When we use acid zinc plating brightener in the production process, sometimes the coating of the workpiece will appear streaks, what is going on?
Bigolly Technology made an analysis based on the field experience and the characteristics of the product's acid zinc plating brightener BZ-525,It was found that when galvanizing, when the surface of the workpiece was linearly blistered, stripes appeared on the surface of the obtained workpiece at the corresponding positions, which indicated that the original stripes were caused by hydrogen evolution.
When the content of NH4Cl increases, [K+] decreases. According to NH4++H2O ⇌ NH3·H2O+H2, the [H+] in the solution increases and the pH value decreases. At this time, the area of Zn2+ adsorption on the surface of the cathode is relatively large, so only in the Hydrogen evolution occurs only when the current density is large enough.And because [H+] is relatively large, when hydrogen evolution occurs, the amount of H2 produced is relatively large, so H2 is not easily adsorbed on the surface of the cathode, but rises to the liquid surface through buoyancy,H2 hindered the deposition of Zn2+ at this position during the floating process, resulting in the appearance of streaks.
When the total salt concentration in the plating solution decreases, [K+] also decreases, and the adsorption sites of Zn2+ on the cathode surface account for most of them, so hydrogen evolution will only occur when the current density is large enough.However, H2 is not easily adsorbed on the surface of the galvanized layer, so it quickly rises to the liquid surface under the action of buoyancy. Due to the floating of H2, the further deposition of Zn2+ at this position is hindered, resulting in streaks.
Therefore, when we produce acid zinc plating brightener, sometimes the coating of the workpiece will have streaks, which is how it comes.