W(n)C(0,+/-) (n = 1-6) clusters are investigated by using the density functional theory (DFT) at the B3LYP/LANL2DZ level. We find that the neutral, anionic and cationic ground state structures are similar within the same size, and constituted by substituting a C atom for one W atom in the structures of W(n+1) clusters. The natural bond orbital (NBO) charge analyses indicate that the direction of electron transfer is from the W atom to the 2p orbital of the C atom. In addition, the calculated infrared spectra of the W(n)C(0,+/-) (n = 2-6) clusters manifest that the vibrational frequencies of neutral, anionic and cationic clusters are similar in a range of 80 cm(-1)-864 cm(-1). The high frequency, strong peak modes are found to be an almost stretched deformation of the carbide atom. Finally, the polarizabilities of W(n)C(0,+/-) (n = 1-6) clusters are also discussed.
Using density functional theory (DFT), we have studied the effect of carbon concentration Z on the shear modulus G, elastic constant c(ij), and Poisson ratio nu of carbides (W(1/2)Al(1/2))C(Z) while the most stable structures are determined by calculating the lowest formation energy. It is found that the maximal G value and the lowest Poisson ratio nu value are reached at Z = 3/4 due to atomic configuration changes, additionally, G values of (W1/2Al1/2) CZ should be lower than that of WC due to lower c(ij) values. The results of electronic analysis show that the increased covalent bonding of C-2p and W-5d contributes to anisotropic c(ij) and G positively and results in a lower nu value because the excess negative charge induced by the substitution of Al(3+) for W(4+) is balanced by decreasing C atoms. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3569851]
Hyun Kwang Seok
Kyung Ho Jung
Yu Chan Kim
Jae-Hyeok Shim
Dong-Ik Kim
Seung-Hee Han
Kyeong Ho Baik
Pil-Ryung Cha
We present tungsten alloy coating of 150-200 mum thickness with improved plasma erosion resistance fabricated by plasma spraying of granular W-SiC composite powders. During increasing the SiC concentration to 8 wt%, we observed the increase in the hardness of the coating from 250 to 440 Hv. The plasma erosion depth of the coating decreased by 10 times compared with pure tungsten in the same erosion environment. [All rights reserved Elsevier].
Ogura, H.
Masuyama, S.
Izuchi, M.
Yamazawa, K.
Arai, M.
Tungsten-rhenium (W-Re) thermocouples are widely used in industry for measurements at high temperatures, up to . Since the electromotive force (emf) of a W-Re thermocouple is known to change during exposure at high temperatures, evaluation of the emf stability is essential for measuring temperature precisely and for realizing precise temperature control used to ensure the quality of products subject to annealing processes. To evaluate precisely the thermoelectric stability around , two Ru-C cells (crucible and Ru-C eutectic alloy) were constructed in our laboratory. The key feature of the cells is that their dimensions are large to ensure there is sufficient immersion available to evaluate the homogeneity characteristics of the thermocouples. By using one of the Ru-C cells, the drift and inhomogeneity of Type C (tungsten-5 % rhenium vs tungsten-26 % rhenium) thermocouples during an exposure to high temperature around were evaluated. Furthermore, to explore possible applications of the eutectic point to other types of high-temperature thermocouples, the drift of an IrRh/Ir thermocouple (iridium-40 % rhodium vs iridium) was also evaluated using another Ru-C cell. The tests with W-Re and IrRh/Ir thermocouples demonstrate that the newly developed Ru-C cells can be used to successfully realize melting plateaux repeatedly. This enables the long-term drift measurements essential for the evaluation and improvement of high-temperature thermocouples. The results obtained in this study will also be useful for evaluating the uncertainty of thermocouple calibrations at around .
J. Ribeiro
D. M. dos Anjos
J. -M. Léger
F. Hahn
P. Olivi
A. R. de Andrade
G. Tremiliosi-Filho and K. B. Kokoh
Binary and ternary Pt-based catalysts were prepared by the Pechini–Adams modified method on carbon Vulcan XC-72, and different nominal compositions were characterized by TEM and XRD. XRD showed that the electrocatalysts consisted of the Pt displaced phase, suggesting the formation of a solid solution between the metals Pt/W and Pt/Sn. Electrochemical investigations on these different electrode materials were carried out as a function of the electrocatalyst composition, in acid medium (0.5 mol dm−3 H2SO4) and in the presence of ethanol. The results obtained at room temperature showed that the PtSnW/C catalyst display better catalytic activity for ethanol oxidation compared to PtW/C catalyst. The reaction products (acetaldehyde, acetic acid and carbon dioxide) were analyzed by HPLC and identified by in situ infrared reflectance spectroscopy. The latter technique also allowed identification of the intermediate and adsorbed species. The presence of linearly adsorbed CO and CO2 indicated that the cleavage of the C–C bond in the ethanol substrate occurred during the oxidation process. At 90 掳C, the Pt85Sn8W7/C catalyst gave higher current and power performances as anode material in a direct ethanol fuel cell (DEFC).
(Ti, W, Mo, V)(C, N) nanocomposite powders with globular-like particle of 10–100 nm were synthesized by a novel method, namely carbothermal reduction–nitridation (CRN) of complex oxide–carbon mixture, which was made initially from salt solution containing titanium, tungsten, molybdenum, vanadium and carbon elements by air drying and subsequent calcining at 300 °C for 0.5 h. Phase composition of reaction products was discussed by X-ray diffraction (XRD), and microstructure of the calcined powders and final products was studied by scanning electron microscopy (SEM) and transmission electron microscope (TEM), respectively. The results show that the synthesizing temperature of (Ti, W, Mo, V)(C, N) powders was reduced greatly by the novel precursor method. Thus, the preparation of (Ti, 15W, 5Mo, 0.2V)(C, N) is at only 1200 °C for 2 h. The lowering of synthesizing temperature is mainly due to the homogeneous chemical composition of the complex oxide–carbon mixture and its unusual honeycombed structure.
(Ti, W, Mo, V)(C, N) nanocomposite powders with globular-like particle of 10–100 nm were synthesized by a novel method, namely carbothermal reduction–nitridation (CRN) of complex oxide–carbon mixture, which was made initially from salt solution containing titanium, tungsten, molybdenum, vanadium and carbon elements by air drying and subsequent calcining at 300 °C for 0.5 h. Phase composition of reaction products was discussed by X-ray diffraction (XRD), and microstructure of the calcined powders and final products was studied by scanning electron microscopy (SEM) and transmission electron microscope (TEM), respectively. The results show that the synthesizing temperature of (Ti, W, Mo, V)(C, N) powders was reduced greatly by the novel precursor method. Thus, the preparation of (Ti, 15W, 5Mo, 0.2V)(C, N) is at only 1200 °C for 2 h. The lowering of synthesizing temperature is mainly due to the homogeneous chemical composition of the complex oxide–carbon mixture and its unusual honeycombed structure.
Bolokang, A. S.
Phasha, M. J.
Oliphant, C.
Motaung, D.
In the current study results of the milled and sintered V W C Co powders are presented Analytical techniques such as SEM equipped with EDS and XRD were used to study microstructure and phase evolution respectively I addition to B1 (VW)C solid solution a rhombohederal V(2)O(3) and new tau type (Cr(23)C(6)) carbide were formed after sintering The possible formation mechanisms behind detected phases are discussed It is evident that complete MA process depends strongly on the starting compositions of pure elements their lattice coherency according to Hume-Rothery rules on crystal structure and atomic size and enough milling time that provides adequate kinetics (C) 2010 Elsevier Ltd All rights reserved