Modélisation du traitement de purification de l'acide phosphorique de voie humide par la méthylisobutylcétone

The present paper reports results for the purification of phosphoric acid by liquid—liquid extraction with methylisobutylketone. The simultaneous effect of some operating parameters, namely concentration of the feed acid, massic ratio of solvent to feed, temperature and number of theoretical stages, on the performances of the extraction step has been examined using a factorial design 2⁴. The established models allowed us to forecast the experimental conditions required to obtain a given yield of P₂O₅ and/or a well‐defined quality of the stripped acid. The optimal conditions have been determined by using a desirability function.     

Application of a factorial design to study a chromate-conversion process

Chromate conversion coatings are commonly deposited on plated zinc to improve the corrosion resistance of the substrates, and to increase the adherence of painted films. The coatings’ properties depend on the composition and the structure of the conversion films as well as on the process parameters. A fractional factorial design was implemented to optimize the experimental conditions of the chromating process (bath composition, rinses composition, draining, treatment time). Surface analytical techniques such as scanning electron microscopy, glow discharge optical spectroscopy, and atomic absorption spectrometry were used to characterize the chromate conversion coatings.     

Effect of Mg Substitution on Room Temperature Dielectric and Magnetic Properties of Sr-Doped Bismuth Ferrite

Mg-co-substituted BiFeO₃ was synthesized. We investigated the structure and multiferroic properties of Sr- and Mg-co-substituted bismuth ferrite. The purity and structural changes induced by Mg doping are confirmed by X-ray powder diffraction and Raman spectra. It was found that a small amount of Mg doping leads to dramatic enhancement in dielectric permittivity, along with an apparent improvement in ferromagnetism .Meanwhile, the co-substitution can effectively reduce the leakage current and increase the dielectric constant. The release of latent magnetization after Sr and Mg co-doping is stronger than the sum of two single dopings, indicating a nonlinear enhancement in Sr and Mg codoping. The ferromagnetism can be ascribed to the creation of unbalanced Fe³⁺ spins and relative long-range coupling mediated by the oxygen vacancies trapped localized electrons. Compared to the pristine bismuth ferrite, Bi_0.95Sr_0.05Fe_0.9Mg_0.1O₃ exhibits more than fivefold improved magnetization with simultaneously improved electrical properties demonstrating the possibility of co-doped BiFeO₃ for practical applications.     

Contribution des fillers calcaires à l’adhérence pâte-granulat. Exemples tunisiens

This article presents compressive test results carried out on a series of hydraulic concrete mixes without admixtures based on Tunisian limestones aggregates. Their estimated strength was calculated with the French model of LCPC (Laboratoire Central des Ponts et Chaussées), which takes into account the effect of bond to the paste and the ceiling effect of the aggregates. To check the experimental values, the parameter of bond had to be associated the content of fillers aggregates, because the performances predicted by the model are lower than the measurements, at least beyond 10% of fillers. The assumption is that the presence of these fine elements, of comparable nature that the aggregates, improves adherence or linking between paste and aggregate, thanks to bringing together the properties of rigidity of the two materials and to a better homogeneity of the system. The relationship found between the calcareous filler ratio and the bond coefficient then makes it possible to extend the forecasts of the model to the hydraulic mixtures containing aggregates crushed limestones, naturally rich in fillers.      

Elaboration and properties of new ceramic microfiltration membranes from natural and synthesised apatite

In this work, we were interested in the development and the characterisation of new mineral microfiltration membranes coated on apatite macroporous supports which are prepared and characterised beforehand. The choice of material is based primarily on its low cost (considering its abundance in the Tunisian layers for natural apatite) and its thermal and chemical resistance. The active layers were prepared from lacunary hydroxyapatite synthesised (HA) and from natural apatite (AB). The membranes were deposited on the tubular support basing of natural apatite, already prepared by the “slip-casting” process. The thermal treatment consists of drying at room temperature for 24 h then a sintering at 600°C for the membrane with HA (MS) and at 750°C for the membrane with AB (MB). The surface and the cross-section morphologies observed through a scanning electron microscope (SEM) are homogeneous and do not present any macro defects (cracks, etc.). The average pore diameters of the active layer are approximately 0.25 μm and 0.2 μm for the MS and MB membrane respectively. The obtained membrane was used to treat cuttlefish effluents generated from the conditioning seawater product industry which consumes a great amount of water where the washing baths are discharged in the littoral of Sfax (Tunisia) (about 1000 m³/d). Cross-flow microfiltration was performed then, in order to reduce the turbidity and chemical oxygen demand (COD). The result showed a high retention of turbidity (99%), conductivity and COD (85%).     

