Abstract
An increase in the phosphorus content in Ni–P coatings (from 6.6 to 13.4%) is shown to be accompanied by amorphization of their structure and a decrease in the anodic dissolution rate (at low overvoltages) by two–three orders of magnitude, whereas the corrosion rate is decreased to a lesser degree. Polarization curves of the coatings measured in 0.5 M H2SO4 comprise two linear segments and no passive range. In the first segment, the b a coefficient is shown to be anomalously high (∼0.4–0.5 V for amorphous alloys), and the dissolution is controlled by transient volume diffusion of nickel and accompanied by surface accumulation of phosphorus. Being added as a stabilizer, thiourea reduces the corrosion resistance of the coatings and increases the dissolution currents, which can be to a considerable degree eliminated by increasing the phosphorus content in the coatings. The adverse effect of Pb incorporation into the coatings manifests itself as a substantial acceleration of their anodic dissolution.
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Petukhov, I.V., Shcherban', M.G., Skryabina, N.E. et al. Corrosion and Electrochemical Behavior of Ni–P Coatings in 0.5 M H2SO4. Protection of Metals 38, 370–376 (2002). https://doi.org/10.1023/A:1019669503487
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DOI: https://doi.org/10.1023/A:1019669503487