Breakaway properties of film formed on copper and copper alloys in erosion-corrosion by mass transfer equation

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Erosion-corrosion tests on copper and three types of copper alloys in a 1 wt% solution of CuCl2 were carried out at various flow velocities using a jet-in-slit testing apparatus, which is capable reproducing various hydrodynamic conditions. A damage profile of a specimen was developed using a surface roughness meter to evaluate locally occurring damage. The damage depth rate for copper, beryllium copper and a 70/30 copper nickel alloy increased with increasing flow velocity, and suddenly increased at a certain velocity, which is called the breakaway velocity. The breakaway velocities at the central and disturbed part of a specimen were different for each sample, indicating that the hydrodynamic conditions of the flowing solution had an effect. The damage depth rate, calculated from the mass transfer equation, which involved mass transfer in the concentration diffusion layer and in the corrosion product film, could be fitted to the experimental data, suggesting that the mass transfer equation can be applied to the evaluation of erosion-corrosion damage. The corrosion product film was exponentially broken away at velocities higher than the breakaway velocity. The breakaway properties of the corrosion product film were confirmed to be different for each material, since the power of the exponential equation was different for each sample.
2008-01-25