It is shown that an electrodeposited Zn-Ni-Cd alloy coating produced from sulfate electrolyte inhibits the discharge of hydrogen on carbon steel. The newly developed ternary alloys have approximately ten times higher corrosion resistance when compared to a Zn-Ni alloy. Hydrogen permeation characteristics of Zn-Ni-Cd alloy coatings were studied and compared with those of a bare and a Zn-Ni alloy coated steel. The transfer coefficient, a, exchange current density, io, thickness dependent adsorption-absorption rate constant, k0, recombination rate constant, k3, surface hydrogen coverage, θH, were obtained by applying a mathematical model to experimental results. Alloys obtained from baths containing higher concentration than 3 g/L of CdSO4 in the sulfate plating bath are seen to have superior permeation inhibition properties compared to the Zn-Ni alloy coating and bare steel. The hydrogen permeation current was zero under normal corroding conditions for Zn-Ni-Cd alloy and it increased to 0.3 mA/cm2 at a cathodic overpotential of 250 mV. The hydrogen permeation current density for steel and Zn-Ni alloy under similar conditions were 62.1 and 1.3 mA/cm2, respectively.
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