Abstract
The alumina dissolution in a cryolite-alumina melt was studied by voltammetry using a new design of the electrochemical sensor. It consisted of a working carbon electrode, shielded with a pyrolytic boron nitride tube, and the counter electrode, forming an alloy with aluminum, with a developed surface. The difference of such electrochemical measuring devices from the known designs is the use of a copper counter electrode (cathode), which forms an alloy with the deposited aluminum. It allows excluding the measurement error associated with the depolarizing effect of the dissolved aluminum. The alumina dissolution process in the NaF-AlF3-(5 wt%)CaF2-Al2O3 melt with a molar ratio of [NaF]/[AlF3] = 2.1 mol mol−1 at 995 °C and the alumina concentration from 0.7 to 4.5 wt% was investigated. According to the linear calculation, the integral alumina dissolution rates varies from 0.02 to 0.35 mol s−1 depending on the initial alumina concentration in the melt. The differential rates of the alumina dissolution for the initial moments of time (0.1–5 s) were also estimated from the obtained empirical dependencies. Its maximum values for equal additions of alumina in the concentration range from 1.2 to 2.8 wt% were from 24 to 37 mol s−1.
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