Investigation On Washing Hydrated Titanium Dioxide Using Ultrasonic Irradiation

Titanium dioxide is one of important inorganic materials, which is widely used in the industries of electronics, paint, metallurgy, papermaking, chemical fiber, plastic, household and personal care chemical industry. In the process of sulfate method, the hydrated titanium dioxide, resulted from the hydrolysis of TiOSO₄, must be washed to remove the impurities before sintering.The hydrated titanium dioxide, washed with magnetic force stirring or ultrasonic irradiation, was characterized by chemical analysis, SEM, XRD, EDS and laser particle size distribution test, to discuss the effects of different wash styles on removing S and Fe, particle size distribution and crystal structure.In the washing process, it was shown that ultrasonic wash (ultrasonic cleaner or ultrasonic disintegrator) can removing impurities faster than stirring. The performance of ultrasonic disintegrator was better than cleaner. More acid was remove from the hydrated titanium dioxide solution by using ultrasonic disintegrator and the concentration of Fe in washings was reduced to 5mg/L before pH value arrived at 1.5. The mass content of Fe element among Fe, S, Ti in the product was under 0.5% by EDS analysis. After ultrasonic washing, the average particle size of the product was decreased from 1.02μm to 0.68μm of raw material and the particle size distribution (D₁₀-D₉₇) became narrow from 0.23³.18μm to 0.17¹.57μm;after stirring washing, average particle size was reduced to 0.99μm and the particle size distribution was 0.22².93μm. According to SEM photographs, the particle size of the product became smaller, particle size and morphology became more uniform and mass congregation was reduced after ultrasonic washing, the same as results obtained by laser particle size distribution.XRD patterns of samples were analyzed and the ordering degree(X) of the hydrated titanium dioxide and titanium dioxide was calculated. The calculation results showed that the X values calculated by (200) crystal face were improved, the X₂₀₀ values of the raw material, the product from stirring wash and the product fromultrasonic wash were 7.55(k 8.146 and 10.960, respectively, the strain was decreased, compared with the feed. After sintered, the ordering degrees of titanium dioxide ordering were improved much more, X200 values of sintered products after stirring wash and ultrasonic wash were 33.453 and 44.646. The results of Rietveld method showed the lattice parameters (a=0.37777nm, c=0.94966nm) of ultrasonic product were more close to the values of anatase standard(PDF21-1272); the occupancies of Ti and O were 1.0 because of ultrasonic washing and tiny effects on the bond lengths and bond angles of titanium dioxide were also induced by ultrasonic washing; the nonisotropic growth phenomenon of hydrated titanium dioxide resulted from hydrolysis process was very serious, dx/dz=0.514, after washed, the nonisotropic growth of grain was decreased and the grain was close to cubic grain. So the crystal structure and growth of hydrated titanium dioxide tend to perfection after washing.