Threshold Effects and Auto Wave Processes in Low-Temperature Chemical Reactions in Irradiated Solids

Abstract

Abstract Fast self-propagating chain reactions (such as chlorination of hydrocarbons, hydrobromination of olefines, and polymerization) can be initiated at low temperatures (down to 4.2 K) by a local mechanical fracture of vitreous and polycrystalline samples which contain stabilized active centres (free radicals) accumulated during previous irradiation by 60Co γ-rays. The dependence of the reaction rate on the strength of a triggering mechanical impact (as well as on the concentration of preaccumulated active centres) is found to be of the threshold type. A sharp isothermal rise in the rate of a chemical reaction synchronous with local brittle fracture, and observed regularities of the reaction zone propagation along an extended sample, distinguish the process from classical thermal self-propagation. In all the systems studied the initial fracture produced autowave propagation of the reaction front along the sample with a rate much above that of heat transfer but much below the sound velocity. The jerky nature of the reaction front motion is established. The suggested treatment of the new observed phenomena is based on the positive feedback between the mechanically triggered and accelerated (via various heterogeneous factors) chemical reaction in irradiated low-temperature solids and the further mechanical impact to the samples caused by this reaction.