Studies on Acceleration of the Low Temperature Zinc Phosphating Processes

Abstract

SUMMARYThe present work aims to discuss the effective means of accelerating the low temperature zinc phosphating processes by employing two methodologies and to evaluate the possible implications of adopting such methodologies in decreasing the processing time. The first one utilizes the galvanic corrosion principle whereas the second one involves the addition of a powerful oxidizing agent, namely, iodine pentoxide to the bath. It is suggested that both methods would impart a higher rate of metal dissolution, which would be helpful in accelerating the rate of deposition. Phosphate coatings were produced on mild steel substrates using a zinc phosphating bath capable of operating at low temperature (27°C). under both uncoupled and galvanically coupled conditions (with stainless steel or copper substrate) and with and without the addition of iodine pentoxide. The study revealed an enhanced dissolution of mild steel when it is galvanically coupled to more noble metals and also when the bath is modified with iodine pentoxide. It is concluded that the processing time of the low temperature zinc phosphating processes can be considerably decreased by adopting either the galvanic coupling methodology or the addition of iodine pentoxide.