Study On Preparation Of Nano-calcium Carbonate And Its Rheology

Controllable preparation of nano-functionalized inorganic materials with specific morphologies and size distribution has become an attractive and challenging research project in material field. So far, among all the nano-powder materials, nano-calcium carbonate is the only one which can be produced in large scale, and are widely used in the functional filler field, such as rubber, plastics, sealants, coatings, ink etc. Thus, nano-calcium carbonate with regular morphology and good dispersive property have superior performance in the application process.In this paper, nano-calcium carbonate with regular morphology, good dispersive property and size controlled was prepared by carbonation-aging method. During the preparation process, the crystal shape modifier-NaHCO3was introduced when the carbonation reaction proceed to a certain extent. Factors affecting the morphology of the calcium carbonate particles, the physical and chemical changes of the system and the mechanism of the crystal shape modifier during the aging process were studied. And the sol-gel transition during the aging and the effects of particle properties on the rheology of the slurry suspension were also investigated. Conclusions were as follows:When carbonation rate was96%,4%NaHCO3was added and aged16h at60℃, then cubic nano-calcium carbonate ranged from100～110nm with regular morphology, good dispersion of particle size distribution range can be obtained. NaHCO3prompted the Ca(OH)2in linear intermediate to tansfer into CaCO3, and separated into a plurality of different diameter of calcium carbonate particles, leading to Ostwald ripening of particles and the surface rearranging etc. With the increase in the addition amount of crystalline modifying agent, the increase in temperature and the extension of the aging time, the particles became more regular and the particles’size also increased. When it exceeded a certain value, the particle size reached the limit and would no longer increased. Elevated aging temperature can accelerate the aging process, but an overhigh temperature transformed calcium carbonate morphology from cubic into flake.Along with aging process, transition from the sol to the gel state occured. When (NaPO3)6, SDBS, and polycarboxylate were added into the system, the system viscosity were reduced, and powder dispersibility were better. Added2%(NaPO3)6at the sol stage of aging, it could inhibit the generation of the gel phenomenon, and produce calcium carbonate particles with regular morphology and good dispersibility.The performance of nano-calcium carbonate has a great impact on the rheological behavior of the suspension. With the increase of the amount of coating agent, the thixotropy gradually increased. When the amount of coating agent exceeded3%, the thixotropy was negative and the absolute value of the thixotropy increased with the coating agent amounts. Yield stress increased initially and then decreased with the increase of coating agent, it reached the maximum at2.5%. When the average diameter increased, the size distribution narrowed and the tacticity higher of nanometer cubic calcium carbonate, the thixotropy and yield stress of the suspension were enhanced.