Electrochemical studies on rhenium in fused LiCl-KCl eutectic

Abstract

Potentiometric and polarographic studies were carried out on Re(IV) and ReO 4 − in the LiCl-KCl eutectic at 450–550°C. The reversible apparent standard potential of the Re(IV)/Re(0) couple here is −0·389 + (5·6 x 10 −4) ( t − 450) V vs the standard Pt(II)/Pt(0) reference. Rhenium metal can be electrodeposited from these melts, but potentials exceeding about −1 V result in predeposition of Li(0) which partly dissolves in the rhenium. Anodic dissolution of rhenium metal produces Re(IV) and Re(III); the latter disproportionates at once to Re(IV) and Re(0). This reaction will support only low current densities. Re(IV) is stable indefinitely in the melt, but addition of K 2ReCl 6 to the melt involves some decomposition to metal during the dissolution process. ReO 4 − can be reduced to Re(0) in the eutectic at −1·2 V with high current efficiency. Stable intermediate oxidation states were not observed.