Abstract
Increasing the removal efficiency of impurities during non-equilibrium solidification of hypereutectic Al-Si alloy remains a great challenge for the upgrading of metallurgical silicon (MG-Si) to solar grade Si (SOG-Si). Hence, a manageable method was provided to enhance the segregation behavior of impurities at the interface front of primary Si/Al-Si melt by introducing a rotating magnetic field (RMF) in the present work. Experimental results showed that electromagnetic stirring can improve the removal efficiency of impurities while achieving the separation of primary Si. The apparent segregation coefficients of the major impurities Fe, Ti, Ca, Cu, B and P were reduced to 7.5 × 10−4, 4.6 × 10−3, 7.9 × 10−3, 3.5 × 10−3, 0.1 and 0.16, respectively, under RMF of 25 mT and cooling rate of 2.5 °C/min. We confirmed that improving the transport driving force of impurities in the growth interface front of primary Si is an effective way to improve the segregation behavior of impurities, which would bring us one step closer to exploiting the economic potential of the Al-Si alloy solidification refining.
Highlights
The accessibility of low-cost solar grade (SOG-Si) is necessary for the increasing use of solar cells
In the coupling refining process, the metallurgical silicon (MG-Si) has to be heated repeatedly to molten state at each step to ensure the efficient removal of all impurities, which inevitably leaded to high energy consumption
This paper will focus on the effect of forced-melt flow generated by rotating magnetic field (RMF) on the removal efficiency of impurities during non-equilibrium solidification of Al-30Si melt, which mainly aimed to verify whether the electromagnetic stirring have reinforcement effect to the segregation behavior of impurities
Summary
The accessibility of low-cost solar grade (SOG-Si) is necessary for the increasing use of solar cells. In the coupling refining process, the MG-Si has to be heated repeatedly to molten state at each step to ensure the efficient removal of all impurities, which inevitably leaded to high energy consumption. The Al-Si alloy solidification refining as a novel metallurgical process, showed significant advantages both production efficiency and economic value because of the low refining temperature as well as the low segregation coefficient of metallic and non-metallic impurities [5,6,7]. The primary Si initially precipitated from hypereutectic Al-Si melt where more impurities were rejected into the Al-Si melt under the effect of solute redistribution [6,7,8], thereby refining the primary Si. the removal efficiency of impurities is limited because of the relatively weak segregation behavior of impurities at the interface
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