The chemical properties of niobium

Niobium is a very stable metal, and its chemical properties are very close to that of tantalum. Niobium has good high-temperature performance under vacuum conditions or protected by coatings, but its high-temperature performance is severely challenged in the atmospheric environment. Niobium is widely used in aviation, aerospace, atomic energy industry and other fields. The temperature requirements for materials used in the atmosphere exceed 1050 ℃ or even reach 1800 ℃, which puts high requirements on the oxidation resistance of niobium and niobium alloys. When the temperature is lower than 200°C, niobium will not be affected by various gases, but when the temperature is around 200°C, niobium begins to slowly oxidize. At this time, niobium reacts with oxygen to form a protective layer on the surface. Oxide film, when the temperature reaches 550℃, the oxidation reaction accelerates to produce Nb2O5 white powder. The reaction of niobium with oxygen generally produces three stable oxides, Nb2O5, NbO, and NbO. Niobium begins to absorb hydrogen at 250°C, forming interstitial solid solution, which embrittles it and deteriorates its plasticity. The interstitial elements carbon, nitrogen, hydrogen, and oxygen have obvious effects on the performance of sawing. If their content is too high, the strength of niobium will increase rapidly, but the plasticity will decrease rapidly.

At lower temperatures, silver reacts with oxygen to increase the thickness of the surface oxide film to form a protective oxide film. Then the oxidation speed slows down, and the reaction speed decreases. The complex oxidation process of niobium and the polycrystalline system of its oxidation products The transformation process is related. When niobium is near 400°C, the protective oxide film gradually forms microscopic bubbles and transforms into a non-protective oxide film; when the temperature is higher than 500°C, the oxidation speed increases rapidly, and the oxidation becomes a direct proportional linear relationship.

The high temperature acid corrosion resistance of niobium is second only to tantalum. At room temperature, niobium is very stable in many inorganic salts, organic acids, mineral acids and their aqueous solutions, but it has poor alkali resistance. Hydrofluoric acid, mixed acid of hydrofluoric acid and nitric acid can corrode.