CORROSION INHIBITION OF CARBON STEEL IN LOW CHLORIDE MEDIA BY AN AQUEOUS EXTRACT OF HIBISCUS ROSA-SINENSIS LINN

The inhibition efficiency (IE) of an aqueous extract of white flower, namely, Hibiscus rosa-sinensis Linn., in controlling corrosion of carbon steel immersed in an aqueous solution containing 60 ppm of Cl^-has been evaluated by the mass loss method. The flower extract (FE) shows good IE. In the presence of Zn²⁺, excellent IE is shown by the flower extract. A synergistic effect exists between the flower extract and Zn²⁺. The mechanistic aspects of corrosion inhibition have been investigated by polarization study and AC impedance spectra. Polarization study reveals that the formulation consisting of flower extract and Zn²⁺ functions as a mixed inhibitor. AC impedance spectra reveal that a protective film is formed on the metal surface. The active principle in the flower extract is quercetin-3-O-glucoside. This has been confirmed by UV-visible absorption spectra. The protective film formed on the metal surface has been analyzed by FT-IR and AFM spectra. It is found that the protective film consists of Fe²⁺-quercetin-3-O-glucoside complex and Zn(OH)₂.     

Confocal ultrafast pump-probe spectroscopy: a new technique to explore nanoscale composites

This article is devoted to the exploration of the benefits of a new ultrafast confocal pump-probe technique, able to study the photophysics of different structured materials with nanoscale resolution. This tool offers many advantages over standard stationary microscopy techniques because it directly interrogates excited state dynamics in molecules, providing access to both radiative and non-radiative deactivation processes at a local scale. In this paper we present a few different examples of its application to organic semiconductor systems. The first two are focussed on the study of the photophysics of phase-separated polymer blends: (i) a blue-emitting polyfluorene (PFO) in an inert matrix of PMMA and (ii) an electron donor polythiophene (P3HT) mixed with an electron acceptor fullerene derivative (PCBM). The experimental results on these samples demonstrate the capability of the technique to unveil peculiar interfacial dynamics at the border region between phase-segregated domains, which would be otherwise averaged out using conventional pump-probe spectroscopy. The third example is the study of the photophysics of isolated mesoscopic crystals of the PCBM molecule. Our ultrafast microscope could evidence the presence of two distinctive regions within the crystals. In particular, we could pinpoint for the first time areas within the crystals showing photobleaching/stimulated emission signals from a charge-transfer state.     

Influence of Si nanoparticles on the electrochemical behavior of organic coatings on carbon steel in chloride environment

Scanning electrochemical microscopy (SECM) is an excellent technique to detect electrochemical processes with high spatial resolution. In this work, the effect of silicon (Si) nanoparticles on the corrosion protection performance of epoxy-coated steel was examined by electrochemical impedance spectroscopy (EIS) and SECM analysis. The EIS was performed in continuous immersion in 0.1?M NaCl_(aq) solution. The addition of Si nanoparticles increased the coating film resistance (R _f) and the charge transfer resistance (R _ct) of coated steel. SECM mapping and line scan analysis was performed in order to estimate the coating performance with Si nanoparticles in 0.1?M NaCl_(aq) solution. SECM results indicated that the tip current at ?0.70?V was decreased by the addition of Si nanoparticles in epoxy film. These results suggested that the dissolved oxygen (DO) was consumed by anodic dissolution of Si nanoparticles. Surface analysis showed that the Si was enriched at the scratched region of the coated steel after a corrosion test. From these results, Si was dissolved as Si ⁿ⁺ and transferred to the scratched area, and then consumed the DO in the solution. Thus, the anodic dissolution of Fe at the scratched area was suppressed by the Si nanoparticles, which implies the sacrificial effect of Si from the coating against the steel corrosion. Hence, it was concluded that the Si nanoparticles had a beneficial effect on enhancing the corrosion resistance of the coated steel.     

A dimensional approach to maternal attachment state of mind: Relations to maternal sensitivity and maternal autonomy support.

