Effect of brighteners on hydrogen evolution during zinc electroplating from zincate electrolytes

Hydrogen evolution during zinc electrodeposition on a steel substrate from zincate electrolytes containing different additives was studied using vario us experimental techniques. The hydrogen evolution reaction is limited by t he electron transfer step. Hydrogen evolution is most intensive during the first seconds from the beginning of electrodeposition due to the lower over potential of hydrogen on steel as compared with that on zinc. The evolved h ydrogen is dissipated in three ways. Most is dissipated to the atmosphere v ia gas bubbles at a constant rate. Some is dispersed in the electrolyte som e diffuses into the steel substrate, predominantly at the commencement of d eposition. The additives affect both the total amount of evolved hydrogen a nd its distribution. The highest amount of hydrogen is evolved in the prese nce of the anisaldehyde bisulphite containing composite additive. The highe st amount of hydrogen included in the substrate and remaining in the electr olyte corresponds to the use of the Na-N-benzylnicotinate containing additi ve. In this case blistering is observed.