• Volume 27, Issue 3

June 2004,   pages  217-322

• Synthesis of BaTiO3 powder from barium titanyl oxalate (BTO) precursor employing microwave heating technique

Cubic barium titanate (BaTiO3) powder was synthesized by heating barium titanyl oxalate hydrate, BaTiO(C2O4)$_{2}\cdot$4H2O (BTO) precursor in microwave heating system in air at 500°C. Heating BTO in microwave above 600°C yielded tetragonal form of BaTiO3. Experiments repeated in silicon carbide furnace showed that BaTiO3 was formed only above 700°C. The product obtained was cubic.

• Synthesis of nanocrystalline SnO2 powder at 100°C

A simple gel to crystal conversion route has been followed for the preparation of nanocrystalline SnO2 at 80–100°C under refluxing conditions. Freshly prepared stannic hydroxide gel is allowed to crystallize under refluxing and stirring conditions for 4–6 h. Formation of nano crystallites of SnO2 is confirmed by X-ray diffraction (XRD) study. Transmission electron microscopic (TEM) investigations revealed that the average particle size is 30 nm for these powders.

• Synthesis and crystal structure determination of Br2SeIBr polyhalogen–chalcogen

In this paper polyhalogen–chalcogen Br2SeIBr was synthesized and the crystal structure was determined by single crystal X-ray diffraction method. This compound was prepared in the temperature range 150–50°C which was brownish-red in colour and crystallized in monoclinic crystal system and space group 𝑃21/c with four molecules per unit cell. Lattice parameters were: 𝑎 = 6.3711(1), 𝑏 = 6.7522(2), 𝑐 = 16.8850(5) Å, 𝛼 = 𝛾 = 90°, 𝛽 = 95·96°, 𝜈 = 722·45 Å3.

• Evaluation of a.c. conductivity behaviour of graphite filled polysulphide modified epoxy composites

Composites of epoxy resin having different amounts of graphite particles have been prepared by solution casting method. Temperature dependence of dielectric constant, tan 𝛿 and a.c. conductivity was measured in the frequency range, 1–20 kHz, temperature range, 40–180°C for 0.99, 1.96 and 2.91 wt% graphite filled and unfilled epoxy composites. It was observed that the dielectric constant, tan 𝛿 and a.c. conductivity increase with increasing temperature. Near the transition temperature the materials show anomalous behaviour for the observed properties. Peaks of dielectric constant, tan 𝛿 and a.c. conductivity were observed to shift towards lower temperature with increasing frequency. Clear relaxation (tan 𝛿) peaks around 169°C were observed in epoxy resin, which shifted to lower temperature side on increasing the frequency. Addition of 2.91 wt% graphite shifted the tan 𝛿 peaks towards higher temperature side by creating hindrances to the rotation of polymer dipoles. Addition of 2.91 wt% graphite leads to an increased relaxation time 𝜏 of dipoles in polysulphide epoxy from 1.44 × 10-5-3.92 × 10-5 (s) at 90°C by creating the hindrance to the rotation of dipoles.

• Synthesis, mechanical, thermal and chemical properties of polyurethanes based on cardanol

Cardanol, an excellent monomer for polymer production, has been isolated from CNSL and allowed to react with formaldehyde in a particular mole ratio in the presence of glutaric acid catalyst to give high-ortho novolac resin. Such characterized polyol has been condensed with diphenylmethane diisocyanate to produce rigid polyurethane. A commercially available polyol, polypropylene glycol-2000 (PPG-2000), has also been condensed with diphenylmethane diisocyanate and polyol to produce tough polyurethane. These polyurethanes were characterized with respect to their resistance to chemical reagents and mechanical properties such as tensile strength, percentage elongation, tear strength and hardness. Differential thermal analysis (DTA) and thermo-gravimetric analysis (TGA) were undertaken for thermal characterization.

