OXYGEN-DEFICIENT ZIRCONIA AND THORIA: THEIR THERMAL SHOCK RESISTANCE AND EQUILIBRIUM OXYGEN PRESSURE.
Final rept. Jun 65-May 68,
ROCKETDYNE CANOGA PARK CALIF
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Initial studies revealed that oxygen-deficient zirconia and thoria are more resistant to thermal shock conditions than the corresponding stoichiometric materials. This program was undertaken to explore and elucidate this phenomenon. To accomplish this objective, the elastic modulus E, thermal expansion a, and strength s were determined for both the oxygen-deficient and stoichiometric materials, and the ratios sEa were compared. Also, replicas of fracture surfaces resulting from thermal shock were studied by electron microscopy. In general, it was found that the increased resistance to thermal shock exhibited by the oxygen-deficient material is not due to any intrinsic differences caused by the oxygen deficiency. Rather, it appears that the metal phase precipitated in the grain boundaries of the oxygen-deficient material provides better intergranular bonding and a means of inhibiting crack propagation to give improved strength. The equilibrium pressure of oxygen over zirconia and thoria was measured over the temperature range 1000-1900C, and the location of the ZrO2-x - Zr boundary was determined microscopically. The results of these measurements are discussed in terms of thermodynamics. Author
- Ceramics, Refractories and Glass