• Jun 19, 2018
  • Pore Size
  • By PTL

Gas Adsorption & Porosimetry Analyses at PTL

At Particle Technology Labs, our trained chemists perform routine as well as advanced material characterization analysis services. They also conduct method developments, validations and execute transfer protocols all while solving complex problems for clients from a variety of industries. These industries include pharmaceutical, environmental, petrochemical, manufacturing, cosmetics, dietary supplements, food and beverage and others.

Among the many types of particle sizing and characterization services offered at PTL, our expert chemists perform analyses using various gas physisorption techniques to determine BET surface area. Porosimetry can be measured using gas adsorption and mercury techniques depending on the material’s pore size. We follow standard methods from various organizations such as ISO, USP, and ASTM where applicable.

To determine the most appropriate techniques for your surface characterization needs, please contact us.

Following is a brief description of PTL’s BET surface area analysis, micropore/mesopore measurement and mercury intrusion porosimetry testing.

BET Surface Area Analysis

Surface area analysis detects and measures the cracks or crevasses, surface roughness, or accessible pores of particles, all of which can greatly affect the performance and behavior of a material. Pharmaceuticals, catalysts, adsorbents, materials for separation technologies, pigments, cosmetics, geologic & construction materials are just some materials that exhibit varying physical properties and effectiveness depending on their surface area and porosity.

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.

Learn more about BET surface area analysis.

Micropore & Mesopore Measurement

Nanoporous materials are found in many research and industrial applications, including controlled drug delivery, energy conversion and storage, etc. A comprehensive characterization of nanoporous materials with regard to pore size, surface area, and pore size distribution is required in order to select and optimize the performance of these materials.

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).

Micropore Measurement

Micropores are defined as pores with internal diameters of less than 2 nm. Characterization of the micropores involves the use of physisorptive gases that can penetrate into the pores under investigation. Gases used are those which are physically bound at the solid surface, a process referred to as physisorption; for example, N2 at 77K, Ar at 87K, and CO2 at 273K. Micropores are filled at very low relative pressure (P/P0), therefore, specialized instrumentation is required to measure these low pressures.

For more detailed information about Micropore analysis click here.

Mesopore Measurement

The fundamental principles and procedures of mesopore measurement are similar to BET surface area analysis using the static volumetric method. First, any excess adsorbed gases are removed from the sample surface using vacuum or inert gas flow, typically at elevated temperature. Then the adsorbate gas, most commonly nitrogen, is allowed to adsorb onto and desorb from the surface at liquid nitrogen temperature at varying relative pressures. The use of other gases such as argon at liquid argon temperature has also been proven beneficial, especially if investigation into the micropore range (pore diameter of < 2 nm) is of interest.

Learn more about Mesopore analysis.

Mercury Instrusion Porosimetry Testing

Mercury porosimetry is widely used in the catalyst and petrochemical industries for determining the pore size and pore volume of catalyst substrates such as silica and alumina zeolites. In the biomedical field mercury porosimetry has been used to characterize tricalcium phosphate granules or strips used in bone grafts. The pharmaceutical industry has found porosimetry useful in evaluating tablets formed using varied compression forces, for example.

The Washburn Equation relates the applied pressure to pore diameter using physical properties of the non wetting liquid (mercury in this case). The physical properties include the contact angle between the mercury and the material, as well as surface tension. Instruments utilized at PTL allow for pressures ranging from approximately 1 psi up to 60,000 psi which correlates to measurement of pores from about 250 µm to 0.003 µm (3 nm). The contact angle of the mercury on the material under test is an important consideration for optimal results. The contact angle can either be provided or measured; otherwise default values can be entered during the analysis. The volume of mercury intruded into the sample is monitored by a capacitance change in a metal clad capillary analytical cell called a penetrometer. The sample is held in a section of the penetrometer cell, which is available in a variety of volumes to accommodate powder or intact solid pieces. Sample size is limited to dimensions of approximately 2.5 cm long by 1.5 cm wide.

Learn more about Mercury Intrusion Porosimetry analysis.

This brief description covers only a small portion of the particle characterization services offered by Particle Technology Labs. For questions, or to discuss your specific testing needs, please contact us.

PTL is a proven cGMP (current Good Manufacturing Practices) compliant laboratory, in accordance with 21 CFR, Part 210 and 211. Our facility is FDA registered and inspected, and we host over 30 audits per year from the world’s largest pharmaceutical companies. We are DEA licensed and approved to handle Schedule II through V Controlled Substances.

BET Specific Surface Area

BET Specific Surface Area is the most widely recognized technique for determining the surface area of solids and powders. The ability to measure a broad range of surfaces from non-porous solids to highly porous powders has proven the technique valuable across multiple industries including pharmaceutical, environmental, automotive, chemical, cosmetic, geological, and food industries.

Learn More About this Technique

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