The system zirconia-scandia was investigated using X-ray diffraction analysis, differential thermal analysis, metallographic analysis, and melting point studies. Results reveal the monoclinic a1 phase (0 to2 mol% sCzO3), the tetragonal a,' phase (5 to 8% Sc2O3), the rhombohedral p phase (9 to 13% ScZO3), the rhombohedral y phase (15 to 23% SCZO~), the rhombohedral 6 phase (24 to 40% SCZO~), and the cubic E phase (77.5 to 100% SczO3). The monoclinic a1 phase and the tetragonal a,' phase were found to transform to the tetragonal a, phase over a wide temperature range depending on composition. The p, y, and a phases transformed to a cubic phase at temperatures of =600", 1100", and 1300"C, respectively. A maximum melting point of =2870"C was found at -10% ScZO3 and a eutectic at ~2400°C at 55% Scz03.
Patterson Air Force Base, Ohio 45433, and University of Illinois at The Zr0,-Hf02 system was investigated by metallographic, X-ray diffraction, and microprobe analysis using arc-melted samples which had been annealed and quenched. T h e monoclinic-tetragonal inversion was investigated by DTA and high-temperature X-ray diffraction analysis. Results reveal that zirconia and hafnia a r e completely miscible in all proportions in the binary system. Within experimental error, the melting points of t h e compositions lie roughly on a straight line connecting t h e melting points of oxides. There is a continuous increase in the monoclinic-tetragonal inversion temperature as the composition moves from ZrOs to Hf02. T h e lattice parameters of the monoclinic phase follow smooth curves which have a negative deviation from Vegard's law.
The vertical section Ti-ZrO, within the Ti-Zr-0 system was investigated by metallographic, X-ray diffraction, electron probe, and melting point studies. Analyses were conducted using arcmelted specimens which had been equilibrated and quenched from temperatures of 6 0 0 O to 16OOOC. The Ti-ZrOl section is similar to the Zr-ZrO, system. At high temperatures, considerable amounts of Zr and 0 go into solid solution in Ti, stabilizing a-Ti to 30 wto/, ZrO,. From 30 to 98 wt% ZrOI an a-Ti + ZrO, region is defined, and a t compositions above 98 wp/, ZrO,, single-phase ZrO,(ss) exists. At low temperatures an a-Ti+ (Ti,Zr),O field exists from 22 to 32 wt% ZrO?; this region decreases in size with increasing temperature until it disappears at 1200°C. Above 32 wC% ZrO,, a three phase a-Ti+ (Ti,Zr),O+ ZrOL field exists; its stability extends from 1200°C a t 30 wvo ZrOz to <500°C at z 7 7 wto/, ZrOL.
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