Effects of polymer corrosion inhibitor on widening etch tunnels of aluminum foil for capacitor

• With PSSA, the exterior surface dissolution of etched Al foil is suppressed.
• With PSSA, the interior surface dissolution of etched Al foil is facilitated.
• With PSSA, the tunnels are widened along the entire length.
• With PSSA, the area and capacitance of etched Al foil are significantly improved.

We investigated the effects of polymeric corrosion inhibitor polystyrene sulfonic acid (PSSA) additive to 3% HNO3 solution on widening tunnels of pre-etched aluminum foil by electrochemical DC etching for aluminum electrolytic capacitors, using scanning electron microscopy and polarization curves. With trace PSSA, the dissolution of exterior surface of etch tunnels of Al foil is suppressed and the dissolution of interior surface of etch tunnels of Al foil is facilitated, respectively. The tunnels transform from circular cone to circular column in shape and pits-merging on the surface is weakened, leading to significant increase in the surface area and specific capacitance of the Al foil. The amounts of reduced thickness and weight of Al foil during the widening process of etch tunnels can be decreased if PSSA is employed.