Pre-formed Insulation Shapes
Silicate bonded perlite can be formed into rigid shapes and makes an insulation material which is conpletely non-flammable. Sodium silicates are widely used as high temperature adhesives and binders. The technology for perlite/sodium composite manufacture is based on the use of solidum silicate as a binder for moulding sand in foundries. Sometimes potassium silicate is preferred for applications where heat insulation and fire resistance are the main objectives as this material has a slightly higher softening point.
Sodium Silicate
Liquid sodium silicate is the most suitable binder for many purposes and is similar to tradiional "waterglass". The liquid sodium silicates are solutions of water soluble glasses manufactured from varied proportions of Na, Co and SiO, 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
Typical Composite Properties
| Thermal Conductivity(ASTM C-177.C-325) | |
| Mean Temp. 250oF (120°C) | 0.40 Btu.in/hft2 deg.F(0.058 W/mK) |
| Mean Temp. 450oF (230°C) | 0.56 Btu.in/hft2 deg.F(0.081 W/mK) |
| Mean Temp. 450oF (350°C) | 0.65 Btu.in/h.ft2 deg.F(0.094 W/m.K) |
| Temperature Limit (ASTM C-447) | 1200°F (650°C) |
| Density (ASTM C-447) | 1-16 lb/ft³ (180-260 kg/m³) |
| Modules of Rupture (ASTM C-203, C-446) Min. | 50-60 lb/in²(0.34-0.41 N/mm²)) |
| Comprehensive Strength (ASTM C-165) Min. | 75-88 lb/in⊃ (0.52-0.61 N/mm⊃) |
| Linear Shrinkage (ASTM C-356) | Less than 2% at 1200°F(650°C) |
| Water Absorption | Under 10% by volume after 24 hours |
| Note: Heating the moulded product within the range 300-500oF (150-260°C), depending on the formulation, enhances the strength and water resistance of the composite material. | |
Formulations
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 speeed of setting 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 whilst lower rations and higher solids contents give greater strength in the finished product
| Setting Process | Silica/Alkali Ratio | Solids Contents |
|---|---|---|
| Gas Injection | 2.00 - 2.50 : 1 | 43 - 50 |
| Liquid Hardeners | 2.00 - 2.90 : 1 | 40 - 45 |
| Solid Hardeners | 2.00 - 2.30 : 1 | 45 - 50 |
Setting Agents
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 whilst lower rations and higher solids contents give greater strength in the finished product
| Gas | Carbon dioxide - usually blown through the moulded shape. |
| Liquid | Glycerol Diacetate plus either Glycerol Triacetate or Ethylene Glycol Diacetate |
| Solid | Calcium silicates e.g. Portland Cenent Calcium sulphates e.g. Gypsum Silicides e.g. Ferrodilicon or Calcium Silicide Silicoflourides or Flourosilicates Ground metallurgical slag Heavy metal salts e.g. Carbonates or Phosphates |
| Suggested formulations using different setting agents | |||
|---|---|---|---|
| Material* | Gas Setting | Liquid Setting | Solid Setting |
| Sodium silicate Solution as % by volume of perlite | 15 - 25% at 68oF (20oC) | 18 - 24% | 25 - 50% |
| * The amount of silicate needed will depend on the particle size, density and absorbency of the perlite used. | |||
Applications
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High Temperature Insulation
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Building Construction
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Fire Protection
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Other Applications
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