The & l-has-van Alphen (dI-ivA)signal of the organic superconductor 13''-(BEDlTF)#SFsCHjCF$ 03O3 shows an inverse-sawtooth wave form which proves the existence of an ideal two-tlmensiond (2D) Fermi surface. The dHvA wave shape cartalmost perfectly be describedby a 2D theosy assuming a constantchemicatpotential. TMseither impIiesthe existence of the predictedquasi-one-dimensional band with an exceptionallylarge densi[yof statesor the chemical potentialmaybe pinneddue to locatized states nearthe Fermienergy.Keywords: Organic superconductors. M~gnetic measurements Organic metals of the type {BEDT-TTF)zX, where BEDT-TTF is bkethyletdthio-tetrathiafulvalene and X represents a monovalent anion, are characterized by their pronounced two-dimensional (2D) electronic structure with, often, negligible dispersion perpendicular to the highly conducting planes [1]. Nevertheless. the de Haas-van Aiphen (dHvA) oscillations in most of these high-quality metals exhibit only minor deviations from the conventional 3D Lifshitz-Kosevich (LK) theory [2]. This is in contrast to magnetoresistance oscillations where in a number of organic metals strong apparent deviations of the Shubnikovde Haas (SdH) signal fkom IX behavior have beersreported (see references in [3]). In transportdata, however, complicated scattering mechanisms are involved and a non-trivial tensor inversion is needed to extract the true SdH signaL Here, we report on true thermodynamic dHvA data which provide experimental evidenee for the existence of a perfeet 2D Fermi liquid in a bulk 3D organic metal.The highquaiity $-(BEDT-T'IT9ZSF5CH2CFZS03 single crystals were grown by cketrocrysb]]ization [4]. The magnetization Ml perpendicular to the applied magnetic field B was measured by means of a cmtilever torque magnetome- tory. The torque is given by ? = M x E which is proportional to B2 for an anisotropic field-independent susceptibility x of the sample. In general, x is a tensor and the absolute value of the torque has th$ form r = AXB2sin229, where AZ is the susceptibility difference between two principal axes of the x tensor and r9is the angle between 1? and one of the prittcipal tensor axes. For a 2D Fermi surface the torque dHvA signal is proportional to dFhiQ, with F = FJCOSQand the angie~between B and the normal to the conducting planes. Fig. l(a) shows the torque signal at Q = -0.7" where the dHvA amplitude is very small and any nonlinearities of the torque signal can be excluded. The dHvA oscillations are sitting on a torque background which follows a B2 behavior up to the highest field. This background signal is up to T = 75 K almost temperature independent and shows a sin2fi dependence as expected for a static field-independent susceptibility (Fig. 2). One principal axis of the x tensor lies at @ = 30". The occurrence of this anisotropic susceptibility is rather unusual for the organic metals and the origin of the signa~in the present material is unclear. It might be a remnant of the local magnetism of the molecular bands.At low fields and high temperat...
While sulfir in diesel fuels helps reduce friction and prevents wear and galling in fuel pump and injector systems, it also creates environmental pollution in the form of hazardous particulate and S02 emissions. The environmental concern is the driving force behind industry's efforts to come up with new alternative approaches to this problem. One such approach is to replace sulfur in diesel fuels with other chemicals that would maintain the antifi-iction and antiwear properties provided by sulfur in diesel fuels while at the same time reducing particulate emissions. A second alternative might be to surface-treat fuel injection parts (i.e., nitriding, carburizing, or coating the surfaces) to reduce or eliminate failures associated with the use of low-sulfir diesel fuels.Our research explores the potential usefulness of a near-frictionless carbon (NFC) film developed at Argonne National Laboratory in alleviating the aforementioned problems. The lubricity of various diesel ftlels (i.e., high-sulfur, 500 ppm; low sulfur, 140 ppm; ultra-clean, 3 ppm; and synthetic diesel or Fischer-Tropsch, zero sulfur) were tested by using both uncoated and NFC-coated 52100 steel <.. specimens in a ball-on-three-disks and a high-frequency reciprocating wear-test rig. The test program was expanded to include some gasoline fuels as well (i.e., regular gasoline and indolene) to further substantiate the usefulness of the NFC coatings in low-sulfur gasoline environments. The results showed that the NFC coating was extremely effective in reducing wear and providing lubricity in lowsulfur or sulfur-free diesel and gasoline fuels. Specifically, depending on the wear test rig, test pair, and test media, the NFC films were able to reduce wear rates of balls and flats by factors of 8 to 83.These remarkable reductions in wear rates raise the prospect for using the ultra slick carbon coatings to alleviate problems that will be caused by the use of low sulfur diesel and gasoline fiels. Surfaces of the wear scars and tracks were characterized by optical and scanning electron microscopy, and by Raman spectroscopy.
