Oxidation and Equilibrium in Nonstoichiometric Zirconium Dioxide Powder

Abstract

Two properties of nonstoichiometric zirconium dioxide powder have been studied. Pressures of oxygen in equilibrium with ZrO2−x , with 0.03 > x > 0, have been determined at temperatures of 900°, 1000°, and 1100°C by passing hydrogen‐water vapor mixtures over the oxide. The measured pressures are in the range 10−20 to 10−12 atm. Rates of oxidation of ZrO1.975 to ZrO2 in oxygen have been measured at 500°–650°C. The activation energy for the oxidation, based on a diffusion mechanism, is 58.0 kcal/mole. A comparison of the rates of oxidation of ZrO1.975 with the rates of oxidation of zirconium metal indicates that different mechanisms are operative.

Oxygen self-diffusion mechanisms in monoclinic ZrO2 revealed and quantified by density functional theory, random walk analysis, and kinetic Monte Carlo calculations

“…In Ref. [3] we see that D tot increases with oxygen partial pressure, which hints at an oxygen-interstitial-dominated mechanism and is in agreement with our prediction. To compare quantitatively with experimentally measured values, we calculate the effective activation energies Q and effective prefactors D * by fitting the total self-diffusivity…”

“…The trend in diffusivity change from 0.03 to 0.13 atm in Ref. [3] is more reliable considering the measurements were performed on samples with the same impurity level. In Ref.…”

“…Symbols in Fig. 4(b) represent experimentally measured values at different oxygen partial pressures as noted in the legend [1][2][3]. It is clear from Fig.…”

“…References [1] and [2] measured conductivity via an 18 O diffusion experiment on ZrO 2 spheres, and Ref. [3] by measuring the oxidation rate of nonstoichiometric ZrO 2 powder to stoichiometric ZrO 2 . It is hard to eliminate the contribution of voids, grain boundaries, or other types of extended defects.…”

“…Oxygen self-diffusion in zirconium oxide has long been a topic of interest [1][2][3][4] in studying the oxidation kinetics of zirconium alloys, which are used as cladding of nuclear fuel in light water cooled nuclear reactors [5]. Zirconium oxide is also widely used in heterogeneous catalysis [6,7], and more recently it was examined for high-k dielectrics in metal-oxide-semiconductor field-effect transistor (MOSFET) devices [8,9] as well as resistive switching devices [10,11].…”