Low shear rate behavior at high solid fractions of partially solidified Al–8 wt.% Cu alloys

International audienceThe rheological behavior at high solid fractions of a partially solidified Al Á/8 wt.% Cu alloy is investigated using shear tests in a Couette viscometer. The effect of grain refinement on the rheological behavior is particularly addressed. Shear experiments have been conducted at three temperatures above the eutectic: 550, 575 and 587 8C. Experimental data reveal a clear difference in the shear response of the refined and unrefined alloys. The grain-refined Al Á/Cu alloy exhibits a quite homogeneous deformation behavior that can be related to the rheology of the viscoplastic solid phase, which is investigated through simple compression tests. On the contrary, rapid strain localization characterizes the shear response of the non grain-refined alloy. The difference in rheological behavior is related to microstructure features that are pertinent to the rheology of partially solidified alloys, solid phase morphology and grain size

Modelling of cyclic visco-elasto-plastic one dimensional behaviour of polyamide-based woven strap

International audienceThis study focuses on modelling of mechanical behaviour of threadlike woven materials or shaped in uniaxial form such as wires, ropes, woven lines, cables, straps, slings etc. The proposed one-dimensional model is based on the superimposition of two stress contributions: a non-Newtonian visco-elastic stress and a time-independent stress. The time-independent stress stands for a particular irreversible behaviour, linked to the loading history. This model neglects the thickness of the time independent hysteresis loops during the unloading-reloading processes while preserving the irreversible character of elastoplastic type behaviour. The model's predictions are compared to a set of experimental results, carried out on polyamide 6-6 (PA66) straps. The model describes the shape of the stress-strain hysteresis loops very well and predicts perfectly the direction of the strain or stress evolution during the creep or relaxation periods, regardless of their position in the first load or in the load-unload branches

"Repellent Effect of Extracts and Essential Oils of Citrus limon (Rutaceae) and Melissa officinalis (Labiatae) Against Main Malaria Vector, Anopheles stephensi (Diptera: Culicidae)"

Repellet effect of extracts and essential oils of Citrus limon (L.) Burm.F., (lemon) and Melissa officinalis, (balm) were evaluated against Anopheles stephensi in laboratory on animal and human and compared with synthetic repellent, N,Ndiethyl- 3-methylbenzamide (Deet) as a standard. Results of statistical analysis revealed significant differences between oils and extracts (P< 0.05) against the tested species, thus oils were more effective than extracts. There was no significant difference between Deet and lemon oil, whereas the difference between lemon and melissa oils was significant. Relative efficacy of lemon oil to Deet was 0.88 whereas it was 0.71 for melissa oil. The results were found marginally superior in repellency for animals than human. Due to advantages of botanic compounds to synthetic compounds we recommend lemon essential oil as an effective alternative to Deet with potential as a means of personal protection against mosquito vectors of disease

Adsorption and corrosion inhibition properties of 5-amino 1,3,4-thiadiazole-2-thiol on the mild steel in hydrochloric acid medium: Thermodynamic, surface and electrochemical studies

International audienceThe inhibition effect of 5-amino 1,3,4-thiadiazole-2-thiol (5-ATT) on the corrosion of mild steel in 1 M HCl solution at 303 K was studied practicing weight loss, electrochemical electrochemical (AC and DC) studies and Xray photoelectron spectroscopy (XPS) methods. The obtained results showed that 5-ATT was an effective inhibitor in HCl medium. The inhibition efficiency, eta(%), increased with the increase in concentration inhibitor but the temperature has almost no effect on the inhibition efficiency of 5-ATT. The activation dissolution thermodynamic parameters were calculated and discussed. Thermodynamic data and XPS analysis clearly show that the adsorption mechanism of 5-ATT on the mild steel surface in 1 M HCl solution is mainly electrostatic-adsorption. Tafel curves reveal that 5-ATT behaves as a mixed-type inhibitor with cathodic predominance and obeyed Langmuir adsorption isotherm. With the aim of extracting the parameters of the electrochemical impedance spectroscopy an appropriate equivalent circuit model was offered

Experimental studies and computational exploration on the 2-amino-5-(2-methoxyphenyl)-1,3,4-thiadiazole as novel corrosion inhibitor for mild steel in acidic environment

International audienceIn the present research, a new 1,3,4-thiadiazole derivative, namely the 2-amino-5-(2-methoxyphenyl)-1,3,4-thiadiazole (5-AMT) was synthesized and investigated as corrosion inhibitor for mild steel (M-steel) in molar hydrochloric acid medium. The experimental studies such as weight loss, potentiodynamic polarization (PDP), Linear polarization resistance (LPR) technique and electrochemical impedance spectroscopy (EIS) were performed in order to evaluate the corrosion protection performance of the tested compound. Based on the experimental outcomes, a protection degree of approximately 98 % was achieved exploiting 5 × 10−4 M of 5-AMT after 1 h of immersion at temperature 303 K. Additionally, PDP study highlighted that the investigated 1,3,4-thiadiazole is of mixed-kind inhibitor. Thermodynamic data from adsorption isotherms and activation energies were determined and discussed. It was shown that the adsorption of 5-AMT molecules fits Langmuir isotherm model. Furthermore, in order to characterize the M-steel surface and to comprehend the adsorption mechanism of 5-AMT, XPS analyses were accomplished. Computational studies by DFT and MD simulation were also conducted to correlate the protection properties and quantum chemical parameters of the investigated inhibitor