Fabrication of zinc‐loaded hollow glass microspheres (HGMs) for hydrogen storage

The greatest challenge for a feasible hydrogen economy lies on the production of pure hydrogen and the materials for its storage with controlled release at ambient conditions. Hydrogen with its great abundance, high energy density and clean exhaust is a promising candidate to meet the current global challenges of fossil fuel depletion and green house gases emissions. Extensive research on hollow glass microspheres (HGMs) for hydrogen storage is being carried out world‐wide, but the right material for hydrogen storage is yet underway. But many other characteristics, such as the poor thermal conductivity etc. of the HGMs, restrict the hydrogen storage capacity. In this work, we have attempted to increase the thermal conductivity of HGMs by ZnO doping. The HGMs with Zn weight percentage from 0 to 10 were prepared by flame spheroidization of amber‐colored glass powder impregnated with the required amount of zinc acetate. The prepared HGMs samples were characterized using field emission‐scanning electron microscope (FE‐SEM), environmental SEM (ESEM), high‐resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy and X‐ray diffraction (XRD) techniques. The deposition of ZnO on the microsphere walls was observed using FE‐SEM, ESEM and HRTEM which was further confirmed using the XRD and ultraviolet–visible absorption data. The hydrogen storage studies done on these samples at 200 °C and 10‐bar pressure for 5 h showed that the hydrogen storage increased when the Zn percentage in the sample increased from 0 to 2%. The percentage of zinc beyond 2, in the microspheres, showed a decline in the hydrogen storage capacity. The closure of the nanopores due to the ZnO nanocrystal deposition on the microsphere surface reduced the hydrogen storage capacity. The hydrogen storage capacity of HAZn2 was found 3.26 wt% for 10‐bar pressure at 200 °C. Copyright © 2015 John Wiley & Sons, Ltd.     

Optimum step length selection rule in modified HL–RF method for structural reliability

This paper presents the implementation concepts of a step length selection rule in a modified Hasofer-Lind and Rackwitz-Fiessler (HL–RF) method in order to improve its performance. Several step length selection rules in the context of structural reliability were studied and implemented in order to make the modified HL–RF method more robust and efficient. It has been demonstrated that a variant of Goldstein's rule, which is popularly known as the Armijo rule, is one of the most efficient step length selection rules. It is observed in this study that a proper step length selection rule will not only make the algorithm more robust but also improves the other parameters such as efficiency, capacity, etc. An iterative procedure, which enables systematic implementation into a computer program has been given. Several case studies have been taken from the literature to demonstrate and validate the proposed algorithm. A general-purpose software has been developed to solve a variety of structural reliability problems including those, which are complex and non-linear. In addition, non-normal distributions, such as lognormal, extreme value distributions, etc., are incorporated in this software.     

Sustainable hydrogen production by catalytic hydrolysis of alkaline sodium borohydride solution using recyclable Co-Co2B and Ni-Ni3B nanocomposites

In this article, we report Co-Co₂B and Ni-Ni₃B nanocomposites as catalyst for hydrogen generation from alkaline sodium borohydride. Kinetic studies of the hydrolysis of sodium borohydride with Co-Co₂B and Ni-Ni₃B nanocomposites reveal that the concentration of NaBH₄ has no effect on the rate of hydrogen generation. Hydrolysis was found to be first order with respect to the concentration of catalyst. The catalytic activity of Co-Co₂B was found to be much higher than that of Ni-Ni₃B as inferred from the activation energies 35.245 KJ/mol and 55.810 kJ/mol, respectively. Co-Co₂B nanocomposites were found to be more magnetic than Ni-Ni₃B. These catalysts showed superior recyclability with almost the similar catalytic activities for several hydrolytic cycles supporting the principles of sustainability. Co-Co₂B catalyst showed hydrogen generation rate of about 4300 mL/min/g which is comparable to most of the reported good catalysts till date.     

Nonlinear thermoacoustics of ducted premixed flames: The influence of perturbation convection speed

When a premixed flame is placed within a duct, acoustic waves induce velocity perturbations at the flame’s base. These travel down the flame, distorting its surface and modulating its heat release. This can induce self-sustained thermoacoustic oscillations. Although the phase speed of these perturbations is often assumed to equal the mean flow speed, experiments conducted in other studies and Direct Numerical Simulation (DNS) conducted in this study show that it varies with the acoustic frequency. In this paper, we examine how these variations affect the nonlinear thermoacoustic behaviour. We model the heat release with a nonlinear kinematic G-equation, in which the velocity perturbation is modelled on DNS results. The acoustics are governed by linearised momentum and energy equations. We calculate the flame describing function (FDF) using harmonic forcing at several frequencies and amplitudes. Then we calculate thermoacoustic limit cycles and explain their existence and stability by examining the amplitude-dependence of the gain and phase of the FDF. We find that, when the phase speed equals the mean flow speed, the system has only one stable state. When the phase speed does not equal the mean flow speed, however, the system supports multiple limit cycles because the phase of the FDF changes significantly with oscillation amplitude. This shows that the phase speed of velocity perturbations has a strong influence on the nonlinear thermoacoustic behaviour of ducted premixed flames.     

