Study On Preparation Of Ultra-fine BaCO₃ Powder By Microwave Homogeneous Precipitation

As a very important barium salt, barium carbonate (BaCO3) is a fundamental chemical industry material widely used in other barium salts, CRT, magnetic ferrites and/or ferroelectric materials, pigment, optical glass, ceramic, electric condensers, metallurgy and chemical industry. With the rapid development of science and technology, it makes increasing requirement for the quality of BaCO3, while the common barium carbonate can't meet these requirments. Duo to its high permeability, low loss and saturation magnetization, ultra-fine barium carbonate has a broad application prospect. And the study of preparation of ultra-fine barium carbonate has become a research hot.Combined with the superiorities of the MW (mircowave) heating and homogeneous precipitation method, the thesis put forward using microwave homogeneous precipitation method to prepare ultra-fine barium carbonate powders. Bariumchloride dihydrate (BaCl2·2H2O) and sodium hydroxide (NaOH) were used as raw materials, and carbamide ((NH2)2CO) was used as precipitation agent. Preparation of ultra-fine barium carbonate powder by conventional and microwave homogeneous prepitation were studied, respectively. The influences of Ba2+concentration, molar ratio of reactants, inculding and NaOH, reaction temperature and time on particle size and productivity were investigated. BaCO3 particles were synthetized by microwave homogeneous prepitation with the help of different additives. Meanwhile, the kinetics of conventional and microwave homogeneous prepitation reactions were studied, and kinetic parameters were obtained. And the BaCO3 particles prepared under the best conditions were analyzed and characterized by XRD, SEM, laser particle size analyzed instrument, differential thermal analysis/thermogravimetric analysis and BET surface area test.The results showed that the best experiment conditions by microwave homogeneous prepitation were that tempreture was 85℃, time was 2h, the concentration of Ba2+ was 0.8 mol/L, n (NaOH)=2.5n (BaCl2-2H2O), n((NH2)2CO:n<BaCl2·2H2O)=6. And the BaCO3 particles have uniform size distribution, with the average size of 1.61μm and surface area of 16.88 m2/g. BaCO3 nanoparticles with different morphologies including needle-like, rod-like, bird's nest-like and flower-like have been successfully synthesized by the microwave homogeneous precipitation method with the help of different additives, such as citric acid (CA), sodium triphosphate (STPP) and ethylene diamine tetraacetic acid (EDTA). The apparent activated energies of conventional and microwave homogeneous prepitation were about 98.38 KJ/mol and 88.40 KJ/mol, respectively.The thesis has proved that microwave homogeneous precipitation is a new method to prepare nanoparticles, which combines the advantages of microwave heating and homogeneous precipitation, with many advantages, including higher temperature rising rate, high reaction rate, good product quality, etc.. And the advantages of the new technology of using microwave homogeneous precipitation to prepare ultra-fine barium carbonate powders are so obvious and tremendous, such as simple process, low cost, high efficency and high quality of products, etc., which will have a significant effect on energy saving, efficency and the product value once applied in the traditional barium carbonate production industry.