![Sample our Physical Sciences journals, sign in here to start your FREE access for 14 days]({"type":"image" , "src" : "/sda/110819/TOC-Subject-Sample-2021-Physical-Sciences.jpg"})
Abstract
Fresh UN powder of a medium particle size (0.3 m2/g) prepared by nitridation of U powder was exposed to O2 at room temperature in a constant volume apparatus. Oxidation was followed by pressure measurement. Under O2 pressures higher than 3 mmHg the powder ignited instantaneously, probably due to local heating in the surface layers of the powder particles. When the O2 pressure was lower, oxidation proceeded in two clearly distinct stages, without N2 release. The first stage terminated instantaneously. Irrespective of differences in powder conditions and pressure, the amount of O2 absorbed in the first stage was found almost invariably to be about 1.7 cm3 STP/m2, which corresponds to the formation of an oxidized layer somewhat thicker than 18Å. The powder particles covered with this layer did not ignite even under 1 atm O2. This oxide coating could be of practical utility for protection against ignition. The second stage proceeded very slow and could be completely suppressed by cooling.