Preparation And Characterization Of TiO₂on The Surface Of Barite Composite Particles By Hydrolyzing-Precipitation Method

Barite is a kind of important industrial mineral raw material with extensive application in various fields including paints, coatings, oil drilling, et al. Barite with the character of chemical stability, low in oil absorption value and similar density to TiO2is suitable to be core material to prepare barite/TiO2composite which has the property of both barite and TiO2. The technology of titanyl sulfate (TiOSO4) hydrolysis precipitation coating on the surface of barite was researched, the structure and property of the composite particle were characterized and the mechanism during the preparation process was studied in this thesis.The effect of granularity of barite under different grinding time on the structure and property of barite/TiO2composite particles was studied. When the grinding time was60min, the prepared composite powder had better coating film. The optimal conditions of TiOSO4hydrolysis and precipitation coating on the surface of barite were as follows:reaction temperature85℃, reaction time3h, TiOSO4dosage2.0g/g, slurry concentration of barite in hydrolysis precipitation system0.5%. The technology to make the crystal type of TiO2conversed during the calcination of barite-TiO2H2O complex and to prepare barite/TiO2composite particles was studied and the optimal calcination conditions were as follows:calcination temperature800℃, calcination time1h, without adding any crystal type conversion agent. The hydrolysis precipitation product barite-TiO2H2O had a high conversion rate to rutile TiO2, reaching90.92%. The oil absorption value and hiding power value of barite/TiO2composite powder were19.10g/100g and13.64g/m2, respectively.The micromorphology and performance of barite/TiO2composite were characterized and evaluated. The surface of barite was coated with TiO2particles uniformly, compactly and firmly in barite/TiO2composite particles. The pigment properties of barite/TiO2was similar to TiO2. When added into construction coating, the coating contrast ratio was86.4%was similar to the coating with the same quality of rutile TiO2(about90%) and higher than anatase TiO2(about82%). Otherwise, barite/TiO2had a strong absorption function to ultraviolet with wavenumber of200nm to400nm.The results of infrared (IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) indicated that it was hydroxyl adsorption or hydrogen bonding action that combined barite and TiO2H2O together in barite-TiO2H2O complex. After calcination, a large number of adsorbed water prolapsed, the hydroxyls which belonged to barite and TiO2H2O condensated, and then a new chemical bond Ba-O-Ti or S-O-Ti bond might be formed. Combining the above analysis, the adsorption schematic diagram of TiO2on the surface of barite could be inferred and the combined form between them could be established. The research showed that the induction mechanism of barite matrix in the process of crystal transformation of TiO2H2O might be that the formation of Ba-O-Ti or S-O-Ti bond played a catalytic role in the transformation of rutile TiO2and this action was stronger than the inhibition action of SO42-, thus the transition temperature of rutile TiO2was decreased.