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

Abstract

Purpose

The 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/approach

The 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.

Findings

Diaspore 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/implications

Only FeSO₄·7H₂O and FeCl₃·6H₂O as iron sources were explored.

Practical implications

The investigation results provide theoretical basis to obtain excellent chromatic waterborne aluminium pigments.

Originality/value

The 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.

Citation

Ma, Z., Wen, Y., Zhang, C. and Wang, J. (2018), "Coloured waterborne aluminium pigments prepared by iron oxides encapsulation method using FeSO₄ and FeCl₃ as iron source", Pigment & Resin Technology, Vol. 47 No. 3, pp. 216-227. https://doi.org/10.1108/PRT-08-2016-0086