Calculated Stability and Structure of Nickel Ferrite Crystal Surfaces in Hydrothermal Environments
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- 作者：Christopher J. O鈥橞rien ; Zs. R谩k ; Donald W. Brenner
- 刊名：Journal of Physical Chemistry C
- 出版年：2014
- 出版时间：March 13, 2014
- 年：2014
- 卷：118
- 期：10
- 页码：5414-5423
- 全文大小：619K
- 年卷期：v.118,no.10(March 13, 2014)
- ISSN：1932-7455
文摘
A comprehensive theoretical investigation of nickel ferrite (NiFe2O4) surfaces is undertaken to understand the structure and stability of nanocrystallites that would be present under conditions of hydrothermal synthesis (HTS). In particular, the focus is on conditions characteristic to an operating pressurized water nuclear reactor (PWR). Solid鈥搇iquid equilibrium is assumed between bulk nickel ferrite and the aqueous environment saturated with respect to nickel ferrite. A theoretical framework is developed in which the surface energies are evaluated in terms of concentrations of aqueous metal cations, pH, temperature, and pressure. The energies of the bare and water terminated surfaces are calculated and discussed. Surfaces that have more metal cations exposed are found to be more stable. Water adsorption on the nickel ferrite surfaces is an exothermic process, with the magnitude of exothermicity decreasing as a function of temperature. At temperatures relevant to operating PWRs, the energy gain due to water adsorption is negligible. The most stable surfaces are along the (111) planes and are predicted to have negative surface energies. This indicates that, in an operating PWR, nickel ferrite tends to increase its surface area, giving rise to a highly porous thermodynamic ground state. This provides an explanation for the porous nature of the nickel ferrite deposits observed to form on PWR fuel rods.