Straining Electrode Behavior of Pure Iron in High Temperature and High Pressure Aqueous Solution

A rapid straining electrode technique has been applied to investigate the initial process of anodic behavior on a newly created surface of pure iron in high temperature and high pressure water. A thin wire electrode was elongated rapidly to yield a newly created surface in 0.1 kmol·m−3 Na2SO4 solution at a constant potential at temperatures up to 573 K. The anodic current increases rapidly to a maximum and decays with time. Exept for the initial region of 0.01–0.1 s, the current density is found to decay following a power law; i=at−n. It is observed that at the passive potential region, the magnetite layer increases in thickness following the parabolic rate law. The rate constant for the growth, however, shows a negative temperature dependence. It is concluded that at higher temperature a more compact film suppressing diffusion through the film and active dissolution is formed. In a temperature range 423–463 K, however, pure iron showed no passive state and dissolved away rapidly.