Dissolution of the oxide film on zirconium

The conductivity of anodic and corrosion films on zirconium was found to increase during heating in vacuum. The conductivity changes at 450~ were studied on anodic films which were 0.6, 0.75, 0.9, and 1.5 ~ in thickness. The change in conductivity was attributed to the diffusion of anion vacancies into the oxide with an estimated diffusion coefficient of 4 • 10 -1~ cm 2 sec -1. Corrosion films produced in water at 350~ appeared to have higher diffusion coefficients. Among the materials zirconium, Zircaloy-1, and Zircaloy-2, specimens of zirconium had the highest corrosion rates and diffusivities (as judged by the conductivity changes). Consequently, an effect of vacuum heating on corrosion was expected and subsequently confirmed. Enhanced oxide growth was observed after corroded specimens were heated at 600~ for 1 min. The increase in weight gain was greater than would be expected from a simple restoration of dissolved oxide.

Section: ~18contrasting

confidence: 56%

The Electrical Resistance of Oxide Films on Zirconium in Relation to Corrosion

Misch¹,

Gunzel²

1959

“…In the case of the oxidation of zirconium metal (6,7,9), there is uncertainty with regard to the nature of the rate law (cubic or parabolic) and the activation energy (18-47 kcal/mole). The oxidation is further complicated by the dissolution of oxygen in the metal (23,24). It is evident, however, that the activation energy for the oxidation of ZrO,.~, 58.0 kcal/mole, is higher than the activation energies found for the oxidation of zirconium.…”

Section: ~mentioning

confidence: 92%

Oxidation and Equilibrium in Nonstoichiometric Zirconium Dioxide Powder

Aronson

1961

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.

“…The thicknesses calculated by Eq. [3] were compared with those determined by an interference color method (22,23) standardized during the present work. At 408~ and an exposure time of 500 hr the thickness for zirconium was 540A calculated by Eq.…”

Section: Resultsmentioning

confidence: 99%

Oxidation of Zirconium and Zirconium Alloys in Liquid Sodium

Mackay¹

1963

The oxidation of zirconium and several zirconium alloys was investigated in the temperature range 400~176 in a static liquid sodium system with oxygen concentration approximately 10 ppm. A transition from a parabolic to a linear rate of oxidation was observed in the temperature region 400~176 for all of the zirconium alloys except Zircaloy-2. Above 500~ the transition was not observed, and a protective film continued to form. Using the parabolic rate equation to describe the kinetics of oxidation, activation energies of 52.9 • 0.5 kcal/mole for unalloyed Zr and 45.3 _+ 1.5 kcal/mole for zirconium alloys were found.