Magneto-dielectric and magneto-conducting fillers based polymer composites: Effect of functionalization,coating and dispersion process on electromagnetic shielding properties

Electromagnetic interference shielding of magneto-dielectric (BaTiO₃-Fe₃O₄) and magneto-conducting (f-MWCNT-Fe₃O₄) fillers based polymer electrolyte composites in the X-band have been studied in the present work. Magneto-dielectric and magneto-conducting fillers have been obtained by in situ preparation of Fe₃O₄ nanoparticles by chemical precipitation in the presence of BaTiO₃ and functionalized multiwalled carbon nanotubes (f-MWCNT). Functionalization of MWCNT has resulted in their strong bonding with the polymer electrolyte adversely affecting the charge transport properties and shielding effectiveness. Dielectric, magnetic and conducting properties of the magneto-dielectric and magneto-conducting fillers are found to be significantly different as a result of coating by Fe₃O₄ nanoparticles on BaTiO₃ and f-MWCNT. Combining two fillers in a single nanocomposite has exhibited non-complimentary addition of their individual properties. The ultra-sonication method of dispersion of the magneto-conducting filler has been found to give better conducting and shielding effectiveness in comparison to the homogenization method due to better disentanglement of the nanotubes.     

(S)-2-(ethyl propionate)-(O-ethyl xanthate)- and (S)-2-(Ethyl isobutyrate)-(O-ethyl xanthate)-mediated RAFT polymerization of vinyl acetate

(S)-2-(Ethyl propionate)-(O-ethyl xanthate) (X1) and (S)-2-(Ethyl isobutyrate)-(O-ethyl xanthate) (X2) were used as the reversible addition-fragmentation chain transfer (RAFT) agents for the radical polymerization of vinyl acetate (VAc). The former showed the better chain transfer ability in the polymerization at 60°C. Kinetic study with both RAFT agents showed pseudo-first order kinetics up to around 85% monomer conversion. Molecular weight of the resulting polymer increased linearly with increase in the monomer conversion up to around 85%. The observed molecular weights calculated from ¹H-NMR spectrum [M_n(NMR)] are close to the corresponding theoretical molecular weights [M_n(theor)]. The corresponding polydispersity index (PDI) of the resulting polymers remained almost constant at around 1.2 up to ∼ 65% monomer conversion and then increased gradually with the further increase in the monomer conversion. Chain-end analysis of the resulting polymers by ¹H-NMR showed clearly that polymerization started with the radical forming out of the xanthate mediator. The negligible homo-chain extension and the hetero-chain extension involving synthesis of poly(VAc)-b-poly(NVP) diblock copolymer were occurred. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Influence of ultra-high residual compressive stress on the static and dynamic indentation response of a chemically strengthened glass

The influence of ultra-high surface compressive stresses (～1 GPa) on the static and dynamic indentation response was investigated on an ion-exchanged glass and compared with the raw glass properties. Static hardness measurements were conducted utilizing a standard Vickers hardness tester (15 s duration), while dynamic hardness measurements were performed using a custom-made dynamic indentation hardness tester (60 μs duration). It was found that there is an 11% increase in static and dynamic hardness from the raw glass to the strengthened glass due to chemical strengthening. The dynamic hardness on the strengthened glass was also 23% greater than the static hardness. Additionally, the strengthened glass exhibited notable radial crack suppression. To examine the subsurface hardness profile, static Vickers indentations were conducted on a lateral surface which was polished to remove the strengthened layer. The hardness profile revealed that the effect of strengthening extended to 3 times the case-depth measured using photoelasticity.     

Structural and functional properties of sol-gel synthesized and microwave heated Pb0.8 Co0.2-zLazTiO3 (z = 0.05–0.2) nanoparticles

The present work reports the effect of La-substitution on structural and functional properties of lead cobalt titanate (PCT) perovskite structure as a function of variation of Co-content. The sol-gel synthesized and microwave heated Pb_0.8 Co_0.2-zLa_zTiO₃ (z?=?0.05, 0.1, 0.15 & 0.2) (PCLT) nanoparticles showed the presence of complete cubic phases while few were noted to be tetragonal lead titanate (PT) phases. The surface morphology was examined by field emission scanning electron microscope (FESEM) and high resolution transmission electron microscope (HRTEM). The HRTEM revealed fibers like nanoparticles at z?=?0.15 and 0.2. The Fourier transform infrared spectra attributed the presence of metal oxide bonds. Furthermore, the wide optical band gap energy (E_op) was acquired to be changing from 2.32 to 3.20?eV. In addition, the electrical parameters such as dielectric constant (ε'), dielectric loss (ε"), ac & dc-electrical conductivity (σ_ac & σ_dc), complex dielectric modulus (M^*) and complex impedance (Z^*) were studied as a function of frequency (f) and composition. Using power law fitting, the σ_dc values were determined. The z?=?0.15 content exhibited high σ_dc of ~ 2.51?×?10^?7 S/cm among all compositions. Besides, the results expressed the existence of short range and long range hopping conduction regions in dielectric modulus spectra. The Nyquist plots were drawn to elucidate the electrical conduction and relaxation mechanism. Later on, ferroelectric hysteresis loops were recorded for z?=?0.05–0.2.     

