Glass transition temperature-structural studies of tungstate tellurite glasses

Raman, IR and DSC studies have been carried on the (100 − x)TeO₂–xWO₃ (TW) glasses with 10 ≤ x ≤ 40 mol%. The Raman, IR spectra of these samples show that glass network consists of [TeO₃]/[TeO₃₊₁], [TeO₄], [WO₄] and [WO₆] groups as basic structural units. The W ion coordination state changes from 4 to 6 when WO₃ concentration increases beyond 30 mol%. Addition of WO₃ oxide to the TW glasses increases the amount of lower coordination of [TeO₃]/[TeO₃₊₁] units and decreases the higher coordination [TeO₄] units, Te–O–Te chains. From DSC thermogram, thermal properties such as the glass transition temperature (T_g), onset crystallization (T_o) of the glass systems were calculated. The compositional variation of glass transition temperature (T_g) is found to linear with an increase in WO₃ content.     

SYNTHESIS OF CARBON NANOTUBES THROUGH CARBON ARC EVAPORATION EMPLOYING Mm, La, AND Ce CATALYSTS

We report the formation of carbon nanotubes (CNTs) in, high density when mischmetal Mm (a natural mixture of several rare earth elements) is used as catalyst. Mm has been found to work as a better catalyst than either lanthanum (La) or cerium (Ce). The formation of composite nanorods when the catalyst La is used in very high concentration (∼90wt.%) has also been described and discussed.     

Characterization of Nanocomposite Polymeric Membrane

Composite membrane has good permeability and selectivity for gases, which depends upon the operating conditions. The solubility and diffusivity of the penetrant in the polymer matrix control the transport through non-porous dense membrane. In the present work, the nano sized particles of Co_0.6Zn_0.4Fe₂O₄ were prepared by the co-precipitation method and characterized by the XRD technique with particle size of 10 nm. Nanocomposite polycarbonate membranes were studied before and after irradiation by the ³⁵Cl⁹⁺ ion of 120 MeV at the Nuclear Science Centre, New Delhi. The distribution of nanoparticles throughout the membrane was characterized by the optical microscope. Gas transport properties of H₂, CO₂ and air for these nanocomposite membranes were investigated. It was found that membrane containing nanoparticles shows low permeability with high permselectivity. After irradiation by swift heavy ions (SHI), high gas permeability and high permselectivity has been observed for these nanocomposite membranes.     

On mean residence times in flow systems

A widely accepted result of residence time theory namely mean residence time is equal to the system volume divided by the flow rate was first offered by Danckwerts[l] and later extended by Buffham[21 and Gibilaro[3] to more general cases. Taking a two section system it is argued and experimentally demonstrated that the above theoretical result is not universal. A possible implication of this result is that even for a single section system the above result may not hold in all the cases. This is also supported by experimental data on a single section system.     

Pressure corrections for the potential flow analysis of Kelvin–Helmholtz instability with heat and mass transfer

Pressure corrections for the viscous potential flow analysis of Kelvin–Helmholtz instability at the interface of two viscous fluids have been carried out when there is heat and mass transfer across the interface. Both fluids are taken as incompressible and viscous with different kinematic viscosities. In viscous potential flow theory, viscosity enters through normal stress balance and effect of shearing stresses is completely neglected. We include the viscous pressure in the normal stress balance along with irrotational pressure and it is assumed that this viscous pressure will resolve the discontinuity of the tangential stresses at the interface for two fluids. It has been observed that heat and mass transfer has destabilizing effect on the stability of the system. A comparison between viscous potential flow (VPF) solution and viscous contribution to the pressure for potential flow (VCVPF) solution has been made and it is found that the effect of irrotational shearing stresses stabilizes the system.     

Studies on dielectric relaxation in ceramic multiferroic Gd1−xYxMnO3

Dielectric study over a broadband was carried out from 10 to 70 K on ceramic Gd_1?xY_xMnO₃ (x=0.2, 0.3 and 0.4). For all the compositions, a prominent sharp peak about ~18 K was observed in the temperature dependence of both ε′(T) and ε″(T) at all frequencies, indicating a long‐range ferroelectric (FE) transition. Using Cole‐Cole fit to the permittivity data, the relaxation time τ and the dielectric strength ?ε were estimated. Temperature variation of τ(T) in the Arrhenius representation is found to be nonlinear (non‐Debyean relaxation), with increasing barrier‐activation energy over successive temperature‐windows. Interestingly, for all the compositions, we witness a jump in τ(T) about the ferroelectric transition temperature, concurred by a broad‐maximum in ?ε(T),signifying the critical slow down of relaxations near long‐range FE‐correlations.     

Non-isothermal crystallization kinetics of TiO2 nanoparticle-filled poly(ethylene terephthalate) with structural and chemical properties

The present research work includes non-isothermal crystallization kinetics of poly(ethylene terephthalate) (PET)–titanium dioxide (TiO₂) nanocomposites as well as structural and chemical properties of these nanocomposites. The average grain size of chemically synthesized TiO₂ nanoparticles has been calculated 19.31 nm by TEM and XRD. The morphology and structural analysis of PET–TiO₂ nanocomposites, prepared via solution casting method, has been investigated using SEM and XRD, respectively. The nature of chemical bonds has been discussed on the basis of FTIR spectra. The effect of TiO₂ nanoparticles and cooling rates on non-isothermal crystallization kinetics of PET was examined by differential scanning calorimetry at various heating and cooling rates. It has been observed that TiO₂ nanoparticles accelerate the heterogeneous nucleation in PET matrix. The crystallization kinetics could be explained through Avrami–Ozawa combined theory. TiO₂ nanoparticles cause to make molecular chains of PET easier to crystallize and accelerate the crystallization rates during non-isothermal crystallization process; this conclusion has also been verified by Kissinger model for crystallization activation energy.     

Immobilization of lanthanum,cerium, and selenium into ceramic matrix of sodium zirconium phosphate

The crystallographic nature of NaCe_0.2Zr_1.8P₃O₁₂, NaSe_0.2Zr_1.8P₃O₁₂, and NaLa_0.13Ce_0.14Se_0.15·Zr_1.58P₃O₁₂ phases has been investigated with the aim of developing methods for radionuclide immobilization into sodium zirconium phosphate (NZP) phase. The phases have the NZP structure, space group \(R\bar 3c\) , Z = 6. Powder diffraction data have been subjected to Rietveld refinement, and satisfactory structural convergence of R-factors was achieved. The PO₄ stretching and bending vibration bands in the IR region have been assigned.