• Volume 25, Issue 2

April 2002,   pages  79-173

• Preparation of high purity tellurium by zone refining

This paper describes purification process of tellurium metal using zone refining technique under high purity hydrogen gas ambient in normal room environment. Process automation by newly designed stepper motor drive and allied process control instruments circumvent the complexity of electrical motors. It is observed that overall impurities have gone down substantially from 4N+ to 5N5 purity with reference to Fe, Mg, Al, Cr, Zn, Bi and Cu. Removal of selenium is effected by hydrogen, which also serves as carrier gas during zone refining. The selenium in tellurium matrix is found to be below detection limits. The zone temperature, zone length and tilt angle maintained in the experiment are adequate to go down to high purity levels.

• Photoelectronic properties of HgI2 crystals for nuclear radiation detection

Photoelectronic properties of red mercuric iodide single crystals, grown from its saturated solution in tetrahydrofuran, have been studied for the wavelength range 450-700 nm at temperatures 80, 110, 175, 235 and 300 K. Various aspects of the optical generation of charge carriers have been discussed. The computer simulation of the room temperature photoconductivity has generated the optimized values of the mobility-lifetime products (𝜇e𝜏e = 5.67 × 10-5 cm2/V, 𝜇h𝜏h = 0.18 × 10-5 cm2/V), and surface recombination velocities (𝑆e = 3.2 × 105 cm/s, 𝑆h = 4.5 × 105 cm/s) of the charge carriers in these crystals. The estimated values of the electron and hole drift lengths for typical electric fields suggest that, under the negative electrode illumination, THF 𝛼-HgI2 crystals have high potential as regards to their use as phptodetectors in most of the scintillation spectrometers.

