Interpretation of phase diagrams of ternary reciprocal systems by complete conversion points
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Interpretation of Phase Diagrams of Ternary Reciprocal Systems by Complete Conversion Points Elena S. Gryzlova and Nina A. Kozyreva
(Submitted 20 November 2000; in revised form 28 February 2001) A new classification of ternary reciprocal systems is proposed taking into account the number of thermal effects in the thermograms of complete conversion points. The classification is useful for general evaluation of the liquid surface of the systems.
Phase diagram construction requires much expenditure of labor, material, and time, so current research efforts are directed toward the minimization of experimental work. At present, there are two main directions of effort: thermodynamic calculations of phase diagram ([1970Kau], [1985Com], [1981Lup], [1992Pel]) and semiempirical approaches, which include analysis of the most informative points in the phase diagram. The latter allow prognosis of liquidus surface features and require limited experimental study of a few samples to confirm the prognosis results ([1984Pro], [1995Roz]). It is most convenient to start consideration of a ternary reciprocal system in the context of the semiempirical approach, with the thermogram record of a point of complete conversion (PCC), which is the intersection point of stable and metastable diagonals in the composition square ([1964Rad], [1978Pos]). This article aims to show the information content of a PCC, which allows a theoretically substantiated prognosis of phase diagrams. For this purpose, a classification of ternary reciprocal systems based on the number of thermal effects in the thermograms of complete conversion points is developed. It has been shown by [1984Pro] and [1978Pos] that examination of the points of complete conversion enables one to solve the following problems connected with the construction of phase diagrams of ternary reciprocal systems:
allows a rational choice of the areas of the phase diagram for more detailed research and to reduce the requisite number of compositions to be experimentally studied. The most complete information on the PCC can be obtained using differential thermal analysis, zone melting, high-temperature x-ray analysis, investigation of microstructure, and chemical analysis. Depending on the chemical reciprocal interaction in the system, the PCC thermograms can show several thermal effects. One can single out the following types (Table 1).
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2. Three Effects in the PCC Thermogram
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determination of the salt pair stability, determination of the phase that occupies the largest field on the crystallization surface, determination of the primary reaction (the exchange reaction or the reaction of complex formation) in the case when a double salt appears in the system, determination of the maximum work of the exchange reaction [1994Gry], and determination of the ternary eutectic temperature.
The solution of the problems listed at the initial consideration of a ternary reciprocal system can greatly reduce expenditure of time and necessary experimental measurement. This
1. Two Effects in the PC
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