Advanced Material Science and Technology

Volumes 675-677

doi: 10.4028/

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Authors: Peter Häussler, Martin Stiehler
Abstract: Structure formation, the condensation of a cloud of atoms to a crystal is still not well understood. Disordered sytems (amorphous/liquid) should be in the center of this research, they are the precursors of any crystal. We consider elementary systems, as well as binary, or ternary amorphous alloys, irrespective whether they are metallically, covalently or ionically bonded and describe the process of structure formation in the formal language of thermodynamics but, as far as we know for the first time, by an extended version (general dynamics), based on the complete Gibbs fundamental equation, applied to internal subsystems. Major structural features evolve from global resonances between formerly independent internal subsystems by exchanging momenta and angular momenta, both accompanied by energy. By this they adjust mutually their internal features and create spherical-periodic structural order at medium-range distances. Under the given external constraints the resonances get optimized by selforganization. Global resonances of the type considered have clearly to be distinguished from local resonances between individual ions (described by quantum chemistry) forming local order. The global resonances cause anti-bonding (non-equilibrium) as well as bonding (equilibrium) states of the coupled total system, occupying the latter to form new structurally extended order. The transition to equilibrium creates entropy which itself leaves the system together with energy. At resonance the energetical splitting between the bonding and anti-bonding state is largest, the creation of entropy and the decrease of the total energy therefore, too. The crystal, finally, evolves by additionally optimizing a resonance based on angular momentum, and the additional adjustments of the local resonances to the global ones, theoretically done by applying Bloch’s theorem.
Authors: Thierry Grosdidier, Bernard Bolle, J.D. Puerta Velásquez, J.X. Zou, Jean-Jacques Fundenberger, Nathalie Allain-Bonasso, P. Chevrier, Albert Tidu
Abstract: This paper reviews some recent results concerning surface integrity of materials processed with two important developing techniques: high speed machining (HSM) – here applied to the difficult case of Ti alloys – and low energy high current pulsed electron beam (LEHCPEB) surface treatment of steels. The effect of the processing parameters on the development of microstructure, texture and residual stresses is detailed for modifications occurring both at the surfaces and sub-surfaces.
Authors: T. Shirasawa, S. Tanaka, T. Muro, Y. Tamenori, Y. Harada, T. Tokushima, T. Kinoshita, S. Shin, T. Takahashi, H. Tochihara
Abstract: The epitaxial silicon oxynitride (SiON) layer grown on a 6H-SiC(0001) surface is studied with core level photoemission spectroscopy. Si 2p spectra show three spectral components other than the bulk one. Chemical shifts and emission angle dependence of these components are well explained within a framework of a determined structure model of the SiON layer.
Authors: Da Chuan Jiang, Wei Dong, Yi Tan, Qiang Wang, Xu Peng, Guo Bin Li
Abstract: The growth in the solar energy technology caused inshortage solar grade Si. As a lowcost, environmental friendly technology, metallurgical method purity silicon is developed significantly. However, as a typical impurity in Si, B is difficult to be removed by directional refining or vacuum melting due to its large segregation coefficient and less evaporation coefficient. In this paper, the big difference of evaporation pressure between Si and B can be applied to separate B from Si, in which, B is remained in molten Si, while most of Si becomes evaporant. Electron beam is applied to scan molten Si and the Si existed in the form of the evaporant is gather on the watercooled crystallizer. The content B in the evaporant is undetectable by ICP-MS.
Authors: Chuan Wu, Ying Bai, Feng Wu, Dan Xian Liu
Abstract: Amorphous Ni-Co-B catalyst was synthesized by a chemical reduction method, and followed by a heat-treating at 100°C, then characterized by X-ray diffraction (XRD), Scanning electronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmetr-Teller (BET) analysis, and adopted to help accelerating hydrolysis reaction of NaBH4 alkaline solution. It is proved that the amorphous Ni-Co-B catalyst is not a simple combination of elemental Ni, Co and B, but a multiplex metal boride. It exhibits an maximum hydrogen generation rate of 210 ml/min/(g catalyst) at 100% H2 utilization, which is potentially to give a successive H2 supply for proton exchange membrane fuel cells.
Authors: Ying Bai, Chuan Wu, Feng Wu, Bo Rong Wu, Shi Chen
Abstract: Spinel LiMn2O4 was synthesized via a solid state reaction, and modified with Al2O3 thin layers by a chemical deposition method. The electrochemical performances of the as-prepared samples were investigated with cyclic voltammetry (CV) and charge-discharge test. It is found that the Al2O3-coated LiMn2O4 help dramatically retaining the discharge capacity upon long-term cycling. The influences of the heat-treating temperature and the coating amount are discussed and compared. The optimized sample is 1% Al2O3/ LiMn2O4 heat-treated at 500oC, which has an initial discharge capacity of 116mAh/g, and a very slight capacity loss of 1.7% at the 50th cycle.
Authors: Wei Dong, Xu Peng, Da Chuan Jiang, Yi Tan, Qiang Wang, Guo Bin Li
Abstract: In order to investigate Ca evaporation behavior in the electron beam melting process, metallurgical-grade silicon was melted in an electron beam furnace with different experimental conditions. The results showed that the content of impurity Ca was significantly decreased in the early time, while these changed slowly with the extension of the melting. The removal rate of Ca was controlled by the transfer of Ca atoms from the bulk liquid silicon to liquid/gas phase interface within the range of experiment temperature.

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