Effect of the sample form on the corrosion behavior of steels for concrete in 3% NaCl medium

Corrosion of steel constitutes a major preoccupation in the field of civil engineering and the building sector. In this paper, we investigated the electrochemical behavior of two steel specimens with different forms (latched steel and smooth steel) in a 3 wt.% NaCl solution. For this purpose, we studied the steel samples by linear polarization, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The surface morphologies of the substrates were examined by scanning electron microscopy coupled with energy diffraction spectroscopy (SEM/EDS). Results of linear polarization, Tafel polarization curves and EIS show that latched steel (LS) is more susceptible to corrosion than smooth steel (SS) in saline solution. Gravimetric and SEM/EDS analysis after 10 days of immersion confirmed the results obtained by electrochemical methods. All of our results are in agreement and demonstrate that the sample form plays a key role in corrosion resistance.

Valorisation des déchets ligno-cellulosiques pour la préparation d’un nouveau matériau composite PVC/farine des noyaux de dattes

Afin de limiter l’utilisation des énergies fossiles et de valoriser les déchets ligno-cellulosiques, les composites à fibres naturelles s’inscrivent dans un contexte favorable qui permettra de répondre à des enjeux environnementaux, économiques et sociaux grâce à leurs propriétés de faible coût, faible densité, renouvelables et de biodégradabilité. L’objectif de cette étude est de développer un nouveau matériau composite constitué d’une matrice thermoplastique, le polychlorure de vinyle (PVC), renforcée par des fibres naturelles à base des noyaux de dattes (FND) avec des taux de charge allant de 10 à 40 % massique. Différentes techniques d’analyses ont été utilisées pour étudier les propriétés mécaniques, morphologiques et la perméabilité d’eau des échantillons obtenus. Les résultats enregistrés indiquent que la contrainte à la rupture diminue avec l’augmentation du taux de charge en FND tandis que la rigidité augmente. L’analyse morphologique par microscopie électronique à balayage (MEB) montre une meilleure dispersion pour de faible taux de charge en FND. Une très faible absorption d’eau a été enregistrée.

Mechanism of action of tin on the semi-conductive properties of PbO layer in lead acid battery

Although antimony in alloys for lead-acid batteries has better mechanical and electrochemical performance, it reduces the excessive potential for hydrogen evolution, resulting in excessive water loss and self-discharge of the battery. This paper aims to examine the action of tin in PbSn using different techniques. In this work, the addition of tin in PbCa was intended to suppress the premature capacity loss (PCL) caused by the substitution of antimony in the PbSb alloy by calcium that has good mechanical properties and a high hydrogen evolution potential (200 mV higher than that of antimony). This substitution induces the formation of a passive film composed mainly of α-PbO. The mechanism of action of tin on the anodic film obtained at 700 mV vs. Hg/Hg2SO4/K2SO4 saturated electrode with Pb – (0–5) wt.% Sn in 0.5 mol/L sulfuric acid solution at 25 °C was studied using electrochemical impedance spectroscopy (EIS), AC voltammetry, Mott–Schottky plots and X-ray diffraction (XRD) of the film obtained. It was found that tin stops the growth of the anodic film due to the co-precipitation of certain conductive oxides which reduce the thickness of the passive film and increase its conductivity. A mechanism of action of tin on the electrochemical behavior of the anodic film was suggested based on the results.

The effect of chemical treatment on the mechanical and thermal properties of composite materials based on clay reinforced with sawdust

This study investigates the effect of the chemical treatment of sawdust on the mechanical and thermal properties of a clay composite reinforced with sawdust in variable mass proportions: 0.5, 1, 1.5, 2 and 2.5%, intended for use as brick in rural houses in desert areas. The sawdust was chemically treated with 5 wt% NaOH and 0.01 wt% KMnO4 solutions. The mechanical test results of the reinforced composite with alkali-treated sawdust show an increase in flexural and compression strength, reaching a maximum value of 0.89 and 4.85 MPa, respectively. However, the thermal test results show a significant decrease in the thermal conductivity of the sawdust-reinforced composite. The best result recorded is that of untreated sawdust, which has a value of 0.37 (W.m−1.K−1) compared to the one reinforced with treated sawdust.

Charpy V notch tests – Risks associated with testing with 3 samples

To estimate the risk of brittle fracture of a component in service, Charpy tests are generally carried out on 3 samples at the same temperature. Work done over many years on welded joint fatigue using probability and statistics has shown that to have a good assessment of minimum strength, it is clearly necessary to have a larger number of test results. In order to analyse the risks associated with this practice of 3 samples tested at the same temperature, a series of 17 Charpy impact test results of samples of the same steel plate was chosen. From this series, by translation, 2 series were generated, one with a test of 3 specimens showing acceptable steel and one with a test of 3 specimens showing unacceptable steel. The 3-test method was applied to these series leading to a possible simulation of 12 tests each. It was found that the 3-test practice leads to a risk of error of 30 to 40%. It is also found that the determination of the transition curve of a DH36 steel finally shows that its temperature for a CV of 27 J is of the order of −50 °C whereas the regulations require only −20 °C. In conclusion, a possible improvement of the test procedure is indicated, which is the subject of a study within the framework of the “CCRS rupture and fatigue” working groups of the Société des Ingénieurs Soudeurs (SIS).

