• Issue front cover thumbnail

      Volume 24, Issue 6

      December 2001,   pages  563-689

    • Phase change induced by polypyrrole in iron-oxide polypyrrole nanocomposite

      Komilla Suri S Annapoorni R P Tandon

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      Nanocomposites of polypyrrole and iron oxide were prepared using simultaneous gelation and polymerization processes. Varied amounts of pyrrole monomer were added to a solution containing iron nitrate as precursor and 2-methoxy ethanol as solvent. The presence of oxide and polypyrrole was confirmed by using X-ray and FTIR techniques. Some of these nanocomposites exhibited magnetic behaviour. SEM studies of powders indicated presence of nanosized particles. Electrical conductivity studies of powders showed a slight variation in conductivity for lower concentration of pyrrole, with a sudden increase in conductivity at 15% of pyrrole concentration. A transition from a nonmagnetic to magnetic phase was also observed at the same concentration.

    • Studies on broad spectrum corrosion resistant oxide coatings

      Someswar Datta

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      The corrosion resistant oxide coatings, developed and applied by the conventional vitreous enamelling techniques, showed superior resistance to a range of mineral acids at various strengths and temperatures, alkaline solutions, boiling water and chrome plating solutions. These coatings possess considerable abrasion and impact resistance as well as high thermal shock resistance. The properties of the coating system have been studied in detail and found to be strongly dependent on composition and processing parameters. These coatings have been characterized by X-ray diffraction analysis and SEM studies. Some of the coating materials have been found to be biocompatible.

    • Metallo–organic compound-based plasma enhanced CVD of ZrO2 films for microelectronic applications

      S Chatterjee S K Samanta H D Banerjee C K Maiti

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      ZrO2 films on silicon wafer were deposited by microwave plasma enhanced chemical vapour deposition technique using zirconium tetratert butoxide (ZTB). The structure and composition of the deposited layers were studied by fourier transform infrared spectroscopy (FTIR). The deposition rates were also studied. MOS capacitors fabricated using deposited oxides were used to characterize the electrical properties of ZrO2 films. The films showed their suitability for microelectronic applications.

    • Preparation of Sm–Ru bimetallic alloy films on Ru(0001) surface by vapour-deposition and annealing

      G Ranga Rao H Nozoye

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      Sm–Ru intermetallic surface alloy films were prepared by vacuum deposition and annealing of rare earth Sm on single crystal Ru(0001) surface. The Ru 3𝑑 and Sm 3𝑑 core level spectra clearly show the formation of surface alloy layers. XPS measurements on surface alloy film revealed an induced peak in the Ru3𝑑 region at lower binding energy by 1 eV compared to the bulk Ru (elemental) suggesting an electronic effect of alloying and Sm–Ru bond formation. The Sm 3𝑑5/2 photoemission peak of Sm film consists of strong features characteristic of Sm(II) with electron configuration 4𝑓6 (5𝑑\ 6𝑠)2 and Sm(III) with electron configuration 4𝑓6 (5𝑑\ 6𝑠)3. It is observed that the Sm(II) feature decreases in intensity upon alloy formation with surface Ru atoms. Oxidation of these films with carbon monoxide indicates alloy breakdown due to the oxidation of Sm atoms selectively. Alloy oxidation also shows a clear shift of Sm 3𝑑5/2 feature.

    • Investigation of surface modifications in ethylene propylene diene monomer (EPDM) rubber due to tracking under a.c. and d.c. voltages

      R Sarathi Uma Maheswar Rao

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      In the present work, tracking phenomena has been studied with the ethylene propylene diene monomer (EPDM) material under the a.c. and d.c. voltages, with ammonium chloride/acid rain solution as the contaminant. It is noticed that the tracking time depends on the conductivity and flow rate of the contaminant. The physico-chemical analyses viz. wide angle X-ray diffraction (WAXD), thermo-gravimetric differential thermal analysis (TG-DTA) and the differential scanning calorimetry (DSC) studies, were carried out and it was concluded that the tracking process is a surface degradation process. The tracking time is different for a.c. and d.c. voltages.

    • Observation of curious spiral growth features in Tl doped Hg bearing high temperature superconducting tapes

      Anjana Asthana O N Srivastava

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      Synthesis of H𝑔(Tl)Ba2Ca2Cu3O8+𝛿 superconducting tapes have been accomplished by annealing the precursor tape, Ba2Ca2Cu3O𝑦 (fabricated by doctor blade tape casting technique) in an environment of H𝑔(Tl) vapour. Characterization of superconducting HTSC tape sample was carried out through XRD, TEM, SEM and R–T measurements. Surface morphological investigations of the as-synthesized H𝑔(Tl)Ba2Ca2Cu3O8+𝛿 HTSC tapes by scanning electron microscope have shown the occurrence of curious growth characteristics resembling spiral like features. These growth spirals encompass nearly the whole grain suggesting that spiral growth led to the formation of small crystal like grains of superconducting material H𝑔(Tl)Ba2Ca2Cu3O8+𝛿. The likely mechanism for the generation of these screw dislocations has been elucidated in terms of incoherent coalescence of growth fronts formed from H𝑔(Tl):1223 and H𝑔(Tl):1234 nuclei.

