A Kinetic Study on the Reaction of Labeled Sulfur Compounds with Steel Surfaces during Boundary Lubrication

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Abstract
The kinetic study of the reaction between steel surfaces and lubricants containing labeled sulfur compounds was carried out by using an NACA-type friction machine with line contact. When the line contact apparatus is used, a correction term should be added to the theoretical equation for a point contact to apply the empirical results. Apparently the effective surface concentration of sulfur compounds decreased markedly as the sliding velocity increased in speed. Elementary sulfur had less than good lubricating properties and readily made surface temperatures rise, but both dibenzyl disulfide and diphenyl disulfide behaved as effective lubricants over the whole range of sliding velocities. The increase of compressive pressure on frictional surface did not affect the chemical activity of the sulfur compounds, but did increase the reacting regions of frictional surface. The thickness of FeS film effective in the reduction of friction was calculated to be about 30–50 layers of FeS under dynamic conditions. The thickness of iron contributing to the reaction was also calculated.