3089.     SCHLEEDE, A., RICHTER, M., AND SCHMIDT, W.  [Zinc Oxide as a Catalyst.]  Ztschr. anorg. Chem., vol. 223, 1935, pp. 49-83; Chem. Abs., vol. 29, 1935, p. 6827.

        ZnO prepared by the thermal decomposition of Zn(NO₃)₂ at 360° luminesces oranged-red when excited by ultraviolet light or X-rays; and it does not catalyze the decomposition of MeOH at 360°.  The luminescence is caused by the presence of twinning planes or boundary surfaces formed by the crystallizing together from the nitrate melt of crystallites into compact particles of ZnO.  The lack of catalytic action is due to the compact nature of the product.  On the other hand, ZnO prepared by the thermal decomposition of hydrated Zn(OH)₂ or ZnCO₃ at 360° does not luminesce, but it is a very active catalyst for the MeOH decomposition.  Inasmuch as this ZnO was not crystallized from a melt, it lacks the twinning planes that cause fluorescence, whereas its noncompact porous character favors catalytic action.  Extreme purity of the initial substances used in preparing the ZnO is not a factor involved in these differences in behavior.  The properties of ZnO prepared by other methods may lie between these 2 extreme cases.  The luminescence of ZnO may e used analytically as an indication of the method of its preparation.  The crystalline structure, size of the crystallites, and surface development of several differently prepared samples of ZnO were studied by means of Debye and Scherrer structure diagrams, by weighing and microcounting, by the determination of the degree of packing when jolted, by precipitation velocities, and by the adsorption of CO₂ and N₂.