This document describes a method for the evaluation of porosity and pore size distribution by physical adsorption (or physisorption). The method is limited to the determination of the quantity of a gas adsorbed per unit mass of sample as a function of pressure at a controlled, constant temperature[1]-[9]. Commonly used adsorptive gases for physical adsorption characterization include nitrogen, argon, krypton at the temperatures of liquid nitrogen and argon (77 K and 87 K respectively) as well as CO2 (at 273 K). Traditionally, nitrogen and argon adsorption at 77 K and 87 K, respectively, allows one to assess pores in the approximate range of widths 0,45 nm to 50 nm, although improvements in temperature control and pressure measurement allow larger pore widths to be evaluated. CO2 adsorption at 273 K – 293 K can be applied for the microporous carbon materials exhibiting ultramicropores. Krypton adsorption at 77 K and 87 K is used to determine the surface area or porosity of materials with small surface area or for the analysis of thin porous films.The method described is suitable for a wide range of porous materials. This document focuses on the determination of pore size distribution from as low as 0,4 nm up to approximately 100 nm. The determination of surface area is described in ISO 9277. The procedures which have been devised for the determination of the amount of gas adsorbed may be divided into two groups:— those which depend on the measurement of the amount of gas removed from the gas phase, i.e. manometric (volumetric) methods;— those which involve the measurement of the uptake of the gas by the adsorbent (i.e. direct determination of increase in mass by gravimetric methods).In practice, static or dynamic techniques can be used to determine the amount of gas adsorbed. However, the static manometric method is generally considered the most suitable technique for undertaking physisorption measurements with nitrogen, argon and krypton at cryogenic temperatures (i.e. 77 K and 87 K, the boiling temperature of nitrogen and argon, respectively) with the goal of obtaining pore volume and pore size information. This document focuses only on the application of the manometric method.
This document describes a method for the evaluation of porosity and pore size distribution by physical adsorption (or physisorption). The method is limited to the determination of the quantity of a gas adsorbed per unit mass of sample as a function of pressure at a controlled, constant temperature[1]-[9]. Commonly used adsorptive gases for physical adsorption characterization include nitrogen, argon, krypton at the temperatures of liquid nitrogen and argon (77 K and 87 K respectively) as well as CO2 (at 273 K). Traditionally, nitrogen and argon adsorption at 77 K and 87 K, respectively, allows one to assess pores in the approximate range of widths 0,45 nm to 50 nm, although improvements in temperature control and pressure measurement allow larger pore widths to be evaluated. CO2 adsorption at 273 K – 293 K can be applied for the microporous carbon materials exhibiting ultramicropores. Krypton adsorption at 77 K and 87 K is used to determine the surface area or porosity of materials with small surface area or for the analysis of thin porous films.
The method described is suitable for a wide range of porous materials. This document focuses on the determination of pore size distribution from as low as 0,4 nm up to approximately 100 nm. The determination of surface area is described in ISO 9277. The procedures which have been devised for the determination of the amount of gas adsorbed may be divided into two groups:
— those which depend on the measurement of the amount of gas removed from the gas phase, i.e. manometric (volumetric) methods;
— those which involve the measurement of the uptake of the gas by the adsorbent (i.e. direct determination of increase in mass by gravimetric methods).
In practice, static or dynamic techniques can be used to determine the amount of gas adsorbed. However, the static manometric method is generally considered the most suitable technique for undertaking physisorption measurements with nitrogen, argon and krypton at cryogenic temperatures (i.e. 77 K and 87 K, the boiling temperature of nitrogen and argon, respectively) with the goal of obtaining pore volume and pore size information. This document focuses only on the application of the manometric method.
ISO 15901-2:2006 describes a method for the evaluation of porosity and pore size distribution by gas adsorption. It is a comparative, rather than an absolute test. The method is limited to the determination of the quantity of a gas adsorbed per unit mass of sample at a controlled, constant temperature. ISO 15901-2:2006 does not specify the use of a particular adsorptive gas, however nitrogen is the adsorptive gas most commonly used in such methods. Similarly, the temperature of liquid nitrogen is the analysis temperature most commonly used. Use is sometimes made of other adsorptive gases, including argon, carbon dioxide and krypton, and other analysis temperatures, including those of liquid argon and solid carbon dioxide. In the case of nitrogen adsorption at liquid nitrogen temperature, the basis of this method is to measure the quantity of nitrogen adsorbed at 77 K as a function of its relative pressure. Traditionally, nitrogen adsorption is most appropriate for pores in the approximate range of widths 0,4 nm to 50 nm. Improvements in temperature control and pressure measurement now allow larger pore widths to be evaluated. ISO 15901-2:2006 describes the calculation of mesopore size distribution between 2 nm and 50 nm, and of macropore distribution up to 100 nm. The method described in ISO 15901-2:2006 is suitable for a wide range of porous materials, even though the pore structure of certain materials is sometimes modified by pretreatment or cooling. Two groups of procedures are specified to determine the amount of gas adsorbed: those which depend on the measurement of the amount of gas removed from the gas phase (i.e. gas volumetric methods), andthose which involve the measurement of the uptake of the gas by the adsorbent (i.e. direct determination of increase in mass by gravimetric methods). In practice, static or dynamic techniques can be used to determine the amount of gas adsorbed. To derive pore size distribution from the isotherm, it is necessary to apply one or more mathematical models, which entails simplifying certain basic assumptions.
ISO 15901-3:2007 describes methods for the evaluation of the volume of micropores (pores of internal width less than 2 nm) and the specific surface area of microporous material by low-temperature adsorption of gases These are comparative, non-destructive tests. The methods use physisorbing gases that can penetrate into the pores under investigation. The method is applicable to isotherms of type I, II, IV or VI of the IUPAC classification (see ISO 15901-2:--, Figure 1, and ISO 9277). The methods in ISO 15901-3:2007 are not applicable when chemisorption or absorption takes place.
COBAZ is the simple and effective solution to meet the normative needs related to your activity, in France and abroad.
Available by subscription, CObaz is THE modular solution to compose according to your needs today and tomorrow. Quickly discover CObaz!
Request your free, no-obligation live demo
I discover COBAZ