# Specific surface area

Scratches, represented by triangular shaped grooves, make the surface area greater

Specific surface area "SSA" is a property of solids which is the total surface area of a material per unit of mass,[1] solid or bulk volume,[2] or cross-sectional 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 particular importance for adsorption, heterogeneous catalysis, and reactions on surfaces.

## Measurement

The value obtained for specific surface area depends upon the method of measurement. Several techniques have been developed to measure the specific surface area of clays, including methylene blue (MB) stain test, ethylene glycol monoethyl ether (EGME) method,[3] Brenauer-Emmett-Teller (N2-BET) adsorption method and Protein Retention (PR) method.[4]

Generally can divided into two methods, one is flowing gas sorption principle (like F-Sorb principle), another one is static volumetric principle (like V-Sorb principle). The first on has a speedy test time and suitable for QC, especially for manufacturers; the latter one is more adaptable for universities, institutes.

### 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.

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.

There are two different measuring methods: flowing gas principle and static volumetric principle. The flowing gas principle has a quick analysis speed, suitable for factory quality control. The static volumetric principle can get a very accurate data, but needs longer time than the first principle. For the static volumetric principle analyzers, some accessories are very important, such as vacuum pump, manifolds system, Dewar, liquid nitrogen monitor, pressure transducers etc. Better to use Germany Leybold brand vacuum pump and pressure transducers, the Dewar volume must be at least 4 liter, otherwise, can not meet super microporous materials analysis, must be stainless steel. The liquid nitrogen level monitor is a must for getting an accurate analysis data. Some brand principle, such as V-Sorb 2800P principle is OK for normal micro samples measurement.

### 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.