Threshold-like features in the magnetic response of iron-filled multi-walled carbon nanotube and polymer composite

The magnetic properties of iron-filled multi-walled carbon nanotubes dispersed in polystyrene (Fe-MWNT/PS) have been investigated as a function of Fe-MWNT concentration (0.1-15 wt%) from 300 to 10 K. Electron microscopy studies indicate that Fe nanorods (aspect ratio similar to 5) remain trapped at various lengths of MWNT and are thus, prevented from oxidation as well as aggregation. The magnetization versus applied field (M-H loop) data of 0.1 wt% of Fe-MWNTs in PS show an anomalous narrowing at low temperatures which is due to the significant contribution from shape anisotropy of Fe nanorods. The remanence shows a threshold feature at 1 wt%. The enhanced coercivity shows a maximum at 1 wt% due to the dominant dipolar interactions among Fe nanorods. Also the squareness ratio shows a maximum at 1 wt%.

Bio-Composite Membrane Electrolytes for Direct Methanol Fuel Cells

A new class of bio-composite polymer electrolyte membranes comprising chitosan (CS) and certain biomolecules in particular, plant hormones such as 3-indole acetic acid (IAA), 4-chlorophenoxy acetic acid (CAA) and 1-naphthalene acetic acid (NAA) are explored to realize proton-conducting bio-composite membranes for application in direct methanol fuel cells (DMFCs). The sorption capability, proton conductivity and ion-exchange capacity of the membranes are characterized in conjunction with their thermal and mechanical behaviour. A novel approach to measure the permeability of the membranes to both water and methanol is also reported, employing NMR imaging and volume localized NMR spectroscopy, using a two compartment permeability cell. A DMFC using CS-IAA composite membrane, operating with 2M aqueous methanol and air at 70 degrees C delivers a peak power density of 25 mW/cm(2) at a load current density of 150 mA/cm(2). The study opens up the use of bio-compatible membranes in polymer-electrolyte-membrane fuel cells. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.030111jes] All rights reserved.

Wavelet based spectral finite element modelling and detection of de-lamination in composite beams

In this paper, a model for composite beam with embedded de-lamination is developed using the wavelet based spectral finite element (WSFE) method particularly for damage detection using wave propagation analysis. The simulated responses are used as surrogate experimental results for the inverse problem of detection of damage using wavelet filtering. The WSFE technique is very similar to the fast fourier transform (FFT) based spectral finite element (FSFE) except that it uses compactly supported Daubechies scaling function approximation in time. Unlike FSFE formulation with periodicity assumption, the wavelet-based method allows imposition of initial values and thus is free from wrap around problems. This helps in analysis of finite length undamped structures, where the FSFE method fails to simulate accurate response. First, numerical experiments are performed to study the effect of de-lamination on the wave propagation characteristics. The responses are simulated for different de-lamination configurations for both broad-band and narrow-band excitations. Next, simulated responses are used for damage detection using wavelet analysis.

Modeling of active fiber composite for delamination sensing

In order to demonstrate the feasibility of Active Fiber Composites (AFC) as sensors for detecting damage, a pretwisted strip made of AFC with symmetric free-edge delamination is considered in this paper. The strain developed on the top/bottom of the strip is measured to detect and assess delamination. Variational Asymptotic Method (VAM) is used in the development of a non-classical non-linear cross sectional model of the strip. The original three dimensional (3D) problem is simplified by the decomposition into two simpler problems: a two-dimensional (2D) problem, which provides in a compact form the cross-sectional properties using VAM, and a non-linear one-dimensional (1D) problem along the length of the beam. This procedure gives the non-linear stiffnesses, which are very sensitive to damage, at any given cross-section of the strip. The developed model is used to study a special case of cantilevered laminated strip with antisymmetric layup, loaded only by an axial force at the tip. The charge generated in the AFC lamina is derived in closed form in terms of the 1D strain measures. It is observed that delamination length and location have a definite influence on the charge developed in the AFC lamina. Also, sensor voltage output distribution along the length of the beam is obtained using evenly distributed electrode strip. These data could in turn be used to detect the presence of damage.

Tribological characteristics of A356 Al alloy-SiC(P) composite discs

The dry sliding wear and friction behaviour of A356 Al alloy and its composites containing 10 and 20 vol.% SiC(P) have been studied using pin-on-disc set up. In these tests, A356 Al alloy and its composites are used as disc whereas brake pad was used in the form of pins. Wear tests were carried out at a load of 192 N and the sliding speed was varied from 1 to 5 m/s. Tests were done for a sliding distance of 15 km. The effects of sliding velocity on the wear rate, coefficient of friction and nature of tribolayers formed on discs have been studied. Wear rates of composites as calculated by weight loss method, found to be negative at sliding speed of more than 2 m/s. Worn surfaces of pins and discs have been analyzed using scanning electron microscope. SEM and EDAX analysis of worn surfaces of composite discs showed formation of tribolayers, consisting of mixture of oxides of Al, Si, Cu, Ca, Ba, Mg, and Fe. In these layers, copper and barium content found to be increase with sliding speed in the case of composites. (C) 2011 Elsevier B.V. All rights reserved.

