Preparation of tantalum powders via the sodium reduction of potassium heptafluorotantalate heat-treated in air

Tantalum powders have been prepared by sodium reduction in melts containing potassium heptafluorotantalate (K 2 TaF 7 ) heat-treated in air. Their specific surface area is three to four times that of powders obtained by reducing unheat-treated K 2 TaF 7 under the same conditions. The increase in specific surface area is due to the reduction of tantalum oxyfluoride complexes (K 3 TaOF 6 and K 2 TaOF 5 ) and Marignac’s salt (K 2 Ta 2 O 3 F 6 ) forming during heat treatment of K 2 TaF 7 . Potassium heptafluorotantalate heat-treated at temperatures from 600 to 670°C is shown to be suitable as a starting material for producing high-capacitance tantalum capacitor powder.