Influence of calcination temperature on the morphology, structure, and spectral performance of chromium oxide

Cr(OH)3 was synthesized by a hydrothermal method using Na2Cr2O7 as precursor and starch as reducing agent. The resulting Cr(OH)3 was then calcined at different temperatures to produce Cr2O3 pigments. X-ray diffraction (XRD), X-ray photoelectron Spectrometer (XPS), UV-Vis-NIR spectroscopy, scanning electron microscopy (SEM) and automated whiteness measurement (AWM) were used to characterize the crystalline phase, reflectivity, morphology and color of Cr2O3. At temperatures below 1000 degrees C, Cr2O3 was identified as the dominant phase during calcination. The results showed that when the calcination temperature was <1000 degrees C, the phase was identified as Cr2O3 . When the calcination temperature was <1000 degrees C, some oxygen atoms (O) escaped from the Cr2O3 crystal structure to from Cr2O2.4, and a shift of the Cr2O3 diffraction peak to a higher angle was observed. XPS analysis revealed that the valence state of O in the samples subjected to calcination at both 700 degrees C and 1200 degrees C remained unchanged. However, the sample treated at 1200 degrees C displayed a distinct CrOx (X < 1.5) peak at 575.25 eV, indicating a lower oxidation state of Cr. Morphologically, a conversion from particle-shaped Cr2O3 to larger plate-like Cr2O2.4 structures was observed, with Cr2O3 being concentrated on the Cr2O2.4. The uneven distribution of crystal particles in chromium oxide samples led to an increase in reflectance and a decrease in brightness as a result of the presence of Cr2O3 and Cr2O2.4 with distinct structural forms.