Corrosion mitigation in supercritical water with chromium ion

It was reported that the chromium ion originated from the autoclave material (Ni-44Cr-1Mo) deposited on the specimen surface as chromium oxyhydroxide (CrOOH), and the protective chromium oxide layer mitigated corrosion of the alloys tested in supercritical water containing sulfuric acid (H2SO4). Based on the report, three kinds of tests were conducted at 400 degrees C and 30 MPa in 0.01 mol/kg H2SO4 aqueous solution containing Cr3+ or Cr6+. Corrosion resistance of the specimens became 1.5 similar to 7.5 times better than specimens without chromium ions, because chromium ions from the aqueous solution was incorporated into the protective chromium oxide on the specimen. It was revealed that reduction of Cr6+ to Cr2O3 (Cr3+) occurred on the specimen surface and in the autoclave. The chemical equations of chromium oxide or chromium oxyhydroxicle scale formed on the specimen surface were evaluated.