Fumed Silica: Properties, Synthesis and Uses

Properties of Fumed Silica

Fumed Silica, also known as pyrogenic silica, is a fluffy, amorphous white powder composed of 96-99.8% SiO2, 0.05-1.3% Al2O3, 0.003-0.06% Fe2O3 and 0.03% TiO2. It has a high specific surface area (200-390 m2/g), nanoscale primary particle size(5-40nm) and a relatively high density of surface silanol groups (1.5-4.51/nm2). The properties of fumed silica can be chemically modified by reacting with these silanol groups. Fumed Silica is available in a variety of types and sizes including hydrophilic, hydrophobic and food grade.

Information on the basic physical and chemical properties of Fumed Silica:

• Cas Num: 112945-52-5

• Chemical formula: SiO2

• Molecular Weight: 60.08

• Appearance: White Powder
  

• Density: ~2.3-4.5 g/cm3
  

• Melting Point: 1,600° C
  

• Boiling Point: 2,230° C
  

• Size Range: 5–50 nm
  

• Specific Surface Area: 200-390 m2/g
  

• Crystal structure: amorphous
  

• Thermal conductivity: 1.5 W/mK
  

• Moisture content: 0.5-2.5% (hydrophilic); 0.5% (hydrophobic)
  

• Chemical resistance: non-reactive with acids with the exception of HF, unstable in alkalis
  

• Density of silanol groups: 1.5-4.5 1/nm2

Synthesis of Fumed Silica

Fumed Silica can be obtained by pyrolysis. In the pyrolysis method, silicon tetrachloride reacts with oxygen in a flame and the SiO2 seeds gradually increase in size or aggregate. The sol-gel method is carried out in the liquid phase, and the synthesis of silica nanoparticles is carried out in the presence of silicon oxide with an acidic or basic catalyst and an alcoholic solvent. When the reaction is carried out under alkaline conditions, it is called the Stöber method.  

Uses of Fumed Silica

Fumed Silica has a wide range of applications in the food, chemical, pharmaceutical, cosmetic and composite industries, where it can be used as an adhesive, antifoam agent, pesticide, thickener, anticaking agent, lubricant, polishing agent, desiccant, sealant, abrasive and so on. It can improve the thermal and mechanical properties of epoxy/fumed silica composites. The addition of nanosilica improves the thermal stability of the composites and slows down the pyrolysis process.Fumed Silica is combined with highly mineralised water to form polymeric fracturing fluids for fracking and oil containment applications, which effectively improves the thixotropy of highly mineralised fracking fluids and enhances the temperature resistance of highly mineralised fracking fluids.

Fumed Silica was also used to deplete lipids and hormones in Taqman assays of human hepatocellular carcinoma cells HuH-7 and the human hepatocyte cell line HepG2. As well as for the preparation of photocatalytic materials, etc.  

References:  

[1] KYUNG-MIN KIM Hyun J K Hoon Kim. Enhancing Thermo-Mechanical Properties of Epoxy Composites Using Fumed Silica with Different Surface Treatment.[J]. Polymers, 2021. DOI:10.3390/polym13162691.

[2] QUAN ZHANG . Application of fumed silica-enhanced polymeric fracturing fluids in highly mineralized water[J]. Journal of Molecular Liquids, 2023. DOI:10.1016/j.molliq.2022.120835.

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