Permeation
Encyclopedia
Permeation, in physics
and engineering
, is the penetration of a permeate (such as a liquid
, gas
, or vapor
) through a solid, and is related to a material's intrinsic permeability. Permeability is tested by permeation measurement, for example by a minipermeameter
.
Abbé Jean-Antoine Nollet
Nollet tried to seal wine containers with a pig's bladder and stored them under water. After a while the bladder bulged outwards. He noticed the high pressure that discharged after he pierced the bladder. Curious, he did the experiment the other way round: he filled the container with water and stored it in wine. The result was a bulging inwards of the bladder. His notes about this experiment are the first scientific mention of permeation (later it would be called semipermeability).
Thomas Graham
Graham experimentally proved the dependency of gas diffusion
on molecular weight, which is now known as Graham's law
.
" measurement technique, and first used scientific methods for measuring permeation rates.
The permeation of films and membranes can be measured with any gas or liquid. One method uses a central module which is separated by the test film: the testing gas is fed on the one side of the cell and the permeated gas is carried to the detector by a sweep gas. The diagram on the right shows a testing cell for films, normally made from metals like stainless steel
. The photo shows a testing cell for pipes made from glass, similar to a Liebig condenser. The testing medium (liquid or gas) is situated in the inner white pipe and the permeate is collected in the space between the pipe and the glass wall. It is transported by a sweep gas (connected to the upper and lower joint) to an analysing device.
qm = Perm A Δp / delta
with qm the mass flow, Perm the specific material permeability, A the surface area, Δp the pressure difference, and delta the material thickness. In Europe the permeability unit is mostly cm3.mm/(m2.Bar.day), so that the gas flow in cm3/day results when the area is given in m2, the thickness in mm, and the pressure difference in Bar.
In American units, the permeability is often given in cm3.mil/(100 inch2.Bar.day) which can be converted to the European unit by dividing by 2.54.
In SI units, it is given in s-1.
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
and engineering
Engineering
Engineering is the discipline, art, skill and profession of acquiring and applying scientific, mathematical, economic, social, and practical knowledge, in order to design and build structures, machines, devices, systems, materials and processes that safely realize improvements to the lives of...
, is the penetration of a permeate (such as a liquid
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...
, gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
, or vapor
Vapor
A vapor or vapour is a substance in the gas phase at a temperature lower than its critical point....
) through a solid, and is related to a material's intrinsic permeability. Permeability is tested by permeation measurement, for example by a minipermeameter
Minipermeameter
In petroleum engineering, a minipermeameter is a gas-based device for measuring permeability in porous rocks.Minipermeametry has been used in the oil industry since the late 1960s without becoming in any way a standard experimental method in core analysis or reservoir characterisation...
.
Description
The permeate always migrates to the lower concentration in three steps:- Sorption (at the interface): Gases, vapour or dissolved chemicals or suspended substances are adsorbed at the surface of the solid.
- DiffusionDiffusionMolecular diffusion, often called simply diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles...
(through the solid): The permeate penetrates the solid material through pores or molecular gaps. - DesorptionDesorptionDesorption is a phenomenon whereby a substance is released from or through a surface. The process is the opposite of sorption . This occurs in a system being in the state of sorption equilibrium between bulk phase and an adsorbing surface...
: The adsorbate leaves the solid as a gas.
Related terms
- Permeate: The substance permeating through the solid.
- Permeability: The grade of transmissibility of a solid, meaning how much penetrates in a specific time, dependent on the type of permeate, pressure, temperature, thickness of the solid and the area size.
- Semipermeability: Property of a material to be permeable only for some substances and not for some others.
- Permeation measurement: Method for the quantification of the permeability of a material for a specific substance.
Abbé Jean-Antoine NolletJean-Antoine NolletJean-Antoine Nollet was a French clergyman and physicist. As a priest, he was also known as Abbé Nollet. He was particularly interested in the new science of electricity, which he explored with the help of Du Fay and Réaumur...
(physicist, 1700–1770)
Nollet tried to seal wine containers with a pig's bladder and stored them under water. After a while the bladder bulged outwards. He noticed the high pressure that discharged after he pierced the bladder. Curious, he did the experiment the other way round: he filled the container with water and stored it in wine. The result was a bulging inwards of the bladder. His notes about this experiment are the first scientific mention of permeation (later it would be called semipermeability). Thomas GrahamThomas Graham (chemist)Thomas Graham FRS was a nineteenth-century Scottish chemist who is best-remembered today for his pioneering work in dialysis and the diffusion of gases.- Life and work :...
