Nitrogen-modified carbon-based catalysts for oxygen reduction reaction in polymer electrolyte membrane fuel cells

Nitrogen-modified carbon-based catalysts for oxygen reduction were synthesized by modifying carbon black with nitrogen-containing organic precursors. The electrocatalytic properties of catalysts were studied as a function of surface pre-treatments, nitrogen and oxygen concentrations, and heat-treatment temperatures. On the optimum catalyst, the onset potential for oxygen reduction is approximately 0.76 V (NHE) and the amount of hydrogen peroxide produced at 0.5 V (NHE) is approximately 3% under our experimental conditions. The characterization studies indicated that pyridinic and graphitic (quaternary) nitrogens may act as active sites of catalysts for oxygen reduction reaction. In particular, pyridinic nitrogen, which possesses one lone pair of electrons in addition to the one electron donated to the conjugated π bond, facilitates the reductive oxygen adsorption.     

Polymeric semiconducting carbon from fullerene by pulsed laser ablation

The polymeric semiconducting carbon films are grown on silicon and quartz substrates by excimer (XeCl) pulsed laser deposition (PLD) technique using fullerene C₆₀ precursor. The substrate temperature is varied up to 300 °C. The structure and optical properties of the films strongly depend on the substrate temperature. The grain size is increased and uniform polymeric film with improved morphology at higher temperature is observed. The Tauc gap is about 1.35 eV for the film deposited at 100°C and with temperature the gap is decreased upto 1.1 eV for the film deposited at 250 °C and increased to about 1.4 eV for the film deposited at 300 °C. The optical absorption properties are improved with substrate temperature. Raman spectra show the presence of both G peak and D peak and are peaked at about 1590 cm^− 1 and 1360 cm^− 1, respectively for the film deposited at 100 °C. The G peak position remains almost unchanged while D peak has changed only a little with temperature might be due to its better crystalline structure compared to the typical amorphous carbon films and might show interesting in device such as, optoelectronic applications.     

Cationization of cotton for industrial scale salt-free reactive dyeing of garments

Reactive dyeing of cotton garments involves two stages, namely exhaustion and fixation of dyes. The exhaustion stage in reactive dyeing requires high quantity of salt. After dyeing process, the highly saline coloured effluent is discharged and the treatment of this effluent at present is not economically viable and making industries look for other alternatives for usage of salt. Cationization of cotton is one of the effective alternatives to overcome the usage of the salt. The present work focuses on the exhaust method of cationization of garments at an industrial scale using 3-chloro-2-hydroxypropyl trimethylammonium chloride as a cationic agent. Two commercially popular reactive dyes namely Navy Blue and Green dyes were chosen for dyeing the garments at 10% shade. The results of dyeing were evaluated on the basis of colour strength, dyeing levelness and colour fastness. The uniformity of dye on the fabrics was evaluated based on dyeing levelness and was found to be good for cationized cotton dyed garments. The fastness properties of dyed fabrics to washing and light were good. The dye utilization in the cationized cotton dyed garments was twice as that of the conventionally dyed cotton garments. The environmental hazard posed by the highly saline coloured effluent could be easily mitigated by the salt-free reactive dyeing process.     

Feasibility Study of Continuous Casting of Steel Billets in Twin-Belt Caster

Metallurgical and Materials Transactions B - Integrated casting and rolling in a series production line is well established for the non-ferrous metals through the use of twin-belt casting...     

Large deflection of constant curvature cantilever beam under follower load

This paper describes a method to analyze for the large deflections of curved prismatic cantilever beams with uniform curvature subjected to a follower load at the tip. The large deflection, the deflection dependent follower load and the initial curved geometry are the important features of the beam considered in this work. Shear force formulation proposed by Lee [Large deflections of cantilever beams of non-linear elastic material under a combined loading. Int J Non-Linear Mech 2002;37(3)] is used for deriving the governing equations. Using this approach, the resulting two point boundary value problem (TPBVP) can be reduced to an initial value problem (IVP). Fourth order Runge-Kutta method along with one parameter reverse shooting method is applied to the numerical solution to the problem. A novel approach presented in this paper of integrating from the free end to the fixed end of the cantilever beam simply replaces the two parameter shooting with a single parameter shooting yielding several advantages. This solution technique is demonstrated for various types of follower tip loads on curved and straight cantilever beams and is validated with existing solutions in the literature.     

