Simulating study of atmospheric corrosion of Zn-Al alloy coating in industrial zone: Structure and properties of zinc hydroxysulfate rust particles prepared in the presence of Al(III)

In order to simulate the atmospheric corrosion of Zn-Al alloy coating on the steels in industrial zone, zinc hydroxysulfate (Zn4(OH)6(SO4)·nH2O: ZHS) rust was artificially synthesized by hydrolyzing the ZnO particles in a mixture of aqueous ZnSO4 and Al2(SO4)3 solutions and the structure and properties of the products were examined by various means. Then, the atomic ratio XAl = Al(III)/(Zn(II) + Al(III)) in the solution was ranged from 0 to 1.0. Adding Al(III) decreased the solution pH before aging to inhibit rust formation. Added Al(III) was easily incorporated in the particles than Zn(II). Increasing XAl turned the major rust following as hexagonal plate-like ZHS particles → hexagonal plate-like Zn-Al layered double hydroxide (LDH) particles → cubic Al6O5(SO4)4·H2O particles. These rust particles possessed a high adsorption affinity to corrosive CO2 gas. From these results, it can be supposed that atmospheric corrosion of Zn-Al alloy coating on the steels in industrial district produces the dense and compact rust layer composed of plate-like ZHS and/or Zn-Al-LDH particles owing to their preferred orientation to suppress further corrosion of steels.