Structure Characteristics of Hydrated Alumina Coated on Titanium Dioxide and Its Effect on Water Dispersibility of Titanium Dioxide

The alumina hydrates were obtained by hydrolysis at different pH with sodium metaaluminate as raw materials.The structure and morphology of the obtained alumina hydrates were characterized by XRD and SEM,and their hydrolysis processes were analyzed by combination with the advantage zones of various monomer aluminum ions existing in aqueous solution.Surface modification of titanium dioxide was carried out by coating sodium metaaluminate at different pH,and the water dispersibility and stability of the modified titanium dioxide were investigated.The results show that amorphous hydrated alumina is obtained at pH=4~5,which exists as aggregate structure with tens of nanometers.Boehmite hydrated alumina is precipitated at pH=6~10 with loose and flocculent morphology.Gibbsite with platy and prismlike structure is formed at pH > 10.Zeta potential on the surface of titanium dioxide varies with the pH value for coating,and the isoelectric point of the coated titanium dioxide is higher than that of the uncoated ones.In the aqueous solution of pH=10,the titanium dioxide modified at pH=4 and 5 has a poor water dispersibility and stability,while the water dispersibility and stability of the titanium dioxide coated at pH=9,10 and 10.5 are significantly improved with comparison to those of the uncoated ones.