• N Venkatramani

      Articles written in Bulletin of Materials Science

    • Investigation of high temperature superconductivity through microwave absorption method

      C M Srivastava N Venkatramani A Datta N S H Rao

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      The field dependence and near zero magnetic field microwave absorption as a function of rf power in YBa2Cu3O7−δ and Bi-Ca-Sr-Cu-O has been studied using a varian ESR spectrometer. A model of microwave absorption built on diamagnetic tensor susceptibility has been proposed which explains the observed results satisfactorily.

    • Propagation of a.c. magnetic field through high-Tc coatings

      J Karthikeyan A S Paithankar P Chaddah N Venkatramani K P Sreekumar V K Rohatgi

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      Studies on the propagation of AC magnetic field through plasma-sprayed superconducting Y1Ba2Cu3O7−x coatings show that complete shielding is achieved up to a certain critical magnetic field strengthH0. Increase in the thickness orJc of the specimen increases theH0 value. Flux-trapping occurs in the specimen at high frequencies and the frequency at which it occurs increases with increase in specimenJc.

    • Thermal plasmas in material processing

      N Venkatramani

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      Thermal plasmas are partially ionized gases at atmospheric pressures, characterized by temperatures in the range of 2000–20,000 K and charged particle number densities in the range of 1019–1021 per m3. Thermal plasmas are produced by plasma torches as a highly constricted jet. The high temperatures, enthalpies and heat fluxes in the plasma jet make it amenable to many chemical and metallurgical processes of industrial importance. The processing environment can be inert as in the case of argon or nitrogen plasmas or can be made reactive by introducing suitable gases. Reactive thermal plasma processing is a novel technique, wherein the plasma enters the reaction scheme, with ions and excited species opening up new channels. This technique is versatile in producing a wide variety of materials like oxides, carbides, borides, aluminides and coatings of diamond, superconductors and bioceramics. In this paper, the basic design of the plasma devices and some of the significant materials-related activities carried out recently at BARC are reported.

    • Particle morphology and size distribution of plasma processed aluminium powder

      P V Ananthapadmanabhan K P Sreekumar N Venkatramani R Kameswaran C C Dias S C Mishra

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      Commercially available aluminium powder has been processed in a thermal plasma jet. The processed powder has been characterized by scanning electron microscopy (SEM) for particle size and morphology. Particle size distribution has been determined by laser scattering technique. Results show that, in contrast to the irregular shapes of the particles of the raw material, majority of the processed powder particles bear spherical or near-spherical morphology. The spherical morphology without sharp edges and corners and particle size distribution in a narrow range ensures free flow of the powder through the powder feed lines, and better spray efficiency, making it ideal for thermal spray applications.

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