ISO 20804:2022 PDF Download

Small-angle X-ray scattering (SAXS) is a method described in the standard ISO 20804:2022 for calculating the precise surface area of porous and particulate systems. It covers both volume-specific surface areas ranging from 0.01 m2cm3 to 1000 m2cm3 and mass-specific surface areas ranging from 1 m2g1 to 2000 m2g1. Both concentrated and diluted systems can use the technique outlined in the standard.

It is significant to note that this standard does not address the estimation of particle size using SAXS, which is restricted to diluted systems in ISO 17867:2020. Additionally, SAXS can only be used to determine surfaces in two-phase systems; systems with more than two phases are outside the purview of this publication.

In this usage, the term "surface" includes any interface between domains of various densities, not just exterior particle surfaces. Any heterogeneous system with interfaces between regions of varying electron density can use the technique.

The specific surface area of both accessible and inaccessible closed holes or inclusions in porous systems can be measured with SAXS, which is a benefit. This contrasts with the gas sorption techniques detailed in ISO 9277:2010.

Additionally, if there is an electron density contrast, SAXS can also be used to estimate the specific surface area of internal interfaces in heterogeneous compact solid systems, such as those between crystalline and amorphous phases. However, materials containing micropores (pore width less than 2 nm) are not covered by the standard.