SYSTEM (LiF)2 – (NaF)2 – (NaCl)2 – Na3FSO4

Abstract

With the differential-thermal method of physico-chemical analysis the stable tetrahedron (LiF)2 – (NaF)2 – (NaCl)2 – Na3FSO4 of four-component mutual system Li, Na // F, Cl, SO4. It was established that the system is eutectic one.The eutectic crystallizes at 543 °C. The system Li, Na // F, Cl, SO4 is characterized by the presence of three compounds: one detectice (Na3FSO4) and two peritectically compounds Li2Na4(SO4)3, LiNaSO4. Four-component reciprocal systems, in the elements of faceting of which include irreversibly-reciprocal or singular three-component systems without compounds, are divided, as a rule, into three tetrahedra. In this case, the composition diagrams of the Li, Na / F, Cl, SO4 system are decomposed taking into account the incongruent and congruent melting compounds, resulting in the revealing the seven tetrahedra.: 1. (LiF)2 – (LiCl)2 – Li2SO4 – (NaCl)2; 2. (LiF)2 – Li2SO4 – (NaCl)2 – Na3FSO4; 3. Li2SO4 – Na2SO4 – (NaCl)2 – Na3FSO4; 4. (LiF)2 – (NaF)2 – (NaCl)2 – Na3FSO4; 5. Li2Na4(SO4)3 – LiNaSO4 – Na3FSO4 – (NaCl)2; 6. LiNaSO4 – Na3FSO4 – Li2SO4 – (NaCl)2; 7. Li2Na4(SO4)3 – Na3FSO4 – Na2SO4 – (NaCl)2. The theoretical analysis of the granular elements of these tetrahedra carried out by us, and later the investigation of the DTA of single compounds in each tetrahedron, shows that the nonvariant points from tetrahedra formed with the participation of incongruent melting compounds migrate to the tetrahedra bordering them with inversion into quaternary peritectics. The lack nonvariant points in the tetrahedra formed with the participation of the incongruent melting compounds: Li2Na4(SO4)3 – LiNaSO4 – Na3FSO4 – (NaCl)2; LiNaSO4 – Na3FSO4 – Li2SO4 – (NaCl)2; Li2Na4(SO4)3 – Na3FSO4 – Na2SO4 – (NaCl)2, confirmed by the absence in the thermograms of DTA unit composition of these tetrahedrons thermoeffect joint crystallization of four phases. In this study, a tetrahedron (LiF)2 - (NaF)2 - (NaCl)2 - Na3FSO4 was selected for experimental investigation, in a composition that does not include peritectic compounds and only one eutectic composition is localized in this system.The choice of this system for experimental research is also due to the fact that its composition includes lithium fluoride, which has a relatively large enthalpy of phase transition, which is one of the determining factors in the selection of heat accumulators, heat carriers for devices that store heat and solar energy.Also the system includes salts widely used in the pulp and paper, textile, food, construction industries. Investigation of phase equilibrium diagrams of such systems allows expanding the areas of application of low melting eutectic compounds.Forcitation:Verdiev N.N., Omarova S.M., Alkhasov A.B., Magomedbekov U.G., Gasangadzhieva U.G., Dvoryanchikov V.I. System(LiF)2 – (NaF)2 – (NaCl)2 – Na3FSO4. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2017. V. 60. N 6. P. 77-82.