• Superconducting YBa2Cu3O7–𝛿 thick film (𝑇c (0)$= 92 K) on a newly developed perovskite ceramic substrate A complex perovskite oxide, YbBa2NbO6, as a non-reacting substrate for YBa2Cu3O7–𝛿 superconducting film has been developed. The dielectric constant and loss factor values of the material are in the range suitable for its use as substrate for microwave application. A YBa2Cu3O7–𝛿 superconducting thick film dip coated on YbBa2NbO6 substrate gave a 𝑇c (0) of 92 K and current density of ∼ 1.3 × 104 A cm-2. • Non-destructive evaluation of defects in ferromagnetic plates using a sensitive magnetic sensor based on second harmonic response of superconducting Bi1.6Pb0.4Sr2Ca2Cu3O10+𝛿 pellet The characteristics of a magnetic sensor, based on the non-linear electromagnetic response of the weak links present in polycrystalline BPSCCO superconductor are reported. The second harmonic response of the sensor in an alternating magnetic field at 40 kHz and at 77 K being a strong linear function of low d.c. field is utilized for magnetic field sensing. The noise limited resolution of the sensor is found to be 3.16 × 10-9 T/√ Hz for 𝐻a.c. = 16 G and frequency 40 kHz. The magnetic sensor has been applied for non-destructive detection of various types of flaws in ferromagnetic plates and also for detection of small magnetic inclusions in a non-magnetic matrix. Our results suggest that the 2𝑓 response based BPSCCO superconductive magnetometer has potential for its appication in the area of non-destructive evaluation of defects in ferromagnetic materials. • Fretting fatigue in AISI 1015 steel A small osillatory movement between two contacting surfaces is termed as fretting and on many occasions it acts as the crack initiation site leading to catastrophic failure of the overall structure. The occurrence of fretting is observed in many engineering structures such as shaft flanges, gas turbines, steel ropes etc. An experimental facility, which can simulate the fretting fatigue in many engineering applications, is the primary requirement of the research program. A laboratory fretting fatigue test facility capable of varying many influencing parameters of fretting fatigue such as slip amplitutde, frequency, contact pressure, etc is designed and developed. Preliminary investigations on plain and fretting fatigue behaviour of AISI 1015 structural steel are reported in this paper. A strength reduction factor of about 1.30 was obtained due to fretting for the test material under the present experimental conditions. Influence of contact load on fretting was also studied. Increasing fretting contact load decreased the fatigue life in the range investigated. Failure analysis showed typical stage I oblique crack growth followed by stage II straight crack perpedicular to the fretting zone. • Rheological properties of boehmite sols during ageing at room temperature (30 ± 1°C) under closed condition Boehmite sols were obtained by peptizing boehmite precipitates with glacial acetic acid. The sols were aged at room temperature (30 ± 1°C) under closed condition. Rheological properties of the sols were studied at different ageing times. The sol characteristics were interpreted by measuring their viscosity, areas of hysteresis of the flow curves and yield stress (𝜏y). Viscosity and the area of hysteresis of the flow curves increased with increasing ageing time of the sols. A sharp change of yield stress was observed during the ageing period from 15 to 36 days. The change in viscous to elastic nature and the appearance of gel point of the sol was observed by studying their oscillatory flow behaviour, i.e. by measuring loss modulus (𝐺''), elastic modulus (𝐺'), and loss tangent (tan 𝛿) of the sols. Gel point of boehmite sol was found at 36 days of ageing under closed condition at room temperature (30 ± 1°C). • Sintering of nano crystalline 𝛼 silicon carbide doping with aluminium nitride Sinterable silicon carbide powders were prepared by attrition milling and chemical processing of an acheson type 𝛼-SiC. Pressureless sintering of these powders was achieved by addition of aluminium nitride together with carbon. Nearly 99% sintered density was obtained. The mechanism of sintering was studied by scanning electron microscopy and transmission electron microscopy. This study shows that the mechanism is a solid sintering process. • Evaluation of thermal shock resistance of cordierite honeycombs A comparative study on thermal shock resistance (TSR) of extruded cordierite honeycombs is presented. TSR is an important property that predicts the life of these products in thermal environments used for automobile pollution control as catalytic converter or as diesel particulate filter. TSR was experimentally studied by quenching (descending test) the heated samples to water or by heating (ascending test) with an oxyhydrogen flame along with crack detection by acoustic emission (AE) method. TSR was also calculated by using coefficient of themal expasion (CTE), modulus of elasticity (MOE) and modulus of rupture (MOR) of the honeycomb samples. Cordierite honeycombs of 200 and 400 cpsi were used for the above study. It was observed that the trends of TSR were same for both the experimental methods as well as by calculation. The ascending test method showed lower TSR values compared to water quench method due to early detection of cracks by AE. Finite element method (FEM) was also used to evaluate the thermal stress distribution in solid cordierite using thermal shock test data. It was observed that the maximum thermal stress calculated by FEM was lower than the strength of the material; therefore, the solid cordierite did not fail during such tests. • Synthesis, structure and characterization of ceramic Ca4Bi2Ti4Nb6O30 The polycrystalline samples of Ca4Bi2Ti4Nb6O30 (herein designated CBTN) were synthesized by the conventional ceramic method. Preliminary X-ray structural study of the compound showed the formation of a single phase solid solution having orthorhombic structure in the paraelectric phase. Measurements of the dielectric constant (𝜀') and dielectric loss (tan 𝛿) as a function of temperarure (-180-200°C) at 1 kHz and 10 kHz and also as a function of frequency (102 Hz to 104 Hz) at five different temperatures [-180°C, -40°C, -10°C, 26°C (room temperature) and 75°C] have shown a dielectric anomaly and a phase transition at -13 ± 1°C in CBTN. • Analysis of filler--fibre interaction in fly ash filled short fibre-epoxy composites using ultrasonic NDE Size and aspect ratio are believed to influence the rheology or the flow in the mixture and in turn the mechanical performance of the composites. Fillers and fibres when used in combination are expected to complement each other's performance resulting in better properties for the composite. They also reduce the extent of matrix polymer required in the system. Composites involving fillers and fibres individually and in combination are studied for the level defect population using NDE and the mechanical performance under compression correlated with such an analysis. It was found that inclusion filler-fibre combination besides yielding better physical properties like density also yielded improved mechanical properties like strength and modulus. These properties showed an improvement of about 30-40% as compared to the ones where a single reinforcement either ash or fibre was used. Further, they exhibited uniform distribution of defects whose population was least compared to the situation where only one component (either filler or fibre) as reinforcement was tried. • Bone growth response with porous hydroxyapatite granules in a critical sized lapine tibial-defect model This study evaluated the tissue reaction to porous hydroxyapatite (HA) granules in a critical sized tibial-defect of New Zealand white rabbits for a period of 2, 6, 12 and 24 weeks. Physicochemical characterizations of the granules were done using transmission electron microscopy, scanning electron microscopy, X-ray diffraction, and fourier transform infrared spectroscopy to analyse the microstrucutre, composition, phase purity crystallinity and functional groups of HA. Prior to in vivo testing, the HA granules had proved to be biocompatible and cytocompatible en route in vitro studies using L929 mouse fibroblast cells. In the histologic evaluation, as early as 2 weeks, bone ingrowth was observed in the pores and interstices of the granules forming a network of bony trabeculae and over 6, 12 and 24 weeks, it was seen that the granules assisted in bone formation. Fluorochrome multilabels of yellow, red and orange lines showed active sites of bone mineralization in progress in the pores and periphery of the granules. Good osteointegration of the granules with the host bone was observed. There was neither inflammation nor fibreous tissue interposition while resorption of the material was in effect a slow process, since the HA granules still persisted after 24 weeks. • Promoting effect of CeO2 on cyclohexanol conversion over CeO2-ZnO mixed oxide materials prepared by amorphous citrate process CeO2-ZnO materials were prepared by amorphous citrate process and characterized by TGA, XRD, UV-DRS and surface area measurements. TGA showed that the citrate precursors decompose in the range 350-550°C producing CeO2-containing catalytic materials. XRD and DRS results indicated the formation of well-dispersed interstitial Zn$_{x}$Ce$^{4+}_{1-2x}$Ce$^{3+}_{2x}\$O2 solid solution on ZnO matrix. Addition of CeO2 to ZnO produced high surface area mixed oxide materials in citrate method. Cyclohexanol conversion reaction was carried out on these catalytic materials to investigate the effect of rare earth oxide on the activity and selectivity. It was found that CeO2 promotes the activity of ZnO without affecting the selectivity to cyclohexanone significantly. The factors such as reaction temperature and WHSV have turned out to be important for cyclohexanol conversion over CeO2-containing ZnO catalyst materials.

