The effect of the additive glycerol on zinc electrodeposition on steel

In this study the characteristics of zinc plating from alkaline baths in the presence of glycerol additive but without other salt additions has been conducted to verify the role of glycerol. The results clearly show under what conditions the influence of glycerol is satisfactory with relation to electrochemical efficiency, adherence, and morphological characteristics. The bath containing 0.050 M glycerol and for deposition current of 12.5 mA /cm exp 2 shows the bst values of electrochemical efficiency, good adherence and morphology to the adhesive film, and optical microscopy, respectively. Until this value of current density, the deposition rate increases; however, after this value and with the increase in the additive concentration, the electrochemical efficiency decreases due to the high hydrogen evolution, which competes with the zinc deposition. An increase of the temperature leads to cathodic depolarization and to a decrease of the zinc deposition efficiency. On the other hand, bath stirring produces an increase in the deposition rate, which consequently increases the deposit thickness. Finally, it can be concluded that glycerol is a good additive for the alkaline zinc bath because it increases the free zinc ion concentration catalyzing zinc deposition, although in the studied conditions the glycerol presence does not show brightening characteristics.