Papers by Author: Da Chuan Jiang

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.