| Barium sulfate is an important inorganic chemical product,which has the advantages of high whiteness,heat resistance,corrosion resistance,chemical stability and low price.Therefore,it is widely used in coating,plastic,rubber,paper,ink and pigment industries.However,there are still some problems in the quality and performance of the products prepared at present: on the one hand,the surface of barium sulfate has high surface energy,and adjacent particles are easy to agglomerate or cake;on the other hand,the surface of barium sulfate has the hydrophilic and oleophobic property,which leads to the poor affinity and compatibility with non-polar or weak polar organic polymers,to separation from the polymer in the application and production,and to remarkable decrease of the mechanical properties of the compound.Therefore,in the preparation process,they are still the focus of current research to make the particles disperse and disagglomerate,and to change their surface properties.The morphology and structure of the product also have a great impact on its performance.The suitable reaction conditions for the preparation of ultrafine barium sulfate from cheap and easily available barium chloride and sodium sulfate with chemical precipitation method were determined by experiments.The amount of polyethylene glycol 1000 was1.2wt%,the temperature was 60°C,the reaction time was 30 min,the dropping speed was40 d/min,and the agitating speed was 300 r/min.Barium sulfate particles with an average diameter of 360.27 nm were obtained.Then the suitable reaction conditions for adding EDTA were determined.The dosage of EDTA was 11.0wt%,the concentration of reactant was 0.4mol/L,the reaction temperature was 45°C,the reaction time was 30 min,the agitating speed was 250 r/min,p H=9.The spherical barium sulfate with an average particle size of 145.14 nm was obtained,which was smaller than that of the product with adding dispersant and had a narrow particle size distribution.The control mechanism of dispersant and crystal control agent to ultrafine barium sulfate was also studied.Sodium stearate was used to modify the superfine barium sulfate in situ,and the suitable technological conditions were determined.The dosage of sodium stearate was0.8wt%,the reaction temperature was 80°C,the reaction time was 45 min,the concentration of reactant was 0.4 mol/L,and the agitating speed was 300 r/min.The spherical barium sulfate with an average particle size of 390.5 nm was obtained.The settling volume of the modified product is 7.0 m L/g,which is larger than that of the unmodified product,indicating that the product has good dispersion and hydrophobic and lipophilic surface.Finally,the modification mechanism of surface modifier was analyzed.The surface of ultrafine barium sulfate prepared from barium carbonate and concentrated sulfuric acid was modified by silane coupling agent.The appropriate reaction conditions were determined.The modifier was silane coupling agent A174,the amount of modifier was 2% of the mass of ultrafine barium sulfate,the reaction time was 1 h,the reaction temperature was 80°C,and the stirring speed was 400 r/min.The ultrafine barium sulfate powder with an average particle size of 342 nm and a particle size distribution of295.3～458.7 nm was obtained.The activity degree of the modified product is 82.83%,and its surface is coated by modifier,the amount of coating is 1.14%,which shows that the product has good dispersion,hydrophobic and lipophilic surface.In addition,the hydrolysis conditions of silane A174 and mixed solvent were determined by measuring the conductivity.Finally,the modification mechanism of silane coupling agent was analyzed. |
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