Process optimization, phase transition kinetics fitting, and correlation between structure, morphology, and hue of iron oxide red pigment produced without ammonia nitrogen

Abstract

The core aspect of the ammonia-free iron oxide red production process is the meticulous regulation of the FeOOH to α-Fe₂O₃ phase transition. The kinetic properties, structural evolution, and the correlation between morphology and hue of this link play a decisive role in the scale-up and optimization of the process. α-Fe₂O₃ was prepared using FeSO₄-7H₂O and NaOH under ammonia-free conditions. The kinetics of crystalline transformation and the correlation between sample morphology and hue were thoroughly investigated by optimizing the preparation conditions, kinetic fitting, and structural characterization. A method for real-time determination of FeOOH and α-Fe₂O₃ during the conversion process has been established based on X-ray diffraction. Moreover, it has been demonstrated that the hue phases of α-Fe₂O₃ are closely related to their chemical compositions and morphologies. This has been achieved through the scanning electron microscope, spectrophotometric chromatography, and other techniques. Furthermore, variations in reaction rates can result in discrepancies between the structural, morphological, and hue parameters of iron oxide red pigments and the anticipated standards. By regulating pivotal parameters throughout the phase transition process, including the concentration of Fe²⁺, the dispersion's pH, and the reaction's duration, it is possible to guarantee that the morphology and hue parameters of iron oxide red align with the specific application requirements.