The Extreme Pressure Lubricating Properties of Some Sulfur Compounds in Mineral Oil and the Effect of Dissolved Oxygen

In the present study, liquid paraffin was blended with monosulfides, disulfides and mercaptanes and tested in the "Soda" Four Ball Machine to evaluate the extreme pressure properties of the sulfur compounds and their influence from the dissolved oxygen in oils. For a low sliding velocity, optimum concentration for maximum load carrying capacity existed for monosulfide and disulfide blends but no such optimum concentration has been found for mercaptane blends except dibenzyl mercaptane. In a high sliding velocity, disulfides are superior in extreme pressure property to monosulfides and especially, dibenzyl disulfide shows a better extreme pressure lubricating property than other disulfides. When the dissolved oxygen is removed from mineral oils, the extreme pressure lubricating properties of monosulfide and disulfide blends fall off markedly within the range of sliding velocity tested. The effect of the dissolved oxygen in oils varies with the sulfur concentration of oils. In a high sliding velocity only dibenzyl disulfide blend is little effected by the dissolved oxygen.