Sciences des matériaux

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STRUCTURAL AND MAGNETIC PROPERTIES OF Fe60–xNix(ZnO)40NANOCOMPOSITES PRODUCED BY MECHANICAL MILLINGAND COATED BY THERMAL SPRAYING ON A STEEL SUBSTRATE

N.Dilmi, N-E.Bacha, A.Younes  (2020)
Publication

This work aims to study the effect of mechanical milling of Fe, ZnO, and Ni elemental powders andthermal spraying processes on chemical composition, structural properties, and magnetic behaviorof the Fe60–xNix(ZnO)40 coatings. As the first step, the FeNi/ZnO composite was synthesized bymechanical alloying process, and afterward, the milled powder was coated by a thermal sprayingtechnique on a steel substrate. Obtained samples were characterized by the methods of X-raydiffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS),atomic force microscopy (AFM), and with help of vibrating sample magnetometer (VSM). Aftermechanical milling, the crystallite size of the powder decreased from 18 to 10 nm, while the latticestrain increased from 0.31 to 0.59%, and a new solid solution FeNi formed after 20 h of milling dueto diffusion of nickel into the iron lattice. After the thermal spraying process, different phasesappeared in a surface coating such as ZnFe2O4, NiFe2O4, and FeNi. The magnetic and structuralproperties of the coated powders are influenced by the change in chemical composition. Thus, theincrease of Ni concentration improved the soft magnetic performance of the coating significantly.The highest saturation magnetization was determined in Fe40Ni20(ZnO)40 sprayed powder. However,the smallest coercivity appeared in Fe50Ni10(ZnO)40 sprayed powder. Voir les détails

Mots clés : FeNi/ZnO nanoparticle coating, Mechanical Alloying, Thermal Spraying, magnetic behavior, Structural properties

Electronic Properties of Carbon Nanotubes

oudjertli salah  (2020)
Article de conférence

Theoretical calculations predicted that carbon nanotubes were to present a metal behavior or semiconductor following their diameter and their chirality, these properties of conduction have inherited the structure of a particular band of graphite. Consequently, a limited number of wave vectors are allowed in this direction, It depends on the diameter and the winding of the graphene sheet on itself. If the edge conditions include the corners of the Brillouin zone, the behavior of the nanotube is metallic, this is the case for all “chair” type nanotubes and a third of “chiral” and “zig-zag” nanotubes. In other cases, the band structure has a bandgap, as a first approximation, inversely proportional at the radius of the nanotube. In addition, STM makes it possible to image the atomic structure of nanotubes and therefore to determine their chirality and their diameter. The transport properties can thus be correlated with the structure of the nanotube, the nanotube would be thus a quantum prototype of wire to a dimension. The various measurements carried out by AFM and STM on nanotubes monofeuillets showed that they behave indeed like such. The possible applications of these properties come within the province of nanoelectronic, not only the use of the nanotube like a molecular discussion thread but also like an active electronic element. Voir les détails

Mots clés : Carbon Nanotubes;STM;AFM

Investigation of Properties of ZnO Nanostructures by First- Principals Calculations

oudjertli salah  (2020)
Article de conférence

Structural and microstructural properties were investigated by first-principals computing. The ZnO powder as Transparent Ceramics exhibited a hexagonal crystal structure with space group p63mc of ZnO. We applied the present first-principals approach to the electronic structure of the ZnO structures. Band structure and density of states of the phase of crystal ZnO computed using first principal methods, confirmed that pure ZnO is a direct band gap semiconductor when obtained in the B4 type structure phase. Voir les détails

Mots clés : ZnO;DFT; FP-LAPW

Electronic Properties of Graphene

oudjertli salah  (2020)
Article de conférence

Winding a graphene sheet around itself creates periodic boundary conditions, perpendicular to the nanotube axis. Therefore a limited number of wave vectors are allowed in this direction. It depends on the diameter and the winding of the graphene sheet on itself [1]. If the edge conditions include the corners of the Brillouin zone, the behavior of the nanotube is metallic. This is the case for all “chair” type nanotubes and a third of “chiral” [2] and “zig-zag” nanotubes. In other cases, the band structure has a band gap, as a first approximation, inversely proportional. at the radius of the nanotube. These properties have been confirmed experimentally by measuring the tunnel current between the tip of an STM (Tunnel Effect Microscope) and a nanotube, which provides a direct estimate of electron density. In addition, STM makes it possible to image the atomic structure of nanotubes and therefore to determine their chirality and their diameter. The transport properties can thus be correlated with the structure of the nanotube. Metal nanotubes have only two one-dimensional conduction bands that cross the Fermi level: all current flows through these two bands and the theory predicts the conductance G0 = 2e2 / h, equal to twice the unit of fundamental conductance. Voir les détails

