Fabrication of transparent spinel polycrystalline materials

A novel polycrystalline material of the spinel-alumina solid solution, MgO . nAl(2)O(3) (1 less than or equal to n < 3): (MgxAl(2-2x/3))Al2O4 (0.4 < x less than or equal to 1.0), was fabricated by reaction sintering using commercial spinel, magnesia and alumina powders as starting materials. The mixed powders of magnesia + alumina or spinel + alumina with the above chemical composition were sintered at 1450-1550 degrees C in air, followed by post-HIPing at 1600-1800 degrees C and 150 MPa in an Ar-gas atmosphere. The resulting polycrystalline materials showed superior properties such as about 90% in-line optical transmittance at 300-5000 nm, 250 MPa in fracture strength and 2.8 MPa m(1/2) in fracture toughness.