Papers by Author: Wen Hui Ma

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Authors: Shao Yuan Li, Wen Hui Ma, Yang Zhou, Xiu Hua Chen, Ming Yu Ma, Yao Hui Xu, Yong Yin Xiao
Abstract: The effect of HF concentration on the surface structure of porous silicon (PS) was carefully investigated by the AFM characterization. The results showed that no pores were present on PS surface which was prepared under the higher concentration of HF (10%). However, the pores were gradually visible with the HF concentration reduction. The main pores diameter was about 100 nm, when the concentration is 5.71%. The data of surface roughness and the main height distribution of the “hill” both showed an increase with the reduction of concentration, from 6.39 nm increase to 16.9 nm and from 30 nm increase to 90 nm, respectively, which implied that the pores were better exposed under the lower HF concentration.
Authors: Jie Xing, Xiu Hua Chen, Wen Hui Ma, Rui Li, Jian Jun Yang, Jie Yu
Abstract: La0.9Sr0.1Ga0.8Mg0.2O2.85 (LSGM) electrolyte films were successfully prepared by slurry spin coating method on porous La0.7Sr0.3Cr0.5Mn0.5O2.75 (LSCM) anode substrates. Ethyl celluloses content, coating cycles for slurry spin coating on the fabrication LSGM electrolyte films were investigated. The compatibility between LSGM and LSCM powders, microstructures and electricity conductivity of fabricated LSGM films were examined using XRD, SEM and electrochemical workstation. The film with good apparent morphology and electrical conductivity were obtained when the operating parameters were setted as the content of ethyl cellulose 10wt%, and the coating cycles 5.
Authors: Yi Mai, Wen Hui Ma, Ke Qiang Xie, Tong Wang, Hu Zhang, Qiang Liu
Abstract: In order to find the most effective hydrometallurgical method of removing iron, aluminum and calcium from MG-Si, a variety of acid leaching methods were presented. The research results show that the order of capacity of metallic impurity removal is HF, HCl, HNO3 and H2SO4. The most effective hydrometallurgical method is the leaching by mixed acid with hydrofluoric acid and sulfuric acid. Removal efficiency of hydrochloric acid pressure leaching can improved as the pressure increases. Sulfuric acid and nitric acid even using high pressure leaching cannot obtain high impurity removal rate. The leaching by hydrofluoric acid or mixed acid containing hydrofluoric acid and sulfuric acid is very effective on removal of iron and aluminum, but less effective on calcium.
Authors: Ming Fang, Cheng Hao Lu, Hui Xian Lai, Liu Qing Huang, Juan Chen, Jin Tang Li, Wen Hui Ma, K.X. Wei, Zhi Lin Sheng, Jian Ning Shen, Xue Tao Luo
Abstract: The distribution of impurities in metallurgical grade silicon before and after slag treatment was investigated for the purpose of upgrading metallurgical grade to solar grade silicon. It was found that metal impurities co-deposited with silicon and formed different intermetallics in the precipitated phase, and these intermetallics such as Si-Fe, Si-Ni, Si-Ti-V and Si-Ca-Al-Fe were substituted by Si-Fe-Ti-V after treatment of Na2CO3-SiO2 slag. Non-metallic impurities B and P were nearly homogeneous distribution in metallurgical grade silicon before and after slag treatment. Moreover, a particular analysis of the microstructure of slag has been carried out, it was determined that metal impurities Al and Ca could easily migrate from silicon to slag phase in the refining process.
Authors: Wen Hui Ma, Yong Jiang, Yang Zhou, Kui Xian Wei, Bin Yang, Yong Nian Dai, Kazuki Morita
Abstract: The structural defects including dislocations and grain boundaries (GBs) in upgraded metallurgical grade silicon (UMG-Si) prepared by vacuum directional solidification were investigated. The results demonstrated that higher withdrawal rates increased the dislocation density. The state of melt growth changed from quasi-equilibrium to non-equilibrium, and the GB type was also highly related to the withdrawal rate, especially for ∑3 boundary. The change of total interfacial energy and increase of carbon concentration may be a possible driving mechanism for this phenomenon.
