Sciences des matériaux

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Étude et réalisation de structure pérovskite non stœchiométrique PbTiO3-δ pour des applications ferroélectrique. 

KHIAT Abdelmadjid (2020)
Thèse de doctorat

Dans ce travail de recherche, nous avons élaboré le matériau PbTiO3-δ à partir les oxydes PbO et Ti3O5 en utilisant  la technique réaction à l’état solide dans un four sous vide. Dans ce travail nous avons étudié trois paramètres, le premier c’est l’effet de la température de calcination sur les propriétés structural (DRX, FTIR, RAMAN, EDX), microstructural (MEB) et magnétique (VSM) de PbTiO3-δ et étudié les propriétés diélectrique (pont d’impédance) de matériau élaboré. Dans l’objectif d’amélioration des propriétés magnétique de PbTiO3-δ, dans la deuxième partie nous avons dopé le PT avec un matériau ferromagnétique Fe d’où nous avons varié la quantité de dopant Fe et étudié l’effet de dopage sur les diffèrent propriété structural, microstructural, diélectriques et magnétiques. Dans la troisième partie nous avons étudié l’effet de la pression de vide de calcination sur les différentes propriétés structurales, microstructural, diélectriques et magnétiques de PbTiO3-δ élaboré par la technique réaction à l’état solide. Voir les détails

Mots clés : PbTiO3-δ, Pérovskite, Lacune d’oxygène, Aditifs, DRX, MEB, Raman, Echographies ultrasonore, Relaxeur

Analyse expérimentale et numérique de l’état mécanique (contraintes résiduelles) et de la résistance à la corrosion des assemblages soudés en acier inoxydable duplex

OUALI Naima (2020)
Thèse de doctorat

Dans le présent travail, l'influence de l'apport de chaleur sur la microstructure, l’évolution des contraintes résiduelles et la résistance à la corrosion d’un assemblage soudé en acier inoxydable Lean duplex UNS 32101 a été étudiée. Trois types d’assemblages ont été réalisés par le procédé TIG (Tungstèn Inhert Gaz) en faisant varier le courant de soudage, afin de générer des apports thermiques et des vitesses de refroidissement différents. Les résultats ont révélé que l'augmentation de l'apport de chaleur entraîne un changement important de la microstructure dans la zone fondue avec une fraction en austénite élevée. Les contraintes résiduelles induites par le soudage ont été mesurées, à la surface et à travers l’épaisseur par la technique de diffraction des rayons X, basée sur la méthode des Sin²ψ. Les résultats ont montré une relation inversement proportionnelle entre l'apport de chaleur et le niveau des contraintes résiduelles de compression, générées à la surface des cordons. Les essais de polarisation potentiodynamiques réalisés dans une solution à 3,5% de NaCl, ont montré une résistance à la corrosion élevée du métal fondu produit avec une faible énergie de soudage (LH 80) Voir les détails

Mots clés : procédé TIG (Tungstèn Inhert Gaz), corrosion, assemblage soudé en acier inoxydable Lean duplex UNS 32101