    • Preparation and characterization of Ag-added Bi1.84Pb0.4Sr2Ca2.2Cu3O10+𝑥 bulk tube conductors for cryogen free superconducting magnet

      S N Ekbote G K Padam M Sharma N K Arora B S Khurana R C Goel D K Suri N Mehra B K Das

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      Bulk tube conductors of Bi1.84Pb0.4Sr2Ca2.2Cu3O10+𝑥 with addition of silver varying from 0 to 25 wt% (not reported earlier) were systematically studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), electrical transport and a.c. susceptibility techniques. The tube conductors formed by cold isostatic pressing (CIP) of the powders obtained from spray drying method have been made successfully. It was found that Ag addition has not only affected the formation of the desired Bi-2223 phase and the microstructure of these large bulk tube samples thereby influencing on the critical current (𝐼c), it also reduces the contact resistance to minimize the cryogen losses. These variations have been found to be Ag content dependent. An optimized value of 10 wt% Ag has been found to produce the best quality tubes showing reproducible 𝐼c value > 120 Amp at 77 K which is in general a requirement to energies of the cryogen free conventional/HTSC superconducting magnets below 20 K.

    • A study of ultrasonic velocity and attenuation on polycrystalline Ni–Zn ferrites

      S R Murthy

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      Polycrystalline NiZn ferrites with different grain sizes (1.2 𝜇m to 10.2 𝜇m) were prepared by the usual ceramic method. The magnetic properties were measured at room temperature. The ultrasonic velocity and attenuation were measured on Ni–Zn ferrite by using the pulse transmission method at 1 MHz, in the temperature range 300–600 K. The velocity was found to be slightly sample dependent at room temperature and decreased with increasing temperature, except near the Curie temperature, 𝑇c, where a small anomaly was observed. The longitudinal attenuation (𝛼l) at room temperature was found to be more sample dependent. The temperature variation of ultrasonic longitudinal attenuation exhibited a broad maximum around 400 K and a sharp maximum just below Curie temperature (𝑇c). The above observations were carried out in the demagnetized state. The application of a 380 mT magnetic field allowed us to reach the saturated state of the sample at all the measuring temperatures. The anomaly observed in the thermal variation of velocities (longitudinal and transverse) and attenuation has been qualitatively explained with the help of the temperature variation of the magneto-crystalline anisotropy constant.

    • A new combustion route to 𝛾-Fe2O3 synthesis

      A Venkataraman Vijay A Hiremath S K Date S D Kulkarni

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      A new combustion route for the synthesis of 𝛾-Fe2O3 is reported by employing purified 𝛼-Fe2O3 as aprecursor in the present investigation. This synthesis which is similar to a self propagation combustion reaction, involves fewer steps, a shorter overall processing time, is a low energy reaction without the need of any explosives, and also the reaction is completed in a single step yielding magnetic iron oxide i.e. 𝛾-Fe2O3. The as synthesized 𝛾-Fe2O3 is characterized employing thermal, XRD, SEM, magnetic hysteresis, and density measurements. The effect of ball-milling on magnetic properties is also presented.

    • Tailoring magnetic and dielectric properties of rubber ferrite composites containing mixed ferrites

      M R Anantharaman K A Malini S Sindhu E M Mohammed S K Date S D Kulkarni P A Joy Philip Kurian

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      Rubber ferrite composites containing various mixed ferrites were prepared for different compositions and various loadings. The magnetic and dielectric properties of the fillers as well as the ferrite filled matrixes were evaluated separately. The results are correlated. Simple equations are proposed to predetermine the magnetic and dielectric properties. The validity of these equations is verified and they are found to be in good agreement. These equations are useful in tailoring the magnetic and dielectric properties of these composites with predetermined properties.

    • Analysis of stainless steel samples by energy dispersive X-ray fluorescence (EDXRF) spectrometry

      M K Tiwari A K Singh K J S Sawhney

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      A simple method for the analysis of stainless steel samples is presented which is based on radioisotope excited energy dispersive X-ray fluorescence (EDXRF) spectrometry and does not require any type-standards. Both absorption and enhancement effects have been taken into account in the fundamental parameter method for quantitative analysis and an iterative approach is followed for calculation of concentrations in steel samples. Non-linear least square fitting (NL-LSF) procedures have been used to determine accurately the fluorescent peak intensities. The method has been tested by analysing several CRM standard reference samples and 304 and 316 steel samples assuming as unknown. The EDXRF results have also been compared with the results of analysis of same samples by vacuum emission spark spectrometry (VES). Obtained values for concentration in steel samples match quite well with their certified values.

