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Table 1 Overview of silica materials and relevant properties

From: The nanosilica hazard: another variable entity

Material Nature of product Crystallinity Particle size Porosity Polarity Purity Applications Ref
Colloidal silica Sol Amorphous 1-1000 nm Dense Hydrophillic Very high Binders, ink [15]
Stober silica Sol Amorphous 10-1000 nm Tunable porosity Hydrophillic Very high Research [16]
Precipitated silica Powder Amorphous 5-6 nm primary particles precipitated to 500 nm - 50 μm aggregates Tunable porosity Hydrophillic Very high Filler
and performance additive
Silica gel Powder Amorphous 0.5 - 5 nm primary particles gelled to networks and milled to 500 μm - 6 mm aggregates Tunable, void spaces between primary particles Hydrophillic Very high Dessicant, filler
and performance additive
Mesoporous silica Powder Amorphous 50 - 1000 nm, aggregated because of calcinations Mesoporous Hydrophobic Very high Drug delivery, catalysis, imaging [8]
Pyrogenic silica (fumed silica) Powder Amorphous 2-50 nm primary particles fused to 1-250 μm aggregates Void spaces between primary particles Hydrophobic Very high Tickner, performance additive [15]
Vitreous silica (fused silica glass) Powder Amorphous 50-2000 μm Dense Hydrophobic (grinded: hydrophilic) Variable Glass [15, 19]
Quartz Powder Crystalline 50 nm- several μm Dense Hydrophobic/(grinded: hydrophilic) Variable Geologic mineral, Piezoelectricity [19, 20]
Cristobalite Powder Crystalline 1 μm - several cm Dense Hydrophobic Variable Geologic mineral [20]
Zeosils (porosil) Powder Crystalline 0.05-5000 μm Porous
Pore diameter: 0.4-1.2 nm
Hydrophillic/hydrophobic Very high Adsorbent [25]
Clathrasils (porosil) Powder Crystalline 0.5-5000 μm Porous
Pore diameter: 0.2-0.3 nm
Hydrophillic/hydrophobic Very high Gas separation [24]
Diatomeus earth, kieselguhr Powder Amorphous, partially crystalline 5-120 μm Dense Hydrophillic/hydrophobic Low (90%) Filter, filling material [15]