Materials for High-Temperature and High-Pressure Hydrogen Peroxide Bleaching Equipment

Abstract

Abstract To determine the suitability of grade 705 zirconium (UNS R60705) as a candidate material of construction for high-temperature and pressure hydrogen peroxide (PHT) pulp-bleaching reactors, a series of electrochemical experiments were carried out in simulated PHT environments. Because the PHT process may be incorporated into a closed cycle mill or a mill that also uses chlorine-based chemicals to bleach pulp, the effect of chloride ion concentration on the corrosion of zirconium in PHT environments was studied. It was found that at the potential measured in PHT environments, zirconium was passive (−100 mV vs saturated calomel electrode [SCE]). Breakdown potentials of ≈ 500 mVSCE were measured in chloride-containing solutions. However, when the chloride ion concentration was increased > 50 ppm, the repassivation potential of the zirconium was reduced significantly. Based on these results, grade 705 zirconium was determined to be suitable for a wide range of PHT process conditions.