Simulation of an industrial nylon 6 tubular reactor

A commonly used energy-efficient nylon 6 reactor is simulated under steady-state conditions. The effects of various operating conditions and parameters, e.g., feed composition, temperature and flow rate, heat transfer coefficients, and reactor dimensions, on the temperature and molecular weight profiles are studied. A temperature maximum is observed in the reactor under usual conditions of operation. The maximum value of the temperature is sensitive to the feed conditions, and one has to ensure that degradation reactions speeded up at high temperatures do not affect product characteristics. The model and the numerical technique used are fairly simple and account for most of the important features of industrial reactors. Hence, these can be used in the development of digital-control algorithms in the future.     

Simulation of AA + B′B″ type reversible polymerizations with mass transfer of condensation product

Simulations have been carried out on AA + B′B″ type reversible polymerizations (where A, B′ and B″ are functional groups, with B′ and B″ reacting with A at different rates) with simultaneous removal of the condensation by-product. Three idealized models of industrial reactors have been considered. These include a wiped-film reactor, a pool-reactor with the reaction mass as the continuous phase and a pool-reactor with vapour as the continuous phase. The degree of polymerization and the concentration of functional groups are obtained as a function of the various rate constants as well as the parameters characterizing the reactor.     

Simulation of reversible nylon-66 polymerization in homogeneous continuous-flow stirred tank reactors

Experimental data of Ogata¹ has been curve-fitted to obtain the forward and reverse rate constants for nylon-66 polymerization. Its molecular weight distribution (MWD) has been simulated in homogeneous continuous-flow stirred tank reactors (HCSTR) for 11 h of residence time when the reaction mass is very close to equilibrium. The set of algebraic equations have been solved using Brown's algorithm,² which was found to be more efficient compared to the Gauss-Jordon techniques of solution. The MWD thus obtained is compared with our earlier simulation of the molecular weight distribution from batch reactors³ and was found to differ significantly. In HCSTR, the weight fraction distribution does not undergo a maximum and the polydispersity index ρ of the polymer formed is much higher than that obtained from batch reactors. The number and weight average of the polymer formed in HCSTR is found to be significantly lower.     

Biomimetic Natural Killer Membrane Camouflaged Polymeric Nanoparticle for Targeted Bioimaging

In the present study, a biomimetic nanoconstruct (BNc) with a multimodal imaging system is engineered using tumor homing natural killer cell membrane (NKM), near‐infrared (NIR) fluorescent dye, and gadolinium (Gd) conjugate‐based magnetic resonance imaging contrast agent onto the surface of a polymeric nanoparticle. The engineered BNc is 110 ± 20 nm in size and showed successful retention of NKM proteins. The magnetic properties of the BNc are found to be tunable from 2.1 ± 0.17 to 5.3 ± 0.5 mm ^?1 s^?1 under 14.1 T, by adjusting the concentration of Gd‐lipid conjugate onto the surface of the BNc. Confocal imaging and cell sorting analysis reveal a distinguishable cellular interaction of the BNc with MCF‐7 cells in comparison to that of bare polymeric nanoparticles suggesting the tumor homing properties of NKM camouflage system. The in vitro cellular interaction results are further confirmed by in vivo NIR fluorescent tumor imaging and ex vivo MR imaging, respectively. Pharmacokinetics and biodistribution analysis of the BNc show longer circulation half‐life (≈9.5 h) and higher tumor accumulation (10% of injected dose) in MCF‐7 induced tumor‐bearing immunodeficient NU/NU nude mice. Owing to the proven immunosurveillance potential of NK‐cell in the field of immunotherapy, the BNc engineered herein would hold promises in the design consideration of nanomedicine engineering.     

Stone–Wales Defect in Graphene

2D graphene the most investigated structures from nanocarbon family studied in the last three decades. It is projected as an excellent material useful for quantum computing, artificial intelligence, and next generation advanced technologies. Graphene exists in several forms and its extraordinary thermal, mechanical, and electronic properties, principally depend on the kind of perfection of the hexagonal atomic lattice. Defects are always considered as undesired components but certain defects in graphene could be an asset for electrochemistry and quantum electronics due to the engineered electronclouds and quantum tunnelling. The authors carefully discuss the Stone-Wales imperfections in graphene and its derivatives comprehensively. A specific emphasis is focused on the experimental and theoretical aspects of the Stone-Wales defects in graphene with respect to structure-property relationships. The corroboration of extrinsic defects like external atomic doping, functionalization, edge distortion in the graphene consisting of Stone-Wales imperfections, which are very significant in designing graphene-based electronic devices, are summarized.