Currently available hard x-ray beams enable some of the techniques traditionally used in the optical regime to now be used in the hard x-ray regime. This program expands the applications of coherent x-ray scattering to investigate dynamics, kinetics and microscopic reversibility in metal and alloy phase transitions.
Materials Science and Engineering
It will examine microscopic reversibility and memory in alloys exhibiting displacive phase transitions, including the Cu-Zn-Al shape memory alloys. It will also examine the relationships between fluctuations, defect pinning and kinetics in these systems as well as in ordering alloys. Finally, the development of heterodyne techniques will be examined for the study of fluctuation dynamics in cases where the inherent sample scattering is relatively weak and diffuse.
Non-Technical: This research program will improve understanding of nanoscale dynamics, i. Such knowledge is important for understanding and developing advanced materials that will form the basis of future communications, computing, chemical processing and other industries. As part of this research program, students at the graduate, undergraduate and high school levels will be involved in learning about new x-ray techniques and materials issues that are at the forefront of current materials research.
Study and Characterization of Magnetic Materials for Beam Intensity Monitors at CERN - INSPIRE-HEP
Through continuing collaborations with scientists at other institutions, both inside and outside the US, these students will have an outstanding opportunity to see a variety of research environments. Carbon , 45 14 , Dora, B. Physical Review Letters , 99 16 , . Peterlik, H. Schubert, U. Structural investigation of alumina silica mixed oxide gels prepared from organically modified precursors.
Journal of Non-Crystalline Solids , , Michel, K. Superposition of quantum and classical rotational motions in Sc2C2 C84 fullerite.
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Supression of crazing in polystyrene cross-linked with a multifunctional zirconium oxo cluster observed in-situ during tensile tests. Macromolecular Rapid Communications , 28 , Reitinger, R.
Korecki, J. Surface diffusion and island growth. Stloukal Eds. Defect and Diffusion Forum; Vol. Trans Tech Publications Inc.. Ayala, P. Pichler, T. The room-temperature solubilities of both Au in Ni and Ni in Au are very small, of the order of 0.
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Since they also have significantly different reduction potentials, chemical synthesis is difficult to perform. AuNi solid solutions have been prepared using an ion beam mixing technique or an electrodeposition technique 14 , 15 , but the obtained alloys are formed as films or on the substrates. Until now, only a few studies reported synthesis of AuNi alloy nanoparticles by chemical reduction methods 16 , The synthesis of stable, homogeneous AuNi alloy particles formed as isolable solids has been so far limited.
The laser ablation of a bulk metal or an alloy target in a liquid has been shown to be an effective approach for synthesis of nanoalloys e.
Jakobi et al. Recently, Zhang et al. Amendola et al. However, the laser ablation products demonstrate relatively wide size distributions and low yields, which is not favourable for some applications. In addition, preparation of the homogeneous alloy targets, especially from bulk immiscible metals, is very challenging. In this context, the pulsed laser irradiation of colloidal nanoparticles in solution 27 seems to be a good alternative. Nanoparticles of AuCo have been obtained by the laser irradiation of Au and Co-oxide dispersed in ethanol solid solutions In this article, the same scheme was applied to the Au-Ni system.
No trace of signal coming from pure elements was observed for the sample.
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Besides the peaks coming from and planes of the Si substrate we observed only two diffraction peaks at Their position was completely different from the position of the strongest peaks which could originate from the pure Au and Ni metals. Since the peak at The same strategy was applied for the peak at The results show that the sample conserves the fcc structure of the components with space group Fm-3m and the lattice constant a, calculated from the peak analysis to be 3. Lattice parameters were calculated using Rietveld refinement 29 with the Fullprof program. The back-scattered electrons BSE magnified image in the inset, which shows atomic number contrast, demonstrates that the composition is the same in all directions in the particle.
It is well known that AuNi alloys are difficult to obtain, because Au and Ni are almost completely immiscible in the bulk phase. Here, however, we obtained Au 0. Why can AuNi alloy particles be formed using our technique? We hypothesise that the agglomerations of nanoparticles, very fast heating, and fast cooling are the main reasons Fig.
Because both types of raw particles are small Fig.
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The raw nanoparticles adhere to each other, and the energy can be easily transferred from Au to NiO. NiO decomposes thermally to Ni by ethanol pyrolysis products 33 Fig. In the experiments conducted with a Nd:YAG laser, the agglomerates can be heated to a very high temperature, due to absorption of the laser-beam energy Fig. This energy can overcome the repulsion force between Au and Ni atoms 34 which must be the reason for their immiscibility. As a result, mutual diffusion of Au and Ni takes place. The intermixed atoms may remain in the intermixed state, leading to the formation of a metastable phase.
Due to such a rapid quenching the Ni atoms cannot be ejected from the Au crystal lattice during the crystallization process. AuNi alloy particles can be formed as a result of these processes Fig.
The material exhibits a soft ferromagnetic state with small remnant magnetization 0. Most importantly, the pulsed laser irradiation is suitable for preparing not only alloy particles made from the bulk miscible metals e. FeNi but also for the alloys that are immiscible under equilibrium e.