Specific surface area

Specific surface area

Specific surface area is a material property of solids which measures the total surface area per unit of mass [http://goldbook.c60.kiev.ua/S05806.pdf IUPAC Compendium of Chemical Terminology 2nd Edition (1997)] , solid or bulk volume [http://web.archive.org/web/20060905224652/http://www.soils.wisc.edu/~ss322/lectures/lec+8-11.pdf] , or cross-sectional area [ [http://www.russellwatergardens.com/SSA.htm What is Specific Surface Area ] ] .

It is a derived scientific value that can be used to determine the type and properties of a material (e.g. soil). It is defined either by surface area divided by mass (with units of m²/kg), or surface area divided by the volume (units of m²/m³ or m-1)

It has a particuliar importance in case of adsorption, heterogeneous catalysis, and reactions on surfaces.

Measurement

The value obtained for specific surface area depends critically upon the method of measurement.

Calculation

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

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.

Gas Permeability

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.

References


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