Amorphe und kristallisierte Oxydhydrate und Oxyde. XLIV. Die Umwandlung des röntgenographisch amorphen Eisen III‐hydroxyds in γ‐Fe₂O₃

Abstract

1. Das mit kochender 1 n‐NaOH behandelte röntgenographisch amorphe Eisen III‐hydroxyd (Orthohydroxydgel) geht in Polyorthohydroxyd über, welches ebenfalls amorph, jedoch alterungsunfähig und schwach ferromagnetisch ist.

Hydrothermal Synthesis of Delafossite-Type Oxides

“…Similar to the original reported syntheses of AgFeO 2 by Krause, polycrystalline CuCoO 2 and AgCoO 2 have been reported for a reaction between the monovalent oxide and CoOOH in boiling NaOH solution . The CuCoO 2 and AgCoO 2 generated from these reactions were not sufficiently crystalline enough to be indexed by PXD and also contained Co 3 O 4 .…”

“…Transition Metals Oxides. The original hydrothermal syntheses of delafossite-type oxides involved the production of the mineral delafossite (CuFeO 2 ) by Emons 59 and its silver analogue (AgFeO 2 ) by Krause . Subsequently, Shannon, Rogers, and Prewitt generated both CuBO 2 (B = Cr, Co, and Rh) and AgBO 2 (B = Cr, Co, and Rh) delafossite-type oxides at higher temperatures and pressures .…”

“…To a certain degree, the difficulty normally encountered in the synthesis of mixed metal oxides of palladium, platinum, and silver, specifically the delafossite-type oxides, has been overcome using low-temperature and/or closed reaction systems. For example, the first polycrystalline silver delafossite-type oxide, silver ferrate (AgFeO 2 ), was prepared at low temperatures (100 °C) by Krause from the combination of a “meta-ferric hydroxide gel” (γ-FeOOH) and Ag 2 O in a boiling NaOH solution . To prepare small single crystals, Croft, Tombs, and England employed thin-walled platinum tubes at higher temperatures (400 °C) and pressures (2700 atm) to synthesize AgFeO 2 from Ag 2 O and Fe 2 O 3 and therefore took advantage of a closed system (hydrothermal conditions) to prevent decomposition of the Ag 2 O .…”

Relationship between morphological and physical properties in nanostructured CuMnO2

“…In this article, we report the synthesis of nanostructured CuMnO 2 samples using a hydrothermal method employed in previous studies, e.g. as described by Krause and Gawryck many years ago [29], and reported in the literature for synthesis of delafossites [15,28,30,31]. Because, the reaction between (OH) and Mn + plays an important role in the formation of MnO octahedron, we use several amounts of NaOH mineralizator, i.e., 1g, 2g and 3g per 35 ml of solution, to turn the reaction rates and the degree of nucleation.…”

Synthesis and characterization of AgFeO2 delafossite with non-stoichiometric silver concentration

“…Among methods of producing silver delafossite materials, it may be distinguished as: (1) low-temperature methods (e.g., hydrothermal synthesis, metathetical reaction, oxidizing fl ux reaction, sol-gel) [10][11][12][13][14], (2) high-temperature synthesis (e.g., solid-state reaction [15][16][17][18][19]) and (3) thin fi lm techniques (e.g., atomic layer deposition, pulsed laser deposition (PLD), chemical vapour deposition (CVD), RF sputtering [6,[20][21][22]). However, they do not always allow obtaining compounds of high purity.…”