Cold ignition of combustion-like waves of cryo-chemical reactions in solids

Fronts of weakly exothermal chemical reaction may propagate in solids at ve ry low temperatures (4 K less than or equal to T less than or equal to 77 K ) thanks to a quite unusual mechanism, involving a feedback between the hea t produced by the reaction and the disruption of the solid matrix. In this class of phenomena, the reaction may be induced by mechanical constraints, without a large elevation of temperature. On the basis of a simple phenomen ological model, we investigate ignition of a propagating front by, initiall y (i) disrupting a localized zone of the solid matrix, or by (ii) introduci ng a temperature jump, leading to a thermal shock with strong temperature g radients. In particular, we show that reaction can be initiated by disrupti ng only a very small fraction of the sample. Applications to the problem of initiation of solid explosives by friction or shocks is briefly discussed.