The surface area determined by BET is thus normally larger than the surface area determined by air permeability. The method used complies with Ph. Eu. by the BET method. G. FAGERLUND (1). The theoretical background of the adsorption isotherm equation of Brunauer, Emmett and Teller is reviewed, together. Abstract. The theoretical background of the adsorption isotherm equation of Brunauer, Emmett and Teller is reviewed, together with the experimental techniques. For the calculation of certain quantities see Table 1 a desorption step is also required where a vacuum is applied in the reverse of Step 5. These have included argon, carbon dioxide, and water. Articles needing additional references from January All articles needing additional references. A minimum of 3 data points is required. Views Read Edit View history. If heating is employed, the recommended temperature and time of outgassing are as low as possible to achieve reproducible measurement of specific surface area in an acceptable time. Measure the volume adsorbed, V a. For this reason, standard BET analysis is most often conducted at the boiling temperature of N 2 77 K. Adsorption of the gas on to the sample occurs, and the pressure in the confined volume continues to fall until the adsorbate and the adsorptive are in equilibrium. In this range BET theory suggests it should form a straight line see Figure 2. It can either be measured initially for an empty tube or it can be measured at the same time as the measurement described below is occurring in a third tube not shown in Figure 3. Gas adsorption also enables the determination of size and volume distribution of micropores 0. The BET method is applicable only to adsorption isotherms of type II disperse, nonporous or macroporous solids and type IV mesoporous solids, pore diameter between 2 nm and 50 nm. Any gas may be used, provided it is physically adsorbed by weak bonds at the surface of the solid van der Waals forces , and can be desorbed by a decrease in pressure at the same temperature. P0 is the saturation pressure of adsorbate at the temperature of adsorption. At this stage most BET methodologies will carry out a dead-volume measurement using an inert gas such as He. Another common problem is insufficient degassing of gas or water of sample. A porous cellular material according to any one of claims 1 to 12 or 23 to 25, wherein the specific surface area of the material, as determined by the B. Geruchskontroll-Zusammensetzung nach Anspruch 1, in der die Siliciumoxid-Verbindung eine B.