The continuous growth of bulk Si in the Si–Al alloy using the temperature gradient zone melting (TGZM) technique is an effective method to separate the primary Si from the eutectic structure in the Si–Al alloy and to remove the majority of impurities, such as metals, B and P elements during the alloy refining process. A Si source was used to maintain the Si concentration in the alloy melt and reduce the influence of the solute-transmitting process by temperature gradient due to the precipitation of the primary Si. Bulk Si could be obtained in the Si–Al alloy through the TGZM process. With the initial temperature of 1461 K and temperature gradient of 1.81 K/mm, the actual growth rate of the bulk Si was 0.000186 mm/s. No inclusions and alloy phases were observed in the bulk Si. The removal rate of Fe impurity was 99.9% and the removal fraction of B, P and Al was 71.2%, 90.2%, 78.5% respectively.

Rigid carbon fiber felt (RCFF) was surface modified with a composite coating via a two-step technique of pasting and chemical vapor deposition. Scanning electron microscopy and X-ray diffraction were performed to analyze the microstructure of the substrate and the composite coating. The effect of the deposition time on solid particle erosion properties of RCFF modified by a composite coating was investigated. The pyrolytic carbon can decrease the surface porosity of a carbon fiber cloth, resulting in a dense composite. Compared with the substrate, the composite coating exhibited good erosion resistance and reduced the mass loss of the substrate by a factor of 19. The strengthening mechanism was discussed in this paper, and crack propagation along the interface between a carbon fiber and pyrolytic carbon sheath was found to occur; the crack propagation is an important factor for improving erosion resistance.

•Si–Al alloy with Sn addition was used for boron removal.•Sn addition effects on the eutectic silicon morphologies of Si–Al.•B was detected in Sn in much higher concentration than in Al by EPMA line analysis.Si–Al and Si–Al–Sn alloy melts were used for silicon purification by alloy solidification refining method. The effects of Sn addition on alloy microstructure, eutectic Si morphology, as well as B distribution were investigated using optical microscopy, scanning electron microscopy, electron probe microanalyzer and inductively coupled plasma mass spectrometer. Primary Si and αAl + Si structures with flake-like eutectic Si were found in Si–Al alloy; while an additional structure of αAl + βSn + Si in Si–Al–Sn alloy was found. Si in αAl + Si eutectic had a globular shape, whereas some Si in αAl + βSn + Si eutectic had an octahedral shape. Compared with primary Si, more boron was found to distribute in final solidified phase during the solidification, i.e. αAl + Si for Si–Al system and αAl + βSn + Si for Si–Al–Sn system. The refining ratio of B decreased with increasing Al content in Si–Al alloy melt, while increased with Sn addition using Si–Al–Sn alloy melt.

A new method for boron removal from silicon using electron beam injection (EBI) is proposed. After thermal oxidation on monocrystalline silicon (100) wafer at 1000 °C for 1 h, EBI was used to induce thermal and negative charging effects to enhance boron diffusion in the oxide film and the silicon substrate. This facilitates boron removal from the silicon substrate. The boron concentration in samples was measured by secondary ion mass spectrometry. The results show that EBI reduced the boron concentration in the silicon substrate by 4.83%.

Solar energy is expected to be in great demand within the next few years. In relation to this, a global shortage in the solar-grade silicon (SoG-Si) used in the production of solar cells has motivated numerous studies on metallurgical-grade Si (MG-Si) refining. However, improvements in this material are limited by the difficulties involved in reducing boron (B) and phosphorus content. The present study investigated the removal of B using (CaF2)-Al2O3-CaO-SiO2 and Na2SiO3-CaO-SiO2 slag in an ambient air atmosphere in order to refine MG-Si. The mass transfer coefficients of B in molten Si (kd[B]=1.19×10−4 cm s−1) and BO1.5 in molten slag (kd(B3+)kd(B3+)=1.01×10−5 cm s−1) were deduced through kinetic analysis. The mass transfer process of boron oxide limited slag refining; however, secondary slag treatment effectively improved the efficiency of B removal. LB was determined by the combined effect of the oxygen partial pressure and the molten slag structure.

A novel method to separate silicon and silicon carbide from kerf loss slurry by Al–Si alloying process has been reported in this paper. The kerf loss slurry was washed and dried, and then aluminum was added on the top of these dry powders with silicon and silicon carbide. The Al–Si alloying process was performed in argon atmosphere using a vacuum carbon tube furnace at 1773 K. In this way, an Al–Si ingot was obtained, on the surface of which a lot of hexagonal crystals were observed. The Al–Si ingot was characterized by X-ray diffraction, scanning electron microscopy, X-ray fluorescence and electron probe micro-analyzer. The X-ray results indicated that the Al4C3 phase was obtained on the top of the cast. The scanning electron microscopy, X-ray diffraction and electron probe micro-analyzer results revealed that the Al–Si alloy without silicon carbide phase formed in the cast, which indicated that silicon and silicon carbide can be separated from slurry by this alloying process.Highlights► Al–Si alloying process is used to separate silicon and silicon carbide. ► Remove the SiC from the kerf loss slurry. ► Obtain the solar grade Si. ► Some hexagonal crystallizes were observed.

The effect of direct electric current on redistribution and microstructure of primary silicon in Al–Si melt during the solidification refining process was studied. Electric current generates a Joule heat, which slows down the cooling rate of the furnace. The precipitated area of primary silicon decreases from 100% to 36.67% with the increase of current density from 0 A/m2 to 1.5×106 A/m2. Furthermore, direct current causes a convection leading to the migration of primary silicon in the opposite direction of electric field, which forms the accumulation area. The morphologies of primary silicon and the redistribution of B impurity were investigated under the effect of electric current.