Mechanical Engineering

ABSTRACT Gadolinia-doped ceria (Ce0.9Gd0.1O1.95, GDC) electrolyte was fabricated by aqueous-based tape casting method for solid oxide fuel cells (SOFCs). The ceramic powder prepared by combustion synthesis was used with poly acrylic acid (PAA), poly vinyl alcohol (PVA), poly ethylene glycol (PEG), Octanol, 2,4,7,9- tetramethyl-5-decyne-4,7-diol ethoxylate and double distilled water as dispersant, binder, plasticizer, defoamer, surfactant and solvent respectively, to prepare stable GDC slurry. The conditions for preparing stable GDC slurries were studied and optimized by sedimentation, zeta potential and viscosity measurements. Green tapes with smooth surface, flexibility, thickness in the range of 0.35e0.4 mm and 45% relative green density were prepared. Conventional and flash sintering techniques were used and compared for densification which demonstrated the possibility of surpassing sintering at high temperatures and retarding related grain growth.

ABSTRACT The impression creep behavior of the aging-treated Cu–6Ni–2Mn–2Sn–2Al alloy and its variants with separate additions of 0.3 wt.% Cr and 0.3 wt.% Zr was investigated in the temperature range 695–795 K and under constant punch stress in the range 300–900 MPa. It was shown that simple theory, based on a steady-state power-law creep equation, has the capacity to describe the impression creep data satisfactorily. The average stress exponents of about 4 together with the activation energies of 194–196.9 kJ mol−1, which are close to 197 kJ mol−1 for lattice self diffusion of copper, suggests that in all of the tested alloys the operative creep mechanism is dislocation climb controlled by lattice diffusion. The creep resistance of the base material was better than that of the Cu–0.3Cr–0.1Ag alloy reported in the literature. Further enhancement in creep resistance was achieved by incorporating Cr and Zr into the base alloy. This was achieved by the precipitation of Cr-rich and Zr-rich particles in the Cu matrix of the Cr- and Zr-containing alloys, which act as dispersion strengtheners in the present alloys.

ABSTRACT Rare earth (RE) - doped ceria powders with a chemical composition of Ce1-x RExO2-x/2 (X: 0.1 and RE: Gd, Sm, Er, Pr, Nd and Y) were prepared by nitrate-fuel combustion method. The TG and DT analyses of the as-synthesized powders showed a complete combustion with a small range endothermic process within a broad exothermic reaction. GDC, SDC, EDC, PDC, NDC and YDC precursors were calcined at 700 °C for 2 h and characterized using XRD, SEM and TEM. Powder characteristics such as morphology, crystallite size, primary particle size, lattice parameter and lattice strain of calcined powders have been studied. All X-ray diffraction patterns of as-synthesized and calcined samples were indexed as fluorite structure. The crystallite size of nano ceria obtained by Scherrer’s formula was between 17 and 19.5 nm and via Williamson-Hall (W-H) plots in the range of 25-38 nm that shows the effect of lattice strain on the average crystallite size. Primary particle size calculated from BET data was in the range of 24-37 nm. TEM images showed fine spherical particles and SAED patterns confirmed fluorite structure of all powders.

ABSTRACT Multi-walled carbon nanotubes were homogenously dispersed into a magnesium alloy (AZ31) using friction stir processing. The microstructural features, mechanical behaviors such as microhardness and wear properties were investigated. The results show a significant improvement in wear resistance in the friction stir processed AZ31 alloy containing multi-walled carbon nanotubes as compared to that of the as-received alloy, which was attributed to its greater microhardness and low coefficient friction due to presence of finer matrix grains and uniform dispersion of multi-walled carbon nanotubes.

ABSTRACT La0.6Sr0.4Co0.2Fe0.8O3-Ce0.9Gd0.1O1.95 (LSCF–GDC) nanocomposite cathode material has been synthesized using a simple combustion process for intermediate and low temperature solid oxide fuel cells (SOFCs). The combusted cathode material was calcined at temperatures 600, 700 and 800°C/2h. The powder properties such as evolution of crystalline phases, thermal decomposition, BET surface area, particle size and morphology are analyzed and reported. The TEM images confirmed that the cathode material has uniform eqiaxial shape and nanometric crystallite size of range from 15 to 45 nm. The electrical conductivity of the sintered LSCF-GDC cathode was examined. Subsequently, the cathode material was applied on GDC electrolyte to obtain a half-cell (electrode/electrolyte structure) configuration. The electrical properties of the half-cell at different temperatures were studied and discussed.

