Corrosion Behavior of Metals in Flowing Ar-42.6%O2-14.7%Br2 Gas Mixture at 700°C

Abstract

The corrosion behavior of pure metals that form the basis of high-temperature superalloys has been investigated in an Ar-42.6%O2-14.7%Br2 gas mixture at 700°C, which was one of the environments encountered in the University of Tokyo (UT)-3 thermochemical water decomposition reaction process to produce hydrogen. The test metals were nickel, chromium, cobalt, copper, iron, titanium, hafnium, zirconium, molybdenum, niobium, tantalum, and tungsten. Thermodynamic phase stability diagrams were constructed for nickel, chromium, iron, cobalt, titanium, tungsten, and zirconium to predict the stable, condensed corrosion products, and the oxides were predicted to be thermodynamically stable phases. Postreaction characterization of the test metals included discontinuous mass-change measurements, scanning electron microscopy, energy-dispersive x-ray analysis, and x-ray diffraction. X-ray diffraction identified oxides as corrosion products for all metals. But low-melting metal bromides were also detected for titanium, tungsten, molybdenum, copper, and iron; these caused rapid consumption of the metals. Although scanning electron microscopy revealed chromium oxide (Cr2O3) scale formation on chromium, energy-dispersive x-ray analysis identified bromine-containing species at the cracked scale/metal interface.