Compositions: ceramic – Ceramic compositions – Refractory
Patent
1989-07-21
1991-06-04
Dixon, Jr., William R.
Compositions: ceramic
Ceramic compositions
Refractory
501 92, 501 96, 501 97, C04B 3556, C04B 3558
Patent
active
050213709
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to ceramic fibers and a process for producing the same and more particularly to ceramic fibers comprising a quaternary system composed of Si, C, N and O, which are excellent in mechanical properties such as tensile strength and tensile modulus and in electrical properties such as electric resistance and permittivity, and it also relates to a process for producing the ceramic fibers.
2. Background Art
Conventional inorganic fibers obtained by using polycarbosilane as starting material, include SiC fibers (see Japanese Patent Nos. 1217464 and 1217465 and the like) and SiON fibers (see Japanese Patent Appln. Laid-Open No. (sho.) 61-12915 (12915/86)).
These conventional fibers have been used not only as reinforcing fibers for a fiber-reinforced metal, a fiber-reinforced plastics and the like, but also as an electric insulating material, a heat-resistant material and the like, because of their excellent properties.
Although the SiC fibers have excellent mechanical properties, they are electrically disadvantageous in that they have a specific resistance of 10.sup.3 to 10.sup.5 .OMEGA..multidot.cm, they exhibit relatively large permittivity and dielectric loss when they are used in the form of a SiC fibers/resin composite material and they have inferior radio wave transmittivity, whereby they are rendered unsuitable for use as a radome or the like.
On the other hand, SiON fibers are advantageous in that they have a specific resistance exceeding 10.sup.10 .OMEGA..multidot.cm, i.e., high electric insulating performance, exhibit lower relative permittivity and dielectric loss when used in the form of a resin composite material than those of the SiC fibers and have radio wave transmittivity superior to that of the SiC fibers. However, the SiON fibers raise a problem that their mechanical properties are inferior to those of the SiC fibers.
The primary object of the present invention is to solve the above-described problems and to provide ceramic fibers having excellent electrical and mechanical properties and a process for producing the same.
DISCLOSURE OF INVENTION
The present inventors have made various studies with a view to solving the above-described problems and, as a result, have found that the above-described problems can be solved by heat treating infusible polycarbosilane fibers in an ammonia gas atmosphere to nitride the fibers and further heat treating the thus obtained nitrided fibers in an inert gas or an atmosphere comprising 1 to 30% by volume of hydrogen chloride with the balance being an inert gas to obtain desired ceramic fibers. The present invention is based on this finding.
The ceramic fibers of the present invention are characterized by comprising a quaternary system composed of Si, C, N, and O.
It is the most desirable that the contents of the elements, i.e., Si, C, N, and O, in the ceramic fibers of the present invention are 40 to 60% by weight, 0.2 to 30% by weight, 5 to 30% by weight, and 5 to 20% by weight, respectively. When the content of each of the elements is in the above-described corresponding range, the ceramic fibers exhibit excellent electrical and mechanical properties, i.e., a specific resistance of 10.sup.6 to 10.sup.10 .OMEGA..multidot.cm, a tensile strength of 300 to 450 kg/mm.sup.2, a tensile modulus of 20 to 40 ton/mm.sup.2, a relative permittivity of 3.0 to 4.0 when in the form of an epoxy resin composite material (percentage volume of fibers: 55%), and a dielectric loss of 0.02 or less when in the form of said composite material.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a flow sheet showing an example of the process for producing ceramic fibers according to the present invention;
FIG. 2 is a graph showing the relationship between the content of each component and the temperature of heat treatment in an ammonia gas in Example 1;
FIG. 3 is a graph showing the relationship between each of the tensile strength and tensile modulus, and the temperature of heat treatment in ammonia gas in Example 1; and
FIG. 4 is
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patent: 4761389 (1988-08-01), Rabe et al.
patent: 4771118 (1988-09-01), Takamizawa et al.
patent: 4869854 (1989-09-01), Takeda et al.
patent: 4870035 (1989-09-01), Takamizawa et al.
Ichikawa Hiroshi
Ishikawa Toshikatsu
Mitsuno Shiro
Teranishi Haruo
Dixon Jr. William R.
Green Anthony J.
Nippon Carbon Co, Limited
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