hide
Free keywords:
Nickel; Phase transitions; Solubility diagrams; Structure elucidation; Solid-phase synthesis
Abstract:
The solid/liquid equilibria in the ternary system Ni(OH)(2)-NiCl2-H2O at temperatures of 25 and 200 degrees 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 degrees C, Ni2Cl(OH)(3) and NiCl(OH) occur as stable phases, whereas a solid solution, NiClx(OH)(2-x) (ss-type-OH), appears as an intermediate phase. At 25 degrees C, two nickel(II) chloride hydroxide hydrates, Ni3Cl2+x(OH)(4-x)center dot 4H(2)O and Ni3Cl(OH)(5)center dot 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 degrees C revealed that Ni2Cl(OH)(3) is the solid phase in both dilute and concentrated NiCl2 solutions at this temperature. In general, all stable and metastable phases in the system Ni(OH)(2)-NiCl2-H2O exhibit very low solubility, but during the very slow phase transformations high hydroxide supersaturations occur that are persistent for years.
