Physique

Nombre total de résultats : 258
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Anode carbon enrichment in GMAW

Flavien Valensi, Nadia Pellerin, Stéphane Pellerin, M. Collumeau, Amar BOUTAGHANE, Francis Briand  (2010)
Publication

The shielding gas used in the welding process has a strong influence on the metal transfer characteristics. When the gas is chemically active the physicochemical properties of the electrodes can be strongly altered which can increase or decrease arc stability. In order to get a better control over the process it is essential to understand how the electrodes are affected. As the electrode extremities are molten they can easily adsorb gases from the shielding gas, which can affect their microstructure. CO2 is one of the most commonly used active shielding gases. It is then interesting to know if the liquid metal at the extremity of the electrode can adsorbed the carbon it supplies, as it has strong influence on steel mechanical properties. Besides, various phases can form during metal cooling, depending on its concentration. It is then possible to get information on the carbon content by studying the ratio between phases. In order to show a possible enrichment, only the relative spatial evolution can be studied and no accurate phase identification is needed. Cross sections of the samples have been studied, using mainly optic microscopy. The two main phase ratio have been calculated after processing the obtained images. The results show a higher ratio of the phase associated to the highest carbon content close to the sample periphery, which support the hypothesis of carbon adsorption by the molten metal. Voir les détails

Mots clés : welding, microstructure, CO2, carbon, anode, Ferrite

Numerical simulation of a low- and a high-electric-field photocurrent decay in aSi:H

Aicha ALLAG, T. SMAIL, M. AOUCHER  (2006)
Publication

We report a numerical simulation of the photocurrent decay (PCD), from the steady state, in two different structure configurations based on the a-Si:H. The standard DOS of the a-Si:H is used. The high-electric-field PCD is considered in a structure configuration based on a metal/a-Si:H junction. Poisson’s and the two continuity equations are numerically solved in a one-dimensional space to calculate the current density. Two different boundary conditions of the a-Si:H film are considered. The low electric field PCD, which may occurs in a coplanar configuration, is calculated from the solution of a system of two non linear coupled rate equations which govern the free carriers concentrations and the different charges on the localized states in the gap. The calculated PCD versus time curves, for the two configurations, show a shoulder around 1μs which separate two main regions. We can see that the initial current decay is dominated by the electron emission from the conduction-band tail and the recombination via the dangling bonds states. The second current decay is mainly due to the electrons emission from the dangling bonds. We show also that the PCD curve tends towards the PCD of the coplanar configuration when the electric field decreases Voir les détails

Mots clés : a-Si:H film, simulation, photocurrent decay, recombination, Metal/semiconductor contact

Precipitation kinetics and mechanical behavior in a solution treated and aged dual phase stainless steel

Riad BADJI, Nabil KHERROUBA, Brahim MEHDI, Bilal CHENITI, M. BOUABDALLAH, C. KAHLOUN, B. BACROIX  (2014)
Publication

The precipitation kinetics and the mechanical behaviour in a solution treated and aged dual phase stainless steel (DSS) are investigated. X-Ray diffraction, transmission and scanning electron microscopy techniques are used to characterize the microstructure and to identify its constituents. The precipitation kinetics analysis shows that the ferrite to σ phase transformation follows the modified Johnson Mehl Avrami (JMA) model containing an impingement parameter c that is adjusted to 0.3. Activation energies calculation leads to conclude that interface reaction is the main mechanism that controls the σ phase formation. Detailed analysis of the extent of the different tensile deformation domains reveals the significant contribution of both σ phase particles and dislocation accumulation to the strain hardening of the material Voir les détails

Mots clés : alloys, aging, microstructure, mechanical properties

Spatial convolution of a stress field analyzed by X-ray diffraction

C. KAHLOUN, Riad BADJI, S. Queyreau, P. Franciosi, B. BACROIX  (2014)
Publication

X-ray stress analysis suffers from homogeneity limitations of the stress field in the analyzed volume. When this homogeneity is not fulfilled, it is possible to reduce the irradiated volume down to stress homogeneity achievement. New limitation however occurs : the diffracting sites become too few for stress homogenization. We show that the diffractometry analysis corresponds to a spatially convoluted stress field. The inverse convolution problem is posed. An example of regularization method is given. Voir les détails

Mots clés : XRD stress measurement, spatial convolution, stress gradient, inverse problem

Abstract factor analysis of spectroscopic data-another statistical fallacy

Rainer BAUSCH, Abdelaziz ABBAS  (1991)
Publication

It is shown that statistical arguments which have been used in published work to correct absorption spectra for medium effects are mathematically unsound and chemically misleading. Understanding this misconception, however, is helpful tomake clear the limits of abstract factor analysis in chemistry. Voir les détails

Mots clés : absorption spectra, abstract factor analysis

Theoretical description of the interactions between a mixture of vapors and a set of chemical sensors by variable temperature

