Nonstationary nucleation (explosive crystallization) in layers of amorphous ice prepared by low-temperature condensation of supersonic molecular beams

Layers of amorphous ice were prepared by deposition of supersonic molecular beams of rarefied vapor on a substrate cooled by liquid nitrogen. Molecular beam entered a vacuum chamber through Laval nozzle, which accelerated it to a supersonic speed. An adiabatic expansion of molecular beam leads to a decrease in the temperature at the nozzle outlet and formation of crystalline nanoclusters of water. Under heating of nonequilibrium condensates one could observe a glass transition (softening) and subsequent spontaneous crystallization. The presence of water clusters introduced into nonequilibrium condensates artificially ensured conditions for the initiation of “hot” centers and a transition to an explosive regime of crystallization in an amorphous medium. A theoretical analysis has been made of the role of the thermal conditions in which the crystallization of an amorphous substance proceeds, with allowance for the nonstationary nucleation.