Formation of Oxide Phases in the System Pr-Fe-O

The formation of oxide phases at 900 °C in the system Fe2O3-“Pr2O3” was investigated. With a decrease in the molar fraction of Fe2O3 a corresponding increase in PrFeO3 was observed. For equal molar fractions of Fe2O3 and “Pr2O3” the formation of PrFeO3 and very small fractions of α-Fe2O3 plus an addi¬tional oxide phase, which could not be identified with certainty, were observed. With further increase in “Pr2O3” fraction the praseodymium oxides Pr6O11 and PrO2 started to become dominant in the phase com¬position. The small fraction (< 0.02) of the same unidentified oxide phase was also obtained when Pr(OH)3 was calcined in air at 900 °C; this was probably a mixture of other praseodymium oxides with different average oxidation numbers of Pr. The results of XRD, 57Fe Mössbauer and FT-IR spectroscopies are discussed. (doi: 10.5562/cca2247

57Fe mössbauer, XRD, FT-IR, FE SEM analyses of natural goethite, hematite and siderite

Natural goethite, hematite and siderite were analysed with 57Fe Mössbauer, XRD and FT-IR. FE SEM images of samples were also taken. The Mössbauer spectra of limonite (α-FeOOH · nH2O) from Budapest (Hungary), Ljubija (Bosnia and Herzegovina) and Korçё (Albania) showed the same type of spectrum, indicating low crystallinity and broad particle size distribution. All goethite particles from these three locations were one-dimensional (1D), but with different nano/microstructures. A very early precursor of limonite from Budapest and Ljubija locations was assigned to FeS2 (pyrite and/or marcasite) which oxidised upon ventilation (oxygenation) under hydrogeothermal conditions, thus producing FeSO4 and Fe2(SO4)3. In the next step limonite deposits were formed. The similarity between this limonite formation under hydrogeothermal conditions and the chemical precipitation of goethite from FeSO4 or Fe2(SO4)3 solutions at laboratory level was briefly discussed. The deposition of lateritic goethite at the Korçë location is presumed to be due to the chemical weathering (tropical conditions) of ultramafic rocks. Under the same conditions and a proper pH the transformation of goethite to hematite is possible. Alternatively, the oxidation of Fe2+ in magnetite and its transformation to hematite via maghemite (γ-Fe2O3) as an intermediate could have taken place. The Mössbauer spectrum of siderite from the Ljubija location showed a quadrupole doublet with asymmetric spectral lines. This asymmetry could be assigned to the Goldanskii-Karyagin effect, however, the contribution of the crystallite texture to this asymmetry cannot be excluded. Hematite and a small fraction of siderite at the Vareš location (Bosnia-Herzegovina) are of metasomatic origin deposited in limestone that now form a series of greatly metamorphosed sedimentary rocks. Hematite particles were deposited in the form of laminates (2D)

Formation of Oxide Phases in the System Eu2O3 - Fe2O3

Evolution of oxide phases in the Eu2O3-Fe2O3 system was investigated by X-ray powder diffraction, 57Fe and 151Eu Mössbauer spectroscopy and Fourier transform infrared spectroscopy. Samples were prepared by the solid state reaction of the corresponding oxides for two molar ratios, Eu2O3 : Fe2O3 = 1:1 and 3:5. After heating the mixed oxide powder with molar ratio Eu2O3 : Fe2O3 = 1 : 1 up to 900 °C, EuFeO3 and traces of Eu2O3 were detected by XRD, while after additional heating up to 1100 °C traces of Eu3Fe5O12 (EuIG) were also detected. 57Fe and 151Eu Mössbauer spectroscopy showed the presence of EuFeO3. For the molar ratio Eu2O3 : Fe2O3 = 3 : 5, EuIG was formed between 1100 and 1300 °C. In the sample produced at 1300 °C, the measured hyperfine fields at the iron sites, at room temperature, were Ha = 495 and Hd = 402 kOe, and the hyperfine fields at the europium sites, at 90 K, were HI = 631 kOe and HII = 572 kOe. Europium orthoferrite was the intermediate phase in the garnet formation. Assignations of IR bands corresponding to EuFeO3 and EuIG are discussed. Mechanical activation of the mixed oxide powder was important for the formation of polycrystalline EuIG, as a single phase

The Effect of Gum Arabic on the Nano / Microstructure and Optical Properties of Precipitated ZnO

The development of the nano/microstructure of ZnO particles precipitated from zinc acetylacetonate showed dependence on the presence of gum arabic. In the absence of gum arabic in near-neutral pH range ZnO rods, some of them hollow, precipitated, whereas in alkaline (NH4OH) medium the multipods (stars) were obtained. A strong effect of gum arabic was noticed both in the near-neutral pH range and in alkaline (NH4OH) medium. In both cases ZnO particles consisted of 1D subunits. The FT-IR spectra of ZnO particles precipitated in the presence of gum arabic showed the IR bands due to the residual content of this biopolymer. Gum arabic formed the corona on ZnO particles and played a key role in the precipitation process from nucleation to the final ZnO product. UV/Vis spectra were also recorded. The PL spectra of ZnO powders dispersed in pure ethanol were very similar. In the presence of ethanol characteristic peaks in the blue emission region were diminishing, thus softening the intrinsic defects responsible for this emission. It was assumed that this effect was due to the covering of oxygen vacancies (VO) at the interface ZnO/C2H5OH with the oxygen atoms present in ethanol. This work is licensed under a Creative Commons Attribution 4.0 International License

Formation of Iron Oxides by Surface Oxidation of Iron Plate

Oxidation of iron plates (α-phase) at high temperatures and in atmospheric conditions was monitored. The composition of oxidation products was analyzed with XRD, Raman and Mössbauer spectros-copies, whereas the morphologies of oxidation products were inspected by FE-SEM. The oxidation products formed at 300 and 400 °C consisted dominantly of magnetite and small fractions of hematite, whereas at 500 and 600 °C hematite was the dominant phase, as shown by XRD. In all these samples Raman spectra showed the presence of hematite in the outer oxidation layer. FE-SEM analysis showed the formation of nanowires at 500 °C and vertically grown hematite spikes against the lower oxidation layers at 600 °C. Oxidation products formed at 800 °C consisted of wüstite (Fe1–xO) as the dominant phase, nonstoichiometric magnetite (Fe3–xO4) and hematite (α-Fe2O3) in small fractions. The surface of these oxidation layers showed a hierarchical microstructure, as well as the hexagonal hematite rods vertically grown against the lower oxidation layers. The formation of the oxidation products can be considered a process which includes the oxidation of α-Fe to Fe1–xO and its transformation to Fe3–xO4 that further transforms to α-Fe2O3, probably via a short-lived γ-Fe2O3 (maghemite) phase. (doi: 10.5562/cca1943