• Terpolymerization of 2-ethoxy ethylmethacrylate, styrene and maleic anhydride: determination of the reactivity ratios

Terpolymerization of 2-ethoxyethyl methacrylate (2-EOEMA), styrene (St) and maleic anhydride (Ma) initiated by benzoyl peroxide was carried out in acetone as common solvent for three monomers. The structure and composition of terpolymer were determined by FTIR spectroscopy by recording analytical absorption bands for St (3002 cm-1), Ma (1781 cm-1) and 2-EOEMA (1261 cm-1) units, respectively. The reactivity ratios for the monomers were calculated according to the general copolymerization equations following the Finnemann–Ross and Kelen–Tudos models. The results show that terpolymerization were carried out through primary complex" mechanism at near-binary copolymerization of [St...Ma] complex with 2-EOEMA. Structure of the resulting terpolymer illustrated by 1H-NMR and differential scanning calorimeter showed reduction in 𝑇g value.

• Analysis of surface degradation of high density polyethylene (HDPE) insulation material due to tracking

In the present work, tracking phenomena has been studied with HDPE material under a.c. voltage, with ammonium chloride as the contaminant. It is noticed that the tracking time depends on the conductivity and flow rate of the contaminant. The diffusion coefficient of the material was obtained. The thermal and chemical stability of the material were identified by carrying out a methodical experimental study. The physico-chemical analyses viz. wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA), were carried out and it was concluded that the mechanism of tracking process is due to the surface degradation. The surface condition of the insulation structure was characterized for any surface discharges or tracking, using the leakage current measurement, utilizing the wavelet concepts.

• Electrical properties of ion irradiated polypropylene films

The effect of high-energy (50 MeV) Li3+ ion beam irradiation on polypropylene (PP) film has been studied in the fluence range 2.4 × 1012-1.5 × 1014 ions/cm2. The a.c. electrical properties of PP films were measured in the frequency range from 0.05–100 kHz, and at temperature range between 30 and 140°C. This study indicates two peaks at 60°C and 120°C with comparatively high magnitudes. There is an exponential increase in conductivity with log of frequency and the effect is significant at higher fluences. The loss factor (tan 𝛿) vs frequency plot suggests that PP film based capacitors may be useful below 10 kHz. The capacitance is constant over a wide temperature range up to 130°C. FTIR spectra of the PP films before and after irradiation indicate that intensity of C–H stretching vibration at 2900 cm-1 is modified. The presence of many new peaks with the increase of fluence suggests the formation of alkanes and alkynes which might be responsible for the observed changes in the dielectric and electrical properties of PP films.

• Investigation of Al–O–Al sites in an Na-aluminosilicate glass

This paper reports the presence of Al–O–Al linkages in an aluminosilicate glass where Si/Al = 1 by using 2D 17O triple quantum MAS NMR technique (3Q MASNMR). The experiments were performed at external magnetic fields of 8.4 and 14.4T. Despite 17OMAS NMR spectra of the sample in both fields do not give much information about the different kinds of linkages in the sample, 3Q MAS NMR spectrum shows clear evidence that there are some amounts of Al–O–Al linkages in the sample giving two completely resolved peaks. These two peaks were attributed to the Si–O–Al and Al–O–Al linkages on the basis of their chemical shifts and, quadrupolar coupling constants which are quite sensitive to the local structure.

• Structural, optical and non-linear investigation of Eu3+: Al(NO$_3)_3$–SiO2 sol–gel glass

Optical absorption and fluorescence spectra of Eu3+ ions in Al(NO$_3)_3$–SiO2 sol–gel glass have been investigated using the Judd–Ofelt theory. JO intensity parameters (𝛺𝜆) and subsequent radiative properties for ${}^{5}D_{0} \rightarrow {}^{7}F_{1,2,4,6}$ transitions are determined. The lifetime (𝜏r) of ${}^{5}D_{0}$ state is computed and along with JO parameters are compared with their corresponding values in other glasses prepared by conventional technique. A structural analysis, using IR and XRD spectra and non-linear parametrization of the silica gel glass is carried out. The study reveals the glass to be a very good third order non-linear amorphous optical material.

