Sciences des matériaux
Steel XC38 protection against corrosion by an organic compound (DHASC) in hydrochloric acid medium
Corrosion in industrial environments is a major factor limiting the lifespan of materials, causing many replacement costs and lost productivity. For a judicious selection of materials in particularly aggressive environments, one must often use standardized laboratory tests and / or factory whose validity and reliability have not always been clearly demonstrated. Corrosion inhibitors are a means of struggle against corrosion of metals and alloys relatively recent. The originality of this method is the fact that the anti-corrosion treatment is not done on the metal itself but through the corrosive environment. The inhibitor molecules may act on different mechanisms, thus giving them dependent inhibition material performance and study environment. In this work we have synthesized and characterized a novel organic compound (DHASC) To identify it, we appealed to the physicochemical methods of analysis: IR, UV-Vis, NMR 1H and voltammetry cyclic organic medium (DMF-Bu4NPF6 0.1M) was platinum electrode. The study of the inhibitory effect of the ligand on the corrosion of carbon steel X52 in hydrochloric acid medium and in the presents inhibition character. The inhibitory efficacy in hydrochloric acid medium, it reaches 69% at a concentration of 10-5M. The application of this new ligand synthesized in everyday life, the water treatment industry in the fight against corrosion. Voir les détails
Mots clés : Corrosion Protection Steel XC38, inhibitor
Microstructural, morphological, mechanical and tribological characterization of nanocrystalline nickel and Ni-Co electrodeposited coatings
The nanocrystalline nickel and nickel-cobalt coatings were electrodeposited on an A60 steel substrate in a modified Watts bath. The observation of the coatings produced by scanning electron microscopy (SEM) showed that the nickel coatings have a granular structure whereas the Ni-Co alloy deposits have a lens-shaped structure with a considerable increase in the grains size of the Ni-Co alloy deposits. Analysis by profilometer confirms these results where we find that the surface roughness of nano-crystalline nickel coatings is less than that of Ni-Co alloy coatings. The results of XRD showed that the nickel coatings having an fcc phase structure while the Ni-Co coatings have a mixed phase structure hcp + fcc. . The study of micro-hardness of the coatings show that this latter follow the Hall Petche effect where nickel deposits which have the small grain size compared to that of the Ni-Co alloy show a higher microhardness to that of Ni-Co coatings. Pin on disk tribometric analysis under unlubricated conditions showed a great improvement of the wear resistance by the addition of cobalt on the nickel coatings, where the friction coefficient and the wear rates are reduced to very significant manner in the Ni-Co coatings compared with nickel coatings. Voir les détails
Mots clés : Nickel coatings, Ni-Co coatings, microstructure, morphology, Micro-hardness, Tribological properties
DFT study of F atom adsorption on Si(001) surface
We have investigated the initial adsorption of an fluorine (F) atom on Si(001) surface by means of first-principles calculations using pseudopotential method implemented in SIESTA code. Three high-symmetric adsorption sites of F on Si(100) were examined : top, bridge and hollow sites. For an F atom adsorbed on perfect Si(001) surface, we found that F atom prefer the bridge adsorption site with a high adsorption energy of 6.47eV. However, in the relaxed case, the adsorption of an F atom leads to a Si(001)-2×1 surface reconstruction and the most stable adsorption site corresponds to the dangling bond site of a Si(100) surface top layer. The Si-F bond is calculated to be 1.67 Å and the adsorption energy of the F atom is evaluated to be 6.51eV. Voir les détails
Mots clés : DFT, SIESTA, Silicon, fluorine, adsorption
Structural, Morphological and Optical Properties of Zn(1−x)CdxO thin films grown on a glass substrate by spray pyrolysis method.
Method on the glass substrate at 450°C.For Cd doping, various concentrations of cadmium nitrate Cd(NO3) (2–8 wt%) was used in the spraying precursor solution. The structural, Zinc oxide (ZnO) and ZnxCd1-xO thin films were deposited using a low cost spray pyrolysis morphological, and optical properties of ZnO and Cd:ZnO films were investigated using X-ray diffraction (XRD), scanning electron microscope(SEM), atomic force microscope (AFM), UV–vis. X-ray diffraction study reveals that the ZnO and Cd:ZnO films are possessing hexagonal wurtzite structure. SEM and AFM studies reveal that the grain size and roughness of the films are decreased with increasing Cd doping concentration. Optical transmittance spectra of the CdO film decreases with increasing doping concentration of cadmium. The optical band gap of the films decreases from 3.25eV to 2.90 eV with increasing concentration of cadmium. On increasing Cd concentration in ZnO binary system, the absorption edge of the films showed the red shifting. Voir les détails
Mots clés : Cd-doped ZnO, Spray pyrolysis, X-ray diffraction, optical properties
Evolution of texture and residual stresses with the thickness for aluminum nitride deposited by dcMS on Si (100)
This work presents a study of XRD measurements on the development of the fiber (0001) and residual stress with the film thickness. Aluminum nitride (AlN) films were deposited by dc magnetron sputtering (dcMS) on Si (100) substrates in Ar-Ngaz mixture, at different thickness. The texture characterizations of the films were performed by X-ray pole figure technique. It was found that with increasing of the thickness the fiber (0001) becomes more marked. The (10-11) and (10-12) FDPs confirm the presence of reinforcements on the (0001) fiber. The angles between these reinforcements are about 60° and 120°. The observed asymmetry increases with thickness and could be connected to the angular differences between the AlN (0001) and Si (100) which lead to a full distortion. The residual stress decreases with the thickness increase. Voir les détails
