Gas Adsorption for Surface Area (BET) determination and Pore Size Analysis (BJH)
Determination of surface area (BET) and pore size distribution (BJH) of solid, porous adsorbent materials is done by Gas Adsorption. Adsorption and desorption isotherms are obtained using Nitrogen at cryogenic conditions under vacuum, and analysis is done using BET and BJH theoretical frameworks. Clients in the USA and worldwide, can get these tests conducted at Infinita Lab, using our network of testing laboratories.... Read More
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Gas Adsorption Test for Surface Area and Pore Size Analysis
Gas Adsorption using BET (after Brunauer, Emmett and Teller) and BJH (after Barrett, Joyner, and Halenda) methods is used to obtain specific surface area, pore size distribution and pore volume of adsorbents. The method is based upon analyzing the physical adsorption and desorption isotherms of a suitable gas in monolayer and multilayer adsorption regions. The most common gas used is Nitrogen though Argon or Krypton may be used, in case more sensitive measurements are needed.
The experiment is commenced by completely removing contamination from the active site by applying heat and vacuum. The adsorbent is placed in an analysis tube under vacuum and cooled to the temperature of liquid nitrogen (77 K). Nitrogen gas is charged to the solid in controlled increments, starting from low pressures. After each increment, the system is allowed to reach steady state and the volume of adsorbed gas is measured. Pressure increments and equilibrium measurements are continued till the saturation pressure is reached and adsorption ceases. An isotherm is plotted showing volume uptake versus relative pressure (ratio of actual to saturation pressures). The low pressure region corresponds to monolayer adsorption while the higher pressure regions show a steep rise in uptake and represent multilayer adsorption. The monolayer segment of the isotherm is used to determine the surface area by the BET method. The BET equation provides a theoretical relationship between volume of adsorbed gas, volume of gas required to form a monolayer and the system pressure. Using the measurements of adsorbed volume in the monolayer segment, the BET surface area can be calculated, knowing Nitrogen molecular size and the BET monolayer volume. The actual surface area correlates very well with the BET surface area.
The BJH method is a procedure for calculating pore volumes and pore size distributions from experimental isotherms, using the Kelvin equation. It applies only to the mesopore and small macropore size range. The Kelvin equation provides a correlation between pore diameter and pore condensation pressure.
To determine the BJH pore volume and pore size distribution, the Nitrogen pressure is increased incrementally followed by measurement of adsorbed volume, in the multilayer adsorption region. At higher relative pressures, capillary condensation occurs and the pores get filled with liquid Nitrogen. The process is then reversed by reducing the relative pressure and measuring desorption equilibria. The adsorption and desorption curves may not coincide and this is termed hysteresis. For mesopores (2 nm to 50 nm diameter), the pressure where the condensation occurs depends on the pore diameter. The pore size distribution is calculated from the desorption isotherm.
Common Uses of BET Surface Area and BJH Pore Size Analysis
Design of separation processes
Characterization of solid porous adsorbents
Characterization and development of nanoscale materials
Development of advanced batteries
Characterization of heterogeneous catalysts
Advantages of BET Surface Area and BJH Pore Size Analysis
It is a non-destructive test
Data on surface area and on pore volumes and distribution can be obtained in the same experiment.
Limitations of BET Surface Area and BJH Pore Size Analysis
Closed pores are not accessible via the material surface and cannot be assessed by this technique
Applicable to Physical adsorption only
Industrial Applications of BET Surface Area and BJH Pore Size Analysis
ASTM E572 test method covers the analysis of stainless and alloy steels by Wavelength Dispersive X-ray Fluorescence Spectrometry (WDXRF). It provides rapid, multi-element determinations with sufficient accuracy to assure product quality.
The ASTM D2674 is a standard test method for the analysis of sulfochromate etches solution used in the surface preparation of aluminum. The ASTM D2674 standard specifies a method for determining the efficacy of an etchant used to prepare the surface of aluminum alloys for subsequent adhesive bonding.
An immunological method for quantization of Hevea Natural Rubber (HNRL) proteins using rabbit anti-HNRL serum. Rabbits immunized with HNRL proteins react to the majority of the proteins present, and their sera have the capability to detect most if not all the proteins in HNRL.
ASTM G65 measures the resistance of metallic materials to abrasion using the dry sand/rubber wheel apparatus. The quality, durability, and toughness of the sample are determined using this test. Metallic materials are ranked in their resistance to scratching abrasion under a controlled environment.
ASTM E2141 test methods provide accelerated aging and monitoring of the performance of time-dependent electrochromic devices (ECD) integrated in insulating glass units (IGU). This test helps to understand the relative serviceability of electrochromic glazings applied on ECD.
ASTM C724 test method is used in analyzing the quality and ease of maintenance of a ceramic decoration on architectural-type glass. This test method is useful in the acknowledgment of technical standards.
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