Silicon and solar-grade silicon production by solar dissociation of Si3N4

The temperature required for carbothermal reduction of silica—in the range 2100–2300 °C—is past the upper limit for combustion process heat. It is therefore an interesting candidate for solar–thermal processing. The production of solar-grade silicon from carbothermally produced silicon requires an energy-intensive long-duree high-temperature purification process. We propose here a two-step solar process for the production of silicon from silica: first, a carbothermal reduction in the presence of nitrogen to yield silicon nitride and second, the solar dissociation of the nitride to yield silicon. This last step could be combined with purification of the silicon if solar-grade silicon is the desired end-product. In this paper, we report on experimental results that indicate that silicon nitride can be dissociated to yield silicon with no detectable nitride content.