Abstract: A process for the purification of a graphite material that includes metal sulfide impurities is provided. The process includes subjecting the graphite material to oxidizing conditions, in the presence of oxygen, to convert the metal sulfide impurities into metal oxides and sulfur dioxide, thereby obtaining a metal sulfide-lean graphite material; subjecting the metal sulfide-lean graphite material to carbochlorination, in the presence of chlorine gas, to convert the metal oxides into metal chlorides and obtain a metal chloride-rich graphite material; and purging the metal chlorides from the metal chloride-rich graphite material, thereby obtaining a purified graphite material.

Abstract: A process for purifying low-purity metallurgical grade silicon, contains at least one contaminant and obtains a higher-purity solid polycrystalline silicon. The process includes containing a melt of low-purity metallurgical grade silicon in a mold having insulated bottom and side walls, and an open top; solidifying the melt by unidirectional solidification from the open top towards the bottom wall while electromagnetically stirring the melt; controlling a rate of the unidirectional solidification; stopping the unidirectional solidification when the melt has partially solidified to produce an ingot having an exterior shell including the higher-purity solid polycrystalline silicon and a center including an impurity-enriched liquid silicon; and creating an opening in the exterior shell of the ingot to outflow the impurity-enriched liquid silicon and leave the exterior shell which has the higher-purity solid polycrystalline silicon.

Abstract: A process for purifying low-purity metallurgical grade silicon, contains at least one contaminant and obtains a higher-purity solid polycrystalline silicon. The process includes containing a melt of low-purity metallurgical grade silicon in a mold having insulated bottom and side walls, and an open top; solidifying the melt by unidirectional solidification from the open top towards the bottom wall while electromagnetically stirring the melt; controlling a rate of the unidirectional solidification; stopping the unidirectional solidification when the melt has partially solidified to produce an ingot having an exterior shell including the higher-purity solid polycrystalline silicon and a center including an impurity-enriched liquid silicon; and creating an opening in the exterior shell of the ingot to outflow the impurity-enriched liquid silicon and leave the exterior shell which has the higher-purity solid polycrystalline silicon.

Abstract: A process and apparatus for purifying low-purity silicon material and obtaining a higher-purity silicon material is provided. The process includes providing a melting apparatus equipped with an oxy-fuel burner, and melting the low-purity silicon material in the melting apparatus to obtain a melt of higher-purity silicon material. The melting apparatus may include a rotary drum furnace and the melting of the low-purity silicon material may be carried out at a temperature in the range from 1410° C. to 1700° C. under an oxidizing or reducing atmosphere. A synthetic slag may be added to the molten material during melting. The melt of higher-purity silicon material may be separated from a slag by outpouring into a mould having an open top and insulated bottom and side walls. Once in the mould, the melt of higher-purity silicon material can undergo controlled unidirectional solidification to obtain a solid polycrystalline silicon of an even higher purity.

Abstract: The self-baking electrode suitable for use in an electric arc furnace comprises an elongated open ended electrically conductive casing for extending generally vertically within the furnace. A central core made of a heat conductive material is disposed within and spaced from the casing. A framework within is securing the central core to an inner surface of the casing for holding centrally the central core within the casing and for preventing an extrusion of the central core downward. The central core is surrounded by a carbonaceous electrode paste devised to cure into a solid electrode upon heating and to bond to the central core. This self-baking electrode allows the production of silicon metal in a Soderberg-type furnace without any modification to the usual slipping system or addition of another slipping system.