The ability of directed streams of three representative hydrocarbon gases - acetylene C₂H₂, ethylene C₂H₄, and ethane C₂H₆ - to provide extended duration lubrication to high temperature sliding contacts via surface deposition of pyrolytic carbon has been demonstrated. One order- and two order-of-magnitude reductions of friction coefficient and wear rate of self-mated silicon nitride sliding contacts can be realized by this technique. The capacity of these gases to provide 'adequate' lubrication at high temperature is illustrated through a mapping of the normal load / temperature / precursor flowrate space over which reduced friction may be maintained. Acetylene was the most effective precursor for pyrolytic carbon deposition, providing adequate lubrication over the broadest range of normal load / temperature / flowrate combinations, while ethane was the least effective. The boundary of regions of adequate lubrication represent the locus of contact conditions with equal rates of lubricous carbon deposition and removal by wear. The shape of this boundary, as explored in the mapping study, supports a proposed model in which the removal rate is proportional to the product of normal load and sliding speed while the deposition rate is proportional to the product of precursor flowrate and an Arrhenius temperature dependence.

Adobe Acrobat File

Published in the Journal Lubrication Science
Volume 12 (2000) pages 169-184