Registration Dossier
Registration Dossier
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EC number: 273-761-1 | CAS number: 69012-64-2 Amorphous silicon dioxide particles from the volatilization and vaporization of furnace feed materials in the manufacture of ferrosilicon and silicon.
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Silica fume is composed of ultra-fine amorphous silicon dioxide particles formed during the manufacture of silicon or ferrosilicon alloys. In the process, quartz mineral is reduced to silicon, and silicon monoxide gas (SiO) is formed as a by-product. This, in contact with oxygen, oxidizes to silicon dioxide (SiO2) which condenses forming ultra-fine spherical particles referred to as silica fume. The primary component of silica fume is amorphous silicon dioxide (≥ 80 wt%). The main impurities include carbon, silicon, silicon carbide (non-fibrous) and oxides of alkaline (earth) metals. Silica fume may also contain traces of crystalline silicon dioxide in the form of quartz or cristobalite. These impurities originate mainly from carry-over of the off-gas from the production process. The concentration of quartz in silica fume is usually below 1.5 wt% (LOQ) and it has been shown to be concentrated in the coarse fraction of silica fume. In the respirable size fraction the concentration is below 0.1%. Primary silica fume particles are in the size range of 0.02 - 1.0 µm (average particle size 0.15 µm). During collection, cooling and bagging, the primary particles form larger agglomerates. The results of the dustiness tests (EN 15051) of densified and undensified silica fume products show that, of the total inhalable silica fume, the proportion of respirable particles is only 1-3 wt%. The solubility of silicon dioxide in water is low. Trace amounts can dissolve in water as monosilicic acid. The solubility depends on the pH, the temperature, the pressure and the type of silicon dioxide polymorph. When the release of silicon from silica fume in different artificial body fluids is compared to the release of silicon from pyrogenic silica (Aerosil Ox50) release from pyrogenic silica (Aerosil Ox50) is somewhat higher than from silica fume. This can be, at least partly, explained by the smaller surface area of silica fume when compared to synthetic amorphous silica. In addition to silicon ions, trace amounts of metals present as impurities are dissolved from silica fume.
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