Oxygen has been removed from three types of charcoal by treating them with hydrogen at 1000°. It has been shown that this results in a lowered water sorption at humidities of less than 80% for all three charcoals. The amount of oxygen so removed has been measured for one of these charcoals (coconut shell). Surface areas are substantially unchanged by the removal of oxygen. Oxidation of the surface is shown to increase the sorption of water by charcoal. It is suggested that the data are in accord with the cluster theory of Pierce and Smith.8

The modified Kozeny equation has been found to be satisfactory for the measurement of the specific surface of inorganic pigments having particle diameters of the order of 0.1 to 0.2 µ to within ±10%. These powders were too fine for visual microscope counting or standard sedimentation methods of specific surface measurement. The results obtained from experimental data were checked against those calculated from electron microscope counting for two of the powders studied and found to be in satisfactory agreement.

'I'he a d s o r p t i o~~ of nitrogen, oxygen, and argon b?. three '\cheson graphites ha-; been n~easured a t liquid nitrogen and liquid oxygen temperatures. The isotherru~ were 'Sype I1 in the B.E.T. classilication and displayed two kinds of hysteresis.The first kind was attributed to the presence of pores ill the graphite and the seco~lcl kind to illtercrystalline swelling. This paper describes an i~~vestigation of three artificial graphites m a~~u f a ctured by the Acheson Colloids Corporation. V e r~. little detailed adsorp~iol~ work has been done with graphites of this type with a view to elucidati~~g their structure. Barrer (2) has measured the adsorption of nitrogen, argoll, ar~cl hydrogen by an Acheson graphite over a considerable temperature range ancl has calculated isosteric heats from the isotherms. He found that the graphite was energetically heterogeneous to all three gases and that the heats in the case of nitrogen were unaffected by the addition of chemisorbed oxygen to the surface of the graphite. He concluded therefore that the heterogeneity was a property of the carbon structure. In the opinion of the authors, the tvealiness of this work lies in the fact that very few adsorption points were measured a t each temperature and no desorption points a t all were determined. Bartell and Dodd (4) measured the adsorption of nitrogen a t liquid nitrogen temperatures by a number of carbons which included two Acheson graphites. The purpose of the work was to measure the surface area of the carbons so that only a small number of points were determined and only i l l the case of the diamond powder were desorption points talien. I t is stated that 110 d e s o r p t i o~~ points were measured for the graphite because reversibility for nitrogen adsorption had been established a t liq~lid oxygen telnperatures. Bartell and Dodd do not indicate to what pressures these measurements were carried, but it will be shown in the present paper that reversibilitl. of the nitrogen isotherm a t 90°1<. is by no means a criterion for reversibility unless pressure measurements are extended to well over an atmosphere. Because of the lack of d a t a on these graphites, it was decided to undertake a detailed s t~~d y of three typical artificial graphites. The first step was to measure isotherms a t low temperatures using as adsorbates ~~i t r o g e n , oxygen, ancl argoll. Uliusual hysteresis effects were encou~~tered and therefore a detailed study was made on one graphite usi~ig nitrogen as the adsorbate. For comparative purposes the nitrogen isotherm of a nonporous carbon black I V~S also determined.

The pore distributions of three activated charcoals have been calculated from the low temperature nitrogen and water isotherms. The method of Barrett, Joyner, and Halenda has been used with the nitrogen data, while the Kelvin equation has been applied to the water isotherm. The two curves coincide if cos 0 = 0.65 is used in the Kelvin equation, where 8 is the wetting angle. This figure is in general agreement with a published figwe obtained by an independent method.

The modified Kozeny equation has been found to be satisfactory for the measurement of the specific surfaces of carbon blacks having average particle diameters ranging from 0.01 to 0.1 μ to within ±10%. Comparative data were obtained from electron microscope counting and from low temperature nitrogen adsorption isotherms. The three methods examined gave results that were in satisfactory agreement, except when the carbon black was porous, and then the adsorption value was extremely large.

The several modified Kozeny equations for the measurement of the specific surface of fine powders by gas-permeability methods have been compared. The equations all give very similar surface area values for a set of experimental data. The physical significance of the empirical constants used is discussed and preference is indicated.

The surface areas, as determined from X-ray diffraction and low temperature nitrogen adsorption data, were compared for a number of carbon blacks and activated charcoals. Comparative data were also obtained on samples of charcoal at various stages of activation and after calcination. The X-ray diffraction data indicated that all the samples examined were composed of small graphitelike crystallites of the same order of magnitude, which had specific surfaces of about 2500 to 3000 sq. m. per cc. The nitrogen adsorption surface of a highly activated charcoal was found to be about equal to the X-ray surface. It is suggested that the crystallite surface represents the potential adsorption surface of a carbonaceous material and, providing that crystal growth does not occur during activation, the activation process makes these surfaces available to external adsorbate.

fhe Kozeny equation for the determination of surface areas by the gaspermeability method has been modified by the introduction of a second term, which takes the form of the Knudsen flow equation. This modified equation gives consistent results for the specific surface of a granular bed of fine particles with mean pressures of the flowing gas ranging from2.6 cm, to almost atmospheric pressure. The results obtained from experimental data are in agreement with those calculated by direct visuai and electron microscope counting. Can. J. Res. Downloaded from www.nrcresearchpress.com by University of Otago on 07/12/15 For personal use only. Can. J. Res. Downloaded from www.nrcresearchpress.com by University of Otago on 07/12/15 For personal use only. Can. J. Res. Downloaded from www.nrcresearchpress.com by University of Otago on 07/12/15 For personal use only.