2019 年 60 巻 5 号 p. 732-736
Acids provide corrosive environments that have their own behavior and characteristics when reacted with metal. Much research has been conducted to determine corrosion behavior of metals in acidic environments; however, little has been published concerning the corrosion behavior of ultralow carbon steel in mixed acid solutions, although such systems are widely used in the textile, chemical, and fertilizer industries. Corrosion behavior of ASTM A1008 ultralow carbon steel in mixtures of HNO3, H2SO4, and HCl was investigated using immersion and polarization methods. The HCl concentration was held constant at 1 M and the HNO3 and H2SO4 concentrations varied to 0.1 M, 0.5 M, and 1.0 M. Under these conditions, a synergistic effect between HNO3 and H2SO4 was observed, which thinned the metal, while HCl caused pitting of the metal surface. The results showed that the corrosion rate of the metal was enhanced as the acid concentrations increased, especially that of HNO3. The corrosion products were identified as iron(III) oxide [Fe2O3] and rhomboclase [H5Fe3+O2(SO4)2·2(H2O)].
