BET Braunauer, Emmett, and

Subsequently, the characterization of the pore structures of the porous materials using gas adsorption method was discussed in detail. The types and characteristics of the adsorption isotherms and the hysteresis loops were introduced. In addition, the BET (Braunauer, Emmett, and Teller) theory92 for the determination of the surface area and various theoretical models for characterization of the pore structures according to the pore size range were summarized based upon the adsorption theory. 

Abet Total Braunauer, Emmett, and Teller (BET) surface... 

In elutriation methods, particles are classified in a column by a rising fluid stream. A series of cyclones are used to separate particles into different size ranges. Gas adsorption of a gas on a powder is another method for determining surface area. Measurements are usually interpreted by using the Braunauer, Emmett, and Teller (BET) theory. 

Another limitation of the Langmuir model is that it does not account for multilayer adsorption. The Braunauer, Emmett and Teller (BET) model is a refinement of Langmuir adsorption in which multiple layers of adsorbates are allowed [29, 31]. In the BET model, the particles in each layer act as the adsorption sites for the subsequent layers. There are many refinements to this approach, in which parameters such as sticking coefficient, activation energy, etc, are considered to be different for each layer. 

Figure 7.12 Adsorption of water by skim milk and sorption isotherms predicted by the Braunauer-Emmett-Teller (BET), Kuhn and Guggenheim-Andersson-De Boer (GAB) sorption models (from Roos, 1997).

Braunauer et al. classified the adsorption isotherms typically into five types (Brunauer, 1938 Adamson, 1990), which are shown in Figure 10-1. Type I is the Langmuir type adsorption and corresponds to a monolayer formation. This isotherm shape, with very high adsorption at low relative pressures, is typically observed for microporous solids (pore diameter <2 nm) having relatively small extmial sinfaces (Meixner, 1999). Type II is very common in the case of physical adsorption on non-porous materials, with relatively strong interaction between adsorbent and adsorbate and corresponds to multilayer formation. This type of adsorption isotherm was theoretically developed by Brunauer, Emmett, Telllo, and called the BET type (Brunauer, 1938). Type IB correspond s to the adsorption with rather small interaction between adsorbent and adsorbate and multi-layer formation, but is rarely observed. Types IV and V are observed in the adsorption on porous materials, where capillary condensation phenomena lead to an increase in the adsorbed amount in the... 

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