Ergebnisse und Probleme von Verbindungen der Systeme Oxyd‐Wasser

Abstract

Vanadinhydroxide 4. Uranhydroxyde V. Bau fester AquoxydeDie bei Verbindungen der Systeme Oxyd-Wasser erzielten neuen Ergebnisse ermoglichen eine Systematik, die das gesamte Gebiet unter Berucksichtigung d e r drei Aggregatzustande unter einem einheitlichen Gesichtspunkt zusammenfa0t. Nach der Art der Wasserbindung werden vier Haupttypen unterschieden: Hydroxyde, Oxydhydrate, Hydronium-Verbindungen und Oxydaquate. Der Stand d e r Forschung wird in den Kapiteln ,,Gasfijrmige Hydroxyde", ,,Verbindungen durch hydrothermale Synthese", ,,Niederwertige Hydroxyde der ubergangsmetalle" und ,,Aufbau von festen Aquoxyden" beschrieben. die a k Schwerpunkte der modernen Entwicklung des Gebietes angesehen werden. 111. Verbindungen durch hydrothermale Synthese 1. System A1,03-H,0 2) R. Fricke u. G. F. Huttig, Hydroxyde und Oxydhydrate. Band IX des Handbuchs der allgemeinen Chemie, herausg. v. P. Walden, Akadem. Verlagsges. m.b.H., Leipzlg 1937. 3 ) 0. Glernser, Fortschr. chem. Forsch. 2, 273 [1951]. Vgl. auch W . 0. Milfigan, J . physic. Colloid Chem. 55, 497 [1951]. 4 ) Vgi. die Arbeiten von A. Simon u. Mitarb., 2.B. 2. anorg. allg. Chem. 242, 313 [1939]; K. W. F. Kohlrausch, Ramanspektren, Verlag Akad. Verlagsges. Becker u. Erler, Leipzlg 1943. 5 ) Lit. bei 0. Glernser3). 0) Fur das bewegliche Wasser (Adsorptions-bzw. Kapillarwasser) geben dieiektrische Messungen eine qualitative Auskunft (0. Glernser, 2. Elektrochem. 44, 341 [1938]; 45, 820 [1939]).

Formation of Environmentally Persistent Free Radicals on α-Al2O3

“…However, heating can reversibly remove the hydroxyl groups on the α-Al 2 O 3 surfaces, 30 as confirmed by IR and NMR measurements. 31,32 The surface is completely dehydroxylated by heating to 450− 600 °C, 30 corresponding to the temperature window of the cooling-down zone of the combustor that typically extends between between 600 and 180 °C. 33 This means that, the reaction between alumina and phenol, in the postcombusion zone of municipal waste incinerators (MWI), involves the dehydroxylated surfaces of α-Al 2 O 3 , most notably near the higher edge of the temperature window.…”

Dissolution of water vapour in ESR-slags of the systems CaO-Al2O3and CaF2-CaO-Al2O3by application of Fourier-Transform-Infrared-Spectroscopy

“…it is worth that E,~C(H20)~P(H20) (19) and the deformation vibration band has to arise in the spectrum at 1595 cm". I[ hydroxide-ions according to reaction (1) are built up, the following relation has to be true: (20) and the deformation vibration band is not allowed to arise in the spectrum.…”

Formation of environmentally-persistent free radicals (EPFR) on α-Al2O3 clusters

“…; adsorption and decomposition) of the hydroxyl groups over alumina surface constitutes a key factor in clarifying the reactive/catalytic nature of alumina. As stated earlier, heating can reversibly remove the hydroxyl groups from the alumina surface, 16,17,25 leading to the formation of Lewis acid-base pair sites, and thus increases the catalytic activity of the surface. Along a similar line of enquiry, Ballinger and Yates 26 have performed a detailed investigation into the correlation between Al-OH group removal and the number of Lewis acid sites via CO molecular adsorption.…”

“…15 Heating and cooling processes can reversibly either add or remove hydroxyl groups from the surfaces, as conrmed experimentally by IR and NMR measurements. 16,17 For instance, X-ray diffraction data by Dyer et al 18 revealed the formation of Al(OH) 3 on the g-Al 2 O 3 surface, which disappeared aer heating to 473.15 K. This has also been conrmed by Raman and infrared spectroscopy where several sharp peaks in the region around 3600 cm À1 have been observed aer hydration of the g-Al 2 O 3 powder. X-ray photoemission experiments by Liu et al 19 pointed out to water dissociation; most likely at surface defect sites.…”