Solubility of the Metal Precursor Ni(NO3)2·6H2O in High-Pressure CO2 + Ethanol Mixtures

The solubility of Ni(NO3)2⋅6H2O in high-pressure CO2 + ethanol mixtures was measured using a high-pressure variable-volume view cell from (308.2 to 353.2 K) and up to 25.0 MPa. This compound has been used previously as a Ni precursor in metal deposition experiments using supercritical CO2. Ni(NO3)2•6H2O was not soluble in pure CO2 but the addition of ethanol into the system allowed the solubilisation of the hydrated salt in the mixture. Mole fraction of Ni(NO3)2•6H2O varied from 1.67 10-4 to 1.97 10-3. At these salt concentrations, the phase diagram of the CO2 + EtOH + Ni(NO3)2⋅6H2O system resembled that of the CO2 + EtOH binary system and, at the studied conditions, a vapourliquid equilibrium was observed. For the higher ethanol concentrations, the bubble points closely matched those of the CO2 + EtOH system. For the lower EtOH concentrations, however, much higher solubilisation pressures were required, due to the release of water molecules from the salt into the solution. Ni(NO3)2⋅6H2O solutions were stable in highpressure CO2 + EtOH mixtures at the studied conditions