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Determination of the standard free energy of formation for niobium and tantalum silicides by means of the three different methods

三种不同方法测定铌硅化物和钽硅化物的标准生成自由能

基本信息

批准号：
14550722
负责人：
FUJIWARA Hiroyasu
金额：
$ 1.98万
依托单位：
Kyoto University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2005
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-14550722/
关键词：
silicide niobium tantalum molybdenum tungsten standard free energy of formation standard enthalpy of formation electro-motive force 熱力学起電力測定標標準生成自由エネルギー国際情報交換インド

项目摘要

The initial objective of this project is determination of the standard free energy of formation for niobium and tantalum silicides by means of EMF measurements, chemical equilibrium and Knudsen effusion method.EMF measurements : applying the silicon concentration cells using molten lithium silicate electrolyte to the niobium-silicon system, the standard free energy of formation for niobium silicides were successfully obtained. In case of the tantalum-silicon system, it was found that tantalum oxide reacts with the constituents of the electrolyte forming intermediate compound. Chemical equilibrium method : silicon distribution between the silver alloy and the mixture of the solid silicides was examined. However, sufficient time to achieve the equilibrium was considered to be unrealistic. Knudsen effusion method : the method was tried, aiming at the tantalum-silicon system, only to obtain unstable values of vapor pressure because of instrumental troubles.Because availability of the EMF method was ensured in the earlier stage of the research project, minor collection to the objectives were decided and the method was expansively applied to the molybdenum or tungsten・silicon system. These metals, molybdenum and tungsten, were known as refractory metals as well as niobium and tantalum. The EMF measurements for these systems were successfully completed. As the results of the experiments, the standard free energies of formation for two niobium silicides, two tungsten silicides and three molybdenum silicides were obtained as functions of temperature. In addition to this, applying the third low method to the results, the values of the standard enthalpy of formation at 298 K for these silicides were also obtained.

本项目的初步目标是通过电动势测量、化学平衡和Knudsen渗流法测定Nb和Ta硅化物的标准生成自由能。电动势测量：将熔融硅酸锂电解液的硅浓差电池应用于Nb-Si系统，成功地获得了Nb硅化物的标准生成自由能。在钽硅体系中，研究发现，钽氧化物与电解液的成分发生反应，形成中间化合物。化学平衡法：考察了硅在银合金和固体硅化物混合物中的分布。然而，有充分的时间来实现平衡被认为是不切实际的。克努森渗入法：针对钽硅体系，由于仪器故障，得到的蒸汽压值不稳定；由于前期保证了电动势方法的可行性，确定了对目标的少量采集，并将该方法推广应用于钼或钨硅体系。这些金属，钼和钨，被称为难熔金属，以及Nb和Ta。成功地完成了这些系统的电动势测量。作为实验结果，获得了两个Nb硅化物、两个钨硅化物和三个钼硅化物的标准生成自由能随温度的变化。此外，对计算结果应用第三低方法，还得到了这些硅化物在298K时的标准生成热值。