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 ⁴A_2g→⁴T_1g and ⁴A_2g→²T_2g 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.