All solid contains channels or cavities, which may be regarded as “pores”. These pores influence the physical exchanges and chemical reactivity of solids with gases and liquids. Porosity influences the behavior of gas adsorption and fluid flow within materials. Porosity is one of the key parameters in applications such as drug delivery, energy storage, gas chromatography, atmospheric gas monitoring, gas storage, contamination removal, etc. This property can also be important in catalysts, construction materials, ceramics, pharmaceutical products, metal powders, membranes, active components in batteries and fuel cells, and oil and gas bearing reservoirs.
Gas Adsorption analysis is commonly used for surface area and porosity measurements. This involves exposing solid materials to gases or vapors at a variety of conditions and quantifying the gas uptake at various pressure ranges.
Specific Surface Area
Specific surface area is defined as the surface area per unit mass of sample or in other words, it is a measure of the exposed surface of a solid sample on the molecular scale. Materials with identical weight and volume may differ in surface activity and adsorption volume according to the specific surface area they exhibit. Surface area is an important physical property that is extensively used in the qualitative assessment of material used in agrochemicals, catalysts, additives, adsorption media and pharmaceutical applications. Any change in the surface area of the material during the manufacturing process can lead to an unexpected change in desired performance material.
We use BET (Brunauer, Emmet, and Teller) theory to determine the surface area; results according to the Langmuir model are also available. We can perform surface area analysis on catalysts, activated carbon, Metal-organic frameworks (MOFs), battery material, absorbants, ceramics, metal powders, etc.
Pore Size Distribution
Pore width in a material can be characterized as containing Macropores (>50 nm or >500Å), Mesopores (2 to 50 nm or 20 to 500Å) and/or micropore (< 2 nm or 20Å). Pore Size Distributions can be determined by either gas adsorption porosimetry (typically N2, Ar or CO2) or mercury intrusion porosimetry. Typically, gas porosimetry measures pores from 0.35 nm to 400 nm in diameter. Mercury porosimetry is applicable to pores from 3 nm up to 900 micrometers in diameter. The pore sizes distribution in the material is determined by the calculating the amount gas adsorbed from low pressures (approximately 0.00001 torr, minimum) to saturation pressure (approximately 760 torr). Isotherms of microporous materials are measured over a pressure range of approximately 0.00001 torr to 0.1 torr. Whereas, the isotherms of mesoporous materials are typically measured over a pressure range of 1 torr to approximately 760 torr.
We can report the pore size distribution using models such as:
T-Plot analysis is also available for total micropore area as well.
Samples are prepared by heating while simultaneously evacuating to remove the impurities. The prepared samples are then cooled to room temperature before starting the analysis.
The porosity analysis is done by measuring the volume of gas that physically bound (physisorption) the solid surface at various pressure pressures. Some of the standard gases that can be used for micropore analysis are N2 at 77K, Ar at 87K, and CO2 at 273K. CO2 gas is commonly used in determining the pore size distribution of the materials with less than 0.7 nm pore width.
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