Linear behaviour in isothermal equilibria involving saturated electrolyte solutions: The H 2 O–Co(NO 3 ) 2 –Ni(NO 3 ) 2 ternary system at low temperature

Widespread Solid Solutions of Hexahydrated Cobalt and Nickel Nitrates: Solid–Liquid Equilibria at 273.15 and 303.15 K and Characterization of Mixed Crystals of Homogeneous Composition

“…As it was observed for the isotherms at 248.15 and 258.15 K and 293.15 K, the solubility curves of the solid phases, shown Figure , have an almost linear behavior. Similarly, the experimental points and the position of the tie-lines indicate that the precipitated solid phases are two series of solid solutions derived from the cobalt and nickel nitrate hexahydrate.…”

“…In the previous publication, it was observed and demonstrated, by using the quasi-ideal model and disregarding the ionic solvation, that the solubility curves of the solid solutions at 248.15 and 258.15 K had a linear behavior. The same observation can be done for the isotherm at 303.15 K.…”

“…The study of the solid–liquid equilibria of the H 2 O–Co­(NO 3 ) 2 –Ni­(NO 3 ) 2 ternary system at 293.15and 248.15 and 258.15 K highlighted the formation of two widespread solid solutions, derived from the stable hydrates of the H 2 O–Co­(NO 3 ) 2 and H 2 O–Ni­(NO 3 ) 2 binaries. At 293.15 K, the solid solution derived from the triclinic nickel nitrate hexahydrate is stable from 0 to 18 x % Co­(NO 3 ) 2 ·6H 2 O; the second comes from the monoclinic cobalt nitrate hexahydrate and is stable from 35 to 100 x % Co­(NO 3 ) 2 ·6H 2 O.…”

“…At 293.15 K, 9 the solid solution derived from the triclinic nickel nitrate hexahydrate is stable from 0 to 18 x% Co(NO 3 ) 2 •6H 2 O; the second comes from the monoclinic cobalt nitrate hexahydrate and is stable from 35 to 100 x% Co(NO 3 ) 2 •6H 2 O. At 258.15 K, 10 the first one is stable up to about 35.5 x% Co(NO 3 ) 2 • 6H 2 O, and the second one is stable from 67.3 to 100 x% Co(NO 3 ) 2 •6H 2 O. These studies show that Co 2+ and Ni 2+ cations, which present similar physicochemical properties (very close ionic radii: 65 and 69 pm for cobalt and nickel ions, respectively, and the same electrovalence), can then easily be exchanged on the crystallographic sites of the structures leading to substitutional solid solutions.…”