Agglomeration of Ash Particles due to Flue Gas Conditioning (a) - - PowerPoint PPT Presentation

(a) Sample CA8S12F1 (b) Sample CA8S12F2 (c) Sample CA8S12F3 (d) Sample CA8S12F4 (e) Sample CA8S12F5 (f) Sample CA8S12F6

Agglomeration of Ash Particles due to Flue Gas Conditioning

SF BFS

SEM micrographs of Silica Fumes & Ground Granulated Blast Furnace Slag (GGBFS/BFS)

Compacted sample Cubic specimen

Determination of fabric structure of fine-grained soils Using SEM

Specimen preparation (Challenges):

• Removal of pore fluid from the specimen without disturbing its microstructure.
• Freeze-drying technique (for swelling/shrinking type of soils)
• Air-drying technique (for non swelling/shrinking type of soils)
• Specimen should be able to withstand the vacuum inside the microscope.
• As illumination is with electrons, specimen should be made to conduct electricity.
• Specimen are coated with a very thin layer of Gold or Carbon (a sputter coater).
• Gold coating film can absorb X-ray signal generated into the specimen.
• For obtaining X-ray spectrum of a non-conducting sample a coating material very

transparent to the X-ray (Carbon) must be utilized.

Kaolinite plate stacks Face-Face interaction

Face-Edge & Edge-Edge interactions

• Geomaterials are composed of wide range of particle sizes and

shapes and are porous in nature.

• A knowledge of pore structure of these materials is important as it can

give insight in to both the microstructure and the performance.

• Rather than measuring the porosity, It becomes more informative if the

manner in which volume is distributed With respect to pore size.

Mercury Intrusion Porosimetry (MIP) Dead end Closed Inter-connected Passing

Non-porous solids (Extremely low surface area) Porous solids medium high surface area, pore volume and dimension Particulates particle size and surface area Catalysts: activated sites on porous support or powder

Porosity

Conical Slits Cylindrical Spherical or Ink Bottle Interstices

Shape of Pores

Micropores: 0 < d < 2 nm (zeolites, carbons, silica fumes) Mesopores: 2 < d < 50 nm (alumina, polymers, catalysts) Macropores: 50 < d < ...nm (rocks, cements, soils, ...)

Bulk, apparent and real density [g/cc] Percentage porosity [%] Pore volume/pore size distribution [pore volume vs pore size] Total pore volume [cc/g] Average pore size Specific surface area [m2/g] Particle size distribution [relative percentage vs particle size]

Pore size classification and parameters

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Pore size distribution

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Particle size distribution

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Bulk density

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Apparent density

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Total porosity

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Pore area distribution

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Low/high specific surface

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Micro/mesopores distribution

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Micro/mesopores total volume

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Real density

Mercury porosimetry Gas adsorption Helium Pycnometry

Characterization schemes

Mercury Porosimetry concept

• Hg is a non-wetting liquid for many

solids

• Hg must be forced to penetrate pores
• Penetration pressure is related to pore

size

• Volume of Hg is related to pore

volume

wetting non wetting

Hg cannot enter pores under vacuum An increasing pressure forces Hg to penetrate all accessible pores

Working principle: P = 2.(T.cosθ)/r ……Washburns Equation

Volume of mercury Pressure

Intrusion curve Extrusion curve

A

Information obtained

• the pore size distribution
• surface area
• equivalent pore size
• critical pore diameter
• distribution of total porosity
• free porosity and trapped porosity

Typical MIP characteristic curve

A: hysterisis