Papers by Author: Wen Hui Ma

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.

Abstract: Coal fly ash (CFA), as a major solid waste of coal-fired power plants in China, is widely applied in building materials, pavement, and soil improvement. However, its potential value hasn’t been fully utilized yet. In recent years, CFA has received attractive attention as a potential raw material to prepare Al-Si alloy because of the main components of SiO₂, Al₂O₃ and a small amount of iron in it. The presence of iron in CFA will benefit the process of carbothermic reduction which can be carried out at lower temperature for preparing Al-Si alloys. On the other hand, the content of iron in the Al-Si alloys products need to be controlled strictly, otherwise it will have the significant influence on the mechanical properties of the alloys and lead to the formation of excessive shrinkage defects. In this paper, we studied the necessity for deironing from Al-Si alloys prepared by CFA via hydrometallurgy pretreatment. Results indicate that the optimal route to prepare the qualified Al-Si alloys products is to remove most of the iron from CFA using hydrometallurgical pretreatment before carbothermic reduction. Other pyrometallurgy refining methods are applied to further deironing if necessary after the primary Al-Si alloys are obtained.

Abstract: Solar grade silicon and modified Al-Si alloys are widely used in the world. These two favored materials are expected to obtain by the electromagnetic directional solidification of hypereutectic Al-Si melts. The segregation of hypereutectic Al-Si alloy is feasible with respect to the process of either pull-up or drop-down in electromagnetic directional solidification. To explore the segregation efficiency, experiments have been conducted in a high-frequency induction furnace with different pulling conditions of hypereutectic Al-Si melts. The results show that the segregation efficiency of dropping-down is higher than that of pulling-up; the slower dropping-down rate lead to higher segregation efficiency in the electromagnetic directional solidification; increasing the temperature gradient may promote the separation efficiency. A separation mechanism model responsible for the formation of the distribution of primary silicon in the cross-sections is also proposed. Wish to provide theoretical basis for the more efficiency of the segregation of hypereutectic Al-Si melts.

Abstract: HfSiN/Cu/HfSiN/SiO₂/Si multilayer films were prepared on Si substrate via magnetron sputtering technology. Annealing experiments of samples among 400°C and 700°C were carried out in order to investigate the anti-diffusion performance of HfSiN thin film to Cu. XRD, AFM and FPP were used to characterize the structure, morphology and the resistivity of the thin films before and after annealing, respectively. The failure temperature and failure mechanism of HfSiN thin film were analyzed. The anti-diffusion failure temperature of HfSiN thin film is 600 °C. And the main reason is that a large number of Cu large particles passed through HfSiN diffusion barrier layer and reacted with Si substrate and oxygen to generate Cu₃Si and CuO with high resistance.

Abstract: Monodisperse mesoporous silica microspheres (MSM-SF) were successfully prepared through PICA and pseudomorphic transformation using silica fume as original silica source. The structure and morphology of spheres were quantitatively investigated by Zata potential and particle size analyzer, N2 sorption isotherms, XRD, SEM and TEM. The results showed that the monodisperse spherical mesoporous silica microspheres (MSM-SF) exhibited uniform spherical morphology, worm-like mesoporous, large BET surface area of 559.9m2/g; its BJH average pore size diameter and total pore volume are 3.3nm and 0.12cm3/g, respectively. This preparation method provides a new synthetic strategy to control the particle morphology and structure simultaneously, meanwhile this method can also significantly reduce the cost of synthesis of mesoporous silica microspheres.

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.

Abstract: The UF resin/SiO₂ composites microspheres with particle size of 2μm were successfully prepared by polymerization of silica sol from base-catalyzed hydrolysis of tetraethyl orthosilicate, and urea-formaldehyde via the PICA approach, and then calcination in air to remove organic UF resin and yield porous silica microspheres. The samples were characterized by Zetasizer NanoZS Instrument, SEM and Nitrogen adsorption-desorption isotherms. The results showed that the synthesized porous silica microspheres with a BET surface area of 67.01m²/g, a BJH average pore size diameter of 37.32 nm and a total pore volume of 0.69cm³/g, respectively.

Abstract: The LSCM (La_0.7Sr_0.3Cr_0.5Mn_0.5O_3-δ) powders were synthesized by glycine-nitrate process (GNP). An anode functional layer (AFL) LSCM was fabricated on an porous NiO-LSCM anode substrate by slurry spin coating. The effect of pore-former, sintering temperature and sintering time on the quality of thin film was investigated. The film with good apparent morphology was obtained when the operating parameters were fixed as follows: the pore-former is ethyl cellulose, the content of ethyl cellulose is 5 wt.%, the sintering temperature is 1000 °C and the sintering time is 4 h.

Abstract: La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85 (LSGM) electrolyte films were successfully prepared by slurry spin coating method on porous La_0.7Sr_0.3Cr_0.5Mn_0.5O_2.75 (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.

Abstract: The anodic current-potential behaviors of PS fabrication by doubled-cell electrochemical etching method have been studied. There are three reaction regions: porous silicon formation region, a transition region and electropolishing region in I-V curves. Polishing current and the HF acid concentration has a directly proportional relationship, the electropolishing current of silicon increased with the increase of the concentration of HF, in a certain concentration range. The electropolishing current of silicon increased with increasing the sweep rate on the condition of the same HF concentration.