SOLID LUBRICATION BY DECOMPOSITION OF CARBON-MONOXIDE AND OTHER GASES

Extended duration high temperature (above 500 degrees C) lubrication of silicon nitride sliding and rolling contacts was accomplished by solid carbon deposited and replenished via the decomposition of carbonaceous gas streams directed towards the tribological surfaces. Injection of carbon monoxide-hydrogen mixtures can lead to reductions in high temperature friction and wear of silicon nitride sliding contacts by factors of up to 10 x and 500 x respectively from the unlubricated case. Similar lubrication is attained by various hydrocarbon gas mixtures, while only a ten-fold reduction in wear is attained by a carbon dioxide-hydrogen mixture. Effective lubrication can be modeled as a favorable balance between carbon deposition from the gas phase and removal by wear. This model is based on the dependencies of solid lubricant deposition and removal processes on temperature, sliding speed, normal load, decomposition activation energy, gas flow rate, and tribosystem properties. The model is checked by the mapping of regions where measured friction indicates that lubrication by CO-H-2 mixtures is adequate, and the identification of a boundary representing the onset of marginally effective lubrication.