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Mechanical shaft seals used in pumps are critically important to the safe operation of the paper, pulp, and chemical process industry, as well as petroleum and nuclear power plants. Specifically, these seals prevent the leakage of toxic gases and hazardous chemicals to the environment and final products from the rotating equipment used in manufacturing processes. Diamond coatings have the potential to provide negligible wear, ultralow friction, and high corrosion resistance for the sliding surfaces of mechanical seals, because diamond exhibits outstanding tribological, physical, and chemical properties. However, diamond coatings produced by conventional chemical vapor deposition (CVD) exhibit high surface roughness (Ra ≥ 1 μm), which results in high wear of the seal counterface, leading to premature seal failure. To avoid this problem, we have developed an ultrananocrystalline diamond (UNCD) film formed by a unique CH4/Ar microwave plasma CVD method. This method yields extremely smooth diamond coatings wi...

A new technique for fabrication of self-lubricating ceramic-based composites has been developed. Multi-channel ceramic matrices with a predetermined number, diameter, and distribution of channels are fabricated and then filled with a lubricant such as polytetrafluoroethylene or perfluoropolyether. Friction coefficients of lubricant-filled silicon nitride against 52100 steel were found to be 0.1 to 0.2, in contrast with pure silicon nitride for which values of 0.6 to 0.7 were found. This friction reduction is insensitive to applied load or to sliding speed. The controlled pattern of porosity allows these materials to have lubricant loading of 7.5 to 10 volume percent, instead of 20–25% typical of traditional self-lubricating materials. This configuration permits higher crushing resistance and stiffness in comparison with conventional self-lubricating antifriction materials. Presented at the 54th Annual Meeting Las Vegas, Nevada May 23–27, 1999

Blisters that develop on carbon-graphite mechanical seal faces are irregularities in surface topography that result in poor sealing performance and a high incidence of catastrophic failure. On first inspection, a blister is a burnished area that is slightly elevated above the surrounding seal surface. In this study, the topography of several hundred blisters was examined with interference microscopy. The shape of the burnished area is typically elliptical or cylindrical. The leading edge against the direction of rotation of the mating seal ring extends abruptly upward from the surrounding seal surface. The trailing surface gradually merges into the parent seal face. Most blisters have a maximum height of 0.25 μm to 0.75 μm (10 μ-in to 30 μ-in). Presented at the 55th Annual Meeting Nashville, Tennessee May 7–11, 2000

Steel (4340) plates were subjected to two different types of unlubricated wear tests. In one case, in which a cylindrical slider and flat plate were used, the contact pressure was 0.13 MPa and the sliding speed was 0.08 m s −1 . Films of Fe 3 O 4 were found to grow from initial values of 2–4 nm to steady state values of 8–14 nm. These results occurred for test conditions in which (1) both the plate and the slider were hardened to Rockwell hardness 55–60 HRC, (2) both plate and slider were tempered to 7–9 HRC and (3) a hardened slider was used with a tempered plate. While most tests were conducted in air under ambient conditions, some testing was done under nitrogen to verify the validity of the analytical procedures. In another type of test, a bolted joint, fabricated from 4340 steel, was loaded to cause slip. Under these conditions, the contact pressure was 50 MPa and the sliding distance was 3.0 mm. The oxide film, again identified as Fe 3 O 4 , grew from an initial thickness of 5 nm to 7–10 nm after slip. The principal investigative technique was ellipsometry which is based on the measurement of changes in the polarization state of light reflected from a specimen surface. This technique permits the determination under ambient conditions of the film thickness in film-substrate systems. Little interference is found from the changes in reflectance caused by development of a wear scar or other locally severe surface damage.

In ellipsometry of rough surfaces, the commonly used parameters, psi and delta, are insufficient to characterize completely the changes in polarization state which occur when light is reflected from a rough surface. When an experimentally determined Mueller matrix is available, parameters indicative of depolarization, cross polarization, and change in ellipticity can be found. When the Mueller matrix is regarded as an operator mapping input polarization states depicted on a Poincare sphere to output states in a similar coordinate system, these new parameters can be illustrated in terms of their effects on the Poincare sphere. The depolarization and cross polarization parameters correlate with specimen roughness and reflectance.