Dielectric spectroscopy techniques as quality control tool: a feasibility study - [feature article]

In this article, the feasibility of using time- and frequency-domain dielectric spectroscopy measurements to monitor the condition of oil-impregnated paper (OIP) condenser bushings is discussed.     

Structural, morphological, and optical properties of TiO2 thin films synthesized by the electro phoretic deposition technique

In this work, we report the structural, morphological, and optical properties of TiO₂ thin films synthesized by the electro phoretic deposition technique. The TiO₂ film was formed on a doped fluorine tin oxide (SnO₂:F, i.e., FTO) layer and used as a photo electrode in a dye solar cell (DSC). Using spectroscopic ellipsometry measurements in the 200 to 800 nm wavelengths domain, we obtain a thickness of the TiO₂ film in the range of 70 to 80 nm. Characterizations by X-ray diffraction and atomic force microscopy (AFM) show a polycrystalline film. In addition, AFM investigation shows no cracks in the formed layer. Using an ultraviolet–visible near-infrared spectrophotometer, we found that the transmittance of the TiO₂ film in the visible domain reaches 75%. From the measured current–voltage or I-V characteristic under AM1.5 illumination of the formed DSC, we obtain an open circuit voltage V_oc = 628 mV and a short circuit current I_sc = 22.6 μA, where the surface of the formed cell is 3.14 cm².     

Microstructural and mechanical features of aluminium semi-solid alloys made by rheocasting technique

The rheocasting process applied by Swirled Enthalpy Equilibration Device (SEED) technique relies on rapid extraction of a controlled quantity of heat from the liquid aluminium alloy via mechanical agitation to form the semi-solid slurry that can be formed under pressure. Microstructural characteristics of both conventional and semi-solid A357 castings under T6 heat treatment conditions were examined using optical and scanning electron microscopy. The fatigue and tensile experiments were applied to evaluate the effect of SEED technique on the mechanical properties of T6-A357 semi-solid alloys and conventional castings. The results showed that the rheocasting–SEED technique has proved successful in producing optimum microstructure of Al–Si–Mg semi-solid alloys providing an excellent combination of quality and mechanical performance as compared to conventional technique.

This paper is part of a Themed Issue on Aluminium-based materials: processing, microstructure, properties, and recycling.     

The dual role of silver during silicon etching in HF solution

ABSTRACT: It was reported that during silicon etching, silver was subjected to have a controversial role. Some researchers debate that silver protects silicon, and, at the same time, other ones confirm that silver catalyzes silicon underneath. In this paper, we give experimental results arguing the dual role that silver has during the formation of silicon nanostructures. We give a proof that the role of silver depends on the experimental details and the intrinsic properties of silver during its deposition on the silicon wafer. Through our investigations, we tracked the silver particles that indicated which mechanism is involved. Characterizations of the prepared samples were made using a Scanning Electron Microscope (SEM).     

Modeling and testing of a 1.2‐kW Nexa fuel cell using bond graph methodology

Confronted by the energy and environmental challenges, fuel cells raise a lot of hope. Fuel cells are expected to be an important power source in the future, and the proton exchange membrane fuel cell (PEMFC) is one of the potential candidates, being highly suitable for certain applications. The electrochemical components, especially a fuel cell, are naturally multidisciplinary components rather well adapted to this approach: chemistry, electrochemistry, thermal and electrical engineering are involved. We propose a PEMFC model using the bond graph method. This model takes into account the different physicochemical phenomena in a fuel cell. The modeling of the activation layer (AL) and gas diffusion layer (GDL) of the cathode side is highlighted. This model is then validated by an experimental work where we have used a 1.2‐kW power PEMFC of the Nexa type from Ballard. The static characteristics of the fuel cell obtained by simulation are in good agreement with those of experiments and also from the literature. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Effect of the etching time on the morphological, optical and electronic properties of silicon nanowires

ABSTRACT: Owing to their interesting electronic, mechanical, optical and transport properties, silicon nanowires (SiNWs) have attracted much attention, giving opportunities to several potential applications in nanoscale electronic, optoelectronic devices and silicon solar cells. For photovoltaic (PV) application, a superficial film of SiNWs could be used as an efficient antireflection coating (ARC). In this work, we investigate the morphological, optical and electronic properties of SiNWs fabricated at different etching time. Characterizations of the formed SiNWs films were performed using a Scanning Electron Microscope (SEM), UV-Vis-NIR spectrophotometer and Light-Beam-Induced-Current (LBIC) technique. The later technique was used to determine the effective diffusion length in SiNWs films. From LBIC investigations, we deduce that the homogeneity of the SiNWs film play a key role on the electronic properties.     

Validation of a methodology for determining the PEM fuel cell complex impedance modelling parameters

In this paper, we present a new methodology for determining the complex impedance parameters for a Proton Exchange Membrane (PEM) Fuel Cell in order to have a general model for embedded diagnosis. The modelling of Fuel Cells is a very important phase because it contributes to a better understanding and representation of the internal phenomena in this type of generator. After obtaining the experimental results of the complex impedance using a realized test bench for Proton Exchange Membrane (PEM) Fuel Cell using an electrochemical method which is the electrochemical impedance spectroscopy (EIS), we treat these results with an identification algorithm based on least squares method in the objective to determine the variations laws of the complex impedance parameters then implement in a PEM Fuel Cell model with Matlab/Simulink software. The established model of the complex impedance is based on electrical components and takes into account the mathematical equations of the different elements. The simulation results of this implemented model inform us about the state of the PEM Fuel Cell and validate the choice of the parameters. The validation of this choice is done by a comparative study using residual analysis method between the experimental and the simulation results. The general model is obtained from the superposition of the measured and theoretical results.