Applied Mechanics and Materials Vols. 446-447

Abstract: The rapid development of nanotechnology has opened up multiple areas of application of titanium silicide nanowires including microscopic fields, sensor and catalyst areas and electrode materials, as well as their potential applications in nanodevices. The preparation of titanium silicide nanowires can be summarized as top-down method and bottom-up method. Its necessary to find some simple and quick ways to prepare titanium silicide nanowires with the desirable pattern. Recent advances in manipulating titanium silicide nanowires are discussed with a focus on the progress of nanowire preparations and applications.

Abstract: The formation mechanism and evolution of liquid pools entrapped within solid grains have been investigated during partial remelting of in-situ Mg₂Si/AM60B composite with fine-grains during partial remelting. The results indicate that the merging of dendrite arms during the initial stage of partial remelting is the main cause for the formation of the entrapped liquid pools. In view of phase transformations, the formation of the entrapped liquid pools is attributed to the reactions of α+β→L and α→L, essentially. The evolution of the liquid pools during latter heating can be divided into two stages: the agglomeration of each others and connection with intergranular liquid.

Abstract: Yttrium oxide nanopowder has been successfully synthesized by a modified transient morphology. In the first step, a foamy structure was produced by combustion synthesis using yttrium nitrate and glycine. This was followed by the addition of sulfate ions and calcination at 1100 °C for 4 h. The sulfated powders were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM). The XRD pattern shows Y₂O₃ single phase after calcination. The TEM images confirm the nanometric size of the particles in the range of 40-100nm.

Abstract: Nanocrystalline Ga doped nickel ferrite [(NiFe_2-xGa_xO₄ (x=0.0, 0.1, 0.3, 0.5 and 0.7)] powders have been synthesized by sol-gel auto-ignition method and the effect of non-magnetic gadillum content on the nanosize particles and magnetic properties has been studied. The X-ray diffraction (XRD) revealed that the powders obtained are single phase with spinel structure. The calculated grain size from XRD data have been verified using transmission electron microscopy (TEM). TEM photograph shows that the powders consist of nanometer sized grain. The size of nanoparticles decreases as the non magnetic Ga content increases. Magnetic hysteresis loops were measured at room temperature with maximum applied magnetic field of 20 KOe. As Ga content increases, the measured magnetic hysteresis curves became border and saturation magnetization (M_S) increased up to x= 0.3 and further increase of x leads the magnetization to decrease. The results are explained according to the assumed cation distribution.

Abstract: This paper describes how glass transition temperature (Tg) and capacitance (Cp) of a nanomodified composite polymer changes as compared to that of its base polymer. Because of its versatile applications, polycarbonate materials (grade PC1100 and PC1220 respectively), which are commercially available, were chosen as the base polymer in this study and nanostructured alumina material was used as filler for fabricating the desired composites by varying the filler weight in the composite materials. The Tg of the composites has been evaluated by differential scanning calorimetry (DSC) technique and Cp of the composites are derived from AC conductivity measurements of the composites. Results show that the Tg decreases as a function of filler load in the composite material whereas capacitance of the composites increase with the filler load in the composites. A filler concentration equal to or greater than 5 wt% in the said composites, the Tg of the composites reduces upto 15°C, whereas Cp shoots up in the pico-farad range with the same level of filler load, as compare to base polymers.

Abstract: Solidification microstructure of Gd-16wt%Co master alloy is characterized by the primary (Gd), CoGd₃, and Co₇Gd₁₂ dendrites plus (Co₃Gd₄+Co₇Gd₁₂) eutectic. In the laser melting conditions, the rapid solidification of melting pool shows three layers along the radial direction. The size of melting pool decreases with the increase of scanning speed. The dendrites are refined and the eutectic disappears in the pool. Near the top of the pool, the metastable phases and the peritectic reaction are restrained in the rapid solidification conditions.

