Semi-continuous production of tantalum powder by electronically mediated reaction (EMR)

Abstract

An electronically mediated reaction (EMR) has been explored to produce tantalum powder semi-continuously by the calciothermic reduction of tantalum chloride (TaCl5). TaCl5 feedstock and reductant calcium alloy were charged into electronically isolated locations in a molten CaCl2 bath at 1123 K. The feed was freshly recharged three times, but the bath was reused without replenishment during four repeated reduction experiments. The current flow through an external path between the feed (cathode) and reductant (anode) locations was monitored. A current between 0.2 and 0.9 amps was measured during the reaction in the external circuit connecting cathode and anode. Tantalum powder was readily obtained after each experiment, but its purity decreased from 95% to 87%Ta as the run number increased. Tantalum powder obtained from EMR was fine compared with that of metal powder metallothermic reduction. Tantalum powder with low aluminum and nickel content was obtained although liquid Ca-Al-Ni alloy was used as the reductant. The results demonstrate the possibility of semi-continuous production of tantalum powder by the EMR without the direct physical contact between the feed and reductant. The mechanism of the calciothermic reduction of TaCl5 in the molten salt was discussed, using an isothermal chemical potential diagram.