Ultrasound–assisted synthesis and characterization of polymethyl methacrylate/reduced graphene oxide nanocomposites

This article reports ultrasound–assisted synthesis of polymethyl methacrylate (PMMA)/reduced graphene oxide (RGO) nanocomposites by in situ emulsion polymerization coupled with in situ reduction of graphene oxide. The thermal degradation kinetics of the nanocomposites was also assessed with Criado and Coats‐Redfern methods. Intense microconvection generated by ultrasound and cavitation results in uniform dispersion of RGO in the polymer matrix, which imparts markedly higher physical properties to resulting nanocomposites at low (≤1.0 wt %) RGO loadings, as compared to nanocomposites synthesized with mechanical stirring. Some important properties of the PMMA/RGO nanocomposites synthesized with sonication (with various RGO loadings) are: glass transition temperature (0.4 wt %) = 124.5°C, tensile strength (0.4 wt %) = 40.4 MPa, electrical conductivity (1.0 wt %) = 2 × 10^?7 S/cm, electromagnetic interference shielding effectiveness (1.0 wt %) = 3.3 dB. Predominant thermal degradation mechanism of nanocomposites (1.0 wt % RGO) is 1D diffusion with activation energy of 111.3 kJ/mol. © 2017 American Institute of Chemical Engineers AIChE J, 64: 673–687, 2018     

Delamination propagation analyses of spar wingskin joints made with curved laminated FRP composite panels

Initiation and propagation of inter-laminar delamination in adhesive bonded spar wingskin joint (SWJ) made with laminated fibre-reinforced plastic (FRP) composite curved panels have been studied employing three-dimensional finite element analyses. In-plane and out-of-plane normal and shear stress distributions are seen to be highly three-dimensional in nature. Tsai-Wu coupled stress failure criteria have been employed to identify critical locations of onset of delamination-induced damage. This occurs underneath the toe-end of the spar overlap and at the inter-laminar surface between the first and second plies of the curved FRP wingskin panel. Significant edge effects on the joint strength have been observed due to the curvature geometry of the composite wingskin panels. Non-linear finite element analyses have been carried out for study of delamination propagation using contact and multi point constraint (MPC) elements. The use of contact elements prevents inter-penetration of delaminated surfaces. Whereas, sequential release of MPC elements facilitates computation of opening, sliding and cross-sliding modes of delamination-induced strain energy release rates (SERR) by using virtual crack closure technique. Variation in delamination lengths significantly effects the variation of peel and inter-laminar shear stresses and different modes of SERRs. Variations on the two delamination fronts are seen to be quite different indicating dis-similar propagation rates. The Mode I SERR (G_I) predominantly governs the delamination propagation in the SWJ.     

On progressively censored generalized exponential distribution

In this paper, we consider the statistical inference of the unknown parameters of the generalized exponential distribution in presence of progressive censoring. We obtain maximum likelihood estimators of the unknown parameters using EM algorithm. We also compute the expected Fisher information matrix using the missing value principle. We then use these values to determine the optimal progressive censoring plans. Different optimality criteria are considered, and selected optimal progressive censoring plans are presented. One example has been provided for illustrative purposes.     

Nanoscale films of organic dyes for broadband environmental sensing

Two types of suitably substituted organic dye molecules namely copper phthalocyanine and Rose Bengal were electrostatically self-assembled on gold-coated glass substrates, the gold surface being modified with poly(allylaminehydrochloridethe). The surface plasmon resonance technique was employed to investigate the sensing properties of organic dyes on exposure to three different volatile organic compounds. The films using phthalocyanine molecules were considered to be an optimal material because of its fast response and full recovery. This behaviour is attributed to the film surface morphology, molecular orientation in the film architecture, and sizes and dipole moments of vapours.     

Wet chemical synthesis of low bulk density aluminium hydroxide powder

Fine, low bulk density aluminium hydroxide powdered gel was prepared by the mild base hydrolysis of an aqueous solution of aluminium sulfate with hydrazine hydrate. Parameters such as method of addition of reactant, initial concentration of Al³⁺, mole ratio, final pH and hydrolysis temperature have a profound effect on the lightness and particle size of the powder. Optimized conditions showed that the final pH, Al³⁺ concentration and method of addition of reactant have a major contribution on the formation of lighter grade powder. Experiments conducted using other bases also produced lighter particles under similar conditions. Deviation from the optimized conditions led to formation of a higher bulk density product. Copyright © 2003 Society of Chemical Industry     

Modification of spin coating method and its application to grow thin films of cobalt ferrite

Spin coating method has been modified to widen its scope for applications. The film deposition assembly is suitably designed. With this modification, it is possible to use common inorganic chemicals in the form of their aqueous solutions as starting materials to grow thin films of binary/ternary oxides. This method is applied to grow thin films of cobalt ferrite. The structure, morphology and magnetic properties of thin films of cobalt ferrite have been determined by using X-ray diffraction, Scanning electron microscopy and vibrating sample magnetometer respectively. The results show that the present technique is useful to deposit thin films of cobalt ferrite, which are qualitatively comparable to the films grown by other wet chemical techniques.     

Microbial recovery of uranium using native fungal strains

Native microorganisms were isolated from water samples collected from uranium mines of Jaduguda, Bhatin and Nawapahar of UCIL India. Ten fungal strains isolated in pure cultures were selected, identified and used in this study. The strains were used for in situ leaching of mainly oxide low grade uranium ore of Turamdih mine. The maximum recovery of 71% uranium was obtained with the strain Cladosporium oxysporum. The other two strains belonging to Aspergillus flavus and Curvularia clavata gave 59% and 50% of metal recovery respectively from the same ore.     

Vacancy-induced electronic states in substoichiometric V2 −x Mo x O3 ±y thin films and powders—A soft X-ray emission study

Vanadium oxide as well as molybdenum oxide thin films have been found to show electrochromism and metal insulator transitions. Incorporation of vanadium ion into molybdenum oxide lattice not only changes the lattice parameters but also shows prominent spectral changes in X-ray emission spectra. K_β1-3 emission spectra of vanadium in different alloy films of V₂O₅-MoO₃ system have been studied here and these have been compared with the X-ray emission spectra of similar composition of V₂O₅-MoO₃ powders. For K_β1-3 emission, the difference in values of asymmetry indices of thin films and powders is marginal, although considerable tailing towards high energy is observed in thin films. By curve fitting procedure, the K_β1-3 emission spectra have been resolved to several gaussian peaks, and these have been explained on the basis of vacancy-induced electronic states, crossover transitions advocated in molecular orbital theory and plasmon oscillation.     

Anisotropic Superconducting Properties of MgB2 and Related Compounds

Anisotropic superconducting properties of inter-metallic compounds MgB₂, Y₂PdGe₃, and CaAlSi with AlB₂ structure are studied by detailed angular dependent transport measurements. MgB₂ and CaAlSi shows appreciable anisotropy of the upper critical field, H _c2, with mass anisotropy parameter =3 and 2, respectively, while Y₂PdGe₃ is almost isotropic. In-plane anisotropy of H _c2 in these hexagonal superconductors is very small, consistent with the prediction based on GL theory.