In the present invention, there is described a setup for producing a self-supporting ceramic body or ceramic composite by the oxidation of a parent metal to form a polycrystalline ceramic material comprising the oxidation reaction product of said parent metal with an oxidant, including a vapor-phase oxidant, and optionally one or more metallic constituents dispersed throughout the polycrystalline ceramic material. The setup is used with a method which comprises the steps of providing at least a portion of said parent metal with a barrier means at least partially spaced from said parent metal for establishing at least one surface of the ceramic body, and heating said parent metal to a temperature above its melting point but below the melting point of the oxidation reaction product to form a body of molten metal. At that temperature, the molten metal is reacted with the oxidant, thus forming the oxidation reaction product. At least a portion of the oxidation reaction product is maintained in contact with and between the molten metal and oxidant to transport the molten metal through the oxidation reaction product toward the barrier means and into contact with fresh oxidant so that the oxidation reaction product continues to form at an interface between the oxidant and previously formed oxidation reaction product. The reaction is continued until the oxidation reaction product contacts the barrier means to produce a ceramic body having the surface established by the barrier means. A shaped ceramic composite is formed by superimposing a barrier means onto either a loose mass of filler material or a self-supporting preform and infiltrating the mass of filler or preform with the polycrystalline ceramic matrix, which grows until it contacts the barrier means.
The process of the present invention comprises a method for fabricating shaped monolithic ceramics and ceramic composites through displacive compensation of porosity, and ceramics and composites made thereby. The method of the present invention includes three basic steps: 1) Synthesis or other acquisition of a porous preform: 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, N.sub.B X.sub.C (s): where MX.sub.C/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.
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, N.sub.B X.sub.C (s): AM(l)+N.sub.B X.sub.C (s)=AMX.sub.C/A (s)+BN(l/g) where MX.sub.C/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.
