IMPROVED PERFORMANCE OF PHOSPHORIC-ACID ANTICORROSIVE PRETREATMENTS WHEN ALUMINUM HYDROXIDE IS ADDED

This work presents the main results of an experimental study carried o ut with rust pretreatments based on phosphoric acid solutions with the addition of aluminium hydroxide. Because the transformation of rust s teel surfaces by phosphoric acid solutions depends strongly on the int erfacial conditions, the first step in this work was the clear definit ion of rust formation conditions and of a reproducible technique for b rushing them to a known degree as defined in standard SIS 055900. Afte r that, the best range of acid concentration was optimised in the case of phosphoric acid solutions and phosphoric acid solutions saturated with aluminium hydroxide. Several characterisation techniques were use d, such as scanning electron microscopy (SEM), energy dispersive spect rometry (EDS), infrared spectrometry (FTIR) and Xray diffraction (XRD) , to interpret the phenomenon of rust transformation. The results obta ined lead to the conclusion that the best anti-corrosive behaviour of phosphoric acid solutions is obtained when they are saturated with alu minium hydroxide.