Vacuum carbon reduction is one of the main methods to produce niobium metal at home and abroad. Using carbon as reducing agent to reduce Nb2O5 to produce niobium bar, the affinity of carbon to oxygen is higher than that of niobium. Its advantages are high yield (> 96%), cheap reductant, low production cost, no sodium reduction and other methods of by-products need wet treatment, can obtain higher purity niobium bar and metal powder. There are two industrial processes of direct carbon reduction and indirect carbon reduction. The former is direct reduction with carbon Nb2O5, reaction temperature of 1800 ~ 1900 ℃, the total equation is:
Nb2O5 nb = 2 + 5 + 5 c co
The sponge niobium produced by direct carbon reduction has a large surface area and low metal impurities and nitrogen content, which is beneficial to the specific capacity of niobium powder. Therefore, this process is suitable for the production of capacitor grade niobium powder. Indirect carbon reduction is to prepare niobium carbide first and then use niobium carbide as reducing agent to reduce Nb2O5.Reaction is:
Nb2O5 + 7 c = 2 NBC + 5 co
NBC Nb2O5 + 5 + 5 = 7 nb co
The characteristics of indirect reduction are large production capacity, stable process, relatively compact metal niobium bar, relatively regular shape and size, suitable for processing niobium bar, niobium ingots and niobium.
