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In this paper a mathematical model is developed to investigate the removal of volatile impurities in molten silicon by electron beam melting (EBM) with a high efficiency and low energy consumption. The temperature distribution of molten silicon is obtained using the commercial software FLUENT. Based on the temperature distribution, the vaporization behaviors of phosphorus and silicon are investigated by Langmiur's vaporization theory. The results show that the evaporation rate of silicon during EBM increases exponentially with the increase of beam power, while, it decreases with the increase of scanning radius. The optimal parameters are discussed from the aspect of efficiency and energy saving. The energy consumption decreases with the decrease of scanning radius and with the increase of the beam power. The optimum values are consider to be with a scanning radius of 0.0339 m and a beam power of 23.4 kW for 0.5 kg silicon when phosphorus is removed from 1.44 × 10−2 to 1 × 10−5 (wt.%).

According to the traditional metallurgical theory, the evaporation process of phosphorus and silicon during silicon refining by electron beam melting (EBM) is discussed and a theoretical model is established to obtain the loss rate of silicon, the removal efficiency of phosphorus and the corresponding energy consumption. The results show that phosphorus can be removed from silicon melt efficiently and quickly by EBM. There is a one-to-one correspondence between the loss of silicon and the removal efficiency of phosphorus, indicating that they have obvious effect on each other, whereas the EB power has little influence on the loss rate of silicon. If the EB power is increased from 9 kW to 21 kW, the melting time can be shortened by 68%, the loss of silicon increased by only 0.1% and the energy consumption decreased by 25%. Based on the theoretical and experimental results, a high-power EBM method is considered to be a better way for the removal of phosphorus with high efficiency and low energy consumption under such experiment conditions.

Solidification rate has a significant influence on purification of silicon due to segregation of impurities at a liquid–solid interface of a solidifying silicon ingot. A mathematical model is developed to evaluate time-dependent position of the liquid–solid interface and solidification rate of electron beam melted ingots. A series of solidification experiments with different cooling rates are conducted to measure position of a line which separates directionally grown columnar crystals visible in cross-sections of the solidified ingots. Results show that not the whole ingot solidifies directionally when the reduction rate of the beam current is larger than 1.67 mA/s. The position of the dividing line depends on cooling rate and the experimental trend is consistent with that resulted from theoretical simulations. Modeling shows that the solidification rate changes fast when the beam current reduces linearly that is detrimental for segregation of impurities. It also predicts that an exponential reduction of the beam current leads to a uniform solidification rate which is beneficial to segregation of impurities, though not all exponential current reductions lead to this kind of solidification behavior.

An experimental investigation into the removal of phosphorus from molten silicon using electron beam melting has been carried out. The time variation of phosphorus content is obtained at the electron beam power of 9, 15, and 21 kW, respectively. The results show that, at a constant power, the content of phosphorus decreases rapidly within the range of approximately 0–900 s after silicon is melted completely, and then tends to level out with further extension of the melting time. The content of phosphorus is decreased from 33.2 × 10 −4 wt.% to 0.07 × 10 −4 wt.% after 1920 s at a power of 21 kW, which achieves the target for solar-grade silicon of less than 0.1 × 10 −4 wt.%. Moreover, the removal reaction of phosphorus by evaporation from the surface of silicon melt during electron beam melting occurs in accordance with the first order kinetics. The mass transfer coefficients in different removal steps are calculated and discussed, which indicate the removal reaction of phosphorus is controlled by both the transport of phosphorus atom from the bulk to the melt free surface and the vaporization from the free melt surface into the gas phase.

In the current study, a new method for the removal of phosphorus in molten silicon, electron beam candle melting (EBCM), is proposed and discussed. The proposed method combines the characteristics of electron beam melting (EBM) and the high saturated vapor pressure of P in molten Si. Simulation results show the existence of three typical temperature distributions and morphologies of the molten pool that correspond to the different radii of the electron beam circular pattern at constant power. The critical molten pool with the maximum surface area and the minimum depth was determined. EBCM resulting in the critical molten pool was proven to be more effective in the removal of P in molten Si compared with EBM. In addition, the energy utilization ratio was enhanced.

Electron beam injection(EBI) is a process of gathering the electrons in materials using electron beam(EB). The EBI technology is proposed for purification of silicon particles by removing metal impurities through high-temperature oxidation, EBI, and HF acid washing processes. Analysis of silicon particle morphology after high-temperature oxidation using digital camera and after EBI using scanning electron microscope(SEM) were conducted. Then, the composition of silicon particles was analyzed using inductively coupled plasma(ICP). The silicon particle colours turned bright after EBI; therefore, EBI can change the thickness of SiO2 films in addition to increasing the temperature of the silicon particles. The results show that this technology is effective in removing metal impurities in silicon particles.

During the refinement of metallurgical-grade silicon (MG-Si), Al and Ca cannot be reduced to a target level by conducting directional solidification only once. Electron beam candle melting (EBCM) is a new method that can be used to further reduce Al and Ca by directly melting Si ingots after directional solidification. A certain stable molten pool with a maximum surface area and a minimum depth exists and is proven to effectively remove Al and Ca. The energy utilization ratio during EBCM is also compared with that of electron beam melting (EBM).

