English: Phase diagram for the ternary system MgO - MgCl
2 - H
2O at 23 °C. Recomputed and redrawn from information in: Ladawan Urwongse and Charles A. Sorrell (1980): "
The System MgO‐MgCl2‐H2O at 23°C".
Journal of the American Ceramic Society, volume 63, issue 9-10, pages 501-504; ]
The stable oxychloride phases at 23 °C are P5 or 5:1:8 = 5 Mg(OH)2 · MgCl2 · 8 H2O and P3 or 3:1:8 = 5 Mg(OH)2 · MgCl2 · 8 H2O. At his temperature, the magnesium chloride crystallizes as the hexahydrate MgCl2·6H2O
The dark blue region comprises the stable clear solutions. Its vertices are pure water, the saturated Mg(OH)2 solution SH, the triple equilibrium compositions S1,S2, S3, and the solid magnesium chloride hexahydrate SC. As mass fractions (not molar fractions), they are
- SH = 0.0044 MgO + 0.9956 H2O (Sol:Mg(OH)2)
- S1 = 0.008 MgO + 0.170 MgCl2 + 0.822 H2O (Sol:Mg(OH)2:P5)
- S2 = 0.010 MgO + 0.222 MgCl2 + 0.768 H2O (Sol:P5:P3)
- S3 = 0.012 MgO + 0.345 MgCl2 + 0.643 H2O (Sol:P3:MgCl2·6H2O)
- SC = 0.469 MgCl2 + 0.531 H2O (Sol:MgCl2·6H2O)
The light blue region is the approximate range of compositions of homogeneous metastable clear solutions and gels that form initially and eventually crystallize as P5, P3, or mixtures with some saturated solution and Mg(OH)
2 or MgCl
2·6H
2O.