Thermodon hollow ash microspheresCenospheres
Thermodon hollow ash microspheres (cenospheres) are a byproduct of certain coal burning power plants.
When pulverized coal is burned a fly ash is produced. Cenospheres are the lighter particles that are contained
within the fly ash as a small proportion. The properties of cenospheres depend on the consistency of the coal used
and the operating parameters of the power plant. Cenospheres have a particle size range of 10-600 micron.
Typical Cenospheres Properties
|Specific Gravity||0.60-0.85 g/cc|
|Bulk Density||0.35-0.45 g/cc|
|Hardness||5-6 Moh Scale|
|Shell Thickness||5-10% Sphere Diameter|
|Crush Strength||120-260 kg/cm2|
|Melting Point||1600 - 1700 °C|
|Thermal Conductivity||0.10 - 0.18W/mK|
|pH in Water||6-8|
Typical Particle Size Distribution
|500 Micron Grade||Value|
|Passing 500 Micron||99.9%|
|Passing 315 Micron||98 - 99%|
|Passing 160 Micron||50 - 70%|
|Passing 100 Micron||20 - 27%|
Advantages of cenospheres
- Spherical Shape. The sphere is a most efficient shape with the lowest surface area compared to volume.
It is this shape which gives cenospheres such a wide variety of uses other than simply being used as a lightweight filler.
The spherical shape means that it takes less resin, binder, water etc. to wet out the surface of cenospheres than any other shaped filler.
This results in low resin or binder demand which in turn allows high solids formulations, lower shrinkage and often lower cost.
Spherical fillers exhibit excellent flow and are easy to spray, pump, trowel etc. Cenospheres are therefore used to considerably improve
workability and ease of use in a wide variety of applications.
Spherical fillers also reduce shrinkage not only because they allow lower binder contents but directly as a result of their shape. At high concentrations, the spheres are packed together but find it difficult to get closer together in the way that irregular shaped fillers can during shrinkage of the binder, evaporation of solvent or water. Spheres therefore help maintain the volume of the original product and as such are excellent fillers for crack and joint compounds, sealants etc.
- Lightweight. The advantages of low density are in many cases quite obvious and clear. The automotive, marine and aerospace industries all
demand the lowest possible weight for plastic parts, sealants, putties, sound dampening etc. and the addition of hollow spheres is an ideal solution.
The density of cenospheres is approximately 25 % of the density of other mineral fillers but cenospheres have a high mechanical strength to withstand
the necessary technological procedures. For example, the use of cenospheres in the automotive industry enables you to reduce the weight of the plastic
parts on their basis up to 30% without compromising the strength characteristics.
The building industry is moving more and more to lightweight products. Low density results in ease of application and use, easier mixing, lower transport costs, low slump and sag, easier sanding, easier cutting, easier drilling.
- Inert. Cenospheres are the silicate spheres of a very low reactivity. Their chemical composition makes them very resistant to acids and alkalis.
They are neutral in pH and do not interfere in chemistry or reaction of the products they are used in. The silica content is amorphous which does however
make the cenospheres slightly pozzolanic and so they will over a period of months react with the free lime liberated as cement hydrates.
This minor reaction is highly desirable in cement as the presence of unreacted free lime deteriorates cementitious products.
- Free Flowing. The free flowing nature of cenospheres means that they are easy to handle in a factory environment. They can be easily gravity fed without blockage and can be pumped in a dry form.
- Insulating. Cenospheres reflect and dissipate heat very effectively because of their inherent physical properties.
Microspheres not only provide excellent thermal insulation but they are also fire resistant.
Cenospheres have a low thermal conductivity coefficient. As a result they have found applications in insulating refractories, oil pipe line insulation, external wall insulation stuccos and many other applications where good thermal insulation is required.
- High Melting Point. Cenospheres have a high melting point of 1200 – 1600 °C which is considerably higher than synthetic glass microspheres. They are therefore excellent for use in high temperature insulating refractories and fire resistant coatings and panels.
