Effect of the chemical modification of the precursor of ZrO2 films on the adhesion of organic coatings

ZrO2 films were deposited on low carbon steel by a sol-gel process as a che mical pretreatment before the application of a polyester paint. The films w ere obtained by a dip-coating technique using solutions of Zr(OBun)(4) cont aining complexing agents (acetylacetone or acetic acid). These additives mo dified the alkoxide at the molecular level, so a new precursor was formed i n solution. This new compound shows slower rates of hydrolysis and condensa tion than Zr(OBun)(4), which allows the stability of solutions and the morp hology of the gel to be controlled. Moreover, the length and the temperatur e of the thermal treatment influence the structure of the gel by reducing t he amount of organic residues. The behavior of the films in promoting the a dhesion of organic coatings was evaluated by measuring the detachment of th e paint from a cross-scratch of samples which had been exposed for differen t times in a salt fog chamber. Tests using electrochemical impedance spectr oscopy were also carried out. According to the results, most of the samples pretreated with zirconia layers showed a good performance, even better tha n commercial chemical treatments, when acetic acid was used as a modifier o f the alkoxide precursors.