[Surface Area] Single-point and Multi-point BET Theories

Basic and simple introduction of the single-point BET, multi-point BET and the differences between of them.

[Surface Area] BET Theory, Equation and Relation with Langmuir Theory

The BET theory introduction and its plot meaning, also with the BET test steps. The BET is an extension of Langmuir surface area and the limitations.

[Surface Area] The Frenkel-Halsey-Hill (FHH) Theory of Multilayer Adsorption

Physisorption at temperatures below the critical temperature Tc and in the complete wetting regime leads to the development of multilayer adsorption by approaching the saturation pressure Po. The BET theory describes adsorption of the first two or three layers in a satisfying way, but fails to assess correctly the range of the adsorption isotherm, which is associated with the development of thick multilayer films.

[Surface Area] Surface Area from Particle Size Distributions

Although particles can assume all regular geometric shapes, and in most instances highly irregular shapes, most particle size measurements are based on the so-called ‘equivalent spherical diameter’.

[Surface Area] The Langmuir Isotherm

The success of kinetic theories directed toward the measurements of surface areas depends upon their ability to predict the number of adsorbate molecules required to cover the solid with a single molecular layer.

[Surface Area] The Brunauer, Emmett and Teller (BET) Theory Equation

During the process of physical adsorption, at very low relative pressure, the first sites to be covered are the more energetic ones. Those sites with higher energy on a chemically pure surface reside within narrow pores where the pore walls provide overlapping potentials.

[Surface Area] Experimental Techniques for Physical Adsorption Measurements

The adsorbed amount as a function of pressure can be obtained by volumetric (manometric) and gravimetric methods, carrier gas and calorimetric techniques, nuclear resonance as well as by a combination of calorimetric and impedance spectroscopic measurements. However, the most frequently used methods are the volumetric (manometric) and the gravimetric methods.

[Surface Area] Reference Materials Standards

Adsorbents are usually characterized using parameters such as specific surface area, pore volume and the pore size distribution. These quantities can be derived by analysis of gas sorption isotherms by applying an appropriate theory used to treat the adsorption and/or desorption data.

[Surface Area] Coolant Level and Temperature Control

In an open dewar the cryogenic coolant such as liquid nitrogen and/or argon will evaporate, and will therefore change the level of cryogen around the sample cell stem and consequently the cold zone and warm zone volumes. Therefore, it is crucial that the specific position of the cryogen level on the sample cell stem is kept constant during the measurement.

[Surface Area] Determining the Surface Area of Solids Using the BET Equation

The surface area of a solid is defined as the external and the accessible internal pore surfaces. It is widely used to characterize materials for adsorption, catalysis and reactions on surfaces, as its value represents the number of potential active sites.

[Surface Area] Using the Krypton Gas for Low Surface Area Samples Determination

The most advanced volumetric sorption analyzers allow surface areas as low as approximately 0.5 - 1 m2 to be measured using nitrogen as the adsorptive.

[Surface Area] Adsorption and Desorption Isotherms by Continuous Flow

To construct the adsorption isotherm, the adsorption, desorption, and calibration cycle shown in below image is repeated for each datum point required. Errors are not cumulative since each point is independently determined. Relative pressures corresponding to each data point are established by measuring the saturated vapor pressure using any of the preceding methods or by adding 15 torr to ambient pressure.

[Surface Area] Dynamic Flow Method

In 1951, Loebenstein and Deitz described an innovative gas adsorption technique that did not require the use of a vacuum. They adsorbed nitrogen out of a mixture of nitrogen and helium that was passed back and forth over the sample between two burettes by raising and lowering attached mercury columns.

[Surface Area] Low Surface Area Measurement

The thermal conductivity bridge and flow circuits are capable of producing a full-scale signal (1.0 mV) when 0.01 cm3 of nitrogen are desorbed into a 30% nitrogen and helium mixture. To achieve stable operating conditions at this sensitivity, the thermal conductivity block requires some time to equilibrate thermally and the system must be purged of any contaminants.

[Surface Area] What are Chemisorption and Physisorption Differences

The main differences between chemisorption and physisorption is: chemisorption may occur only in a monolayer on a surface, it is unilayer, directionial and strong; whereas physisorption is usually accompanied by multilayer adsorption, it is weak, non-directtional and non-specific, depending upon the temperature.