Method for making porous, crushable core having an integral outer barrier layer

A method for simultaneously forming a dense integral barrier layer on selected surfaces of a fired ceramic article and for increasing the continuous porosity content and the crushability characteristics thereby 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 aluminate, and magnesia doped alumina, the particle size of the alumina flour and the reactant figitive 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 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;
• (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, and
• (e) oxidizing at least a portion of the suboxides of alumina to form a dense integral barrier layer of alumina at the surface of the ceramic article.