Sciences des matériaux
Effects of Fe substitution by Nb on physical properties of BaFeO3: A DFT + U study
The structural, electronic, magnetic and thermal properties of BaFe1xNbxO3 perovskites oxides are investigatedusing the Density Functional Theory (DFT). The Generalized Gradient Approximation (GGA) andon-site Hubbard potential corrections (GGA + U) are considered. According to the formation energiesand phonon spectra, the stoichiometric BaFeO3 and BaNbO3 oxides have a stable cubic phase. The GGA+ U calculations show a half metallic behavior of BaFeO3 with a large exchange splitting, in agreementwith previous experimental and theoretical works. The Fe substitution by Nb for x = 0.5 leads to a surprisinginsulating ground state. The values of the band gap is 0.40 eV and 1.84 eV using GGA and GGA + U,respectively. For x = 0.875 and x = 1, the corresponding alloys are metallic and non-magnetic, while forx = 0.5 and x = 0.625 the antiferromagnetic ground state is found using GGA + U. For the remaining Nbcompositions a half metallic character is noticed with a ferromagnetic state. The quasi-harmonicDebye model is successfully applied to study the temperature evolution of lattice parameters and bulkmoduli for different Nb compositions. Voir les détails
Mots clés : BaFe1-xNbxO3 perovskites, Structural properties, Magnetic moments, Density Functional Theory, GGA + U, Quasi-harmonic Debye model
Large scale and facile synthesis of Sn doped TiO2 aggregates usinghydrothermal synthesis
Sn doped TiO2 aggregates have been successfully prepared via one pot hydrothermal technique. Differentmethods were used to characterize prepared Sn doped TiO2 aggregates such as DRX, XPS, N2 adsorption (BET),FEGSEM and UV –Vis spectroscopy. It was illustrated that the size, the morphology and the phase of preparedTiO2 aggregates is strongly influenced by the amount of added Sn doping. In addition, it was demonstrated thatthe prepared aggregates properties is influenced by the synthesis temperature. Furthermore, it was shown thatthe prepared Sn doped TiO2 aggregates are of high crystallinity. The influence of added Sn dopant amount on theoptical and structural properties of the prepared Sn doped TiO2 aggregates have been investigated. Voir les détails
Mots clés : Hydrothermal, Sn doping, TiO2, Nanoparticles assembly, optical properties
EVOLUTION OF THE MICROSTRUCTURAL PARAMETERS OF COLD WORK Ti-6-Al-4V ALLOY.
AbstractThe aim of this work is to investigate cold worked Ti-6Al-4V (α+β) alloy. The alloy was examined by X-ray diffraction using Rietveld refinement method. MAUD software (Materials Analysis Using Diffraction) was used to analyze the microstructural parameters evolution (crystallite size, root mean square strain (r.m.s) and dislocation density. The Crystallite size is smaller in the β-phase compared to the α-phase. Microstrain and dislocation density are higher in the α-phase than those found in the β-phasefor the as received material. The microstructural parameters of Ti-6Al-4V alloy exhibit typical values of cold deformation state. The results show that the deformation process reducesthe crystallite size (coherent diffraction domains) from 520 to 210 ? in the α-phase. Consequently, the r.m.s increases from 5 E-4to 32 E-4and the dislocation density increases from 2.92 E+10to 4.6 E+11m-2after 85 % thickness reduction. Voir les détails
Mots clés : Ti-6Al-4V alloy, cold working, crystallite size, dislocation density
Pulsed eddy current signal analysis of ferrous and non-ferrous metals under thermal and corrosion solicitations
Most metals endure in contact with ambient air, liquids or other metals the phenomena of oxidation. The kinetics of the corrosion can be significant and destroy the metal. The marine corrosion or soil affects many materials, more than ever if it touches the pipeline, ship hulls or buried pipes. The investigation of NDT methods to predict corrosion behavior can be a rational solution to prevent from this kind of industrials problems.Eddy current and pulsed eddy current (PEC) are proposed as a powerful Nondestructive Testing and Evaluation (NDT&E) technique. The application of this kind of technique in the industrial domain is used in detection of the defects, particularly in the determination of corrosions information contained in the received signal gives the possibility allow to use the PEC in the Non Destructive Evaluation of materials that can be analysed. The work in this papers explain the behaviour of the eddy current, pulsed Eddy Currents and various electromagnetic parameters in the analysed samples. We have showed in this work that all microstructure modifications of the samples were detected and can be quantified by Pulsed eddy current measurements. Modifications of the microstructure obtained by air cooled, quenched and corroded samples in aluminium, heat treatment changement in mild steel were evaluated by PEC. Voir les détails
Mots clés : pulsed eddy current (PEC), ), lift off variation, corrosion
Electrocatalytic oxidation of ascorbic acid at polypyrrole thin film incorporating palladium particles
In this paper, we report a simple sensing strategy for electrochemical determination of ascorbicacid (AA) using a combination of polypyrrole (PPy) thin film and palladium particles composites deposited onto n-doped silicon (Si) substrate. A two-step electrochemical process was employed to synthesize the composite films: At first, PPy film (average thickness 200 nm) was electro-generated on Si substrate from an organic solution of the pyrrole under galvanostatic conditions. Secondly, palladium particles were electrodeposited on PPy/Si surface from a separate solution by chronoamperometry technique. The surface morphology analysis of the obtained composites shows a uniform dispersion of palladium particles onto the polymer matrix and reveals that the electrodeposition time has a significant effect on the amount and size of the incorporated palladium particles. The electrochemical reactivity of the Pd–PPy/Si-modified electrodes towards the oxidation of AA was studied by cyclic voltammetry method in 0.1 M, pH 7.0 phosphate buffer solution. The oxidation current was proportional to the concentration of AA in the range of 0.5–10 mM with a detection limit of 0.2 mM. Voir les détails
Mots clés : ascorbic acid, composite, electrocatalysis, Electropolymerization, palladium, Polypyrrole
Microstructure and microindentation of Ti3SiC2–Titaniumfiller brazedjoints by tungsten inert gas (TIG) process.
