Abstract

The partial and integral thermodynamic functions of mixing and evaporation for the melts of Pb–Ca system have been calculated from the vapor pressure data determined by boiling point method with involvement of published data. The formation of alloys containing <66.67 at % Ca is endothermic and accompanied by disorder growth, but it is exothermic at >66.67 at % Ca and leads to ordering in the system. Melting enthalpy of Ca₂Pb of 13 ± 1.6 kJ/mol was found from the difference in sublimation and evaporation enthalpies. Based on the data on vapor pressure for the components, Pb–Ca constitution diagram has been supplemented by the fields of liquid and vapor coexistence under atmospheric pressure and vacuum of 1.33 and 0.7 kPa. The existence of two azeotropic mixtures with calcium concentration of 37.6 and 81.3 at % and boiling points of 2217 and 1635°C (2490 and 1908 K), respectively, has been revealed. When pressure (boiling point) decreases, the composition of azeotropic mixtures change according to Vrevskii laws. The position of field borders of vapor–liquid equilibrium indicates the impossibility of separation of Pb–Ca system into metals by distillation.

中文翻译：

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铅钙体系熔体中的溶液热力学和等熵混合物

摘要

根据沸点法测定的蒸气压数据，结合已发表的数据，计算了Pb-Ca系统熔体混合和蒸发的部分和整体热力学函数。含<66.67 at％Ca的合金的形成是吸热的，并伴随无序生长，但在> 66.67 at％Ca时放热，导致系统中的有序化。Ca _2的熔融焓从升华和蒸发焓的差异中发现Pb为13±1.6 kJ / mol。根据组件的蒸气压数据，在大气压力和真空度为1.33和0.7 kPa的情况下，液体和蒸气共存的领域补充了Pb-Ca构成图。已经发现存在两种共沸混合物，其钙浓度分别为37.6和81.3 at％，沸点分别为2217和1635°C（2490和1908 K）。当压力（沸点）降低时，共沸混合物的组成根据Vrevskii定律改变。气液平衡的场边界位置表明不可能通过蒸馏将Pb-Ca系统分离成金属。