Wüest M. 51 Wykes M. 82 Yamaguchi M. 17 Ybarra G. 129 Yubero F ...

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JUNE 28 WEDNESDAY MORNING RIVA-SS-WEM-OR.8 THE TRIBOLOGICAL BEHAVIOUR OF W-S-C FILMS IN PIN- ON-DISK TESTING AT ELEVATED TEMPERATURE. M. Evaristo, T. Polcar, A. Cavaleiro, ICEMS -Faculdade de Ciências e Tecnologia da Universidade de Coimbra, Dep. Eng. Mecânica, Rua Luís Reis Santos, 3030-788 Coimbra, Portugal Transition metal dichalcogenides (TMD) are well known for their self lubricant properties, due to unique crystal structure. However, the structure of TMD presents some drawbacks, particularly, they have low hardness making them inappropriate to applications requiring high load bearing capacity. Moreover, TMD films exhibit morphologies with high porosity promoting oxidation, particularly in humid atmosphere or elevated temperature. Several approaches have been used to increase the mechanical properties of TMD thin films. One of the most successful is either doping TMD with a metal, which increases hardness, or the deposition of an interlayer improving adhesion. MoS 2 is one of the most studied TMD, showing good results when deposited with an interlayer and doped with Ti, Cr, and other metals. There is a reference in literature showing that WS 2 has higher oxidation resistance than MoS 2 (about 100ºC), therefore, it is a good candidate for films with good tribological behaviour at high temperatures. Previous works showed that the hardness and adhesion of W-S films doped with C or N deposited with a Ti interlayer significantly increased compared to pure WS 2 . The analysis of friction and wear behaviour at elevated temperatures was the main aim of this study. W-S-C films were deposited by magnetron sputtering in an Ar atmosphere with a Ti interlayer. A carbon target with several pellets of WS 2 incrusted in the zone of the preferential erosion was used. The number of pellets was changed to modify the carbon content in the films, which varied from 26 up to 70at.%. Doping W-S films with carbon lead to a substantial increase of the hardness in the range 4 to 10GPa; the maximum of hardness was obtained for coatings with the carbon content of 40at.%. The XRD diffraction patterns showed that there was a loss of crystallinity with the increase of the carbon content in the film. SEM images of the cross section of the films showed decrease of the dimensions of the columnar structure and decrease of the porosity as the carbon content in the films increased. The coatings were tested by pin-on-disk from room temperature (RT) up to 400ºC. At RT, the friction coefficient was in range 0.3-0.1, and the wear rate decreased with the carbon content. At temperatures higher than 100ºC, the friction is below 0.1 for all compositions, which can be explained by the atmosphere drying. The tribological behaviour of the coatings with increasing temperatures depends on the films carbon content. For low carbon content up to 40at.%, the wear rate was almost independent of the temperature up to 300º, while it increased dramatically in case of coatings with high carbon content. The highest carbon content (∼70at.%) coatings were peeled off from the substrate at temperatures exceeding 100 ºC. In general, the limiting temperature for W-S-C coatings is 400ºC. 96
JUNE 28 WEDNESDAY MORNING RIVA-SS-WEM-OR.7 AB INITIO CALCULATIONS FOR THE EXCITED STATE AND THE CATION OF DIPHENYL ETHER AND COMPARISON WITH REMPI EXPERI- MENTS. M. Guerra and A. C. S. Paiva. CEFITEC Department of Physics, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2<strong>82</strong>9-<strong>51</strong>6, Caparica, Portugal. The structure and minimum energy conformations of diphenyl ether (Ph 2 O) both for the ground state and the first excited state are calculated using HF/6-311++G**, MP2/6-311++G**, BLYP/6- 311++G** and B3LYP/6-311++G** ab initio and density functional computations. Potential energy surfaces are also obtained for the rotation of the phenyl rings relatively to the C-O-C plane both for the neutral molecule and the positive ion. The global minimum of the Ph 2 O potential energy surface was found to be a “twisted” conformation and it doesn’t change with the excitation to the first excited state nor with a single ionization, altough the C-O-C-C dihedral angle varies slightly and the molecule floppyness decreases. An initial study of the molecule fragmentation was performed at B3LYP/6-311++G** theory level. The spectra of Ph 2 O cooled in a supersonic jet expansion, obtained with one-color resonance enhanced two-photon ionization suggests the existence of different conformations [1] . The first excited state low-frequency vibrations for three of the conformers were investigated using a Configuration Interaction aproach (CI-Singles) and Complete Active Space Multiconfiguration Self Consistent Field (CASSCF) method. The comparison between the calculated and observed spectra for all the conformers thus allows us to assign the major bands. Keywords: Conformational analysis; Diphenyl ether; Photoionization; Ab initio calculation [1] A. C. S. Paiva et al., International Journal of Mass Spectrometry 221 (2002) 107-115 95
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Wüest M. 51 Wykes M. 82 Yamaguchi
Page 3 and 4: Oliveira F. J. 140 Orts M.J. 76 Ota
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PARALLEL SESSIONS 7
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PLENARY 5
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JUNE 26, 2006 Morning Session INDEX
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Sigilum Universitatis Studii Salama
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