Effect of Metal Doped Zinc Oxide Nanorods on Photoelectrical Characteristics of ZnO/Polyaniline Heterojunction

The n-type vertically aligned metal doped ZnO nanorods (NRs) and p-type proton acid doped polyaniline (PANI) inorganic/organic heterojunction diodes have been fabricated. Aluminium (Al) and iron (Fe) doped ZnO NRs were grown on seed ZnO layer on fluorine doped tin oxide coated glass substrates by high temperature chemical bath deposition method. The elemental analysis using EDAX confirm doping of Al and Fe in ZnO. The morphology of doped ZnO nanorods and ZnO/PANI heterojunction exhibit well defined uniform nanorod arrays and interface between nanorods and polyaniline matrix respectively. The dark current–voltage curves confirmed the rectifying diode like behaviors of the heterojunctions, whereas under illumination, the junction revealed good sensitivity to UV and visible range with increased current densities. The highest ideality factor and lowest barrier height was found for FeZnO/PANI heterojunction under dark and under light compared to that of ZnO/PANI, AlZnO/PANI. This research is innovative with respect to low cost synthesis of efficient and sensitive hybrid p–n junction diodes and possibly serves as the building blocks for future optoelectronic applications.     

An Extended Mohr–Coulomb Model for Fracture Strength of Intact Brittle Materials Under Ultrahigh Pressures

An extended Mohr–Coulomb model is proposed to represent the pressure‐dependent strength of intact structural ceramics under quasi‐static and dynamic loading rates at high pressures. A plot of normalized shear stress versus hydrostatic pressure for a range of structural ceramics revealed that despite the differences in material properties, test methods, and strain rates, the failure strength data fall in a narrow range, which can be represented by a unified model. The overall deformation behavior of structural ceramics and their strain rate dependence of strength in multiaxial loading at high pressure beyond Hugoniot elastic limit (HEL) can be explained by an exponential pressure dependence in the Mohr–Coulomb model. The analysis also suggests that the influence of strain rate on strength of a ceramic diminishes with increase in confinement pressure.     

Synthesis,Structural and Luminescence Studies of Pyrochlore Phase Free TiO2:Dy3+ Produced by Solid‐state Reaction Method

TiO₂:Dy³⁺ powders without any secondary phases have been prepared by solid‐state reaction through the optimization of synthesis conditions, doping amount and subsequently through a purification step. The maximum dysprosium solubility was found at 0.43 mol% in the range 800–900°C. The Rietveld refinement was performed to calculate the amount of phases and lattice constants. The effect of synthesis conditions and doping on strain and crystallite size is also discussed. Room temperature photoluminescence of TiO₂:Dy³⁺ shows blue and yellow color emission. It is shown that yellow emission can be enhanced with the reduction of the pyrochlore phase Dy₂Ti₂O₇.     

Oxidation resistance,residual strength,and microstructural evolution in Al2O3-MgO–C refractory composites with YAG nanopowder

The decisive role of nanostructured yttrium aluminium garnet (YAG;Y₃Al₅O₁₂) powder addition on oxidation resistance, residual strength and microstructural evolution were studied in Al₂O₃-MgO–C refractory composites. Oxidation index and rate constant calculations indicated that the oxidation resistance was almost 70 % improved for the nano-YAG containing refractories oxidized in air at 1600 °C. Residual compressive strength (R_c) estimations showed that there was nearly 75 % strength retained in these oxidized refractories fortified with nano-YAG. Residual bending strength (R_b) estimations based on cyclic thermal shock, exhibited that there was almost 70 % thermal shock resistance enhancement in refractories reinforced with nano-YAG, showed a good agreement between R_b and R_c values. These beneficial properties were attributed to the formation of a well-sintered framework of YAG/Spinel bonding grains throughout the dense oxidized layer microstructure of these new class of refractories. The concept of interfacial toughening and implications of these results to practical applications are discussed.     

Highly porous metal organic framework derived NiO hollow spheres and flowers for oxygen evolution reaction and supercapacitors

In this study, metal-organic-framework (MOF) derived porous NiO hollow spheres and flowers were obtained using facile solvothermal synthesis and heat treatment. After pyrolyzing, the flower like and hollow spherical like morphology of NiO nanoparticles was successfully inherited from the initial MOF-based templates. The electrochemical studies demonstrated that the porous NiO hallow spheres unveiled a better supercapacitive performance (specific capacitance (C_s) = 1058 F g^?1 at current density (j) = 2 A g^?1) and oxygen evolution reaction (OER) catalytic activity (overpotential (?) = 323 mV) compared to porous NiO flowers (C_s = 857 F g^?1 at j = 2 A g^?1 and ? = 346 mV). Moreover, excellent capacity retention of over 93% was obtained in porous NiO-hs nanoparticles even after 5000 cycles. The fabricated NiO//Fe₂O₃ asymmetric supercapacitor delivered an energy density (E) of 35.75 W h Kg^?1 under power density (P) of 780 W kg^?1 and showed promising stability over 3000 cycles. Considering the ease of preparation and high catalytic activity and supercapacitive performance, these prous NiO hallow structures can be considered as a potential electrode material for next generation energy storage devices and OER catalysts.