Diffusion of hydrogen in a steel substrate absorbed during zinc and zinc-silica electroplating

In the present study, hydrogen penetration during zinc and zinc-silica (SiO2) plating and hydrogen diffusion under natural storage were investigated using quantitative measurement and an electrochemical technique. Most of the hydrogen was found to have penetrated into the steel substrate at the initial stage of electroplating. However, hydrogen content in the zinc-plated specimen decreased faster than that in the Zn-SiO2-plated one. This indicated that the hydrogen diffusivity in the Zn-SiO2 composite was greater than that in the pure zinc layer. Furthermore, hydrogen permeation through zinc and Zn-SiO2 electrodeposit was studied using an electrochemical technique with bilayer specimens of Fe/Zn or Zn-SiO2 electrodeposit. The hydrogen diffusion coefficient of the pure zinc layer was on the order of 10(-11) cm(2)/s while that of the Zn-SiO2 composite was much higher. Analyses of the coating microstructures were applied to explain the hydrogen diffusivity difference between these two kinds of coatings.