METHOD OF PREPARING PURE NIOBIUM Russian patent published in 1999 - IPC

FIELD: nonferrous metallurgy. SUBSTANCE: method includes reductive melting of niobium pentoxide with aluminum and calcium followed by repeated electron-beam refining remelting. To reduce number of energy-intensive remeltings, they are preceded by thermal vacuum calcination of crude niobium ingots. Calcination leads to improved quality of ingot surfaces: removed residual slag, graphite, and other inclusions, and also partially degassed metal. Calcination of ingots placed in graphite crucible is carried out for 2.5-3.0 hr at temperature by 100-150 C superior to melting point of slag and residual pressure up to 0.4 kPa. Cooling is carried out under vacuum and calcination in induction vacuum kiln. EFFECT: reduced number of electron-beam remeltings and by 22% consumption of power. 2 cl, 1 tbl