Multicriteria optimization of mechanical and morphological properties of chromium electrodeposits under reverse pulse plating

In this work, a central composite design experiment was performed to estimate the effect of the electroplating parameters (temperature of electrolyte, cathodic and anodic pulse current densities, and cathodic and anodic pulse lengths,) on four properties of hard chromium electrodeposits. The studied responses were the hardness (Hv), the roughness quantified by the two criteria R_a (nm) and R (μm)), and the specific abrasive energy, E_s (μJ μm⁻³). Analysis of the responses using optimal path technique did not lead to a common set of experimental conditions which fulfilled the required properties. Thus, the desirability function approach has been employed in order to find the best compromise between the different experimental responses. The optimal conditions are: electrolyte temperature: 49.9 °C; cathodic pulse current density: 42.0 A dm⁻²; anodic pulse current density: 51.5 A dm⁻², cathodic pulse length: 6.23 s and anodic pulse length: 28.5 ms. Under these conditions, the estimated response values are 738 Hv, 262 nm, 2.61 μm and 0.027 μJ μm⁻³ for hardness, R_a, R and specific abrasive energy respectively, validated experimentally. The resultant coating, examined by AFM, exhibits a nodular fine-grained morphology.     

Gray-level grouping (GLG): an automatic method for optimized image contrast enhancement--Part I: the basic method.

Contrast enhancement has an important role in image processing applications. Conventional contrast enhancement techniques either often fail to produce satisfactory results for a broad variety of low-contrast images, or cannot be automatically applied to different images, because their parameters must be specified manually to produce a satisfactory result for a given image. This paper describes a new automatic method for contrast enhancement. The basic procedure is to first group the histogram components of a low-contrast image into a proper number of bins according to a selected criterion, then redistribute these bins uniformly over the grayscale, and finally ungroup the previously grouped gray-levels. Accordingly, this new technique is named gray-level grouping (GLG). GLG not only produces results superior to conventional contrast enhancement techniques, but is also fully automatic in most circumstances, and is applicable to a broad variety of images. An extension of GLG, selective GLG (SGLG), and its variations will be discussed in Part II of this paper. SGLG selectively groups and ungroups histogram components to achieve specific application purposes, such as eliminating background noise, enhancing a specific segment of the histogram, and so on. The extension of GLG to color images will also be discussed in Part II.     

Enhancement in Magnetic Properties of Mg-Doped Strontium-Substituted Bismuth Ferrite Prepared by Solid-State and Sol-Gel Methods

We report a potential way to effectively improve the magnetic properties of BiSrFeO3 (BSFO) through Mg ²⁺ ion substitution at the Fe sites of BFO lattice. Polycrystalline Bi_0.95Sr_0.05Fe_0.98Mg_0.02 O ₃ (BSFMO) powder was prepared through optimized solid-state (SS) and sol-gel (SG) reaction methods. The effect of preparation routes on the crystal purity and multiferroic properties of the BSFMO was investigated. The purity and structural changes induced by Mg doping are confirmed by X-ray powder diffractometer and IR spectra. Enhanced magnetic properties are observed in Mg-substituted samples, which simultaneously exhibit ferromagnetic and superparamagnetic properties at room temperature. The improved magnetic properties and soft nature obtained by Mg doping in BSFO particles demonstrate the possibility of BFO particles to practical applications.     

Image Processing-Based Mine Detection Techniques: A Review

Various mine detection techniques are reviewed with particular emphasis on signal and image processing methods. Based on the target, mines are classified into two types; anti-tank mine (ATM) and anti-personnel mine (APM). Because of the variety of mine types, current mine detection techniques are diversified. The assumption is made that most mine detection techniques consist of sensor, signal processing, and decision processes. For the sensor part, ground penetration radar (GPR), infrared (IR), and ultrasound (US) sensors are reviewed and their characteristics are summarized for the corresponding output signals. For the signal processing and decision parts, a set of image processing techniques including filtering, enhancement, feature extraction, and segmentation are surveyed. Segmentation is used to extract mine signal from various competing signals. For most image processing techniques covered by this paper, mine detection related experimental results are included or reproduced from existing works.