THE JOURNAL OF
PHYSICAL(a CHEMISTRY (Registered in
U.S. Patent Office)
Cop)right, IOGO, by t h e American Clieinical Soclety)
HEATS OF ,iL>SOIIPTIOS ASD ADSOIWTIOS ISOTHERMS 1:011 LOJY BOILISG GASES ADSORBED O S GlI,\PHOS B r E:. I,. PACEASD A. It. SIEBERT .\lorley Clieiiizcal Laboralcry, Western Resrrw Lnzveiaiiy, Clelelaritl, Ohio RecezLed Julg 7 , 1959
T h e results of a calorimetric investigation of the equilibrium pressures and diffrrential heats of adsorption for nitrogen argon, neon, cirthodeiiteriiim, par:thydrogen and helium (He4) adsorbed on Graphon in the neighborhood of their respective boiling prsints arc presented.
Introduction X number of recent papers hare directed attention to the fact that aiiomnlously high surface areas are obtained when the BET' multilayer theory is used with gases with very low boiling points. Schaeffer, et U Z . , ~ report a surface area with helium adsorbed on carbon black which is two t'o threefold greater t'haii t,hat obtained with nitrogen. This result :has been confirmed3 for both He3 and He4 on a,ctivated charcoal. Tykodi and Aston4 also report unexpectedly high areas for the case of neon adsorbed on titanium dioxide. The presrmt inreRtiga,tion was undertaken in part t o make a comprehensire study of the anomaly for all readily available lorn boiling gases on a surface of reasonably well-know1 structure. As a result, areas by th'e BET method have been determined from equilibrium pressures of nitrogen, argon, neon, orthodeut,erium, parahydrogen and helium (He4) adsorbed 011 the same surface a t the normal boiling point of each gas. Graphon was used as an adsorbent because it, has a high area surface endowed wit,h an uiiiisually high degree of uniformity. Since the magiiitude of the interaction of adsorbed molecules wit'h the adsorbent surface and n-it,h each oi;her is of interest, differentid heats of :i,dsorpt,ionwere measured calorimetrically aiid cor, I'. 11. I?lnnlett a n d E. Teller, J . A m . C h e m . Sor,., 60, :309 (1938). ( 2 ) TV. D. SriiaPfiiar. V;. 17. Smith a n d C. R. Kendell, ibid., 71, 861 (1940). f S ) c'. J . IlolTni:rn, 1'. .J. 1 : ~ I c ~ ~ L i ani1 i t y E. I'. I i a i n ~ n c l ,.I. Cheni.
. G.
A s t o n :mil C;. D. Schrcincr, J . A m . C h e m .
related viitli the results from the equilibrium pressure measurements. Experimental The gitsrs which 1%-ereused in the investigation w r e commercially available with purities of 99.5Y0 or greater. The helium was further purified by passage over activated charcoal a t liquid nitrogen temperatures. The hydrogm and deuterium were converted to approximately 957, parahydrogen and orthodeuterium prior to use. The calorimetric apparatus and procedure has been described previously .545 The sample of Graphon was obtained from Godfrey L. Cabot Laboratorirs, Boston, llassachusetts. The m e w rition and general characteristics of Graphon have hben given hv Schaeffer and co-\~orkrrs.' S - R a y diffr'tction measrirements condiictrd on tbe particwlar sample uscd here g:tve a c spacing oi 6 96 its compared t o 6.10 for ~true graphite. Excrntinn for one helirim isotherm at 4.2"1
