Microsphere is a waste product created as a result of hard coal combustion in power plants. This is a ball with a diameter of 10-800 microns filled with a gas (mainly CO2 and NO2). Walls of balls have a thickness of 0.2-3 microns, and this causes that the microsphere has a large volume with a relatively low specific gravity. The material consists essentially of silicon dioxide (SiO2), aluminum oxide (AL2O3), magnesium oxide (MgO), iron trioxide (Fe2O3), potassium oxide (K2O), calcium oxide (CaO) and trace impurities of other metals.
Chemical Composition
| SiO2 | 54,4 | ± | 5,0% |
| AL2O3 | 26,6 | ± | 5,0% |
| Fe2O3 | 5,5 | ± | 0,6% |
| CaO | 1,1 | ± | 0,2% |
| MgO | 1,6 | ± | 0,2% |
| SO2/SO3 | 0,6 | ± | 0,3% |
| K2O + Na2O | 1,2 | ± | 0,4% |
| TiO2 | 0,8 | ± | 0,3% |
| Cl | 0,2 | ± | 0,1% |
Vestigial elements
| As | 34 | ÷ | 42 |
| Ba | 240 | ÷ | 330 |
| Cd | 19 | ÷ | 22 |
| Co | 24 | ÷ | 44 |
| V | 60 | ÷ | 69 |
| Cr | 80 | ÷ | 120 |
| F | 130 | ÷ | 170 |
| Ni | 66 | ÷ | 90 |
| Pb | 66 | ÷ | 90 |
Granulation
| 0 – 120 µm | – | 15 – 20 % |
| 120 – 160 µm | – | 10 – 15 % |
| 160 – 320 µm | – | 65 – 75 % |
| 320 – 500 µm | – | 5 – 10% |
Ignition losses
In temperature 900 °C – less than 5 %
Physical properties
- Color: light gray
- Bulk density in dry state: 400 ± 30 [kg/m3]
- Specific gravity of envelope: 2200 ± 200 [kg/m3]
- Relative density: 690 ± 50 [kg/m3]
- Mohs hardness: 6 ± 1
- Thermal conductivity: 0,07 ± 0,03 [W/m2K]
- pH of aqueous extract: 7 ± 1
- Melting point: 1495 ± 10 [°C]
- Internal pressure of balls: 0,2 ± 0,1 [bar]
- Falling parts – max. 5 %
- Content of water in the dry microsphere: < 0,5 %
Application
Main advantages of the microsphere as a material are very low bulk density, excellent insulating and acoustic properties, high heat resistance and high sinterabillity. These features cause that the microsphere is an excellent filler or lightweight composite materials with excellent isothermal properties. It found a specific use in the production of refractory materials, building industry and automotive mastic.
Microsphere, as a technologically treated waste, is considered to be a product (thermal insulation material). However, as a waste present in small quantities in the production scale of combustion waste (it is estimated that it constitutes approx. 3-5% of fly ashes) it is not defined in the Polish Standard and the European Standard. Moreover, it does not have the Technical Approval. Microsphere does not show any features considered to be dangerous for people and environment. It is a natural material, both physically and chemically, neutral to people and environment. The use of material safety data sheet is not is not required.