Sciences des matériaux
SYNTHEASE NOUVEAUX VERRES A BASE D’OXYDES D’ANTIMOINE Sb2O3-PbCl2-As2O3 / AgCl ET LEURS CARACTERISATIONS
Le développement rapide de la technologie photonique nécessite de plus en plus des matériaux efficaces adaptés aux appareils photoniques tels que les matériaux pour amplificateurs et lasers de forte puissance. L’amplification optique basée sur le principe de l’effet laser peut être obtenue dans des matrices cristallisées ou vitreuses grâce aux émissions radiatives des ions de terres rares. Les verres sont parmi les matrices intéressantes pour leur transparence dans une large région optique et pour leur aptitude à recevoir de grandes quantités d’ions de terres rares. Ils peuvent être utilisés comme matériaux infrarouge dans le domaine militaire, la chirurgie et la médecine aussi bien sous forme de fibres qu'à l'état d'échantillons massifs (lentilles, hublots, etc...). A cet effet, une nouvelle famille de verres stables d’oxydes et d’halogénures dans les systèmes ternaires Sb2O3-PbCl2-As2O3 et Sb2O3-PbCl2-AgCl a été mise au point avec une pureté dépassant 98%. Plusieurs caractérisations ont été réalisées sur deux systèmes ternaires à savoir l’analyse thermique différentielle, la méthode de la poussée d’Archimède, la microindentation pour la détermination des propriétés élastiques des composants, les Ultra-violets et infra rouge pour l’obtention des propriétés optiques. Les résultats obtenus par la DSC (Differential Scanning Calorimetry) ont montré que certaines compositions ne présentent pas de pics de cristallisation d’où leur grande stabilité thermique. Il apparaît que la structure de ces verres est plus ouverte d’où les faibles valeurs des propriétés mécaniques. Les verres à base de silice sont opaques aux infrarouges à partir de 2,5 à 3 microns, alors que les verres halogénés et oxyhalogénés sont transparents jusqu'à 7 et 8 microns. Voir les détails
Mots clés : oxyhalogénés, DSC, verre, optique, vitreuses, transparence
The corrosion resistance ofsupermartensitic steels compared to martensitic steels in different corrosion media
The supermartensitic stainless steels deduced from the refinement of the compositionof martensitic steels, have a low carbon content with 13% of chromium, 5% of nickel and 2%of molybdenum, this new generation of steel has an improved ductility with a good resistancemechanical and excellent resistance to corrosion. In this work, a comparative study of thecorrosion behavior of these two stainless steels in different aggressive chlorinated andsulphurized media was carried out. Stationary (polarization curves) and transient(electrochemical impedance) electrochemical methods have been applied. The rate ofcorrosion as a function of time was determined by the mass loss method and thecharacterization of the surface condition was studied by optical microscopy. Two types ofcorrosion were observed: uniform corrosion in which the half-reactions are homogeneouslydistributed in 0.5M H2SO4, followed by localized corrosion observed in 0.5M NaCl for bothsteels. According to the polarization curves, the corrosion potential differs betweenmartensitic steel and supermartensitic steel where it has a higher potential with -0.342 V / Ag/ AgCl in 0.5M H2SO4 and -0.339 V / Ag / AgCl in 0.5M NaCl. In parallel, the polarizationresistance given by EIS shows that in both media, supermartensitic steel is more resistant thanmartensitic steel where it has an Rp equal to 7200 Ohm in 0.5M H2SO4 and 8340 Ohm 0.5MNaCl. These results are confirmed by the optical microscope microstructure. Voir les détails
Mots clés : corrosion, martensitique stainless steel, supermartensitique stainless steel
Elaboration and characterization of electrodeposited cuprous oxide onto a sliver substrate
In this work, cuprous oxide thin films were prepared by using electrodeposition technique at different applied potentials from aqueous alkaline cupric sulfate solution with lactic acid at 70°C onto a sliver were investigated. The effects of deposition potential on the electrochemical, surface morphology, structural and, electrical properties of cuprous oxide thin films were investigated.The XRD measurements indicated that all the obtained films display a cuprous oxide cubic structure with a strong preferential orientation of the (111) direction.thin films, electrochemical, cuprous oxide, XRD Voir les détails