Measurement of Gibbs energies of formation of CoF2 and MnF2 using a new composite dispersed solid electrolyte

Gibbs energies of formation of CoF2 and MnF2 have been measured in the temperature range from 700 to 1100 K using Al2O3-dispersed CaF2 solid electrolyte and Ni+NiF2 as the reference electrode. The dispersed solid electrolyte has higher conductivity than pure CaF2 thus permitting accurate measurements at lower temperatures. However, to prevent reaction between Al2O3 in the solid electrolyte and NiF2 (or CoF2) at the electrode, the dispersed solid electrolyte was coated with pure CaF2, thus creating a composite structure. The free energies of formation of CoF2 and MnF2 are (± 1700) J mol−1; {fx37-1} The third law analysis gives the enthalpy of formation of solid CoF2 as ΔH° (298·15 K) = −672·69 (± 0·1) kJ mol−1, which compares with a value of −671·5 (± 4) kJ mol−1 given in Janaf tables. For solid MnF2, ΔH°(298·15 K) = − 854·97 (± 0·13) kJ mol−1, which is significantly different from a value of −803·3 kJ mol−1 given in the compilation by Barinet al.

Activity of TiO2 in the System ZrO2-TiO2 and Gibbs Energy of Formation of ZrTiO4

The activity of Ti02 in single and two··phase regions of ihe system ZrOrTi02 has heen measured lIsing solid state cells based on yttria··doped tho ria (YDT) as the solid electrolyte at 1373 K. The cells used can be represented as: Pt, Tio.07PtO.Y3 + Zrj.,Tix0 2 / YDT / Ti02 + Tio.07Pto.93, Pt Pt, Tio.07Pto.93 + ZrJ.xTix02 + ZrTi04 / YDT / Ti02+ Tio.07PtO.93, Pt In each cell the composition of Pt-Ti alloy was identical at hoth electrodes. The emf of the cell is therefore directly related to the activity of Ti02 in oxide phase or oxide phase mixture: aTiO~ :;: cxp (-4FE/RT). The activity coefficient of Ti02 in th~ zirconia-rich solid solution with monoclinic structure (CUl2 2" XTi02 2" 0) can be expressed as:In the zirconia-rich solid solution with tetragonal structure (0.085 2" X ri02 2" 0.03), the activity coefficient is given by:In YTi02 (± 0.012) = 2.354 (1-XTiO? )2 +0.064 The standard Gibbs energy of formation of ZrTi04 is -5650 (± 200) J/mol at 1373 K .

Gibbs energy of formation of CaCu3Ti4O12 and phase relations in the system CaO-CUO/CU2O-TiO2

he standard Gibbs energy of formation of CaCu3Ti4O12 (CCTO) from CaTiO3, CuO and TiO2 has been determined as a function of temperature from 925 to 1350 K using a solid-state electrochemical cell with yttria-stabilized zirconia as the solid electrolyte. Combining this result with information in the literature on CaTiO3, the standard Gibbs energy of formation of CCTO from its component binary oxides, CaO, CuO and TiO2, has been obtained: View the MathML source (CaCu3Ti4O12)/J mol−1 (±600) = −125231 + 6.57 (T/K). The oxygen chemical potential corresponding to the reduction of CCTO to CaTiO3, TiO2 and Cu2O has been calculated from the electrochemical measurements as a function of temperature and compared on an Ellingham diagram with those for the reduction of CuO to Cu2O and Cu2O to Cu. The oxygen partial pressures corresponding to the reduction reactions at any chosen temperature can be read using the nomograms provided on either side of the diagram. The effect of the oxygen partial pressure on phase relations in the pseudo-ternary system CaO–CuO/Cu2O–TiO2 at 1273 K has been evaluated. The phase diagrams allow identification of secondary phases that may form during the synthesis of the CCTO under equilibrium conditions. The secondary phases may have a significant effect on the extrinsic component of the colossal dielectric response of CCTO.

Structure and temperature dependence of conductivity of Ag2.5Se‐Se composite

Rapid solidification of Ag‐53 at. % Se alloy resulted in the formation of a composite mixture of Ag2.5Se and Se. The microstructure consists of spherical Se grains of 2–20 μm size, randomly distributed in a matrix of Ag2.5 Se. The Se grains were found to be layered hexagonal while the Ag2.5 Se had an orthorhombic crystal structure. The unit cell size of this phase, however, was twice that reported for the equilibrium orthorhombic Ag2 Se compound. The conductivity σ variation with temperature in the range 80–320 K was found to be similar to that observed in degenerate semiconductors. The σ decreased from 295 Ω−1 cm−1 at room temperature to a saturation value of 70 Ω−1 cm−1 for temperatures <80 K. The results are discussed in terms of percolation conduction in the Ag2.5 Se phase.

Composite instantaneous comparators basis for design and their transient performance

Principles of design of composite instantaneous comparators (a combination of amplitude- and phase- comparison techniques) are laid out to provide directional, directional-reactance, nonoffset-resistance and conductance characteristices. The respective signals provided by the voltage transformer and the current transformer are directly used as relaying signals without resorting to any form of mixing. Phase shifts required, are obtained by using magnetic ferrite cores in a novel manner. Sampling units employing a combination of ferrite cores and semiconductor devices provide highly reliable designs. Special attention is paid to the choice of relaying signals, to eliminate the need for any synchronisation or modification and to avoid `image¿ characteristics. These factors have resulted in a considerable simplification of the practical circuitry. A thyristor AND circuit is employed in dual comparator units to provide the final tripping, and leads to a circuit which is much less sensitive to extraneous signals than a single-thyristor unit.