Microspheres Basics
Microsphere is referred to as the tiny little balls with diameter
less than 2mm. It has enormous functions due to the shape being
sphereical, chemical containing alumina and surface being smooth and non-porous.
Cenosphere
Cenospheres, also referred to as hollow ceramic microspheres, is a non-porous, inert, hollow, alumina-silicate, micro balls that is formed by burning of pulverized coal during power generation process.
PFA (abbreviation of pulverized fuel ash) and bottom ash are the two forms of ash to be disposed by power companies in bulk volume. Cenospheres is a part of PFA accounting 1% of its volume. which has to be separated by water. For many years water has been the major way of transporting PFA to a final settling reservior about 20km away from the power station, making collecting of cenospheres possible.
| power station | thickening tank | pfa reservior | harvesting at pfa reservior |
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In some power stations, cenospheres can also be harvested at the thickening tanks built inside a power complex.
| collecting on top of tank | collecting inhouse |
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The tiny little balls become useful functional fillers after a series of process such as collecting, drying, particle size classification and in some cases special treatment to reduce biological activities such as fungi/yeast or bacteria.
| harvesting at reservior | harvesters' drier | classifying | packaging |
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more images...
Hollow Glass Microspheres
Also called 'glass bubbles', hollow glass microspheres are made of soda lime borosilicate. Unlike the cenospheres, these 'lovely bubbles' are totally manufactured based on technical requirements demanded by specific applications. in other words, it is under control all the way from particle size, true density (effective particle density), isostatic crush strength to volume of production.
Comparison
Glass bubbles have some unique features that cenospheres do not have. While cenospheres also have some properties that glass bubbles do not match.
| Product name | glass bubble | cenosphere |
|---|---|---|
| true density | 0.15-0.6g/cc | 0.5-0.9g/cc |
| color | white | light gray/gray |
| isostatic crush strength | 300-30000psi | 1500-6000psi |
| melting point (degree C) | not applicable | 1250-1750 |
| Al2O3 | nil | 25-43% |
| Fe2O3 | nil | 0.5-6% |
| pH | 9-10 | 6-8 |
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