The Nature and Origin of Tribochemistry

Abstract

Tribochemistry can be defined as the chemical reactions that occur between the lubricant/environment and the surfaces under boundary lubrication conditions. The precise nature of the chemical reactions is not well understood. What causes the reactions to take place is also a subject of speculation. Surface analysis of the surface and the reaction products yields insufficient information for a full understanding of the nature and origin of the chemical reactions. The reaction mixture is complex and the quantity is very small. Classical analytical techniques provide elemental concentration but the organic portion of the reaction products eludes definition. Recent observation of surface emissions of electrons, charged particles, from rubbing surfaces invites speculation that this emission provides the source of energy causing tribochemical reactions to take place. This study reviews our current knowledge of tribochemistry and examines the issue of the source of tribochemistry in boundary lubrication. Experiments were designed to examine the issue of whether mechanical disruption of surface bonds can lead to the formation of reaction products. The second issue is whether these reaction products correspond to those observed under normal rubbing conditions. Thermally induced reaction products were also examined for comparison. Surfaces covered with a monolayer of stearic acid molecules were scratched by a glass lens covered with a layer of diamond particles. Unidirectional scratches were made at 20-30 nm depth. The reaction products were monitored by a grazing angle FTIR capable of detecting the spectrum of a monolayer. The spectrum was then compared with the spectrum from a thermally heated case and a rubbed case. Results suggest that such scratching indeed produces similar reaction products.