Tantalum also has excellent chemical properties and high corrosion resistance. It does not react to hydrochloric acid, concentrated nitric acid and aqua regia under either hot or cold conditions. But tantalum corroded in hot concentrated sulfuric acid, and under 150 ℃, tantalum is not concentrated sulfuric acid corrosion, only in the higher temperature will have a reaction, 1 year, in the 175 degrees of sulfuric acid corrosion of thickness is 0.0004 mm, the tantalum in 200 ℃ of sulfuric acid soaking for one year, the surface damage of only 0.006 mm. At 250 degrees, the corrosion rate increased to 0.116 mm per annum. At 300 degrees, the corrosion rate increased to 1.368 mm per annum after 1 year of immersion. The corrosion rate of fuming sulfuric acid (containing 15% SO3) was more serious than that of concentrated sulfuric acid. The surface was corroded to a thickness of 15.6 mm by soaking in the solution of 130 degrees for one year.
Tantalum can also be corroded by phosphoric acid at high temperature, but this reaction usually occurs at more than 150 degrees. Immerse it in 85% phosphoric acid at 250 degrees for one year, and the surface will be corroded by 20 millimeters. In addition, tantalum can be rapidly dissolved in the mixture of hydrofluoric acid and nitric acid, and it can also be dissolved in hydrofluoric acid. However, tantalum is more afraid of strong base. Tantalum will be rapidly dissolved in 40% caustic soda solution at 110 degrees, while potassium hydroxide solution at the same concentration will be rapidly dissolved at 100 degrees. In addition to the above, common inorganic salts generally do not corrode tantalum below 150 degrees. It has been proved that tantalum has no effect on alkali solution, chlorine gas, bromine water, dilute sulfuric acid and many other agents at room temperature, and only reacts under the action of hydrofluoric acid and hot concentrated sulfuric acid. Such cases are relatively rare in metals. However, at high temperature, the oxide film on tantalum surface is destroyed, so it can react with a variety of substances.
At room temperature, tantalum can react with fluorine. At 150 degrees, tantalum is inert to chloro-bromo-iodine, and at 250 degrees, tantalum is still resistant to corrosion of dry chlorine gas. When heated to 400 degrees in chlorine gas containing water vapor, tantalum remains bright. When heated to 500 degrees, tantalum begins to be corroded. Hydrogen chloride reacts with tantalum at 410 degrees to produce pentachloride, and hydrogen bromide reacts with tantalum at 375 degrees. When heated to 200 degrees or lower, S interacts with Ta, and carbon and hydrocarbons interact with tantalum at 800-1100 degrees.