Abstract: Deposition precipitation method was employed to synthesize carbon nanofiber based Cu-ZrO₂ catalyst (Cu-ZrO₂/CNF). Carbon nanofibre of herringbone type was used as a catalyst support. Prior deposition of catalyst particles, carbon nanofibre was oxidized to (CNF-O) with nitric acid solution. Catalyst was characterized by X-ray diffraction (XRD), Fourier Transmission Infrared (FTIR), Transmission Electron Microscopy (TEM) and Temperature-Programmed Reduction (TPR). Highly loaded, well-dispersed and thermally stable catalyst particles with average size of 4 nm were obtained by deposition precipitation method. Reaction studies confirmed the activity of the catalyst towards methanol formation.

Abstract: n-Type nanocrystalline FeSi₂/intrinsic Si/p-type Si heterojunctions were prepared by FTDCS. In order to estimate their diode parameters such as ideality factor, barrier height and series resistance, their current-voltage characteristics were measured in the temperature range from 300 to 77 K and analyzed on the basis of thermionic emission theory and Cheungs method. Based on thermionic emission theory, the ideality factor was calculated from the slope of the linear part from the forward lnJ-V characteristics. The barrier height was calculated once the saturation current density was derived from the straight line intercept of lnJ-V plot at a zero voltage. The obtained results exhibit an increase of ideality factor and a decrease of barrier height at low temperatures, which might be owing to inhomogeneity of material and non-uniformity of charge at the interface. Based on Cheungs method, the ideality factor and barrier height were estimated from y-axis intercept of dV/d (lnJ)J plot and y-axis intercept of H(J)J plot, respectively. The series resistance was analyzed from the slopes of dV/d (lnJ)J and H(J)J plots. The values of ideality factor and barrier height obtained from this method are in agreement with those obtained from the thermionic emission theory. The obtained series resistances from dV/d (lnJ)J and H(J)J plots, which were approximately equal to each others, were increased as the temperature decreased. This result should be owing to the increased ideality factor and remarkably reduced carrier concentrations at low temperatures.

Abstract: Aluminum (A356)-SiC metal matrix composites were fabricated by using liquid metallurgy route. To improve the interfacial bonding between the Al and SiC, an attempt has been made to coat the SiC particles with Ni and Cu. Electroless process was used for coating the reinforced particle. This surface modification due to electroless coating on SiC particles was confirmed with SEM/ EDS analysis. Processing parameters such as melt temperature, stirring speed, stirring time, and preheating temperature were optimized. SiC content in Al-SiC MMC were taken from 5 to 15% and effect of Ni and Cu coating was studied using hardness measurements. Influence of coated SiC particles in Al-SiC showed significant improvement in hardness values. Moreover, micro structural examination clearly demonstrated that Cu coating on SiC particles resulted in good metallurgical boding as compared to SiC particles with Ni coating. As a result, the hardness values of Al-SiC (Cu) exhibited better hardness values as compared to Al-SiC (Ni) MMCs. As expected, high SiC content in types of Al-SiC MMCs showed high hardness values as compared to low SiC content and base alloy. The present investigation suggests that Cu coating on SiC particles are more suitable as compared to Ni coating on SiC particles to synthesis Al-SiC MMCs.

Abstract: We have performed the electronic and phonon band structures of B_xIn_1-xN for various concentration of Boron using the pseudopotential method. The electronic band structure calculation was done using the GW approximation while the phonon band structure was done using the density functional perturbation theory. All calculations were done within the frame work of the density functional theory (DFT). From our calculations, the direct band gap for B_0.25In_0.75N, B_0.5In_0.5N and B_0.75In_0.25N were found to be 0.024eV, 2.2 eV and 6.01 eV respectively while the indirect band gap obtained were 0.59 eV, 3.24 eV and 6.9 eV. For the phonon calculations, it was also observed that an increase in the Boron content results in corresponding increase in the frequency of the topmost LO at the zone centre. For B_0.25In_0.75N, B_0.5In_0.5N and B_0.75In_0.25N, the topmost LO obtained were 735 cm^-1, 885 cm^-1 and 1105 cm^-1 respectively. We also saw that as the Boron concentration decreases, the number of optical bands across which the acoustic bands overlap increases.