Synthesis and characterisation of iron oxides: Effect of calcination temperature and their application as inorganic pigment

Abstract

This research aimed to investigate the effect of calcination temperature on the phase, morphological and optical properties of iron oxides: hematite (α-Fe₂O₃), magnetite (Fe₃O₄) and goethite (α-FeOOH), synthesised by co-precipitation, aiming at their applications as pigments. The sample was characterised by thermogravimetric (TG) analysis, X-ray diffractometry (XRD), scanning electron microscopy (SEM) and static light scattering (SLS) for structural analyses; colorimetry and ultraviolet–visible absorption spectroscopy to analyse optical properties. The TG and XRD analysis show that above 600°C, magnetite and goethite samples were transformed into hematite, showing excellent thermal stability. The magnetite showed smaller and more homogeneous particle sizes, as observed in SLS and SEM analysis. Colorimetric analyses revealed evident changes in colour and brightness, especially for goethite, which exhibited the highest total colour variation (60.1) at 800°C compared with the samples not calcinated. Furthermore, the tests highlighted that materials obtained through goethite synthesis are more promising as industrial pigments.