Development of an automated gas adsorption apparatus for the characterization of the surface area, pore size distribution, and density of powdered materials

Abstract

An automated apparatus for the characterization of the surface area, pore size distribution, and density of powdered materials is described. A newly developed liquid nitrogen level control system maintains the nitrogen level around the tube containing the sample within ±0.2 mm of the initial predefined level. The dosing volume and pneumatically operated control valves are maintained at 25.00±0.05 °C. Equilibrium pressure is measured with the accuracy of ±0.05% of reading. The apparatus may be operated either in a manual or an automatic mode. The control software developed, using the VISIDAQ Version 3.11 software package, operates involving equilibrium and barometric pressure measurements, opening and closing pneumatically operated valves, and transferring experimental data to MS EXCEL spreadsheets. The subroutines developed within the spreadsheet program plot the adsorption and desorption isotherms, calculate the sample specific surface area and density, and provide αs- and t-plots and mesopore and micropore size distributions. Specific surface areas were defined using the Brunauer–Emmett–Teller method of analysis. The apparatus accuracy was tested via surface reference materials. These included garnet, kaolinite, and carbon black with quoted multiple-point surface areas of 3.00±0.30, 16.45±0.8, and 113±5 m2/g. Our values were 2.84±0.28, 16.02±0.8, and 110±5 m2/g. Specific surface areas as low as 0.2 m2/g have been reproducibly measured using this apparatus. Results of nitrogen adsorption on activated carbon B1 together with specific surface area determination, evaluation of α-plot, and micro-, and mesopore size distributions are reported. Automatic pressure and flow controllers allow adsorption and desorption isotherm definition either in continuous or in conventional static flow volumetric modes.