Electrical conductivity of Gd doped BiFeO3---PbZrO3 composite

The composite, 0.5(BiGd_0.15Fe_0.85O₃)---0.5(PbZrO₃), was synthesized using the solid-state reaction technique. The formation of the compound was confirmed by XRD with an orthorhombic structure at room temperature. The impedance parameters were studied using an impedance analyzer in a wide range of frequency (10²---10⁶ Hz) at different temperatures. The Nyquist plot suggests the contribution of bulk effect and a slight indication of grain boundary effect and the bulk resistance decreases with a rise in temperature. The presence of temperature-dependent relaxation process occurs in the material. Electrical modulus reveals the presence of the hopping mechanism in the materials. The value of exponent n, pre-factor A and σ_dc were obtained by fitting ac conductivity data with Jonscher’s universal power law. The activation energies calculated from the ac conductivity were found to be 0.50, 0.46, 0.44, 0.43, 0.42 and 0.38 eV at 1, 10, 50, 100, 500 kHz and 1 MHz respectively in the temperature region of 110°C---350°C. The dc conductivity was found to increase with the rise in temperature. The activation energy calculated from complex impedance plot and from the fitted Jonscher’s power law are very close, which results similar type of charge carrier exist in conduction mechanism of the material.     

Cold Model-Based Investigations to Study the Effects of Operational and Nonoperational Parameters on the Ruhrstahl–Heraeus Degassing Process

The circulation rate of steel is known to play a vital role in the superlative performance of the Ruhrstahl–Heraeus (RH) degasser. Numerous experiments were conducted on a physical model for the RH degassing process, which was established at IEHK, RWTH-Aachen University. The model was developed with a scale ratio of 1:3 to study the RH process. This study is conducted to show the effects of operational and nonoperational parameters on the circulation rate of liquid water in the model. The effects of lift gas flow rate, submerged depth of snorkels, water level in vessel, etc. on the circulation rate are studied. The mixing characteristics are studied with the help of current conductivity experiments for different lift gas flow rates and water levels in the vacuum vessel. Finally, the relationship between dimensionless numbers is derived with the help of the experimental data obtained from the cold model.     

High tolerance to spherical aberrations and defects of focus with a birefringent lens

We report a systematic investigation of the imaging behavior of an optical system consisting of a lens from a uniaxial birefringent crystal sandwiched between two linear polarizers into which primary spherical aberration has been introduced. The proposed system has higher tolerance to primary spherical aberration and has a larger depth of focus than an imaging system found with an isotropic lens. Some specific cases are computed and illustrated graphically.     

Preliminary studies on NiAl/Nb2Be17 reaction and effectiveness of BeO as an interfacial reaction barrier

Alloys based on the ordered B2 NiAl phase are being considered as potential high-temperature structural materials. One drawback for this material is its lack of high-temperature strength,[1] which can be overcome by reinforcing the alloy with high-strength fibers. Like any other composite system, a suitable reinforcement material must have a matching coefficient of thermal expansion (CTE) with the matrix in addition to high-temperature strength and be chemically compatible with the matrix. Although there are many high-melting ceramic materials which are thermodynamicalry stable in the NiAl matrix, [2] the high CTE of NiAl,[3] 16 X 10⁻⁶ K⁻¹ at 1200 K, makes it difficult to find a suitable ceramic reinforcement material with a matching CTE. Thus, there is a need to develop high CTE fibers for the NiAl matrix. One group of materials with matching CTE[3] to NiAl are the Be-rich intermetallic compounds called beryllides (CTEs in the range of 16 to 18 × 10⁻⁶ K₋₁ at 1200 K) of formula M₂Be₁₇, M₂Be₁₃, or M₂Be₁₂ (where M = Ta, Nb, Ti, Zr, Hf, or Y). Matching CTEs with the NiAl matrix along with their good high-temperature strength[4] and low densities[4] make Be-rich intermetallic compounds attractive as candidate reinforcement materials for the NiAl matrix.     

Preparation and characterization of aluminium alloy sheet Aramid fibre-laminated composites

Laminated composites consisting of alternate layers of aluminium alloy sheets and unidirectional Kevlar-49 fibre epoxy composites were prepared using two different aluminium alloys DTD 687 and aluminium-lithium alloy. Tensile, compressive and interlaminar shear strengths of the laminates were measured. The residual stresses in the aluminium alloy sheets arising out of thermal mismatch between aluminium alloys and aramid fibres were also measured. It is found that the laminates have lower density, higher tensile strength and marginally lower Young’s modulus as compared with monolithic alloy sheets.     