- Hard. With a Mohs hardness of 5 – 6, cenospheres have a hard surface that provides excellent erosion and weather resistance. The glassy shell of the cenospheres is totally impermeable to liquids and gases.
- Low Oil Absorption. Cenospheres have an oil absorption of approximately 16 g oil/100 g. When it is considered that cenospheres are only 25 %
of the density of most other commonly used fillers, this figure is equivalent to a level of 4 g oil/100 g.
This means cenospheres have one of the lowest oil absorption levels of any available filler. This low figure is due to the spherical, low surface area shape and the glassy, smooth, totally non-porous shell of the cenospheres. Cenospheres are an ideal choice therefore when formulating to low binder level without high viscosity increase.
- Good Packing Factor. The ratio between bulk and true density for cenospheres is small resulting in a very high packing factor of 60 – 65 %.
This means that although the true density of cenospheres is only 25 % of say calcium carbonate, a 20 kg bag of cenospheres is only twice the size
as a 20 kg bag of carbonate.
This property is a major cost saving in terms of transport since four 20 tonne trucks of other minerals can be replaced by only one 20 tonne truck of cenospheres. Warehouse storage area and cost is also considerably reduced.
- Low Cost. Cenospheres several times cheaper than the artificial hollow glass microspheres. In comparison with the less expensive fillers, microspheres financially more efficient due to the economy in the loading-unloading works and the reduction of weight.
- Oil and gas industry: tampon lightweight cements in construction of wells. During a cementing job, cenospheres decrease the slurry density without increasing the water content. This in turn provides better compressive strength to the cement.
- Construction: Cenospheres have been widely used in the construction industry for many years.
From roofing materials to stuccos and grouts, new applications and products continue to be developed.
The quantity of cenospheres used within the construction industry continues to grow today as more and more
companies realize the advantages cenospheres bring to their products.
Applications in cement: ultra-light concrete, heat-insulating plaster and masonry mixes, and other types of dry building mixtures, heat- and sound-insulating coatings in roofing and facade constructions, floors, concrete repair mortars, fibre reinforced concrete boards, external wall insulation base coat, renders / stuccos, ceramic tile adhesives, floor levelling compounds, fire protection coatings and boards, gunniting cements, ship deck underlayments, tile backer boards.
- Ceramic products: light ceramic wall materials and coatings. Cenospheres are widely used in the construction of refractories. They are more heat resistant than metals and required for heating applications above 600C.
- Paint and varnish materials: thin-layer energy-saving and fire-retardant paints. Such coatings are stronger and more durable. They have a more hardened surface and are resistant to most chemicals.
- Plastics: manufacture of different boats, buoys, life vests, modules buoyancy submarines and submersibles, heating mains insulation.
Applications in epoxe resins: concrete repair mortars, moulds and modelling compounds, tooling blocks, radomes, syntactic buoyancy foams, marble floor tile adhesives, tile cement and grouts, honeycomb and void filler pastes, coatings and paints, decorative duilding profiles.
Applications in polyurethanes: plywood patching compound, synthetic wood, foam carpet backing, electric potting and jointing compounds, de-burring chips, pipe-line insulation, rigid and flexible moulds, coatings (high solids, low slump, corrosion resistant).
Applications in PVC: cushion floor, homogenous safety flooring, car underbody coatings and seam sealants, steering wheels, roofing membranes, air filter seals, shoe soles.
Applications in latex emulsions: latex carpet backing foams, gypsum board joint compounds, veneering plasters, crack fillers, anti-condensation paints, textured paints, non-slip paints.
Applications in unsaturated polyester resins: sandwich panel cores, moulding compounds, cast sanitaryware, tenpin bowling ball cores, buttons, carbody putties, adhesives.
- Chemical industry: catalysts for neutralization of waste water, sensitizers of emulsion explosives, tyres production, abrasive tools of high performance, furniture moldings.
- Other: radar absorbing paints, plastics (stelth coatings), electromagnetic shielding, conductive composites, infra-red reflectors, aerospace composites.
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