Niobium and tantalum often accompany each other, 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 columbite. The general corrosion resistance of niobium is higher than that of titanium and zirconium and slightly lower than that of tantalum, and since the price of niobium is lower than that of tantalum, niobium can be used as a substitute for the more expensive tantalum in certain corrosive media. At the same time, the relative density of niobium is only about 1/2 of that of tantalum, and in the case of the same component size, the amount of niobium is only about 1/2 of that of tantalum, which can reduce costs.
Niobium and tantalum, are generated by the surface of the dense oxide film and become passivated corrosion-resistant metal, thus niobium corrosion resistance performance of some and tantalum close. Niobium is mainly used in some temperature is not high reducing strong acid medium, but in hydrofluoric acid, hot concentrated sulfuric acid, sodium hydroxide, potassium hydroxide and other media is not corrosion resistant, in the hot concentrated hydrochloric acid and hot concentrated phosphoric acid in the corrosion rate is also high in these media should be careful when applying niobium.
The boiling point of niobium is 4927 ℃, melting point is: 2468 ℃, belongs to refractory metal. Niobium can be molded at a medium temperature of 350~400 °C, at a high temperature of 950~1000 °C, and can be completely annealed at about 1200 °C. Niobium can be formed in air from 230~400 °C at a high temperature of 950~1000 °C. Niobium oxidizes in air from 230 ℃, and then strongly oxidizes at 300 ℃, and when the temperature is higher than 400 ℃, the oxide film breaks down and falls off, greatly accelerating the oxidation rate. Nitriding of niobium starts at 600 °C in air. Niobium in hydrogen-containing media, 250 ℃ ~ 950 ℃ will absorb hydrogen. Therefore, welding and heat treatment of niobium should be carried out in a vacuum or under inert gas protection, i.e. thermal processes above 300 °C should be carried out in a vacuum or under the protection of inert gas or high temperature paint. When niobium equipment and containers are exposed to the atmosphere, the application temperature should not generally exceed 230 ℃, and the temperature can only be increased appropriately if it is ensured that they are not exposed to the atmosphere. Niobium should be protected during welding by high-purity inert gases in the same way as tantalum and should also be placed under inert gas protection at temperatures above 230 °C. It is advisable to use inert gases when the niobium weldments have cooled down to a minimum. It is advisable to cool the niobium weldments to 200 °C before stopping the supply of inert gas.
Niobium has been used in pressure vessels, but there is no formal niobium vessel standard. Pure niobium is mainly used in pressure vessels, and the addition of about 1% zirconium improves strength, but corrosion resistance and plasticity are slightly reduced.
