Silicon dioxide: Powder Flow Measurements of Fumed Silica
Pyrogenic silicon dioxide, also known as fumed silica, belongs to the group of silicon dioxides with the molecular formula SiO2. Fumed silica is produced via flame hydrolysis, the so-called "Aerosil® Process", during which amorphous SiO2 particles are created with particle sizes between 7 and 40 nm (primary particles) and a specific surface of 50-80 m2•g-1. However, these particles are not stable and form agglomerates whose size vary between 0.1 and 100 µm. Implementing changes in the process parameters can alter particle size, particle morphology and specific surface and, thus, allows for the manipulation of the fumed silica’s functional properties. Fumed silica is applied as filler material to improve the technical properties of other materials, e.g. to stabilize solid particles in liquid media, to intensify color depth or to enhance flowability.
We analyzed the flow behavior of two samples of fumed silica (Aerosil®) obtained from Evonik Industries AG (Essen, Germany). Sample A (Aerosil® R 974) was a hydrophobic silica which was additionally treated with dimethyldichlorosilane and had a specific surface of 150-190 m2•g-1. Sample B (Aerosil® R 106) was treated with octamethylcyclotetrasiloxane and was also a hydrophobic acid. It displayed a specific surface of 220-280 m2•g-1.
We used an Anton Paar MCR 502 equipped with a Powder Cell. The glass frit had a porosity of 10-16 µm and an ITO-coated measuring glass was used. Furthermore, we used a 2-blade stirrer as measuring geometry.
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