Making ceramic articles having a high degree of porosity and crushability characteristics

A method for increasing the porosity and the crushability characteristics of cores and molds for investment casting including the process steps of

• (a) preparing a material composition consisting essentially of an organic binder, a reactant fugitive filler material and an alumina flour which is one selected from the group consisting of alumina, yttrium aluminate, lanthanum alumina, and magnesia doped alumina, the particle size of the alumina flour and the reactant fugitive filler material is less than about 300 microns, and the binder consists of less than 50 percent by volume;
• (b) working a portion of the material composition to produce a preform of a predetermined shape;
• (c) heating the preform in a controlled atmosphere to remove the organic binder from the preform while retaining substantially all of the reactant fugitive filler material therein and to obtain desired green strength, and
• (d) firing the preform in a controlled atmosphere to react the alumina and the reactant fugitive filler material to produce at least one or more suboxides of alumina to produce a ceramic article having a predetermined continuous porosity content, grain morphology, and crushability characteristics.