University of Oregon chemists have developed a boron-nitrogen-based liquid-phase storage material for hydrogen that works safely at room temperature and is both air- and moisture-stable -- an accomplishment that offers a ...
Materials Science
Nov 22, 2011
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Researchers have demonstrated how a gas escapes ice at an extremely cold temperature, providing insight into star formation in interstellar clouds. The mechanism by which hydrogen sulphide is released as gas in interstellar ...
Astronomy
Feb 6, 2018
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More efficient catalytic converters on autos, improved batteries and more sensitive gas sensors are some of the potential benefits of a new system that can directly measure the manner in which nanocrystals adsorb and release ...
Nanomaterials
Aug 6, 2013
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Researchers from the Ohio State University have developed a rapid, multiplexed genotyping method to identify the single nucleotide polymorphisms (SNPs) that affect warfarin dose. The related report by Yang et al, "Rapid ...
Analytical Chemistry
Feb 25, 2010
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Honda Motortoday announced the development of a new catalyst which reduces by 50% the use of rhodium, one of the precious metals used in a catalyst. Honda will adopt this new catalyst first to the North American version of ...
Materials Science
Sep 6, 2012
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0
(Phys.org) -- Once impossible, scientists can now eavesdrop on microbes, thanks to a new technique from scientists at Pacific Northwest National Laboratory and three universities. Microbes converse by releasing simple and ...
Cell & Microbiology
Jul 26, 2012
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Even the merest of microbes must be able to talk, to be able to interact with its environment and with others to not just survive, but to thrive. This cellular chatter comes in the form of signaling molecules and exchanged ...
Biochemistry
May 10, 2011
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The desorption of CO ice induced by ultraviolet (UV) radiation is a phenomenon that occurs in some cold parts of the universe, which has often also been replicated in laboratory settings. While this phenomenon is now well-documented, ...
Pollutants can find themselves ensnared underground with few options for escape, according to a study by scientists at Iowa State University, University of Texas at Arlington, and Pacific Northwest National Laboratory. The ...
Materials Science
Oct 14, 2010
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Studying the photochemistry, or chemical results of light, has shown that ultraviolet radiation can set off harmful chemical reactions in the human body and, alternatively, can provide "photo-protection" by dispersing extra ...
General Physics
Jul 17, 2018
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Desorption is a phenomenon whereby a substance is released from or through a surface. The process is the opposite of sorption (that is, either adsorption and absorption). This occurs in a system being in the state of sorption equilibrium between bulk phase (fluid, i.e. gas or liquid solution) and an adsorbing surface (solid or boundary separating two fluids). When the concentration (or pressure) of substance in the bulk phase is lowered, some of the sorbed substance changes to the bulk state.
In chemistry, especially chromatography, desorption is the ability for a chemical to move with the mobile phase. The more a chemical desorbs, the less likely it will adsorb, thus instead of sticking to the stationary phase, the chemical moves up with the solvent front.
In chemical separation processes, stripping is also referred to as desorption as one component of a liquid stream moves by mass transfer into a vapor phase through the liquid-vapor interface.
After adsorption, the adsorbed chemical will remain on the substrate nearly indefinitely, provided the temperature remains low. However,as the temperature rises, so does the likelihood of desorption occurring. The general equation for the rate of desorption is:
R = rNx,
where r is the rate constant for desorption, N is the concentration of the adsorbed material, and x is the kinetic order of desorption.
Usually, the order of the desorption can be predicted by the number of elementary steps involved:
Atomic or simple molecular desorption will typically be a first-order process (i.e. a simple molecule on the surface of the substrate desorbs into a gaseous form).
Recombinative molecular desorption will generally be a second-order process (i.e. two hydrogen atoms on the surface desorb and form a gaseous H2 molecule).
The rate constant r may be expressed in the form
where A is the "attempt frequency" (often the Greek letter ν), the chance of the adsorbed molecule overcoming its potential barrier to desorption, Ea is the activation energy of desorption, k is the Boltzmann constant, and T is the temperature.
This text uses material from Wikipedia, licensed under CC BY-SA