Abdelaziz ABBAS, Ahcene BOUABDELLAH  (2007)
Publication

A sensor system is expected to detect gas concentrations of interest within low-ranges. The interactions between a sensor array and mixture of vapors hang not only on mixture composition and temperature but also on the partial sensitivities of the array elements. The aim of this paper is to find a useful equation in differential form that relates the change of sensors partial sensitivities to mixture component concentrations and temperature. This kind of equations is known in the thermodynamic of miscellaneous as equations of Gibbs–Duhém Voir les détails

Mots clés : adsorption, chemical sensors, sensor array, mixture of vapors, functions of state, equations of Gibbs-Duhem

Theory of solids/gas mixtures multi-interfaces: Application to the steady state interactions between a sensor array based on metal oxide semiconductor detectors and a mixture of vapours

Abdelaziz ABBAS, Ahcene BOUABDELLAH  (2010)
Publication

The aim of this paper is to find useful relationships in differential form that describe the isothermal steady state interactions between a sensor array based on metal oxide sensors and a mixture of vapours. These equations of state relate the variation of partial molar intensive quantities (as the change of the sensor molar partial sensitivity or molar adsorptions enthalpy), to gas mixture components concentrations and sensor array parameters. This kind of equalities is known in the thermodynamic of miscellaneous as Gibbs–Duhem equations. Voir les détails

Mots clés : Metal oxide sensors, Gas mixtures, Freundlich adsorptions isotherm, Sensitivity, Selectivity, Gibbs–Duhém equations, Adsorptions enthalpy change

Chemical Sensor Array Modeling: Application to Resistive Based Chemo Sensors

Abdelaziz ABBAS, Ahcene BOUABDELLAH  (2014)
Publication

The aim of paper is to develop analytical mathematical models that describe the thermo dynamical equilibrium of resistive chemical sensor arrays /mixture of vapors multi-system. By using the Gibbs Duhem formalism, state equations in differential form, that the variations of intensive quantities (e.g. sensors partial sensitivity) as function of the gas mixture components concentrations and sensor array parameters describe, have been developed. Moreover, the responses of the sensor arrays as function of gas mixture components concentrations were modeled. Voir les détails

Mots clés : resistive chemo-sensors, sensor array, vapors mixture, modeling, Metal Oxide Sensors (MOS), Conducting Polymer Sensors

NONDESTRUCTIVE EVALUATION OF THE CARBON CONTENT IN STEEL

A. Badidi Bouda, H. Belkhelfa, W. Djerir, and R. Halimi  (2014)
Publication

The aim of this work is to propose an experimental method to evaluate the steel carbon content by ultrasound. The sample is immersed in a water tank in order to analyze it under various incidences of sound waves. Longitudinal wave velocities are measured by immersion by using a 5-MHz frequency probe. Transverse wave velocities are measured in a contact mode by using a 4-MHz transverse wave transducer. The attenuation coefficients of ultrasonic longitudinal and transverse waves are deduced from three successive basic echoes through the sample. The effects of some heat treatments on ultrasonic parameters are also studied. The measurement of ultrasonic parameters in steel offers an interesting possibility of tracing the carbon content and, at the same time, provides information on the steel structure and its elasticity Voir les détails

Mots clés : carbon content, steel, ultrasonic waves.

Theoretical estimation of the production of biogasfrom the landfill of Batna city and its electricalconversion by a SOFC

B. Mebarki, B. Adouane, F. Khaldi, S. Dehimi, D. Haddad  (2015)
Publication

Amongst the interests in fuel cells is exploring the possibility of using different fuel types;one of them is biogas or Landfill gas (LFG) from landfills or from controlled digesters.Biogas; a gas produced by an anaerobic digestion of organic waste represents an environmentalproblem that could turn to a renewable energy source. The valorization ofbiogas into energy (electricity, heat, fuel) will save other sources of energy. The authors ofthe study are interested in evaluating three technologies: fuel cells, micro turbines andinternal combustion engine.In this paper, we discussed the conversion of biomass into electricity in two steps: thefirst step (biomass-to-biogas) is based on an evaluation of biogas potential generated bysolid waste of landfill the Batna city (Algeria) by the kinetic model (U.S.EPA, 1993). In thesecond step (biogas-to-electricity), the paper considers the technology of a stack of standardsolid oxide fuel cells (Ni-YSZ/YSZ/LSM) SOFC; this allowed us to determine the besttemperature, hydrogen concentration and electrolyte thickness for maximum powerdensity in the fuel cell SOFC. At a temperature T = 1273 K and thickness of electrolyte of theorder of 0.1 mm and at higher hydrogen concentration, a maximum power density ofP = 1.4 W/cm2 was obtained. Voir les détails

Mots clés : LFG, Biogas, Anaerobic digestion, Electricity, SOFC