Diagrammatic Representation of Direct Electrolytic Reduction of SiO[sub 2] in Molten CaCl[sub 2]

The direct electrolytic reduction of solid and an reference electrode in molten were investigated at . An electrode separated by a mullite tube was confirmed to be a stable reference electrode. The electrochemical window of this melt was at . The formation potential of alloys was measured. Combining these experimental data and the reported thermochemical data, a diagram was constructed which shows the equilibrium potentials for the silicon species in molten containing ions at , where the electrode potential vs was plotted against the negative logarithm of the activity of oxide ions in the melt . The potential- diagram explained the behavior of an -contacting electrode during the direct electrolytic reduction to silicon and suggested a formation of an intermediate of solid , which was confirmed by X-ray photoelectron spectroscopy analysis.