高压条件下输运系数的熵标度关系和Stokes-Einstein关系对金属熔体的适用性研究

The transport properties of liquid metals under high pressure conditions are of central importance to the evolution and dynamics of the Earth, and also play an important role in the design and preparation of advanced materials. However, a consensus about the transport properties of liquid metals under pressure has not yet been reached. According to the entropy scaling law (ESL) for transport coefficients, the transport coefficients of liquids can be expressed as single-valued functions of the excess entropy. In the Stokes-Einstein relation (SER), the product of self-diffusion coefficients and viscosity linearly depends on the temperature. The validities of the ESL and SER have been studied for a number of liquids under ambient pressure conditions, and found that the ESL holds well for simple liquids but fail for some complex liquids, the SER works as a good approximation at temperature above a guard temperature. To the best of our knowledge, the validities of the ESL and SER for realistic liquid alloys under high pressure conditions, however, is not clear. To solve these problems, we file the application. The iron-based, copper-based, and zirconium-based alloys will be used to simulate the transport process of liquid metals under high pressure conditions, in this work. We attempt to clarify the validity of the ESL and SER for realistic liquid alloys under high pressure conditions, establish the range of validity, and propose a way (or parameters) to predict the validity. We believe that this work will provides theoretical foundation for the application of the ESL and SER in liquid alloys under high pressure conditions, and a useful ingredient in understanding transport properties of planet’s cores and designing of advanced materials.

高压下金属熔体输运性质的研究不仅在地球物理领域具有重要意义，而且可以为新材料合成与制备技术的发展提供理论指导。然而，人们对高压下金属熔体输运性质的认识还存在很大差异。输运系数的熵标度关系 (ESL) 将输运系数表示为过剩熵的单值函数，在Stokes-Einstein关系 (SER) 中自扩散系数和粘度系数的乘积与温度成正比。常压条件下的研究表明：ESL适用于简单液体，但对一些复杂液体却不使用；SER对合金熔体只在某一转变温度之上成立。然而，它们在高压下的适用性却未得到系统研究，为此我们提出了本项目的申请。项目拟通过模拟高压下铁基、铜基、锆基等合金熔体的输运过程，探讨输运性质和结构性质之间以及扩散和粘度之间的关系，论证ESL和SER在高压下的适用性，明确适用条件，寻找预测（判断）适用性的方法（参数）。从而为其在高压熔体中的应用提供理论依据，为深入了解地球、开发新材料提供理论参考。

高压下金属熔体输运性质的研究具有重要意义，Stokes-Einstein关系 (SER) 和输运系数的熵标度关系 (ESL)在熔体输运性质之间以及输运性质同结构性质之间建立了桥梁。本项目通过模拟铁基、铜基、锆基、镍基等合金熔体在较大温度和压强范围内的输运性质和结构性质，系统研究了ESL和SER在合金熔体中的适用性，给出预测（判断）适用性的参数、方法。首先，合金熔体的粘度和组分原子扩散系数随温度和压强的变化关系的研究表明：当压强保持不变时，在高温范围内输运系数随温度的变化服从Arrhenius关系，在低温范围内服从non-Arrhenius关系；当保持温度不变时，在低压范围内和高压范围内组分原子的扩散系数随压强的变化满足不同的指数关系，而粘度系数随压强的变化在整个压强范围内满足同一指数关系。其次，关于SEL和ESR适用范围的研究表明：在恒压条件下SER在两倍的玻璃化转变温度以上的温度范围内对于合金熔体适用；在恒温条件下SER在转变压强以下对合金熔体适用，该给定温度为转变压强条件下合金熔体的玻璃化转变温度的两倍；SER的适用范围与ESL的适用范围相近。关于适用性预测方法和参数的研究表明：SER的失效源于合金熔体的组分原子扩散系数的解耦，而组分原子扩散系数的解耦可以归因于组分原子局域原子结构的解耦。组分原子扩散系数的解耦和局域原子结构的解耦可以分别用自扩散系数的比值和偏对关联熵的比值随温度的变化表示。并且偏对关联熵的比值很容易从实验数据（对分布函数）得到，可以用来预测ESL和SER在合金熔体中的适用性。