Corrosion Pretreatments for Copper-Zinc Alloys

Combinations of four different types of zinc complexing agents with benzotriazole (BTA), an efficient complexant and corrosion inhibitor for copper, were tested as pretreatment inhibitors for 70/30 and 60/40 brasses in aerated 3% NaCl solutions. Alkyl dithiocarbonates, of C6 to C8 chain length, proved superior to: 2, 5-dimercaptothiadiazole (DMTDA), sodium-diethyldithiocarbamate (DDC), and sodium diethyldithiophosphate (DEDTP), in combination with BTA under a variety of test conditions. Apart from acting as an acid inhibitor for 70/30 brass exposed to acidic NaCl solutions, the DMTDA was also an effective partner inhibitor for BTA. Combinations of the other two complexing agents (DDC and DEDTP) plus BTA actually accelerated the corrosion of 70/30 brass but provided good protection of 60/40 brass in the NaCl solutions. Scanning electron micrographs showing surface topographies of test specimens with and without these inhibitor pretreatments are presented. Galvanostatic polarization curves are shown to help evaluate the inhibiting action of each inhibitor combination.