Liste des publications

Nombre total de résultats : 469
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Effect of heat treatment on surface hardness and tribologicalbehavior of XC38 steel—approach by the experiments plans

M Bourebia, S Meddah, H Hamadache, A Taleb, A Gharbi, L Laouar  (2019)

This work aims at predicting the micro-hardness of XC38steel using the experiments plans as well asstudy of tribological behavior of thissteel. The heat treatments were considered by adopting thefactorial plans 22 methodology at two factors (temperature ‘T’ and holding time ‘t’), each at two levels(-1, +1). The results obtained allowed lead to a mathematical model predicting the micro-hardness‘Hv’ in every point of the study field. Moreover, the curves of the responses surfaces clearly show theinfluence of two factors studied (T, t) on ‘Hv’. Mechanical characterization of treated samples showedasignificant increase in the micro-hardness, which achieve to 76% for the treated sample at 850 °Cduring 2 h compared to untreated state. An investigation of wear tracks morphology shows thatfriction under a load of 10 N results in predominant adhesive wear, while a load of 2 N favorabrasive wear. Voir les détails

Mots clés : heat treatment, factorial plans, prediction, superficial hardness, tribological behavior

Physical and photo-electrochemical characterizations of ZnO thin films deposited by ultrasonic spray method: Application to HCrO4−photoreduction

N. ZEBBAR, M. Trari, M. Doulache, A. Boughelout, L. CHABANE  (2014)

ZnO thin films, prepared by ultrasonic spray onto glass substrate, crystallize in the wurtzite structure. The XRD pattern shows preferential orientation along the [0 0 2] direction. The films deposited at 350 consist of 60 nm crystallites with an average thickness of ∼150 nm and SEM images show rough surface areas. The gap increases with increasing the temperature of the substrate and a value of 3.25 eV obtained for films deposited at 350?C. ZnO is nominally non-stochiometric and exhibits n-type conduction because of the native defects such as oxygen vacancies (VO) and/or interstitial zinc atom (Zni) which act as donor shallows. The conductivity is thermally activated and obeys to an exponential type law with activation energy of 57 meV and an electron mobility of 7 cm2V−1s−1. The capacitance-voltage (C−2measurement in acid electrolyte (pH ∼ 3) shows a linear behavior with a positive slope, characteristic N-type conduction. A flat band potential of −0.70 VSCE and a donors density of 5.30 × 1016cm−3are deter-mined. The Nyquist plot exhibits two semicircles attributed to a capacitive behavior with a low density of surface states within the gap region. The centre is localized below the real axis with a depletion angle of 16?ascribed to a constant phase element (CPE) due to the roughness of the film. The energy band diagram assesses the potentiality of ZnO films for the photo-electrochemical conversion. As application, 94% of chromate (3.8 × 10−4M) is reduced after 6 h under sunlight (AM 1) with a quantum yield of 0.06%and the oxidation follows a first order kinetic. Voir les détails

Mots clés : ZnO, thin film, Ultrasonic spray, Photo-electrochemical, Chromate, Sunlight


Omar Fethi BENAOUDA, Azzedine Bendiabdellah, KAHLA SAMI  (2019)

This paper proposes a new diagnostic technique based on Park vectors associated with polar coordinates for the detection and location of open circuit (OC) faults, as well as the integration of fault-tolerant reconfigurable inverter in order to enable continuity of service of the wind farm system. The model used is that of a variable speed wind turbine coupled to a double-fed induction generator (DFIG) connected to the power grid via a fault-tolerant converter to improve performance after the appearance of the fault. This converter is used based on IGBT to obtain an acceptable accuracy with high switching frequencies. This model is well suited for the observation of harmonics and the dynamic performance of the control system over relatively short periods of time (typically hundreds of milliseconds to one second). This method allows extracting the maximum wind energy during a low wind speed by optimizing the turbine speed while minimizing the mechanical stress on the turbine during gusts of wind. To illustrate the diagnostic improvement of fault-tolerant inverter open circuit faults, several results are presented and discussed in this article. Voir les détails

Mots clés : DFIG Turbine, Inverter, diagnosis, Detection, Location, Reconfiguration, fault, Open-Circuit, IGBT


Omar Fethi BENAOUDA, Azzedine Bendiabdellah, KAHLA SAMI  (2019)

