Physique
First-principles prediction of the structural, elastic and mechanical properties of of hydrides Ba2RuH6
We report a systematic study of the structural, elastic and mechanical properties of the ternary ruthenium-based hydrides Ba2RuH6 within first-principles approach. The elastic behavior of a cubic monocrystalline is characterized completely by ¶three elastic constant independent C11, C12 and C44.We note here the absence of any experimental or theoretical data on the single-crystal and polycrystalline elastic moduli and their related properties elastic constants for the studied materials to be compared with our findings. Voir les détails
Mots clés : Ruthenium-based hydrides; First-principles calculations; Elastic constants; Mechanical properties.
CHARACTERISTICS OF CALAMINE AND NATURAL PIGMENT FOR ANTI-RUST PAINTINGS
Abstract.This work has a double objective. On the one hand, the valorization of natural raw materials, in particular, the oolithic iron ores which do not find their use in iron and steel because of their high phosphorus content and on the other hand the recycling of steel by-products.. The ultimate goal is to synthesize an anti-corrosion paint.In this first part, we will study the characterization of these two components by their chemical analysis, their grinding (fineness) and their thermal analysis (TGA, DSC).Chemical analysis showed that the pigment contains 53.18% of total iron and gangue dominated by silica. Calamine in turn contains 73.83% of iron in the form of iron oxides (FeO, Fe3O4 and Fe2O3).Iron pigment is composed mainly of hematite with a little of goethite.Grinding tests showed that the scale is much more suitable for grinding than pigment. The granulometric analysis measured by a laser granulometer (Hydro 2000MU) gave us a volume distribution of the particles with a size between 0.7 and 32 microns for scale and between 0.6 and 40 microns for the pigment and Their specific areas are 1.6 and 1.5 m2 / g..Thermogravimetric analysis (TGA) and the thermal variation of flow (DSC) showed that the iron pigment loses weight with phase dissolution by consuming energy when the temperature increases. Scale gains weight by the formation of new phase with heat.Exploration picture by scanning electron microscope of red iron pigment shows a grain aggregate formed rounded over at least iron oxide and gangue. The analysis by EDS shows a predominance of iron with a relatively large matrix containing the four predominant oxides in the case of iron ore deposits. Chemical elements forming these four oxides are silicon, calcium, aluminum and magnesium.The observation scale milled for 5 min SEM showed a homogeneous structure composed of sizes of iron oxide grains and shapes ranging from 1 µm to 10 µm. Voir les détails
Mots clés : Pigment iron, scale (calamine), iron oxides, grinding, Simultaneous thermal analysis.
Etude de l’effet des conditions de polarisation sur le mode de relaxation principale (α) du PLA par la technique des courants thermostimulés (CTS)
Dans ce travail nous nous sommes intéressé à l’étude de l’influence des conditions de polarisation (champ et température), sur le mode de relaxation principal(α) du polylactic acide (PLA) par la technique des courants thermo-stimulés (CTS). L’influence du champ électrique se traduit parune augmentation linéaire de l’intensité du thermocourant relatif au mode α ainsi que celle de la polarisation totale de ce pic, affirmant ainsi le caractère dipolaire de la relaxation. L’élévation de la température de polarisation conduit à une augmentation progressive de l’intensité et de la polarisation jusqu’à saturation au voisinage de la transition vitreuse. Les énergies d’activations évaluées par la méthode des demi-hauteurs, augmentent pour des températures de polarisation inférieures à 70°C, puis rejoignes un palier de saturation. Un tel résultat est dû à un processus thermiquement activé et à une distribution du temps de relaxation. La température de transition vitreuse Tgaugmente avec la vitesse de chauffage. Ce résultat confirme la nature cinétique de la transition vitreuse. Voir les détails
Mots clés : Transition vitreuse, relaxation, PLA, CTS.
Eddy current characterization and Magnetic properties of iron alumina nanostructured alloy
The mechanical alloying technique has been used to synthesis iron alumina nanostructred powder in a high energy planetary ball-mill PM400. Electromagnetic and magnetic characterizations of the powders was investigated by eddy current and vibrating sample magnetometer, the impedance, the coercivity and saturation magnetization of the iron alumina mixtures changes in function of x% (wt). Voir les détails
Mots clés : iron alumina, electromagnetic and magnetic properties, Eddy Current, VSM.
ELABORATION et CHARACTERISATION des COUCHES MINCES DES OYDES DE CUIVRES (CuO)
Copper oxide thin films were deposited by a low-cost and simple spray pyrolysis technique on glass substrate at 485°C, The aqueous copper nitrate Cu(NO3)2,6H2O with the different concentrations (0.1 M , 0.3M) used as a source of copper. The structural, morphological, and optical properties of the CuO thin films were studied by X-ray diffraction (XRD), Scanning electron microscopy (SEM), UV-vis-spectrophotometer. The X-ray diffraction patterns confirm the presence of CuO phases with preferential orientation along (-111), (111). The optical direct gap energy for Copper oxide calculated from optical absorption measurement is 2.82 eV , which is quite comparable with the report value Voir les détails
Mots clés : Copper oxide, Spray pyrolysis, Thin films
Electrical Characteristics of SnS /ZnS Heterojunction
Thin sulphide (SnS) is a promising candidate for a low cost, no toxic solar cells absorber layer. In this paper thin films of SnS were prepared by spray pyrolysis onto glass and ZnS/FTO coated glass substrates at different substrate temperatures in the range 250-400°C. SnS were characterized with X-rays diffraction and scanning electron microscopy and UV visible transmittance. The electrical properties of SnS/ZnS heterojunctions were determined using recording their current-voltage I(V) and capacitance-voltage (C-V) characteristics at ambient and at different measurement temperatures from 28-94°C. The results analysis indicate that the saturation current varied from 0.68 to 2.8 µA and series resistance from 191 to 800 ? , The structures ideality factor is ranged from 1.37 to 2.7. The diffusion potential (Vd) was determined by the intercept of extrapolation of 1/C2-V curve to the abscise axis (V=0) we found Vd values ranged from 0.67 to 1.2 V. Voir les détails
Mots clés : Tin sulfide; thin films; solar cell; spray pyrolysis; SnS/CdS Heterojuction.
