Characterization and treatment effects on Mutaka kaolin for additive in coatings: Mineral composition, thermal and...

Previous studies in Uganda have primarily explored kaolin's applications in composites, pottery, bricks, and insulation, neglecting its potential for coatings and paints, which is crucial for industrialization and saving foreign exchange. This study investigates the transformation of kaolin through various treatments and analyzes their impacts on its physical and chemical properties for potential use in coating applications. Thermal analysis, X-ray Fluorescence Spectroscopy (XRF), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), and transmission electron microscopy (TEM) techniques were employed to assess these alterations. The results show that thermal treatment of kaolin at 45.9 °C had minimal impact on mass loss, while the crystallinity of kaolinite was found to be lost around 600 °C, resulting in structural changes. XRF result demonstrates variations in SiO₂ and Al₂O₃ composition, with low TiO₂ content desirable for paint and coating applications. XRD results showed well-defined diffractions associated with kaolinite in all treated and untreated kaolin samples. The presence of K-feldspar and quartz are also identified. However, the thermal treatment at 800 °C transforms kaolinite into metakaolin, essential for enhancing coating properties. SEM-EDS results indicate increased porosity and reduced impurities in the thermal-treated sample, which might enhance the whiteness and suitability of pigment and binder dispersion in coatings. TEM images confirmed the hexagonal nature of kaolinite platelets and demonstrated the amorphous nature of kaolin nanoparticles with ammonium molybdate treatment, which led to the delamination and exfoliation of kaolinite layers, improving dispersibility. Kaolin thermally treated exhibited good crystallinity, solid growth, cubic morphology, and uniform size distribution. These findings suggest that tailored treatments can optimize kaolin's properties, making it a promising additive for high-performance coatings.