Tribochemical reactions of silicon nitride in aqueous solutions

The purpose of this investigation was to gain information on the reaction intermediates and products of the tribochemical reactions of silicon nitride in aqueous solutions. A tribochemical reaction is a chemical reaction accelerated by simultaneous friction. The chemical changes at the sliding interface "silicon nitride - polymer" in CrO3, H2O, KMnO4, and SiO2-containing slurry have been monitored by using in situ infrared spectroscopy. In situ infrared spectrometer utilizes attenuated total internal reflection in a germanium crystal with a silicon nitride film deposited onto it, with a polymer counterface sliding against the sample in a solution. Growth of a surface chromium-containing layer has been detected at very low sliding velocity (v<1 mm/s), in accord with previous tribological tests. At higher sliding velocities, no accumulation of reaction intermediates, other than surface silanol groups (Si-OH), has been observed, suggesting that silicon nitride is removed directly from the surface. Possible chemical reactions of silicon nitride and chromium oxide are discussed.