Sciences des matériaux
Natural extract of Opuntia ficus indica as green inhibitor for corrosion ofXC52 steel in 1M H3PO4
The purpose of this study is to evaluate the anti-corrosive effect of natural extract of Opuntia Ficus Indica (O.F.I) for XC52steel in 1M H3PO4. Experimental work has been achieved by weight loss, potentiodynamic polarization and EISmeasurement, as well as SEM surface characterization. Among the results obtained, we can mention an inhibitory efficiencyof 90% by gravimetric method and 83.9% by electrochemical method at 10% (v/v) of O.F.I. Moreover, The O.F.I extract actsas a mixed inhibitor; however, adsorption free enthalpy indicates a physisorption. The adsorption obeys the Langmuirisotherm model. These results have been improved by SEM micrographs Voir les détails
Mots clés : corrosion, Opuntia ficus indica, EIS, green inhibitor, XC52 steel
Effect of microstructure and precipitation phenomena on the mechanical behavior of AA6061-T6 aluminum alloy weld.
In the present study, the effect of microstructure and precipitation phenomena on the micro hardness, tensile strength, impacttoughness, and electrochemical behavior of tungsten inert gas (TIG)-welded AA6061-T6 aluminum alloy are investigated. Themicrostructure features showed mainly the grains of aluminum solid solution with the presence of some precipitates at the grainboundaries. Scanning electron microscope micrographs exhibited the presence of Fe-based intermetallic and B-equilibriumprecipitates throughout a-Al grains. In the heat-affected zone (HAZ), the dissolution, over-aged, and coalescence of precipitatesare observed; their hardening effects disappear and a decrease in strength and hardness are noticed. The fracture toughness valuesof each zone at different temperatures using Charpy V-notch test remained constant where the HAZ presents the highest absorbedenergy. However, the temperature did not have a significant effect on the absorbed energy for each zone. In addition, the fracturedsurface of base metal (BM) and HAZ are characterized by dimple-like structure and they are larger in the HAZ. The electrochemicalbehavior of each zone of the weld evaluated in NaCl + H2O2 solution revealed that the corrosion current density of BMand HAZ is lower than that of molten zone (MZ), which displays high corrosion current density in this electrolyte and would befastest to corrode. Voir les détails
Mots clés : Aluminum alloys, TIG welding, precipitates, microstructure, Fractography, Electrochemical behavior
Early stages of copper microparticles electrodeposition on polypyrrole film
In this work, we studied the electrodeposition of copper (Cu) microparticles on polypyrrole (PPy) ?lms using cyclic voltammetry and chronoamperometry techniques. The initial stages of Cu deposition were investigated by performing current transients. Models based on Scharifker and Hills calculations were established to determine the nucleation and growth type. The results suggest that the deposition of Cu proceeds via an instantaneous nucleation followed by three-dimensional (3D) di?usion-limited growth. The values of the number density of active sites N∞ and di?usion coe?cient D were also determined. Voir les détails
Mots clés : composites, copper, electrodeposition, polymer, thin film
Effect of heat treatment on surface hardness and tribologicalbehavior of XC38 steel—approach by the experiments plans
This work aims at predicting the micro-hardness of XC38steel using the experiments plans as well asstudy of tribological behavior of thissteel. The heat treatments were considered by adopting thefactorial plans 22 methodology at two factors (temperature ‘T’ and holding time ‘t’), each at two levels(-1, +1). The results obtained allowed lead to a mathematical model predicting the micro-hardness‘Hv’ in every point of the study field. Moreover, the curves of the responses surfaces clearly show theinfluence of two factors studied (T, t) on ‘Hv’. Mechanical characterization of treated samples showedasignificant increase in the micro-hardness, which achieve to 76% for the treated sample at 850 °Cduring 2 h compared to untreated state. An investigation of wear tracks morphology shows thatfriction under a load of 10 N results in predominant adhesive wear, while a load of 2 N favorabrasive wear. Voir les détails
Mots clés : heat treatment, factorial plans, prediction, superficial hardness, tribological behavior
Magnetic and structural Behavior of Fe-CoO Nanocomposites Mechanically Milled
The Fe60(CoO)40 nanostructured alloys have been prepared from pure iron and cobaltoxide powders by mechanical alloying technique within a high energy planetary ball-mill.Morphology, microstructural and magnetic properties of this powder were investigated by aScanning Electron Microscope (SEM), X-ray diffraction (XRD) and Vibrating samplemagnetometer (VSM). The effect of time of milling on magnetic behaviour of Fe(CoO)nanostructured composite has been investigated. Apparition of new phase polycrystallinesample having a size in the range of 12 and 26 nm, it is confirmed by X-ray diffraction testing.The enhanced magnetic properties and structural behaviour of the nanoparticle are due by thediminution of size of crystallite. After 40 hours of milling, the appearance of spinel structureof CoFe2O4. The reduction in particle size leads to a significant increase in magnetichardening, the coercive field at room temperature increases from 6 Oe to 208 Oe Voir les détails
Mots clés : Fe60(CoO)40 nanostructured alloys, Mechanical Alloying, Magnetic Properties
Annealing duration in?uence on dip-coated CZTS thin ?lms properties obtained by sol-gel method
The e?ect of annealing duration on structural and optical properties of dip-coated crystallineCZTS thin ?lms was studied. The obtained samples were investigated by several techniques suchas XRD, Raman spectroscopy, SEM, UV–vis spectroscopy and Photoluminescence. Being con-?rmed by Raman spectroscopy, XRD analysis reveals the formation of kesterite tetragonal phasewith preferential orientation along (112) direction. The grain size tends to increase as the an- nealing duration increases, a result con?rmed by SEM. The last shows smooth, uniform, homo-geneous and densely packed grains. Optical measurement analysis reveals that layers have re- latively high absorption coe?cient in the visible spectrum with a band gap reduction of1.62−1.50 eV which is quite close to the optimum value for a solar cell. The photoluminescence distinguishes broad bands that have maximums of intensity limited between 1.50 and 1.62 eV, corresponding to the optical band gap of the CZTS. Voir les détails
