The effect of temperature on the properties of calcined red iron oxide pigments

Abstract

Abstract The effect of calcination temperature on the properties of red iron oxide pigments obtained from FeSO 4 , 7H 2 O by calcination at constant temperatures over the range from 700 to 900 °C, has been investigated. It was found that the particle diameter increased from 0.065 μm at 700 °C to 0.25 μm at 900 °C; the increase was gradual up to 800 °C and abrupt at 850 and 900 °C. The colour changed from red with decreasing yellowish hue between 700 and 750 °C, to red with increasing bluish hue between 750 and 900 °C; the dominant wavelength increased from 599 nm at 700 °C to 610 nm at 900 °C. The tinting strength was found to vary irregularly with temperature, and to pass through a maximum at 750 °C. The oil absorption was found to decrease with temperature and to be a linear function of the specific surface area.