Corrosion Products Formed on Confined Hot-Dip Galvanized Steel in Accelerated Cyclic Corrosion Tests

Different cyclic accelerated corrosion tests have been performed on perforation coupons made of hot-dip galvanized steel (e.g.. in confined configuration). Two designs of experiments (DOE) made of nine accelerated tests each were used to study the influence of a selection of important climatic parameters such as the concentration of sodium chloride (NaCl. 1 wt.% and 0.5 wt.%), the drying level (45% and 70% relative humidity [RH]). the basic humidity cycle (12 h and 24 h), the frequency of salt spray (two and seven times per week). and the temperature (35 degrees C and 45 degrees C). The nature of the corrosion products collected from the perforation coupons has been determined using Fourier transform infrared spectroscopy (FTIR). Vie three main phases formed after exposure to different corrosion tests were Zn-5(OH)(8)Cl-2 center dot H2O (simonkolleite). Zn-5(OH)(6)(CO3)(2) (hydrozincite). and ZnO (zincite). A statistical analysis of the results has shown that large amounts of zinc oxide were correlated to parameters that increased the corrosion rate of hot-dip galvanized steel such as the frequency of salt spray resulting in the formation of red rust. A possible mechanism is discussed. From the results, it is also obvious that: the amount of ZnO may be a valuable tracer of the severity of the test: for confined hot-dip galvanized steel.