ZnO, Zn(OH)2, Zn5(OH)8Cl2·H2O, ZnCO3, and Zn5(CO3)2(OH)6 synthetic powders were prepared by chemical or solid-state method. Their crystalline phase structure, thermal behavior, and morphology were examined. Characteristic infrared absorbance bands were estimated by means of FT-IR ATR spectroscopy. X-ray photoelectron spectroscopy (XPS) allowed to calculate the modified Auger parameters (α ′) thereof to 2010.2, 2009.3, 2009.4, 2009.7, and 2009.8 eV, respectively for ZnO, Zn(OH)2, Zn5(OH)8Cl2·H2O, ZnCO3, and Zn5(CO3)2(OH)6. Finally, comparison of surface composition may be crucial to evaluation of the unknown experimental spectra of corrosion products formed on the surface of zinc alloy coatings exposed in NaCl solution.
Mn-Zn ferrites were obtained by the sol-gel autocombustion methods. The effect of the precursor used in the sol-gel autocombustion synthesis on the ferrite's microstructure was examined. The as-obtained powders were characterized by XRD, FTIR, SEM, and TG/DTA. All ferrite powders obtained from different organic precursors, after gel autocombustion, were pure spinel phase, without secondary phases. The average crystallite size, estimated from Scherrer equation, was the smallest for ferrite obtained from a mixture of fuels/precursors (citric acid and EDTA). This ferrite powder has sponge-like microstructure with large pores, but it is less agglomerated than the material obtained from glycine as the fuel.
Manganese−zinc ferrites were obtained through combined coprecipitation and sol−gel autocombustion methods. The effect of the precursor used in the sol−gel autocombustion synthesis on the ferrite's structural and catalytic properties was examined. The ferrite powders were characterized by XRD, BET, SEM, TG/DTA, and TPR-H 2 , and their acidic−basic properties were determined using cyclohexanol and the TPD-NH 3 test. The ferrite powder obtained from the hydroxide precursor (SC1-OH) has a larger specific surface area (16.41 m 2 /g), a larger crystallite size (35.6 nm), and a more heterogonous structure, which make it a more active catalyst. This is also achieved because of the existence of both acidic and basic centers on its surface. The ferrite obtained from the oxalate precursor (SC2-C2O4) has smaller (29.6 nm) but more aggregated particles. As a catalyst, it is more selective to dehydrogenation, which is related to its higher reducibility. The SC2-C2O4 sample also exhibits higher selectivity to ketone, and it is a much more efficient catalyst at higher temperatures.
Cerium molybdenum oxide hydrate microflakes are codeposited with nickel from a deep eutectic solvent-based bath. During seven days of exposure in 0.05 M NaCl solution, the corrosion resistance of composite coating (Ni/CeMoOxide) is slightly reduced, due to the existence of some microcracks caused by large microflakes. Multielemental analysis of the solution, in which coatings are exposed and the qualitative changes in the surface chemistry (XPS) show selective etching molybdenum from microflakes. The amount of various molybdenum species within the surface of coating nearly completely disappear, due to the corrosion process. Significant amounts of Ce3+ compounds are removed, however the corrosion process is less selective towards the cerium, and the overall cerium chemistry remains unchanged. Initially, blank Ni coatings are covered by NiO and Ni(OH)2 in an atomic ratio of 1:2. After exposure, the amount of Ni(OH)2 increases in relation to NiO (ratio 1:3). For the composite coating, the atomic ratios of both forms of nickel vary from 1:0.8 to 1:1.3. Despite achieving lower corrosion resistance of the composite coating, the applied concept of using micro-flakes, whose skeleton is a system of Ce(III) species and active form are molybdate ions, may be interesting for applications in materials with potential self-healing properties.
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