Study of Condensation and Crystallization Processes During the Formation of Gas Hydrates in Supersonic Jets

The stability of gas-saturated layers of amorphous ice created via the deposition of supersonic molecular beams of rarefied water vapor and methane on a substrate cooled with liquid nitrogen was experimentally studied. The adiabatic expansion of the molecular vapor beam at the exit from the supersonic nozzle leads to a decrease in temperature and the formation of crystalline nanoclusters in the flow. The presence of ready crystalline centers in nonequilibrium amorphous condensates shifts the onset of crystallization to low temperatures. The shape of the signal of differential thermal analysis, which consists of several exothermic peaks, indicates crystallization from different centers and a random nature of their distribution in the volume of the amorphous medium. Methane hydrate forms during the crystallization of water-gas condensates. Under conditions of deep metastability, the avalanche-like nucleation of crystallization centers captures gas molecules; therefore, they are not displaced by the movement of the crystallization front.