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Comparison is made among calculated heats of formation of ordered transition metal compounds, experimental heats obtained by Kleppa and coworkers, and parameters appropriate to CALPHAD constructs. The calculated heats are precise representatives of band theory granted the class of local density potential which was employed; comparison with experiment suggests that they are less accurate than is desired. The issue of the stability of excited phases against local distortion is explored indicating that some systems,which are normally presumed to be metastable, are not. This has consequences for CALPHAD phase diagram constructs and suggests that entropy is an important contribution to the local stability of some high- temperature phases.

Based on an assessment of the available experimental thermochemical and phase diagram information available, the phase equilibria of the C-Hf-Zr system were calculated. The G of the individual phases was described with thermodynamic models. The liquid phase was described as a substitutional solution using the Redlich-Kister formalism for excess G. Graphite was treated as a stoichiometric phase. The solid solutions of carbon in α(Hf,Zr) and β(Hf,Zr), as well as the non-stoichiometric phase (Hf,Zr)C1−x, were represented as interstitial solid solutions using the compound energy model with two sublattices. The parameters in the models were determined by computerized optimization using selected experimental data. A detailed comparison was made between calculation and experimental data.

The interfacial reactions of FeO/Cr, Cu2O/Ni, Cu2O/Fe, and Ti/Al2O3 at elevated temperature and the corrosion behavior of low Cr steels in an aqueous system in a CO2 environment were analyzed by applying the chemical potential diagrams for the Fe-Cr-O, Cu-Ni-O, Cu-Fe-O, Ti-Al-O, Fe-C-O-H-e-, and Fe-Cr-C-O-H-e- systems. These diagrams were constructed using the Gibbs energy changes for formation of the compounds involved. The reaction paths and the diffusion behavior of these interfacial reactions were reasonably explained by a simple model based on a steady state approximation and local equilibrium at the interface, which predicts that the reaction path should be represented by simple lines in the chemical potential diagrams.