Perlite/silicate composites for high temperature insulation and formed shapes

 

 

Both flat rounded of socium silicate perlite insulation

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 "water glass." The liquid sodium silicates are solutions of water soluble glasses manufactured from varied proportions of Na2C03 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.

TYPICAL PROPERTIES OF PERLITE/SODIUM SILICATE COMPOSITES
Thermal Conductivity at mean temp. 120°C 0.058 W/m.K
Thermal Conductivity at mean temp. 230°C 0.081 W/m.K
Thermal Conductivity at mean temp. 350°C 0.094 W/m.K
Thermal Limit (ASTM C-447) 650°C
Density ASTM C-447) 180-260 kg/m3
Modulus of Rupture (ASTM C-203,C-446) minimum 0.34-0.41 N/mm2
Compressive Strength(ASTM C-165) minimum 0.52-0.61 N/mm2
Linear Shrinkage (ASTM C-356) less than 2% at 650 °C
Water Absorption under 10% by volume after 24 hours

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 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.

Setting agents

  • Gas Carbon dioxide (usually blown through the molded shape)
  • Liquids Glycerol Diacetat plus either
    • Glycerol Triacetate
      or
    • Ethylene Glycol Diacetat
  • Solids
    • Solids Calcium silicates - e.g. Portland Cement
    • Calcium Sulphate - e.g. gypsum
    • Silicides-g.g. Ferrosilicon or Calcium Silicate
    • Silicofluorides or fluorosilicates
    • Ground metallurgical slab
    • Heavy metal salts-e.g. carbonates or phosphates
Setting Process Silica/Alkali Ration Solids Content %
Gas Injection 2.00--2.50:1 43-50
Liquid Hardeners 2.50--2.90:1 40-45
Solid Hardeners 2.00--2.30:1 45-50
SUGGESTED FORMULATIONS USING DIFFERENT SETTING AGENTS
Material* Gas Setting Liquid Setting Solid Setting
Sodium silicate solution as % by volume of Perlite 2.5-5% 5-10% 5-15%
Setting agent as % by weight of sodium silicate 15-25% at 20°C 8-14% 25-50%
(*amount of silicate needed will depend on the particle size, density, and absorbency of the Perlite used.)
APPLICATIONS OF PERLITE/SILICATE COMPOSITES
High Temperature Insulation Fire Protection Building Construction Other Applications
  • Pipe covering
  • Furnace lining
  • Industrial ovens/kilns
  • Domestic oven lining
  • Fire bucks and stoves
  • Chimney insulation
  • Foundry molds and coves
  • Runner insulation shapes Refractory shapes
  • Fire doors
  • Fire resistant coatings
  • Steelwork cladding
  • Roof truss insulation
  • Fire-safe cabinets
  • Document boxes
  • Computer disk storage Electrical control boxes
  • Ceiling tiles Acoustical panels
  • Sandwich panels
  • Wall insulation blocks
  • Cryogenic tank base insulation Decorative moldings and shapes Sprayed coatings
  • Acid resistant blocks
  • Roofing tiles
  • Liquid waste solidification
  • Asbestos encapsulation
  • Oil absorbents Welding rod coatings
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