The Effect of NO, HNO2 and HNO3 On Corrosion of Stainless Steel by H2SO4★

Earlier work by other investigators has shown that nitrous acid is involved in the passivation of iron in concentrated nitric acid solutions. This paper describes the effect of nitric oxide, HNO2 and HNO3 on the corrosion of active Type 302 stainless steel by 10 percent H2SO4. Specimens of Type 302 stainless steel, activated by abrading on 240 grit emery cloth and exposed to 10 percent H2SO4 solutions, were passivated by bubbling nitric oxide through the solution. Bubbling oxygen through the solution did not passivate these abraded specimens. Abraded specimens exposed to an atmosphere of nitric oxide before immersion in nitric oxide-free H2SO4 remained active. Spot tests of 10 percent H2SO4 treated with nitric oxide revealed the presence of nitrite and nitrate ions in the solution. The addition of one part of 10 percent HNO3 to 60 parts of 10 percent H2SO4 was found to produce passivity of abraded stainless steel specimens exposed to the solution. 4.3.2