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(Final Project: Applications of Gas Adsorption)
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=== Adsorption Thermodynamics ===
== Adsorption Thermodynamics ==
=== Vapor Pressure ===
== References ==
== References ==

Revision as of 15:24, 2 January 2009

Nick Hutzler

I am a second year Physics graduate student in the Doyle Lab. I am working on an experiment to measure the electron electric dipole moment using a cryogenic molecule beam.

Final Project: Applications of Gas Adsorption


Adsorption is the physical process where molecules (or atoms, though we shall use the word "molecule" to include those as well) in a fluid phase stick become bound to the surface of another solid or liquid. Adsorption is a very broad term that can include a gas or liquid adsorbing onto a liquid or solid through electrostatic attractions, chemical bonds, or some combination of both. In this discussion we will focus primarily on the adsorption of gases onto solid.

Adsorption terminology. (From [Ke])

Before proceeding, let's introduce some terminology. In adsorption, the fluid-phase adsorptive molecules sticks onto the adsorbent and become adsorbate. When adsorbate unsticks from the adsorbent, whether spontaneously or induced, it is called desorption.

Types of Adsorption

Adsorption can be classified by whether the mechanism is "physical" (physisorption) or "chemical" (chemisorption) in nature. Because we will be focusing on physisorption, we then discuss several different adsorption mechanisms that would be classified as physical. The lists presented in this section are adapted from [Ke].

Physisorption vs. Chemisorption

  • Physisorption is classified by weakly bound adsorbate, usually by van der Waals or London dispersion forces. An important feature of this type of adsorption is that it is reversible; specifically, desorption can be induced by raising the temperature of the adsorbent, or by decreasing the pressure of the adsorptive. The adsorptive does not suffer any type of chemical change when being adsorbed.
  • Chemisorption is classified by strongly bound adsorbate, usually as a result of chemical bonds. Because chemical reactions occur, this process is typically irreversible, and the characteristics of the mechanism are strongly dependent on the species involved. Therefore, we will not focus on this type of adsorption.

Types of Physisorption

Adsorption Thermodynamics

Vapor Pressure


[Ke] Keller & Staudt, Gas Adsorption Equilibria

[We] Welch, Capture Pumping Technology