Phase Equilibria and Physical Properties of Oxygen‐Deficient Zirconia and Thoria

The compositions of anion‐deficient zirconia and thoria in equilibrium with O 2 were measured from 1 to 10 −6 atm and 1400° to 1900°C; for ZrO 2‐ x (po 2 in atm, and T in °K), log x∼−0.890‐[(0.400×10 4 )/ T ]‐[(log p )/6]; for ThO 2‐ x , log x∼−1.870‐[(0.340×10 4 )/ T ]‐[(log p )/6]. The ZrO 2‐ x ‐Zr boundary was located at x=0.014 at 1800°C; thoria was single‐phase over the entire range. Consistent results were obtained when O 2 /inert gas mixtures were used, but use of H 2 /H 2 O and CO/CO 2 at 1000° to 1200°C gave abnormal and, in the latter case, erratic data; side reactions in these atmospheres are inferred. The monoclinic‐tetragonal phase change of ZrO 2 and the lattice thermal expansion, room‐temperature Young's modulus, and strength properties of ZrO 2 and ThO 2 bodies were not appreciably altered by oxygen deficiency. The lattice dimensions decreased slightly with departure from stoichiometry.