Mots clés : Graphene, STM, Nanotube

Elaboration et caractérisation des couches minces de matériau CZTS (Cu2ZnSnS4) obtenues par voie sol gel : Applications a la photovoltaïque

BENACHOUR Med Cherif (2020)
Thèse de doctorat

Récemment, un travail considérable a été fait sur le semi-conducteur de composé quaternaire Cu2ZnSnS4 (CZTS), en raison de sa simplicité, son faible coût et surtout sa souplesse dans la combinaison de plusieurs composés chimiques, pour en faire une bonne couche absorbante pour les cellules solaires à couches minces et générateur d'énergie thermoélectrique. Les couches minces CZTS sont une sorte de semi-conducteur à bande interdite directe de type p avec une valeur de bande interdite de Eg ≈ 1,5 eV pour la conversion d'énergie photoélectrique et sont caractérisés par un grand coefficient d'absorption (> 104 cm− 1). De cette manière, le but du présent travail est d'étudier les paramètres de la température de recuit et la durée de recuit optimale pour la formation de couche mince CZTS pur. Pour cela, nous avons développé un procédé simple et non toxique sans sulfuration utilisant le procédé sol gel et les voies de vide pour préparer les couches minces de phase CZTS pure déposés sur des substrats en verre par la technique de dip-coating et recuits à différentes température et avec de durées différentes. Nos avons étudié l'effet de la température de recuit sur les propriétés optiques des couches minces CZTS. Ces dernières ont été déposées par technique de dip-coating utilisant la méthode sol-gel. Nous avons constaté que l'augmentation de la température de recuit de 200 à 500 °C pendant une heure réduit la bande interdite d'énergie de 1,72 à 1,50 eV. Ainsi, ils nos jugé que ces couches minces sont bons pour les cellules solaires. Ainsi, la considération de ces résultats nous a incités à étudier l'effet de la durée de recuit de 5 à 60 min sur les propriétés des couches minces CZTS. Les échantillons obtenus ont été étudiés par plusieurs techniques telles que la XRD, la spectroscopie Raman, la SEM, Microscopie à force atomique (AFM), la spectroscopie UV-vis et la photoluminescence. Confirmée par spectroscopie Raman, l'analyse XRD révèle la formation d’un composé monophasé Cu2ZnSnS4, de composition quasi-stoechiométrique, dans la structure tétragonale de kestérite avec une orientation préférentielle le long de la direction [112]. La taille des grains a tendance à augmenter à mesure que la durée du recuit augmente et la température du recuit augmente aussi, ce résultat confirmé par SEM. L’étude de la morphologie par le MEB et l’AFM confirme que les films minces, ainsi élaborés sont homogènes, sans fissuration, de structure nanométrique et possédant une très faible rugosité (de l’ordre de 1 nm).L'analyse des mesures optiques montre que ces couches minces ont un coefficient d'absorption relativement élevé dans le spectre visible avec une réduction de bande interdite de 1,62−1,50 eV, ce qui est assez proche de la valeur optimale pour une cellule solaire. La photoluminescence (PL) distingue des bandes larges qui ont des maximums d'intensité limités entre 1,50 et 1,62 eV, correspondant à la bande interdite optique du CZTS. et limités augmentant avec l'augmentation de temps de recuit.L'étude des propriétés électriques à l'aide de la méthode de deux points (I=f(V)) a également montré que l'augmentation du temps de recuit améliore les propriétés électriques de la structure.De plus, l'étude a abordé le problème des phases secondaires et a suggéré une voie pour éviter leur sa formation. Voir les détails

Mots clés : CZTS, Dip-Coating, sol gel, DRX, Cellule solaire.

Comparative study of the corrosion behavior of the high strength steel after thermal and thermomechanical treatments

D Berdjane, B Maalem, O Ghelloudj, A Gharbi, L Tairi, S Djemili  (2020)
Article de conférence

The corrosion behaviour of X80 steel samples rolled and other quench-tempered in 3.5% NaCl have been studied. Optical microscopy, scanning electron microscopy, potentiodynamic polarization tests and electrochemical impedance measurements are the techniques used to characterize the samples. The results show that the tempered steel has a low corrosion current density compared to the rolled steel. The impedance measurements show the presence of a single capacitive loop attributed to the load transfer phenomenon. Voir les détails

Mots clés : HSLA grade steel X80, corrosion, structure, thermomechanical treatment.