Removal of heavy metal ions from aqueous solutions using carbon aerogel as an adsorbent

The removal of Cd(II), Pb(II), Hg(II), Cu(II), Ni(II), Mn(II) and Zn(II) by carbon aerogel has been found to be concentration, pH, contact time, adsorbent dose and temperature dependent. The adsorption parameters were determined using both Langmuir and Freundlich isotherm models. Surface complexation and ion exchange are the major removal mechanisms involved. The adsorption isotherm studies clearly indicated that the adsorptive behaviour of metal ions on carbon aerogel satisfies not only the Langmuir assumptions but also the Freundlich assumptions, i.e. multilayer formation on the surface of the adsorbent with an exponential distribution of site energy. The applicability of the Lagergren kinetic model has also been investigated. Thermodynamic constant (K(ad)), standard free energy (DeltaG(0)), enthalpy (DeltaH(0)) and entropy (DeltaS(0)) were calculated for predicting the nature of adsorption. The results indicate the potential application of this method for effluent treatment in industries and also provide strong evidence to support the adsorption mechanism proposed.     

Surface modified superparamagnetic nanoparticles for drug delivery: Interaction studies with human fibroblasts in culture

The concept of drug delivery using magnetic nanoparticles greatly benefit from the fact that nanotechnology has developed to a stage that it makes possible not only to produce magnetic nanoparticles in a very narrow size distribution range with superparamagnetic properties but also to engineer particle surfaces to provide site specific delivery of drugs. The size and surface characteristics of the nanoparticles are crucial factors that determine the success of the particles when used in vivo. The aim of this study was to modify the surfaces of the magnetic nanoparticles with PEG to improve the biocompatibility of the nanoparticles by resisting protein adsorption and increasing their intracellular uptake. In this study, the poly(ethyleneglycol) (PEG) modified superparamagnetic iron oxide nanoparticles have been prepared and their influence on human dermal fibroblasts is assessed in terms of cell adhesion/viability, morphology, particle uptake and cytoskeletal organisation studies. Various techniques have been used to determine nanoparticle-cell interactions including light, fluorescence, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The modification of nanoparticle surface induced alterations in cell behaviour distinct from the unmodified particles, suggesting that cell response can be directed via specifically engineered particle surfaces.     

Possibility of an optical focal shift with polarization masks

The polarization phase shift (PPS) has emerged as an important analytical tool in optical metrology. The present study utilizes the concept of controlling the polarization phase in applications such as focal shift and automatic focusing. When elliptically polarized light, in general, is incident upon a circularly symmetric polarization mask consisting of circular and annular zones with each zone having a unique linear polarizability, the polarization-phase difference introduced between the polarization-masked zones is also circularly symmetric. With the mask at the lens aperture, the polarization phase introduced is multiplicative with the lens function and is shown to result in a shift of the Gaussian focus plane. Because the polarization phase can be controlled by variation of the polarization parameters, the effective focal length of the imaging system can be varied within a small range. A study of the point-spread functions at the shifted focal planes has shown that the quality of the focal patch in these planes is comparable with that produced by a diffraction-limited imaging system at Gaussian focus. The shift of focus can be achieved by control of the polarization of the input beam. It is anticipated that this technique may find application in areas for which dynamic focusing within a small range is required.     

High-pressure sintering of cubic boron nitride

Cubic boron nitride (cBN) powder was compacted at high pressure and high temperature using a solid solution of titanium carbide and titanium nitride (TiC _x N_1–x ) as binding material in the presence of a small amount of aluminium. Different compositions of (TiC _x N_1–x ), 0<x<1 were used as binders. The weight percentage of cBN, TiC _x N_1–x and aluminium were optimized and found to be critical; any marked deviation from these optimized values deteriorated the quality of compacts. Various high-pressure sintering parameters such as pressure, temperature and sintering time, etc, were optimized for this binder. The compacts were also characterized using X-ray diffraction, scanning electron microscopy and microhardness measurements. The microstructural and X-ray diffraction observations indicated no marked changes in the compacts as the value ofx in TiC _x N_1–x was varied, but the microhardness was found to depend on the value ofx.