pp 1-3 February 2007 Single Crystals
Thermoluminescence (TL) characteristics of NaYF4 crystals doped with Sm3+ have been studied after 𝛾-ray irradiation. Dependence of luminescence efficiency on Sm3+ concentration and radiation dose has been measured and possible applications of NaYF4 : Sm3+ as a novel phosphor for TL dosimetry have been investigated. The efficiency of 0.3 mole% Sm3+ doped NaYF4 crystal has been found to be maximum and comparable with commercial thermoluminescence dosimetric (TLD) materials.
pp 5-7 February 2007 Thin Films
In this paper, we present preparation and characterization of Al–Sb bilayer thin films. Thin films of thicknesses, 3000/1000 Å and 3000/1500 Å, were obtained by the thermal evaporation (resistive heating) method. Vacuum annealing and rapid thermal annealing methods were used to mix bilayer thin film structure. Results obtained from optical band gap data and Rutherford back scattering spectrometry showed mixing of Al–Sb bilayer system.
pp 9-17 February 2007 Thin Films
Barium strontium titanate ((Ba0.87Sr0.13)TiO3–BST) ceramic powder was prepared by mechanochemical process. The thick films of different thicknesses of BST were prepared by screen-printing technique and gas-sensing performance of these films was tested for various gases. The films showed highest response and selectivity to ammonia gas. The effect of film thickness on gas response was also studied. As prepared BST thick films were surface modified by dipping them into an aqueous solution of titanium chloride (TiCl3) for different intervals of time. Surface modification shifted response to H2S gas suppressing the responses to ammonia and other gases. The surface modification, using dipping process, altered the adsorbate–adsorbent interactions, which gave the unusual sensitivity and selectivity effect. Sensitivity, selectivity, thermal stability, response and recovery time of the sensor were measured and presented.
pp 19-21 February 2007 Nanomaterials
We report here for the first time a novel method of preparing nano-crystalline metatitanate, MgTiO3 geikielite, with crystalline size varying from 20–40 nm. The preparation has been carried out by coprecipitation method involving titanium hydroxide and magnesium nitrate solution. The samples were characterized by using transmission electron microscopic, powder XRD and FT–IR spectroscopic studies. The sample annealed at 900 K for 2 h show ten X-ray diffraction peaks corresponding to the pure geikielite phase. FT–IR spectra of the nano-crystalline geikielite exhibit strong broad vibrational bands near 1000, 650 and 470 cm-1 arising from normal vibrations of the TiO3 group.
pp 23-29 February 2007 Nanomaterials
Pyrolysis of ruthenocene carried out in an atmosphere of argon or hydrogen is found to give rise to spherical nanoparticles of carbon with diameters in the 10–200 nm range. Pyrolysis of ruthenocene as well as mixtures of ruthenocene and ethylene in hydrogen gives rise to spherical nanoparticles, which contain a high proportion of 𝑠𝑝3 carbon. Under certain conditions, pyrolysis of ruthenocene gives rise to graphite coated ruthenium nanoparticles as well as worm-like carbon structures. Pyrolysis of mixtures of ruthenocene and ferrocene gives rise to nanoparticles or nanorods of FeRu alloys, the composition depending upon the composition of the original mixture. Nanorods of the Ru and FeRu alloys encapsulated in the carbon nanotubes are also formed in the pyrolysis reaction.
pp 31-35 February 2007 Nanomaterials
Hybrid materials, which consist of organic–inorganic materials, are of profound interest owing to their unexpected synergistically derived properties. These hybrid materials replaced the pristine polymers due to their higher strength and stiffness in the recent years. In the present work, studies concerning the preparation of poly (methyl methacrylate) (PMMA), PMMA/SiO2, and PMMA/TiO2 nanocomposites are reported. These nanocomposite polymers were synthesized by means of free radical polymerization of methyl methacrylate using benzoyl peroxide as an initiator in a water medium. Further `sol–gel’ transformation based hydrolysis and condensation of Ti and Si alkoxides were used to prepare the inorganic phase during the polymerization process of MMA.
