SILICON-NITRIDE BOUNDARY LUBRICATION - LUBRICATION MECHANISM OF ALCOHOLS

This paper describes the lubrication mechanism of alcohols with silico n nitride under boundary lubrication conditions. Dynamic wear tests an d static chemical reaction studies were conducted to study the chemica l interaction between alcohols and silicon nitride. Direct evidence of chemical reactions occurring between alcohols and silicon nitride was collected. -chromatography-graphite-furnace-atomic-absorption (GPC-GF AA) analysis detected the presence of high molecular weight (HMW), sil icon-containing, metalloorganic compounds in the wearing contact. Seco ndary ion mass spectrometry (SIMS) analysis of the reaction products f rom wear tests revealed the formation of silicon alkoxides. These alko xides subsequently reacted to form HMW products which had been indepen dently verified as capable of lubricating silicon nitride surfaces. A two-ball collision test was used to verify the lubricating quality of the film generated from the wear test. A lubrication mechanism is prop osed in which alcohols adsorb and react with the oxide/hydroxide layer of Si3N4 to produce a bonded surface silicon alkoxide. Subsequent tri bochemical reactions prompted by the surface disruption from the weari ng contact cause the formation of free silicon alkoxides. These specie s then proceed to form a variety of silicon-containing high molecular weight products that have demonstrable lubricating ability. This mecha nistic understanding provides a framework of Si3N4 lubrication.