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[en] Bi-22l2 tubes for fault current limiter (FCL) were fabricated by centrifugal melting process. SrSO4 (10 wt. %) was added to Bi-2212 powder to lower the melting point of Bi-22l2 and to improve the mechanical properties. The BSCCO powder was completely melted at 1300 degree C using the RF furnace and then poured into rotating steel mold. The steel mold, preheated at 450 degree C - 550 degree C for 2 hour was rotated at 1020 - 2520 RPM. The solidified BSCCO tube was cooled down to room temperature in the furnace for 48 hours and separated from the mold between Bi-2212 and the mold. ZrO2 solution was used to separate it easily from the mold and Ag tape was attached in the mold inner wall of the mold to analysis electrical property. Bi-22l2 tube was often cracked when the cooling rate was high. BSCCO tubes with 70 φ x 100 mm, 50 φ x 100 mm and 30 φ x 150 mm size were fabricated by centrifugal melting process. The Jc3 of tubes with 50 φ x 100 mm x 4.0 t and 50 φ x 100 mm x 4.0 t were 178 and 74.2 A/cm2 at 77K, respectively. The processing condition for Bi-2212 tube fabrication was investigated using XRD and SEM analyses.
[en] The study of variation of the size, armchair and zigzag types effects on the melting process of graphene nanoribbon. A numerical thermodynamical model has been devoted for the study. The phase transition has first order behaviour. The formation of different defects, ring size and coordination number is dependent on the size and the edge type of GNR. The nuclei of heating appear at temperature around 2300K and that can be considered as pre-melting point. The melting process shows the case that the results of Berezinsky-Kosterlitz-Thouless-Nelson-Halperin-Young (BKTNHY) theory cannot be applied. (author)
[en] Two experimental approaches dealing with the determination of melting at high static pressures are described and analyzed. With the sample squeezed inside a diamond anvil cell, high temperatures up to the solid-liquid transition are obtained using Nd:YAG laser heating. Two methods have been investigated. In the first technique, the heating is accomplished with a pulsed laser and the brief radiation variations (t < 10 ms) emitted from the sample are recorded with two high-speed infrared detectors. The melting location is defined by a plateau or changes of slope of the signals, and the temperatures are calculated by assuming a constant value of emissivity factor at the end of the transition over the studied pressure range. The second system employs a continuous laser and a two-dimensional CCD detector to measure temperatures using multispectral pyrometry. Melting is detected from criteria related either to textural change in the sample involving interference contrast under a laser illumination or to the specific variations of temperatures and emissivity as a function of laser power. Thermal radiation is fitted to Planck's law with temperature and emissivity as the free parameters. Advantages and drawbacks are presented from results obtained on pure uranium
[en] Solid–solid (SS) phase transformations via nanometer-size intermediate melts (IMs) within the SS interface, hundreds of degrees below melting temperature, were predicted thermodynamically and are consistent with experiments for various materials. A necessary condition for the appearance of IMs, using a sharp interface approach, was that the ratio of the energies of SS and solid–melt (SM) interfaces, kE, were >2. Here, an advanced phase-field approach coupled with mechanics is developed that reveals various new scale and interaction effects and phenomena. Various types of IM are found: (i) continuous and reversible premelting and melting; (ii) jump-like barrierless transformation to IMs, which can be kept at much lower temperature even for kE<2; (iii) unstable IMs, i.e. a critical nucleus between the SS interface and the IM. A surprising scale effect related to the ratio of widths of SS and SM interfaces is found: it suppresses barrierless IMs but allows IMs to be kept at much lower temperatures even for kE<2. Relaxation of elastic stresses strongly promotes IMs, which can appear even at kE<2 and be retained at kE=1. The theory developed here can be tailored for diffusive phase transformations, formation of intergranular and interfacial phases, and surface-induced phase transformations
[en] Investigation on refining of rhenium of different initial purity of vacuum melting and zonal recrystallization were carried out. The rhenium purity was checked by the mass-spectrographic and chemical methods, and also by measuring the relative residual resistances. It is shown that the highest degree of purification is achieved by using initial rhenium obtained by hydrogen reduction after removal of low-volatility impurities. Single crystals of rhenium with a ratio of Rsub(298K)/Rsub(4.2K) exceeding 30000 and with a content of the main component of 99.9998 wt.% were obtained