Metal matrix composites – From science to technological significance

Steels for bearings

Mechanochemistry means mechanical breakage of intramolecular bonds by external force and must be differentiated from molecular solid-state chemistry, where contacts between micronized molecular solids are created by the mechanical action for mutual approach of the reacting centers. After an outline of the mechanistic differences, the varied mechanochemistry is discussed. Grinding, milling, shearing, scratching, polishing, and rapid friction (for polymers also cutting, kneading, extruding) provide the mechanical impact for mechanochemistry, while sonication and shock waving for intramolecular bond breaking are generally described as thermal processes. The various types of mechanophysics (e.g., mechanoelectricity, conformational changes, thixotropy, rheopexy, stirring of Newtonian liquids or suspensions, etc.) are not treated here. Mechanochemistry covers solid-state reactions of infinitely covalent crystals, brittle metals, polymers, molecular solids with weak covalent bonds, strong intramolecular bond breakage in shearing Bridgman's anvil or by friction at lubrication of rapidly moving cold contacting surfaces, and single bond breaking or cutting. The diverse wealth of practical applications of mechanochemistry is outlined with typical examples for ceramics, mechanical alloying, hydrogen storage, organic syntheses, waste remediation, leachings, surface plasmas, radical formation, explosives, nanotube formation, nanoparticles grafting, polymer technology, radical initiation, scratch-less polishing, wear protection, lubrication, mechanochromism, nano-dissection, and many more.

http://webpages.iust.ac.ir/naimi/Lectures/Current%20Topics%20in%20Synthetic%20Organic,%20PhD/Kaupp,%20MechanochemistryReprint.pdf

Mechanochemistry: the varied applications of mechanical bond-breaking

Thermoelectrics, an environmentally-friendly source of electrical power

The tribological performance of room-temperature ionic liquid of alkylimidazolium tetrafluoroborate was evaluated using an Optimol SRV oscillating friction and wear tester in air and a CZM vacuum friction tester in vacuum (1×10-3 Pa) using a steel/steel (SAE52100) contact. From the results, the ionic liquid exhibits excellent friction-reduction, antiwear proprieties, both in air and vacuum, which are superior to phosphazene (X-1P) and perfluoropolyether (PFPE). During friction, the ionic liquid forms a surface protective film mainly composed of FeF2 and B2O3, which contributes to low friction and wear.

Tribological Performance of Room-Temperature Ionic Liquids as Lubricant

A capillary viscometer was used to measure viscosity as a function of pressure, temperature, and shear stress for a number of lubricants. Measurements were made at 38 C, 99 C, and 149 C (100 F, 210 F, and 300 F), gauge pressure to 5.5 × 108 N/m2 (8 × 104 psi), and shear stresses to 106 N/m2 (14.5 psi). At 38 C (100 F), the order of the pressure-viscosity coefficients for the unformulated fluids was: fluorinated polyether > synthetic hydrocarbon > naphthenic mineral oil > synthetic paraffinic oil (lot 4) > C-ether ≅ synthetic paraffinic oil (lot 3) > polyalkyl aromatic > advanced ester. All pressure viscosity coefficients decreased with increasing temperature. Fair agreement was obtained when pressure-viscosity coefficients at 38 C (100 F) and 6.9 × 107 N/m2 (104 psi) were compared to data from other investigators using different techniques (optical elastohydrodynamics, oscillating crystal, and low shear capillary viscometry). Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME...

Pressure-viscosity measurements for several lubricants to 550 meganewtons per square meter /80,000 PSI/ and 149 C /300 F/

