SEDIMENTATION OF METALLIC PARTICLES IN OILS AND EMULSIONS

Sedimentation tests have been used to analyse the interaction forces b etween micrometric carbonyl iron and steel particles suspended in mode l liquids and emulsions which are representative of rolling lubricants of the steel industry. In non-emulsified liquids, the stability and t he final packing of the suspension depend on the polarity of the liqui d, the nature of the various additives and their mutual solubilities. In cyclohexane solutions of fatty acids, the aggregation of the partic les and the suspension stability can be changed in a continuous way wi th the solute concentration. The final solid volume fraction also vari es and follows a saturation-like behaviour with two plateaux, the valu es of which depend on the type of particle. Carbonyl iron suspensions reach the closest packed value (0.62) for concentrated solutions and t he parking limit (0.38) at intermediate concentrations. Steel suspensi ons exhibit very low packing densities (from 0.07 to about 0.20). Sedi mentation of steel suspensions in industrial emulsions depends strongl y on the oil concentration and the results can be interpreted by compa rison with model suspensions.