Colour performance investigation of a Cr2O3 green pigment prepared via the thermal decomposition of CrOOH

In this study, Cr2O3 green pigments were prepared using two types of CrOOH, α-CrOOH and γ-CrOOH, and the resulting pigments were characterised. The thermal decomposition behaviours of the two types of synthesised CrOOH were discussed. The resulting Cr2O3 pigments were characterised using X-ray diffraction (XRD), scanning electron microscope (SEM), International Commission on Illumination (CIE-L⁎a⁎b⁎) and ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS). The key factors and mechanism that influenced the preparation of the Cr2O3 green pigments were studied. The results revealed that γ-CrOOH produces Cr2O3 that is more homogeneous, has a uniform size of 200–400 nm and a yellowish-green colour compared to α-CrOOH, which produces Cr2O3 with non-uniform sizes and a brownish-green colour. In addition to the different particle morphologies and sizes, the change in the crystal field, which leads to a shift in the 4A2g→4T1g and 4A2g→2T2g transition, also affects the colour of the pigment. Lastly, a series of Cr2O3 green pigments displaying a wide range of colours were prepared by calcining mixtures of α-CrOOH and γ-CrOOH with different compositions.