Micromechanical based model for predicting aged rubber fracture properties

Environmental aging induces a slow and irreversible alteration of the rubber material’s macromolecular network. This alteration is triggered by two mechanisms which act at the microscale: crosslinking and chain scission. While crosslinking induces an early hardening of the material, chain scission leads to the occurrence of dangling chains responsible of the damage at the macromolecular scale. Consequently, the mechanical behavior as well as the fracture properties are affected. In this work, the effect of aging on the mechanical behavior up to fracture of elastomeric materials and the evolution of their fracture properties are first experimentally investigated. Further, a modeling attempt using an approach based upon a micro-mechanical but physical description of the aging mechanisms is proposed to predict the mechanical and fracture properties evolution of aged elastomeric materials. The proposed micro-mechanical model incorporates the concepts of residual stretch associated with the crosslinking mechanism and a so-called “healthy” elastic active chain (EAC) density associated with chain scission mechanism. The validity of the proposed approach is assessed using a wide set of experimental data either generated by the authors or available in the literature

Hybrid electrode obtained by sol-gel derived Ni0.3Co2.7O4 nanoparticles incorporated into polypyrrole: Electrocatalysis of O2 reduction

A hybrid electrode was formed on glassy carbon (GC) electrode with polypyrrole (PPy) and mixed valence Ni0.3Co2.7O4 nanoparticles to study their behaviour towards the oxygen reduction reaction (ORR). The oxide nanoparticles were prepared by sol-gel route using various parameters and characterized by XRD, SEM, EDX and BET methods. The result showed that desired oxide was obtained and nanocrystallites exhibit a specific surface area ranging from 39 to 73 m2/g with diameter varying from 13 to 25 nm. The hybrid electrode was then fabricated by electropolymerization of pyrrole (Py) in the presence of the smallest Ni0.3Co2.7O4 nanoparticles in KCl (0.15 mol/L) at room temperature and characterized by EDX, SEM and LSV methods. Investigation of the hybrid electrode confirmed that O2 reduction mechanism changes by applying potential. Thus, at low overpotential the O2 reduction involves two electrons and provides H2O2, with cathodic transfer coefficients (β) of 0.33 and exchange current density ( j0) of about 8×10-3 mA/cm2, while, at high overpotential H2O2 is further reduced into H2O. The results also show that sol-gel method led to the preparation of Ni0.3Co2.7O4 nanoparticles having a spinel structure with a desired stoichiometry which exhibits a high electrocatalytic activity for reducing oxygen mostly to H2O2

Etude electrochimique des processus de corrosion d'un alliage Fe-36 Ni sous des couches minces d'elecrolyte, a l'air libre ou en situation de confinement

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Enhancing epidemic management: agent-based simulation and remote diagnosis

The objective of this work is to analyze the spread of contagious diseases using a multi-agent simulation and a remote diagnostic system. The simulation is carried out using information on patients and the environment. The novelty of this work lies in proposing a new agent architecture that combines both independent and random behavior to better simulate individuals in the real world. We have proposed two communication methods between the agents either by a direct exchange of messages or by placing objects in a common space. The various simulations have enabled the prediction of the time required to transition from a normal state to a critical condition. A comparative study between the proposed diagnostic method and alternative techniques has demonstrated its superiority in accuracy

Mixed oxide-polyaniline composite-coated woven cotton fabrics for the visible light catalyzed degradation of hazardous organic pollutants

International audienc

Polyaniline-Grafted RuO2-TiO2 Heterostructure for the Catalysed Degradation of Methyl Orange in Darkness

International audienc

Artemisia Herba Alba Essential Oil as Green Corrosion Inhibitor for Aluminum in Hydrochloric Acid Solution

International audienceArtemisia herba-alba essential oil extract was investigated as green inhibitor for aluminum corrosion in 1 M HCl solution. The chemical analysis obtained by gas chromatography and gas chromatography-mass spectrometry, revealed 68 components. The inhibition efficiency was determined by weight loss measurements, potentiodynamic polarization, electrochemical impedance spectroscopy and scanning electron microscope. The results revealed an increase of inhibition efficiency by maximum 92% trough increasing the oil concentration to 3 g/L at 333 K. The oil compounds adsorb by physisorption, follow Langmuir adsorption isotherm and act as mixed type inhibitors. The EIS results confirmed the adsorption mechanism process and the SEM observations

Electrical, dielectric and photocatalytic properties of Fe-doped ZnO nanomaterials synthesized by sol gel method

Fe-doped ZnO nanoparticles were synthesized by sol gel technique. Fine-scale and single phase hexagonal wurtzite structure in all samples were confirmed by SEM and XRD, respectively. The band gap energy depends on the amount of Fe and was found to be in the range of 3.11–2.53 eV. The electric and dielectric properties were investigated using complex impedance spectroscopy. AC conductivity data were correlated with the barrier hopping (CBH) model to evaluate the binding energy (Wm), the minimum hopping distance (Rmin) and the density of states at Fermi level, N(EF). Fe doping in ZnO also improved the photocatalytic activity. Thus, the sample Zn0.95Fe0.05O showed high degradation potential towards methylene blue (MB), i.e. it degrades 90% of BM in 90 min under UV light

Impact of Aqueous Extract Artemisia Herba-Alba Leaves as a Green Inhibitor against Acid Activation of 2024 Aluminum Alloy

International audienceThis work is part of the development of new bio-sourced corrosion inhibitors from an abundant resource that can replace conventional synthetic inhibitors that are harmful to both human health and the environment. The corrosion inhibition performance of an aqueous extract of Artemisia herba-alba on the corrosion of 2024 aluminum alloy in a 1 M hydrochloric acid solution is investigated by weight loss method, electrochemical (linear polarization, potentiodynamic polarization, and electrochemical impedance spectroscopy) and SEM techniques. The extract shows excellent corrosion-inhibiting properties on aluminium alloy with a maximum inhibition efficiency of 93% at 0.6 g/L. The adsorption of the natural extract obeys the extended Langmuir isotherm equation adsorption model for multicomponent systems. Temperature studies show that the efficiency of the extract decreases with increasing temperature and that the corrosion activation energies increase in the presence of the extract. Liquid chromatography/high resolution mass spectrometry is used to identify the chemical constituents of the natural extract, and the most abundant phytochemicals for each subclass of metabolite are investigated using density functional theory (DFT) calculations. This study paves the way for further development of a plant that is particularly abundant in the desert regions of North Africa and has until now been used mainly for food for livestock and for pharmaceutical applications

A unified mechanical based approach to fracture properties estimates of rubbers subjected to aging

In this work, the influence of aging on the mechanical properties at break of rubber materials are examined. When subjected to physical-chemical aging, the structure of the rubber network is deeply modified through two main mechanisms: crosslinking and chain scission. These aging mechanisms act both on the mechanical behaviour and on the fracture properties of the rubber materials. The goal of this work is to propose a predictive mechanical tool able to give estimates of these mechanical properties. To address this issue, an hyperelastic constitutive model based upon the energy limiter approach, was coupled with physical-chemical parameters in order to capture the whole mechanical behaviour of the damaged materials beyond the fracture. That allows fracture stress and strain estimates. A wide set of materials and experimental data extracted from the literature or obtained in our team were selected based upon the aging mechanism they can exhibit. We found that the elastically active chains concentrations and the swelling rate can be used as relevant indicators of damage either for crosslinking or chain scission process. These parameters are then introduced as damage parameters in the mechanical modelling. The proposed approach leads to very satisfactory predictions, either to capture the whole mechanical behaviour in uniaxial tension or in terms of stress and strain at break estimates