Surface morphological and impedance spectroscopic studies on the interaction of polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP) with mild steel in acid solutions

The inhibition of mild steel corrosion in aerated acid mixture of 0.5 N H₂SO₄ and 0.5 N HCl solution was investigated using potentiodynamic polarization studies, linear polarization studies, electrochemical impedance spectroscopy, adsorption, and surface morphological studies. The effect of inhibitor concentration on corrosion rate, degree of surface coverage, adsorption kinetics, and surface morphology is investigated. The inhibition efficiency increased markedly with increase in additive concentration. The presence of PEG and PVP decreases the double-layer capacitance and increases the charge-transfer resistance. The inhibitor molecules first adsorb on the metal surface following a Langmuir adsorption isotherm. Both PEG and PVP offer good inhibition properties for mild steel and act as mixed-type inhibitors. Surface analysis by scanning electron microscopy (SEM) and atomic force microscopy (AFM) shows that PVP offers better protection than PEG.     

Electrochemical studies on the interaction of l-cysteine with metallic copper in sulfuric acid

Amino acids have been widely used as green corrosion inhibitors for an array of metals. Considering its importance in corrosion chemistry, studies were undertaken with the objective to discovering the inhibitory effect of a sulfur-containing amino acid, l-cysteine, on copper in different concentrations of sulfuric acid (0.5, 1.0, and 1.5 M) at different temperatures. Techniques like the weight loss method, electrochemical impedance spectroscopy, potentiodynamic polarization (Tafel), and adsorption studies were employed. Results revealed that l-cysteine do offer an attractive inhibition efficiency. However, with an increase in the concentration of the inhibitor, corrosion rates decreased irrespective of the temperature gradients. This is due to surface adsorption of the inhibitor molecules on the metal which has contributed to a decreased double-layer capacitance and increased polarization resistance. With the increase in the concentration of the medium, the corrosion rate was also enhanced and this is due the liberation of a high quantum of H⁺ ions. Based on the results of Tafel polarization studies, it is evident that the amino acid, l-cysteine, could act as a mixed type inhibitor. The importance of l-cysteine in the corrosion of copper metal has been highlighted in this paper.     

Physicomechanical properties of nanocomposites based on cellulose nanofibre and natural rubber latex

Cellulose nanofibres (CNF) with diameter 10–60 nm were isolated from raw banana fibres by steam explosion process. These CNF were used as reinforcing elements in natural rubber (NR) latex along with cross linking agents to prepare nanocomposite films. The effect of CNF loading on the mechanical and dynamic mechanical (DMA) properties of NR/CNF nanocomposite was studied. The morphological, crystallographic and spectroscopic changes were also analyzed. Significant improvement of Young’s modulus and tensile strength was observed as a result of addition of CNF to the rubber matrix especially at higher CNF loading. DMA showed a change in the storage modulus of the rubber matrix upon addition of CNF which proves the reinforcing effect of CNF in the NR latex. A mechanism is suggested for the introduction of the Zn–cellulose complex and its three dimensional network as a result of the reaction between the cellulose and the Zinc metal which is originated during the composite formation.     

Asymptotic synchronization of continuous/discrete complex dynamical networks by optimal partitioning method

The synchronization problem for both continuous and discrete‐time complex dynamical networks with time‐varying delays is investigated. Using optimal partitioning method, time‐varying delays are partitioned into l subintervals and generalized results are derived in terms of linear matrix inequalities (LMIs). New delay‐dependent synchronization criteria in terms of LMIs are derived by constructing appropriate Lyapunov–Krasovskii functional, reciprocally convex combination technique and some inequality techniques. Numerical examples are given to illustrate the effectiveness and advantage of the proposed synchronization criteria. © 2014 Wiley Periodicals, Inc. Complexity 21: 193–210, 2015     

Evolution of coercivity and its angular dependence in CoFe nanostructures subjected to field cooling

Evolution of coercivity and its angular dependence in CoFe nanostructures subjected to field cooling has been investigated in this work. Spherical CoFe grains with an average diameter of 30 nm were grown on a silicon substrate using electron beam evaporation. Further, the as‐deposited sample was subjected to field cooling. The morphology and topography of the sample before and after field cooling were characterized by atomic force microscopy and SEM. Magnetic force microscopy indicated that there is a good uniformity of magnetization throughout the sample after field cooling. Vibrating sample magnetometer measurements indicate that the coercivity in CoFe nanostructures is dependent on shape of the nanostructures. Copyright © 2013 John Wiley & Sons, Ltd.     

