Microsphere (other names: cenosphere, microbolit, Hollow Glass Spheres) are spherical silica-alumina particles (small balls) filled with carbon dioxide and nitrogen, obtained by means of special processing of fly ash in combustion of coal at high temperatures.
Walls of the balls have thickness from 0.2 to 3 microns. This structure makes that a microsphere occupies a large volume at a minimum weight, i.e. has a low specific gravity. It is 2.5 to 3.5 times lighter than water. Diameter of a single ball varies from 100 to 500 microns.
Microsphere is a light, heat- and fire-resistant filler of composites and is used primarily as:
- Component for insulation screeds (the so-called hot plaster) and insulation prefabricated construction elements,
- Component for production of thermal and acoustic insulation of very high heat and fire resistance,
- Filler in plastics, paints, varnishes, etc.
- Filler of holes in oil and gas mining industries,
- Component of insulating powders for thermal insulation of alloy steel ingots.
Dry microsphere also confirmed its usefulness as a component of:
- Cement ceiling insulation,
- Plasters with high thermal and acoustic insulation, especially in construction,
- Tiles and insulation decorative fittings,
- Insulating-damping mastics in automotive industry.
Basic directions of the use of microspheres:
- With thermosetting plastics – dry microsphere with polyester and epoxy resins gives foams of a reduced density, increased stiffness, heat insulation and resistance to heat and fire at lower manufacturing costs.
- With thermoplastic plastics – dry microsphere, if compared with typical fillers such as chalk, asbestos or fiberglass, gives products of a significantly lower density, higher stiffness, stability and better surface smoothness. Dry microsphere as an additive to sealants and putties protects against volume cracks and makes possible reduction of consumption of mainly synthetic rubber, replacing it partially,
- Dry microsphere is particularly useful as a filler of foams (PVC, polyurethane, and others), which require low shrinkage and high stability of form.
- Dry microsphere is a perfect filler for a variety of surface coatings, particularly thermo-insulating and damping (insulation screeds in construction, insulation of tanks, swimming pools, insulating – damping mastics).
- Dry microsphere perfectly binds with water glass at a higher pressure, that’s why this composite is widely used as a material for light panels and the insulating covers.
- Addition of microsphere to conventional binding material allows production of hot plaster, light firebrick, light plaster, insulating boards and fittings.
Microsphere gives final materials properties such as light weight, fire resistance, thermal insulation and acoustic insulation.
An example of chemical composition
|An example of chemical composition|
|K2O + Na2O||1,2||±||0,4 %|
|Trace elements. Maximum values in ppm:|
|0 – 120 µm||–||15 – 20 %|
|120 – 160 µm||–||10 – 15 %|
|160 – 320 µm||–||65 – 75 %|
|320 – 500 µm||–||5 – 10%|
- colour – light gray to dark gray
- Bulk density in the dry state – 400 ± 30 [kg/m3]
- Shell gravity – 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]
- Softening temperature – 1220 ± 10 [°C]
- Internal pressure of balls – 0,2 ± 0,1 [bar]
- Falling parts – max. 5 %
- Content of water in dry microsphere – < 0,5 %
Loss on roasting
Changes in weight on roasting at temperature 900°C – less than 5% by weight
- glass – strong signal
- mullite – weak signal
- quartz – very weak signal
Detailed tests of chemical composition and physical properties are performed at customer’s order.