Hi Jagan,

I have two ideas which may solve your purpose those are appended below.

1) You can assume individual particle as a spherical in shape, then measure the individual diameter of particles of a representative sample viz., SEM. Hence, the formula for volume calculation of sphere can be applied.

2) You can get the specific surface area in mm2/mm3 using a Laser Particle Size Analyzer whose theory is based on the preliminary assumption that the particle is spherical in shape.

Best wishes,

Bhupendra

Gas displacement methods (pycnoneter)

Pycnometer is the best idea.