Platinum–Vanadium Oxide Nanotube Hybrids

The present contribution reports on the features of platinum-based systems supported on vanadium oxide nanotubes. The synthesis of nanotubes was carried out using a commercial vanadium pentoxide via hydrothermal route. The nanostructured hybrid materials were prepared by wet impregnation using two different platinum precursors. The formation of platinum nanoparticles was evaluated by applying distinct reduction procedures. All nanostructured samples were essentially analysed by X-ray diffraction and transmission electron microscopy. After reduction, transmission electron microscopy also made it possible to estimate particle size distribution and mean diameter calculations. It could be seen that all reduction procedures did not affect the nanostructure of the supports and that the formation of metallic nanoparticles is quite efficient with an indistinct distribution along the nanotubes. Nevertheless, the reduction procedure determined the diameter, dispersion and shape of the metallic particles. It could be concluded that the use of H2PtCl6 is more suitable and that the use of hydrogen as reducing agent leads to a nanomaterial with unagglomerated round-shaped metallic particles with mean size of 6–7 nm

Self Assembly and Properties of C:WO3 Nano-Platelets and C:VO2/V2O5 Triangular Capsules Produced by Laser Solution Photolysis

Laser photolysis of WCl6 in ethanol and a specific mixture of V2O5 and VCl3 in ethanol lead to carbon modified vanadium and tungsten oxides with interesting properties. The presence of graphene’s aromatic rings (from the vibrational frequency of 1,600 cm−1) together with C–C bonding of carbon (from the Raman shift of 1,124 cm−1) present unique optical, vibrational, electronic and structural properties of the intended tungsten trioxide and vanadium dioxide materials. The morphology of these samples shows nano-platelets in WOx samples and, in VOx samples, encapsulated spherical quantum dots in conjunction with fullerenes of VOx. Conductivity studies revealed that the VO2/V2O5 nanostructures are more sensitive to Cl than to the presence of ethanol, whereas the C:WO3 nano-platelets are more sensitive to ethanol than atomic C

Synthesis and properties of willemite Zn2SiO4, and M2+: Zn2SiO4 (M = Co and Ni)

Fine particles of willemite, alpha -Zn2SiO4, were prepared by both solution combustion and sol-gel methods. Both processes yield single-phase, large-surface area (26- and 78-m(2)/g), sinteractive willemite powders. Thermal evolution of crystalline phases was studied using X-ray powder diffraction patterns. The combustion method favors low-temperature formation of willemite compared to the sol-gel method. The powders, when uniaxially pressed and sintered at 1300 degreesC, achieved 78-80% theoretical density. The microstructures of the sintered body show the presence of equiaxed 0.5- to 4-mum grains. Blue pigments of willemite doped with Co2+ and Ni2+ were also prepared by the combustion process

Combustion synthesis, characterization, sintering and microstructure of mullite-cordierite composites

Mullite and cordierite are promising materials for electronic packaging due to their dielectric constant and coefficient of thermal expansion being lower than that alumina [1-5]. Recent advances in very large scale integrated circuits (VLSI) have led to materials with low dielectric constant and thermal expansion tailored over a wide range. Cordierite- dispersed-mullite composites allow a selection of materials with a wide range of values of dielectric constant and thermal expansion [6]. Mullite/ cordierite composites have been prepared by the sol-gel method using metal alkoxides [7] or by the use of composite sols [8, 9]. Such composites have aslo been prepared by solid state mixing of mullite and cordierite in the desired ratio [10]

Mullite-zirconia composites

Mullite-zirconia composite powders were prepared by the combustion of an aqueous heterogeneous redox mixture consisting of Al(NO3)(3), Zr(NO3)(4)/ZrO(NO3)(2), silica fume and urea/diformyl hydrazine at 500 degrees C. X-ray diffraction data showed that a large amount of tetragonal zirconia existed in the composite powders in spite of high temperature calcination. Milled composite powders showed enhanced densification compared to the unmilled powders and the microstructure of the sintered (1600 degrees C) compacts showed the presence of spherical zirconia grains in intergranular positions along with elongated mullite grains

Combustion synthesis and properties of mullite-zirconia composites

Mullite-zirconia composite powders were prepared by the combustion of an aqueous heterogeneous redox mixture consisting of $AI(NO_3)_3, Zr(NO_3)_4/ZrO(NO_3)_2$, silica fume and urea/diformyl hydrazine at $500^o C$. X-ray diffraction data showed that a large amount of tetragonal zirconia existed in the composite powders in spite of high temperature calcination. Milled composite powders showed enhanced densification compared to the unmilled powders and the microstructure of the sintered $(1600^o)$ compacts showed the presence of spherical zirconia grains in intergranular positions along with elongated mullite grains

