• Volume 16, Issue 5

      October 1993,   pages  331-402

    • Surface alloying of pure iron by molybdenum and tin by a continuous wave CO2 laser

      I S Batra K Bhanumurthy S K Khera A K Sinha A R Biswas V I Titov M B Ignatiev A Uglov

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      It is now well established that considerable improvement in the mechanical/chemical properties of near surface regions of materials can be achieved by the process of laser surface alloying. The change in chemistry at the surface is attained through the process of melting and mixing of a predeposited coating and a thin layer of the substrate. Rapid solidification of this molten region at the surface then results in the development of very interesting microstructural features. In the present work, an attempt was made to surface alloy pure iron by molybdenum and/or tin by using a continuous wave CO2 laser. Morphology of the resulting microstructural features was examined by optical as well as scanning electron microscopy and the compositional details were determined using an electron probe microanalyser. Microhardness measurements were carried out as a function of depth from the laser-treated surface. This paper discusses the results of these investigations and delineates the roles of the various parameters on the chemistry and microstructure of the surface alloys formed as a result of laser treatment.

    • Deposition of polymer bilayer configuration by pulsed laser ablation and its use for study of polymer-polymer interface

      Sangeeta Kale J P Jog V M Nadkarni

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      Thin films of polyphenylene sulphide (PPS) and polyethylene (PE) polymers have been deposited in a bilayer configuration using pulsed excimer laser ablation. Such bilayer specimens have been annealed at different temperatures, up to a maximum of 120°C, and for different time intervals, up to a maximum of 110 min, to investigate the evolution of the interface. By employing the technique of spectroscopic ellipsometry, the nature and the degree of thermally induced polymeric transport across the interface are brought out.

    • Self-propagating high-temperature synthesis of titanium borides

      S K Roy A Biswas S Banerjee

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      The application of self-propagating high-temperature synthesis (SHS) to prepare a few borides of titanium was investigated. Using the plane wave propagation mode, the synthesis of titanium borides in the cold-pressed cylindrical specimens of the component powder mixtures was effected and was studied as a function of boron content in the initial mix and the specimen size. SHS reaction in compacts having diam. of 6 mm or less and high bulk density could not be initiated and/or sustained and was considered to be a result of rapid heat dissipation.

    • High temperature phase transition in KH2PO4 crystal

      Humayun Khan A H Khan

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      DTA, weight loss, infrared and dielectric measurements have been performed on KH2PO4 (KDP) single crystal as well as on different particle size specimens. DTA result reveals two endothermic peaks. The lower peak at 180°C is particle size dependent and vanishes in specimen of particle size ≤ 0·1 mm. Dielectric measurements also show similar behaviour. No significant weight loss of the crystal was noticed when kept at 180°C. We are inclined to believe that fragmentation of crystal is likely to be responsible for the transition rather than PO4-group rotation or decomposition of KDP.

    • Studies on impurity incorporation in cadmium oxalate crystals grown by gel method

      N Jagannatha P Mohan Rao

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      Aspects of gel growth of cadmium oxalate single crystals doped with monovalent (Li+, Na+, K+ and NH4+) and divalent (Ca2+, Co2+, Ni2+ and Zn2+) cation impurities are discussed. The growth experiments were carried out by single diffusion method. In this paper the effect of composition of the supernatant solution is considered. Rigorous characterization involves determination of composition of cations by employing atomic absorption spectrophotometer and of anions by titration method. The Pauling radius, hydration energy and distribution coefficient of the cations are tabulated and the results are described and discussed.

    • Thin conducting polypyrrole film on insulating surface and its applications

      S K Dhawan D C Trivedi

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      An electrically conductive plastic material was obtained by the polymerization of pyrrole on insulating polymeric materials and nylon cloth impregnated with the oxidant by vapour phase technique, resulting in a uniform, smooth and adherent coating of conducting polymer having a surface resistance ranging from 200 Ω/□ to 20 kΩ/□, which makes it suitable for applications as an antistatic material.

    • Effect of substitution at the barium site in YBa2Cu3O7-δ

      N S Raman B Viswanathan

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      The oxygen content in YBa2Cu3O7-δ has been varied by substitution at Ba site with Sr or K and its influence on the structural and superconducting properties has been studied. These properties are compared with that of unsubstituted YBa2Cu3O7-δ prepared by quenching. The increase inδ value of YBa2Cu3O7-δ decreases theTc drastically, whereas in YBa2-χKχCu3O7-δ system increase in theδ value (as high as 0·92) does not affect the superconducting transition temperature, which remains above 77 K. In the YBa2-χSrχCu3O7-δ system, as Sr content increases there is marginal decrease in the oxygen content as well as in the superconducting transition temperature.

    • Nonlinear electrical transport in K-TCNQ at low temperatures

      D P Goswami M L Kalra

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      A remarkable nonlinearity has been observed for electric transport in K-TCNQ (potassium tetracyanoquinodimethane) quasi-one-dimensional conductor. The negative differential resistance region appears afterVm (turn over voltage), beyond which voltage goes down with increase of current. A possible mechanism is discussed in terms of dynamics of charged solitons and domain walls in one-dimensional molecular stacks of these types of crystals.

    • Microhardness studies on some alum crystals

      G Sangaiah K Kishan Rao

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      Microhardness studies were carried out using four alums. The hardness of these crystals was found to be more than alkali halides but was comparable with alkaline earth nitrates. The load variation of hardness has been discussed. Hardness results on these alums have been analysed taking into account the structure. It was observed that hardness varied witha−4, wherea is the lattice constant. Preliminary results on dislocation etching are reported.

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