In this study, lanthanum and Co-, Ni-based oxides at different compositions were prepared by the sol-gel citrate method. Ammonium carbonate and citric acid were used as complexing agent and solvent. The oxides were characterized by scanning electron microscopy-energy-dispersive spectroscopy, X-ray diffraction, and the Brunauer-Emmett-Teller method. Surface area analysis was carried out and the effects of substitution of cobalt and nickel on the physical properties of the synthesized oxides were investigated.
Room temperature ferromagnetic properties of Zn-Mn-O show evident dependence on manganese concentration and preparation conditions. We systematically studied series of samples with manganese concentration ranging from 0 to 10 at.%, prepared in air at thermal treatment temperatures ranging from 400 to 900°C. The samples were investigated by X-ray diffraction, TEM, magnetization measurements and XPS spectroscopy. XPS analyses of surface composition, chemical bonding and XPS depth profiling were successfully employed on powder revealing the chemical composition at the surface of the grains and underneath. The study emphasizes important role of the grain surface in observed room temperature ferromagnetism. It seems that the ferromagnetic phase is correlated with oxygen build up at the surface.
Cadmium oxide nanostructures were prepared by microwave assisted wet chemical technique at different time intervals. Results on structural, optical, and thermal properties of the CdO nanostructures as a function of the microwave irradiation were reported. The X-ray diffraction data indicates that the sample showed perfection in the microstructural improvement as a function of microwave irradiation. Surface morphological changes with different time of microwave irradiation were recorded by transmission electron microscope and the particle size were found in the ranges from 5 to 30 nm. Chemical composition and thermal stability of the samples were analyzed by energy dispersive X-ray spectrum and thermogravimetric analysis, respectively. The band gaps were shifted towards the blue region due to the Moss-Burstein effect and it exhibited direct band transitions, which corresponds to optical band gaps of 3.92-4.20 eV and contrast behavior of optical properties of CdO nanostructure in UV and IR regions were registered. Room temperature photoluminescence spectra revealed that the intensity of luminescent emission tends to decrease with the increase in exposure of microwave irradiation.
Article presents results on the analysis of secondary phases formed in the medium-term static isothermal ageing welding joints of a SUPER 304H (675°C/2×10⁴ h). The investigations of the precipitates were focused on the occurrence of σ-phase because its formation leads to significant deterioration of mechanical properties. The microstructure was investigated on microscopic level by scanning/transmission electron microscopy. The distribution and quantification of brittle σ-phase were studied on macroscopic level by color etching method using light optical microscopy. The effect of microstructural changes (σ-phase formation) on the impact strength of an aged base material was investigated. For comparison impact tests on received state material were also performed. The results showed that long-term ageing led to the significant reduction of impact strength as a result of the formation of the σ-phase. It was found that the σ-phase distribution is influenced by welding process. The influence of brittle σ-phase on long-term durability of the degraded steel regarding its insufficient impact strength has been discussed.
The present transmission lines of populous cities will have to be changed with an ability to work at higher temperatures without any weight and cross section changes. Innovative thermal-resistant alloy conductors (T-ACSR) operate in the range of about 150-200°C instead of 75°C which is the standard ACSR type conductor service temperature. In this study, the manufacturing procedure of Al-Zr alloy wire, used as high-temperature conductor wires, have been introduced. The Al-Zr alloy has been cast in a permanent mold than being extruded to a diameter of 10 mm at 400°C. After that the extruded rods have been cold drawn to a diameter of 3.02 mm. Elongation and tensile strength values of the cold drawn wire have been achieved by tensile test at elevated temperatures. Also, microstructural analysis and dispersion hardening procedure have been investigated. The results show that tensile strength and thermal-resistant property are improved by the addition of Zr.
K-feldspars in pegmatites from Luc Yen gem mining area, Yen Bai province, Vietnam were studied by X-ray fluorescence, X-ray powder diffraction and the Raman spectroscopy. Chemical analysis determined the K-feldspars in the form: of (K_{0.8909}Na_{0.0388}Ca_{0.002}Pb_{0.0042}Cs_{0.0024}Rb_{0.0338})(Al_{0.9975}Fe_{0.0053}Ti_{0.0004})Si_{2.988}O₈. Both X-ray powder diffraction and Raman spectroscopy indicated Luc Yen K-feldspars as orthoclase phase. Together with the values of Al content of the T1 tetrahedral sites in orthoclase, it is understood that Luc Yen pegmatites are of young ages (Cenozoic) and shallow intrusive types.
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