Elaboration et caractérisation d’un composite à base de diatomite

BENAYACHE Sihem (2020)
Thèse de doctorat

Des composites à base de matériau à changement de phase ont été élaborés par la méthode d’imprégnation de la paraffine à la diatomite brute, la diatomite calcinée, le kaolin, et le mélange kaolin/diatomite brute pour le stockage de l’énergie thermique dans les bâtiments. Le matériau à changement de phase a été optimisé à partir de la cire de paraffine (CP) et l’huile de paraffine (PL). Un ciment a été élaboré avec différents dosages de la diatomite brute. Les propriétés structurales, microstructurales et thermiques ont été étudiée par diffraction des rayons X (DRX), microscopie électronique à balayage (MEB), spectroscopie infrarouge à transformée de Fourier (FT-IR), calorimétrie différentielle à balayage et analyse thermogravimétrique (DSC-ATG).La diatomite brute est formée de trois phases : le quartz, la calcite, et la silice amorphe.Après calcination, les phases formées sont le quartz α, le quartz β, la cristobalite et le silicate bicalcique. Le kaolin est constitué essentiellement de kaolinite. Les micrographies MEB montrent que le MCP est bien imprégné dans les pores de la diatomite. Les résultats FT-IR révèlent l'absence d'interaction chimique entre la paraffine et la diatomite. Le compositeparaffine/diatomite calcinée présente une température de fusion de 28,44°C et une chaleur latente d'environ 56,40 J/g. La température de transition de phase et la chaleur latente ducomposite paraffine/diatomite brute sont de l’ordre de 28,78°C et 41,26 J/g, respectivement. Les composites PC-PL/diatomite sont de bons matériaux pour le stockage de l'énergie thermique dans les bâtiments en raison de leur fiabilité thermique. L’ajout de 5% de diatomite brute pour la fabrication du ciment conduit à l’amélioration de sa résistance mécanique en compression. Voir les détails

Mots clés : Diatomite ; Matériau à changement de phase ; Stockage de l’énergie thermique ; DRX ; MEB ; DSC

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

Investigation of diclofenac sodium adsorption by a purified Algerian diatomite using hydrochloric acid

W. Ghabeche, S. Boukhezar, K. Chaoui, S. BENAYACHE, H. MERADI  (2020)
Publication

The objective of this investigation is to use hydrochloric acid (HCl) at different concentration as a chemical treatment for the Algerian diatomite (DE) in order to get it ready for further applications oriented towards pharmaceutical aspects. Commercial diclofenac sodium (DS) is used to study adsorption on DE in aqueous laboratory conditions. It is found that DE contains roughly 60% SiO2 and 13% CaO. Its morphology is characterized by a porous structure composed of several broken and compacted diatomic aggregates, containing cylindrical and alveolus forms of varying diameters, girdle bands and other clayey compounds. The hydrochloric acid treatment is proven to be one attractive choice as it entails a significant raise of SiO2 and facilitates reducing most of impurities. After 10% HCl (DE-10) treatment of crude DE, the amount of SiO2 increased by over 64%. The result showing DS adsorption as a function of time is optimal for DE-10 as the quantity of the absorbed DS on treated DE (qt ) reached 60 mg/g and maintained this equilibrium level from 90 up to 120 min. The pseudo second order model has been successfully applied. The quantity of the absorbed DS on treated DE at equilibrium (qe ) and the pseudo second order rate constant (k2) for the case DE-10 are found 114.94 mg/g and 1.3 10−4 g mg−1 min−1 respectively. Voir les détails

Mots clés : diatomite, hydrochloric acid treatment, diclofenac sodium, adsorption, pseudo second order model

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

THE EFFECT OF Ti ADDITION ON MICROSTRUCTUREAND MAGNETIC PROPERTIES OF NANOCRYSTALLINEFeAl40 ALLOY POWDERS PREPAREDBY MECHANICAL ALLOYING

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

Recent research on nanocrystalline FeAl alloys has shown that these alloys are of high importancedue to their promising structural and mechanical properties, particularly magnetic behavior. Thiswork aims at studying the synthesis, structural and magnetic characterization of nanocrystallineFeAl alloy powders, prepared by a mechanical alloying process (MA), as well as the effect of Tiaddition on the magnetic properties of a compound. The powder morphology, phase transformation,crystallite size, micro-stress evolution, and magnetic properties were investigated by X-raydiffraction (XRD), scanning electronic microscopy (SEM), and vibrating samples magnetometer(VSM). It has been found that at the final stage of mechanical alloying the bcc-disordered FeAlphase and nanocrystalline Fe(Al, Ti) solid solution occurred for the FeAl40 and FeAl40Ti3 alloys,respectively. The milling time and the addition of titanium affect the powder morphology anddecrease the size of the particles. The average crystallites size of 17.2 and 11.2 nm was reached atthe end of 30 h of milling, and the lattice strain increased up to 0.3 and 0.21% for the FeAl40 andFeAl40Ti3 alloys, respectively. Also, the magnetic properties attributed to microstructural changeswere investigated. It has been established that the change in magnetic behavior occurs mainly due tothe formation of a supersaturated Fe(Al, Ti) solid solution. Magnetic properties of the samples arehighly influenced by the addition of the Ti element into FeAl40 alloy, as well. The magnetism of theFeAl40Ti3 compound is reported to be higher than that of FeAl40. Voir les détails

