Technical parameters of niobium

Niobium and tantalum often occur together, but the content of niobium in the earth's crust is about 2.4 × 10-3%, 10 times that of tantalum, mainly in the form of niobium. Generally niobium corrosion resistance is higher than titanium, zirconium and slightly lower than tantalum, because the price of niobium is lower than tantalum, so niobium can be used in some corrosive media instead of more expensive tantalum. At the same time, the relative density of niobium is only about 1/2 of tantalum, and the consumption of niobium is only about 1/2 of tantalum in the same component size, which can reduce the cost.

Niobium, like tantalum, becomes passivated corrosion resistant metal by forming dense oxide film on its surface, so niobium's corrosion resistance is close to tantalum's. Niobium is mainly used in some of the temperature is not high reducible strong acid medium, but in hydrofluoric acid, hot concentrated sulfuric acid, sodium hydroxide, potassium hydroxide and other media is not corrosion resistant, in hot concentrated hydrochloric acid and hot concentrated phosphoric acid corrosion rate is also high, niobium should be carefully applied in these media.

The boiling point of niobium; 4927 ℃, melting point is: 2468 ℃, belongs to refractory metal. Niobium can be formed in 350~400 ℃ medium temperature, 950~1000 ℃ high temperature molding, can be fully annealed at about 1200 ℃. Niobium in the air from 230 ℃ began to oxidize, 300 ℃ began to strongly oxidize, the temperature is higher than 400 ℃ oxidation film damage and fall off, greatly accelerate the oxidation rate. Niobium begins nitriding in air at 600 ℃. Niobium in hydrogen-containing medium, 250 ℃ ~950 ℃ will absorb hydrogen. Therefore, the welding and heat treatment of niobium should be carried out in vacuum or under the protection of inert gas, that is, the thermal process above 300 ℃ should be carried out under the protection of vacuum or inert gas or high temperature coating. When niobium equipment and containers are exposed to the atmosphere, the application temperature should not exceed 230 ℃, only in order to ensure that the atmosphere is not exposed to, the temperature can be appropriately increased. Niobium, like tantalum, is protected by high purity inert gas during welding, and it should also be protected by inert gas at temperatures above 230 ℃. It is best to cool niobium welds to 200 ℃ and then stop supplying inert gas. Niobium materials have been used in pressure vessels, but there is no standard for niobium vessels. In pressure vessels, pure niobium is mainly used. Adding about 1% zirconium can improve the strength, but the corrosion resistance and plasticity are slightly reduced.