Compositions: ceramic – Ceramic compositions – Refractory
Patent
1994-07-25
1995-10-17
Brunsman, David
Compositions: ceramic
Ceramic compositions
Refractory
501 97, 501 98, 501 92, 10628711, C04B 3558, C04B 3580, C04B 4187
Patent
active
054591147
DESCRIPTION:
BRIEF SUMMARY
This application is a filing under 35 U.S.C. 371 of PCT/JP93/01730 filed Nov. 26, 2993.
DESCRIPTION
Method for Producing Ceramic Products
TECHNICAL FIELD
The present invention relates to a method for producing ceramic products, and the ceramic products provided by the present invention include fiber reinforced ceramics and high density ceramics, which may be suitably used as structural materials in harsh environments of high temperature, corrosion, etc. More specifically, it relates to fiber reinforced ceramics made by reinforcing a silicon nitride-type matrix with metal or inorganic fiber, and to ceramic products which have been highly consolidated by impregnation into porous ceramics.
BACKGROUND ART
Ceramics have excellent heat resistance, corrosion resistance and heat insulating properties in comparison to metal materials, and thus they have received attention as structural materials in place of metals in harsh environments of high temperature, corrosion, etc. However, ceramics cannot be deformed in the same way as metal materials, and stress becomes concentrated on defects in the material and flaws on the surface to lead to easy breakage, giving them the disadvantage of poor fracture toughness. In order to improve this fracture toughness of ceramics, particles or fibers are dispersed in the matrix to absorb the rupture energy.
Methods for the production of fiber reinforced ceramics are largely classified into three types: powder sintering methods, CVD (CVI) methods and impregnation methods.
(1) In powder sintering methods, a reinforcing material such as whiskers or the like is mixed with powder which forms a matrix, and this mixture is sintered at a high temperature of 1600.degree. C. or above. Since powder sintering requires high-temperatures to obtain a consolidated sintered body, its disadvantages include that it can only be used for a limited reinforcing materials.
(2) CVD (CVI) methods involve deposition of a ceramic matrix from a gaseous precursor into spaces in a preform, which is made of inorganic fibers, whiskers or the like. In the CVD (CVI) method, the substance which is to form the ceramic matrix may also be filled into fine pores, but a large number of pores are left as closed pores, and it is generally difficult to fill more than 80% of the pores. Other problems encountered include long production time, high production costs and difficulty of application to large-sized forms due to limits of the apparatuses.
(3) Impregnation methods involve impregnating a polymer which is converted into ceramic after heat treatment, into a preform made of inorganic fibers, whiskers or the like, and then firing it to form a matrix. By repeating the steps of impregnation and heating it is possible to obtain a more consolidated fired body, and this method may be applied to structures with complex shapes and to large-sized forms. In addition, because the firing is performed at a lower temperature than in powder sintering, there is no limit to the type of reinforcing material which may be used.
Ceramic composite materials prepared by thermal decomposition of a ceramic precursor polymer to obtain a matrix are found described in European Patent No. 0,125,722, U.S. Pat. No. 4,117,057 and U.S. Pat. No. 4,460,638. The drawback of these methods is that the polymer must be diluted to about 50% with an organic solvent for its impregnation into the preform. Since the polymer used is a solid or highly viscous liquid, it must be diluted with a solvent to adjust it to a viscosity suitable for impregnation. This solvent must be removed after the impregnation however, and therefore a drying process is necessary, and since pores are left after drying the resulting material has a low density and low strength.
A method designed to improve this is described in Japanese Unexamined Patent Publication (Kokai) No. 2-188471, in which method polysilazane is impregnated without dilution with a solvent. When liquid polysilazane is used, curing and infusibility treatment are necessary after impregnation in order to keep the sha
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Walker, B. F., Jr., et al, Ceramic Bulletin, 62(8) 916-923(1983) no month avail., "Preparation and Properties of Monolithic and Composite Ceramics Produced by Polymer Pyrolysis".
Fitzer, E. et al, Nippon Cermaics Society, 2008, 159(1988)no month avail."Composite Ceramics produced by Polymer Pyrolysis(1) Silazane System".
Aoki Tomoko
Isoda Takeshi
Kaya Hiroshi
Morozumi Hiroki
Nakahara Hirohiko
Brunsman David
Meller Michael N.
Tonen Corporation
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