Free flowing powders consisting of minute microspheres, usually hollow often obtained from pulverised fuel ash are stated as cenospheres.

This study was undertaken to have an idea about the physical and chemical characteristics of cenospheres and to suggest their uses with the help of existing facilities.

Methodology used for this purpose 

  • Microscopy to find out size, shape and colour
  • FTIR to measure the glass content
  • TGA to find out the eruption temperature of the spheres and subsequent loss in weight due to entrapped air bubble coming out.
  • Classical analysis and ICP-OES for measuring be chemical constituents.



Microscopy revealed that Cenospheres are spherical hard particles coloured whitish black to greyish black. size of spheres having average diameter 145 micrometer .Outer shell of the spheres are hard coated with glass.

Bulk density of the spheres were done in a graduated Egartz tube and was found to be 0.44 g/ml. That means they are lighter than water, probably due to air being entrapped within the spheres.

Solubility study
Spheres are found to be insoluble in water,1(N) HCL and 1(N) NaOH and have almost nil absorption of water.

Chemical Composition



TGA study of the spheres were taken up to find out the temperature at which the spheres break and the resultant loss in weight due to loss of entrapped airs. The spheres broke out in the range of 315℃ to 375℃ and the loss in weight is 7.13%.Suggesting 7.13% wt of air was entrapped.

Ceno3                 Absorptiogram of this sphere in an IR range done by FTIR
Glass content = 68.5%

Standard Glass sample

Cenosphere sample

Microscopy has suggested that the outer part of the sphere are glasses. FTIR study of the spheres were taken up to find out the glass content in wt %.spheres were grounded and made a powder of 200 mesh and its absorptiogram was made. From the graph it was found that glass content of the powder was 68.5%.But the powdered sample was (100-7.13)%of the total mass. So the glass content is( 68.50*0.9278)=63.62%


  • Cenospheres are minute microspheres coated with glass on the outer surface. They are extremely light due to air having engulfed within the spheres.
  • Cenospheres are aluminosilicates being very high fusion temperature. Although they erupt in the temperature zone due to expansion of the volume of the entrapped air so they can be used as an insulator up to the 315 ℃ temperature.
  • Cenospheres can also be used as water repellant coating over Ceramics, Automotives paints and in construction.
  • They can be used as a filler materials of the polymers plastics.

Usefulness of these study of the properties of Cenospheres provided us the reason for different uses of Cenosphere in different areas.

Contributed by: Alakta Saha (Central Laboratory) with the help of MSK Udayan laboratory under the guidance of Prof. Barun Gupta