The Corrosion of Titanium in Alkaline Peroxide Bleach Liquors Available to Purchase

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/y 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 bleach liquor solutions (>8.38 mm/y). The preliminary results of inhibitor 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 corrosion of titanium exposed to 5 g/L of H₂O₂ in NaOH solutions of pH 12. It was also found that in simulated paper mill chemistries, i.e., basic solutions containing 3.7 g/L sodium silicate and 0.6 g/L EDTA (ethylenediaminetetraacetic 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) in the 0.1-0.5 g/L range also was shown to inhibit corrosion in the NaOH solution, but only after prior exposure to H₂O₂.