Ignition Behavior of Plutonium Metal and Certain Binary Alloys

Abstract

The ignition behavior of plutonium and binary alloys containing nominally 2 a/o additives was studied by two methods in air and oxygen. Ignition temperatures in both air and oxygen lie in two regimes. Cubes, 5 mm on an edge, ignite near 500°C while thin foils, less than 0.2 mm thick, ignite near 300°C. The transition from one regime to the other occurs sharply at a specific area that depends on whether ignition takes place in air or in oxygen. The existence of two regimes is consistent with a change of oxidation kinetics between 300° and 400°C which is characterized by a minimum in oxidation rate near 400°C. The effects of additives are sometimes significant and must be considered in each regime and on the position of the transition between them. In the high temperature regime: (i) Increased resistance to ignition and oxidation is found on addition of aluminum, copper, gallium, or silicon; (ii) The same ignition and oxidation behavior as plutonium occurs with addition of nickel, chromium, uranium, cerium, or iron; and (iii) Decreased resistance to ignition and oxidation results from addition of carbon, cobalt or manganese. In the low temperature regime: (i) Increased resistance to ignition and oxidation is produced by additions of aluminum, cerium, carbon, cobalt, gallium, manganese or possibly chromium; (ii) The same ignition and oxidation behavior as plutonium is obtained with addition of nickel or silicon; and (iii) Decreased resistance to ignition and oxidation follows from addition of iron or uranium.The transition from the high temperature regime to the low temperature regime does not occur in air for alloys of aluminum, cerium, carbon, or cobalt for specimens with specific areas of up to about 1 cm2/g. Addition of silicon, nickel, manganese, or uranium have little influence on the transition in air which occurs at a specific area of 1.5 cm2/g for pure plutonium. The presence of moisture had a negligible effect on the ignition temperatures of pure plutonium and the aluminum alloy.