Effect of Solution Heat Treatment on Corrosion Kinetics Of Zirconium in 20 Percent Hydrochloric Acid At High Temperature and Pressure

Abstract

Abstract An investigation has been made of the influence of amount and distribution of precipitate phase on the corrosion kinetics of “low purity” zirconium in 20 percent hydrochloric acid at 200 C. It was found that minimum corrosion rates, coincident with minimum values of activation energy and frequency factor in the Arrhenius relationship, were obtained by solution heat treatment at 700 C followed by water quenching. Such heat treatment gave a corrosion rate equivalent to that of alpha annealed iodide zirconium. A maximum corrosion rate was obtained by a beta solution treatment at 890 C followed by water quenching, whereas beta solution treatment at 1000 C gave sharply reduced corrosion rates. Nature of distribution of the precipitate phase profoundly influenced corrosion rate. A discontinuous pattern of intergranular and transgranular globular particles was substantially less deleterious than the same amount of impurity phase finely disseminated throughout the microstructure. The results of the investigation are discussed in terms of the possible roles of chlorine and hydroxyl ions in the corrosion mechanism. Relative effects on corrosion kinetics of statistical distributions of active sites (each characteristic of lattice configurations produced by lattice defects, solute atoms and precipitation phenomena) are also considered.