    • Fine structure at the diffusion welded interface of Fe3Al/Q235 dissimilar materials

      Wang Juan Li Yajiang Wu Huiqiang

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      The interface of Fe3Al/Q235 dissimilar materials joint, which was made by vacuum diffusion welding, combines excellently. There are Fe3Al, FeAl phases and 𝛼-Fe (Al) solid solution at the interface of Fe3Al/Q235. Aluminum content decreases from 28% to 1.5% and corresponding phase changes from Fe3Al with DO3 type body centred cubic (bcc) structure to 𝛼-Fe (Al) solid solution with B2 type bcc structure. All phases are present in sub-grain structure level and there is no obvious brittle phases or micro-defects such as pores and cracks at the interface of Fe3Al/Q235 diffusion joint.

    • Effect of zirconium addition on the recrystallization behaviour of a commercial Al–Cu–Mg alloy

      K T Kashyap

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      It is well known that the second phase particles have an effect on recrystallization and grain growth behaviour of an alloy. Particularly the bimodal distribution of second phase particles has an effect which is opposite in sense where coarse second phase particles (> 1 𝜇m) stimulate nucleation while fine particles exhibit Zener drag.

      In the literature, the effect of zirconium addition to aluminium alloys has been well documented in order to produce superplasticity by giving ultra fine grain size to the alloy. Addition of zirconium produces Al3Zr particles which pin the grain boundaries during recrystallization and grain growth.

      In the present work, zirconium was added to a commercial Al–Cu–Mg alloy and by heat treatment Al3Zr particles were precipitated and after forging, the grain size was an order of magnitude lower than the alloy without zirconium.

      Transmission electron microscopy was employed to characterize the second phase particles, i.e. Al3Zr particles and found to be rod shaped and identified to be cubic ordered 𝐿12 phase with a lattice parameter of 0.408 nm. Further, it was observed that fine (100 nm) Al3Zr particles promote only continuous recrystallization which is polygonization of subgrains and subgrain growth.

      It was found that the fine dispersion of Al3Zr particles inhibits both recrystallization and grain growth in the commercial Al–Cu–Mg alloy.

    • An X-ray diffraction study of defect parameters in a Ti-base alloy

      G Karmaker P Mukherjee A K Meikap S K Chattopadhyay S K Chatterjee

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      Detailed studies based on the well established method of Fourier line shape analysis have been made on the X-ray diffraction profile of hexagonal titanium alloy of nominal composition Ti–6.58% Al–3.16% Mo–1.81% Zr–0.08% Fe–0.012% N–0.0078% C. While deformation fault probability, 𝛼, has been found to be quite high compared to that of pure titanium, the deformation growth fault parameter, 𝛽, shows a negative value ruling out the presence of growth fault in this alloy in the deformed state.

    • Development of calcium phosphate based bioceramics

      Amit Sinha A Ingle K R Munim S N Vaidya B P Sharma A N Bhisey

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      Two bioceramics (Ca–P–O glass and A–W glass ceramic) were produced using conventional methods of ceramic technology. X-ray powder diffraction patterns were used for identifying the phases and 3-point bend test was carried out for the determination of fracture strength of the bioceramics. Biocompatibility of both ceramics was evaluated using animal model experiments. Histological studies showed that A–W glass ceramic implanted in the tibia of rat formed an intimate contact with newly grown bone and provided enough strength to the bone to bear the animal weight. Implants made of Ca–P–O glass was almost fully resorbed and was replaced by new bone. The implants made of both the bioceramics were biocompatible and did not exhibit any kind of adverse effect to the surrounding tissues.

    • Homogenization of zinc distribution in vertical Bridgman grown Cd0.96Zn0.04Te crystals

      J K Radhakrishnan B S Sunderseshu Meenakshi Srivastava G L Seth R Raman R C Narula R K Bagai

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      One of the most pressing issues in the growth of high quality single crystal Cd0.96Zn0.04Te material, is to achieve homogenization of the high axial variation of Zn concentration, caused by the larger than unity segregation coefficient of Zn in CdTe. This is achieved in our crystals

      1. by thermal annealing of the CdZnTe crystal, which redistributes the as grown Zn distribution by solid state diffusion of Zn (this solid state diffusion of Zn occurs at three stages

      2. during the growth when the solidified crystal is near to the melting point temperature,

      3. during the post growth annealing of the crystal at a high temperature and

      4. during the cooldown to room temperature) and

    • by the reduction of Zn segregation during the growth stage by enhanced convective mixing of the melt, through a proper choice of ampoule and furnace dimensions.

    • By adopting suitable growth parameters and sufficient post growth annealing it has been possible to grow Cd0.96Zn0.04Te crystals, which have nearly 75% of their fraction within 1% Zn concentration variation.

  • Surface studies on as-grown (111) faces of sodium bromate crystals

    K Kishan Rao V Surender

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    Single crystals of sodium bromate are grown at various supersaturations ranging from 3% to 8%. Surface studies have been carried out on as-grown and etched (111) faces of these crystals. Typical and systematically oriented growth hillocks are observed almost on all the faces. Further dislocation studies are made to understand the growth history of these crystals. These studies suggest that the crystals grow by 2D-growth mechanism. In addition to this, studies are also conducted on the formation of overgrowths and inclusions in these crystals.

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