Polythermal study of magnesium oxide solubility in molten K2SrCl4

• Solubility of MgO in K2SrCl4 melt in 923–1023 K temperature range was found.
• The change of MgO solubility with the temperature agrees with the Shreder equation.
• Acidity of K2SrCl4 melt is higher than that of CsCl-KCl-NaCl eutectic.
• Change of Ba2+ by Sr2+ in molten chlorides causes increase of their oxoacidity.

Solubility products of MgO in molten (KCl + SrCl2) with composition corresponding to congruent compound K2SrCl4 at T = 923, 973 and 1023 K were determined by a potentiometric titration method using Pt(O2)|ZrO2(Y2O3) indicator electrode. The solubility product indices (pKs,MgO, mole fractions) were found to decrease with the temperature elevation by such a manner (9.92 ± 0.13) at 923 K, (9.34 ± 0.11) at 973 K and (9.08 ± 0.13) at 1023 K. The slope of logKs,MgO − T−1 plot in the studied temperature range (ca. 76 kJ·mol−1) corresponds to value of fusion enthalpy of MgO (77 kJ·mol−1). A comparison of MgO solubilities in the molten K2SrCl4 with the similar results obtained for (CsCl + KCl + NaCl) (0.455:0.245:0.300) and (KCl + LiCl) (0.41:0.59) eutectic melts shows that the values for K2SrCl4 melt are intermediate between those for low-acidic (CsCl + KCl + NaCl) and merely acidic (KCl + LiCl). The oxobasicity indices pIL of K2SrCl4 in the studied temperature range change from 2.26 to 2.45 with the temperature rise.