Particle Adhesion and Removal in Model Systems, VII. Hematite Particles on Steel at 22 and 210 C

The adhesion of uniform spherical hematite particles on steel beads and their removal from the same substrate was studied by a batch technique at two different temperatures (22 and 210 C). The applicability of the technique was tested at 22 C and it was found that the experimentally determined rate constant agreed with the theoretically calculated value. Particle detachment was observed over the pH range which causes steel and hematite to be of the same sine charge, thus insuring electrostatic repulsion. At 210 C, the measurements were carried out at pH 8.6 in the presence of varying concentrations of NaNO₃ and compared to analogous data at 22 C. With the addition of the electrolyte, the deposition is increased and the removal is decreased at both temperatures, although the former effect is more pronounced at 22 C. While a deposition/removal equilibrium appears to be established at low temperature, the process is essentially irreversible at the high temperature. The studied system serves as a model for the interactions of rust particles with steel, and particularly for the crud deposition and removal in water cooled nuclear reactors. It is apparent that the corrosion products dispersed in aqueous solution will more strongly adhere to steel at higher temperatures and consequently be more difficult to remove.