Total surface of a finely divided solid per unit of mass
Scratches, represented by triangular-shaped grooves, make the surface area greater.
Specific 🤑 surface area (SSA) is a property of solids defined as the total surface area (SA) of a material per unit 🤑 mass,[1] (with units of m2/kg or m2/g). Alternatively, it may be defined as SA per solid or bulk volume[2][3] (units 🤑 of m2/m3 or m−1).
It is a physical value that can be used to determine the type and properties of a 🤑 material (e.g. soil or snow). It has a particular importance for adsorption, heterogeneous catalysis, and reactions on surfaces.
Measurement [ edit 🤑 ]
...and plastic Białecki rings of increased SSA
Values obtained for specific surface area depend on the method of measurement. In adsorption 🤑 based methods, the size of the adsorbate molecule (the probe molecule), the exposed crystallographic planes at the surface and measurement 🤑 temperature all affect the obtained specific surface area.[4] For this reason, in addition to the most commonly used Brunauer–Emmett–Teller (N 🤑 2 -BET) adsorption method, several techniques have been developed to measure the specific surface area of particulate materials at ambient 🤑 temperatures and at controllable scales, including methylene blue (MB) staining, ethylene glycol monoethyl ether (EGME) adsorption,[5] electrokinetic analysis of complex-ion 🤑 adsorption[4] and a Protein Retention (PR) method.[6] A number of international standards exist for the measurement of specific surface area, 🤑 including ISO standard 9277.[7]
Calculation [ edit ]
The SSA can be simply calculated from a particle size distribution, making some assumption 🤑 about the particle shape. This method, however, fails to account for surface associated with the surface texture of the particles.
Adsorption 🤑 [ edit ]
The SSA can be measured by adsorption using the BET isotherm. This has the advantage of measuring the 🤑 surface of fine structures and deep texture on the particles. However, the results can differ markedly depending on the substance 🤑 adsorbed. The BET theory has inherent limitations but has the advantage to be simple and to yield adequate relative answers 🤑 when the solids are chemically similar. In relatively rare cases, more complicated models based on thermodynamic approaches, or even quantum 🤑 chemistry, may be applied to improve the consistency of the results, but at the cost of much more complex calculations 🤑 requiring advanced knowledge and a good understanding from the operator.[8]
Gas permeability [ edit ]
This depends upon a relationship between the 🤑 specific surface area and the resistance to gas-flow of a porous bed of powder. The method is simple and quick, 🤑 and yields a result that often correlates well with the chemical reactivity of a powder. However, it fails to measure 🤑 much of the deep surface texture.
See also [ edit ]
