SILICON-NITRIDE BOUNDARY LUBRICATION - EFFECT OF OXYGENATES

A ball-on-three-flat (BTF) wear tester was used to investigate the bou ndary lubricating characteristics of oxygenates on a commercial silico n nitride. A wide variety of oxygen-containing compounds were tested n eat and/or at 1% by weight in a paraffin oil. Compounds containing hyd roxyl functional groups were more effective compared to a base case of neat paraffin oil. Decreases of up to 58% in friction coefficient, an d 95% in wear were obtained. In most cases, films were observed in and around the wear scar, suggesting chemical reactions had taken place i n the contact. Additional wear tests, conducted using neat shorter-cha in linear primary alcohols, i.e., 6-10 carbons, demonstrated boundary lubrication protection, with longer chain length providing better anti wear performance. A study of several C-8 compounds with specific oxyge n-containing functional groups (primary alcohol, secondary alcohols, a cid aldehyde, and ketone) demonstrated that the primary alcohol had th e strongest boundary lubricating effect. Varying the amount of water i n the alcohols had little effect on friction and wear, suggesting that the boundary lubrication effects observed were not merely due to diss olved water in these fluids, but some characteristic chemical interact ion with the hydroxyl functional group of the alcohols and acids.