Direct Addition of Grignard Reagents to Aliphatic Carboxylic Acids Enabled by Bulky turbo-Organomagnesium Anilides

The synthesis of ketones through addition of organometallic reagents to aliphatic carboxylic acids is a straightforward strategy that is limited to organolithium reagents. More desirable Grignard reagents can be activated and controlled with a bulky aniline-derived turbo-Hauser base. This operationally simple procedure allows the straightforward preparation of a variety of aliphatic and perfluoroalkyl ketones alike from functionalized alkyl, aryl and heteroaryl Grignard reagents.     

A sustainable method of mitigating acid corrosion of mild steel using jackfruit pectin (JP) as green inhibitor: Theoretical and electrochemical studies

This study is attempted to develop a green corrosion inhibitor from a waste material of Jack fruit (Artocarpus heterophyllus). This method is therefore quite valuable to health, environment, and economic point of view. Pectin is isolated from the jackfruit peel waste using 0.05 ?N oxalic acid and used as an inhibitor for mild steel corrosion in acidic environment as it is highly water soluble. 250–1000 ?ppm of pectin was used in this study at a temperature range of 303–323 ?K. The protection efficiency of jack fruit pectin (JP) in 0.5 ?M HCl was evaluated by conventional weight loss and electrochemical techniques. The potentiodynamic polarization results revealed that JP could effectively reduce the corrosion of mild steel in acidic medium at 1000 ?ppm concentration with an inhibition efficiency of 89.75% and corrosion rate of 2.392 mpy. The mixed type behavior of the inhibitor is identified from Tafel polarization studies. Electrochemical impedance spectroscopy (EIS) measurements suggest that the corrosion inhibition process is kinetically controlled. adsorption and kinetic behavior of the inhibitor also have been studied. Surface manifestations were followed using FESEM and AFM techniques. DFT calculations and Monte Carlo simulations were also carried out to corroborate the experimental results with theoretical outputs and succeeded to a great extent.     

Reactive sensing capability towards the working electrical and chemical conditions of poly (aniline –co–o-toluidine) copolymers

Conducting polymers are considered as reactive gels which can sense the working ambient through their unique electrochemical reaction. Copolymers of aniline with o-toluidine for three different monomer compositions were synthesized chemically and were characterized using FTIR and UV-Vis spectroscopy, SEM, TGA, and cyclic voltammetry. The electrochemical reactive sensing characteristics with respect to the electrical and chemical working conditions of the copolymers were verified and compared through Chronopotentiometric responses in aqueous solutions of HCl by changing the reaction variables: applied current and chemical environment (electrolyte concentration) at a fixed constant charge. The consumed electrical energy during the electrochemical reaction of the copolymers varies linearly with the driving current and follows a logarithmic dependence on the electrolyte concentration. The consumed electrical energy during the reaction was found to act as the sensing parameter. At the same experimental condition, the sensitivity was associated with the conductivity of the copolymers. The highly conducting composition gives the highest sensitivity. These experimental results were fitted with the theoretical equation.

     

On exponential stability of second order delay differential equations

We propose a new method for studying stability of second order delay differential equations. Results we obtained are of the form: the exponential stability of ordinary differential equation implies the exponential stability of the corresponding delay differential equation if the delays are small enough. We estimate this smallness through the coefficients of this delay equation. Examples demonstrate that our tests of the exponential stability are essentially better than the known ones. This method works not only for autonomous equations but also for equations with variable coefficients and delays.