Effect of Copper Addition on Corrosion Behavior of High-Performance Austenitic Stainless Steel in Highly Concentrated Sulfuric Acid Solution—Part 1 Available to Purchase

The effects of Cu addition on the corrosion behavior of austenitic stainless steel in 18.4 N sulfuric acid (H₂SO₄) at 80°C to 120°C was investigated through anodic polarization, cathodic polarization, long-term immersion, x-ray photoelectron spectroscopy (XPS) analysis, and scanning Auger microscopy (SAM). The addition of 3.2% Cu in the alloy enhanced the corrosion resistance greatly in highly concentrated H₂SO₄ by decreasing corrosion current density, current density of hydrogen evolution, critical current density, and passivation current density. The dissolution rates of each of the elements in the alloy resembled that of the elements in pure metal form. The protective surface film was heavily enriched with the noble metallic Cu and cupric oxide (CuO) from the selective dissolution of the active metallic Fe, Ni, and Cr. In addition, the corrosion resistance seemed to be associated with nickel oxide (NiO), molybdenum dioxide (MoO₂), tungsten trioxide (WO₃), molybdenum oxy-hydroxide (MoO[OH]₂), molybdate $(MoO42−)$⁠, tungstate $(WO42−)$⁠, and chromate $(CrO42−)$ contained in the protective surface film. The stainless steel with 18%Cr-21%Ni-3.2%Mo-1.6%W-0.2%N-3.2%Cu-0.035%C displayed a noticeably better corrosion resistance than the commercial super austenitic stainless steels such as UNS S32654 and at least as good as the Ni-based alloys such as CW12MW in a sulfate $(SO42−)$ environment.