Study On The Preparation Of Titanium Dioxide Compound Pigments Based On Kaolin Substrates

Titanium dioxide is one of white pigments which extensively used in industry and had optimum function at present. It widely applied in coating material , papermaking , plastic, rubber, cosmetics. As the world industry develops swiftly and fast in recent years, the demands of titanium dioxide are increased by astonishing speed, which causes the price rise unceasingly. In this case, the main user of titanium oxide was forced to exploit the substitute item to reduces the cost. In the homeland, the upscale rutile titanium oxide mainly relies on the import due to the restriction of technology. Though the research of titanium dioxide substitution has gotten certain achievements, it remains at the initial stage. The main problem was the low whiteness, the high oil absorption, and the low hiding power.In this article, we used kaolin with big reserves and low price as substrates. We adopt the method of sol-gel and mechanochemistry individually, and prepare kaolin-titanium dioxide compound pigments successfully. Through single factor experiment, the technological conditions of preparing kaolin-titanium dioxide compound pigments had been ascertained with the method of sol-gel: the dosage of tetra-n-butyl titanate-6mL, the consumption of Su Zhou 1^# calcined kaolin-20g, the pulp concentration-11%, the hydrolysis temperature - 40℃, the aging time-16H, the calcination temperature-800℃, the calcination time-3H,the dosage of rutile accelerator Zn(NO₃)₂-0.2%. The test result indicated the whiteness of the production which prepared with the method of sol-gel could be heighten from 90.0% to 94.0%, the oil absorption could be reduced from 56.0mL/100g to 35.5mL/100g, 325 mesh residue less than or equal to 0.20%, volatile at 105℃less than or equal to 0.3%. X-ray diffraction spectrograms display that the titanium oxide crystals are translated into rutile from anatase after adding rutile accelerator Zn(NO₃)₂. This was ascribed to the heterovalent isomorphic replacement. Transmission electron microscope results indicate that the surfaces of the kaolin are coated with a layer of compact and even nanoparticles of titanium oxide, which could be considered as a membranous layer structure. The pH values of the pulp have obvious influences to the effect of titanium oxide coating.The process conditions of preparing kaolin-titanium dioxide compound pigments had been ascertained with the method of mechanochemistry: the mass ratio of titanium oxide and kaolin- 6 ? 10, the grinding rotation-700r/min, the grinding time -50m.The calcined kaolin with high surface activity should be used as proper stuff. Through the test, the whiteness of the production with the method of mechanochemistry could be heighten from 90.0% to 92.5%, the oil absorption could be reduced from 54.0mL/100g to 23.0mL/100g, 325 mesh residue less than or equal to 0.10%. Scanning electron microscope results indicate that the regular particle shapes of processed kaolin have changed to more round with the method of mechanochemistry.Experiment results indicated that the method of mechanochemistry could reduce the oil absorption of compound pigments obviously, but improve the whiteness difficultly. The whiteness of the pigments processed with the method of sol-gel is higher than that with the method of mechanochemistry. The results also indicated that the main factor affecting oil absorption of kaolin-titanium dioxide compound pigments could be: the quality of basic materials,the coating condition,the particle shapes.