Electron beam melting is an effective method to remove volatile impurities in silicon, during which impurities such as P, Al and Ca etc. can be removed to less than 0.3×10-4wt.%. However, so far there is few research on the influence of electron beam parameters, such as beam density and beam size, on molten pool morphology, hence electron beam melting process has not been completely understood, which leads to low energy utilization. In this paper, on the basis of beam size calibration, the influence of beam density and beam size on molten pool morphology is investigated and the concept of melting angle is proposed to characterize molten pool morphology. At the same time, the optimal molten pool morphology for impurities removal and the corresponding electron beam parameters are also analyzed.

Small amounts of metallurgical grade silicon were melted in an electron beam furnace in different experimental conditions in order to investigate the aluminum (Al) evaporation behavior during the electron beam melting (EBM) process. Impurity was significantly decreased in the early periods of melting at 9, 15, and 21 kW. These changes slowed down with the extension of the melting time. Moreover, the removal reaction of Al by evaporation from molten silicon during the EBM process occurred in accordance with the first order kinetics. The calculated mass transfer coefficients of Al at 1941, 1964, and 2051 K increased with the increase of melting temperature. The removal rate of Al was controlled by the transportation of Al from the bulk of silicon metal to the molten/vacuum interface within the range of the experimental temperature.

The purification of metallurgical-grade silicon (MG-Si) has been investigated during electron beam melting (EBM) process. The results show that the phosphorus, calcium and aluminum contents decrease significantly after melting, and magnesium is partially removed. However, no significant change in content for boron and iron has been found. Langmuir’s equation and Henry law were used to derive the removal efficiency for each impurity element. The free surface temperature was estimated by the Hertz-Knudsen-Langmuir equation and silicon’s vapor pressure equation. Good agreement was found between measured and calculated impurities’ removal efficiency for phosphorus, calcium and aluminum, magnesium, boron and iron. The deviation between the two results was also analyzed in depth.

In order to investigate Ca evaporation behavior in the electron beam melting process, metallurgical-grade silicon was melted in an electron beam furnace with different experimental conditions. The results showed that the content of impurity Ca was significantly decreased in the early time, while these changed slowly with the extension of the melting. The removal rate of Ca was controlled by the transfer of Ca atoms from the bulk liquid silicon to liquid/gas phase interface within the range of experiment temperature.

The effects of melting condition on the dephosphorization behavior in metallurgical grade silicon (MG-Si) by electron beam melting (EBM) were investigated in this study. Experiment results showed that phosphorus content decreased by evaporation with the increase of melting time, and evaporation rate increased with the increase of electron beam power. Phosphorus content decreased to below 0.1 ppmw by EBM treatment at 21 kW for 1800 seconds. The dephosphorization reaction was found to follow the first order kinetics. Dephosphorization rate was controlled by free evaporation.

The electron beam injection (EBI) process involves offering electrons around silicon powder, whose surface was oxidized, and subsequently the powder is washed by HF acid so as to remove the SiO2 film. The new electron beam injection process, in which micro electric filed formed between Si and SiO2 film will accelerate impurities diffusion from Si to SiO2 film, was developed and applied to eliminate the transition-metal impurities of MG-Si. It is proved to be effective to remove transition-metal impurities from metallurgical grade silicon (MG-Si). By applying the electron beam injection method, the removal rate of 10% to 59% was achieved during the refining process. The efficiency of impurity removal originates from two aspects: the impurity concentration gradient on both sides of Si/SiO2 interface; the micro electric field formed from Si to SiO2 film. A further increase in the removal rate can be realized by controlling the processing parameters.

The growth in the solar energy technology caused inshortage solar grade Si. As a lowcost, environmental friendly technology, metallurgical method purity silicon is developed significantly. However, as a typical impurity in Si, B is difficult to be removed by directional refining or vacuum melting due to its large segregation coefficient and less evaporation coefficient. In this paper, the big difference of evaporation pressure between Si and B can be applied to separate B from Si, in which, B is remained in molten Si, while most of Si becomes evaporant. Electron beam is applied to scan molten Si and the Si existed in the form of the evaporant is gather on the watercooled crystallizer. The content B in the evaporant is undetectable by ICP-MS.

The numerical program LS-DYNA, is used to simulate the process of the projectile with high rotating speed penetrating into the moving vehicular door. Because of the moving of the vehicular door, the projectile will turn, and the ballistic trajectory will migrate. The paper provides a method to calculate the projectile’s angle of turning’s curve. In the process of the penetration, the projectile’s moving speed is 300 m/s, rotating speed is 0, 3600 n/s and 6370 n/s. The vehicular door’s moving speed is 0, 40 m/s and 80 m/s. The projectile is the semi-sphere nose projectile whose diameter is 7.62 mm; the vehicular door’s thickness is 2 mm. The material model is the JOHN-COOK material model that can characterize strain, strain rate hardening and thermal softening effects. Through comparing with the results by simulation to study the effects of the projectile’s final velocity, the angle of rotation and the ballistic trajectory’s migration with different projectile’s rotating speeds and the vehicular door’s moving speeds.

An experimental investigation into the removal of aluminum (Al) and calcium (Ca) from molten silicon by using electron beam melting was carried out. Based on the distributions of Al and Ca along the growth direction of the ingot under different solidification conditions, the influence of segregation and evaporation behaviors on the removal of such impurities with both high saturated vapor pressure and low segregation coefficients was investigated. The results showed that the distributions of impurities depend upon the interaction between segregation and evaporation, so that the removal efficiency can be further improved by adjusting the melting parameters. Compared with the traditional electron beam melting process, the energy consumption decreases by 20% during the whole melting and solidification process. It is considered to be a more effective way for the purification of silicon and the reduction of energy consumption by electron beam melting.