paper

Chemical Influences on Ice Crystal Growth from Vapor

arXiv:1101.0127

Abstract

We present an investigation of chemical influences on the growth of ice crystals from water vapor. In one set of experiments, we grew ice crystals in a vapor diffusion chamber, observing crystal morphologies at temperatures from 0 C to -25 C in different background gases and with a variety of gaseous chemical additives. In a second set of experiments, we measured ice crystal growth rates at -5 C and -15 C in a free-fall flow chamber, using normal laboratory air and ultra-clean nitrogen gas, both with and without chemical additives. Conclusions from these experiments include:\ 1) In nitrogen gas at a pressure of one atmosphere, no tested chemical additives at concentrations below 10 ppm produced any observable changes in ice crystal growth morphologies; 2) Growth in ultra-clean nitrogen gas was not significantly different from growth in ordinary laboratory air; 3) Chemical additives affected plate-like dendritic growth at -15 C more readily than growth at higher temperatures; 4) Chemical additives tended to promote the growth of columnar crystals over plate-like crystals; 5) Ice growth in air, nitrogen, helium, argon, hydrogen, and methane gases at a pressure of one atmosphere yielded essentially the same temperature-dependent crystal morphologies.

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