Atmospheric corrosion tests of several delta phase alloys of plutonium

Abstract

A study of the oxidation of delta-phase, binary plutonium alloys containing small additions of aluminum, cerium, hafnium, zinc and zirconium has been conducted. The oxidation rates at 75° C in moist air are all lower than the oxidation rate of unalloyed plutonium under the same conditions. The results do not appear to be in accord with the simple theory of the influence of solute additions on the oxidation rate as proposed by Wagner and Hauffe. A size rule was suggested for deciding a priori whether a solid-solution miscibility gap between oxide phases might occur. This rule was only partially successful in predicting which oxide phases would be observed to form separate layers. It is interesting that the zirconium and hafnium alloys were found to form ZrO 2 and HfO 2 as separate phases in the oxide layer. These separate oxide phases are to be expected on the basis of the size-factor rule discussed above. There is no evidence, however, that Al 2O 3 or ZnO, in which smaller metal-oxygen distances occur, were present as separate phases in the oxidation products. For thermodynamic reasons, ZnO should not appear in the products. The special reasons that Ce 2O 3 and Al 2O 3 might not be detected have been discussed. The analyses of Wagner concerned with the formation of single or duplex oxide films have been discussed and it is shown that the formation of HfO 2 and ZrO 2 as well as Al 2O 3 and Ce 2O 3 should occur. The apparent reduction in rates can be rationally interpreted on this basis.