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  • 1
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    Interfacial chemistry of a perfluoropolyether lubricant studied by X-ray photoelectron spectroscopy and temperature desorption spectroscopy (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: 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-).
    Keywords: NONMETALLIC MATERIALS
    Type: Journal of Vacuum Science and Technology A (ISSN 0734-2101); 11; 2; p. 354-367.
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  • 2
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    The Clouds and the Earth's Radiant Energy System Elevation Bearing Assembly Life Test (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The Clouds and the Earth's Radiant Energy System (CERES) elevation scan bearings lubricated with Pennzane SHF X2000 and 2% lead naphthenate (PbNp) were life tested for a seven-year equivalent Low Earth Orbit (LEO) operation. The bearing life assembly was tested continuously at an accelerated and normal rate using the scanning patterns developed for the CERES Earth Observing System AM-1 mission. A post-life-test analysis was performed on the collected data, bearing wear, and lubricant behavior.
    Keywords: Mechanical Engineering
    Type: 33rd Aerospace Mechanisms Symposium; 197-212; NASA/CP-1998-209259
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  • 3
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    The Effect of ODC-Free Cleaning Techniques on Bearing Lifetimes in the Parched Elastohydrodynamic Regime (1997)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: A parched elastohydrodynamic rig was used to determine relative bearing lifetimes as a function of cleaning procedures in a series of accelerated tests. Two ODC-free cleaning procedures (super critical CO2 and ultraviolet-ozone) were compared to a CFC-113 control. Bearings (52100 steel) were run in the counter rotating mode (equivalent to 4600 rpm) with a full complement (i.e. no retainer) and a single charge of lubricant (Krytox 143 AC). Test conditions included: an air atmosphere, 445N load, approx. 1.0 GPa mean Hertz stress. There was approximately a 50% reduction in life with bearings cleaned with UV/ozone and a 70% reduction in life with SFE CO2 when compared to the Freon control. Possible reasons for these decreases in lifetimes are presented.
    Keywords: Engineering (General)
    Type: Second Aerospace Environmental Technology Conference; 709-721; NASA-CP-3349
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  • 4
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    The Effect of Stress and TiC Coated Balls on Lubricant Lifetimes Using a Vacuum Ball-on-Plate Rolling Contact Tribometer (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: A vacuum ball-on-plate rolling contact tribometer was used to determine the relative lifetimes of a perfluoropolyether (Krytox 143 AC) on 440C stainless steel. The effect of mean Hertzian stresses (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 micro-g of lubricant, an initial vacuum level of less than 1.0 x 10(exp -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 PFPE lubricant is considered to be the reason for this enhancement. Decreasing lifetime with increasing stress levels correlated well with energy dissipation calculations.
    Keywords: Mechanical Engineering
    Type: 33rd Aerospace Mechanisms Symposium; 237-245; NASA/CP-1998-209259
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  • 5
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    Research on liquid lubricants for space mechanisms (1998)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: Four research areas at the NASA Lewis 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.
    Keywords: Nonmetallic Materials
    Type: Fortieth Anniversary: Pioneering the Future; 299-310; NASA/CP-1998-207191
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  • 6
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    The Role of Bearing and Scan Mechanism Life Testing in Flight Qualification of the MODIS Instrument (2001)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: The Moderate Resolution Imaging Spectroradiometer (MODIS) is an instrument aboard the Terra (EOS AM-1) satellite and has been operating successfully since December 1999. MODIS has been viewing the entire Earth's surface and gathering data to better understand the global dynamics and processes occurring on land, in the oceans, and in the lower atmosphere. All observations are made through an extremely high resolution, optically and mechanically precise, scan mirror motor/encoder assembly. The reliable performance of this assembly depends on two duplex bearing pairs lubricated with Pennzane, a synthetic hydrocarbon, formulated with lead napthanate. This paper describes the results of accelerated and operational life tests. It also describes the post-test analyses of the disassembled bearings. Analyses were performed using micro-Raman, micro-FTIR, X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), and Size Exclusion Chromatography (SEC). In general, the three sets of bearings in each of the test stations were in very good condition after accumulating 68, 144, and 209 million revolutions, respectively. Some of the bearings exhibited lubricant degradation, indicated by viscous lubricant deposits on the cage and raceways.
