CO, O(2), and H(2) adsorption on a clean W(2)C(0001)root 13 x root 13 R +/- 13.9 degrees reconstructed surface at room temperature (RT) were investigated using high-resolution electron energy loss spectroscopy (HREELS). The W(2)C(0001) adsorbs CO molecularly and adsorbs O(2) dissociatively, but does not adsorb H(2) at RT. In the CO adsorption system, two C-O stretching (antisymmetric CCO stretching) modes were found at 242.3 meV (1954 cm(-1)) and at 253.0 meV (2041 cm(-1)). The low-frequency site is occupied at first with subsequent conversion to the high-frequency site with increasing coverage. Additionally, a small peak was apparent at 104.5 meV (843 cm(-1)), and a middle peak at 50-51 meV (400-410 cm(-1)), which are assignable to a symmetric stretching mode and a hindered translational mode, respectively, of a CCO (ketenylidene) species. These observations are consistent with the CO adsorption model on top of the surface carbon. For oxygen adsorption, two adsorption states were found at 65.2-68.1 meV (526-549 cm(-1)) and 73.6 meV (594 cm(-1)): typical frequencies to oxygen adsorption on metal surfaces. Results suggest that atomic oxygen adsorption occurred on a threefold hollow site of the second W layer. (C) 2011 American Institute of Physics. [doi:10.1063/1.3650246]
The enhancement of efficiency in gas turbine engines requires the development of new superalloys capable of withstanding higher temperatures. The development of novel industrial cast and wrought (C&W) disk alloys with required combination of strength, creep and fatigue resistances at 700°C is particularly desired due to the expensive cost of powder metallurgy. In this context, new C&W disk alloys were recently developed to fulfill these requirements. TMW4 shows higher properties than the current C&W disk alloy despite an expensive cost due to its high cobalt content, where as 718Plus presents a moderate cost with restricted creep properties at 700°C compared to the current U720Li disk alloy. The new nickel base superalloys developed by Aubert & Duval were therefore designed to offer a better compromise between high temperature properties at 700°C and cost. This paper describes the alloy metallurgical features and is especially focused on the alloy design which is extensively based on phase diagram modeling. The study was firstly carried out on small ingots of 6 kg to optimize the chemistry before forging 200 kg ingots by industrial processes. The ability to be processed by the conventional cast & wrought route and the control of the highly expensive elements contents confer to the alloys an attractive cost comparable to that of 718Plus alloy. The high amount of ’ and the molybdenum-tungsten levels insure higher creep and tensile properties than those obtained with 718Plus.
Schoenung, J. M.
The effect of the laser engineered net shaping (LENS) process on the microstructure and mechanical properties of (Ti,W)C-Ni solid solution cermets was investigated. Nano-(Ti,W)C-Ni powder was synthesised, spray dried and densified by two different processes: sintering and LENS. Furthermore, all results were compared with conventional micrometre sized TiC-WC-Ni cermets. Solid solution (Ti,W)C-Ni cermets made by sintering resulted in a coreless and ultra fine microstructure, while the LENS processed specimens revealed inhomogeneous microstructure and particle coarsening. The hardness values of the LENS processed specimens range from 15 to 20 GPa, which is higher than for the ultra fine and conventional sintered composites (~12 GPa). The measured toughness values show greater variability.
This article investigates W. C. Handy's collection of blues and jazz compositions Blues: An Anthology (1926) in light of Paul Whiteman's pre-eminent role in 1920s American popular music culture. It explores Whiteman's autobiographics, on the one hand, and the correspondence between Handy and the author of the anthology's foreword, Edward Abbe Niles, on the other, in order to demonstrate how Handy's self-determined voice asserted itself against both the discursive power of the Whiteman-led symphonic jazz movement and the appropriative impulse of primitivist jazz and blues historiography.
Hitherto, limestone has been recognised as a suitable substitute for cement replacement. The present study was an experimental investigation of the properties of Portland limestone cement and the effects of water-to-cement (w/c) ratio on performance of concretes containing it. The Portland limestone cement concrete specimens (containing 14% limestone) with w/c ratio of 0·35, 0·45 and 0·55 were experimentally compared to ordinary Portland cement concrete specimens. The results demonstrated that w/c ratio has a prominent effect on the performance of Portland limestone cement concretes, with higher w/c resulting in weaker performance. Therefore Portland limestone cement containing 14% limestone can be considered as a low-cost, effective and available supplementary cementing material.
Milling was carried out in flowing argon but was interrupted at regular time intervals to take samples for X-ray diffraction (XRD). Because of exposure to air during the interruptions the powder was partly oxidized. The oxides formed did not appear in XRD patterns because they were of extremely fine grain size. As a result of the loss of V and W through oxidation, free carbon was also found in the final powder. The lattice parameter of the (V,W)C powder increased with milling time up to a maximum, then it decreased, which suggests that the amount of W in (V,W)C increased with milling time up to a maximum and then decreased. The crystallite size of the (V,W)C powder was calculated from the X-ray data and was found to be in the nm range (down to approximately 8 nm). Subsequent uninterrupted milling produced a powder which was freer from oxides and free carbon. (C) 2008 Elsevier B.V. All rights reserved.