Fused Silica

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Product Description
Benefits & Application Details


Fused silica is an angular “shaped” silica produced by grinding and milling high purity silica/quartz. Fused silica therefore has the same intrinsic properties as any other silica.

Its chemical formula is SiO2

At Sibelco high purity quartz is being used to make fused silica.


Quartz (silica, SiO2) is the core mineral within the Sibelco group and can be found in a broad number of applications, such as glass, ceramics, filtration, construction, and polymers. 


Other than grinding and milling high quality quartz (to obtain fused silica) Sibelco has other capabilities to process quartz: 

  • Classifying quartz to obtain materials with specific certain, but not milled nor calcined – the material is called Silica Sand. Products are called Silica Sand.(for more information see elsewhere in the tool under Quartz).
  • Milling, drying and classifying quartz – the material is called Quartz Flour. Products are called Silverbond (M). (for more information see elsewhere in the tool under Quartz).
  • Calcining quartz (high temperature treatment – the crystal structure changes) – the material is called Cristobalite. If additionally milled it is called Cristobalite flour. Products are called Sibelite. (for more information see elsewhere in the tool under Cristobalite).
  • High temperature treatment of high purity quartz to obtain spherical particles – the material is called spherical silica and products are called Megasil SS (for more information see elsewhere in the tool under Spherical Silica)


Quartz can be characterised by:

  • Relatively high Mohs hardness of 7
  • Low electrical conductivity
  • Easy to wet
  • High inertness in various media
  • Shape (depending on the source, quartz particles can have an angular or more rounded shape)


Note when using quartz: depending on the particle size distribution of the product, it can be labelled (STOT RE 2 or STOT RE 1). For more detailed information, visit  www.safesilica.eu.

Basic properties

Property Value Unit
Moisture [%]
pH 7 [-]
Hardness (Mohs) 7 [-]
Refractive index 1.55 [-]
Colour (D65/ 10°) L* 93 – 96 [-]
L.O.I. < 0.3 [%]
Density 2.2-2.6 g/cm3

Fused silica is often used for providing the same benefits as spherical silica, but in lower end applications (e.g. transistors instead of semi-conductors):

  • Dimensional stability
  • Reinforcement
  • Processing (flowability)


Thus fused silica is mostly used in epoxy molding formulations, where it not only provides mechanical strength, but foremost provides dimensional stability (minimizing thermal stress). As the particles of fused silica are angularly shaped and not spherical they do not allow for loadings in the epoxy-resin as high as possible with spherical silica (70 – 90 %).  For the same reason the flowability of the formulation containing fused silica is not as good as when spherical silica would have been used. 


These features make fused silica an important raw material for not only for use in transistor production but also in less intricate and demanding applications in adhesives and insulating materials.

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