tailieunhanh - Electromotive Force and Measurement in Several Systems Part 10

Tham khảo tài liệu 'electromotive force and measurement in several systems part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 7 Electromotive Force Measurements in High-Temperature Systems Dominika Jendrzejczyk-Handzlik and Krzysztof Fitzner AGH University of Science and Technology Laboratory of Physical Chemistry and Electrochemistry Faculty of Non-Ferrous Metals Krakow Poland 1. Introduction Stability of phases existing in chemical systems is determined by its Gibbs free energy designated as G. The relative position of Gibbs free energy surfaces in the G-T-X composition space determines stability ranges of respective phases yielding a map called the phase diagram. Since the knowledge of phase equilibria is essential in designing new materials determination of Gibbs free energy for respective phases is being continued on both theoretical as well as experimental ways. While in principle chemical potentials of pure substances are needed to derive Gibbs free energy of formation of the stoichiometric phases it is not the case for the phase solid or liquid with variable composition. As an example in Fig 1 AGm for three different systems is shown. shows free energy of formation of the intermetallic stoichiometric Mg2Si phase recalculated per one mole of atoms Turkdogan 1980 . Figlb illustrates Gibbs energy of formation of one mole of liquid In-Pb solution Hultgren 1973 . Finally demonstrates Gibbs energy of formation of the solid phase wustite FeO Spencer Kubaschewski 1978 . Fig. 1. Gibbs free energy of formation of a stoichiometric Mg2O phase b liquid In-Pb solution c solid phase FeO wustite. In the last two cases experimental information about chemical potentials of both components in the solution partial Gibbs energies was necessary to obtain AGm vs. composition dependencies at fixed temperature. 126 Electromotive Force and Measurement in Several Systems In general there are four experimental methods namely calorimetry vapour pressure electrochemical and phase equilibration one can use to obtain thermodynamic functions which describe properties of respective phases solid or .

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