(chemist, 1805–1869)
Graham experimentally proved the dependency of gas diffusionDiffusion
Molecular diffusion, often called simply diffusion, is the thermal motion of all particles at temperatures above absolute zero. The rate of this movement is a function of temperature, viscosity of the fluid and the size of the particles...
on molecular weight, which is now known as Graham's law
Graham's law
Graham's law, known as Graham's law of effusion, was formulated by Scottish physical chemist Thomas Graham in 1846. Graham found experimentally that the rate of effusion of a gas is inversely proportional to the square root of the mass of its particles...
.
Richard Barrer (1910–1996)
Barrer developed the modern "BarrerBarrer
A Barrer is a non-SI unit of gas permeability used in the contact lens industry. It is a bulk property. It is named after Richard Barrer.-Definition:1 Barrer = 10-11 cm cm-2 s-1 mmHg-1. or...
" measurement technique, and first used scientific methods for measuring permeation rates.
Permeation in everyday life
- Packaging: The permeability of the package (materials, seals, closures, etc) needs to be matched with the sensitivity of the package contents and the specified shelf lifeShelf lifeShelf life is the length of time that food, drink, medicine, chemicals, and many other perishable items are given before they are considered unsuitable for sale, use, or consumption...
. Some packages must have nearly hermetic sealHermetic sealA hermetic seal is the quality of being airtight. In common usage, the term often implies being impervious to air or gas. When used technically, it is stated in conjunction with a specific test method and conditions of usage.-Etymology :...
s while other can (and sometimes must) be selectively permeable. Knowledge about the exact permeation rates is therefore essential. - Tires: Air pressure in tires should decrease as slowly as possible. Therefore it is good to know which gas permeates least through the rubber wall.
- Insulating material: Water vapour permeation of insulating material is important as well as for submarine cables to protect the conductor from corrosion.
- fuelFuelFuel is any material that stores energy that can later be extracted to perform mechanical work in a controlled manner. Most fuels used by humans undergo combustion, a redox reaction in which a combustible substance releases energy after it ignites and reacts with the oxygen in the air...
systems: To meet legal regulations, e.g. CARB (California Air Resource Board) for Low Emission Vehicles, it is essential to use barrier materials for fuel hoses and tanks.
Permeation measurement
Stainless steel
In metallurgy, stainless steel, also known as inox steel or inox from French "inoxydable", is defined as a steel alloy with a minimum of 10.5 or 11% chromium content by mass....
. The photo shows a testing cell for pipes made from glass, similar to a Liebig condenser. The testing medium (liquid or gas) is situated in the inner white pipe and the permeate is collected in the space between the pipe and the glass wall. It is transported by a sweep gas (connected to the upper and lower joint) to an analysing device.
Simple approximation
The mass flow qm through a barrier layer can within certain pressure limits be linearized and approximated by:qm = Perm A Δp / delta
with qm the mass flow, Perm the specific material permeability, A the surface area, Δp the pressure difference, and delta the material thickness. In Europe the permeability unit is mostly cm3.mm/(m2.Bar.day), so that the gas flow in cm3/day results when the area is given in m2, the thickness in mm, and the pressure difference in Bar.
In American units, the permeability is often given in cm3.mil/(100 inch2.Bar.day) which can be converted to the European unit by dividing by 2.54.
In SI units, it is given in s-1.
See also
- Moisture vapor transmission rateMoisture Vapor Transmission RateMoisture vapor transmission rate , also water vapor transmission rate , is a measure of the passage of water vapor through a substance....
- Oxygen transmission rateOxygen Transmission RateOxygen transmission rate is the measurement of the amount of oxygen gas that passes through a substance over a given period. It is mostly carried out on non-porous materials, where the mode of transport is diffusion, but there are a growing number of applications where the transmission rate also...
- Carbon dioxide transmission rateCarbon Dioxide Transmission RateCarbon dioxide transmission rate is the measurement of the amount of carbon dioxide gas that passes through a substance over a given period...
- Hermetic sealHermetic sealA hermetic seal is the quality of being airtight. In common usage, the term often implies being impervious to air or gas. When used technically, it is stated in conjunction with a specific test method and conditions of usage.-Etymology :...
External links
Further reading
- Yam, K. L., "Encyclopedia of Packaging Technology", John Wiley & Sons, 2009, ISBN 978-0-470-08704-6
- Massey,L K, "Permeability Properties of Plastics and Elastomers", 2003, Andrew Publishing, ISBN 978-1-884207-97-6
- ASTM F1249 Standard Test Method for Water Vapor Transmission Rate Through Plastic Film and Sheeting Using a Modulated Infrared Sensor
- ASTM E398 Standard Test Method for Water Vapor Transmission Rate of Sheet Materials Using Dynamic Relative Humidity Measurement
- ASTM F2298 Standard Test Methods for Water Vapor Diffusion Resistance and Air Flow Resistance of Clothing Materials Using the Dynamic Moisture Permeation Cell
- F2622 Standard Test Method for Oxygen Gas Transmission Rate Through Plastic Film and Sheeting Using Various Sensors