Abstract
We clarified the controlling factors of the particle size of the amorphous silica synthesized by wet and dry processes. In the wet process using methyl-trimethoxy-silane as a starting monomer, the obtained particle size can be easily controlled by changing the reaction time appropriately. However, to obtain larger particles, a relatively long time is needed. After the condensation reaction was conducted for 50h, the silica particles (D50: 3μm) were synthesized by calcination at 550oC in air. To synthesize larger silica particles, we used silica-seed particles (8μm) to obtain very large spherical silica particles (D50: 20μm). Thus, although the wet process needs a relatively long reaction time, it is very useful for synthesizing spherical silica particles with a wide range of particle size. In the dry process, we used methyl-trimethoxy-silane (MTMS), tetra-ethoxy-silane (TEOS), and octamethyl-cyclotetrasiloxane (OMCTSO) as the starting materials. In this process, the size of the silica particles was dominated by the molecular structure of the monomer, in particular, the number of silicon atoms contained in the monomer and the bulkiness of the substituent group. The largest silica particles were synthesized from OMCTSO, which contains the largest number of silicon atoms.
Highlights
Amorphous silica particles have been widely used in many applications including paints, plastic compounds, and so on
We describe the important determining factors of the particle size of spherical silica particles synthesized by wet and dry processes
Remarkable growth of the particle size can be observed during the condensation reaction carried out for 50 h. This result shows that the obtained particle size can be controlled by changing the reaction time, a relatively long time is needed to produce larger particle sizes
Summary
Amorphous silica particles have been widely used in many applications including paints, plastic compounds, and so on. The production processes of amorphous silica are classified into wet (alkoxide-derived silica, sodium silicate-derived silica) and dry (fumed silica) processes [1]-[5]. Of these processes, the wet process can strictly control the particle-size with a regular morphology and a narrow size distribution, a relatively long manufacturing time is required; the wet process is not suitable for industrial mass production. The dry process is a simple and instantaneous reaction that leads to better mass production, though control of the frame temperature and factory design are relatively difficult [6], [7].
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