Synthesis and characterization of morphologically different high purity gallium oxide nanopowders

High purity gallium oxide nanopowders have been synthesized by using a simple precipitation technique with calcination at elevated temperature. From the X-ray pattern, the phase purity of the synthesized powders was confirmed as β-Ga₂O_3. Elemental quantification (stoichiometry) of Ga₂O₃ was also examined from the X-ray energy dispersive analysis (EDAX). Based on the recorded Fourier Transform Infrared (FTIR) spectrum of Ga₂O_3, the IR bands due to Ga–O bond and crystal lattice vibrations have been identified in the wavenumber range 400–4,000 cm⁻¹. From the measured SEM images, it is obvious to notice that the pH value has been playing a dominant role in obtaining morphologically different gallium oxide nanopowders. Thermogravimetric analysis reveals 8.3% of weight loss when the sample was heated to the temperature of 1,100 °C from the room temperature, which also shows a crystalline phase transformation. It is very interesting to report that a broad blue emission at 455 nm has been measured from the synthesized gallium oxide nanopowders.     

Development of calibration models for quality control in the production of ethylene/propylene copolymers by FTIR spectroscopy,multivariate statistical tools,and artificial neural networks

Principal component regression (PCR), partial least squares (PLS), StepWise ordinary least squares regression (OLS), and back‐propagation artificial neural network (BP‐ANN) are applied here for the determination of the propylene concentration of a set of 83 production samples of ethylene–propylene copolymers from their infrared spectra. The set of available samples was split into (a) a training set, for models calculation; (b) a test set, for selecting the correct number of latent variables in PCR and PLS and the end point of the training phase of BP‐ANN; (c) a production set, for evaluating the predictive ability of the models. The predictive ability of the models is thus evaluated by genuine predictions. The model obtained by StepWise OLS turned out to be the best one, both in fitting and prediction. The study of the breakdown number of samples to be included in the training set showed that at least 52 experiments are necessary to build a reliable and predictive calibration model. It can be concluded that FTIR spectroscopy and OLS can be properly employed for monitoring the synthesis or the final product of ethylene–propylene copolymers, by predicting the concentration of propylene directly along the process line. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Empirical approach to develop a multilayer icebonded abrasive polishing tool for ultrafine finishing of Ti-6Al-4V alloy

This paper covers the development of a multilayer icebonded abrasive polishing (IBAP) tool for multistage polishing of Ti-6Al-4V alloy specimens based on a systematic study that determined the number of layers, thickness of each layer, and the type, size and concentration of abrasives in each layer. Based on this study, a three-layered IBAP tool with the bottom layer consisting of soft aluminum oxide abrasives of 3?µm size with 5% concentration, the middle layer with moderately hard silicon carbide abrasives of 8?µm size with 10% concentration and the top layer with hard boron carbide abrasives of 15?µm size with 30% concentration was formulated for ultrafine finishing of Ti-6Al-4V alloy specimen in a single setup. The performance of the three-layered IBAP tool assessed in terms of finish and morphology over the work surface showed 81% improvement in surface finish, showing its effectiveness over a single-layered IBAP tool. Polishing studies have clearly demonstrated the generation of ultrafine surfaces, yielding a finish of 37?nm while the morphological studies on the polished surface have shown a nearly scratch-free surface on the Ti-6Al-4V alloy.     

Novel wet-chemical synthesis and characterization of nanocrystalline CeO2 and Ce0.8Gd0.2O1.9 as solid electrolyte for intermediate temperature solid oxide fuel cell (IT-SOFC) applications

Novel wet-chemical methods of synthesis have been adopted to synthesize nano-crystalline CeO₂ and Gd-substituted compositions aiming to explore an efficient oxide ion conducting solid electrolyte for intermediate temperature solid oxide fuel cell (IT-SOFC) applications. Nano-crystalline CeO₂ powders were synthesized by combustion method using redox mixture of cerric ammonium nitrate or cerium nitrate and maleic acid or 1,3-dimethylurea and compared with high surface area CeO₂ powders prepared by hydrothermal technique with microwave precipitated precursor from aqueous solutions of (NH₄)₂Ce(NO₃)₆ and urea. The grain size achieved by the hydrothermal technique is ∼7 nm which is smaller than that of commercial nano CeO₂ powders. Conventional or microwave sintering was used to prepare dense Ce_0.8Gd_0.2O_1.9 pellets from the ceria powders made of redox mixture of cerium nitrate, 1,3-dimethylurea (DMU) and Gd₂O₃ as the starting ingredients. The samples were characterized by X-ray diffractometry (XRD), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), and ac impedance spectroscopy. The ionic conductivity measured for the pellet sintered at 1400 °C is 1 × 10⁻² and 2.4 × 10⁻² S/cm at 700 °C and 800 °C respectively.     

