Short fibres can be made from the filaments by chopping or other processes.
A particularly important use of ceramic fibres is as reinforcements for glass, metal and ceramic products, to prevent catastrophic failure of the products under stress. A serious problem can be that the fibre that in itself has good properties from a mechanical point of view may not be chemically or physically compatible with the matrix into which it is to be incorporated as a reinforcement. Ceramic materials also have many other uses, and show a very wide range of electrical properties, from insulators through semiconductors to superconductors.
Known methods of making ceramic fibres include chemical vapour deposition and pyrolysis of a given polymer. The former is slow and expensive, and tends to give stoichiometric, monolithic, inflexible fibres of large diameter. The latter gives monolithic nonstoichiometric fibres which are more flexible. Both give fibres that can be reactive with the matrix unless they are reprocessed to coat them.
My International Patent Application PCT/GB91/00604, Publication No WO 91/16479, discloses methods of making a range of ceramic materials which can be tailored and selected for a wide range of purposes, and the disclosure of that publication is incorporated herein by reference, especially as concerns spinning and pyrolysis techniques. The method that is described in detail is to pyrolysis a dispersion of an organo-metallic ceramic precursor in a carrier comprising an organic polymer, The use of the carrier polymer enables many organo-metallic ceramic precursors to be used that otherwise could not be used, because of handling difficulties, and the use of at least two components also permits wide variation and control of the chemistry of the feedstock for pyrolysis. The dispersion of organo-metallic ceramic precursor in the polymer can also allow mixing of the distinct starting materials down to a molecular level, much more intimately than is possible by mixing separate powders, and this can give a more homogeneous product.
In applying that invention to the preparation of ceramic fibres, that application refers in broad terms to a method comprising spinning a plurality of polymeric materials each comprising at least one ceramic precursor into a composite fibre, and thereafter pyrolysing the composite fibre to form a composite or multicomponent ceramic fibre of non-homogeneous composition. All the examples given describe the use of at least one organic polymer, which is not in itself a ceramic precursor, carrying a dispersion of the organo-metallic ceramic precursor.
I have now discovered that the conjugate spinning techniques described in my earlier application for the preparation of c
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