Journal of Solution Chemistry

, Volume 18, Issue 12, pp 1133–1152 | Cite as

Solubility and phase behavior of nickel oxide in aqueous sodium phosphate solutions at elevated temperatures

  • S. E. ziemniak
  • M. E. Jones
  • K. E. S. Combs


A platinum-lined, flowing autoclave facility was used to investigate the solubility/phase behavior of nickel oxide (NiO) in aqueous sodium phosphate solutions between 290 and 560 K. A layer of hydrous nickel oxide was concluded to exist on the nickel oxide surface below 468 K; only at higher temperatures did the anhydrous nickel oxide phase control the nickel ion solubility behavior. The measured solubility behavior was examined via a nickel(II) ion hydrolysis/complexing model and thermodynamic functions for the hydrolysis/complexing reaction equilibria were obtained from a least-squares analysis of the data. The existence of two new nickel ion complexes are reported for the first time: Ni(OH)2(HPO4)= and Ni(OH)3(H2PO4)=. The positive entropy change associated with the formation of Ni(OH)3(H2PO4)= leads to its dominance in alkaline phosphate solutions at elevated temperatures.

Key words

Nickel oxide aqueous solutions metal ion hydrolysis phosphato-complexing equilibrium constant thermodynamics dehydration pressurized water hydrothermal solutions corrosion 


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Copyright information

© Plenum Publishing Corporation 1989

Authors and Affiliations

  • S. E. ziemniak
    • 1
  • M. E. Jones
    • 1
  • K. E. S. Combs
    • 1
  1. 1.Knolls Atomic Power LaboratoryGeneral Electric CompanySchenectady

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