pp 37-41 February 2007 Catalysis
The photocatalytic degradation of indigo carmine dye was studied using hydrothermally prepared TiO2 impregnated activated carbon (TiO2 : AC). A comparison between the degradation of the indigo carmine dye using commercial TiO2 and TiO2 : AC revealed the efficiency of the title compound. The degradation reaction was optimized with respect to the dye concentration and catalyst amount. The reduction in the chemical oxygen demand (COD) revealed the mineralization of dye along with colour removal. The active compound like TiO2 was impregnated onto the activated carbon surface under mild hydrothermal conditions (< 250°C, P ∼ 40 bars). The impregnated activated carbon samples were characterized using powder X-ray diffraction (XRD) and scanning electron microscope (SEM).
pp 43-49 February 2007 Catalysis
Zirconium(IV) tungstoiodophosphate has been synthesized under a variety of conditions. The most chemically and thermally stable sample is prepared by adding a mixture of aqueous solutions of 0.5 mol L-1 sodium tungstate, potassium iodate and 1 mol L-1 orthophosphoric acid to aqueous solution of 0.1 mol L-1 zirconium(IV) oxychloride. Its ion exchange capacity for Na+ and K+ was found to be 2.20 and 2.35 meq g-1 dry exchanger, respectively. The material has been characterized on the basis of chemical composition, pH titration, Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis. The effect on the exchange capacity of drying the exchanger at different temperatures has been studied. The analytical importance of the material has been established by quantitative separation of Pb2+ from other metal ions.
pp 51-56 February 2007 Polymers
The electrical conductivity of polyaniline doped polyvinylchloride (PVC) and poly(methyl methacrylate) (PMMA) thin films has been measured by studying the 𝐼–𝑉 characteristics at various temperatures in the range 323–363 K. The results are presented in the form of 𝐼–𝑉 characteristics and analysis has been made by interpretation of Poole–Frenkel, Fowler–Nordheim, Schottky ln(𝐽) vs 𝑇 plots, Richardson and Arrhenius plots. The analysis of these results suggests that Schottky and Richardson mechanisms are primarily responsible for the observed conduction.
pp 57-63 February 2007 Electrochemistry
Electro-polymerization of orthonitroaniline was carried out on graphite electrode in hydrochloric acid medium. Zinc–nickel alloy deposition was carried out in the presence of polynitroaniline in acid sulphate bath. The bath constituent and bath variables were optimized through Hull cell experiments. The current efficiency and throwing power were measured. High shift of potential towards more cathodic direction was observed in presence of addition agent. Corrosion resistance test revealed good protection of base metal by zinc–nickel coating obtained from the developed electrolyte. SEM photomicrograph shows fine-grained deposit in the presence of addition agent. The consumption of brightener in the lab-scale was 0.01 gL-1 for 1000 amp-h.
pp 65-68 February 2007 Glasses
The high field electrical switching behaviour of lithium–phospho–vanadate glasses has been studied by determining the current–voltage characteristics. The investigated glasses exhibit temperature, thickness and composition dependent trends. At low current, the 𝐼–𝑉 characteristics obey Ohm’s law followed by a negative resistance region where the bulk behaviour dominates and at higher values of current the sample goes to a low resistance state. The studied glasses exhibit memory type switching. It is suggested that electrical switching is due to the formation of conducting channels that are due to electronic origin while thermal effects dominate once the channels are formed resulting in crystallization.
pp 69-71 February 2007 Steel
Plastic flow behaviour of low carbon steel has been studied at room temperature during tensile deformation by varying the initial strain rate of 3.3 × 10-4 s-1 to a final strain rate ranging from 1.33 × 10-3 s-1 to 2 × 10-3 s-1 at a fixed engineering strain of 12%. Haasen plot revealed that the mobile dislocation density remained almost invariant at the juncture where there was a sudden increase in stress with a change in strain rate and the plastic flow was solely dependent on the velocity of mobile dislocations. In that critical regime, the variation of stress with time was fitted with a Boltzmann type Sigmoid function. The increase in stress was found to increase with final strain rate and the time elapsed in attaining these stress values showed a decreasing trend. Both of these parameters saturated asymptotically at a higher final strain rate.
Volume 42 | Issue 5