Article

We have used stopped-flow kinetic studies to conduct an investigation into the acid neutralization reaction between overbased detergent additives and aqueous acid dispersed as w/o microemulsion droplets. Water-soluble pH indicators have been used to monitor the change in pH during the reaction. The acid neutralization rate was found to be dependent on the concentration of overbased additive, the temperature of the system, and the hydrocarbon chain length of the solvent. The systems are of importance in relation to the mechanism of acid neutralization by engine lubricants.Key words: overbased detergent additive, acid neutralization, pH indicator, stopped flow.

Antiwear Mechanism of ZDDP in the Presence of Calcium Sulfonate Detergent

Interactions between zinc dithiophosphate (ZDDP) antiwear additive and commercial calcium sulfonate detergent are studied using a plane/plane contact configuration friction machine lubricated under boundary conditions. Comparative tests have allowed us to envisage three types of interactions, respectively, due to, — first: chemical interaction between both additives in the oil phase leading to an effective ZDDP concentration decrease. — second: detergent effect due to the presence of the calcium sulfonate surfactant molecule, preventing basal materials from agglomerating during running. — third: specific role due to the overbasing agent, considered as a colloidal dispersion. When an overbased detergent is used, the two latter contributions are predominant. This study suggests that a new approach in boundary lubrication should be envisaged in relation to the evolution of the interface products which must be regarded as a highly concentrated colloidal system.