    Keywords: Spacecraft Instrumentation and Astrionics
    Type: 35th Aerospace Mechanisms Symposium; 1-14; NASA/CP-2001-209626
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  • 7
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    Thermal-oxidative pretreatment and evaluation of poly(hexafluoropropene oxide) fluids (1995)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Two commercial poly(hexafluoropropene oxide) fluids were thermally pretreated at 343 C in pure oxygen. IR and nuclear magnetic resonance(NMR) spectra indicate that this pretreatment was effective in removing hydrogen end-capped impurities. A decrease in the quantity of volatile material produced during thermal oxidative decomposition and increase in the thermal decomposition temperature indicated improvement in the stability of the fluids. However, this pretreatment failed to render the fluids completely stable in oxidizing atmospheres at 316 C in the presence of metal alloys.
    Keywords: INORGANIC AND PHYSICAL CHEMISTRY
    Type: STLE Tribology Transactions (ISSN 0569-8197); 38; 3; p. 571-576
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  • 8
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    Determination of the thermal stability of fluids by tensimetry - Instrumentation and procedure (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A computerized tensimeter and experimental procedure for determination of the thermal decomposition temperature (T sub d) of perfluoro alkylethers were developed and tested. Both the apparatus and the procedure are described in detail. Results of testing with bis(2-ethylhexyl) phthalate and trimethylolpropane triheptanoate demonstrate that the reciprocal of the decomposition temperature is a linear function of the logarithm of the gas volume/heated liquid volume ratio. The T sub d obtained for each compound at a gas volume/heated liquid volume ration of one was similar to the value previously reported using an isoteniscope technique. Results of testing with a polymer of hexafluoropropylene oxide demonstrate that this instrument and procedure can be used to determine the T sub d of perfluoro alkylethers.
    Keywords: NONMETALLIC MATERIALS
    Type: STLE Tribology Transactions (ISSN 0569-8197); 33; 519-527;
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  • 9
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    A preliminary study of ester oxidation on an aluminum surface using chemiluminescence (1987)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The oxidation characteristics of a pure ester (trimethyolpropane triheptanoate) were studied by using a chemiluminescence technique. Tests were run in a thin-film micro-oxidation apparatus with an aluminum alloy catalyst. Conditions included a pure oxygen atmosphere and a temperature range of 176 to 206 C. Results indicated that oxidation of the ester (containing 10 to the minus 3rd power M diphenylanthracene as an intensifier) was accompanied by emission of light. The maximum intensity of light emission (I sub max) was a function of the amount of ester, the concentration of intensifier, and the test temperature. The induction period or the time to reach one-half of maximum intensity (t sub 1/2) was an inverse function of test temperature. Decreases in light emission at the later stages of a test were caused by depletion of the intensifier.
    Keywords: NONMETALLIC MATERIALS
    Type: ASLE Transactions (ISSN 0569-8197); 30; 211-219
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  • 10
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    The preparation of new perfluoro ether fluids exhibiting excellent thermal-oxidative stabilities (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A series of low molecular weight perfluoroalkyl ethers (PFAEs) were synthesized by direct fluorination. Viscosity-temperature properties and oxidation stabilities were determined. Viscosity-temperature correlations indicated that increases in branching and increases in the size of the branching substituent caused a deterioration in viscometric properties (i.e., an increase in ASTM slope). In addition, increasing the ratio of carbon to oxygen in these compounds also increased the ASTM slope. Preliminary oxidation stability measurements indicated that highly branched PFAE fluids (i.e., those containing quaternary carbons) may be less stable than either those containing a single trifluoromethyl pendant group or those containing no branching at all.
    Keywords: CHEMISTRY AND MATERIALS (GENERAL)
    Type: I & EC - Industrial and Engineering Chemistry Research (ISSN 0888-5885); 27; 8, 19
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