PHASE EQUILIBRIA IN THE ZrO2–Yb2O3 SYSTEM AT 1100 °С

Abstract

Phase equilibria in the binary ZrO 2 – Yb 2 O 3 system at 1100°C were studied by X-ray diffraction and petrography in the overall concentration range. The samples of different compositions have been prepared from nitrate acid solutions by evaporation, drying, and calcinations at 1100oC. To study phase relationships at 1100°C the as-prepared samples were thermally treated in the furnace with heating elements based on Fecral (H23U5T) at 1100°C (for 12415 in air). The heating rate was 3.5°C/min. It was established that in the ZrO 2 –Yb 2 O 3 system there exist fields of solid solutions based on cubic (C) modifi cation of Yb 2 O 3 , tetragonal (T) crystal modifications of ZrO2, cubic modifi cation of ZrO 2 with fluorite-type structure (F) and δ-phase of Yb 4 Zr 3 O 12 which are separated by wide two phase fields (F + T) and (F + δ) and (δ+C). The boundaries of the homogeneity fi eld for C-Yb 2 O 3 solid solutions were determined from samples containing 80-100 mol % Yb 2 O 3 at heat treatment 1100°C (12415 h). The lattice parameter of the unit cell decreased from а = 1.043 nm in pure Yb 2 O 3 to а = 1.0402 nm for sample containing 25 mol % ZrO 2 - 75 mol % Yb 2 O 3 . The solubility of Yb 2 O 3 in the T-ZrO 2 is low and amounts to 0.5 mol%, as evidenced by XRD analysis results. It is the solid solutions based on tetragonal modification of zirconia cannot be quenched from high temperatures due to low stability of T-ZrO 2 under cooling with furnace conditions. The diffraction patterns recorded at room temperatures included the peaks of monoclinic phase M-ZrO 2 was found. The homogeneity fi eld of F-ZrO 2 in the concentration range of 85-75 mol % ZrO 2 at 1100 °C was established. The lattice parameters of the unit cell increased from а = 0.5124 nm for sample containing 85 mol % ZrО 2 -15 mol % Yb 2 O 3 to а = 0.5152 nm the two-phase (F+δ) sample containing 75 mol % ZrО 2 -25 mol % Yb 2 O 3