Stress distribution in thick-walled cylinder due to non-uniform radial pressure on the example of reinforcement corrosion in concrete

This paper presents an analytical solution to the non-uniform pressure on thick-walled cylinder. The formulation is based on the linear elasticity theory (plain strain) and stress function method. As an example, the proposed solution is used to model the stress distribution due to non-uniform steel reinforcement corrosion in concrete. The model is formulated considering different scenarios of corrosion pressure distribution. It is validated against the finite element model for different cases of non-uniform pressure distributions. The results show that the corrosion-induced cracks are likely to start just beyond the anodic zone. This is confirmed by the experimental tests on concrete cylinder exposed to non-uniform accelerated corrosion of steel reinforcement. The model can be effectively used to calculate the distribution of corrosion-induced stresses in concrete.     

Improvement of corrosion protection of steel by incorporation of a new phosphonated fatty acid in a phosphorus-containing polymer coating obtained by UV curing

Six formulations containing diacrylate monomers (from 89 to 92.5% (w/w)) as well as a phosphonated methacrylate monomer (from 1 to 10% (w/w)) were prepared. All formulations were UV-cured and the corrosion performance of the resulting coatings applied onto a steel substrate was assessed by electrochemical impedance spectroscopy (EIS). It was first shown that the coatings containing phosphonic acid methacrylate (MAPC1(OH)₂) instead of methacrylate phosphonic dimethyl ester (MAPC1) presented higher corrosion protection related to the strong adhesive properties of phosphonic acid on the metal substrate. A minimum MAPC1(OH)₂ content of 2.5% was determined to provide the highest impedance values (best efficiency). Then, a new bio-based compound, i.e. phosphonic acid-bearing oleic acid (phosphonated fatty acid), was synthesized and added as an inhibitor to the formulations. In the presence of this compound, the corrosion protection was notably improved. The beneficial effect of phosphonated fatty acid was explained by its inhibitive action at the steel/coating interface and by the improvement of the barrier properties.     

Photocatalytic degradation of methyl orange dye by NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles under visible irradiation: effect of varying the synthesis temperature

Nanoparticles of nickel ferrites (NiFe₂O₄) were synthesized at different temperature of synthesis (25, 50 and 80 °C) through the chemical co-precipitation method. The synthesized powders were characterized using X-ray diffraction for crystallite size and lattice parameter calculation. It reveals the presence of cubic spinel structure of ferrites with crystallite size between 29 and 41 nm. Transmission electron microscopy and scanning electron microscopy showed uniform distribution of ferrite particles with some agglomeration. The Fourier-transform infrared spectroscopy showed absorption bonds, which were assigned to the vibration of tetrahedral and octahedral complexes. Raman spectroscopy is used to verify that we have synthesized ferrite spinels and determines their phonon modes. The thermal decomposition of the NiFe₂O₄ was investigated by TGA/DTA. The optical study UV–visible is used to calculate the band gap energy. Magnetic measurements of the samples were carried out by means of vibrating sample magnetometer and these studies reveal that the formed nickel ferrite exhibits ferromagnetic behavior. Photoluminescence showed three bands of luminescence located at 420, 440 and 535 nm. The photocatalytic properties of nickel ferrite (NiFe₂O₄) nanoparticles were evaluated by studying the photodecomposition of methyl orange as organic pollutant models and showed a good photocatalytic activity.     

An improved radial impulse turbine for OWC

Traditionally, wells turbines have been widely used in OWC plants. However, an alternative has been studied over recent years: a self-rectifying turbine known as an impulse turbine. We are interested in the radial version of the impulse turbine, which was initially proposed by M. McCormick. Previous research was carried out using CFD (FLUENT^®), which aimed to improve knowledge of the local flow behavior and the prediction of the performance for this kind of turbine. This previous work was developed with a geometry taken from the literature, but now our goal is to develop a new geometry design with a better performance. To achieve this, we have redesigned the blade and vane profiles and improved the interaction between them by means of a new relation between their setting angles. Under sinusoidal flow conditions the new design improves the turbine efficiency by up to 5% more than the geometry proposed by Professor Setoguchi, in 2002. In this paper, the design criteria we have used is described, and the flow behavior and the performance of this new design are compared with the previous one.     

Electrochemical oxidation of hydroquinone, resorcinol, and catechol on boron-doped diamond anodes

The electrochemical oxidation of aqueous wastes polluted with hydroquinone, resorcinol, or catechol on boron-doped diamond electrodes has been studied. The complete mineralization of the organic waste has been obtained independently of the nature of each isomer. No aromatic intermediates were found during the treatment, and solely aliphatic intermediates (carboxylic acids C4 and C2, mainly) were detected in the three cases. Although as from the bulk electrolyses study no differences in the electrochemical oxidation of dihydroxybenzenes seem to exist, different voltammetric behavior between resorcinol and the other two isomers was obtained in the voltammetric study. Catechol and hydroquinone have a reversible quinonic form, and a cathodic reduction peak appears in their voltammograms. The characterization of the first steps in the electrochemical oxidation of the three dihydroxybenzenes showed the formation of a larger number of intermediates in the oxidation of catechol, although no carbon dioxide was detected in its oxidation. Conversely, the oxidation of resorcinol and hydroquinone lead to the formation of important concentrations of carbon dioxide. The nondetection of aromatic intermediates, even if small quantities of charge are passed, confirms that the oxidation must be carried out directly on the electrode surface or by hydroxyl radicals generated by decomposition of water.     

