Research On Preparation Of High Purity Silicon By Metallurgical Method

As the traditional energy sources continue to decrease sharply, it is very important to undertake the development and utilization of the new energy. The solar energy is sufficient resources and clean, safe and convenient advantages.etc. In the past decades, photovoltaic industry has been rapid developed by the support of governments and research institutions. However, due to the production of solar grade silicon by Modified Siemens process with disadvantages of high energy consumption, high pollution and costs, the research on the metallurgical production process of the low energy consumption, low pollution and costs is becoming imminently significant.Polysilicon contains the metal impurity elements, such as Al, Fe, Ca, Ti, etc, and non-metallic impurity elements, like B and P, etc. This paper studied using the process of slag refining, low temperature alloy and directional solidification to remove impurity elements in metallurgical grade silicon. Using slag refining and low temperature alloy method can reduce the energy consumption and equipment cost, at the same time ensure impurities removal efficiency, slag oxidation refining is an effective way to remove B impurity, and metal impurity elements also have a better removal effect; Method of low temperature Al-Si alloy has a better removal effect on various impurity elements, but it will cause large losses of aluminum by acid cleaning. When using magnetic field to separate Al-Si alloy, the rich silicon parts through acid cleaning can reduce the loss of aluminum, and also can ensure the purification effect of silicon, adding Ti element has a certain effect on removing B impurity in silicon. Directional solidification process can obtain bulky columnar grain structure, and the distribution of impurities is uniform, and removal efficiency from different parts of the ingot was analyzed.(1) Using SiO2-CaO-Al2O3-MgO quaternary slag to slag refining, when the proportion of slag with silicon is15%, slag basicity of CaO/SiO2=1.1, refining temperature at1773k, refining30min, the distribution proportion of B in slag and silicon has maximum, LB=7.8; at the same time, metal impurity elements of Al, Ca and Ti in silicon have good removel effect, the removel rate is93.2%、20.7%�'�34.8%respectively.(2) Using magnetic field to separate Al-Si alloy, when the primary silicon is partial gathered in magnetic field, the content of silicon has more than80%in silicon rich layer; metal and nonmetallic impurities of silicon have obvious removal effect after aciding, in which the removal rate of Fe, Ti, Ca, B, P is over95%; the content of Fe, Ti, B, P is 18～32ppmw,2.8～3.0ppmw,2.0-2.2ppmw,0.8-1.4ppmw respectively, however the content of aluminum is bigger, but diameter of primary silicon particle grinding tiny is helpful for aluminum impurity removal; adding a small amount of Ti element in Al-Si melt, there will be a good effect to remove B elements in silicon, and the content of B can be reduced to1.2ppmw, which removal rate is98.2%.(3) Directional solidification process can make ingot with bulky columnar crystal, and impurity elements are not gathered in the grain boundary; the removal rate of impurities such as Fe, Ca, Ti element is89.2%,98.8%and89.2%respectively at the bottom of the ingot, but the impurity elements is enriched more at the top of ingot, so truncated ingot can obtain high purity polycrystalline silicon.