Donald R. Wheeler

On the mechanism of lubrication by tricresylphosphate /TCP/ - The coefficient of friction as a function of temperature for TCP on M-50 steel

A pin-on-disk tribometer was used to study the coefficient of friction as a function of temperature for tricresylphosphate (TCP) on CVM M-50 tool steel under the following conditions: TCP was present in a liquid reservoir (bulk lubrication), and TCP was applied as a liquid layer directly to the disk (limited lubrication). Under limited lubrication conditions, experiments were performed in dry (< 100 ppm H2O) air, dry (< 20 ppm H2O) nitrogen, dry nitrogen with the disks heated to 700°C, then cooled to room temperature before the TCP was applied and the measurements made (preheated disks), and moist nitrogen using preheated disks. The coefficient of friction decreased at a characteristic temperature, Tr Tr values observed were: 265°C for bulk lubrication conditions in dry air, 225°C for limited lubrication conditions in dry air, and 215°C for limited lubrication conditions in dry nitrogen. The use of preheated disks produced a sharp failure temperature at 218°C which was taken as the temperature about which...

The adsorption and thermal decomposition of tricresylphosphate (TCP) on iron and gold

Because tricresyl-phosphate (TCP) is a common antiwear additive in lubricants, there is great interest in its interactions with metal substrates. The TCP was allowed to adsorb on polycrystalline iron and gold at room temperature. X-ray photoelectron spectroscopy (XPS) was used to analyze the adsorbed species. The substrate was then heated in steps to 330 C, and the changes in the adsorbate were analyzed after each step. On both substrates saturation adsorption occurred at about one monolayer, but the sticking coefficient was less on gold than on iron. Comparison of the XPS spectra of TCP on each substrate with the spectrum from condensed TCP indicated nondissociative adsorption on gold, possibly by dipole-induced dipole interaction. On iron, there was apparently additional interaction between the substrate and the tolyl groups on the TCP molecule. TCP began to desorb molecularly from gold as soon as the gold was heated above room temperature. The desorption was complete by 200 C. However, when the iron substrate was heated, TCP did not desorb but decomposed between 150 and 250 C.

Tribological Performance of Some Pennzane®-Based Greases for Vacuum Applications

Commercial greases for space applications usually fulfill the requirements imposed by the severe conditions of use (load, ultrahigh vacuum, speed, etc.). The main requirement is their ability to create an elastohydrodynamic lubrication film, boundary film, or both, for the speed, load, and temperature conditions under which the mechanisms will operate. Three greases, all based on a multiply alkylated cyclopentane (Pennzane®) base oil, were studied. The thickeners were an n-octadecylterephthalamate soap, a lithium soap, and a urea derivative. A four-ball tribometer and a spiral-orbit tribometer were employed to evaluate the greases under ultrahigh vacuum. The results indicated that all three greases yielded very low wear rates and extended lifetimes. In addition, routine physical property data are reported for each grease.

The Effect of Stress and TiC Coated Balls on Lifetime of a Perfluoropolyalkylether Using a Vacuum Rolling Contact Tribometer

A vacuum spiral orbit tribometer (SOT) was used to determine the relative lifetimes of a branched perfluoropolyalkylether (PFPAE) on 440C stainless steel. The effect of varying the mean Hertzian stress (0.75, 1.0, 1.5 and 2.0 GPa) and the use of TiC coated balls on lubricant lifetime was studied. Other conditions included: ∼100 rpm, ∼50 μg of lubricant, an initial vacuum level of < 1.3 × 10−6 Pa (< 1.0 × 10−8 Torr), and room temperature (∼23 °C). Increasing the mean Hertzian stress from 0.75 to 2.0 GPa results in an exponential decrease in lubricant lifetime for both material combinations. However, substituting a TiC ball for the 440C ball quadrupled lifetime at low stress levels (0.75 and 1.0 GPa) and doubled life at higher stresses (1.5 and 2.0 GPa). The reduced reactivity of the TiC surface with the PFPAE lubricant is considered to be the reason for this enhancement. Decreasing lifetime with increasing stress levels correlated well with energy dissipation calculations. Presented as a Society of Tribologists and Lubrication Engineers Paper at the ASME/STLE Tribology Conference in Seattle, Washington, October 1–4, 2000

The Influence of Sizings on the Durability of High-Temperature Polymer Composites

To increase performance and durability of high-temperature composites for potential rocket engine components, it is necessary to optimize wetting and interfacial bonding between high-modulus carbon fibers and high-temperature polyimide resins. Sizings commercially supplied on most carbon fibers are not compatible with polyimides. In this study, the chemistry of sizings on two high-modulus carbon fibers (M40J and M60J, Toray) was characterized as was the chemistry of PMR-II-50 fluorinated polyimide resin. The carbon fibers were characterized using single filament wetting, scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopic measurements. The polyimide matrix resins were coated onto glass filaments for characterization by wetting measurements. Surface energy components were obtained by wetting with nondispersive (methylene iodide), acidic (ethylene glycol), and basic (formamide) probes. A continuous desizing system that uses an environmentally friendly chemical-mechanical process was developed for tow level fiber. Composites were fabricated with fibers containing the manufacturers sizing, desized, and further treated with a reactive finish. Results of room temperature tests after thermal aging show that the reactive finish produces a higher strength and more durable interface compared to the manufacturers sizing. When exposed to moisture blistering tests, however, the better-bonded composite displayed a tendency to delaminate, presumably due to trapping of volatiles.

Quantitative characterization of an x-ray source in an x-ray photoelectron spectroscopy system

The x-ray spectrum from a dual anode x-ray source in an x-ray photoelectron spectroscopy system was calculated by the NIST Desk Top Spectrum Analyzer used for synthesizing spectra in energy dispersive x-ray analyzers commonly found in scanning electron microscopes. The energy flux was obtained by integrating over the x-ray energy spectrum. The energy flux from the source was measured by a silicon photodiode. Very good quantitative agreement was found between the flux obtained from the calculated spectra and the flux measured by the photodiode, indicating that the calculated spectra are, in fact, physically valid for this source. The calculated spectra were used to obtain the energy deposition as a function of depth below the irradiated surface of polytetrafluoro- ethylene, a material used in spacecraft and exposed to the space radiation environment.