Chemical Aspect for Advanced Lubricants

Abstract

In order to understand lubricating mechanism for advanced lubricants, lubricating properties of lubricants composed of additives and base oils are reviewed from the viewpoint of chemical interaction of lubricant components and material surface. The structure of lubricating films formed on material surface which affects lubricating property are controlled by the balance of chemical interaction between additives, base oil and surface. Lubricity of organic phosphates as an anti-wear additive and MoDTC as a friction modifier is closely dependent on the solubility of the additives in base oils. Thickness and structure of the tribofilm formed from thickeners, over-based calcium sulfonate and MoDTC are controlled by the balance between formation and degradation of the films. A dynamic model of tribofilm formation is proposed. The important role of nascent surfaces on tribochemical reactions of additives is reviewed. Although additives having a polar functional group such as organic phosphate interact with metal oxide under mild conditions, non-polar additive such as organic sulfide chemisorb on nascent metal surface formed under severe conditions. Additives should be selected on the basis of surface chemistry dependent on lubricating conditions.