• Comparative investigation on the effect of alkaline earth oxides on the intensity of absorption bands due to Cu2+, Mn3+ and Cr3+ ions in ternary silicate glasses

Absorption characteristics of Cu2+, Mn3+ and Cr3+ ions in ternary silicate (20Na2O.10RO.70SiO2, where R=Ca, Sr, Ba) glasses were investigated. The intensities of absorption bands due to Cu2+ ion was found to increase with increasing ionic radii of the alkaline earth ions whereas it was found to decrease in case of Mn3+ and Cr3+ ions with increasing ionic radii of the alkaline earth ions. The results were discussed in the light of relation between linear extinction coefficients of these ions and coulombic force of alkaline earth ions. The change in intensities of Cu2+, Mn3+ and Cr3+ ion is attributed due to change in silicate glass compositions.

• Structural and electrical properties of amorphous carbon–sulfur composite films

In this paper, we discuss the synthesis of carbon–sulfur composite (𝑎-C:S) films by vapour phase pyrolysis of maleic anhydride and sulfur. Structural changes in the system are analysed by scanning electron microscopy and powder X-ray diffraction. Microhardness test depicts an increase in the value of hardness with an increase in sulfur concentration. Electrical conductivity of composite samples varies with sulfur concentration. Magnetoresistance (MR) measurements show a drastic increase in the value of MR for the samples prepared at &lt; 900°C. Thermal stability of these samples is analysed by thermogravimetric analysis, which depends on the host structure and the amount of intercalated species.

• Studies on tin oxide films prepared by electron beam evaporation and spray pyrolysis methods

Transparent conducting tin oxide thin films have been prepared by electron beam evaporation and spray pyrolysis methods. Structural, optical and electrical properties were studied under different preparation conditions like substrate temperature, solution flow rate and rate of deposition. Resistivity of undoped evaporated films varied from 2.65 × 10-2 𝛺-cm to 3.57 × 10-3 𝛺-cm in the temperature range 150–200°C. For undoped spray pyrolyzed films, the resistivity was observed to be in the range 1.2 × 10-1 to 1.69 × 10-2 𝛺-cm in the temperature range 250–370°C. Hall effect measurements indicated that the mobility as well as carrier concentration of evaporated films were greater than that of spray deposited films. The lowest resistivity for antimony doped tin oxide film was found to be 7.74 × 10-4 𝛺-cm, which was deposited at 350°C with 0.26 g of SbCl3 and 4 g of SnCl4 (SbCl3/SnCl4 = 0.065).

Evaporated films were found to be amorphous in the temperature range up to 200°C, whereas spray pyrolyzed films prepared at substrate temperature of 300–370°C were polycrystalline. The morphology of tin oxide films was studied using SEM.

• Designing of high-resolution photoresists: use of modern NMR techniques for evaluating lithographic performance

Applications of improved 1-D/ 2-D NMR spectroscopic techniques have been reviewed for quantitatively estimating the incorporation of different monomers and degree of linearity in resin microstructure. Comparison of the NMR data with those from lithography leads to a distinct correlation between resin microstructure and lithographic performance. A novel photoresist mechanism is proposed in a positive photoresist; also, using modern NMR techniques, the crosslinking mechanism in a negative photoresist has been studied.

• Effect of sodium dodecyl sulfate on flow and electrokinetic properties of Na-activated bentonite dispersions

The present study reports the effect of anionic surfactant sodium dodecyl sulfate (SDS, C12H25 OSO3Na) upon the electrokinetic (electrophoretic mobility, zeta potential) and rheological (viscosity, yield value) properties of the Ca-bentonitic clay found in Turkey and its Na-activated form. The SDS dispersant was added in different concentrations in the range of 1 × 10-5-5 × 10-2 mol/l. The results show that the viscosity and zeta potential values of bentonite dispersion are affected by the addition of anionic surfactant. The obtained data are analysed by considering the kind of exchangeable cations. Thixotropic property effect was observed in bentonite dispersions.

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• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019