The fabrication of near net-shaped spinel bodies by the oxidative transformation of Mg/Al2O3 precursors

The feasibility of transforming shaped Mg-Al2O3-bearing precursors into mon olithic spinel (MgAl2O4) bodies with a retention of shape and dimensions ha s been demonstrated. Dense, shaped precursors (disks, bars) were fabricated by the pressureless infiltration of molten Mg into porous Al2O3 preforms. After solidification (and machining, in the case of bar-shaped specimens), the Mg-bearing precursors were oxidized in flowing O-2(g) at 430-700 degree s C. Postoxidation annealing at 1200 degrees C resulted in the conversion o f MgO and Al2O3 into MgAl2O4. After sintering at 1700 degrees C, spinel bod ies that retained the precursor dimensions (to within 0.65%) were produced. Phase and microstructural analyses at various stages of processing are dis cussed.