Performance comparison of AlGaAs,GaAs and InGaP tunnel junctions for concentrated multijunction solar cells

Four tunnel junction (TJ) designs for multijunction (MJ) solar cells under high concentration are studied to determine the peak tunnelling current and resistance change as a function of the doping concentration. These four TJ designs are: AlGaAs/AlGaAs, GaAs/GaAs, AlGaAs/InGaP and AlGaAs/GaAs. Time‐dependent and time‐average methods are used to experimentally characterize the entire current–voltage profile of TJ mesa structures. Experimentally calibrated numerical models are used to determine the minimum doping concentration required for each TJ design to operate within a MJ solar cell up to 2000‐suns concentration. The AlGaAs/GaAs TJ design is found to require the least doping concentration to reach a resistance of <10⁻⁴ Ω cm² followed by the GaAs/GaAs TJ and finally the AlGaAs/AlGaAs TJ. The AlGaAs/InGaP TJ is only able to obtain resistances of ≥5 × 10⁻⁴ Ω cm² within the range of doping concentrations studied. Copyright © 2010 John Wiley & Sons, Ltd.     

Optimizing the physical properties of calcium nanoferrites to be suitable in many applications

Calcium nano ferrite with composition CaGd_xEr_yFe_2?x?yO₄ (x?=?y?=?0.0, x?=?0.025, y?=?0.05) was prepared by citrate gel auto combustion method. The prepared samples showed orthorhombic phase structure and the crystallite sizes were found in the range of 32.1–35.3 nm. Detailed observation via the Field Emission Scanning Electron Microscopy (FESEM) showed that the calcium ferrite nano-particles were spherical and capsule like formation shape. The hysteresis loop confirms the magnetic behavior of the investigated samples, which is then discussed on the basis of super exchange interactions. Magnetic parameters such as saturation magnetization, coercivity, and retentivity were obtained. Greater than six-fold increase in coercivity (≈2085 Oe) was observed in calcium nanoferrites compared to the doped samples (≈360 Oe). The CaFe₂O₄-type structure includes edge- and corner sharing BO₆ octahedral, constituting a very unique network similar to perovskite-related nanoparticles. This structural network leads to an improvement in the physical properties of the investigated samples. Great efforts have been made to synthesize pure nanoferrite samples without any secondary phases even after the substitution of low soluble rare earth ions. Special attention should be given to calcium ferrite nanoparticles which are suitable candidates to be used in the manufacturing of bone-like scaffolds, hyperthermia treatment of cancer and biological activity.     

Electrochemical treatment of the pollutants generated in an ink-manufacturing process

The effluents of ink-manufacturing processes contain a large variety of pollutants such as dyes, surfactants, biocides, water soluble solvents, etc. In this work, the electrochemical oxidation of several dyes (methylene blue and rhodamine B), solvents (monoethylene glycol, diethylene glycol and glycerol) and surfactants (sodium dodecylbenzenesulfonate) has been studied. To carry out the electrolyses, a bench-scale plant with a single-compartment electrochemical flow-cell was used. Boron doped diamond (BDD) was used as anode and stainless steel (AISI 304) as cathode. For all the compounds tested, the conductive diamond electrooxidation allows achieving the almost complete removal of COD of the waste with a very high current efficiency. The efficiencies of the electrochemical processes seem to depend on the current density and on the nature of the anions contained in the waste (chlorine, sulphate, phosphate). Thus, it has been observed that the use of chloride media favours the treatment of dyes. On the contrary, the use of sulphate- or phosphate-containing solutions improves the removal of the aliphatic compounds studied (solvents). These results suggest an important role of the mediated electrochemical processes on the overall performance of the reaction system.     

Particleboards production from date palm biomass

Date palm biomass is a renewable natural resource that has not widely been utilized in industry. The objective of this study was to examine some chemical properties of date palm trunk and rachis (holocellulose, cellulose, lignin and extractives) and to evaluate their suitability to produce composite panels. Particleboards were produced using trunk and rachis as an alternative raw material for forest products industry in the presence of two types of polycondensation resins (phenol–formaldehyde and melamine urea–formaldehyde) which were selected as binding agents. The panels were tested for their physical (water absorption and thickness swelling) and mechanical (modulus of rupture, modulus of elasticity and internal bond strength) properties. The internal bond strength of date palm trunk and date palm rachis based boards met the requirements of the general purpose product standards (EN 312) at 0.70 g/cm³ density. The panels made with phenol–formaldehyde resin showed better performance with respect to the panels made with melamine urea–formaldehyde. In addition, the particleboard made with date palm trunk particles had better quality compared to the particleboard made from date palm rachis particles. Based on preliminary results of this work, raw materials from date palm trunks and rachis can have a promising potential in the manufacture of particleboards and as a substitute for wood in board production.     

Electrochemical degradation of an anionic surfactant on boron-doped diamond anodes

In this work, the electrochemical oxidation on boron-doped diamond of synthetic wastes polluted with surfactant sodium dodecylbenzenesulfonate (SDBS) has been studied. Results show that SDBS can be successfully removed with this technology inside different current densities and concentration ranges. The oxidation of the SDBS seems to occur in two main sequential steps: the first is the rapid degradation of SDBS, and the final is the less efficient oxidation of aliphatic intermediates to carbon dioxide. The nature of supporting electrolyte (NaCl, Na(2)SO(4) and K(3)PO(4)) influences on the efficiency of the electrochemical oxidation process. The treatment of the NaCl solution seems to be more efficient in the chemical oxygen demand (COD) removal, while the sulphate and specially the phosphate media improve the TOC removal. However, in spite of this observation, chemical oxidation of SDBS by different types of oxidants cannot explain alone the results of the electrochemical oxidation with diamond anodes. This suggests that the synergistic effect of the different oxidation mechanisms that occurs into the electrochemical cell (direct oxidation and mediated oxidation by hydroxyl radicals and by oxidants formed from the electrolyte) is the responsible of the great efficiencies obtained with this technology in the treatment of organics.