Authors: Yun Lei, Wen Hui Ma, Kui Xian Wei, Ji Jun Wu, Guo Qiang Lv, Yong Nian Dai, Kazuki Morita
Abstract: This work investigates the removal of B in Si by the addition of Zr in the electromagnetic solidification refinement of silicon-aluminum melts. As Zr has a strong affinity for B and can form the thermodynamically stable compound of ZrB2, the B content of lower-grade Si is expected to be effectively removed by adding a small amount of Zr to the Si-55 at% Al melt. The results show that Zr is strongly responsible for the decrease in B content of refined Si. The removal fraction of B significantly increased from 60.2% to 97.3% by adding a small amount of Zr (0 to 3500 ppmw). In addition, the removal fraction of Zr from Si was found to be as high as 98.6%; however, its residual content in the refined Si was significantly larger than its solid solubility in Si, possibly due to the non-equilibrium solidification occurring during the refining process.
Authors: Shu Wen Yang, Shao Yun Shan, Wen Hui Ma, Hua Wang
Abstract: Porous silicon nitride ceramics with high-porosity were fabricated by carbothermal reduction reaction between silicon dioxide and carbon. The influences of carbon sources on microstructure and phase composition of the samples were studied. The result showed that the resultant porous silicon nitride ceramics using nano-meter carbon powder (C(n)) had finer microstructure, more uniform pore structure than those using activated carbon powder (C(a)). In order to illuminate the reaction and growth mechanism of b-Si3N4 grains, a series of intermediate sintering processes were investigated. X-ray diffractometry showed a difference in phase composition for the samples using the different carbon sources.
Authors: Jiao Li, Xiu Hua Chen, Wen Hui Ma, Cong Zhang, Kui Xian Wei
Abstract: The multicrystalline silicon wafers purified by directional solidification route were used to introduce copper impurities. The resistivity and minority carrier lifetime of multicrystalline silicon wafers were investigated by four-point probe resistivity tester and μ-PCD, respectively. Annealing temperature, atmosphere and cooling rate were researched. It was found that copper contaminants have a greater impact on the electrical properties of multicrystalline silicon. Research results showed that copper impurities tend to exist at defect sites at high temperature, and high annealing temperature, argon atmosphere and slow cooling conditions make more impact on the electrical properties of multicrystalline silicon than low annealing temperature, air atmosphere and fast cooling.
Authors: Xiang Yang Mei, Wen Hui Ma, Kui Xian Wei, Yong Nian Dai
Abstract: The main raw material of solar energy is multi-crystalline silicon. Directional solidification technique is one important technological process of metallurgy purification technology for multi-crystalline silicon. It can purify metallurgical grade silicon by removing metal impurities and control crystal growth at the same time. In experiment, metallurgical grade silicon by acid leaching pre-treatment, was purified by our self-assembled directional solidification furnace. The sample was analyzed by electron-prode micro analysis (EPMA). According to the results, the removal efficiency of Fe and Al is 96.3% and 96.7%, respectively. The removing mechanism of metal impurities and the difference between theory value and experiment value were also discussed. The segregation effect in directional solidification is the reason of removing Fe, but analgesic effects of the segregation effect combined with vacuum volatilization are that of removing Al. When the silicon ingot was cooled down, lengthways section of silicon ingot was cut and etched, crystal growth was studied. The results indicate that columnar crystal growth shows diverging tendency from the bottom to the top of silicon ingots, and solidification interface shape is convex. The reasons may be the nucleation of new crystals on crucible sidewall is very serious and the pulling rate is too high.
Authors: Wen Hui Ma, Xiang Yang Mei, Kui Xian Wei, Shao Yu Tang
Abstract: The pot material of Sb-doped n-type mono-crystal silicon was purified by our selfassembled vacuum directional solidification furnace. In the experimental, the pulling rate was 7μm/s, 10μm/s, 20μm/s, 30μm/s and 40μm/s, respectively. The experimental concentration of Sb, Al and Fe at 0.3 proportion of silicon ingot bottom to the top is detected and the theoretical concentration is calculated. The experimental results show that the pulling rate causes a great effect to concentration of Sb and a small effect to concentration of Fe. At the same time, the theoretical distribution concentration and experimental distribution concentration were compared. The experimental route provided a promising idea for complex utilization of the pot material.
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