Herein we study the joining of Ti3SiC2- a MAX phase - with a Tifiller (Ti3SiC2/Ti-filler) using a TIG-brazingprocess. The microstructures of the interfaces were investigated by scanning electron microscopy and energydispersive spectrometry. When Ti3SiC2comes into contact with the molten Ti -filler during the TIG-brazingoperation, it starts decomposing into TiCxand a Si-rich liquid. Simultaneously, the molten Ti infiltrates into theTi3SiC2resulting in a 200 µm thick duplex region, comprised of TiCxand a Ti-rich phase with some dissolved Si.Both Si and C are found in the solidified Ti; the Si source is from the Si-rich liquid, while the presence of Cindicates that some of the C diffused into the Ti. Upon cooling, C- containing Ti- rich lamellae form the solidifiedTi. Microindentation results of the decomposed Ti3SiC2layer show an increase in hardness and a decrease inelastic modulus relative to T3SiC2. Notably, no cracks were observed Voir les détails
Mots clés : MAX Phases, Microstructures, Joining, hardness, Micro-indentation
Structural modification, photoluminescence, andmagnetic property enhancement with Er3+ doping,of sol–gel TiO2 thin films
Nanocrystalline undoped and Er3+ doped TiO2 thin films were prepared by sol–gel dip-coatingtechnique onto glass substrates. Post-deposited films were annealed at 450 °C for 1 h. Differentialscanning calorimetric analysis showed that undoped film crystallization occurred at 339 °C, whileit appears at lower temperature for Er:TiO2. X-ray diffraction and Raman spectroscopy resultsindicate that the films crystallize only into anatase phase, and the crystallite size decreases from24.3 to 21.16 nm with increasing Er3+ doping ratio. The photoluminescence (PL) spectra arecomposed of two broad peaks at 520–570 nm and 640–680 nm assigned to (2H11/2, 4S3/2)–4I15/2 and4F9/2–4I15/2 transitions of Er3+ ions, respectively. PL emission intensities increase gradually raisingthe erbium doping ratio. Vibrating sample magnetometer results of undoped TiO2 thin films reveala ferromagnetic behavior at room temperature and erbium doping leads to an enhancement of thesaturated magnetic moment (Ms). Voir les détails
Mots clés : TiO2 doped Er3+, Sol–gel, Photoluminescence, Magnetic Properties
Microstructural Study of Thin Films CuFe Obtained by ThermalEvaporation of Nanostructured Milled Powde
Commercial copper and iron powders were used as starting materials. These powderswere mechanically alloyed to obtain Cu(100-x) Fex supersaturated mixture. The milling duration waschosen in such a way as to obtain a nanostructured mixture and to form a supersaturated solidsolution of CuFe; the powder mixture was used to deposit CuFe on a glass substrate.The elaboration of our films has been carried out using thermal evaporation process (physical vapordeposition) under 1 × 10-6 mbar vacuum from an electrically heated tungsten boat, using thesupersaturated solid solution Cu(100-x) Fex powder obtained by mechanical alloying. The filmsdeposition has been done on glass substrates. In this study, we present the composition effect on thestructural and magnetic proprieties of Cu(100-x) Fex powder and thin films. The chemicalcomposition, structural and magnetic proprieties of milled powders and thin films were examinedby SEM, TEM, XRD, XRF and VSM. Voir les détails
Mots clés : thin film, CuFe Solid Solution, microstructure, DRX, MET, VSM
Structural, microstructural and thermal characterization of Fe- doped ZnO powder nanostructures prepared by mechanical alloying
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
Microstructural Analysis and Mechanical Properties of Cr 13 Ni 5 Mo 2 Super Martensitic Stainless Steel
Super martensitic stainless steel Cr 13 has been widely used in many applications particularly in the oil field for their superior mechanical properties and a corrosion resistance. In the present work, we study the microstructure and mechanical properties of a super martensitic stainless steel Cr 13% Ni 5% Mo 2% after quenching treatment at 1050 °C and tempering at 700 °C for 1 hour. Chemical analyzes were obtained by X-ray fluorescence and EDS / SEM. The experiment results that microstructure after heat treatment consisted of martensite and residual austenite estimated at 29%.For mechanical analysis, several methods of investigation were used namely micro indentation, testing tensile and charpy impact test. The friction wear is investigated in dry conditions and ambient air by pin-on-disk tribometer at 2, 6 and 10N load against WC ball. The friction coefficient (COF) varied from 0.62 to 0.56 and wear rate varied from 2.4 10-3 (mm3/N.m) to 0.6 10-3 (mm3/N.m). The wear mechanism was studied by scanning electron microscopy. Voir les détails
Mots clés : Super Martensitic Stainless Steel, heat treatment, structure, mechanical properties, wear.