Fig. 1: Deliquescence surfaces of mixed hydrated Mg- and Ca- perchlorate/chloride salt mixtures calculated using thermodynamic models.
From: Cryogenic origin of fractionation between perchlorate and chloride under modern martian climate
a–c show the ternary system Mg(ClO4)2 + MgCl2 + H2O with the lowest eutectic of thermodynamically stable state (a: Mg(ClO4)2•6H2O + MgCl2•12H2O + ice) and metastable state (b: Mg(ClO4)2•6H2O + MgCl2•8H2O + ice; c: Mg(ClO4)2•6H2O + MgCl2•6H2O + ice). d shows the ternary system Ca(ClO4)2 + CaCl2 + H2O under a thermodynamically stable state with the lowest eutectic of Ca(ClO4)2•6H2O + CaCl2•6H2O + ice. Colored deliquescence surfaces represented by the legend are the interfaces for the phase transition of ternary ClO4−-Cl−-H2O systems in each salt mixture. The dark cyan planes and dark red planes are the lower- and upper- T boundaries between which ClO4−/Cl− fractionation can occur. The lower- T boundary plane intercepts the minima of the ternary deliquescence surfaces, below which no deliquescence would occur. The upper- T boundary plane intercepts the minima of the binary deliquescence surfaces of the chloride-water system (i.e., ClO4−/Cltotal molar ratio = 0), above which both ClO4− and Cl− can be completely dissolved and no ClO4−/Cl− fractionation would occur.