Structural, microstructural and thermal characterization of Fe- doped ZnO powder nanostructures prepared by mechanical alloying

oudjertli salah, Bensalem Rachid, Alleg Safia, J J Suñol, Mohamed Bououdina  (2017)
Publication

ZnO powder nanoparticles mechanically alloyed were doped with iron to investigate their structural and microstructural properties using X-ray diffraction (XRD) and differential scanning calorimetry (DSC) for examined 1% Fe doped ZnO. The ZnO starting pure powder exhibited a hexagonal crystal structure with space group p63mc of ZnO, however with the introduction of 1% Fe in the ZnO milled powder, the hexagonal ZnO phase remained unchanged, whereas the microstructural parameters were subject to significant variations due to the introduction of Fe atoms into the ZnO hexagonal matrix to replace oxygen ones. The size of crystallites and microstrains are found milling time dependent. Voir les détails

Mots clés : ZnO, XRD, DSC

PURIFICATION OF CARBON NANOTUBES

Salah OUDJERTLI  (2018)
Publication

Nanotubes have never ceased to make object of research around the world. The scientific community has high hopes on these nanomaterials seen their exceptional properties and their various applications. The as-prepared CNTs contain impurities such as metal catalysts, amorphous carbon, and multi-shelled carbon particles. These impurities must be removed to realize the intrinsic properties of the CNTs. Purification is an essential issue to be addressed. Here we present an overview of the purification of carbon nanotubes, based on two methods of purification, filtration and acid treatments. Voir les détails

Mots clés : CNTs, Filtration, acidacid treatments treatments

IDENTIFICATION OF THERMAL AND MICROSTRUCTURAL PROPERTIES OF HOT ROLLING SCALE

B. Maalem, D. BERDJANE, L. Tairi, Y. Faci, S. Djemili  (2019)
Publication

A significant amount of scale is produced during casting of ingots and processing of hot-rolled products. In manufacturing steel, during the various rolling operations, the amount of scale produced is approximately 0.1% of the annual production of the rolling mills. The quality of the thin sheet during rolling is affected by the behavior of the iron oxide layers formed on their surfaces. For this reason, acids and oils are used for the descaling of slabs and billets by means of pressurized water. The calamine, contaminated by these various acids and used oils, is rejected and stored involuntarily on important areas and pollutes soil and groundwater. Micrographic observations as well as X-ray diffraction analysis have shown that calamine consists mainly of iron oxides. Hematite and magnetite become the main components for oxidation times greater than 1 hour. Characterization tests have shown that calamine is dense (ρ = 4.8 g/cm3), its particle size is variable depending on the degree of oxidation (from 0.5 to 10 mm). Simultaneous thermal analysis showed that an increase in mass of the calamine sample with a release of heat. Studies are underway for the physico-chemical characterization of the soils of the storage areas. Voir les détails

Mots clés : Scale, Risks, soil, thermal analysis, granulometry, X-ray diffraction

Effect of thermal spray process on chemical composition, magnetic behaviour, structure and mechanical properties of coatings based on milled Fe, Co a nd Al2O3 powder

A. Younes, N.Dilmi, A.BOUAMER  (2020)
Publication

Coated steel substrate by FeCo/Al2O3 nanoparticle with various Co concentrations realized by a thermal spraying process, preliminary powder alloy was elaborated by mechanical alloying technique for 20 h of milling time. The aims of this work are to study the effect of thermal spraying process and mechanical alloying on chemical composition, magnetic behaviour, structure and mechanical properties of coating. After mechanical alloying, the crystallite sizes of the powder were decreased from 18 to 7 nm and the lattice strains increased from 0.36 to 0.56%. This is due to the phenomenon of diffusion of cobalt in the iron lattice and the milling effect. After thermal spraying, many different phases appeared in the coating, such as Al2FeO4, CoAl2O4, CoFe and CoFe2O4. Magnetic behaviour was influenced by this change in the chemical composition of coating. The maximum saturation magnetization was found in Fe40Co20(Al2O3)40 sprayed powder, however, the minimum coercivity was found in Fe50Co10(Al2O3)40 sprayed powder. Mchanical properties parameters such as microhardeness and Young’s modulus were enhanced by the change in chemical composition during mechanical alloying and thermal spraying process. Voir les détails

Mots clés : FeCo/Al2O3 nanoparticle coating, Mechanical Alloying, Thermal Spraying, magnetic behaviour, structural and mechanical parameters