Friction and Wear of Silicon Nitride Lubricated by Humid Air, Water, Hexadecane and Hexadecane + 0.5 Percent Stearic Acid

Abstract

Friction and wear of hot-pressed Si3N4 sliding on itself at low velocity (1 mm/s) were measured at room temperature in humid air, water, pure hexadecane and in hexadecane with 0.5 percent stearic acid. The friction coefficients in air and water are 0.75 and 0.65, respectively. In hexadecane with stearic acid, the friction coefficient is 0.1, somewhat higher than for metals. In pure hexadecane, the friction coefficient is 0.12, much lower than for metals, suggesting strong adsorption of the hydrocarbon. The wear rate is approximately constant k = 5 × 10−11 kg/Nm in humid air and water. It is much lower in hydrocarbon lubricants and varies with (sliding distance)2/3 in dexadecane and with (sliding distance)1/3 with stearic acid. A tribochemical reaction occurs between silicon nitride and water in all four environments; in the hydrocarbons the reaction is with water dissolved in the fluids.