A study of metal ignitions II. The spontaneous ignition of zirconium

Abstract

In continuation of an investigation of the spontaneous ignition of titanium, the behavior of zirconium was determined. It was found that zirconium sheet, varying in thickness from 0.010 to 0.250 in., could be ignited by exposing it rapidly to oxygen under pressure. The ignition limits, in terms of oxygen pressure and concentration, necessary to produce spontaneous ignition, were determined for zirconium and Zircaloy. Ignition resulting from the breaking of 1 4 in. bars (in tension) was also investigated. The ignition limits were of the same order of magnitude, that is about 500 p.s.i.g. of oxygen. One of the most interesting aspects of these phenomena is the relative unimportance of the protective oxide layer. Where oxide-free samples required a minimum oxygen pressure of about 300 p.s.i.g. for spontaneous ignition, oxidized samples would be ignited with about 450 p.s.i.g. of oxygen. This suggests that under some conditions an oxide layer does not result in a diffusion-controlled mechanism.