Tribochemistry of n‐hexadecane in different material systems

Abstract

AbstractHexadecane is widely used as the model base oil to investigate both tribological effectiveness and tribochemical reaction mechanisms of various antiwear and extreme pressure additives. On the other hand, it is well known from existing references that hexadecane, similarly to hydrocarbon oils, oxidizes during the lubrication process of tribological systems. It has frequently been pointed out that carboxylic acids are formed which — reacting with rubbing surfaces — generate soaps. Most recent studies, however, demonstrate that the oxidation process under friction conditions is very complex and the major oxidation compounds from hexadecane under boundary friction conditions relate to other oxygenates than carboxylic acids.This paper aims to examine what types of surface compound are generated from the hexadecane lubricant in the friction contact zone. Tribological tests were performed on a ball‐on‐disc tribometer. The discs used were made from several materials (steel, aluminium, brass, bronze). Fourier transform infrared (FTIR) microspectrophotometry and techniques involving a scanning electron microscope equipped with an energy‐dispersive spectrometer were used to analyse tribochemical reaction products formed on different substrates. Analytical results obtained clearly demonstrate a similar tribochemical reaction process operating on all the metals tested. The FTIR results obtained allowed new absorption bands to be discovered and accounted for. These absorption bands have been assigned to specific complex compounds. Copyright © 2006 John Wiley & Sons, Ltd.