SnS Thin Films Prepared by Chemical Spray Pyrolysis method
Tin sulfide (SnS) is interesting semiconductor that found application is several fields such as photovoltaic and gas sensor due to its interesting optical and electrical properties. In the present study, chemical spray pyrolysis deposition (CSP) was used to deposit tin sulfide (SnS) thin films onto glass substrates at 350°C. The starting solutions were prepared by the dilution of SnCl2 and thiourea in distilled water. The structural, optical and electrical, properties of the films were determined using X-ray diffraction, UV visible transmittance and Hall Effect measurements respectively. The influences of flow rate (10, 15 and 20 ml/h) in the structural, optical and electrical properties were determined. The XRD data confirms that the films prepared at low flow rate are a mixture of SnS and Sn2S3 phases. However, when the flow rate is increase; structures of the films are amorphous. From the UV-visible transmittance in the visible range we noticed that films optical band gap value ranged from 1.2 to 1.5 eV. The Hall Effect measurements indicate that SnS thin film exhibits p-type conduction with a conductivity decrease by two orders from 5.15x10-3 to 5.8x10-7 (?.cm)-1. Voir les détails
Mots clés : Tin sulfide, solar cell, UV-visible, spary pyrolysis
Effect of Grain Size of Nano Composite on Raman and Magnetic Proprieties
Based Iron-cobalt alloys exhibit particularly interesting Raman and magnetic properties, with high Curie temperatures, the highest saturation magnetizations, high permeability, and low losses and is relatively strong and partial oxidation of Fe and Co. The cost of these alloys has confined them, since their discovery by Elmen in 1929, to applications where the volume is small and high magnetic performances are critical. Sintering is the procedure of formation and compaction of a material. We have prepared the nano crystalline alloy by the mechanical milling process in a high energy planetary ball-mill PM400. Morphological, micro-structural, magnetic characterizations of the powders milled several times were investigated by scanning electron microscopy, X-ray diffraction, vibrating manometers sample and Raman spectroscopy. The coercivity value increase during millingtime from 0.018 to 185.9 Oe and saturation magnetization value from 42.7 to 51.1 emu/g, respectively. Voir les détails
Mots clés : Mechanical Alloying, Nanostructured FeCo, Magnetic and Raman characterization
Structural optical magnetic properties of Co doped -MoO3sprayedthin films.
this works deals with the synthesis of Cobalt doped MoO3thin films which were grown on glass sub-strates by the spray pyrolysis at 460?C. First, X-ray diffraction analysis shows an orthorhombic structurerelated to -MoO3allotropic variety with (020) and (040) preferred orientations. The surface topogra-phy performed by atomic force microscopy (AFM) shows that the grain size varies from 150 to 280 nm.Second, optical parameters, such as optical band gap, Urbach energy, refractive index and dielectricconstants were studied in terms of Co content. This optical study shows a direct transition of all pre-pared thin films and normal dispersion of the refractive index showing both Cauchy and Wemple &Di-dominico variations. On the other hand, PL measurements show transition bands mainly in blue andgreen domains related to band-to-band transitions as well as to oxygen vacancy in all films. Finally, mag-netic measurements at room temperature using vibrating sample magnetometer (VSM) technique reveala ferromagnetic behavior of such doped films. Voir les détails
Mots clés : MoO3, Thin films, optical properties, Magnetic Properties, Spray pyrolysis
Spatio-temporal aspects of the domain propagation in a spin-crossover lattice with defect
the collective spatiotemporal dynamics of the metastable high-spin state (HS) upon relaxation towards the low-spin (LS) is investigated using an electro-elastic model which includes the change of the spin states and the lattice volume at the transition. The present work focusses on the case of a lattice in which is embedded a structural defect in the center, represented here by a hole with a fixed size. The simulations are made on a 2D rectangular-shaped and compared to those of an ideal system. To account for the volume change, we set the distances between the sites as spin-dependent which requires the use of Monte Carlo simulations on spin states and atomic positions to solve the present problem. It is found that the presence of the defect affects the dynamics of the spin-crossover transformations which starts stochastically from a corner of the lattice, then propagates in the first stage along the width (shortest distance to the surface), before to proceed via a second longitudinal regime whose velocity slows down significantly at the vicinity of the defect, which plays the role of a pining center. After a while, the interface leaves the defect, and accelerates when it approaches the lattice's border. We have also investigated the spatial dependence of the displacement field, from which we derived the distribution of the divergence and rotational of the displacement field, which directly connects to the trace of the strain tensor and to shear strains respectively. Valuable information on the relaxation process of the elastic field are derived and discussed in direct relation with the presence of the defect. Voir les détails
Mots clés : Spin Crossover, Phase transition;, Interface propagation;, Spatiotemporal effects, elasticity