Étude de l’influence de l’incorporation de la poudre de bois d’Eucalyptus camaldulensis Dehn algérien sur la cinétique d’hydratation du coulis de ciment

Pour réduire le problème d’incompatibilité entre le bois et le ciment, un traitement du renfort bois, par de l’eau bouillante peut être une solution afin d’éliminer les composés qui inhibent la prise du ciment. L’effet de la teneur de poudre de bois d’Eucalyptus camaldulensis Dehn naturel et traité thermiquement à l’eau bouillante sur la cinétique d’hydratation a été étudié par calorimétrie isotherme, conductimétrie et thermogravimétrie (ATG). La poudre de bois diminue légèrement la consommation du gypse et retarde l’hydratation des phases silicates. À des concentrations massiques élevées de 25 % et 30 %, le bois retarde fortement la précipitation de la portlandite. À des teneurs de 10 % en masse de poudre de bois, le traitement n’a pas montré d’efficacité sur la cinétique d’hydratation ; à 20 % de bois traité, l’hydratation du ciment est accélérée par rapport au témoin. Les extractibles du bois n’ont pas affecté la formation de l’ettringite due à la présence d’ions de sulfate de bois.

Structural and properties evolution of copper–nickel (Cu–Ni) alloys: a review of the effects of alloying materials

Copper–nickel alloy has the potential in sustaining the recent demands in advanced marine engineering applications. It has been found advantageous over other copper alloys due to the unique properties and corrosion resistance they possess. However, the structure of Cu–Ni alloy alone is not sufficient to withstand many applications, as the structure cannot perform efficiently in an aggressive environment. The performance of this alloy inherently depends on carefully select alloying compositions, as the alloying elements are associated with the precipitation of intermetallic particles that will enhance mechanical properties and corrosion resistance when designing the component of Cu–Ni alloys. A combination of alloying elements has been conceptualized in the designing of copper–nickel alloy. This review described the role of alloying elements in modifying the microstructural features through phase transformation and how it affects the improvement of the mechanical and physical properties of Cu–Ni based alloys. The effect of alloying elements on the structure and properties of Cu–Ni alloys have been critically summarized based on surveying the works done by authors on this category of structural modification binary Cu–Ni alloy.

Caractérisation nano-mécanique et tribologique des revêtements TiO2 et TiN déposés sur acier inoxydable 316L pour applications biomédicales

Dans ce travail, nous avons développé des couches nanométriques biocompatibles à base de titane (TiN et TiO2) sur acier inoxydable 316L, par CAE-PVD (Cathodic Arc Evaporation), qui est un procédé efficace pour la synthèse de revêtements de haute qualité. Nous avons axé notre étude sur une caractérisation mécanique et tribologique des revêtements par des tests d’indentation et des rayures. Les résultats obtenus montrent une morphologie dense et uniforme couplée à des propriétés mécaniques et interfaciales importantes. Les revêtements TiN et TiO2 ont montré une dureté comprise entre 5,9 GPa et 8,23 GPa. La mesure de l’adhérence par des tests de rayure a montré que les deux revêtements ont une qualité d’adhérence légèrement différente. Les couches développées en TiN et TiO2 ont montré des charges de cohésion critiques comprises entre 1,8 N et 3,3 N avec une charge d’adhérence critique de 13,1 N. Les propriétés tribologiques ont été étudiées, en utilisant un test de Scratch multi-passes à charge constante, ce qui a permis de déterminer le coefficient de frottement et le taux d’usure énergétique. Les coefficients de frottement des deux couches étudiées sont du même ordre de grandeur (0,1), mais on peut dire que la résistance au frottement varie d’une couche à l’autre. L’énergie spécifique d’usure était comprise entre 3,09 × 10−5 J/μm3 et 8,36 × 10−5 J/μm3, et elle n’a pas changé après immersion de la couche de TiN pendant 48 h dans une solution de NaCl à 3 %. Le film mince de TiN, connu pour sa biocompatibilité et ses performances biologiques, a montré des propriétés mécaniques et tribologiques qui lui permettent d’être utilisé dans les implants de hanche et de genou.

Valorization of glass powder waste, crushed and dune sands in the mix design of ultra-high performance fiber reinforced concrete: Assessing effect of waste variability

This work deals with the valorization of industrial glass waste as supplementary cementitious materials in Ultra High Performance Fiber-Reinforced Concrete (UHPFRC). It aims to take advantage of this type of by-product in order to improve both fresh and hardened performances of conventional cementitious materials. This study concerns the use of glass powder originating from different locations with slight variation in their chemical composition (named transparent, smoked, and opaque) as a supplementary cementitious material (substitution ratio: 20% of the cement weight). Series of standardized tests were performed to characterize the influence of these glass powders on both fresh state properties (slump flow) and hardened state properties of tested UHPFRC. Mechanical properties are measured after cure periods lasting from 2 to 28 days. The study on the microstructure of hardened concrete was made using scanning electron microscopy and water penetration. Obtained results show the beneficial effect brought by the addition of a significant dosage of glass powder (here 20% of the cement weight) on the behavior of concrete in its fresh and hardened state.

Optimization of phosphogypsum conversion into calcium carbonate and lithium sulfate monohydrate

Phosphogypsum (PG) is an acidic by-product generated during the production of phosphoric acid. Usually this by-product is stockpiled or dumped into water bodies, which causes several environmental pollution problems. The aim of this work is to reduce this environmental risk by producing CaCO3 and Li2SO4.H2O from the conversion of PG by Li2CO3. To optimize the reaction conditions, four parameters have been investigated such as the initial concentration of the reagents, the reaction duration, the temperature and the gypsum purity. In addition, the nature of the resulting products was proved principally by X-ray diffraction technic. The obtained results show that the initial concentration of the reagents and the reaction duration are the most influential parameters, while the temperature has no significance effect on this reaction. Also, the acidity and the presence of impurities into PG induce its reactivity compared than commercial gypsum. The purity of the formed CaCO3 and Li2SO4.H2O at the optimum conversion of PG is 96.08 and 98.71% respectively.