Patent ID: 7828998

Claim:
A method for making a material having a controlled microstructure comprising: providing ceramic mineral material particles comprising a metal oxide dopant; consolidating a plurality of said particles into aggregates comprising a plurality of said particles; heating said aggregated particles in a reducing atmosphere under conditions of controlled oxygen fugacity so as to at least partially reduce said dopant to at least one of a lower metal oxide and free metal and form a metastable, transient liquid phase amongst said particles, said liquid phase comprising said at least one of a lower metal oxide and free metal; whereby said liquid phase promotes sintering of said aggregated particles and forms islands comprising said free metal in the interior of and on the surface of said aggregated particles; and heating in an oxidizing atmosphere said aggregated particles having said islands comprising said metal formed therein, so as to cause at least a portion of the material comprising said islands in the interior of said aggregated particles to be taken up by said aggregated particles, the talking up of the material comprising said islands forming an inner region of said aggregated particles with a plurality of voids and forming an outer shell region with fewer voids than said inner region.