Mots clés : Mechanical Alloying, nanocrystalline materials, lattice strain, crystallite size, magnetic behavior.

Mechanical and structural behaviour of TiAlV nanocrystalline elaborated bymechanical milling technique

A.ABADA, S.Bergheul, A.Younes  (2020)
Publication

The aim of this study is to fabricate the Ti50Al40X1 0 nanostructured alloy (X: V) from pure titanium,aluminium, and vanadium powders by using a high-energy planetary ball mill with increasingmilling time from 10 to 80 h. Morphology, structural, and mechanical properties of this alloy wereinvestigated by a SEM, XRD, and nano-indentation testing. The effect of milling time on structural,morphological, and mechanical properties has been investigated. Microstructural characterisationshowed a decrease of average particle size during milling time. Crystallite size decreased from 49to 6.02 nm and lattice strain increased from 0.15% to about 0.89% during mechanical alloying. Inaddition, the mechanical properties of Ti50Al40V1 0 nanostructured materials were stronglydepended on the microstructure and crystallite size of new phases that appear during mechanicalmilling. Microhardness of the Ti50Al40V1 0 alloy increases with milling time from 261 to 738 Hv.These changes could be attributed to the crystallite size and the strain variations during milling. Voir les détails

Mots clés : crystal microstructure, Mechanical milling, Microstructural properties, nanostructured alloy, hardness testing

The influence of vacuum pressure on the electrical properties of PbTiO3-δ ceramics

Khiat Abd elmadjid, Felicia Gheorghiu, Mokhtar Zerdali, Saad Hamzaoui  (2020)
Publication

PbTiO3-δ ceramics were successfully prepared by the traditional solid state reaction method using different vacuum pressures during calcinations step and then sintered at 1150 °C/2h. The present study was focused on the influence of vacuum pressure variation on the electrical properties of PbTiO3-δ ceramics. The room temperature XRD patterns indicate the crystallization of the perovskite structure for all the ceramics. The dielectric permittivity is increasing with decreasing of vacuum pressure due to the increasing of oxygen vacancies with reaching the high vacuum. Resistivity decreased with temperature increasing which proves the semiconductor character of present PbTiO3-δ ceramics. The electrical characterization indicates that PbTiO3-δ ceramics prepared using three different vacuum pressures during calcinations step are suitable for room temperature applications in microelectronics. Voir les détails

Mots clés : PbTiO3-δ ceramics, vacuum pressure, oxygen vacancies, Electrical properties, resistivity

Physical properties investigation of Fe1−xAlx(x≤50%-at) alloys using DFT and Wagner-Schottky model

I Berrached 1, M Gallouze 1, L Rouaiguia 1, L Rabahi 1, T Grosdidier 2, M Drir A Kellou  (2020)
Publication

Atomistic modeling based on the Density Functional Theory (DFT) is used to study thestructural, magnetic, electronic and mechanical properties of Fe1−xAlx alloys (x≤50%-at) with and without B, C and N additions over the selected range of Al atomic concentration. It is shownthat a singularity around x Al ∼ 40%-at is observed for the lattice parameters while the magneticmoment decreases uniformly without unexpected trend. The enthalpies of formation indicatethat the presence of B stabilizes the system for Al concentration in the range of 25%-at Voir les détails

Mots clés : iron aluminides, Magnetic Properties, elastics proprieties, Electronic structures, DFT calculations, thermal defects, Wagner-Schottky Model