The specific surface area and the pore size distribution are fundamental parameters for the characterization of solids. Properties such as porosity, strength, hardness, permeability, separation selectivity, corrosion, thermal stress resistance, etc. can be directly correlated to the porous structure of a material. These properties can be easily investigated by the physisorption technique which can be carried out by the SA-9600 surface area analyzer.
Idealized physisorption model.
Clean solid surfaces adsorb surrounding gas molecules and Brunauer, Emmett and Teller theory (BET) provides a mathematical model for the process of gas sorption. This physical adsorption of a gas over the entire exposed surface of a material and the filling of pores is called physisorption and is used to measure total surface area and pore size analysis of nanopores, micropores and mesopores.
The specific surface area of a powder is estimated from the amount of nitrogen adsorbed in relationship with its pressure, at the boiling temperature of liquid nitrogen under normal atmospheric pressure. The measurement process of physisorption involves chilling the surface of the measured powder, using nitrogen to adhere to the surface -adsorption, then taking the chilling away – leading to desorption.
Adsorption and desorption correlate to changes in thermal (or electrical) conductivity over time.
This process can be applied one time for a single point measurement, or several times for a multi-point measurement. In general, a surface area result obtained by the multipoint method using nitrogen as the adsorbate is somewhat more reliable than a single point measurement, but the SA-9600 is built to provide high sensitivity results even with single point analysis. The SA-9600 performs these measurements using the flowing gas method which has several advantages, mostly speed of analysis.
Example multi-point analysis from the SA-9600.
BET Flowing Gas Surface Area Analyzers