Papers by Keyword: Oxide

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Authors: Xin Wang, Ya Yu Wang, Wei Tao Zheng, Zan Wang
Abstract: Nitrogen-doped carbon nanotubes (N-CNTs) were synthesized using air as the nitrogen carrier gas and CH4 as the carbon source by plasma-enhanced chemical vapor deposition over a thin catalyst film of Fe50Ni50. Transmission electron microscopy and high resolution transmission electron microscopy measurements have indicated that the N-CNTs grew with a tip-type growth mode. When H2 was added to the CH4/air plasmas during the N-CNTs growth stage, it was found that Fe/Ni oxide nanowire was filled into the nanotube. However, without adding H2 in the CH4/air mixture plasma, only metal oxide nanoparticle was found on the tip of the N-CNT.
Authors: Zheng Li, Y.G. Xiao, M.H. Tang, J.W. Chen, H. Ding, S.A. Yan, Y.C. Zhou
Abstract: A theoretical model for radiation effect in a metal-ferroelectric-semiconductor (MFS) field-effect transistor was proposed by considering the fixed charges (Qfx) and interface charges (Qit) induced by ionizing radiation. In this model, the energy band-bending and surface charge in Si at a given gate bias were calculated systematically as a function of fixed charges (Qfx) and interface charges (Qit). The drain-source current (ID) was derived in an exact form without any approximation. All modeling done in this work was generalized to both n and p type Si substrates with an easy sign of the Fermi level potential in the formalism. The derived results demonstrate that the symmetry of polarization versus gate voltage curve of the MFS structure degrades when Qfx and Qit increase, which can explain the imprint behavior successfully. Additionally, the residual polarization in the ferroelectric field-effect transistor decreases with increasing Qfx and Qit, which can account for the polarization reduction. As expected, the calculated transfer characteristic of the ferroelectric FET shows that the subthreshold voltage is significantly affected by Qfx and Qit. This investigation may provide some useful insights for the space applications of ferroelectric FET’s.
Authors: Bei Yue Ma, Ying Li, Jing Kun Yu
Abstract: The latest development of ZrC-SiC, ZrO2-SiC and ZrO2-mullite high performance composites synthesized from zircon was reviewed. The future development of synthesizing high performance composites from cheap materials and simple preparation technology was prospected.
Authors: John C. Burford, Jerry Sokolowski
Abstract: Traditional gravity pour down-sprue methods of filling moulds in the making of aluminum castings inherently lead to oxide and air bubble entrainment. The reason for this is found in the high velocities the metal flow experiences during the filling of a mould. The Nemak Windsor Aluminum Plant (WAP) produces cylinder blocks using the low-pressure Cosworth process, which includes low velocity up-hill filling of the sand mould package. This doctrine is followed in all except one part of the process: the runner system. The nature of the resulting defect is generally known as Head Deck Porosity. Runners were cast full in open production runners at three different velocities with the resulting quickly chilled castings analyzed using X-ray radioscopy, and Scanning Electron Microscopy. Results reveal that the subject bubble porosity is indeed the result of air entrained during initial transient flow within the production runner system whose velocity is higher than the critical value of 0.5ms-1. This theoretical value is corroborated by experimental results. In addition, a new "sessile" runner of optimized shape, filled at a velocity slower than the critical value, is proposed and analyzed using Magmasoft mould fill modelling software. The design can potentially replace the existing runner providing a casting free of entrained air.
Authors: Jun Hu Liu, Bart Blanpain, Patrick Wollants
Abstract: TiB2 coatings were plasma sprayed in air and were studied by XPS. There are five elements in the top surface of the studied coatings, namely, B, C, N, O and Ti. Oxygen pick-up in the coatings results in formation of oxides of boron and titanium. Nitrogen was shown to exist in N-Ti and O-N-Ti in the coating. Depending on the spraying parameters, mono-boride as well as di-boride was also detected in the studied coatings. With careful peak fitting it was shown that oxygen may exist in the coating as dissolved atomic O in addition to as lattice oxygen in the oxide of boron and titanium.
Authors: Toshinobu Chiba
Authors: Michal Krzyzanowski, W. Mark Rainforth
Abstract: Understanding and prediction of physical phenomena in different scales at the same time that are taking place at the tool/workpiece interface during high shear processing is done in different ways combining the latest finite element (FE) and discrete element (DE) analysis technology. The high shear processing is observed during hot rolling of aluminium, when it produces a highly deformed subsurface layer; and also during friction stir welding (FSW), when it results in significant heat generation and flow. The FE analysis is used for macro-scale simulation while the DE method is applied to simulate meso-scale phenomena taking place in the thin, sometimes a few micron thicknesses, surface layer. Different FE models and numerical techniques combined with DE based transient dynamics approaches are discussed in this work.
Authors: Eui Gyun Na, Seung Kee Koh, Dong Whan Lee
Abstract: The purpose of this study is to find out the AE characteristics and fracture mechanisms through AE signal analysis for the weldment, PWHT specimen and basemetal of the pressure vessel steel. Charpy sized specimens were taken from the multi-passed weld block. Specimens were given to four point bend and AE tests. Lots of AE signals were emitted from the weldment compared with the basemetal and PWHT specimen. Besides, amplitude for the weldment was the largest, followed by PWHT specimen and basemetal and more AE counts for the weldment were emitted in the process of deformation. Lots of microcracks around the notch for the weldment were formed so that more AE signals were produced. In addition, second phase particle such as MgO for the basemetal acts as AE source. However, in case of weldment, debonding mechanisms between matrix and hard oxides which are formed during welding in air attributed to the emission of AE signals and softened particles for the PWHT specimen cause to produce the low level AE signals.
Authors: Alain C. Pierre
Abstract: Aerogels are often largely mesoporous solids, with a porosity which may exceed 90 vol% and a specific surface area up to 1000 m2 g-1. Such materials were first obtained by Kistler in 1932, and designate gels in which the liquid was replaced with a gas without collapsing the gel solid network. Contrary to xerogels dried from wet gels by evaporation with an important shrinkage, the first aerogels were obtained by a “supercritical drying” technique in which the liquid which impregnated the gels was evacuated after being transformed to a supercritical fluid. The diversity in nature of the solid constituting the rigid network is very large. It includes simple oxides, multi oxide compositions, organic and hybrid organic-inorganic polymers and carbon. This diversity as well as the high specific pore volume and surface area make aerogels applicable either as catalysts or as catalyst supports. Besides, molecular catalysts such as transition metal complexes or enzymes can easily be immobilized in aerogels, which opened the road to new supported molecular catalysts and biocatalysts. This communication reviews the synthesis and properties of oxide aerogel catalysts.
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