Phase Formation and Solubilities in the Ternary System Ni(OH) 2 –NiCl 2 –H 2 O at 25 and 200 °C

The solid/liquid equilibria in the ternary system Ni(OH) 2 –NiCl 2 –H 2 O at temperatures of 25 and 200 °C have been investigated by applying equilibration periods of up to 45 months (3 years and 9 months). The equilibration process was studied by isothermal saturation methods using different solids as starting materials. At 200 °C, Ni 2 Cl(OH) 3 and NiCl(OH) occur as stable phases, whereas a solid solution, NiCl x (OH) 2– x (ss‐type‐OH), appears as an intermediate phase. At 25 °C, two nickel(II) chloride hydroxide hydrates, Ni 3 Cl 2+ x (OH) 4– x · 4H 2 O and Ni 3 Cl(OH) 5 · 4H 2 O, are formed. The latter phase was characterized for the first time and a structural model was created from a Rietveld refinement of the powder X‐ray diffraction pattern. A systematic investigation of the solubilities at 25 °C revealed that Ni 2 Cl(OH) 3 is the solid phase in both dilute and concentrated NiCl 2 solutions at this temperature. In general, all stable and metastable phases in the system Ni(OH) 2 –NiCl 2 –H 2 O exhibit very low solubility, but during the very slow phase transformations high hydroxide supersaturations occur that are persistent for years.