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Fly Ash Characterization

cenospheres are a useful and valuable byproduct from flyash


Fly ash is the finest coal combustion product generated during the burning of pulverized coal for power generation. Consisting of small particles of inorganic minerals, with some carbon, it is characterized by high flowability due to its near-spherical particle shape. Because of its mineral chemistry, particularly rich in silica, it normally exhibits pozzolanic and sometimes cementitious behavior. It is, therefore, an important (cost-reducing) additive in cement and can also be used to stabilize loose soils for geotechnical engineering.

When characterizing the textural properties of flyash, apart from particle size, one needs to focus on true surface area (for this represents adsorption capacity/reaction potential), density (volume filling behavior), hygroscopicity, i.e. water sorption and ammonia adsorption/desorption characteristics (i.e. its interaction with flue gases).

Quantitative measurements of ammonia uptake are normally done on manometric/volumetric sorption analyzers like Quantachrome's Autosorb-iQ to produce what are called "isotherms". The temperature required to desorb the ammonia which represents the strength of NH3 binding to the surface, is done by ramping the temperature and monitoring the concentration of ammonia. See, for example, the Autosorb iQ-C. This analyzer can be used for a host of chemisorption and physisorption studies. See also this paper regarding the role of unburnt carbon in ammonia adsorption.


Some fly ash particles are hollow glassy microspheres. These “cenospheres” are recovered by skimming off floaters from fly ash ponds (see image at left). Their low cost (compared to mined and engineered materials) make them ideal as lightweight extenders in construction materials, paints and oil well cements, plus thermal and sound barriers.

Two physical characteristics stand out above all others: density and crush strength. A complete crush strength distribution measurement, from atmospheric pressure to as much as 60,000psia, can be determined in a few minutes by automatic mercury porosimeters.

Abbreviated Quantachrome Fly Ash Reference List
These papers cite the use of Quantachrome's products and the list represents a fraction of all such papers. If you would like more examples, please contact us here.

"Removal of dyes from aqueous solution using fly ash and red mud" S.Wang, Y.Boyjoo, A.Choueib and Z.H.Zhu (2005) Water Research, 39, 129-138.

"Synthesis of ZSM-5 zeolite from lignite fly ash and rice husk ash" M.Chareonpanich, T.Namto, P.Kongkachuichay and J.Limtrakul (2004) Fuel Processing Technology, 85, 1623-1634.

"Study on the weathering resistance of fly ash-lime compacts" S.Li, J.Hu, L.Biao and X.Li (2004) Cement and Concrete Research, 34, 753-758.

"Size distribution of unburned carbon in coal fly ash and its implications" I.Kulaots, R.H.Hurt and E.M.Suuberg (2004) Fuel, 83, 223-230.

"Catalytic oxidation of gaseous reduced sulfur compounds using coal fly ash" J.R.Kastner, K.C.Das and N.D.Melear (2002) Journal of Hazardous Materials, 95, 81-90.

"Characterization of differing forms of unburned carbon present in fly ash separated by density gradient centrifugation" M.M.Maroto-Valer, D.N.Taulbee and J.C.Hower (2001) Fuel, 80, 795-800.

"Investigation of fly ash carbon by thermal analysis and optical microscopy" R.Hill, R.Rathbone and J.C.Hower (1998) Cement and Concrete Research, 28, 1479-1488.

"Pore structures of fly ashes activated by Ca(OH)2 and CaSO4.2H2O" W.Ma, C.Liu, P.W.Brown and S.Komarneni (1995) Cement and Concrete Research, 25, 417-425.

Due to copyright restrictions, Quantachrome cannot supply copies of the above papers but we will be pleased to direct you the the appropriate authors so you may make your request to them. Ask here

Suggested Reading

"The Properties and Use of Coal Fly Ash: A Valuable Industrial By-Product"

"Use of Fly Ash In Concrete"

"Fly Ash in Concrete (RILEM Report 7)"

"Flue Gas and Fly Ash"

"Chemistry of Trace Elements in Fly Ash"

"Fly Ash in Concrete: Production, Properties and Uses (Advances in Concrete Technology)"

"Materials Science of Concrete: Cement and Concrete-Trends and Challenges

Standards (methods, specifications etc)

Click on links to order online / download. Note: provision of these links does not imply that Quantachrome's products are suitable for any or all of stated methods. This feature is provided as a convenience to those in the ash and cement communities. Quantachrome cannot entertain any questions regarding proper use of these standards. In such cases, you should contact the publishers.

Standard Guide for Characterization of Coal Fly Ash and Clean Coal Combustion Fly Ash for Potential Uses, ASTM D5759-95(2005) ASTM International

Standard Practice for Characterizing Fly Ash for Use in Soil Stabilization, ASTM D5239-04(2004) ASTM International

Fly ash for concrete. Definitions, requirements and quality control, BS/EN 450:1995 (1995)

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