Fracture toughness of plain concrete from three-point bend specimens

A simple method is proposed for determining the fracture toughness of plain concrete from three-point bend specimens, based on the concept of effective notch depth to account for the non-linear pre-peak load-deflection behaviour. The fracture toughness so determined is shown not to depend on the specimen size. The method improves an earlier version of the effective crack model in several ways. First, it is no longer necessary to linearize the pre-peak non-linearity, thereby eliminating the inaccurate task of establishing the limit of elastic response. Secondly, regression expressions for determining the effective notch depth should be far more accurate because they are based on an analysis of not only the authors’ test data but that of several researchers around the world. Thirdly, these expressions do not depend on the size of the test specimen. It is shown that the predictions of the effective crack model are in good agreement with two other non-linear process zone models, as far as three-point notched beam specimens are concerned.     

Size-effect prediction from effective crack model for plain concrete

The size effect predicted by the authors' effective crack model is compared with that of the fictitious crack model (cohesive crack model) using the methodology proposed by Planas and Elices. It is shown that for notched three-point bend laboratory-size speciments., the predictions of the two models are totally indistinguishable from one another. However, the fracture loads predicted by the two models for increasing sizes are still very close so that in the asymptotic limit (of infinite size) the prediction differ by no more than about 17%.

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Résumé On compare l'effet d'échelle prévu par le modèle de fissuration établi par les auteurs avec le modèle de fissuration fictive (modèle de fissuration cohérente) en utilisant la méthodologie proposée par Planas et Elices. On montre que pour les corps d'épreuve entaillés pour l'essai de flexion ‘3 points’, les prévisions de deux modèles ne se démarquent absolument pas l'une de l'autre. Cependant, les charges de rupture prévues par les modèles pour des dimensions croissantes sont encore très proches, de sorte qu'à la limite asymptotique (à l'infini), l'écart entre les prévisions ne dépasse pas 17% environ.

     

Thermomechanical analysis of direct chill casting using finite element method

The transient nature of the start-up phase is the most critical phase in the direct chill (DC) casting during which the quality of the ingot is questioned. The hot crack and cold crack are the two major problems in the DC casting which originate during and after the solidification. In this work, the thermal, metallurgical, and the mechanical fields of DC casting are modeled. The attention is focused on the mushy state of alloy where the chances are high for the hot tearing. The heat conduction and metallurgical phase-change phenomenon are modeled together in a strongly coupled manner. An isothermal staggered approach is followed to couple the thermal and mechanical parts within a time step. Finite element method is used to discretize the thermal and mechanical field equations. A temperature-based fixed grid method is followed to incorporate the latent heat. The mushy state of alloy is characterized through the Norton-Hoff viscoplastic law and the solid phase is modeled through the Garafalo law. An axisymmetric round billet is simulated. The casting material is considered as AA1201 aluminum alloy. It is found that all the components of stress and viscoplastic strain are maximum at the billet center. Further, the start-up phase stresses and strains are always higher than the steady state phase. Therefore, the chances of hot crack formation are higher during the start-up phase and specifically at the billet center. It is proved that through the ramping procedure, the vulnerability of start-up phase can be lowered.     

Preparation of poly(vinylidene fluoride)–polypyrrole composite films by electrochemical synthesis and their properties

Composite films of poly(vinylidenc fluoride–polypyrrole (PVDF–PPy) were prepared by electrochemical polymerization of pyrrole on a very thin PVDF matrix film (～ 0.5 μm). The polymerization was carried out in aqueous media using stainless steel, coated with PVDF matrix, as a working electrode, and p-toluene sulfonate (PTS), as a dopant. The films were prepared at different voltages for different durations of time in order to optimize the conditions of composite formation. The resulting films were characterized by studying IR spectra, conductivity, SEM, XRD, and tensile strength measurements. The mechanical properties of the composites were found to have improved, while the conductivity remained more or less same as that of pure PPy. © 1995 John Wiley & Sons, Inc.     

Fabrication of PANI–ZnO nanocomposite thin film for room temperature methanol sensor

In the recent past, polymer–metal oxide nanocomposites have been identified as one of the key and new class of materials for fabricating gas sensors owing to their swift redox characteristics. In this line of thought, chemical oxidative process was employed to synthesize zinc oxide (ZnO) and polyaniline (PANI) nanocomposite thin films with different mass concentrations of ZnO to explore their gas sensing signatures. X-ray diffraction patterns and Fourier transform infrared spectra confirmed the formation of pure ZnO and PANI–ZnO composites. Field emission scanning electron micrographs revealed the leaf like structure of ZnO, porous nature of PANI and the uniformly distributed blend of these two structures for the composite films. Further, the room temperature gas/vapour sensing characteristics revealed the selective nature of nanocomposite films towards methanol vapour in the presence of other vapours with better response, swift response and recovery times of 7 and 20 s respectively.