THE CORROSION BEHAVIOR OF TITANIUM (GRADE-2) IN ALKALINE PEROXIDE BLEACH LIQUORS

An experimental program to determine the effects of hydrogen peroxide (H2O2) and of potential corrosion inhibitors on the corrosion behavior of titanium has been developed Corrosion rates less than 0.25 mm/year were observed in laboratory bleach liquor at pH 12 to which 5 g/L of H2O2 were added. At pH 13, with 10 g/L H2O2, the corrosion rates were unacceptably high in both sodium hydroxide (NaOH) and laboratory bleac h liquor solutions (>8.38 mm/ year). The preliminary results of inhibi tor studies indicated that the addition of 3.7 g/L sodium silicate or 0.01 g/L calcium nitrate [Ca(NO3)(2)] effectively inhibited the corros ion of titanium exposed to 5 g/L of H2O2 in NaOH solutions of pH z 12. It was also found that in simulated paper mill chemistries, i.e., bas ic solutions containing 3.7 g/L sodium silicate and 0.6 g/L EDTA (ethy lenediaminetetraacetic acid), corrosion rates increased markedly with the addition of 5 g/L H2O2. However, subsequent additions of peroxide resulted in corrosion rates which were even lower than those found in NaOH. This is believed to be due to the formation of a black scale on the surface of the sample. The addition of magnesium sulfate (MgSO4) i n the 0.1-0.5 g/L range also was shown to inhibit corrosion in the NaO H solution, but only after prior exposure to H2O2.