Journal of Colloid and Interface Science, Vol.309, No.2, 412-418, 2007
Grain sizes, surface areas, and porosities of vapor-deposited H2O ices used to simulate planetary icy surfaces
Mean grain sizes and specific surface areas (SSAs) of ice substrates formed by vapor deposition at low temperatures are of importance in simulating external surfaces of icy satellites in the solar system. Environmental scanning electron microscopy (ESEM) was used to obtain granule sizes and to observe the phase of ice granules prepared on borosilicate, silicon, and metallic plates. Ices prepared at a temperature lower than 140 K appear to be amorphous, and their granule sizes are typically submicrometer. At slightly warmer temperatures, near 180-200 K, ice films are composed of either hexagonal or cubic granules with sizes up to a few micrometers. When briefly annealed to even warmer temperatures, ice granule sizes approach similar to 10 mu m. SSAs of ice substrates were determined from BET (Brunauer, Emmett, and Teller) analysis of gas adsorption isotherms in the temperature range from 83.5 to 261 K. SSAs decrease drastically from 102 m(2)/g at 83.5 K to 0.87 m(2)/g at 150 K and further decrease slowly to 0.22 m(2)/g at 261 K, suggesting that the transition from amorphous to crystalline forms occurs at similar to 150 K. The overall decrease in SSAs is primarily due to metamorphism and sintering. These results are comparable to recent field and laboratory measurements. Possible implications for theoretical models of icy satellites of outer planets using remote sensing techniques are also discussed. (C) 2007 Elsevier Inc. All rights reserved.