Control The Morphology And Size Distribution Of Precipitated Barium Sulfate

The addition of barium sulfate in polymers can result in materials possessing higher stiffness, strength, and corrosion resistance when compared with that of conventional filled polymer composites. However, can the particles achieve a stable dispersion in the polymer remains a key problem. Small particles can easily agglomerate into larger particles because of the high surface activity and high surface energy during the preparation process. The strong polarity of BaSO₄ surface and the weak particle-polymer affinity lead to the phase separation of composites and deterioration of the polymer properties. Thus, controlling the particle size and modifying surface of BaSO₄ particles during the preparation process are current hot topics in the field of solid state materials.Submicron BaSO₄ particles were synthesized in the presence of D5040 at 30℃, by the precipitation method, using Ba（OH）2 as reactants. Using H2SO₄ as precipitant, when the weight ratio of D5040 to BaSO₄ particles was 1.0wt.%, the as-synthesized BaSO₄ particles were spheres with an average diameter of 0.5μm. And the action mechanism of D5040 was discussed further. The double electrical layer model of the solid-solution interface at a particle of BaSO₄ was presented. Using（NH₄）2SO₄ as precipitant, when adding 0.4% D5040, the average size of BaSO₄ was 0.45μm. Keeping the BaSO₄ in ethanol, the PSD and mean particle size of the sample showed little change when the preservation time was prolonged to 7 days.Well-dispersed BaSO₄ particles were synthesized in the presence of D5040 with BaCl₂ and（NH₄）2SO₄ as reactants. When the weight ratio of D5040 to BaSO₄ was 1.2wt.%, the as-prepared BaSO₄ particles were spheres at pH=9.5 and the PSD arranges from 0.25μm to 0.85μm and mean size is 0.53μm. When adding EDTA in the preparation of BaSO₄, spherical BaSO₄ aggregates with an average size of 0.5 μm were synthesized at pH=7. The as-synthesized BaSO₄ particles were comprised many interconnected nanoballs, of which the surface properties were affected by the EDTA anions. The adsorption of EDTA anions reversed the charge and weakened the surface polarity of BaSO₄, instigating the formation of aggregates by a self-assembly and transformation process. The resulting Ba SO₄ particles formed at pH 9–10 were ellipsoidal and featured smooth surfaces. Based on the zeta potential of BaSO₄, variations in the morphology induced by changes in pH were closely related to the adsorption of mono- and multivalent anions onto the electrical double layer of BaSO₄.Hydrophobic barium sulfate was fabricated by the direction of cocoate anions. At 30℃, when the weight ratio of sodium cocoate to BaSO₄ particles was 2.0wt.%, the active ratio of the product reached 99.43% and the contact angle was greater than 120°. This method could not only simplify the complex modification process, but reduce energy consumption. The as-synthesized BaSO₄ particles were ellipsoidal and that their surfaces were affected by cocoate anions. The adsorption of cocoate anions induced a change of the BaSO₄ particles surface from hydrophilic to hydrophobic. Due to the roughened structure and the surface hydrophobicity, when adding the hydrophobic BaSO₄ into PVC, the mechanical properties of PVC composite materials were significantly improved.