Means of processing and storage of information on phase diagrams

To solve many petrological problems, it is necessary to know the conditions of phase equilibria in natural geochemical systems, which are displayed gr aphically as phase diagrams. Description of a phase diagram should include: a) system name, which is usually composed of symbols, chemical formulas, o r trivial component names; b) set of variable thermodynamic parameters and their variation ranges; c) topological description of the phase diagram; an d d) quantitative model for the diagram (phase diagram metrics). The inform ation on a phase diagram in reference-books and databases should satisfy pa rticular requirements: a) completeness sufficient for understanding the pha se diagram structure (topologic completeness) and enabling one to determine a set of equilibrium phases and their compositions at any point of the pha se diagram field (metric completeness); b) agreement with the natural laws and with other diagrams having the same components; and c) inclusion of dat a evidencing the reliability of the phase diagram and the accuracy of deter mination of the spatial location of its elements and of the composition of equilibrium phases. A quantitative description of a phase diagram should permit one to determin e which of its elements contains a specified point of the field of phase co mposition and of the thermodynamic variables of the phase diagram, as well as to estimate the compositions of all equilibrium phases at this point. Th e authors present the requirements to quantitative information on a phase d iagram (accuracy of description of experimental data, agreement of the phas e diagram elements with each other and with reference data, absence of fals e peculiarities which may appear on constructing a model, and compactness). Some problems of constructing analytical models for phase diagram elements are discussed. The paper also considers error models and the peculiarities of data approximation on using the parametric and nonparametric methods of experimental-data processing. The authors outline the approaches to constr uction of thermodynamic models for a phase diagram, based on processing of data on the thermodynamic properties of system phases or system processes a nd on the conditions of phase equilibria. In conclusion, a problem of a det ailed description of a phase diagram, sufficient for solving different prob lems, is considered.