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31.
Nicholaos G. Demas Jing Zhang Andreas A. Polycarpou James Economy 《Tribology Letters》2008,29(3):253-258
The tribological behavior of a wide range of compositions using blends of aromatic thermosetting polyester (ATSP) with polytetrafluoroethylene
(PTFE) has been investigated. PTFE was chosen as the blending material because of its low coefficient of friction and good
performance at high temperatures and resistance to chemicals. ATSP blends were used to specifically combat some of the shortcomings
of PTFE like its extremely low wear resistance and poor mechanical properties, and special processing requirements due to
its high melt viscosity. Controlled tribological experiments simulating an air conditioning compressor operating with R134a
refrigerant under realistic operating conditions were carried out with different ATSP/PTFE compositions, as well as four different
state-of-the-art commercially available composites containing carbon fibers, graphite and PTFE. It was found that the newly
synthesized composites exhibited superb tribological characteristics as far as low friction and low wear were concerned. The
wear performance of PTFE was greatly improved, while it was shown that greater amounts of ATSP used in the blend lead to lower
wear and the amount of ATSP did not significantly alter the friction coefficient. Material transfer and development of a weak
film on the disk surface was observed, especially for the blends with higher PTFE content. 相似文献
32.
N. Guskos J. Typek G. Zolnierkiewicz K. Wardal A. Guskos P. Berczynski D. Petridis 《Materials Science-Poland》2013,31(4):587-594
Two composites consisting of γ-Fe2O3 (maghemite) nanoparticles covered by two different oxygen-based free radicals derived from a 4-(methylamino)phenol sulphate and 8-hydroxy-1,3,6-trisulfonic trisodium salt acid were prepared and investigated by the magnetic resonance method in the 4–300 K range. Both composites displayed broad and very intense ferromagnetic resonance (FMR) lines originating from γ-Fe2O3 agglomerated nanoparticles. The FMR spectrum was fitted satisfactorily at each temperature by two Landau-Lifshitz functions reflecting the existence of magnetic anisotropy in the investigated system. The temperature dependence of the obtained FMR parameters (resonance field, linewidth, integrated intensity) was studied and the results were interpreted in terms of magnetic interactions between free radicals and nanoparticle agglomerates. A comparison with previously studied similar systems containing maghemite nanoparticles was made and conclusions about the role of free radicals were drawn. 相似文献
33.
Theodoros K. Katranas Konstantinos S. Triantafyllidis Athanasios G. Vlessidis Nicholaos P. Evmiridis 《Catalysis Letters》2007,118(1-2):79-85
In this work we prepared various zeolite-X and USY samples partially exchanged with copper, iron and platinum. These samples
were characterized by XRD, Chemical Analysis, SEM-EDS, N2-adsorption–desorption, ammonia-TPD, and tested as catalysts in high temperature (400 and 550 °C) propane transformation.
The obtained results revealed the strong effect of Si/Al ratio in faujasite zeolite structure, the number and strength of
acid sites and of the presence of different metal ions in countered ion sites, on the catalytic activity and selectivity of
zeolite-X and USY. The highest propane dehydrogenation activity was achieved with the platinum-exchanged X zeolite (∼11.2%
propylene yield, ∼31% selectivity). On the contrary USY zeolites showed high cracking capability and relatively low dehydrogenation
activity excepting the platinum-exchanged sample which yielded notably high aromatization products. 相似文献
34.
N. Guskos E. A. Anagnostakis G. Zolnierkiewicz J. Typek A. Biedunkiewicz A. Guskos P. Berczynski 《Materials Science-Poland》2012,30(1):23-31
Two nanocrystalline samples of TiC+SiC+20%C (sample 1) and Si3N4+Si(C,N)+Ti(C,N)+1%C (sample 2) were prepared by non-hydrolytic sol-gel method. The latter sample was produced from sample 1, by subjecting it to additional annealing at high temperature. XRD measurements showed the presence of aggregates of cubic SiC+TiC nanoparticles (10 to 30 nm in size). In both samples, a very narrow electron paramagnetic resonance (EPR) line originating from localized magnetic centers was centered at g eff??2. At T = 130 K, we registered the linewidths ??H pp = 1.41(2) G and ??H pp = 2.92(2) G for the sample without and with thermal annealing, respectively. For the non-annealed sample, the resonance line was fitted by a Lorentzian line in the low temperature range, and by a Dysonian line above 70 K, which indicates a significant change in electrical conductivity. Therefore, thermal annealing can significantly improve the transport properties of samples. An analysis of the temperature dependence of the EPR parameters (g-factor, linewidth, integrated intensity) showed that thermal annealing has a significant impact on the reorientation processes of localized magnetic centers. 相似文献
35.
Kyriaki Polychronopoulou Jungkyu Lee Christos Tsotsos Nicholaos G. Demas Ryan L. Meschewski Claus Rebholz Andreas A. Polycarpou 《Tribology Letters》2011,44(2):213-221
Ti-based protective thin films with thicknesses below 100 nm, intended for miniature applications were deposited using physical
vapor deposition magnetron sputtering. X-ray diffraction (XRD), scanning electron microscopy, and atomic force microscopy
were employed for the assessment of microstructure, morphology, film thickness, surface topography, and roughness. XRD pattern
showed the formation of f.c.c TiN, TiCN, and TiC phases with different preferred orientations for films prepared in Ar/N2, Ar/N2 + C2H2, and Ar/C2H2 gas mixtures, respectively. Nanotribological performance was investigated using multipass nanoscratch technique at variable
applied normal loads (100–400 μN). The nanoscale coefficient of friction was found to be in the 0.08–0.1 range, a sufficiently
low value showing the potential of these films for miniature applications, such as microelectromechanical systems. The nanowear
resistance at mean contact pressures in the range of 5–8.5 GPa for each sample was evaluated in terms of the average residual
wear depth and an abrasive-dominated wear mechanism was found. 相似文献
36.