Com un ca,]ons O Hexavalent Fluorides of Tantalum and

It has been found that hexavalent compounds of tan-talum and niobium can be prepared by the electrol-ysis of solutions of the pentavalent antalum and niobium fluorides dissolved in molten alkali fluorides with any suitable conducting cathode and an inert anode such as graphite. It is known that similar elec-trolysis of molten chlorides, mixed chlorides and fluo-rides, and mixed fluorides and oxides does not produce these higher valence tantalum and niobium compounds, but instead produces chlorine or oxygen at the anode. Only in the case of an essentially pure fluoride system does one observe that no gas is produced at the anode, but that instead, the higher valence tantalum or nio-bium fluoride is formed. It is noteworthy that copious fluorine evolution occurs at the anode when the molten alkali fluoride mixture alone is electrolyzed with a graphite anode. On addition of a few per cent of either KfTaFv or KfNbF7 gas evolution instantly ceases, and formation of the hexavalent compounds takes place. For example, a solution used for plating tantalum (1) containing 14.2 w/o (weight per cent) K2TaFv dissolved in Fl inak z was electrolyzed in an argon at-mosphere with a graphite anode and copper cathode at 770 ~ and anode and cathode current densities of 100 ma/cm 2 for 21 hr to convert 71 % of the contained tantalum to the hexavalent state. This was confirmed 1 Fl inak is the eutectic mixture of KF, NaF, and LiF.-0. I +0. I ~"x,,,,,,