Cet article propose une nouvelle technique de diagnostic basée sur les vecteurs de Park associés aux coordonnées polaires pour ladétection et la localisation des défauts de circuit- ouvert (CO), ainsi que l’intégration de l’onduleur reconfigurable à tolérance depanne afin de permettre la continuité de service du système du parc éolien. Le modèle utilisé est celui d'une éolienne à vitessevariable couplée à une génératrice asynchrone à double alimentation (GADA) connecté au réseau électrique via unconvertisseur à tolérance de panne pour améliorer les performances après l’apparition du défaut. Ce convertisseur est utilisé àbase d’IGBT pour l’obtention d’une précision acceptable avec des fréquences de commutation élevées. Ce modèle est bienadapté pour l'observation des harmoniques et la performance dynamique du système de contrôle sur des périodes de tempsrelativement courtes (généralement des centaines de millisecondes à une seconde). Cette méthode permet d'extraire l'énergiemaximale du vent lors d’une faible vitesse du vent en optimisant la vitesse de la turbine tout en minimisant les contraintesmécaniques sur la turbine pendant les rafales de vent. Pour illustrer l’amélioration de diagnostic des défauts en circuit ouvert duconvertisseur à tolérance de panne, plusieurs résultats sont présentés et discutés dans cet article. Voir les détails

Mots clés : Génératrice asynchrone à double alimentation (GADA) Turbine, Onduleur, diagnostic, détection, localisation, Reconfiguration, défaut, Circuit- ouvert, Insulated gate bipolar transistor (IGBT).

Diagnosis Method for GTO Open Switch FaultApplied to Reconfigurable Three-Level 48-PulseSTATCOM

Omar Fethi BENAOUDA, Azzedine BENBIABDELLAH, Bilal Djamal Eddine CHERIF  (2019)

In the recent years, several research worksare focusing on the use of STATCOM in electrical net-works because it is used to regulate the voltage, to im-prove the dynamic stability of the power system be-sides allowing better management of the power ?ow.All these positive tasks have guaranteed an importantposition of STATCOM within a family of Flexible Al-ternating Current Transmission System (FACTS). Inthis paper study, the control and operation of a threelevels 48-pulse GTO based STATCOM is implementedwith series connected transformers. The system may,unfortunately, be prone to GTO switch faults and there-fore may a?ect reactive power transiting. In this pa-per, a new diagnostic approach is proposed based onthe Single-Sided Amplitude Spectrum (SSAS) methodof the three-leg converter currents for detection and lo-calization of open-circuit faults. The integration of theSTATCOM recon?gurable fault tolerant to the systemis also considered to ensure service continuity. Sev-eral results are presented and discussed in this paperto illustrate the performance of the STATCOM fault-tolerant diagnostic. Voir les détails

Mots clés : Detection, diagnosis, FACTS, GTO, open switch fault, recon?guration, SSAS, STATCOM

Experimental investigation of notch effect and ply number on mechanicalbehavior of interply hybrid laminates (glass/carbon/epoxy)

Leila Belgacem, Djamel Ouinas, Jaime Aurelio Viña Olay, Antonio Argüelles Amado  (2018)

The great advantages of hybrid composite materials reside in the synergistic effect of their constituent materialsand that make them very attractive for advanced applications. Nevertheless, the interactive effect of the intrinsicproperties of each element further complicates understanding of their behavior. In this study, an experimentalanalysis of the mechanical behavior of interply hybrid laminates (glass/carbon/epoxy) and the estimation of thehybridization effect with respect to mono-reinforced laminates were carried out. It has been found that theincorporation of 25% carbon fibers in the glass/epoxy laminates contributes significantly to improving theirtensile mechanical properties but they degrade as the number of glass plies increase. In addition, investigationswere carried out on the sensitivity of these materials to geometric imperfections. To this end, the influence of acircular notch has been highlighted. From the results obtained, it was found that the greatest loss of properties isrecorded for the hybrid materials; however, they remain the most resistant. Voir les détails

Mots clés : Hybrid composite materials, laminates, notch, mechanical properties

Early stages of copper microparticles electrodeposition on polypyrrole film

DEHCHAR Charif, Imene CHIKOUCHE, Ali SAHARI, Ahmed ZOUAOUI  (2019)

In this work, we studied the electrodeposition of copper (Cu) microparticles on polypyrrole (PPy) ?lms using cyclic voltammetry and chronoamperometry techniques. The initial stages of Cu deposition were investigated by performing current transients. Models based on Scharifker and Hills calculations were established to determine the nucleation and growth type. The results suggest that the deposition of Cu proceeds via an instantaneous nucleation followed by three-dimensional (3D) di?usion-limited growth. The values of the number density of active sites N and di?usion coe?cient D were also determined. Voir les détails

Mots clés : composites, copper, electrodeposition, polymer, thin film

Improved Cu2O/AZO Heterojunction by Inserting a Thin ZnO Interlayer Grown by Pulsed Laser Deposition.

