Chemical equilibria and particle morphology of boehmite (AlOOH) in sub and supercritical water

Yukiya Hakuta, Tadafumi Adschiri, Hideyuki Hirakoso, Kunio Arai

Research output: Contribution to journalConference articlepeer-review

53 Citations (Scopus)


In a recent study, we proposed a supercritical water crystallization method for production of metal oxide particles. Around the critical point, the morphology of boehmite (AlOOH) particles varied greatly with the reaction temperature, pressure and concentration of aqueous aluminum nitrate solution. In this study, the relationship between the morphologies of particles obtained and the chemical species in solution is discussed. For estimation of chemical species concentrations, evaluation of equilibrium constants of the hydrothermal reactions around the critical point is required. For this, a model based on the Gibbs energy change by temperature, solvent effects and ion-ion interactions is employed. The solvent effect was calculated by the Born equation. The effect of ion-ion interaction was calculated by the extended Debye-Huckel equation. Using this model, the distribution of chemical species for the AlOOH system (Al3+, Al(OH)2+, Al(OH)2+, Al(OH)3, Al(OH)4-, NO3-) in subcritical (350°C, 30 MPa) and supercritical water (400°C, 30 MPa) was estimated. The particle morphology seems to be determined by selective adsorption of positive charged species, Al(OH)2+, on the negatively charged faces of AlOOH crystal.

Original languageEnglish
Pages (from-to)733-742
Number of pages10
JournalFluid Phase Equilibria
Publication statusPublished - 1999
EventProceedings of the 1998 8th International Conference on Properties and Phase Equilibria for Product and Process Design - Noordwijkerhout, Netherlands
Duration: 1998 Apr 261998 May 1


  • Boehmite
  • Chemical equilibria
  • Hydrothermal synthesis
  • Morphology
  • Supercritical water


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