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

An automated apparatus for the characterization of the surface area, pore s ize distribution, and density of powdered materials is described. A newly d eveloped liquid nitrogen level control system maintains the nitrogen level around the tube containing the sample within +/-0.2 mm of the initial prede fined level. The dosing volume and pneumatically operated control valves ar e maintained at 25.00 +/-0.05 degreesC. Equilibrium pressure is measured wi th the accuracy of +/-0.05% of reading. The apparatus may be operated eithe r in a manual or an automatic mode. The control software developed, using t he VISIDAQ Version 3.11 software package, operates involving equilibrium an d barometric pressure measurements, opening and closing pneumatically opera ted valves, and transferring experimental data to MS <emph EXCEL spreadshee ts. The subroutines developed within the spreadsheet program plot the adsor ption and desorption isotherms, calculate the sample specific surface area and density, and provide <alpha>(s)- 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 su rface reference materials. These included garnet, kaolinite, and carbon bla ck with quoted multiple-point surface areas of 3.00 +/-0.30, 16.45 +/-0.8, and 113 +/-5 m(2)/g. Our values were 2.84 +/-0.28, 16.02 +/-0.8, and 110 +/ -5 m(2)/g. Specific surface areas as low as 0.2 m(2)/g have been reproducib ly measured using this apparatus. Results of nitrogen adsorption on activat ed carbon B1 together with specific surface area determination, evaluation of alpha -plot, and micro-, and mesopore size distributions are reported. A utomatic pressure and flow controllers allow adsorption and desorption isot herm definition either in continuous or in conventional static flow volumet ric modes. (C) 2001 American Institute of Physics.