Mots clés : AlN thin films, DC-PVD, Fiber texture, Asymmetry
The Inhibition Effect of Gum Arabic on the Corrosion of Carbon Steel in Hcl Medium
The inhibition effect of exudate gum from Acaciatrees (Gum Acacia, GA) on the corrosion of carbon steel API 5LX60in acidic media1 M was studied by weight loss,electrochemical polarization methods; also, surface morphology.The results of weight loss and electrochemical polarization methods indicated that the inhibitor efficiency (I%) increased with increasing inhibitor concentration.The results show that GAis a good inhibitor in 1 M . The maximum percentage inhibition efficiency was found to be 92% at 4 g L. The adsorption of GA on pipeline API 5L X60 steel surface obeys Langmuir adsorption isotherm, and involves physical adsorption. Polarization curves reveal that GA acts as a mixed-type inhibitorin sulfuric acid. Voir les détails
Mots clés : Gum Arabic, corrosion, steel, inhibition efficiency, inhibitor
NUCLEATION AND FORMATION OF OXIDE FILM UNDER A MAGNETIC FIELD
Nucleation and formation of an oxide film in contact with sliding unidirectional dry were studied in a vacuum chamber with and without the application of a magnetic field to identify the role of the intensity of magnetic field on the oxidation wear. The wear tests of AISI 1045 steel / steel AISI 1045 Were are carried in a tribometer pin on disc in three different gas environments: In ambient air, in oxygen at 105Pa and under vacuum at 5.10-5 Pa. The formation of the oxide film depends strongly on the partial pressure of oxygen and the intensity of the magnetic field. After de delimination of the first wear debris, these wear debris compacted to form the oxide film. Voir les détails
Mots clés : friction, wear, Oxidation, environment gas
Identification of Fe-Al intermetallic phases in aluminide coatings on mild steel
Mild steel were coated by hot-dipping in molten aluminum bath at 800°C and 1000°C for 90 minutes. Phase identification of the Fe-Al intermetallic compounds in the hot-dipped aluminide mild steel was carried out by using a combination of scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), and electron backscatter diffraction (EBSD). The results showed that the intermetallic layer growing toward the steel substrate possessed a tongue-like morphology. The intermetallic layer of the hot dipped was composed of minor monoclinic FeAl3 and major orthorhombic Fe2Al at the temperature of 800°C and 1000°C. But at the interface intermetallic/steel, the intermetallics compounds formed in this level are FeAl cubic and Fe35Al at the temperatures of 1000°C and 800°C respectively. These intermetallics compounds which appear in very thin layer, at the interface, are tangent toward the steel. Voir les détails
Mots clés : Mild steel, Hot-dipping, intermetallic Compounds, Aluminide layer, EBSD.
A comparative study of potentiostatic and pulsed Electrodeposition of ZnS nanostructures
Electrochemical, structural and optical properties of ZnS thin films deposited by either potentiostatic or pulsed electrodeposition were investigated. The grown thin films of ZnS from the both processes were studied by means of Mott-Schottky (MS), AFM, XRD, Raman and UV-Vis spectrometry. The deposits of ZnS were grown using an aqueous solution containing 10-3M Na2S2O3 and 10-4M ZnSO at pH=2,4. The electronic properties using Mott-Schottky confirm the n type conductivity, the AFM shown a strongly changement on the surface of the obtained film for both method. The XRD and Raman show that the deposited films are polycrystalline in nature and crystallize with blende structure in both processes, while the optical properties of the deposited ZnS thin films have a band gap equal to 3.5eV. Voir les détails
Mots clés : ZnS, Mott-schottky, pulse, potentiostatic, XRD
Corrosion study of Neodymium-Iron-Boron alloys: Neutron reflectometry of the ultra-thin polymer film interfaces and effectiveness of polymer coatings
Neodymium-iron-boron alloys are very sensitive, particularly to the air humidity. The aim of this work is to study the effectiveness of polymer coatings against corrosion in the cases cited above. This work is financially supported by the Research Thematic Agency in Science and Technology. In this context we introduced the neutron reflectometry to study the ultra-thin polymer film interfaces of polymethylmethacrylate (PMMA). Reflectometry experiments were conducted at the nuclear research center of Draria (Algiers). The preparation of the PMMA films is performed by means a technique based on depositing a thin film on a planar solid surface. This method known as the “spin-coating’’ provides dense, homogeneous materials very thin after a rapid evaporation of the total solvent. First, we realized calibration settings "zero" reflectometer: one seeks the zero position of the detector, the optimal position of the sample and its angle of rotation. The measured reflectivity as a function of the scattering vector Q, gives information on the thickness of layers, roughness of multilayer system. From the spectrum of the reflectivity vs. the wave vector (scan Θ-2Θ of the PMMA film), we find a thickness of the PMMA film. Electrochemical measurements were performed in a three electrode cell using an VoltaLab Master4, Model 273A potentiostat. The samples of Nd-Fe-B magnets covered by the PMMA film are used as working electrode in the NaCl (0.5M) solution, a platinum wire as counter electrode and a saturated calomel electrode (SCE) as reference electrode. The polarization parameter values, corrosion current density (Icorr) and the polarization resistance (Rp) were determined. The corrosion rate values obtained show interesting perspectives for our work. The corrosion resistance is improved in the presence of PMMA layers. We note that for variable thickness of PMMA film 485nm and 1,5µm the polarization resistance are 518Ωcm² and 6550Ωcm² respectively. The corrosion rate values obtained show interesting perspectives for our work. The corrosion resistance is improved in the presence of PMMA layers Voir les détails
Mots clés : rare earths, magnet, corrosion, polymer coatings