ABSTRACT Size controlled cubic Fe3O4 nanoparticles in the size range 90-10 nm were synthesized by varying the ferric ion concentration using the oxidation method. A bimodal size distribution was found without ferric ion concentration and the monodispersity increased with higher concentration. The saturation magnetization decreased from 90 to 62 emu/g when the particle size is reduced to 10 nm. The Fe3O4 nanoparticles with average particle sizes 10 and 90 nm were surface modified with prussian blue. The attachment of prussian blue with Fe3O4 was found to depend on the concentration of HCl and the particle size. The saturation magnetization of prussian blue modified Fe3O4 varied from 10 to 80 emu/g depending on the particle size. The increased tendency for the attachment of prussian blue with smaller particle size was explained based on the surface charge. The prussian blue modified magnetite nanoparticles could be used as a radiotoxin remover in detoxification applications.

ABSTRACT Fe3O4 nanoparticles were surface modified with Prussian blue (PB) and the nanoparticles were used for the removal of cesium (Cs) ion. The attachment of PB with the Fe3O4 and their morphology were explained based on the studies by transmission electron microscope and BET measurements. The Cs ion adsorption studies have shown that the Cs removal efficiency reached maximum within 120 min. The adsorption kinetics studies using Lagergren pseudo-first-order kinetic model suggest the values of the amount of metal ion adsorbed at equilibrium (q e) and adsorption rate constant (k 1) as 22 mg/g and 0.015 min−1, respectively. The capture efficiency of the prepared nanoparticles was studied by varying the flow channel diameter, applied magnetic field, and the fluid flow velocity. The study suggests that PB-Fe3O4 nanoparticles could be used for the detoxification of Cs where the flow velocity is in the range of few tens of cm/s.

Abstract106Ru, 144Ce and 152+154Eu radiotracers sorption experiments (pH: 1–6) have been carried out with polycrystalline columnar/microcrystalline calcite and aragonite obtained from a stalagmite of Dharamjali cave, India. The different domains of the sample were powdered and thoroughly studied using electron microscopic and X-ray spectroscopic techniques. Both 106Ru and 144Ce exhibited higher sorption within calcite varieties compared to aragonite and increased with rising pH, while it showed reverse relation in case of 152+154Eu. Further, it is noted that aragonite offers the highest Kd values for 152+154Eu, whereas 106Ru and 144Ce prefer calcite.

The chemical synthesis of shape and composition controlled Fe based binary alloys has been challenging due to the highly oxidizing nature of Fe. Here, we report the physical properties of flower-like Fe50Co50 nanoparticles prepared by a unique polyol process based on the addition of precursors at the elevated temperature. The magnetic properties are correlated through synchrotron radiation based X-ray diffraction and 57Fe Mossbauer spectrometry. Transmission electron microscopy analysis exposed the flower-like morphology of the FeCo particles. The FeCo nanoparticles showed a coercivity of 440 Oe, attributed to the shape anisotropy of the flower-like shape. Room temperature Mossbauer investigation revealed hyperfine fields of 34.9 and 36.7 T, suggesting two different Fe environments in the disordered state. Mossbauer analysis also showed the presence of superparamagnetic Fe-oxide with a relative fraction of 17%.

Fast recombination of photoinduced charge carriers is a major problem in the case of semiconductor based photocatalysts, which must be solved for their potential application in photocatalysis. In this work, photostable CdS QDs/BiOI composites have been successfully fabricated by a two-step precipitation–deposition method. The prepared samples were characterized by X-ray diffraction (XRD), UV–vis diffuse reflection spectroscopy (UV–vis DRS), photoluminescence (PL) spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Mott–Schottky, and electrochemical impedance analysis. The potential applications of CdS QDs/BiOI composite materials have been tested toward decolorization of rhodamine B (RhB) solution and hydrogen generation under solar light and visible light irradiation, respectively. It has been observed that hydroxyl radicals, electrons, and holes played a major role in decolorization of RhB solution. Among all prepared photocatalysts, 4% CdS QDs/BiOI composite wa...