Adsorption & Porosimetry

The surface area and porosity of a material can critically affect its behavior in many applications, and therefore should not be underestimated. Surface area depends upon various factors such as particle size, the presence of cracks or crevasses, surface roughness, and accessible pores. The characteristics of the pores, such as size, volume, and shape can also greatly affect the performance of the material.

Materials that exhibit varying physical properties and effectiveness depending on their surface area and porosity include, but are not limited to: pharmaceuticals, catalysts, adsorbents, materials for separation technologies, pigments, cosmetics, geologic and construction materials.

The BET (Brunauer, Emmett and Teller) Theory is commonly used to evaluate the gas adsorption data and generate a Specific Surface Area (SSA) result expressed in units of area per mass of sample (m2/g). Briefly, this method involves allowing a clean and dry sample to adsorb a select inert gas such as nitrogen or krypton at liquid nitrogen temperature. The BET theory is subsequently applied to interpret the adsorption data into information on the surface area.

To determine the porosity of a material, various techniques may be employed depending on the size of the pores present and the chemical characteristics of the material. Per the International Union of Pure and Applied Chemistry (IUPAC), porous materials can be categorized as containing micropores (< 2 nm in pore diameter), mesopores (2-50 nm in pore diameter), and/or macropores (> 50 nm in pore diameter).

Mercury porosimetry can be used to analyze materials with pore diameters of around 0.003 µm (or 3 nm) to 250 µm. For samples with pore diameters of approximately 300 nm or below, gas physisorption techniques can be used in conjunction with the most appropriate theory for data interpretation. The specific pore size range that can be analyzed depends on various factors such as the choice of gas, analysis temperature, and relative pressures.

PTL can advise on the most appropriate techniques suitable for your needs. We have capabilities for mercury porosimetry and various choices of gas physisorption techniques for BET surface area and porosity determination. PTL can also follow standard methods from various organizations such as ISO, USP, and ASTM.