AMORPHOUS SOLIDS IN WATER AND ICE: A REVIEW

Abstract

Amorphous forms are non-crystalline materials which possess no long-range order. Amorphous solid water is most abundant form of solid water in the universe. Its saturation vapor pressure and thermodynamic properties, however, are still a topic of research by the scholars. We have investigated the saturation vapor pressure over vapor-deposited amorphous ice at temperatures between 133 and 147 K using a novel experimental method (1). The new method determines the absolute vapor pressures and the sublimation rates by measuring the mass growth rates of ice-covered nanoparticles under supersaturated water vapor conditions. It is observed that the vapor pressure of amorphous solid water is up to a factor of 3 higher than that predicted by current parameterizations, which are based in part on calorimetric measurements. The calorimetric measurements can be reconciled with data by acknowledging the formation of nano-crystalline ice as an intermediate ice phase during the crystallization of amorphous ice. The proposed value for the enthalpy of crystallization of amorphous solid water of ΔH = 2312 ± 227 J/mol, which is about 1000 J/mol higher than the current consensus. The results shine a new light on the abundance of water ice clouds on Mars and mesospheric clouds on Earth and alter our understanding of ice formation in the stratosphere. Keywords:, .