Fig. 4: Morphodroms of spherulitic structures from mixed salt solutions.
From: Controlled spherulitic crystal growth from salt mixtures
Solubility isotherms at T = 21 ∘C for two ternary systems: a Na2SO4--FeSO4--H2O and b Na2SO4--MgSO4--H2O. In both panels, black lines represent calculated solubilities by the molality-based model, accompanied by initial molal concentrations from evaporative droplet experiments shown as dots, triangles, and circles that correspond to Fig. 2. The phases are labeled as follows: (1) Na2SO4 ⋅ 10H2O (mirabilite); (2) Na2SO4 (thenardite, phase V); (3) Na2SO4 (phase III); (4) FeSO4 ⋅ 7H2O (melanterite); (5) Na2Fe(SO4)2 ⋅ 4H2O (double salt bloedite-Fe); (6) MgSO4 ⋅ 7H2O (epsomite); (7) Na2Mg(SO4)2 ⋅ 4H2O (double salt bloedite-Mg). The intersections at the y-axis (labeled as \({m}_{0}^{* }\)(1), \({m}_{0}^{* }\)(2), and \({m}_{0}^{* }\)(3)) indicate the solubilities of the sodium sulfate phases without the introduction of divalent ions. The ranges of x-values where sodium sulfate spherulites precipitation is detected are highlighted in yellow: for Na2SO4--FeSO4--H2O, 0.03 < xFe < 0.29 in (a) and for Na2SO4--MgSO4--H2O, 0.07 < xMg < 0.38 in (b). The dashed arrow indicates the trajectory of a drying mixed salt solution (x = 0.12) upon evaporation crossing the solubility of phase III (red dot).
