Particle adhesion and removal in model systems. Part 2.—Monodispersed chromium hydroxide on steel

Abstract

The adhesion of uniform spherical colloidal particles of chromium hydroxide (modal diameter 0.28 µm) on stainless steel surface and their subsequent removal by rinse solutions of various pH and Ca(NO₃)₂ concentrations were studied using the packed column technique. The particles were deposited on steel at pH 5. The pH of the rinse solution had to be adjusted to ≈ 11 before appreciable particle desorption occurred, although the isoelectric point of the steel used was ≈ 5 and that of the chromium hydroxide particles was ≈ 8. Desorption increased at still higher pH, reached a maximum at pH ≈ 12, and then decreased again with increasing rinse solution pH. An addition of Ca(NO₃)₂ in concentration as low as 10^–3 mol dm^–3 completely inhibited the removal of chromium hydroxide from the steel surface at pH 11.7. The results obtained are analysed in terms of the existing theory of the electrical double layer and the diffusional escape of the particles across the interaction energy barrier. No chemical bonding between the particles and the substrate could be detected.