1233.    GRAUE, G., AND KOCH, H. W.  [Diffusion of Gases in Solids, Studies on Iron Oxide and Iron Aluminum Oxide.]  Ber. Deut. Chem. Gesell., vol. 73, B, 1940, pp. 984-995; Chem. Abs., vol. 35, 1941, p. 3151.

       Atomic pores of highly dispersed materials remain accessible by the addition of certain substances.  Effect of Al₂O₃ (A) was studied on increasing the accessibility to gases of the inner surface of röntgenographically amorphous Al₂O₃-Fe₂O₃ (AF) catalysts obtained by precipitation at 20°.  The porosity was determined by the Hahn built-in radioactive-substance emanation method.  On heating (AF) the atomic diffusion pores decrease to nearly zero at 600°; for pure Fe₂O₃ (F) corresponding parts of the curve lie about 100° lower.  The density of Fe₂O₃ increases on heat treatment from 3.7 and 3.3 at 250° and 4.9 and 4.4 at 450° to 5.1 and 5.1 above 600° as measured by the emanation and the xylene-20°-pycnometric methods, respectively.  Although pure (F) rapidly ages to a maximum density of 5.1 when heated at 450°, the (AF) catalysts age only slowly and still show differences in density as measured by the 2 methods.  The absolute rate of diffusion of gases in (AF) as measured by the emanation method is greater than in (F), and increases again at high temperatures, but the Tammann position-exchange temperature is about 820° for the (AF) and only 620° for (F) catalysts.  Above 600° for (F) and 700° for (AF) diffusion into the lattice leads to abnormally high values of the density which are not observed by the xylene method.  Debye-Scherrer X-ray photographs give the same maximum for both, but the observed intensities of the maximum are greater for (F) than for (AF).  It is concluded that (A) is dissolved in the (F) lattice and that its addition in some way hinders the mobility of the lattice constituents until higher temperatures are reached.