Materials for high-temperature and high-pressure hydrogen peroxide bleaching equipment

To determine the suitability of grade 705 zirconium (UNS R60705) as a candi date material of construction for high-temperature and pressure hydrogen pe roxide (P-HT) pulp-bleaching reactors, a series of electrochemical experime nts were carried out In simulated P-HT environments. Because the P-HT proce ss may be incorporated Into a closed cycle mill or a mill that also uses ch lorine-based chemicals to bleach pulp, the effect of chloride ion concentra tion on the corrosion of zirconium In PHT environments was studied. It was found that at the potential measured in P-HT environments, zirconium was pa ssive (-100 mV vs saturated calomel electrode [SCE]). Breakdown potentials of approximate to 500 mV(SCE) were measured In chloride-containing solution s. 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 w ide range of P-HT process conditions.