ISO 15901-2:2022 pdf – Pore size distribution and porosity of solid materials by mercury porosimetry and gas adsorption — Part 2: Analysis of nanopores by gas adsorption.
1 Scope 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 - . 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 CO 2 (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. CO 2 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
2 Normative references The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 3165, Sampling of chemical products for industrial use — Safety in sampling ISO 8213, Chemical products for industrial use — Sampling techniques — Solid chemical products in the form of particles varying from powders to coarse lumps ISO 9277, Determination of the specific surface area of solids by gas adsorption — BET method ISO 14488, Particulate materials — Sampling and sample splitting for the determination of particulate properties
3? Terms? and? definitions For the purposes of this document, the following terms and definitions apply. ISO and IEC maintain terminological databases for use in standardization at the following addresses: — ISO Online browsing platform: available at https:// www .iso .org/ obp — IEC Electropedia: available at https:// www .electropedia .org/ 3.1 adsorbate adsorbed gas 3.2 adsorption enrichment of the adsorptive at the external and accessible internal surfaces of a solid 3.3 adsorptive gas or vapour to be adsorbed 3.4 adsorbent solid material on which adsorption occurs 3.5 adsorption isotherm relationship between the amount of gas adsorbed and the equilibrium pressure of the gas at constant temperature 3.6 adsorbed amount amount of gas adsorbed at a given pressure, p, and temperature, T 3.7 equilibrium adsorption pressure pressure of the adsorptive in equilibrium with the adsorbate 3.8 monolayer amount amount of the adsorbate that forms a monomolecular layer over the surface of the adsorbent 3.9 monolayer capacity volumetric equivalent of monolayer amount expressed as gas at standard conditions of temperature and pressure (STP)