Synthesis and characterization of iron oxides and their application as inorganic pigments in white paint

Abstract

The tones of iron oxide pigments range from yellow, red, brown and green to black. Iron oxide pigments are non-toxic and have a nanometric particle size, which makes them ideal for use as pigments. The current study synthesised synthetic inorganic pigments based on iron oxides using the alkaline precipitation method. This approach to the synthesis of iron oxide pigments makes them less expensive for obtaining reproducible colours. Iron salts (iron (III) chloride, iron (III) nitrate, iron (II) sulphate [ferrous sulphate] and iron (III) sulphate) have been combined with alkaline solutions (sodium hydroxide, potassium hydroxide and ammonium hydroxide) to form coloured iron oxides, which are widely known as natural inorganic pigments. The 12 samples produced in four different colours (red, yellow, brown and black) were left in aqueous suspension and dispersed in commercial real white estate paint, to evaluate their behaviour as pigments. Structural characterisation (X-ray diffractometry), composition (X-ray fluorescence by dispersive energy), thermal analysis (i.e. thermogravimetric analysis and the differential thermal analysis) and spectroscopy (FTIR and photoacoustic), as well as colorimetry, were performed. The phases indexed by X-ray diffractometry were goethite, haematite, magnetite and lepidocrocite. The inorganic pigments produced are compatible with natural inorganic pigments. They also showed dispersion compatibility in commercial white paint without changing the surface coating powder and are therefore an alternative to synthetic inorganic pigments.