• Carbonaceous alumina films deposited by MOCVD from aluminium acetylacetonate: a spectroscopic ellipsometry study

Spectroscopic ellipsometry was used to characterize carbonaceous, crystalline aluminium oxide films grown on Si(100) by low-pressure metal organic chemical vapour deposition, using aluminium acetylacetonate as the precursor. The presence of carbon in the films, attribured to the use of a metalorganic precursor for the deposition of films, was identified and analysed by secondary ion mass spectroscopy and X-ray photoelectron sectroscopy, for the elemental distribution and the chemical nature of the carbon in the films, respectively. Ellipsometry measurments over the photon energy range 1.5-5 eV were used to derive the pseudo-dielectric function of the aluminium oxide-containing films. Multi-layer modelling using linear regression techniques and the effective medium approximation were carried out to extract the structural details of the specimens. The excellent fit between the simulated and experimental optical data validates the empirical model for alumina-containing coatings grown by MOCVD.

• A study on the behaviour of M-type barium hexagonal ferrite based microwave absorbing paints

This paper deals with development of single- and double-layer microwave absorbing paints using Mn-substituted barium hexagonal ferrite. The comparative studies of both theoretical and experimental results at Ku band have been reported. It has been found that the single layer absorbing paint exhibits peak absorption of 12.3 dB at 17.4 GHz for a thickness of 1.12 mm. Double layer absorbing paint with each layer of different composition of ferrite gives a broad band characteristics, but at the cost of lowered absorption.

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• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019