The characteristics used to describe powders include porosity, true volume, bulk volume, apparent density, true density, and bulkiness.
Where,
Porosity can be expressed as = Void × 100
Where, Void can be defined as = [{V (bulk) – V (true)} ÷ V (bulk)]
This value should be determined experimentally by measuring the volume occupied by a selected weight of a powder V (bulk) and the true volume V (true) of a powder is the space occupied by the powder exclusive of spaces greater than the intramolecular space.
Therefore, porosity is = [{V (bulk) – V} ÷ V (bulk)] × 100
And the bulk volume is = true volume + porosity.
Example
A selected powder has a true density (ρ) of 3.5 g/cc. Experimentally, 2.5 g of the powder measures 40 mL in a cylindrical graduate. Calculate the true volume, void, and porosity.
We know that,
True Density = mass (weight) / volume
Thus,
True Volume = mass (weight) / true density = 2.5 g/(3.5 g/cc) = 0.715 cc
Void = [{V (bulk) – V (true)} ÷ V (bulk)] = [(40 – 0.715) ÷ 40] = 0.982
Porosity = Void × 100 = 0.982 × 100 = 98.2%
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