Preparation and characterisation of silicon dioxide obtained via emulsion method
Purpose ? Proposes to investigate preparation of amorphous silica via precipitation reaction from aqueous solution of sodium metasilicate and hydrochloric acid in emulsion medium, focusing on determination to optimise the dispersive and morphological properties of silicas studied. Design/methodology/approach ? The silicas obtained were analysed using modern research techniques, such as scanning electron microscopy for studies on particle surface morphology and dynamic light scattering technique for studies on particle structure and their tendency for agglomeration. Moreover, the sedimentation characteristics of the silica powders were evaluated. Findings ? The properties of silicas precipitated from emulsion systems depend on several variables but the amount and concentration of the applied reagents and pH of the emulsion are of critical importance. Using 16, 14 or 12?wt% solution of sodium metasilicate (per SiO
2 content) and 5.0, 4.3 or 3.7?wt% solution of hydrochloric acid, the particles obtained were of best dispersive parameters. Mean diameter, polydispersity, shape and sedimentation of particles reflect the applied preparation procedure. Several of the silicas obtained manifest tendency for formation of secondary agglomerates and aggregates. The pH of the solution obtained from two mixed emulsions exerts a pronounced influence on quality and properties of the prepared silica. The best silica is obtained at pH 6-7. In the cases where the emulsion has been dosed with ?pure? sodium metasilicate solution, particles of irregular shape of high mean particle diameters, with a tendency to form large particle accumulations, have been formed. Research limitations/implications ? In the precipitation reaction, aqueous solution of sodium metasilicate, hydrochloric acid and emulsifiers in the form of non-ionic surfactants were used as substrates. The organic phase involved cyclohexane. Alternatives could be explored. Practical implications ? The method developed provides a novel and practical solution to precipitation of hydrophilic/hydrophobic silica fillers. Originality/value ? The method for obtaining amorphous types of silica could find numerous applications, particularly as polymer fillers.
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