Mots clés : Thin films, electrochemical, cuprous oxide, XRD
Synthesis and characterization of Co doped ZnO prepare by dip-coating method
Abstract In this work, we studied deposited Cobalt- doped ZnO ( ZnO:Co ) thin films via dip-coating technique onto glass substrate, Zinc acetate dehydrate, cobalt acetate, 2- methoxyethanol and ethanolamine were used as starting materials. Then we have characterized them as X-ray diffraction , UV- visible, atomic force microscopy (AFM ). It is found that all the thin films have good crystallinity and a preferential orientation crystallites a long [002] of ZnO with wurtzite structure, and AFM have provided the information on morphology of this films where the size grain and average surface roughnes (Rms).thin films, ZnO, ( ZnO:Co ),dip-coating Voir les détails
Mots clés : Thin films, ZnO, ( ZnO:Co ), Dip-Coating
Electrochemical, Structural, and optical properties of Tin oxide thin films
ABSTRACT SnO2 thin films were electrodeposited on fluorine tin oxide substrate in nitric acid solution. The potential was swept from -0.4 to -1.6V with a rate of 50 mV/s. The films were found uniform, adherent to the substrate and amorphous. The XRD patterns reveal that after heat treatment at 500 °C for 1h, the films turn out to be crystalline in nature. Indeed, the film becomes composed of SnO2 nanocrystallite with a casseterite tetragonal structure. The nanocrystallite size is about 50 nm. The films thickness was found to be approximately 592nm and 563 nm for asdeposited and heat-treated SnO2 thin films, respectively. Some optical parameters of these films such as refractive index (n), extinction coefficient (k), absorption coefficient (α) and band gap were studied. Voir les détails
Mots clés : Thin films, SnO2, XRD
Study of structural and thermal properties of SiO2 and Al2O3 in the Diatomite
Diatomite, also known as diatomaceous earth, is the naturally occurring fossilized remains of diatoms. Diatoms are single-celled aquatic algae. They belong to the class of golden brown algae known as Bacillariophyceae. Diatomite is a near pure sedimentary deposit consisting almost entirely of silica. The Greeks first used diatomite over 2,000 years ago in pottery and brick.In this work we determine the structural and thermal properties of SiO2 and Al2O3 in the diatomite using the plane wave method and linearized augmented (LAPW) in the functional theory of density (DFT).The potential for exchange and correlation is calculated by the generalized gradient approximation (GGA).Regarding thermal properties, we calculated the free enthalpy G, S entropy, specific heat C, thermal conductivity λ ..... etc of SiO2 and Al2O3 component. The temperatures used in this work are 1400, 1450 and 1500 respectively;The results are in good agreement with some experimental data. Voir les détails
Mots clés : DFT1, diatomite, thermal proprieties
Effect of Immersion Time and Cooling Mode on the Electrochemical Behavior of Hot-Dip Galvanized Steel in Sulfuric Acid Medium
In this work, we investigated the influence of galvanizing immersion time and cooling modes environments on the electrochemical corrosion behavior of hot-dip galvanized steel, in 1 M sulfuric acid electrolyte at room temperature using potentiodynamic polarization technique. In addition, the evolution of thickness, structure and microstructure of zinc coatings for different immersion times and two cooling modes (air and water) is characterized, respectively, by using of Elcometer scan probe, x-ray diffraction and metallography analysis. The analysis of the behavior of steel and galvanized steel, vis-a-vis corrosion, by means of corrosion characteristic parameters as anodic (βa) and cathodic (βc) Tafel slopes, corrosion potential (Ecorr), corrosion current density (icorr), corrosion rate (CR) and polarization resistance (Rp), reveals that the galvanized steel has anticorrosion properties much better than that of steel. More the immersion time increases, more the zinc coatings thickness increases, and more these properties become better. The comparison between the two cooling modes shows that the coatings of zinc produced by hot-dip galvanization and air-cooled provides a much better protection to steel against corrosion than those cooled by quenching in water which exhibit a brittle corrosive behavior due to the presence of cracks. Voir les détails
