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Porosity is the value used to describe how much empty, or void, space is present in a given sample. This attribute is commonly measured in regards to the soil since appropriate porosity levels are necessary for plants to grow. Porosity can be calculated theoretically using equations and given values, which is the case when you are faced with exam questions. Porosity can also be determined by finding the values needed to solve the equations experimentally, either in the lab or in the field.

There are a number of methods for calculating porosity:

1-Calculating Porosity Theoretically by Volumes.

2-Calculating Porosity Theoretically by Densities.

3-Calculating Porosity Experimentally by Saturation.

4-Calculating Porosity in the Field by Taking Core Samples.

For more on this topic, please see the publication contained in the following link:

http://www.wikihow.com/Calculate-Porosity

Also, below there is have valuable information about the porosity, which written by Dr. Martin A Thomas on else topics: (Dr. Thomas has more than thirty-five years of industrial experience in the characterization of powders and porous materials)

Porosity being a dimensionless VOLUME parameter. Sometimes (though always incorrectly) the term BET is used to denote a complete measured gas sorption isotherm. If you have that data set, and the isotherm plateaus at the high P/Po values, one can reasonably estimate the total pore volume, per unit mass of your sample - so long as there are no pores/cracks/voids larger than about 400nm (gas sorption is generally blind to anything larger than this, though if you are lucky you can push the technique to about 500nm - though some workers in the field will choke at anything over 200nm!!).

Still not enough data for POROSITY. This is the fraction (usually expressed as a percentage) of pore volume to the whole volume of the particle(s). To arrive at gross particle volume, it is acceptable to simply invert the particle true density (measured by gas pycnometer, or from crystallographic data, or from reliable literature source). This number you arrive at is the "specific volume" of the solid phase ONLY. Add this specific i.e. SOLID volume to the PORE volume (make sure units are same, usually, both will be in cc/g = cm3/g = ml/g). Now you can easily find POROSITY by dividing PORE volume by this new SUM of volumes.

If you have no idea, or cannot measure, the true density of the SOLID phase, then one must measure the APPARENT density of the particles (which includes the volume of solid and pores)...there's more than one way to do that usually (depending on the physical form of the sample).

Now, if your gas sorption isotherm does NOT plateau, or by visual (including optical microscopy) inspection, you know there to pore greater than can be measured by gas sorption, one must (i) use a different technique for measuring total pore volume (mercury porosimetry is OK for non-microporous materials), or (ii) compute total pore volume from apparent density and true density.

Hoping this will be helpful,

Arabkhani

Thank you Mr. Arabkhani for your valuable input ..I have attached the data available for my sample..from this will i be able to calculate porosity? my sample is silica spheres..so how can i calculate its density?