Thermodynamic description of Si-B binary system

AbstractThe Si-B binary system was thermodynamically assessed and described using the CompuTherm Pandat software. The solution phases, including Liquid, diamond-Si and β-B were treated as substitutional solution phases, of which the Gibbs energies were expressed with Redlich-Kister polynomial functions. Meanwhile, the compounds, SiB3, SiB6, SiBn, were modeled as stoichiometric compounds. The thermodynamic parameters formulating the Gibbs energies of various phases were obtained and the equilibrium and transition of phases were discussed. The existent forms for Si-B phases in MG-Si melt were forecast

Synthesis and Photoluminescence Property of Silicon Carbide Nanowires Via Carbothermic Reduction of Silica

Silicon carbide nanowires have been synthesized at 1400 °C by carbothermic reduction of silica with bamboo carbon under normal atmosphere pressure without metallic catalyst. X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy, transmission electron microscopy and Fourier transformed infrared spectroscopy were used to characterize the silicon carbide nanowires. The results show that the silicon carbide nanowires have a core–shell structure and grow along <111> direction. The diameter of silicon carbide nanowires is about 50–200 nm and the length from tens to hundreds of micrometers. The vapor–solid mechanism is proposed to elucidate the growth process. The photoluminescence of the synthesized silicon carbide nanowires shows significant blueshifts, which is resulted from the existence of oxygen defects in amorphous layer and the special rough core–shell interface

Removal of B from Si by Hf addition during Al–Si solvent refining process

A small amount of Hf was employed as a new additive to improve B removal in the electromagnetic solidification refinement of Si with an Al–Si melt, because Hf has a very strong affinity for B. The segregation ratio of Hf between the solid Si and Al–Si melt was estimated to range from 4.9 × 10−6 to 8.8 × 10−7 for Al concentrations of 0 to 64 at.%, respectively. The activity coefficient of Hf in solid Si at its infinite dilution was also estimated. A small addition of Hf (<1025 parts per million atoms, ppma) significantly improved the B removal. It was confirmed that the use of an increased Hf addition, slower cooling rate, and Al-rich Al–Si melt as the refining solvent removed B more efficiently. B in Si could be removed as much as 98.2% with 410 ppma Hf addition when the liquidus temperature of the Al–Si melt was 1173 K and the cooling rate was 4.5–7.6 K min–1. The B content in Si could be controlled from 153 ppma to 2.7 ppma, which meets the acceptable level for solar-grade Si

Technical research on vacuum distillation to purify magnesium to 99.99% purity

In this study, the distribution and evaporation principles of impurities in distilled magnesium metal were investigated using a low vacuum (8 × 10 ^4 Pa) distillation purification experiment and theoretical analysis. Provided all other factors remain unchanged (distillation time, pressure, and total area of evaporation), the optimum temperature for preparing high-purity Mg (99.99%) is 750 °C. A detailed analysis of purified Mg was obtained by inductively coupled plasma mass spectrometer (ICP-MS) for 10 major impurity elements. After distillation at 750 °C, low vapor pressure impurities in condensed magnesium, including Si, Mn, Al, Fe, Cu, Ni, and Sn were significantly reduced as other impurities were slightly reduced. Our analysis confirmed a decrease in the following impurities: Fe, Si, Mn, Cu, and Al were reduced from 21.8, 78.6, 68.4, 4.4, and 39.4 ppm to 1.2, 9.3, 6.0, 1.0, and 5.4 ppm, respectively; satisfying the 99.99% Mg standard. The evaporation rate and separation coefficient were calculated under experimental conditions. To better describe the distillation process of metallic magnesium under low vacuum conditions, the mean free path is also calculated in this study under actual conditions

Preparation of lithium using vacuum carbothermal reduction of LiAlO2

In this study, we investigated the preparation process of lithium metal using a novel carbothermic reduction process. Herein, thermodynamic calculations and experimental research methods were used to investigate the novel carbothermal reduction process of LiAlO _2 for preparing lithium metal in a vacuum. The results suggest that the temperature of the chemical reaction can be significantly reduced by reducing the pressure in the system. When the system pressure was 10 Pa, the reduction temperature, reduction time, molar ratio of C/LiAlO _2 , and reduction rate were 1623 K, 120 min, 0.9, and 79.01%, respectively. Furthermore, the lithium content in the reduction residue was 2.1 wt%, suggesting the presence of the LiAl _5 O _8 phase. Under these conditions, when 20% CaO was added, the reduction rate of lithium increased to 99.38%, and the lithium in the reduction residue takes the form of CaAl _2 O _4 . This shows that CaO, as an additive, can promote reduction, compromise the effect of LiAl _5 O _8 , and increase the reduction rate of lithium

Preparation of Nickel Nanoparticles by Direct Current Arc Discharge Method and Their Catalytic Application in Hybrid Na-Air Battery

Nickel nanoparticles were prepared by the arc discharge method. Argon and argon/hydrogen mixtures were used as plasma gas; the evaporation of anode material chiefly resulted in the formation of different arc-anode attachments at different hydrogen concentrations. The concentration of hydrogen was fixed at 0, 30, and 50 vol% in argon arc, corresponding to diffuse, multiple, and constricted arc-anode attachments, respectively, which were observed by using a high-speed camera. The images of the cathode and anode jets were observed with a suitable band-pass filter. The relationship between the area change of the cathode/anode jet and the synchronous voltage/current waveform was studied. By investigating diverse arc-anode attachments, the effect of hydrogen concentration on the features of nickel nanoparticles were investigated, finding that 50 vol% H2 concentration has high productivity, fine crystallinity, and appropriate size distribution. The synthesized nickel nanoparticles were then used as catalysts in a hybrid sodium&ndash;air battery. Compared with commercial a silver nanoparticle catalyst and carbon black, nickel nanoparticles have better electrocatalytic performance. The promising electrocatalytic activity of nickel nanoparticles can be ascribed to their good crystallinity, effective activation sites, and Ni/NiO composite structures. Nickel nanoparticles prepared by the direct current (DC) arc discharge method have the potential to be applied as catalysts on a large scale