Chemical Stripping
In chemical stripping, the coating to be stripped must be oxidized from the metallic state to an ionic state. Therefore, an active ingredient in any stripper must be an oxidizing agent. Depending upon the type of stripping process (immersion or electrolytic), the oxidizing action comes from the use of selective chemistry, electric current or both.
Selectivity is required to prevent attack on the base materials while allowing complete stripping of the metallic coating. Selective stripping can be achieved in several ways:
1) If the metal to be removed is more electrochemically active than the substrate (for example, zinc on steel), then selectivity can be obtained by using various electrolytes such as inhibited hydrochloric acid or sodium hydroxide (caustic soda).
2) By incorporating chelating or complexing agents in the stripping solution that have a greater affinity for the metal being removed than for the base material.
3) By adding inhibitors to stripping processes to chemically or physically adsorb onto the substrate and “protect” it from the stripping action. For example, to remove a nickel deposit from copper-plated steel while leaving the copper intact, organic sulfur compounds are added to the stripping solution.
4) By using special activators to help initiate the stripping action on the plated part without damaging the substrate. This is especially important if the plating is aged or heat treated such as electroless nickel deposits on steel.
Other components found in metal stripping solutions include rate accelerators, electrolytes (for conductivity) and water.
Taken from the sight below
Stripping of Plated Finishes : Products Finishing
