A high temperature mass spectrometric study of the thermodynamic properties of Cu-Mg solid alloys

Abstract

Received 5 June 1998; Revised 2 July 1998; Accepted 4 July 1998Studies of the Cu-Mg binary system were encouraged for technological reasons by the general interest for a better theoretical understanding of its properties, including its thermodynamics, and by the need for a simple system for examining some new experimental and computational models. In the first comprehensive studies 1-3 the general features of the Cu-Mg phase diagram were revealed by methods of microscopy and thermoanalysis, also the problems of preparation of the samples of alloys were discussed in detail. The ranges of solubility of terminal solutions of Cu and Mg were determined 4-6 by microstructure analysis and measurements of the electrical conductivity of alloys. By X-ray diffraction together with thermal analysis and micrography 7,8 the existence of the non-stoichiometric phase MgCu 2 was confirmed. More recent experimental work focused primarily on the thermodynamic properties of Cu-Mg alloys. In these studies e.m.f.9,10 and calorimetric 11-13 methods were used, as well as vapor pressure measurements.14-17 The main purpose of the theoretical studies confined to the Cu-Mg system 18,19 was to develop computational methods and to provide the data for further investigations of ternary and industrial multicomponent alloys based on Cu-Mg.Amongst the experimental methods that allow the study of the thermodynamic properties of the Cu-Mg system the Knudsen effusion mass spectrometry has an advantage, providing the simultaneous measurement of the partial vapor pressures of all components of the alloy. However, the results of Smith and Christian 14 obtained by the effusion method without a mass spectrometric analysis of the vapor phase do not fit well with the data reported by other authors and hence were not taken into account. 19,20 The values of activities reported in Ref. 20 measured by the mass spectrometric method are in better agreement with the results obtained by other methods. For a further assessment of the validity of the data found by the effusion method a more detailed analysis of these data is performed, the thermodynamic functions are derived and the results are discussed. EXPERIMENTALThe present study was carried out using the high temperature mass spectrometric Knudsen effusion method.21-23 A quadrupole mass spectrometer QMG 420 (Balzers, Liech Heinstein) was attached to a vacuum chamber containing a high temperature furnace and a temperature regulated support with an effusion cell. The assembly made it possible to perform complete vaporization experiments as well as comparison of ion currents in both direct and successive modes. A detailed description of the experimental setup can be found in Ref. 24. SamplesThe samples of Cu-Mg alloys containing 41.0, 70.5, 80.0 atomic fraction Mg were prepared in tantalum crucibles by melting pure Cu and Mg (99.99% purity). They were heated in vacuum to 50 K above the melting point and kept at this temperature for 15 min. The vertical dimensions of the resulting sample pieces (`4 mm) are suppose...

High Temperature Mass Spectrometric Study of Thermodynamic Properties and Vaporization Processes of Oxide Systems: Experiment and Modeling

“…The further development of high temperature mass spectrometric studies considered may be connected also with the modifications of various types of mass spectrometers as were done using QMS 420 mass spectrometer that was applied for the Knudsen effusion studies [16,[97][98][99] or with the creation of new original methodologies of determination of physicochemical properties such as [100] where the changes in the refractive indexes of glasses in the B 2 O 3 -SiO 2 system were calculated from the mass spectrometric experiment using the complete isothermal vaporization method.…”