James L. Lauer

Lubrication by a smectic liquid crystal

The hydrodynamic aspects of lubrication by the smectic A liquid crystal octylcyanobiphenyl (8CB) were investigated in a thrust bearing and in the concentrated ball-on-flat contact. Both bearings were run with a Newtonian mineral basestock for comparison and performed as expected; friction followed the Stribeck curve in the thrust bearing and the film thickness increased with (velocity)2/3 in the elastohydrodynamic lubrication of the point contact. The lubricating behavior of the smectic liquid crystal is qualitatively different from that of the Newtonian fluid. Curves of friction coefficient vs velocity × viscosity/load cannot be superimposed to form a Stribeck curve. The higher the load, the lower the velocity at which low friction is maintained, which is opposite to the behavior of Newtonian fluids. In concentrated contact (EHD lubrication) the smectic gives a friction coefficient that is constant with velocity and lower than the minimum value with the Newtonian fluid. The fluid film thickness varies wi...

Tribochemical Lubrication of Ceramics by Carbonaceous Vapors

Friction coefficients of less than 0.02 and negligible wear have been attained and continuously maintained in a pin-on-disc apparatus between a sapphire pin and discs of Sialon, silicon carbide, zirconia or zirconialalumina as long as a carbonaceous gas or vapor, such as ethylene, propane, benzene, or 1-propanol, was supplied to the conjunction region. Mean contact pressures were around 300 MPa and bulk temperatures were varied between ambient and 700°C. For every ceramic and vapor combination some temperature ranges exhibited high friction and wear, others very low friction and wear. Raman and Auger spectroscopies of the carbonaceous deposits formed in the wear tracks show significant differences depending on the temperature range and the feed gases or vapors supplied. In general, friction and wear reduction occurred in two steps at different rates. The tribochemistry involved is likely to comprise hydrocarbon acid-catalytic cracking at low temperatures and pyrolysis at high temperatures. Presented as a ...

Solid lubrication by decomposition of carbon monoxide and other gases

Abstract Extended duration high temperature (above 500°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 × and 500 × 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.

High Temperature Solid Lubrication by Catalytically Generated Carbon

The wear process in bearings generates a clean active surface. Carbon is known to form readily on catalytic surfaces through the reduction of carbon oxides or hydrocarbons. Carbon, through the adsorption of hydrocarbons, water vapor, or oxygen, becomes an effective lubricant. If these three phenomena can be made to work together, a new concept of high temperature lubrication would be available. This paper presents laboratory investigations towards the development of this concept. Carbon has been successfully produced through catalytic reduction of ethylene on a variety of metallic and ceramic surfaces containing nickel. This carbon has been shown to reduce friction at a sliding interface at elevated temperatures. Presented as a Society of Tribologists and Lubrication Engineers paper at the STLE/ASME Tribology Conference in San Antonio, Texas, October 5–8, 1987

Alignment of fluid molecules in an EHD contact

Dichroic infrared emission spectra have been obtained from an operating elastohydrodynamic contact under conditions showing unequivocally that the molecules of the fluid are aligned under shear flow in the bulk of the fluid and that the extent of the alignment is increased by the presence of an additive in a small concentration. This work applied particularly to polyphenyl ether and to 1,1,2-trichloroethane as the additive, but similar results have been obtained with polycyclohexyls and the same additive. The observation of two separate glass transition for the polycyclohexyl solution is an indication of the occurrence of a phase separation in the Hertzian inlet zone. A model has been developed to explain the effect of these phenomena and their relation to traction. Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in New Orleans, Louisiana, October 5–7, 1981

Investigation of Frictional Transfer Films of PTFE by Infrared Emission Spectroscopy and Phase-Locked Ellipsometry

When a PTFE sheet was rubbed lightly and unidirectionally over a smooth surface of stainless steel an essentially monomolecular transfer film was formed. By special ellipsometric and emission infrared spectroscopic techniques it was possible to show that the film was 10–15 A thick and birefringent. From the intensity differences of infrared bands obtained with a polarizer passing radiation polarized in mutually perpendicular planes, it was possible to deduce transfer film orientation with the direction of rubbing. After standing in air for several weeks the transfer film increased in thickness by as much as threefold. At the same time both the index of refraction and the absorption index decreased. Examination of the surfaces by optical and electron microscopies showed that the films had become porous and flaky. These observations were consistent with previous tribological measurements. The coefficients of friction and were decreased with the formation of the transfer film but increased again as the film ...

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 microaystalline graphitic or vitreous. Wear under operating conditions is less than 2 nm/min. Presented at the 35th STLE/ASME Tribology Conference in Fort Lauderdale, Florida October...

Lubricants and lubricant additives under shear studied under operating conditions by optical and infrared spectroscopic methods

A physical basis was sought for differences in fuel economy with a typical petroleum lube base stock when various additives were present. The kinematic viscosity was maintained at 7.1 cS at 100°C by blending. Film thickness, temperature, and traction were determined for a ball/plate contact under elastohydrodynamic conditions. Different additives produced considerably different results. Invariably, small film thicknesses paralleled low temperatures in the conjunction region, low traction and high fuel economy. Zinc dithiophosphate (ZDDP) was unique in that it always increased film thickness, but increased traction only at high loads and low speeds while decreasing it otherwise. Other additives, e.g. friction modifier (FM) and viscosity index (VI) improver and combinations decreased film thickness and traction. To help determine the reasons for these behaviors—whether surface or bulk effects—polarized infrared emission spectra were collected from an operating mock journal bearing. Adherent layers do not ch...

Lubrication of Si3N4 and steel rolling and sliding contacts by deposits of pyrolyzed carbonaceous gases

Abstract Pin-on-disk and four-ball tests with steel and silicon nitride surfaces canbe lubricated by carbon deposited as a result of pyrolysis in the tribo-contacts of ethylene or other carbonaceous gases at bulk temperatures in excess of 500°C. The carbon deposits were analyzed and shown to be different for different gases. Substantial improvements could be achieved by insertion of a hot wire into the ethylene stream. This was shown to be equivalent to an admixture of a small amount of acetylene. Since carbon deposit formation from pure ethylene was enhanced by the presence of acetylene carbon, the carbon and not the gaseous acetylene was the catalyst for enhanced formation of lubricating carbon. Lubrication was also achieved with the carbon formed from a feed gas of carbon monoxide and hydrogen.

Fourier emission infrared microspectrophotometer for surface analysis—I. Application to lubrication problems

Abstract A Beckman-RIIC FS-720 far-infrared interferometer was converted into an emission microspectrophotometer for surface analysis. To cover the mid-infrared as well as the far-infrared the Mylar beamsplitter was made replaceable by a germanium-coated salt plate, and the Moire fringe counting system used to locate the moveable Michelson mirror was improved to read 0.5 μm of mirror displacement. Digital electronics and a dedicated minicomputer were installed for data collection and processing. The most critical element for the recording of weak emission spectra from small areas was, however, a reflecting microscope objective and phase-locked signal detection with simultaneous referencing to a blackbody source. An application of the technique to lubrication problems is shown.