| 摘要 |
The present invention is a method for fabricating shaped monolithic ceramics and ceramic composites, and the ceramics and composites made thereby. The method of the present invention includes three basic steps: (1) Synthesis or other acquisition of a porous preform with an appropriate composition, pore fraction, and overall shape is prepared or obtained. The pore fraction of the preform is tailored so that the reaction-induced increase in solid volume can compensate partially or completely for such porosity. It will be understood that the porous preform need only be sufficiently dimensionally stable to resist the capillary action of the infiltrated liquid reactant; (2) Infiltration: The porous preform is infiltrated with a liquid reactant; and (3) Reaction: The liquid reactant is allowed to react partially or completely with the solid preform to produce a dense, shaped body containing desired ceramic phase(s). The reaction in step (3) above is a displacement reaction of the following general type between a liquid species, M(l), and a solid preform comprising the compound, NBXC(s): AM(l)+NBXC(s)=AMXC/A(s)+BN(l/g) where MXC/A(s) is a solid reaction product (X is a metalloid element, such as, for example, oxygen, nitrogen, sulfur, etc.) and N(l/g) is a fluid (liquid or gas) reaction product. A, B and C are molar coefficients.
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