The Corrosion Behavior of Niobium in Hydrochloric Acid Solutions

Studies to better understand the corrosion behavior of niobium in hydrochloric acid solutions have been conducted as part of the Bureau of Mines' effort to conserve the United States' mineral resources. A study of the general corrosion behavior of niobium as a function of acid concentration, time, oxygen, and added ferric ion is reported. Weight loss (corrosion) tests were performed in air saturated (agitated and static) and helium saturated (agitated) hydrochloric acid solutions ranging from 1N to 10N at temperatures from 35 to 100 C and exposures up to 60 days. The 30 day corrosion rates ranged from 0.0 μm/y in 35 C air saturated (agitated) 1N HCl to 230 μm/у in air saturated (static) 9.8N HCl at 85 C. Although the corrosion rates decreased rapidly for times up to 30 days, the rates for 30 and 60 days were essentially identical. The presence of air did not affect the corrosion rate of niobium, while the presence of only 70 ppm of ferric ion reduced the corrosion rate in most air saturated 5N and 10N HCl solutions.