Mots clés : cooling mode, hot-dip galvanization, Metallography, Potentiodynamic polarization, steel, X-ray diffraction, zinc coating
Study of physico-chemical properties of diatomiteAlgeria: Application to the thermal insulation ofliquid steel bath
The purpose of this paper is to characterize and to evaluate the diatomite powder of Sig region (West Algeria) withoutfluorine by powder generally used in tundish to thermal insulation of steel bath contain fluorine, that affecting the environment andhealth of workers. Thermal and physicochemical characterization showed different endothermic and exothermic peaks. Thescanning microscopy method was used and a large porosity was observed, which is very beneficial for improving the thermalconductivity of the product. The trial industrial in steelwork with diatomite powder, showed a weak loss temperature of steel (10 °Cmax), and filled fully function in thermal insulation of the steel bath. Voir les détails
Mots clés : diatomite, fluorine, Tundish, steelwork, thermal insulation, DSC
STRUCTURAL AND MAGNETIC PROPERTIES OF Fe–Co/Al2O3NANOCOMPOSITE POWDER PRODUCEDBY MECHANICAL ALLOYING
The effect of milling time and addition of elements on the microstructure, magnetic and mechanicalproperties of the Fe–xCo (x = 0, 5, 10, and 20 wt.%) matrix nanocomposite reinforced with 40 wt.%Al2O3 during mechanical alloying is examined. Fe–Al2O3 and Fe–Co–Al2O3 alloys are milled for 5,15, 20, and 30 h and 20 h, respectively. The balance between the welding and fracturing and asteady-state situation is found out in the Fe–Co–40 wt.% Al2O3 nanocomposite after 20 h, due to theCo introduction into the Fe matrix, but not in the Fe–Al2O3 nanocomposite. After 30 h of milling, theaverage crystallite size was 5 nm in the Fe matrix. The lattice strain increased to ~0.64% in the Fematrix after ?30 h of milling and in the binary Fe–20 wt.% Co matrix after 20 h of milling; theaverage crystallite size was 3 nm. The lattice strain increased to ~0.56% for the Fe–20 wt.% Comatrix after ?20 h of milling. The coercive field (Hc) increased from 6.407 to 82.027 Oe, while thesaturation magnetization (Ms) decreased from 20.732 to 15.181 emu/g in the Fe matrix duringmilling. The Hc and Ms are maximum for the binary matrix (20 and 10% Co, respectively) Voir les détails
Mots clés : Fe–Co matrix nanocomposite, alumina, Mechanical Alloying, microstructural evolution, magnetic properties.
DFT calculations of structural magnetic and thermal properties of C15 C14 and C36 Laves phases in Fe-Nb-Zr
The Pseudo-Potential Density Functional Theory (PP-DFT) method is applied to investigate the C15, C14and C36 Laves phases within the Fe-Nb-Zr system. The lattice parameters, bulk moduli, heats of formationand magnetic moments are predicted considering various spin configurations. ZrFe2 andZr0.5Nb0.5Fe2 are found to be ferromagnetic in the C15 and C36 structures, respectively. NbFe2 is predictedto be ferrimagnetic in C36. The magnetic states dependency of these compounds on the volumecompression shows interesting magnetic transition from the low to high spin state. This transition ismore pronounced for NbFe2 and Zr0.5Nb0.5Fe2. The thermal properties of NbFe2 and Zr0.5Nb0.5Fe2 are wellpredicted by using the quasi-harmonic Debye model. The obtained linear volume expansion for ZrFe2 isin excellent agreement with the experimental value at 800 K. The vibrational entropies of the studiedalloys confirm the coexistence of the three Laves phases at high temperature. Voir les détails
Mots clés : Laves Phases, Magnetism, Thermal Properties, DFT, Quasi-harmonic Debye model