The aim of this study was to examine the developmental significance of the newly developed dimensional approach to attachment state of mind by investigating its capacity to predict individual differences in the quality of two caregiving behaviors—maternal sensitivity and maternal autonomy support—that are linked to numerous important child outcomes. Seventy-one upper-middle-class, predominantly French-speaking and Caucasian dyads participated in 3 home visits (34 girls). The Adult Attachment Interview (AAI) was administered when the infants were 8 months old, maternal sensitivity was assessed when they were 12 months old, and maternal autonomy support was assessed at 15 months. The results revealed that, above and beyond SES, maternal sensitivity was negatively related to the dismissing dimension of the AAI, whereas maternal autonomy support was negatively linked to the preoccupied/unresolved dimension. In contrast, the traditional AAI categories were not significantly linked to parenting. These results speak to the relevance of using a continuous approach to attachment state of mind when predicting individual differences in specific caregiving behaviors. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Collective cell guidance by cooperative intercellular forces

Cells comprising a tissue migrate as part of a collective. How collective processes are coordinated over large multi-cellular assemblies has remained unclear, however, because mechanical stresses exerted at cell-cell junctions have not been accessible experimentally. We report here maps of these stresses within and between cells comprising a monolayer. Within the cell sheet there arise unanticipated fluctuations of mechanical stress that are severe, emerge spontaneously, and ripple across the monolayer. Within that stress landscape, local cellular migrations follow local orientations of maximal principal stress. Migrations of both endothelial and epithelial monolayers conform to this behaviour, as do breast cancer cell lines before but not after the epithelial-mesenchymal transition. Collective migration in these diverse systems is seen to be governed by a simple but unifying physiological principle: neighbouring cells join forces to transmit appreciable normal stress across the cell-cell junction, but migrate along orientations of minimal intercellular shear stress.     

Highly transparent and organosoluble polyimides derived from 2,2′‐disubstituted‐4,4′‐oxydianilines

Polypyrrole (PPy) and Polypyrrole‐ZnO (PPy‐ZnO) nanocomposites were electrodeposited on mild steel and its corrosion protection ability was studied by Tafel and Impedance techniques in 3.5% NaCl solution. Pure Polypyrrole film was not found to protect the mild steel perfectly but the coating with nano‐sized ZnO (PPy‐ZnO) has dramatically increased the corrosion resistance of mild steel. Electrochemical Impedance Spectroscopy (EIS) measurements indicated that the coating resistance (R_coat) and corrosion resistance (R_corr) values for the PPy‐ZnO nanocomposite coating was much higher than that of pure PPy coated electrode. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Influence of shallow and deep cryogenic treatment on the residual state of stress of 4140 steel

The present research work studies the effect of cryogenic treatment on the residual stress state in 4140 steel. Two kinds of cryogenic treatment, namely shallow (SCT, −80 °C × 5 h) and deep cryogenic treatment (DCT, −196 °C × 24 h) were carried out between quenching and tempering in conventional heat treatment process. The results evidenced an increase in the compressive residual stress in steel are subjected to cryogenic treatment before tempering. X-ray diffractometry revealed that residual stresses are relieved during tempering, according to the redistribution of carbon in martensite and the precipitation of transition carbides. While conventional heat treatment (CHT) and shallow cryogenic treatment (SCT) promote a tensile state of residual stress, DCT shows a compressive residual stress.     

Cycle synthesis and optimization of a VSA process for postcombustion CO2 capture

A systematic analysis of several vacuum swing adsorption (VSA) cycles with Zeochem zeolite 13X as the adsorbent to capture CO₂ from dry, flue gas containing 15% CO₂ in N₂ is reported. Full optimization of the analyzed VSA cycles using genetic algorithm has been performed to obtain purity‐recovery and energy‐productivity Pareto fronts. These cycles are assessed for their ability to produce high‐purity CO₂ at high recovery. Configurations satisfying 90% purity‐recovery constraints are ranked according to their energy‐productivity Pareto fronts. It is shown that a 4‐step VSA cycle with light product pressurization gives the minimum energy penalty of 131 kWh/tonne CO₂ captured at a productivity of 0.57 mol CO₂/m³ adsorbent/s. The minimum energy consumption required to achieve 95 and 97% purities, both at 90% recoveries, are 154 and 186 kWh/tonne CO₂ captured, respectively. For the proposed cycle, it is shown that significant increase in productivity can be achieved with a marginal increase in energy consumption. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4735–4748, 2013     

Ionic conduction in poly(vinyl chloride)/poly(ethyl methacrylate)-based polymer blend electrolytes complexed with different lithium salts

Poly(vinyl chloride)/poly(ethyl methacrylate)-based polymer blend electrolytes comprising propylene carbonate as a plasticizer and a lithium salt LiX (X = BF₄⁻, ClO₄⁻, CF₃SO₃⁻) are prepared by a solvent casting technique. The electrolytes are subjected to characterization by ionic conductivity, X-ray diffraction, Fourier transform infrared spectroscopy and thermogravimetic/differential thermal analysis. The electrolytes that contain LiBF₄ exhibit maximum conductivity and are thermally stable up to 254 °C.