Design of Ultra-Wideband Monopulse Receiver

In this paper, we propose a novel amplitude-comparison monopulse receiver architecture for ultra-wideband radars. This monopulse receiver consists of four ridged-horn antennas placed in a square-feed configuration, a comparator circuit that generates the monopulse sum and difference signals, cross-correlation receivers that detect the monopulse signals, and an amplitude-comparison monopulse processor that determines the target's angular position. The derived monopulse sum and difference signals are verified through measurements. The derived sum and difference patterns are compared with measured patterns, and they show good agreements-measured 3-dB beamwidth=6.4deg(derived=6deg), measured unambiguous tracking range=plusmn5deg(derived=plusmn5deg), and measured sum pattern sidelobe level=-6 dB (derived=-8 dB)     

Design of an integrated UWB antenna with dual band notch characteristics

A miniaturized couple-line-fed planar ultra-wideband (UWB) antenna is proposed, which has a dual band-notched characteristic as well as two integrated monopoles. Narrowband notches are generated at frequencies of 3.5 GHz and 5.5 GHz using independently controlled bent resonators, whereas the monopoles are designed for radiation at 900 MHz and 2.4 GHz. The proposed design is simulated with full wave solvers and verified with measurements. A good agreement is observed between the simulations and measurements for the antenna's return loss, gain and radiation pattern performances.     

A wide-ranging review on Nasicon type materials

Nasicons (sodium super ion conductors) are a class of solid electrolytes. Their structure, compositional diversity, evolution, and applications are reviewed. A wide range of materials is considered based on crystalline and glassy Nasicon compositions.     

Laser diagnostics of soot precursors in a heavy-duty diesel engine at low-temperature combustion conditions

To better understand in-cylinder soot formation processes for modern, low-emissions, low-temperature combustion (LTC) operating conditions in diesel engines, soot and its precursors are imaged by laser diagnostics in a heavy duty optical engine. Virtually simultaneous images of planar laser-induced incandescence of soot (soot-PLII) using 1064 nm excitation and combined soot-PLII and planar laser-induced fluorescence of poly-cyclic aromatic hydrocarbons (PAH-PLIF) using 532 nm excitation reveal the temporal and spatial evolution of soot and its precursors during combustion. With increasing dilution of the intake air stream by various levels of nitrogen to simulate the use of exhaust-gas recirculation (EGR) to achieve LTC, the residence time of PAH increases as soot formation is delayed. At zero dilution (21% intake oxygen), soot appears nearly simultaneously with PAH, while at higher dilution (12.7% or 9.5% intake oxygen), soot formation is delayed by hundreds of microseconds to a millisecond or more. At all dilution levels, at its onset, PAH rapidly fills most of the downstream cross-section of the jet, with a relatively uniform fluorescence intensity distribution. The spatial evolution of soot, however, shifts from a relatively rapid filling of the downstream head of the jet at low dilution, to inception at the midstream periphery of the jet followed by a gradual progression downstream at high dilution. Effects of fuel-bound aromatics are also explored by comparing soot and PAH formation for a representative diesel fuel containing 27% aromatics by weight to that for neat n-heptane. The residence time of PAH before the onset of soot is slightly longer with the non-aromatic fuel, but otherwise the spatial and temporal evolution of PAH-PLIF and soot-PLII are indistinguishable from that of the diesel fuel at LTC conditions. Spectral analysis shows a characteristic soot emission spectra from 1064 nm excitation, while 532 nm excitation yields significant short-wavelength emission that cannot be attributed solely to soot incandescence, and is likely due to fluorescence of large PAH soot precursors. No narrow spectral features, such as from C2 or C3 emission, are apparent in the spectra, even at high laser fluence.     

Low sintering effect on structural,electrical and magnetic properties of rare-earth metal ion Er3+-substituted nickel–zinc spinal ferrites

Journal of Materials Science: Materials in Electronics - The nano-crystalline particles of erbium-substituted Ni–Zn ferrites with compositional formula Ni0.7Zn0.3ErxFe2?xO4...