Method of making core shell structured articles based on alumina ceramics having spinel surfaces

A method for preparing an alumina ceramic article comprising:

• compacting a mixture of a first concentration of particulate aluminum oxide and a second concentration of particulate zirconium oxide alloy, said zirconium oxide alloy consisting essentially of zirconium oxide and a secondary oxide selected from the group consisting of MgO, CaO, Y.sub.2 O.sub.3, CeO.sub.2, Sc.sub.2 O.sub.3 rare earth oxides, and combinations of these secondary oxides;
• wherein zirconium oxide alloy has a concentration of said secondary oxide of, in the case of Y.sub.2 O.sub.3, about 0.5 to about 5 mole percent;
• in the case of MgO, about 0.1 to about 1.0 mole percent, in the case of CeO.sub.2, about 0.5 to about 15 mole percent, in the case of Sc.sub.2 O.sub.3, about 0.5 to about 7.0 mole percent and in the case of CaO from about 0.5 to about 5 mole percent, relative to the total of said zirconium oxide alloy, said compacting further comprising forming a blank;
• providing contact between said blank and a dopant oxide selected from the group consisting of MgO, ZnO, FeO, CoO, NiO, and MnO, said contact being subsequent to said forming of said blank;
• and
• sintering said blank in contact with said dopant oxide, said sintering further comprising diffusing said dopant oxide into the shell of said blank, converting said aluminum oxide particles in said shell into cubic spinel, and converting said zirconium oxide alloy particles in said shell from a tetragonal crystal structure to cubic and monoclinic crystal structures;
• wherein said first concentration is from 50 weight percent of the total of the first and second concentrations to 75 weight percent of the total of said first and second concentrations, and wherein said first concentration is sufficient to prevent retention of said zirconium oxide alloy particles in said shell in a predominantly tetragonal crystal structure;
• whereby said prepared ceramic article has a core consisting essentially of sintered particles of (1) said zirconium oxide alloy in a tetragonal crystal structure and (2) aluminum oxide, and a shell consisting essentially of sintered particles of (a) zirconium oxide alloy in non-tetragonal crystal structures and (b) cubic spinel.