Chiang Mai Journal of Science

The stable and metastable phase equilibria of the ternary system MgSO₄–MgB₄O₇–H₂O at 273 K were measured respectively using isothermal solubility equilibrium method and isothermal evaporation crystallization method. The solubilities and densities of equilibrium liquid phase in the system were determined. Based on the experimental data and the corresponding equilibrium solid phase, the stable and metastable phase diagrams and their corresponding density versus composition diagrams in this system were plotted, respectively. A comparative analysis of the stable and metastable phase diagrams were made, in addition to, compared with stable phase diagrams at 273 K and 298 K in the system. Experimental results show that both the stable and metastable phase diagrams are constituted by a eutectic point for (MgSO₄∙7H₂O+MgB₄O₇∙9H₂O), two univariant solubility curves, two solid phase crystalline regions corresponding to MgSO₄∙7H₂O and MgB₄O₇∙9H₂O. Compared with the stable phase diagram, the sizes of the crystalline regions are different in the metastable phase diagram. Both the stable and metastable phase equilibria in the system at 273 K are simple cosaturated type and there are no complex salt or solid solution were found.