Department of Physics, Michigan Technological University, Houghton, Michigan, USA.
J Phys Chem A. 2011 Jun 16;115(23):5729-34. doi: 10.1021/jp103373u. Epub 2010 Nov 18.
Unlike reversible phase transitions, the amount of heat released upon freezing of a metastable supercooled liquid depends on the degree of supercooling. Although terrestrial supercooled water is ubiquitous and has implications for cloud dynamics and nucleation, measurements of its heat of freezing are scarce. We have performed calorimetric measurements of the heat released by freezing water at atmospheric pressure as a function of supercooling. Our measurements show that the heat of freezing can be considerably below one predicted from a reversible hydrostatic process. Our measurements also indicate that the state of the resulting ice is not fully specified by the final pressure and temperature; the ice is likely to be strained on a variety of scales, implying a higher vapor pressure. This would reduce the vapor gradient between supercooled water and ice in mixed phase atmospheric clouds.
与可逆相变不同，亚稳过冷液体冻结时释放的热量取决于过冷程度。尽管地球上的过冷水无处不在，对云动力学和成核有影响，但对其冻结热的测量却很少。我们已经进行了在大气压力下冻结水释放热量的量热测量，作为过冷度的函数。我们的测量表明，冻结热可能大大低于从可逆静力学过程预测的值。我们的测量还表明，最终压力和温度并不能完全确定所得冰的状态；冰可能在各种尺度上受到应变，这意味着蒸气压更高。这将降低混合相大气云中过冷水和冰之间的蒸汽梯度。
