CONTINUOUS HIGH-TEMPERATURE LUBRICATION OF CERAMICS BY CARBON GENERATED CATALYTICALLY FROM HYDROCARBON GASES

Carbonaceous (graphitic) lubricants are stable even at temperatures above 500°C and replenishable by catalytic decomposition of gaseous hydrocarbons on the wear surfaces themselves. Thus nickel-containing steels become coated with lubricating carbon when exposed to ethylene gas at 500°C. The wear process itself removes the surface carbon, exposing active metal capable of forming more carbon so that the process can continue. Ceramics such as alumina, can be coated with nickel/nickel oxide and support the same process while being sufficiently wear-resistant during startup. Friction coefficients drop from 0.6 to 0.04 upon introduction of ethylene into the conjunction region of a sapphire or quartz pin/ceramic disc. Silicon nitride and carbide exhibit the same behavior even without nickel coating. AES and Raman show the carbon as microcrystalline graphitic or vitreous. Wear under operating conditions is less than 2 nm/min. © 1990 Taylor & Francis Group, LLC.