Coloured waterborne aluminium pigments prepared by iron oxides encapsulation method using FeSO4 and FeCl3 as iron source

Abstract

PurposeThe purpose of this study is to evaluate the role of encapsulation pH and iron source on the anchorage mode and performance of iron oxide-encapsulated aluminium pigments.Design/methodology/approachThe coloured waterborne aluminium pigments were prepared at pH 5-7.5 by using FeSO4 and FeCl3 as iron source. The anchorage mode of iron oxides on aluminium was characterized using optical microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction. Furthermore, the pigmentary performance was characterized through anticorrosion test and multi-angle spectroscopy.FindingsDiaspore and boehmite could form from H2O2 oxidizing aluminium. Both low pH and FeSO4 systems are beneficial for diaspore, inducing green rust anchor on the aluminium to form goethite. Either in FeSO4 or FeCl3 system, slightly high pH is beneficial for the formation of boehmite, which occurred together with ferrihydrite to form denser coating with yellowness and excellent anticorrosion property. At pH above 7, the formation of dendritic iron oxide is detrimental to the anticorrosion property and the glossiness.Research limitations/implicationsOnly FeSO4·7H2O and FeCl3·6H2O as iron sources were explored.Practical implicationsThe investigation results provide theoretical basis to obtain excellent chromatic waterborne aluminium pigments.Originality/valueThe method for investigation of encapsulation mechanism by surveying the structure of iron oxides on aluminium, which varies with the pH of the system and iron sources, is novel.