Niobium and tantalum often occur together, but the content of niobium in the earth's crust is about 2.4 × 10 -3%, which is 10 times that of tantalum, and it mainly exists in the form of columbite. Generally, the corrosion resistance of niobium is higher than titanium and zirconium but slightly lower than tantalum. Since the price of niobium is lower than tantalum, niobium can be used to replace the more expensive tantalum in some corrosive media. At the same time, the relative density of niobium is only about 1/2 of tantalum. Under the same component size, the dosage of niobium is only about 1/2 of tantalum, which can reduce costs.
Niobium, like tantalum, relies on the formation of a dense oxide film on the surface to become a passivating corrosion-resistant metal. Therefore, the corrosion resistance of niobium is close to that of tantalum. Niobium is mainly used in some strong reducing acid media with low temperature. However, it is not corrosion resistant in hydrofluoric acid, hot concentrated sulfuric acid, sodium hydroxide, potassium hydroxide and other media. It is not corrosion resistant in hot concentrated hydrochloric acid and hot concentrated phosphoric acid. The corrosion rate is also high, so caution should be used when applying niobium in these media.
The boiling point of niobium is: 4927 ℃, the melting point is: 2468 ℃, it is a refractory metal. Niobium can be molded at medium temperatures of 350~400°C, high temperature molding at 950~1000°C, and can be completely annealed at around 1200°C. Niobium begins to oxidize in air at 230°C, and begins to oxidize strongly at 300°C. When the temperature is higher than 400°C, the oxide film is destroyed and falls off, greatly accelerating the oxidation rate. Niobium begins to nitride in air at 600°C. Niobium will absorb hydrogen in a hydrogen-containing medium at 250 ℃ ~950 ℃.
