Brunauer-Emmett-Teller specific surface area

BET SSA, Brunauer Emmett Teller specific surface area SSA, specific surface area DBPA, dibutyl phthalate absorption OAN, oil absorption number. 

BET SSA Brunauer-Emmett-Teller specific surface area... 

Another example of a DMC-catalyzed esterification reaction is the esterification of free fatty acids with glycerol [32]. This reaction again used Zn-Fe(II)-DMC as a catalyst yet the activity of the material could be tuned by varying the synthesis temperature. As such, DMCs with different acidities (as evidenced by NHj-TPD), crystallite sizes (calculated from the Debye-Scherrer equation), particle sizes (studied with scanning electron microscopy (SEM)), and BET (Brunauer, Emmett and Teller) specific surface areas were obtained. The highest catalytic conversions were observed for the catalysts synthesized at elevated temperatures these materials featured both the highest specific surface area and the largest number of acid sites. 

In writing the present book our aim has been to give a critical exposition of the use of adsorption data for the evaluation of the surface area and the pore size distribution of finely divided and porous solids. The major part of the book is devoted to the Brunauer-Emmett-Teller (BET) method for the determination of specific surface, and the use of the Kelvin equation for the calculation of pore size distribution but due attention has also been given to other well known methods for the estimation of surface area from adsorption measurements, viz. those based on adsorption from solution, on heat of immersion, on chemisorption, and on the application of the Gibbs adsorption equation to gaseous adsorption. 

BET method. The most commonly used method for determining the specific surface area is the so-called BET method, which obtained its name from three Nobel prize winners Brunauer, Emmett and Teller (1938). It is a modification of the Langmuir theory, which, besides monolayer adsorption, also considers multilayer adsorption. The equation allows easy calculation of the surface area, commonly referred to as the BET surface area ( bet). From the isotherms also pore-radii and pore-volumes can be calculated (from classical equation for condensation in the pores). 

A commonly used method of determining the specific surface area of a solid is by the adsorption of a gas onto the solid and the determination of the monolayer capacity. Most methods make use of the Brunauer, Emmett, and Teller equation, commonly referred to as the BET equation, for calculating the surface area on the basis of monolayer adsorption. The BET equation can be written as... 

Specific surface area (SSA), total pore volume and average pore diameter were measured by N2 adsorption-desorption isotherms at 77K using Micromeritics ASAP 2020. The pore size was calculated on the adsorption branch of the isotherms using Barrett-Joyner-Helenda (BJH) method and the SSA was calculated using the Brunauer-Emmett-Teller (BET) method. 

The intrinsic dissolution rates of pharmaceutical solids may be calculated from the dissolution rate and wetted surface area using Eq. (36) or (37). For powdered solids, two common methods are available the powder intrinsic dissolution rate method, and the disc intrinsic dissolution rate method. In the former method, the initial dissolution rate of one gram of powder is determined by a batch-type procedure as illustrated in Fig. 13A. The initial wetted surface area of one gram of powder is assumed to equal the specific surface area determined by an established dry procedure, such as monolayer gas adsorption by the Brunauer, Emmett, and Teller (BET) procedure [110]. 

The number of gas molecules can be measured either directly with a balance (gravimetric method) or calculated from the pressure difference of the gas in a fixed volume upon adsorption (manometric method). The most frequently apphed method to derive the monolayer capacity is a method developed by Brunauer, Emmett, and Teller (BET) [1], Starting from the Langmuir equation (monolayer adsorption) they developed a multilayer adsorption model that allows the calculation of the specific surface area of a sohd. The BET equation is typically expressed in its linear form as... 

Finally, the other factor that could contribute to the improved performance of the nanotubule electrode is its higher surface area. This higher surface area would make the true current density at the nanotubular material lower than at the control material. In order to access the contribution of surface area, Brunauer-Emmett-Teller (BET) measurements were made on both the nanotubular and control electrodes [124], The specific surface areas were found to be 40 m g (nanotubule electrode) and 13 m g (control electrode). This factor of 3 increase in surface area cannot account for the factor of 12 improvement in capacity observed at the highest current... 

Ball et al. investigated the effect of carbon surface area on carbon corrosion at 1.2 V for 24 h and found that, for commercial carbon blacks, cumulative carbon corrosion correlated with carbon BET (Brunauer Emmett Teller) area, although when analyzed as specific carbon corrosion (weight of carbon corroded per unit of carbon area), some variation was observed. The effect of Ft on carbon corrosion has also been studied and conflicting results have been reported. Roen, Paik, and Jarvi found that Ft did increase carbon corrosion... 

EA = elemental analysis IR = infrared spectroscopy PXRD = powder X-ray diffraction BET = Brunauer-Emmett-Teller method (specific BET surface area) and BJH = Barrett-)oyner-Halenda method (determination of pore volume and diameter), both determined by nitrogen physisorption ... 

