Pengfei Xing

Effect of erbium on properties and microstructure of Al-Si eutectic alloy

Eutectic Al-12.6 wt.%Si alloys with various contents of the rare earth element Er were prepared by the conventional casting technique. The effect of Er on the microstructure and properties of the eutectic Al-Si alloys was investigated using optical microscopy, scanning electron microscopy as well as the friction and wear tests. It was found that the addition of Er obviously improved the anti-wear properties, and reduced the friction coefficient of the alloys. The appropriate addition of Er would change the size and shape of the eutectic silicon, and thereby refine the microstructure of the Al-Si alloys. The refinement mechanism was also discussed.

Glass transition, crystallization kinetics and pressure effect on crystallization of ZrNbCuNiBe bulk metallic glass

The glass transition behavior and crystallization kinetics of Zr48Nb8Cu14Ni12Be18 bulk metallic glass have been investigated by differential scanning calorimetry and x-ray powder diffraction (XRD). The activation energies of both glass transition and crystallization events have been obtained using the Kissinger method. Results indicate that this glass crystallizes by a three-stage reaction: (1) phase separation and primary crystallization of glass, (2) formation of intermetallic compounds, and (3) decomposition of intermetallic compounds and crystallization of residual amorphous phase. The pressure effect on crystallization is studied by in situ high-pressure and high-temperature XRD using synchrotron radiation. Two crystallization temperatures, observed by in-situ XRD, behave differently with varying pressure. The onset crystallization temperature increases with pressure with a slope of 9.5 K/GPa in the range of 0 to 4.4 GPa, while the another crystallization temperature keeps almost unchanged in the app...

Rapid recovery of polycrystalline silicon from kerf loss slurry using double-layer organic solvent sedimentation method

The rapid development of photovoltaic (PV) industries has led to a shortage of silicon feedstock. However, more than 40% silicon goes into slurry wastes due to the kerf loss in the wafer slicing process. To effectively recycle polycrystalline silicon from the kerf loss slurry, an innovative double-layer organic solvent sedimentation process was presented in the paper. The sedimentation velocities of Si and SiC particles in some organic solvents were investigated. Considering the polarity, viscosity, and density of solvents, the chloroepoxy propane and carbon tetrachloride were selected to separate Si and SiC particles. It is found that Si and SiC particles in the slurry waste can be successfully separated by the double-layer organic solvent sedimentation method, which can greatly reduce the sedimentation time and improve the purity of obtained Si-rich and SiC-rich powders. The obtained Si-rich powders consist of 95.04% Si, and the cast Si ingot has 99.06% Si.

On the heating rate dependence of crystallization temperatures of metallic glasses

It is well known that the crystallization temperatures of metallic glasses show strong dependence on the heating rate. The right relationship between the crystallization temperatures and the heating rate are very important in illustrating crystallization behavior and in evaluating thermal stability of the metallic glasses. Up to now, the dependence is usually illustrated using Kissinger equation, Ozawa equation, Augis–Bennett equation, Lasocka equation, and Vogel–Fulcher–Tammann (VFT) nonlinear equation. The paper aims to exam the relationship between the crystallization temperature and the heating rates for several metallic glasses, mainly rare earth-based and Zr-based metallic glasses. The validity of the relationship has been evaluated using additional experimental data at even lower or/and higher heating rates as well as the continuous heating transformation diagrams for the metallic glasses. The difference of the five equations has been compared in the paper. Among the five equations, the Kissinger, ...

Removal of phosphorus from metallurgical grade silicon by Ar-H2O gas mixtures

Abstract The removal of phosphorus in metallurgical grade silicon (MG-Si) by water vapor carried with high purity argon was examined. The effect of the nozzle types, refining time, refining temperature, refining gas temperature and refining gas flow rate on the phosphorus removed was investigated by the self-designed gas blowing device. The optimal refining conditions are nozzle type of holes at bottom and side, refining time of 3 h, refining temperature of 1793 K, refining gas temperature of 373 K, refining gas flow rate of 2 L/min. Under these optimal conditions, the phosphorus content in MG-Si is reduced from 94×10 −6 initially to 11×10 −6 (mass fraction), which indicates that gas blowing refining is very effective to remove phosphorus in MG-Si.

Recovery of high purity silicon from SoG crystalline silicon cutting slurry waste

Abstract The recovery of high-purity Si from the cutting slurry waste of SoG-Si was investigated. The composition and size distribution of cutting waste were characterized. The Si-rich powders were obtained from the cutting waste using a physical sedimentation process, and then further purified by removing impurity using acid leaching. The effects of process parameters such as acid leaching time, temperature and the ratio of solid to liquid on the purification efficiency were investigated, and the parameters were optimized. Afterwards, the high-purity Si ingot was obtained by melting the Si-rich powders in vacuum furnace. Finally, the high purity Si with 99.96% Si, 1.1×10 −6 boron (B), and 4.0×10 −6 phosphorus (P) were obtained. The results indicate that it is feasible to extract high-purity Si, and further produce SoG-Si from the cutting slurry waste.

High temperature dephosphorization behavior of monazite concentrate with charred coal

Abstract Dephosphorization behavior of monazite concentrate with charred coal at high temperature was investigated. It is found that the roast temperature is the main factor for the dephosphorization of the monazite. The high dephosphorization efficiency can be reached at the temperatures ranging from 1 200 to 1 400 °C. When the monazite pellets, made by pressing mixture of the monazite, charred coal and water into mould, were roasted at 1 400 °C for 2 h, 98% of phosphorus was removed from the monazite pellets. The roast time has little effect on the dephosphorization efficiency. Meanwhile, the particle size of the charred coal also has great influence on the dephosphorization efficiency of the monazite, and it is better to control particle size around 150 (m, while Fe and Fe 2 O 3 have neglectable effect on the dephosphorization of the monazite.

High temperature dephosphorus behavior of Baotou mixed rare earth concentrate with carbon

Abstract Based on the carbothermal reduction technology applied in industry, the dephosphorization behavior of Baotou mixed rare earth concentrate (Baotite) with carbon at high temperature was investigated. The experimental results showed that both the charred coal and the coking coal were effective carbonaceous reductants for the dephosphorization of the Baotite. Among them, the charred coal was more suitable for the dephosphorus due to its high carbon content and lower volatile and ash. When the rare earth pellets, made by pressing the mixture of the Baotite, charred coal and water in mould, were roasted at 1500 °C for 2 h, its dephosphorus rate was as high as 98%. Roasting temperature was a main factor for the dephosphorus rate, and roast time was the second one. The size of both charred coal and coking coal also had influence on the dephosphorus, and was better less than 150 μm.

Kinetic study on the non-isothermal crystallization of Gd53Al24Co20Zr3 bulk metallic glass

Gd-based bulk metallic glass has drawn strong attention because of its large magnetic entropy changes. Thermal stability of metallic glass is a very important issue for its application. In the paper, crystallization behavior of Gd53Al24Co20Zr3 bulk metallic glass was investigated using non-isothermal differential scanning calorimetric (DSC) technique. Attention was given to the analytic details. The crystallized volume fractions as a function of temperature were derived from the DSC signals, where heat capacity change between amorphous phase and crystalline phase was considered. The local activation energies at different crystallized volume fraction were estimated using Doyle-Ozawa and Agrawal methods. The results suggested that the Doyle-Ozawa equation was appropriate to get local activation energy due to its simplicity and accuracy. The local activation energy depended on the crystallized volume fraction. Function reflecting crystallization mechanism was also deduced. The crystallization mechanism of the Gd-based bulk metallic glass was discussed.