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      Volume 27, Issue 6

      December 2004,   pages  483-578

    • Synthesis and infrared spectra of alkaline earth metal carbonates formed by the reaction of metal salts with urea at high temperature

      S M Teleb D El-Sayed Nassr E M Nour

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      The metal carbonate, MCO3 (M = Ca, Sr and Ba), was synthesized by a novel method of reacting aqueous solution of each of Ca2+, Sr2+ and Ba2+ salts with urea at high temperature, ∼ 80°C. The reaction products were characterized through elemental analysis and infrared spectra. The infrared spectra of the products are the same as those of the corresponding commercially obtained carbonates. A general reaction describing the formation of MCO3 is proposed.

    • Synthesis of nanocrystalline TiO2 by tartarate gel method

      S R Dhage S P Gaikwad V Ravi

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      A gel was formed when a mixture of TiOCl2 and tartaric acid was heated on a water bath. Ultrafine powders of TiO2 in the anatase phase were formed, when the gel was decomposed at 623 K and the mole ratio of tartaric acid to titanium was 2. The anatase phase was converted into rutile phase on annealing at higher temperatures, > 773 K. When initial ratio of titanium to tartaric acid was < 2, the decomposition of gel leads to the formation of mixed phases of rutile and anatase. However, pure rutile phase was not formed by the decomposition of gel for any ratio of tartaric acid and titanium. These powders were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and surface area measurements. The average particle size obtained for anatase phase was 3 nm whereas it was 30 nm for rutile phase. Raman scattering experiments were also performed to confirm both anatase and rutile phases.

    • Adsorption study of Pb2+ ions on nanosized SnO2, synthesized by self-propagating combustion reaction

      Arunkumar Lagashetty A Venkataraman

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      Novel combustion synthetic route for the synthesis of nanosized SnO2 is reported. X-ray, tap and powder densities of SnO2 are calculated. Adsorption of Pb2+ ions on combustion derived nanosized SnO2 is studied. The as synthesized SnO2 and lead ions adsorbed SnO2 are characterized by X-ray diffraction (XRD), scanning electron micrograph (SEM), and infrared spectroscopic (IR) techniques. The eluent is characterized by atomic absorption spectroscopy (AAS) and solution conductivity (SC) to know the reduction in the concentration and increase in conductance of lead solution after adsorption on the SnO2 surface. The potential use of solid adsorbents for the adsorption of heavy metal pollutants is envisaged in the present work.

    • Infrared reflection absorption study of water interaction with H-terminated Si(100) surfaces

      G Ranga Rao

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      Water adsorption on clean and hydrogenated Si(100) surfaces was studied under ultra high vacuum conditions using surface infrared spectroscopy. The study shows that H–Si–Si–OH and SiH2 species are formed on Si(100)–(2 × 1) and Si(100)–(2 × 1)–H surfaces, respectively. The reactivity behaviour of Si(100)–(3 × 1)–H and Si(100)–(1 × 1)–H is similar, both stabilizing oxygen inserted silicon dihydrides.

    • Silicon—a new substrate for GaN growth

      S Pal C Jacob

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      Generally, GaN-based devices are grown on silicon carbide or sapphire substrates. But these substrates are costly and insulating in nature and also are not available in large diameter. Silicon can meet the requirements for a low cost and conducting substrate and will enable integration of optoelectronic or high power electronic devices with Si based electronics. But the main problem that hinders the rapid development of GaN devices based on silicon is the thermal mismatch of GaN and Si, which generates cracks. In 1998, the first MBE grown GaN based LED on Si was made and now the quality of material grown on silicon is comparable to that on sapphire substrate. It is only a question of time before Si based GaN devices appear on the market. This article is a review of the latest developments in GaN based devices on silicon.

    • Temperature dependence of pulse-induced mechanoluminescence excitation in coloured alkali halide crystals

      Namita Rajput S Tiwari B P Chandra

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      In practice, the relative efficiencies of different crystals are often determined under identical conditions of temperature and excitation. If the temperature of a crystal is increased or decreased with respect to room temperature, luminescence efficiency may get increased or decreased according to the composition of the crystal. When coloured crystals of NaCl, NaBr, KCl and KBr are excited by pulse-induced excitation at different temperatures, the mechanoluminescence (ML) intensity increases with temperature. The ML intensity of first peak, 𝐼ml, second peak, 𝐼_m2 and the total ML intensity, 𝐼T, initially increase with temperature and then tend to attain an optimum value for a particular temperature of crystals. The ratio, 𝐼m2/𝐼ml, is found to increase with increasing temperature of the crystals. The expression derived on the basis of rate equations, are able to explain the temperature dependence of ML intensity on several parameters.

    • Estimation of embrittlement during aging of AISI 316 stainless steel TIG welds

      J Nayak K R Udupa K R Hebbar H V S Nayak

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      Weldments of AISI grade 316 stainless steel, having a ferrite content of 4–6% and a variety of nitrogen concentrations were prepared using a modified element implant technique. Charpy impact specimens prepared from these weldments were subjected to a variety of aging treatments. Impact toughness decreases with aging time at all aging temperatures. Nitrogen is found to be beneficial to toughness. An empirical relation connecting the aging temperature, aging time and nitrogen content with toughness has been developed which can be used to estimate the time for embrittlement.

