LiF – Li2SO4 – NaCl SYSTEM

DOI: 10.6060/tcct.20165911.5424
Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2016. V. 59. N 11. P. 46-49

The secant triangle of LiF - Li2SO4 - NaCl quaternary reciprocal system Li, Na // F, Cl, SO4 was studied with the differential thermal (DTA) and X-ray diffraction (XRD) methods of physical and chemical analysis. It was found that for this system the eutectic composition crystallizing at 447 ° C is realized. DTA was carried out using the STA 449 F3 device for simultaneous thermal analysis in an inert gas (argon). For XRD the diffractometer «Empy-real» was used. Data were treated applying «PANalytical» ICSD Data base. The study of T-x diagram containing alkali metal ions systems allow to develop new salt compositions which can be used as electrolytes of molten chemical power sources in electric welding fluxes of nonferrous metals, coolants, etc. Many industries demand the salt eutectic compositions. They are used in solar energy, for the storage medium and high-grade heat as a heat store. One of the valuable properties of heat store is the value of the phase transition enthalpy (en-ergy content) of the eutectic composition. Eutectic compositions, arranged in sections of four-component mutual systems with three-character, are the most energy-intensive, that is they possess the greatest enthalpies of phase transitions. In this connection in given work as the research object the cross-section of a stable LiF - Li2SO4 - NaCl quaternary reciprocal sys-tem Li, Na // F, Cl, SO4 were chosen. It should be noted that the heat of polymorphic transi-tion for lithium sulphate exceeds the heat of fusion. An experiment planning was carried out according to the general rules of the projection-thermo graphic detection method of hetero-geneous equilibria for multi component condensed salt systems. It allows carrying out the experiment with minimum of time to reveal the parameters of invariant compositions. Origi-nally, one dimensional poly thermal section crossing the fields of lithium fluoride and sodium chloride crystallization was studied with DTA. The study of this section allows revealing in the field of lithium fluoride crystallization the individual composition showing the ratio between of lithium fluoride and sulfate in the ternary eutectic point. The content of the third compo-nent (sodium chloride) in the eutectic and temperature of eutectic crystallization was deter-mined with the study of poly thermal section drowned from crystallization pole of sodium chloride through the composition showing the constant ratio of lithium fluoride and sulphate up to confluence of thermo effects of primary and tertiary crystallizations. The phase compo-sition of the eutectic was confirmed with XRD. For this purpose the eutectic composition was initially melted in an inert atmosphere (argon), and then the composition was kept in the same medium at 10 ° C below the melting point of the eutectic (437 °C) for 10 h.

Key words: multi component reciprocal system, liquidus, phase transition enthalpy, eutectic, heat transfer fluids, heat acc umulators

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2016, Т. 59, № 11, Стр. 46-49

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