Hiroyuki Baba

Purification of metallurgical silicon up to solar grade

A new production process of solar-grade silicon (SOG-Si) for small demand which is made from metallurgical-grade silicon (MG-Si) is proposed here, based on the findings of silicon refining stage in NEDO (New Energy and Industrial Technology Development Organization) Direct Reduction Process. SOG-Si trially produced was made into a multicrystalline cell through NEDO Project and the conversion efficiency was max. 10.9%.

Purification of Metallurgical Silicon up to Solar Grade

A new production process of solar-grade silicon (SOG-Si) for small demand which is made from metallurgical-grade silicon (MG-Si) is proposed here, based on the findings of silicon refining stage in NEDO (New Energy and Industrial Technology Development Organization) Direct Reduction Process. SOG-Si trially produced was made into multicrystalline cell through NEDO Project and the conversion efficiency was max. 10.9 %.

Boron Removal in Molten Silicon with Steam Added Plasma Melting Method

Oxidation and removal of boron from molten silicon by a steam-added plasma melting method was investigated as an important part of a sequential metallurgical process for producing high-purity solar grade silicon (SOG-Si) from commercially available metallurgical grade silicon (MG-Si). Experiments were carried out with the mass of silicon per charge varied in the range from 0.6 to 300 kg, corresponding to the laboratory scale to industrial scale. Boron was removed to ½B� < 0:1 mass ppm, which is the permissible boron content for SOG-Si. The deboronization rate was proportional to the steam content, 3.2th power of the hydrogen content of the plasma gas, boron content of the molten silicon, and area of the dimple formed by the plasma gas jet, and was inversely proportional to the mass of the molten silicon. A thermodynamic study showed that preferential oxidation of boron in molten silicon is positively related to higher temperatures, supporting the conclusion that this plasma method, which causes a local increase in the temperature of the reaction surface, is in principle advantageous.

Removal of Boron from Molten Silicon by Argon-Plasma Mixed with Water Vapor

Removal of boron from molten silicon was investigated using Ar plasma mixed with water vapor in view of developing a new process for solar-grade silicon (SOG-Si). The raw silicon was induction-melted and blown with a plasma flame of Ar gas with water vapor. It was concluded that the concentration of boron in silicon was decreased from 20 ppmw down to 0.1 ppmw or less by the plasma treatment for 300 minutes, and the rate of removing boron is proportional to both of the concentration of H2O in Ar plasma and the reaction area on the molten surface formed by blowing of the plasma. Presumably, the boron atoms were removed as volatile boron oxides. The kinetic analysis revealed the first order character of the reaction.