"活度"质疑

为研究二元系溶液中组元摩尔分数和气相中蒸气压的规律,考察了48个化合物在熔点固液相变的熔化熵变,发现相变时没有发生显著的化合物分解.在假设二元系溶液中存在化合物分子的情况下,组元在全浓度范围符合拉乌尔定律,不存在Lewis定义的"活度";通过与Mg-Si、In-Sb和Fe-Mn三个二元系实测活度结果对比,证实了计算的平衡摩尔分数即为活度值,二元金属熔体不存在所谓"活度"的观点.推导了在二元系金属熔体存在一个金属间化合物条件下平衡的摩尔分数的通用公式,以及相应的A2B或AB型金属间化合物的一般公式.将二元系溶液划分为大于纯组元熔点的温度、小于纯组元熔点温度但高于液相线和低于液相线的三个区间,提出了适应不同区间的广义拉乌尔定律的关系式.

Activity query

To investigate the laws relating to the mole fraction of a component in a binary solution and its vapor pressure,the entropies of dissolution from the solid phase to the liquid phase of 48 typical compounds were assessed and the compounds were confirmed to not decompose during the phase transition processes.Under the condition where a compound also exists in a binary liquid melt,both of the components in the whole concentration range obey Raoult's law.Specifically,there is no such thing as an "activity" as defined by Lewis.The so-called "activity" is actually the balance mole fraction in the case where all components in the system are considered by comparing with the measured activity data for Mg-Si,Sb-In,and Fe-Mn binary systems.It is verified that the calculated equilibrated mole fraction represents the activity,thereby the binary metallic melts involve no activity.In addition,a general formula is deduced for the equilibrium mole fraction in the binary system in the case where the melt contains one intermetallic compound.In particular,the cases corresponding to A2B-type or AB-type intermetallic compounds were discussed.Finally,a broad sense Raoult's law was proposed that it is applicable in all three regions in binary solution divided by different temperatures:(I)the region corresponding to temperatures above the melting point of the component,(II)the region corresponding to temperatures lower than the melting point of the pure component but greater than the liquidus temperature,and(III)the region corresponding to temperatures lower than the liquidus temperature.