Brunauer, Emmet, Teller

Azo-bis-isobutyronitrile average polymer chain concentration 4-aminotoluene (p-toluidine) Brunauer-Emmet-Teller cross-linking degree Cross Polarization-Magic Angle Spinning Nuclear Magnetic Spectroscopy Cyclic voltammetry N, A-dimethylformamide... 

The determination of the specific surface area of a zeolite is not trivial. Providers of zeolites typically give surface areas for their products, which were calculated from gas adsorption measurements applying the Brunauer-Emmet-Teller (BET) method. The BET method is based on a model assuming the successive formation of several layers of gas molecules on a given surface (multilayer adsorption). The specific surface area is then calculated from the amount of adsorbed molecules in the first layer. The space occupied by one adsorbed molecule is multiplied by the number of molecules, thus resulting in an area, which is assumed to be the best estimate for the surface area of the solid. The BET method provides a tool to calculate the number of molecules in the first layer. Unfortunately, it is based on a model assuming multilayer formation. Yet, the formation of multilayers is impossible in the narrow pores of zeolites. Specific surface areas of zeolites calculated by the BET method (often termed BET surface area) are therefore erroneous and should not be mistaken as the real surface areas of a material. Such numbers are more related to the pore volume of a zeolite rather than to their surface areas. 

While for macroporous structures the inner surface can be calculated from the geometry, meso and micro PS layers require other methods of measurement First evidence that some PS structures do approach the microporous size regime was provided by gas absorption techniques (Brunauer-Emmet-Teller gas desorption method, BET). Nitrogen desorption isotherms showed the smallest pore diameters and the largest internal surface to be present in PS grown on low doped p-type substrates. Depending on formation conditions, pore diameters close to, or in, the microporous regime are reported, while the internal surface was found to... 

Method to determine the specific surface with nitrogen adsorption following Brunauer, Emmet, Teller. 

The most widespread method in determining the specific surface area of solid substrates is without doubt the Brunauer-Emmet-Teller (BET) method.3 It is based on a kinetic model of the adsorption process by Langmuir,7 in which the surface of the solid was regarded as an array of adsorption sites. A state of dynamic equilibrium... 

The method as a rule used for the determination of the specific surface of a material is the Brunauer-Emmet-Teller (BET) method [2,4,5], The BET theory of multilayer adsorption for the calculation of specific surface area, S, was originally developed by Brunauer, Emmett, and Teller [2,4,5], The adsorption process, within the frame of the BET theory, is considered as a layer-by-layer process. In addition, an energetically homogeneous surface is assumed so that the adsorption field is the same in any site within the surface. Additionally, the adsorption process is considered to be immobile, that is, each molecule is adsorbed in a concrete adsorption site in the surface. Subsequently, the first layer of adsorbed molecules has an energy of interaction with the adsorption field, and a vertical interaction between molecules after the first layer,, is explicitly analogous to the liquefaction heat of the adsorbate. Besides, adsorbed molecules do not interact laterally. 

Less favorable is the situation with analyses of obtained data, viz. the most common cases of solids containing both micro- and meso-pores. Here the Brunauer-Emmet-Teller (BET) isotherm is nearly always incorrectly applied. The t-plot method [1] is only of limited applicability because it requires knowledge of adsorption isotherms on non-porous solids of the same chemical nature as the measured sample (master isotherm). Only recently it was shown in this Laboratory [2] that an extension of BET isotherm together with non-linear parameter fitting could solve this problem. 

Brunauer-Emmet-Teller (BET) estimated surface areas [23], For example, from Figure 5.9, graphite felt electrodes show poor volume-normalized ORR current density compared to carbon nanofibers and multiwaUed carbon nanotube (MWCNT)-based electrodes. However, the results also reveal that CNTs and porous carbon tubes exhibit dramaticaUy lower ORR current densities when normalized to B ET surface area, while graphite felt electrodes perform better, perhaps indicative of agglomeration of the carbon tubes, preventing enzyme adsorption over the entire area. Further research on methods to permit dispersion of nano-tubes, while retaining electrical conductivity and adsorption of enzymes oriented for DET, is warranted. 

Usually the plaques produced by either method are coined (compressed) in those areas where subsequent welded tabs are connected or where no active material is desired, eg, at the edges. The uncoined areas usually have a Brunauer-Emmet-Teller (BET) area in the range of 0.25—0.5 m2/g and a pore volume >80%. The pores of the sintered plaque must be of suitable size and interconnected. The mean pore diameter for good electrochemical efficiency is 6—12 Jim, determined by the mercury-intrusion method. 

Nitrogen BET (Brunauer-Emmet-Teller) adsorption is a reliable method for determining the specific surface and pore volume [76]. Evaluation of the specific surface area using the BET method is based on several assumptions that deviate from the behavior of adsorbed molecules on the real surfaces. Despite the cer-... 

Brunauer-Emmet-Teller (BET) Isotherm If a gas continues to adsorb on a surface after a monolayer is achieved, the process essentially represents a condensation and the overall process is represented by this isotherm (Fig. 3.4). The mass of gas adsorbed per unit mass of adsorbent (X) is expressed as follows ... 

The specific surface area of ACC was calculated according to Brunauer, Emmet, Teller method using the linear part of the nitrogen adsorption isotherm shown in Fig. 21.2. Sgg.j, was determined as 1,870 m g . The total volume of pores. 

So the whole set of equations can be solved in one stroke. Applications for this technology are the Brunauer - Emmet - Teller adsorption isotherm, various polymerization reactions and depolymerization reactions, and counting problems in statistical thermodynamics. 

During physical adsorption, each adsorbed molecule forms a new active site for the remaining gas molecules, but there is no reason why this process should limit itself to only one layer. The Brunauer-Emmet-Teller theory, which originates from the Langmuir theory, allows us to obtain a relation (BET eqiration) involving a parameter that expresses the influence of the solid s global surface area, that is to say, the area exposed to gas aetion. 

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