    • Preparation and thermomechanical properties of stir cast Al–2Mg–11TiO2 (rutile) composite

      S K Chaudhury A K Singh C S S Sivaramakrishnan S C Panigrahi

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      Al–2Mg–11TiO2 composite was successfully prepared by the conventional vortex method. The macrostructural observation revealed columnar structure with rutile particles being distributed throughout the matrix in the form of agglomerates. Microstructural observation showed the presence of micro voids in the particle-enriched zone. Electrical resistivity measurement showed a phase transformation at 360°C, which was consistent during DSC studies due to the precipitation of TiAl3 phase. As-cast composite was both hot rolled and cold rolled successfully to 50 and 40% reduction, respectively. The mechanical properties of the thermomechanically-worked composite were studied. From fractographic analysis, it was clear that the crack had nucleated at the particle/matrix interface and propagated through the matrix by microvoid coalescence. Ultimate tensile strength of cold worked composite was found to be better than the hot worked material.

    • DSC and conductivity studies on PVA based proton conducting gel electrolytes

      S L Agrawal Arvind Awadhia

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      An attempt has been made in the present work to prepare polyvinyl alcohol (PVA) based proton conducting gel electrolytes in ammonium thiocyanate (NH4SCN) solution and characterize them. DSC studies affirm the formation of gels along with the presence of partial complexes. The cole–cole plots exhibit maximum ionic conductivity (2.58 × 10-3 S cm-1) for gel samples containing 6 wt% of PVA. The conductivity of gel electrolytes exhibit liquid like nature at low polymer concentrations while the behaviour is seen to be affected by the formation of PVA–NH4SCN complexes upon increase in polymer content beyond 5 wt%. Temperature dependence of ionic conductivity exhibits VTF behaviour.

    • Functionalized polymer networks: synthesis of microporous polymers by frontal polymerization

      N S Pujari A R Vishwakarma T S Pathak A M Kotha S Ponrathnam

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      A series of glycidyl methacrylate (GMA)–ethylene dimethacrylate (EGDM) copolymers of varying compositions were synthesized by free-radically triggered thermal frontal polymerization (FP) as well as by suspension polymerization (SP) using azobisisobutyronitrile [AIBN] as initiator. The two sets of copolymers were characterized by IR spectroscopy and mercury intrusion porosimetry, for determination of epoxy number and specific surface area. Frontal polymerization was more efficient, yielding greater conversions at much shorter reaction times. The self-propagating frontal polymerization also generates microporous material with narrow pore size distribution. It yields higher internal pore volume and surface area than suspension polymerization, surface morphologies are, however, inferior.

    • Role of tin as a reducing agent in iron containing heat absorbing soda–magnesia–lime–silica glass

      Aman S P Singh

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      The role of tin as a reducing agent in a 18Na2O.2MgO.8CaO.72SiO2 glass containing a definite amount of total, 𝛴 Fe = [Fe2+] + [Fe3+], was investigated with different concentrations of total tin, 𝛴 Sn = [Sn2+] + [Sn4+], by absorption spectra of iron ions in the optical range 300–1200 nm recorded on a JASCO-7800 spectrophotometer. The single broad absorption band for Fe2+ ion was marked at 1055 nm in the near infrared region and a narrow weak band for Fe3+ ion at its 𝜆max at around 380 nm was observed in the silicate glass. The proportion of ferrous iron was found to increase in the glass in the beginning with the addition of tin up to 0.788% 𝛴 Sn and then it approached a maxima with 1.182% 𝛴 Sn. Further addition of tin was found to be futile for the constant iron concentration of 0.875% for achieving higher [Fe2+]/[Fe3+] ratio for maximum heat absorption due to Fe2+ ion in the glass. The mechanism of the process was discussed on the basis of Sn2+/Sn4+ and Fe2+/Fe3+ mutual redox interaction in the molten glass at 1400°C. The suitable limit of tin was suggested to be 0.788 ≤ 𝑥 ≤ 1.182% by wt for 0.875% of total iron for getting maximum ferrous ion in the glass.

    • Crystallization kinetics of amorphous Te𝑥(Bi2Se3)1–𝑥 glasses

      Manish Saxena

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      The activation energy plays a dominant role in deciding the utility of the material for the specific purpose—here storage. The dependence of the peak temperature of crystallization (𝑇p) on the composition and heating rate (𝛽) has been studied here. From the heating rate dependence, 𝑇p, the activation energy for crystallization (𝐸c) has been evaluated. The activation energy, 𝐸c, calculated using three different approaches is found to decrease with the increase in Bi content. This analysis helps in finding the suitability of an alloy to be used in phase transition optical memories/switches. The results have been analysed using Kissinger’s equation for non-isothermal crystallization of materials.

    • Impedance analysis of Pb2Sb3LaTi5O18 ceramic

      C K Suman K Prasad R N P Choudhary

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      Polycrystalline sample of Pb2Sb3LaTi5O18, a member of tungsten–bronze (TB) family, was prepared using a high temperature solid-state reaction technique. XRD analysis indicated the formation of a singlephase orthorhombic structure. The dielectric studies revealed the diffuse phase transition and the transition temperature was found to be at 52°C. Impedance plots were used as tools to analyse the sample behaviour as a function of frequency. Cole–Cole plots showed Debye relaxation. The activation energy was estimated to be 0.634 eV from the temperature variation of d.c. conductivity. The nature of variation of d.c. conductivity with temperature suggested NTCR behaviour.

    • Zeolite from fly ash: synthesis and characterization

      Keka Ojha Narayan C Pradhan Amar Nath Samanta

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      Coal fly ash was used to synthesize X-type zeolite by alkali fusion followed by hydrothermal treatment. The synthesized zeolite was characterized using various techniques such as X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, BET method for surface area measurement etc. The synthesis conditions were optimized to obtain highly crystalline zeolite with maximum BET surface area. The maximum surface area of the product was found to be 383 m2/g with high purity. The crystallinity of the prepared zeolite was found to change with fusion temperature and a maximum value was obtained at 823 K. The cost of synthesized zeolite was estimated to be almost one-fifth of that of commercial 13X zeolite available in the market.

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