Diffusion of Oxygen in Zirconium and Its Relation to Oxidation and Corrosion

Abstract

The diffusion of oxygen in zirconium and dilute zirconium alloys has been studied in the temperature range of 400° to 5857deg;C by observing the rates of dissolution of anodically deposited interference oxide films. The diffusion coefficient of oxygen in zirconium depends on the grain orientation and varies by a factor of two among different orientations. Macroscopically observed average values obey the equation D,cm2/sec=9.4exp][ )(−51,780±220/RTwhere the activation energy for the diffusion of oxygen in zirconium is 51.78 kcal/mole. No macroscopic differences were observed in the diffusion coefficients of the various dilute alloys. Oxidation and corrosion rates have been observed to have an orientation dependence similar to that observed in the diffusion study. The mechanism of oxidation and corrosion is discussed in terms of diffusion of oxygen and adherence of oxide films.

Corrosion of Fusion Welded Magnesium-Aluminum Alloy, AZ31: Effects of Microstructure and Composition in Isolated Weld Zones

“…Mg was additionally tested in a range of environments in this work. A well-defined inductive loop was seen in both this study (not shown) and the literature 38,39,44,[82][83][84] when HP Mg and AZ31B were tested in MgCl 2 solution; also reported in NaCl + Subsequently the AC current density cannot fluctuate with coverage and R t overestimates R P . In order to fully capture this characteristic response of Mg, the inductive loop must be analyzed in the determination of corrosion rate when it appears in the data and R P must be calculated by considering low frequency EIS data even if Z" is positive by extrapolation to the zero frequency…”

“…This last point merits specific attention, since recent criticisms of EIS for Mg have suggested that EIS determined corrosion rates are significant underestimations of the actual rate determined by mass loss and are very similar to corrosion rates determined from a simple three component (Randle's type) equivalent circuit to determine R t 86 . It is however noted that in that work 86 , there was no concurrent validation via ICP-OES (as herein), and the values of B used were below any ever reported (included the authors own), whilst finally the inductive loop is an irrefutable feature of the data (documented by many 38,39,44,50,[82][83][84][87][88][89] ) and it cannot be summarily ignored. As such, a method for treating EIS data for Mg, based on analyses of R p and more typically reported Tafel slope values, is included in the present paper.…”

“…It has been reported that these IMPs appear in weld structures after processing for a multitude of processes (i.e., TIG, laser welding, FSW) [84][85][86][87] . The presence of these phases will therefore affect the subsequent corrosion properties of the weld.…”

“…In low [Cl -] environments, the corrosion rate decreases as the grain size decreases. 84,85 However, in more aggressive environments, such as 0.6 M NaCl, the opposite trend was seen. 86,87 Also, there has been little experimental evidence to explain why these trends are seen.…”

TOTAL HEMISPHERICAL EMISSIVITY OF PRE-OXIDIZED AND UN-OXIDIZED ZR-2.5Nb PRESSURE-TUBE MATERIALS AT 600 °C TO 1000 °C UNDER VACUUM

“…The dissolution rate of the oxide layer inside Zr-2.5Nb alloy is required to model this phenomenon and quantify its behaviour. Earlier oxide dissolution studies are limited to pure zirconium at low temperatures below 600°C [12,13], and thus provide some guidance for determining the oxide dissolution (and re-oxidation) kinetics in Zr-2.5Nb alloy pressure-tube materials. Increasing the initial oxide layer thickness in the Zr-2.5Nb pressure-tube material is expected to provide a thicker oxide layer that would remain after heating within the high temperature range of 600°C to 900°C.…”