Metastable phase selection and partitioning in ZrO2-MgO processed from liquid precursors

This paper reports on aqueous mixtures of either zirconium acetate or zirconium nitrate and magnesium nitrate that were dried and subsequently pyrolyzed at fast heating rates (upquenching) to form metastable crystalline phases of ZrO2 with various degrees of MgO supersaturation. The crystallization temperature was determined to be 380 degrees C for the zirconium acetate, and 270 degrees C for the zirconium nitrate at a heating rate of 5 degrees C/min. The crystalline structures were characterized as a function of MgO content and thermal history for specimens containing 0 to 30 mol % MgO. Upquenching to 900 degrees C, where monoclinic (m) ZrO2 and MgO are the equilibrium phases, yielded single-phase tetragonal (t) ZrO2 (<8 mol% MgO), single-phase cubic (c) ZrO2 (9 to 17 mol% MgO), and two-phase c-ZrO2 + MgO structures (>17 mol% MgO). The composition for which T0(t/c) = 900 degrees C was estimated as 9 ± 1 mol% MgO