Hydriodic acid is a solution of hydrogen iodine (HI) in water that is a highly corrosive. This strong mineral acid and when compared to HCl or HBr is even more corrosive as the larger iodine atoms could dissociate from the hydrogen atoms more easily. This makes HI an extremely corrosive acid to deal with and the strongest in the halide group. Industrially, hydroiodic acid (HI) is mainly used in the production of acetic acid, as a source of iodine in chemical synthesis, and as a reducing agent
Because of hydroiodic acid’s extreme corrosiveness, few metals can withstand its attack especially at elevated concentrations and temperatures. In these cases tantalum metal can be used as it shows no corrosion attack to hydroiodic acid through a range of temperatures and concentrations.