Mots clés : Kesterite, sol-gel, Thin films, Dip-coating CZTS, Photoluminescence
Annealing duration influence on dip-coated CZTS thin films properties obtained by sol-gel method
The effect of annealing duration on structural and optical properties of dip-coated crystallineCZTS thin films was studied. The obtained samples were investigated by several techniques suchas XRD, Raman spectroscopy, SEM, UV–vis spectroscopy and Photoluminescence. Being con-firmed by Raman spectroscopy, XRD analysis reveals the formation of kesterite tetragonal phasewith preferential orientation along (112) direction. The grain size tends to increase as the an- nealing duration increases, a result confirmed by SEM. The last shows smooth, uniform, homo-geneous and densely packed grains. Optical measurement analysis reveals that layers have re- latively high absorption coefficient in the visible spectrum with a band gap reduction of1.62−1.50 eV which is quite close to the optimum value for a solar cell. The photoluminescence distinguishes broad bands that have maximums of intensity limited between 1.50 and 1.62 eV,corresponding to the optical band gap of the CZTS.Kesterite,Sol-gel,Thin-film,Dip-coating,CZTS,Photoluminescence Voir les détails
Mots clés : Kesterite, sol-gel, Thin-film, Dip-Coating, CZTS, Photoluminescence
Optimization of TIG Welding Process Parameters for X70-304LDissimilar Joint Using Taguchi Method
The optimization of mechanical properties of the welded joints requires a statisticalapproach such as Taguchi experimental designs associated with experimental techniques andlaboratory characterizations. The aim of this work is to propose a method of optimization of themechanical performances of a TIG dissimilar welding of two grades of steels: a high strength lowalloy steel X70 and an austenitic stainless steel 304L. The experimental designs were chosenaccording to the Taguchi method L9. The metallurgical characterization includes opticalmicroscopy, SEM microscopy, EDX analyses and mechanical tests to establish a relationshipbetween welding parameters, microstructures and mechanical behavior in different dissimilar weldregions. The results showed that the hardness is more strongly related to microstructural evolutionthan tensile strength of dissimilar joint. It was found that gas flow is the main significant TIGwelding parameter affecting dissimilar weld characteristics. Voir les détails
Mots clés : hardness, tensile test, ANOVA, Dissimilar welds, Taguchi method
CHARACTERIZATION OF IRON ORE AND SCALE FOR SYNTHESIZING VINYL PAINT
As part of the development of iron ore deposits in Algeria and a concern for the preservation of the environment, we are planning to characterize two materials for a possible synthesis of vinyl paint in this study. Iron ore is a red iron oxide pigment with an oolitic structure containing phosphorus. The second material is a steel by-product (scale) that should be recycled. This study covers the characterization of these two components through Chemical analysis, Particle size analysis, Thermal analysis (TGA, DSC), the Observation by SEM, X-Ray Diffraction analysis and Spectrophotometric analysis. Chemical analysis showed that the pigment contains 53.18% of total iron and mostly the gangue is dominated by silica and alumina. Scale in turn contains 73.83% of iron in the form of iron oxides (FeO, Fe3O4 and Fe2O3). Grinding tests illustrated that the scale is much more suitable for grinding than pigment. The granulometric analysis gave a volume distribution of the particles with a size between 0.7 and 32 µm for scale and 0.6 to 40 µm for the pigment and their specific areas are 1.6 and 1.5 m2/g. TGA and 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 a new phase with heat. Scanning electron microscope of red iron pigment showed a grain aggregate formed rounded over at least iron oxide and gangue. The EDS analysis illustrated a predominance of iron with four predominant oxides in the case of iron ore deposits. Chemical elements forming these four oxides are silicon, calcium, aluminum and magnesium. The SEM of scale showed a homogeneous structure composed of sizes of iron oxide grains and shapes ranging from 1 µm to 10 µm. X-ray diffraction analysis showed that the iron in the pigment is in the form of hematite (Fe2O3) and goethite (FeO(OH)). A tiny portion is combined with silica as fayalite (Fe2SiO4). The iron in the calamine is in the form of the three oxides (FeO, Fe2O3 and Fe3O4). Spectrophotometric tests showed that both materials have virtually no absorption and maximum reflection (100%) in the visible range Voir les détails
Mots clés : Pigment iron, scale (calamine), Simultaneous thermal analysis, X-ray diffraction, Spectrophotometry
Nitriding effect on structural stability and magnetic properties of FeAl alloys:DFT study
Using the DFT calculations, the phase stability, structural deformation and magnetic momentof Fe-riche FeAl alloys in presence of different percents of nitrogen were calculated. Theformation enthalpy of these Fe-Al alloys indicates that N preferred the octahedral site than thesubstitution one. Significant changes occur in this energy, affected by N and Fe contentcausing local distortions. From 25 at.% N, the phenomenon of saturation appeared and thesubstitution takes place. The addition of 6 at.% N stabilizes Fe 9 Al 7 and Fe 10 Al 6 . The presenceof N atom leading to decrease the total magnetic moment of FeAl nitride when the magneticorder is antiferromagnetic between N and Fe atom. This magnetic moment increased by theferromagnetic coupling between Fe and N, thus increasing the Fe local magnetic moment andthe magneto-volume effect. Voir les détails
Mots clés : Nitriding, Magnetic Properties, Structural Stability., FeAl Alloys, DFT