A SVET investigation on the modification of zinc dust reactivity

Weldable primers are thin zinc-rich organic coatings that are weldable due to the electrical conductivity provided by the zinc dust. They are used in the automotive industry to provide corrosion protection in regions of difficult access. The zinc particles are highly susceptible to corrosion attack and, due to the small thickness, the protection conferred by these systems is limited.In this work, corrosion inhibitors, two inorganic (cerium and lanthanum nitrates) and two of organic nature (benzotriazole and 2-mercaptobenzothiazole), were tested in order to reduce the reactivity of zinc dust. The samples used were of three kinds: a commercial weldable primer, pure zinc metal sheet and zinc dust. The corrosion testing was done in 0.05 M NaCl using the scanning vibrating electrode technique (SVET) that showed to meet well the purposes of the work. According to the results, all tested inhibitors can be used to reduce the corrosion of zinc and to increase the service life of weldable primers. The organic inhibitors were the best in retarding the degradation of the weldable primer during immersion in 0.05 M NaCl. Conversely, the corrosion inhibition of zinc dust was successful only with the inorganic inhibitors, principally cerium nitrate.