不一致凝固中晶核形成的自由能：模拟1型极地平流层云中含水硝酸液滴结晶的意义
Free energy of formation of a crystal nucleus in incongruent solidification: Implication for modeling the crystallization of aqueous nitric acid droplets in type 1 polar stratospheric clouds
摘要：
利用经典成核理论的形式，我们推导出一个表达式的可逆功$W_*$形成的二元晶核在液体二元溶液的非化学计量组成（不一致结晶）。与MacKenzie、Kulmala、Laaksonen和Vesala（MKLV）的常规表达式[J.Geophys.Res. 102，19729（1997）]相比，新表达式应用于含水硝酸（NA）液滴的结晶，更充分地考虑了硝酸蒸气的影响。通过使用现有的实验数据对与极地平流层云（PSC）相关的含水NA液滴的不一致结晶进行比较，MKLV和修改后的表达式的平均液-固界面张力$σ^{ls}$的硝酸二水合物（NAD）晶体的预测。基于MKLV表达的预测比基于我们修改的表达的预测高约5%。这导致NAD晶核的固-气界面张力$σ^{sv}$的两个表达式的预测之间的类似差异。后者可以通过分析的晶体成核率在水溶液NA液滴的实验数据和利用的优势，在小液滴和其在大的晶体成核的表面刺激模式的忽略不计。应用该方法，我们的$W_*$表达式提供了NAD的$σ^{sv}$在92 dyn/cm至100 dyn/cm范围内的估计，而MKLV表达式预测其在95 dyn/cm至105 dyn/cm范围内。$W_*$的两个表达式的预测成为一致的结晶的情况下，这也证明了我们的方法的成核的硝酸三水合物（NAT）晶体在PSC液滴的化学计量组成。
英文摘要：
Using the formalism of the classical nucleation theory, we derive an expression for the reversible work $W_*$ of formation of a binary crystal nucleus in a liquid binary solution of non-stoichiometric composition (incongruent crystallization). Applied to the crystallization of aqueous nitric acid (NA) droplets, the new expression more adequately takes account of the effect of nitric acid vapor compared to the conventional expression of MacKenzie, Kulmala, Laaksonen, and Vesala (MKLV) [J.Geophys.Res. 102, 19729 (1997)]. The predictions of both MKLV and modified expressions for the average liquid-solid interfacial tension $σ^{ls}$ of nitric acid dihydrate (NAD) crystals are compared by using existing experimental data on the incongruent crystallization of aqueous NA droplets of composition relevant to polar stratospheric clouds (PSCs). The predictions based on the MKLV expression are higher by about 5% compared to predictions based on our modified expression. This results in similar differences between the predictions of both expressions for the solid-vapor interfacial tension $σ^{sv}$ of NAD crystal nuclei. The latter can be obtained by analyzing of experimental data on crystal nucleation rates in aqueous NA droplets and exploiting the dominance of the surface-stimulated mode of crystal nucleation in small droplets and its negligibility in large ones. Applying that method, our expression for $W_*$ provides an estimate for $σ^{sv}$ of NAD in the range from 92 dyn/cm to 100 dyn/cm, while the MKLV expression predicts it in the range from 95 dyn/cm to 105 dyn/cm. The predictions of both expressions for $W_*$ become identical in the case of congruent crystallization; this was also demonstrated by applying our method to the nucleation of nitric acid trihydrate (NAT) crystals in PSC droplets of stoichiometric composition.
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