Zirconia nanoparticle synthesis in sub and supercritical water — particle morphology and chemical equilibria

چکیده مقاله

Zirconia nanoparticles were prepared in supercritical water using hydrothermal method, where particle mor- phologywas found to depend on the reaction temperature and pressure, pH and precursor concentration.Having calculated the equilibrium constant using revised HKF (R-HKF) and Sue-Adschiri-Arai (SAA) thermodynamic models, the relationships between particlemorphological characteristics and distribution of zirconium chemical species (including Zr 4+, ZrOH3+,ZrO2, Zr(OH)2 2+, Zr(OH)3 +, Zr(OH)4, Zr(OH)5 −,NO3 −) in subcritical and supercrit- ical water were studied. Results indicated that Zr(OH)2 2+ was the dominant species at lower pH, while at higher pH, Zr(OH)5 −− became the dominant one. Distribution of zirconium species as well as different phases of ZrO2, suggested that, Zr(OH)2 2+ and Zr(OH)5 −− ions most likely play a significant role in the synthesis of monoclinic and tetragonal phases, respectively.