Niobium preparation methods
Main niobium preparation methods are carbothermal reduction process, niobium and aluminium reduction process and sodium reduction method. Niobium is produced by molten salt electrolysis process, and niobium reduction process.
Vacuum carbon reduction method
Vacuum carbon reduction is one of the main methods for producing niobium. Carbon reduction is usually carried out in a vacuum tube furnace. The method uses the affinity of carbon to oxygen more than that of niobium to oxygen, and uses carbon as reducing agent to restore Nb2O5 to produce niobium bars. The utility model has the advantages of high product yield (> 96%), cheap reducing agent, low production cost and no by-product of sodium reduction, and needs wet processing to obtain the high-purity niobium bars and metal powder.
There are two processes such as direct carbon reduction and indirect carbon reduction in industry. The niobium is produced by direct carbon reduction and looks like sponge, with large surface area, low metal impurities and nitrogen content, and is favorable to the specific capacity of niobium powder. Therefore, the process is suitable for producing niobium powder at the capacitor level. Indirect reduction is characterized by large equipment production capacity and stable process. The obtained metal niobium strip is relatively compact and has a relatively good shape and size. It is suitable for making niobium bars, niobium ingots and niobium processing materials.
Sodium thermal reduction method
Niobium is seldom used in the manufacture of capacitors, so sodium reduction is less used.
The electrolytic methods of niobium, include electrolysis of molten salt and electrolysis of aqueous solution. The production of niobium powder by molten salt electrolysis is simple and the production cost is low.
In addition to the above method, in recent years, the people developed nitride to produce niobium, the niobium oxide or niobium iron as raw material, ammonia or nitrogen and carbon react to produce niobium nitride, and niobium nitride thermal decomposed metal niobium in vacuum and 2103 ~ 2373K temperature.
Niobium compounds can be prepared by reduction of niobium powder, niobium or niobium sponge is brittle impurity, but these products also contain a certain amount of niobium, including hydrogen, oxygen and nitrogen impurity is especially easy to niobium brittle, so it needs further clear. The main purposes of niobium refining are two, that is, purification and densification, and the two processes are usually performed simultaneously in industrial production.
As a result of strong affinity on oxygen and carbon, and therefore niobium can not be used with container manufacturing oxygen and carbon material, and must be carried out at high temperature under high vacuum, which not only makes the refining process is complicated, and the equipment requirements are high. The main methods of niobium refining are vacuum sintering, such as niobium vacuum sintering, arc melting, niobium vacuum arc melting, electron beam melting, niobium electron beam melting, etc.. Among them, the refining effect of electron beam smelting is the best and the most widely used. In order to obtain the best purification effect, several refining methods, such as the niobium strip sintered by sintering, are used in the refining process, and then the electron beam melting is adopted.