Porosimetry is an
analytical technique Analytical technique is a method used to determine a chemical or physical property of a chemical substance, chemical element, or mixture. There is a wide variety of techniques used for analysis, from simple weighing to advanced techniques using high ...
used to determine various quantifiable aspects of a material's
porous
Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measure ...
structure, such as pore diameter, total pore volume,
surface area, and
bulk
Bulk can refer to:
Industry
* Bulk cargo
* Bulk liquids
* Bulk mail
* Bulk material handling
* Bulk pack, packaged bulk materials/products
* Bulk purchasing
*
Baking
* Bulk fermentation, the period after mixing when dough is left alone to f ...
and absolute
densities.
The technique involves the intrusion of a
non-wetting liquid (often
mercury) at high
pressure
Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...
into a material through the use of a porosimeter. The pore size can be determined based on the external pressure needed to force the liquid into a pore against the opposing force of the liquid's
surface tension.
A force balance equation known as
Washburn's equation
In physics, Washburn's equation describes capillary flow in a bundle of parallel cylindrical tubes; it is extended with some issues also to imbibition into porous materials. The equation is named after Edward Wight Washburn; also known as Lucas� ...
for the above material having
cylindrical pores is given as:
:
:
= pressure of liquid
:
= pressure of gas
:
= surface tension of liquid
:
=
contact angle
The contact angle is the angle, conventionally measured through the liquid, where a liquid–vapor interface meets a solid surface. It quantifies the wettability of a solid surface by a liquid via the Young equation. A given system of solid, liq ...
of intrusion liquid
:
= pore diameter
Since the technique is usually performed within a
vacuum
A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or " void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often di ...
, the initial gas pressure is zero. The
contact angle
The contact angle is the angle, conventionally measured through the liquid, where a liquid–vapor interface meets a solid surface. It quantifies the wettability of a solid surface by a liquid via the Young equation. A given system of solid, liq ...
of
mercury with most solids is between 135° and 142°, so an average of 140° can be taken without much error. The
surface tension of mercury at 20 °C under vacuum is 480
mN/
m. With the various substitutions, the equation becomes:
:
As pressure increases, so does the cumulative pore volume. From the cumulative pore volume, one can find the pressure and pore diameter where 50% of the total volume has been added to give the median pore diameter.
See also
*
BET theory
Brunauer–Emmett–Teller (BET) theory aims to explain the physical adsorption of gas molecules on a solid surface and serves as the basis for an important analysis technique for the measurement of the specific surface area of materials. The obs ...
, measurement of specific surface
*
Evapoporometry Evapoporometry is a method used to determine pore-size in synthetic membranes. Based on the Kelvin equation, this technique is most accurate for detection of pore diameters between 4 nm to 150 nm.
Theory
Evapoporometry uses modified forms ...
*
Porosity
Porosity or void fraction is a measure of the void (i.e. "empty") spaces in a material, and is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Strictly speaking, some tests measur ...
*
Wood's metal
Wood's metal, also known as Lipowitz's alloy or by the commercial names Cerrobend, Bendalloy, Pewtalloy and MCP 158, is a metal alloy that is useful for soldering and making custom metal parts, but which is toxic to touch or breathe vapors from. ...
, also injected for pore structure impregnation and replica
References
Measurement
Scientific techniques
Porous media
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