PERLITE/SILICATE COMPOSITES FOR HIGH TEMPERATURE INSULATION
AND FORMED SHAPES
Perlite/Silicate Composites
Expanded perlite granules can be bonded to form rigid shapes for a very wide
range of applications. The most suitable binder for many purposes is a liquid
sodium silicate similar to traditional "waterglass". The liquid sodium silicates are
solutions of water soluble glasses manufactured from varied proportions of
Na2CO3 and SiO2, providing a wide range of chemical and physical properties.
Sodium silicates are widely used as high temperature adhesives and binders
due to the following properties.
- Low cost
- Inorganic
- Easy to handle
- Rapid controlled set
- High strength
- Insolubility (when aired)
- Chemical stability
Silicate-bonded perlite makes an insulation material which is completely
non-flammable, the refractory nature of the bond being a major advantage.
Potassium silicate is sometimes preferred for applications where heat insulation
and fire resistance are the main objectives. This material has a slightly higher
softening point than its sodium counterpart.
Sodium silicate is widely used as a binder for molding sand in foundries. The
technology for perlite/sodium silicate composite manufacture is based largely on
this foundry industry experience.
Perlite/Sodium Silicate Technology
A wide range of formulations of perlite, sodium silicate solution and setting agent
can be used, together with additives to control the absorbency of the perlite and
the speed of setting of the mix. General guidelines are given as a starting point.
Soluble Silicate Grades
The choice of grade of sodium silicate solution depends on the application and
setting process being used. Generally, a higher silicate to alkali ratio gives
faster setting while lower ratios and higher solids contents give greater strength
in the finished product.
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