A. Boughelout, R. MACALUSO, I. CRUPI, B. MEGNA, M.S. AIDA and M. KECHOUANE.  (2019)

Cu2O/ZnO:Al (AZO) and Cu2O/ZnO/AZO heterojunctions have been deposited on glass substrates by a unique three-step pulsed laser deposition process. The structural, optical, and electrical properties of the oxide films were investigated before their implementation in the final device. X-ray diffraction analysis indicated that the materials were highly crystallized along the c-axis. All films were highly transparent in the visible region with enhanced electrical properties. Atomic force and scanning electron microscopies showed that the insertion of a ZnO layer between the Cu2O and AZO films in the heterojunction enhanced the average grain size and surface roughness. The heterojunctions exhibited remarkable diode behavior and good rectifying character with low leakage current under reverse bias. The presence of the ZnO interlayer film significantly reduced the parasitic and leakage currents across the barrier, improved the quality of the heterostructure, made the energy band between AZO and Cu2O layers smoother, and eliminated the possibility of interface recombination, leading to much longer electron lifetime. Voir les détails

Mots clés : Heterojunctions, ZnO, Cu2O, AZO, pulsed laser deposition, solar cells.

Rhodamine (B) photocatalysis under solar light on high crystallineZnO films grown by home-made DC sputtering.

A. Boughelout, N. ZEBBAR, R. MACALUSO, Z. Zohour, A. Bensouilah, A. Zaffora, M.S. Aida, M. Kechouane, M. Trari.  (2018)

ZnO thin films were deposited by home-made DC sputtering of zinc target under mixed gases(Argon, Oxygen) plasma on glass substrates. Films were deposited by varying oxygen partialpressure (PO2) from 0.09 to 1.3 mbar in the deposition chamber, at a fixed substrate temperatureof 100 °C. The samples were characterized by photoluminescence (PL), X-ray diffraction (XRD),optical transmissions (UV–vis), scanning electron microscopy (SEM) and electrical (Hall effect)measurements. The results indicate that by varying the oxygen pressure in the depositionchamber, the films show a precise and well defined photoluminescence emissions for each rangeof pressure covering almost the entire visible domain (UV, UV-Violet, Violet, Blue, and Red) withhigh intensities. Moreover, the deposited films have different defects levels. The XRD analysisindicates that the films are well grown along the c-axis peak, but with different crystallinequality. Optical measurements reveal a high transmission, up to 90%, in the spectral regionbetween 400 and 2500 nm and a large variation of the optical band gap (3.16 – 4.34 eV). As anapplication of the deposited ZnO films, the photo-catalytic degradation of a synthetic solution ofRhodamine B (RhB) poured on a ZnO thin film was successfully achieved and an elimination rateof 38% was obtained after exposing the film to solar light for 3 h. Voir les détails

Mots clés : ZnO thin films, sputtering, Photoluminescence, Rhodamine (B), Solar light, Photocatalysis.

Cr(VI) photocatalytic reduction under sunlight followed by Cr(III) extraction from TiO2 surface

Ridha Djellabi, Fouzi M.Ghorab, Sana Nouacer, Abdelaziz Smara, Ouahida Khireddine  (2016)

The main objective of this work was the extraction of Cr(III) from TiO2 surface deposited after Cr(VI) reduction by TiO2 solar photocatalysis. The results show that the reduction of Cr(VI) to Cr(III) by TiO2 under natural sunlight is total after 2 h using tartaric acid (A.T) as a hole scavenger under the following conditions: [Cr(VI)]: 20 ppm, [TiO2]: 2 g/L, [A.T]: 60 ppm and pH: 2.2. The produced Cr(III) is divided between deposited onto TiO2 surface (39.75%) and in the solution (60.25%). The Cr(III) removal from TiO2 surface by the sequential extraction after three washing were 90.13% and 42.62% using citric acid and EDTA respectively. Voir les détails

Mots clés : Chromium, Reduction, Deposition, Solar light, extraction, TiO2 surface