Characterization of blue CoAl ₂O ₄ nano-pigment synthesized by ultrasonic hydrothermal method

Nano-sized CoAl ₂O ₄ pigments, which have received significant attention as a coloring agent in glaze and bulk tile compositions, were successfully synthesized by substituting mechanical stirring during hydrothermal process with ultrasonic irradiation. Difference in physicochemical and optical properties of the CoAl ₂O ₄ pigments prepared by an ultrasonic-assisted-hydrothermal method was characterized using simultaneous thermo-gravimetric and differential thermal analysis (TG-DTA), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), diffuse reflectance spectroscopy, CIELAB colorimetric analysis, and testing in ceramic glazes and bodies. The ultrasonic-assisted CoAl ₂O ₄ pigments present a narrow particle size distribution with vivid blue color, and better thermal stability, allowing their use for ceramic inks processed at high temperature. Application of ultrasonic irradiation during the hydrothermal process produces nano-sized powders with better physicochemical and optical properties.