Oxide and Hydroxide Systems with Poorly Crystalline Phases

Metal Oxide and Hydroxide Systems with Poorly Crystalline Phases 

Metal oxide and hydroxide systems serve many functions, including roles as pigments, in mineralogy, and also in catalysis. The classic techniques used in such investigations have included diffraction (especially X-ray diffraction XRD), thermal analysis, transmission electron microscopy, Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy (see also Chapters 2 and 4). Until the introduction of voltammetry in the analysis of immobilized microparticles, electrochemical studies had been confined to solid electrolyte cells (Chapter 12), normally functioning at elevated temperatures. Unfortunately, these studies proved to be inapplicable for analytical characterization, and consequently a series of systematic studies was undertaken using immobilized microparticles of iron oxides and oxide-hydrates (for reviews, see 

Following the application of aqueous electrolyte solutions, the major potential of electrochemical studies became more clear, in that  

Kovanda et al. [67] have employed not only the voltammetry of immobilized microparticles but also several solid-state analytical techniques when studying the thermal behavior of a layered Ni-Mn double hydroxide. The important advantage of these electrochemical experiments was that they proved the presence of substantial amounts of amorphous compounds. Moreover, distinct signals could be identified for the reductive dissolution of the different phases. 

In another study, Grygar et al. [68] investigated the formation of mixed Cu-Mn, Cu-Mn-Al, Cu-Mg-Mn, and Cu-Mg-Mn-Al oxides by the calcination of amorphous basic carbonates, or by the calcination of hydrotalcite-like precursors. A combination of XRD and electrochemical measurements (again reductive dissolutions in aqueous electrolytes) led to the crystalline and amorphous phases being identified, and their formation during the thermal treatment elucidated. 

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