Application of the levitation technique for investigation of metal alloys and phase equilibria in slags

Experimental methods, based on electromagnetic levitation, have been developed for preparation and investigation of copper-rich alloys, and for the determination of oxide-metal phase equilibria. These techniques involve high-temperature equilibration, rapid quenching and chemical analysis of the phases using electron probe X-ray microanalysis. The experiments can be carried out in the temperature range 1373-1873 K (= 1100 degrees C-1600 degrees C). A developed calibration method, using phase equilibria data in known oxide systems, was applied for pyrometric temperature measurements. Described methods of the application of the electro-magnetic levitations were used for in-situ formation of Cu-based alloys and for formation of Ca-ferrite slags equilibrated with metallic copper

Edge-to-site reduction of Bethe-Peierls approximation for nearest neighbor exclusion cubic lattice particle systems and thermodynamic modeling of liquid silicates

We study an interacting particle system on the simple cubic lattice satisfying the nearest neighbor exclusion (NNE) which forbids any two nearest sites to be simultaneously occupied. Under the constraint, we develop an edge-to-site reduction of the Bethe-Peierls entropy approximation of the cluster variation method. The resulting NNE-corrected Bragg-Williams approximation is applied to statistical mechanical modeling of a liquid silicate formed by silica and a univalent network modifier, for which we derive the molar Gibbs energy of mixing and enthalpy of mixing and compare the predictions with available thermodynamic data. (c) 2007 American Institute of Physics

Investigation of the Epitaxial Graphene/p-SiC Heterojunction

There has been significant research in the study of in-plane charge-carrier transport in graphene in order to understand and exploit its unique electrical properties; however, the vertical graphene–semiconductor system also presents opportunities for unique devices. In this letter, we investigate the epitaxial graphene/p-type 4H-SiC system to better understand this vertical heterojunction. The I–V behavior does not demonstrate thermionic emission properties that are indicative of a Schottky barrier but rather demonstrates characteristics of a semiconductor heterojunction. This is confirmed by the fitting of the temperature-dependent I–V curves to classical heterojunction equations and the observation of band-edge electroluminescence in SiC

Coronavirus-positive Nasopharyngeal Aspirate as Predictor for Severe Acute Respiratory Syndrome Mortality

Severe acute respiratory syndrome (SARS) has caused a major epidemic worldwide. A novel coronavirus is deemed to be the causative agent. Early diagnosis can be made with reverse transcriptase-polymerase chain reaction (RT-PCR) of nasopharyngeal aspirate samples. We compared symptoms of 156 SARS-positive and 62 SARS-negative patients in Hong Kong; SARS was confirmed by RT-PCR. The RT-PCR–positive patients had significantly more shortness of breath, a lower lymphocyte count, and a lower lactate dehydrogenase level; they were also more likely to have bilateral and multifocal chest radiograph involvement, to be admitted to intensive care, to need mechanical ventilation, and to have higher mortality rates. By multivariate analysis, positive RT-PCR on nasopharyngeal aspirate samples was an independent predictor of death within 30 days

Improved GaN-based HEMT performance by nanocrystalline diamond capping

As a wide-bandgap semiconductor, gallium nitride (GaN) is an attractive material for next-generation power devices. To date, the capabilities of GaN-based high electron mobility transistors (HEMTs) have been limited by self-heating effects (drain current decreases due to phonon scattering-induced carrier velocity reductions at high drain fields). Despite awareness of this, attempts to mitigate thermal impairment have been limited due to the difficulties involved with placing high thermal conductivity materials close to heat sources in the device. Heat spreading schemes have involved growth of AIGaN/GaN on single crystal or CVD diamond, or capping of fullyprocessed HEMTs using nanocrystalline diamond (NCD). All approaches have suffered from reduced HEMT performance or limited substrate size. Recently, a "gate after diamond" approach has been successfully demonstrated to improve the thermal budget of the process by depositing NCD before the thermally sensitive Schottky gate and also to enable large-area diamond implementation

Phase Equilibria in the System “MnO”-CaO-MgO-SiO2-Al2O3with Al2O3/SiO2 Weight Ratio of 0.17 and MgO/CaO Weight Ratio of 0.25 at Mn-Si Alloy Saturation

Liquidus isotherms and phase equilibria have been determined experimentally for a pseudo-ternary section of the form “MnO”-(CaO + MgO)-(SiO +Al O) with a fixed Al O /SiO weight ratio of 0.17 and MgO/CaO weight ratio of 0.25 for temperatures in the range 1 393-1 673 K. The primary phase fields found in the investigated section include manganosite (Mn, Mg, Ca)O; dicalcium silicate α-2(Ca, Mg, Mn)O·SiO; merwinite 3CaO (Mg, Mn)O 2SiO; melilite [2CaO·(MgO, MnO, AlO)·2(SiO· , Al O )]; wollastonite [(Ca, Mg, Mn)O·SiO ]; diopside [(CaO, MgO, MnO, Al O )·SiO ]; tridymite (SiO ); rhodonite [(Mn, Mg, Ca)O·SiO ]; anorthite (CaO·Al O 2SiO ) and tephroite [2(Mn, Mg, Ca)O·SiO ]. The liquidus temperatures and primary phase fields are significantly different to those in the ternary system “MnO”-CaO-SiO , but are close to those previously reported pseudo-ternary section “MnO”-(CaO + MgO)-(SiO +Al O ) for Al O /SiO weight ratio of 0.17 and MgO/CaO weight ratio of 0.17. The partitioning of CaO, MgO and MnO between liquid and solid phases was measured using EPMA, and the extents of solid solutions for a range of bulk compositions and temperatures were characterised

Thermodynamic Database for the Al-Ca-Co-Cr-Fe-Mg-Mn-Ni-Si-O-S System and Applications in Ferrous Process Metallurgy

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Freeze lining formation of a synthetic lead slag

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Improved copper smelter and converter productivity through the use of a novel high-grade feed

Copper sulphide processing technologies face increasing pressures associated with decreasing concentrate grade leading to increasing thermal inefficiency and lower productivity. Impurity concentrations are on average increasing, creating potential environmental risk and additional treatment costs. In copper flash smelters dust, partially oxidised materials and fume formed from the condensation of volatile impurities, are routinely recycled to the feed. In the converting stage the heat balance is maintained by charging anode reverts and other inert materials. In both cases, the thermal energy available from sulphide oxidation is not fully utilised or optimised. The productivities of both smelter and converter stages can be potentially increased through the addition of a high copper, low iron, low impurity precipitated copper product. Calculations are carried out for fayalite smelter and calcium ferrite converter slags using an optimised FactSage thermodynamic database. The potential for significant increases in smelter and converter productivities using existing technologies are predicted