Studies on nanocrystalline La1-x CaxMnO3 (0.0 \leq x \leq 0.5) manganites

Nanocrystalline CMR materials La1-x Ca xMnO3 (0.0 \leq x \leq 0.5) have been prepared by a low temperature solution combustion (LCS) method. Powder X-ray diffraction patterns of the as made phase – pure powders reveals that undoped and doped manganites are cubic in phase. The stabilization of cubic phases in doped La-manganites is due to substitution of Ca2+ in La3+ sites, resulting in higher Mn4+ content . The Mn4+ present in the samples was determined by iodometric titration as function of calcium doping. The homogeneity, microstructure and particle size of the compounds were examined by SEM. Both undoped and doped lanthanum manganites show two active IR vibrational modes at 400 and 600 cm-1. Metal – insulator transition temperature (TM-I) is observed in the range 235-117 K for calcium doped samples. These values are low compared to the samples prepared by ceramic route. This difference in transition temperature may be due to smaller particle size in the range 30-50 nm

EPR Study of Fe3+Fe^{3+}- and Ni2+Ni^{2+}-Doped Macroporous CaSiO3CaSiO_3 Ceramics

Thermally stable macroporous $CaSiO_3$, $Fe^{3+}-$ and $Ni^{2+}-$doped (0.5 to 5 mol%) ceramics have been prepared by solution combustion process by mixing respective metal nitrates (oxidizers), fumed silica. Diformol hydrazine is used as a fuel. The combustion products were identified by their X-ray diffraction and thermal gravimetry/differential thermal analysis. Single phases of \beta-$CaSiO_3$ and \alpha-$CaSiO_3$ were observed at 950 and 1200 °C, respectively. The phase transition temperatures of combustion-derived $CaSiO_3$ were found to be lower compared to those obtained via solid-state reaction method. It is interesting to note that with an increase in the calcination temperature the samples become more porous with an increase in the pore diameter from 0.2 to 8 \mu m. The electron paramagnetic resonance (EPR) spectrum of $Fe^{3+}$ ions in $CaSiO_3$ exhibits a weak signal at g = 4.20 ± 0.1 followed by an intense signal at g = 2.0 ± 0.1. The signal at g = 4.20 is ascribed to isolated $Fe^{3+}$ ions at rhombic site. The signal at g = 2.0 is due to $Fe^{3+}$ coupled together with dipolar interaction. In $Ni^{2+}$-doped $CaSiO_3$ ceramics the EPR spectrum exhibits a symmetric absorption at g = 2.23 ± 0.1. This deviation from the free electron g-value is ascribed to octahedrally coordinated $Ni^{2+}$ ions with moderately high spin–orbit coupling. The number of spins participating in resonance and the paramagnetic susceptibilities have been evaluated from EPR data as a function of $Fe^{3+}$ as well as $Ni^{2+}$ content. The effect of alkali ions (Li, Na and K) on the EPR spectra of these ceramics has also been studied

Vanadium oxide nanorings: Facile synthesis, formation mechanism and electrochemical properties

This paper describes the hydrothermal synthesis of vanadium oxide nanorings and nanobelts from aqueous precursors without using any template. These nanorings are formed via the acidification of sodium metavanadate solution. A simple ion intercalation/de-intercalation process occurs under mild hydrothermal conditions leading to the self-rolling of exfoliated vanadium oxide nanobelts. The structure and morphology of the products are characterized by XRD, SEM, TEM and charge-discharge measurement. XRD pattern reveals that the products consist of V2O5 nanorings and Na0.3V2O5 nanobelts evidenced by SEAD pattern and EDS. Highly magnified TEM images exhibit nanorings made of nanoribbons of width about 300 nm and thickness of about 60 nm. Electrochemical analyses revealed that the V2O5 nanorings/nanobelts delivers an initial lithium-ion intercalation capacity of 280 mAh(-1) and reaches a stabilized capacity of 200 mAh g(-1) at a current density of 100 mAg(-1). (C) 2016 Elsevier Ltd. All rights reserved

Electron Paramagnetic Resonance studies of Mn2+ activated willemite phosphor

Manganese activated willemite phosphor (Zn2-xMnxSiO4) (0.1\leq x \leq 0.5) have been synthesized by a novel low-temperature initiated, self-propagating, gas producing combustion process. The crystal structure and lattice parameters calculated form XRD confirm that Zn2-xMnxSiO4 has a rhombohedral structure (space group R3H). The DTA shows a small broad exothermic peak at 910 degree C can be attributed to the conversion of \beta-willemite to \alpha-willemite phase. The EPR spectra of Mn2+ ions exhibit a sextet hyperfine structure centered around g \cong 2.02 with a total peak width of \cong 490 G. The hyperfine splitting (A) for Mn2+ indicates that the Mn2+ is in an ionic environment. The number of spins participating in resonance (N) and the calculated paramagnetic susceptibility increases with x. The Mn ions in doped Zn2SiO4 also have 4-coordination because they replace some of the Zn2+ ions in the lattice