Scufing is a major problern that lirnits the life andreliability of sliding rribo-coniponents. Wl~en sc~iffing occurs, friction force rises sharply and is accompanied by an increase in noise and vibration; severe wear and plastic deformation also occur on the damaged surfnce. Attempts have been made over the years to combat scuffing by enhancing the surface properties of the rnachir~e elements, and by methods involving lubricant formulation and coating application. In this study, the a~ithors evaluated the scufing performance of an aniorphous, near-frictionless carbon (NFC) coating that provides super-low friction under dry sliding conditions. The test configicration used a ball-on-jlat contact in reciprocating sliding. The coatirlg was deposited on H I 3 steel. An uncoated 52100 steel ball was tested against varioits coatedjlats in room air Compared to uncoated surfaces, the carbon coatirlg increased the scufing resistance of the sliding surfnces by two orders of niagnitude. Microscopic analysis shows that scriffing occrtrred on coated surfaces only if the coating had been completely removed. I f appears that depending on coating rype, the authors observed that coating failure occurs before scuffing failure by one of two distinct niechanisms: the coating failed in a brittle manner and by spalling, or by gradual wear:
The subm"tted manuscript has been createdby the University of Chicagoas Operatorof Argonne NationalI.abaratoryunderContractNo. W-31-I09-ENG-38 withthe U.S. Departmentof Energy. The U.S. Govemmantretainsforitself,and otheraactingon its behalf,a paid-up,nonexclusive, Irrevocabletwldw"de Iicenssin said a"cfe to reproduce, preparederivativevmrke,oisbibute tX)pieS to the public,and perfomrpubfidyand cfkplaypubfidy,by or on behalfof the Government. August 1999Paper to be presented at 2000 SAE InternationalFuture TRIBOLOGICAL BEHAVIOR OF NEAR-FRICTIONLESS CARBON COATINGS IN HIGH-AND LOW-SULFUR ABSTRACTThe sulfur content in diesel fuel has a significant effect on diesel engine emissions, which are .currently subject to environmental regulations. It has been observed that engine particulate and gaseous emissions are directly proportional to fuel sulfur content. With the introduction of low-sulfur fuels, significant reductions in emissions are expected. The process of sulfur reduction in petroleum-based diesel fuels also reduces the lubricity of the fuel, resulting in premature failure of fuel injectors. Thus, another means of preventing injector failures is needed for engines operating with low-sulfur diesel fuels. In this study, we evaluated a near-frictionless carbon (NFC) coating (developed at Argonne National Laboratory) as a possible solution to the problems associated with fuel injector failures in lowIubricity fuels. Tribological tests were conducted with NFC-coated and uncoated H13 and 52100 steels lubricated with high-and low-sulfur diesel fuels in a high-frequency reciprocating test machine. The test results showed that the NFC coatings reduced wear rates by a factor of 10 over those of uncoated steel surfaces. In low-sulfur diesel fuel, the reduction in wear rate was even greater (i.e., by a factor of 12 compared to that of uncoated test pairs), indicating that the NFC coating holds promise as a potential solution to wear problems associated with the use of low-lubricity diesel fuels.
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