Mechanism of the Reaction of Hydrogen with Zirconium: I . Role of Oxide Films, Pretreatments, and Occluded Gases

Abstract

Previous studies have shown the reaction of zirconium with hydrogen to be sensitive to surface preparation, surface films, heat treating cycles, cold working of the metal, and nonmetallic impurities.Experiments were made on the rate of reaction of high purity zirconium with pure hydrogen using a sensitive microbalance method, and an all glass and ceramic vacuum system to minimize contamination.The effect of a preliminary vacuum heating cycle on rate of reaction with hydrogen at 150°C was studied by varying the temperature of the vacuum heating cycle from 150° to 700°C. Samples having the room temperature oxide present showed only a slow rate of reaction, while samples heated to 700°C for one hour showed a rate of reaction 7700 times as great. Results also showed that the oxide film was effectively removed by heating in a vacuum for one hour at 500°C.A study was made of the thickness and nature of the oxide film. Thus, the film formed in air at room temperature was more resistant to hydrogen attack than thicker oxides formed at higher temperatures. Studies on the effect of small quantities of oxygen and nitrogen in solid solution indicate only minor effects. Results suggest that considerable revision is necessary in concepts of the mechanism of the hydrogen reaction on metals.