No abstract

The direct carbothermic reduction process from high-purity silica is promising for next-generation low-cost silicon solar cells. In this process, the granulation process is essential to avoid blowout of the silica powder. In this study, we investigated the effect of binders on this reduction process using four kinds of binders. The real-time monitoring of the chamber pressure and quadrupole mass spectroscopic analysis indicated the sign of the blowout phenomena of the generated CO gas and decomposition gas of the binders. In the case of starch and sucrose, the strengths of granules were not enough to the process with the pressure of the generated CO gas, while the granules with enough strength, namely, the ones with polyvinyl alcohol (PVA) and carboxymethyl cellulose (CMC), resulted in silicon yield of 33.8% and 27.8%, respectively.

For many years the production of solar-grade silicon remained a costly process resulting in a large amount of carbon gas being emitted, and so the process still requires improvement to suppress carbon emission. The starting point of the processes is to produce raw silicon materials from a natural resource via mostly carbothermic reduction. However, this process is very complicated and SiO and SiC form as by-products. Further improvement of the carbothermic reduction process requires an understanding in real time of the reactions occurring and the weight change during heating. In particular, the behavior of the SiO by-product plays a major role in the production of silicon because the loss of Si is caused by the escape of SiO gas. In this study, we developed an in-situ weight measuring system for our induction heating furnace, and successfully suppressed much of the error in weight by improving the crucible con guration. The real-time monitoring of the crucible weight loss during the reaction may assist in understanding of the carbothermic reduction process in a more detailed fashion.