Specific surface area (SSA) is a property of
solid
Solid is one of the four fundamental states of matter (the others being liquid, gas, and plasma). The molecules in a solid are closely packed together and contain the least amount of kinetic energy. A solid is characterized by structura ...
s defined as the total
surface area
The surface area of a solid object is a measure of the total area that the surface of the object occupies. The mathematical definition of surface area in the presence of curved surfaces is considerably more involved than the definition of ...
of a material per unit of
mass
Mass is an intrinsic property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different element ...
, (with units of m
2/kg or m
2/g) or solid or bulk
volume
Volume is a measure of occupied three-dimensional space. It is often quantified numerically using SI derived units (such as the cubic metre and litre) or by various imperial or US customary units (such as the gallon, quart, cubic inch). Th ...
(units of m
2/m
3 or m
−1).
It is a physical value that can be used to determine the type and properties of a material (e.g.
soil
Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former ...
or
snow
Snow comprises individual ice crystals that grow while suspended in the atmosphere
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet ...
). It has a particular importance for
adsorption,
heterogeneous catalysis, and
reactions on surfaces.
Measurement
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.
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, electrokinetic analysis of complex-ion adsorption
and a Protein Retention (PR) method. A number of international standards exist for the measurement of specific surface area, including ISO standard 9277.
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. 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.
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.
{, class="wikitable"
, + Selected Materials with High Surface Areas
, -
! Typical surface area (m
2/g)
! Material
! Application
, -
, 7140
,
Metal–organic framework
, gas absorption
, -
, 900
,
Faujasite
, catalyst
, -
, 500 - 3000
,
activated carbon
Activated carbon, also called activated charcoal, is a form of carbon commonly used to filter contaminants from water and air, among many other uses. It is processed (activated) to have small, low-volume pores that increase the surface area avail ...
, gas and solute absorption
, -
, 200
,
alumina[{{cite journal , volume=42 , doi=10.1021/ie50487a024 , title=Alumina Surface Area Measurements , year=1950 , last1=Russell , first1=Allen S. , last2=Cochran , first2=C. Norman , journal=Industrial & Engineering Chemistry , issue=7 , pages=1332–1335 ]
,
catalyst support
, -
See also
*
Surface-area-to-volume ratio
References
Porous media
Surface science