The surface area of a powder can critically affect its behavior in many applications.  The technique is referenced by several standard organizations such as ISO, USP and ASTM.  Pharmaceuticals, catalysts, activated carbons, pigments and numerous other materials exhibit varying physical properties and effectiveness depending on their surface area.

The surface area of a powder is determined by the physical adsorption of a gas (normally Nitrogen or Krypton) onto the surface of the sample at liquid nitrogen temperatures.  The choice of gas to be used is dependent on the expected surface area and the properties of the sample.  Once the amount of adsorbate gas has been measured (either by a volumetric or continuous flow technique), calculations which assume a monomolecular layer of the known gas are applied.

The BET (Brunauer, Emmett and Teller) Theory is commonly used to evaluate the gas adsorption data and generate a Specific Surface Area result expressed in units of area per mass of sample (m²/g).  The data from certain sample types such as zeolites, activated carbon, catalysts and various nanoparticles often use an alternative theory referred to as the Langmuir equation for the data reduction process.  Additional data processing can provide information on mean pore size and pore size distribution of the substrate if sufficient data points are collected.

Prior to analysis, the sample must be preconditioned to remove physically bonded impurities from the surface of the powder.  This is typically accomplished by applying elevated temperature to the sample in conjunction with vacuum or continuously flowing inert gas.  This process must be carefully controlled and monitored in order to generate the most accurate and repeatable results.  PTL can advise whether Static Pressure (Volumetric) or Dynamic Flow (Continuous Flow) will be most suitable for you, and/or whether Nitrogen or Krypton is best in any particular case.  Our lab is well equipped with instruments capable of either adsorption technique, and we possess the technical expertise to provide meticulously executed surface area analysis using the most appropriate gas and procedure.  The Static Pressure analyses can be extended in-house to provide pore size and pore size distribution information as well.

Utilizing gas adsorption to determine surface area and pore size data has proven essential to many of our clients.  The influence of surface area on a powder’s behavior can not be underestimated.  We look forward to discussing how gas adsorption can help your project succeed.