AN INVESTIGATION OF THE USE OF RADIOACTIVE ISOTOPES FOR DETERMINING THE SURFACE AREA OF POWDERED MATERIALS BY SORPTION METHODS

摘要

A technique was developed for accurate surface area determinations, particularly for relatively low-surface materials, by radioassay of sorbed fatty acids labeled with carbon-14;it consists of the following steps: (l) weigh approximately one gram of oven-dried powder into a sample jar or flask;(2) vacuum dry 3 hours or longer;(3) cool sample, add 10 ml of radiostearic acid-benzene solution (7 to 8 grams per liter;0.1 to 0.2 millicurie per gram of acid) and shake vigorously;(4) let sample equi¬librate in water bath one hour at 15 C, with occasional shaking;(5) decant the solution into a centrifuge tube, stopper, and centrifuge briefly;(6) decant to another tube, stopper, and let solution reach room tempera¬ture before plating;(7) pipette 0.1-ml aliquots of this solution and of original solution to chilled, 25-mm watch glasses and place in refrigerator for slow solvent evaporation;and (8) count plates with a thin end-window Geiger counter and correct counts for self-absorption. The surface area is then calculated from the equation given below.