QuynhGiao N. Nguyen t and William R. Jones, Jr. (Fellow, STLE)NASA Glenn Research CenterCleveland, Ohio 44135AbstractThe vapor pressures and wear characteristics are critical properties for liquid lubricants to assure long-term reliability and performance in space applications. Vapor pressures, obtained using a Knudsen celltechnique, and wear properties, obtained using a vacuum four-ball apparatus, were measured for a series ofunformulated liquid lubricants. These included: two multiply alkylated cyclopentanes (MACs) (X-1000 and X-2000), two linear perfluoropolyalkylethers (PFPAEs) (Z-25 and 815Z), and four silahydrocarbons (a tri-,a tetra-and two pentas). Vapor pressures were measured at three elevated temperatures (423,448 and 498K) andextrapolated to room temperature 298K. The lowest 298K vapor pressure of 5.7 x 1014 Pa, was obtained with thePFPAE fluid (815Z) and the highest value with the low molecular weight MAC (X-1000) at 3.6 x 10.7 Pa. Inaddition, vacuum wear rates were determined for some of the lubricants. The lowest wear rates (approximately 3x 1011 mm3/mm) were observed for three of the silahydrocarbons while the highest wear rates (approximately 2 x10.9mm3/mm) were observed with the two PFPAE fluids (Z-25 and 815Z). The MAC (X-2000) yielded a wear rateof about 101° mm3/mm. The results indicated that the silahydrocarbon class of liquid lubricants offers the betterpotential for space applications.KeywordsFluorocarbons, Hydrocarbons, Space Vehicles, Synthetic Lubricants, Vapor Pressure, Wear Testing DeviceIntroductiont Work performed as a contractor for AYT Corporation, Brookpark, Ohio 44142This report is a preprint of an article submitted to a journal forpublication. Because of changes that may be made before formalpublication, this preprint is made available with the understandingthat it will not be cited or reproduced without the permission of theauthor.

https://ntrs.nasa.gov/api/citations/20020024445/downloads/20020024445.pdf

For space applications

The interfacial chemistry of Fomblin Z25, a commercial perfluoropolyether used as lubricant for space applications was studied with different metallic surfaces: 440C steel, gold, and aluminum. Thin layers of Fomblin Z25 were evaporated onto the oxide-free substrates, and the interfacial chemistry was studied using XPS and TDS. The reactions were induced by heating the substrate and by rubbing the substrate with a steel ball. Gold was found to be completely unreactive towards Fomblin at any temperature. Reaction at room temperature was observed only in the case of the aluminum substrate, the most reactive towards Fomblin Z25 of the substrates studied. It was necessary to heat the 440C steel substrate to 190 C to induce decomposition of the fluid. The degradation of the fluid was indicated by the formation of a debris layer at the interface. This debris layer, composed of inorganic and organic reaction products, when completely formed, passivated the surface from further attack to the Fromblin on top. The tribologically induced reactions on 440C steel formed a debris layer of similar chemical characteristics to the thermally induced layer. In all cases, the degradation reaction resulted in preferential consumption of the difluoroformyl carbon (-OCF2O-).

Interfacial chemistry of a perfluoropolyether lubricant studied by x‐ray photoelectron spectroscopy and temperature desorption spectroscopy

The mechanisms operative in thermal oxidative degradation of Fomblin Z and hexafluoropropene oxide derived fluids and the effect of alloys and additives upon these processes are investigated. The nature of arrangements responsible for the inherent thermal oxidative instability of the Fomblin Z fluids is not established. It was determined that this behavior is not associated with hydrogen end groups or peroxy linkages. The degradation rate of these fluids at elevated temperatures in oxidizing atmospheres is dependent on the surface/volume ratio. Once a limiting ratio is reached, a steady rate appears to be attained. Based on elemental analysis and oxygen consumption data, CF2OCF2CF2O2, no. CF2CF2O, is one of the major arrangements present. The action of the M-50 and Ti(4 Al, 4 Mn) alloys is much more drastic in the case of Fomblin Z fluids than that observed for the hexafluoropropene derived materials. The effectiveness of antioxidation anticorrosion additives, P-3 and phospha-s-triazine, in the presence of metal alloys is very limited at 316 C; at 288 C the additives arrested almost completely the fluid degradation. The phospha-s-triazine appears to be at least twice as effective as the P-3 compound; it also protected the coupon better. The Ti(4 Al, 4 Mn) alloy degraded the fluid mainly by chain scission processes this takes place to a much lesser degree with M-50.

/pdf/thermal-oxidative-degradation-reactions-of-linear-4aa83t1uk6.pdf

Thermal oxidative degradation reactions of linear perfluoroalkyl ethers

Four research areas at the NASA Glenn Research Center involving the tribology of space mechanisms are highlighted. These areas include: soluble boundary lubrication additives for perfluoropolyether liquid lubricants, a Pennzane dewetting phenomenon, the effect of ODC-free bearing cleaning processes on bearing lifetimes and the development of a new class of liquid lubricants based on silahydrocarbons.

/pdf/research-on-liquid-lubricants-for-space-mechanisms-5fzpk2y9hv.pdf

Research on Liquid Lubricants for Space Mechanisms

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