Wheeler [16] proposed that the mean radius, r, and length, L, of pores in a catalyst pellet (of, for that matter, a porous solid reactant) are determined in such a way that the sum of the surface areas of all the pores constituting the honeycomb of pores is equal to the BET (Brunauer, Emmett and Teller [17]) surface area and that the sum of the pore volume is equed to the experimental pore volume. If represents the external surface area of the porous particle (e.g. as determined for cracking catalysts be sedimentation [18]) and there are n pores per unit external area, the pore volume contained by nSx cylindrically shaped pores is nSx nr L. The total extent of the experimentally measured pore volume will be equal to the product of the pellet volume, Vp, the pellet density, Pp, and the specific pore volume, v. Equating the experimental pore volume to the pore volume of the model... 

Brunauer-Emmett-Teller (BET) analysis was carried out on the ceramic aggregate with both nitrogen and krypton as adsorbates. The sample was crushed and dry sieved, and the fraction between 74 and 589 micrometer was retained for analysis. Results were repeatable, and consistent for the two gases. Over the range of firing and proportioning conditions studied, specific surface area of the ceramic aggregate was between 0.3 and 6 m Vg, which can be compared, for example, to a non-porous... 

Gas Adsorption by the Brunauer, Emmett, and Teller (BET) Method. The specific surface area of porous or finely divided solids is measured. The method is limited to solids that do not react with the gas used (e.g., while the gas is adsorbed), and nonmicroporous materials. For standards, see Table 1 ( Specific Surface, BET Method and N2 Adsorption ). 

Sorption Analysis. Specific surface areas and porosity can be calculated from the adsorption isotherm of nitrogen at — 196 °C. The method of Brunauer, Emmett, and Teller [4.29] is generally accepted for the evaluation of specific surface areas (BET surface area in square meters per gram). The two-parameter equation is applicable to carbon black. The BET surface area comprises the outer surface area as well as the surface area of the pores. 

The most well-known method for determining the specific surface area of powders is based on a theory of multimolecular adsorption of gases developed by Brunauer, Emmett, and Teller (BET) (1). The BET method involves the determination of the quantity of a gas which, when adsorbed on the surface of the solid, would completely cover the solid with a monolayer of the gas. 

There are various kinds of polytetrafluoroethylene. One is granular polymer consisting of spongy, white particles having a median size of about 600/l The specific surface of this polymer is on the order of 2 m2/g (determined by nitrogen adsorption and calculations by the method of Brunauer, Emmett, and Teller). Since this specific surface area is about 1700 times the observed outer surface of the particles, these measurements confirm the porous, spongelike structure that can be seen in the photomicrograph of a cross section of several particles in Fig. la. 

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. 

Other methods that have been used to determine specific surface areas of cements include the Wagner turbidimeter (W16) and BET (Brunauer-Emmett-Teller) gas adsorption. The former, as eonventionally used, gives very low results beeause of a false assumption that the mean diameter of the particles smaller than 7.5 pm is 3.8 pm, which is much too high. The BET method gives results two to three times higher than the air permeability... 

In principle, isotherms at low partial pressures of the sorbate may be used to determine specific surface areas by the Brunauer-Emmett-Teller (BET) method (G64). In this method, it is assumed that molecules of the sorbate are adsorbed on surfaces that can include the walls of pores, provided that the distance between molecules on opposing walls is large compared with molecular dimensions. From a plot derived from the isotherm, and given the effective cross-sectional area of the sorbate molecule, the specific surface area of the sorbent and the net heat of adsorption are obtained. Using water as sorbate, specific surface areas of about 200 m per g of D-dried paste have typically been obtained for mature cement pastes of normal w/c ratios... 

Specific surface area was calculated from the Brunauer-Emmett-Teller (BET) equation for N2 adsorption at 77 K (Micromeritics, ASAP 2010) [10], The t-method of de Boer was used to determine the micropore volume [11]. The pore size distribution curves of micropores were obtained by the Horvath-Kawazoe (H-K) method [12]. 

The sigmoidal shape of the nitrogen isotherm of Figure 1 is quite amenable to analyses by the Brunauer-Emmett-Teller (BET) multilayer theory (8). The BET surface area calculated is 2.8 mVg. This value is quite consistent with the predominant l-to-10- xm size distribution observed on this sample with an optical microscope. Assuming cubic habits and density of about 2.3 g/cm, we find the range of specific surface area to be 0.26 to 2.6 m /g. Apparently the sorbed N2 does penetrate into the internal portion of the particles only to a limited extent. 

We have continued to report BET sorption capacities (expressed as specific surface areas) in light of current practices. Such practice allows us to compare our results to those reported by others where no other measure of sorption capacity is given. This is really a tribute to the landmark work of Brunauer, Emmett, and Teller (8), for providing a comprehensive and useful tool for studying surface phenomena. The fault lies in the application of the theory beyond its realm of applicability. Even the concept of internal surface area derived in this manner is misleading. Actually, the BET sorption capacity is only a measure of the sorption capacity in the region of the knee and probably should be reported in concentration terms (mmol/g, mg/g, cm (STP)/g, etc.) to avoid providing an erroneous concept to the novice. 

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