Acta Metall Sin  2019, Vol. 55 Issue (2): 281-290    DOI: 10.11900/0412.1961.2018.00215
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Influence of Hydrostatic Pressure on the Thermodynamics and Kinetics of Metal Corrosion
Rongyao MA1,2, Lin ZHAO1, Changgang WANG1, Xin MU1, Xin WEI1, Junhua DONG1, Wei KE1
1 Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
2 University of Chinese Academy of Sciences, Beijing 100049, China
Abstract

In recent years, researches on deep sea corrosion have attracted much attention of many researchers. The high hydrostatic pressure is a distinctive feature of deep-sea environment. The hydrostatic pressure affects the corrosive behavior of metallic materials by modifying the composition, structure and compactness of corrosion products, changing the polarization processes of cathode electrode and anode electrode, altering pitting nucleation rate and growth rate, impacting on chemical reaction rate and equilibrium constant, and varying hydrogen diffusion rate and coverage. However, in essence, the influence of hydrostatic pressure on the corrosion behavior of different metal materials is the manifestation of the thermodynamic and kinetic parameters of the corrosion electrode process caused by hydrostatic pressure. At present, the mechanism of effect of hydrostatic pressure on the thermodynamics and kinetics of corroding electrode processes is unclear yet. In addition, the concerns about the effects of hydrostatic pressure on the chemical properties of materials and seawater are comparatively low. Based on thermodynamics and kinetics, the effects of hydrostatic pressure on the activities of electrode material and ions in environment, including on the solubility, fugacity or activity of gases in environment are analyzed. The influence of hydrostatic pressure on pH value and chemical equilibrium is also discussed. The relationships between hydrostatic pressure and equilibrium electrode potential, as well as the exchange current density, are analyzed. The theoretical model of the effect of hydrostatic pressure on the corrosion behavior of active metals is established. The studies have shown that hydrostatic pressure would increase the activities of materials, ions and dissolved gas in environments, and this is closely related to their partial molar volume. The hydrostatic pressure would magnify the difference in the activity of heterogeneous materials. The larger the partial molar volume difference of the heterogeneous materials, the more obvious the difference in activity. Increasing hydrostatic pressure reduces the equilibrium electrode potential of iron and aluminum anode dissolution reaction while reducing its exchange current density. Increasing hydrostatic pressure increases the equilibrium electrode potential of oxygen reaction and decreases its exchange current density. Increasing hydrostatic pressure reduces the equilibrium electrode potential of hydrogen evolution reaction and increases its exchange current density.

 ZTFLH: O646.6 TG171
Fund: Supported by National Key Research and Development Program of China (No.2017YFB0702302) and National Natural Science Foundation of China (Nos.51671200 and 51501204)
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 Fig.1  Activities of pure Fe and pure Al at different pressures (p—hydrostatic pressure, $p?$—standard pressure, a(p) and a$(p?)$—activities at p and $p?$, respectively) Fig.2  Activity of Cl- in 0.725 mol/L NaCl solution at different pressures (aB(p), aB$(p?)$—activities of B at p, $p?$, respectively; $κ?B$—partial molar compressibility of B at $p?$) Fig.3  Activity of dissolved oxygen at different pressures Fig.4  Equilibrium constants, ion product constants, and neutral pH values for pure water ionization reactions at different pressures (Ka(p), $Ka(p?)$—chemical reaction equilibrium constants at p, $p?$; Ksw(p), $Ksw(p?)$—ion product constants at p, $p?$; subscript i of Ki(p) and $Ki(p?)$ means a or sw) Fig.5  Equilibrium electrode potentials of some electrode reactions at different pressures (Δφe—the change of equilibrium electrode potential with the change of pressure from $p?$ to p) Fig.6  Exchange current densities of certain electrode reactions at different pressures (i0(p), i0$(p?)$—exchange current densities at p, $p?$, respectively; CP—compressed air, calculate the fugacity of O2 by Eq.(22); DO—dissolved oxygen, calculate the activity of O2 by Eq.(16))