• Volume 7, Issue 1

      March 1985,   pages  1-81

    • Foreword

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    • Diffusion in metallic glasses

      D Akhtar B Cantor RW Cahn

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      Rutherfordα-particles backscattering technique was employed for measurements of diffusion rates in metallic glasses. Effects of relaxation, crystallization and plastic deformation on diffusion rates were also investigated.

      It has been observed that the diffusion rates of a metallic solute are of the same orders of magnitude in both metal-metal and metal-metalloid glasses. A higher diffusivity is likely if there is a large difference between melting points of the solute and matrix. Relaxation has no effect on diffusion, however, diffusivity increases on crystallization. An increase in diffusivity is also observed on plastic deformation of metallic glass.

    • Self diffusion studies on cobalt thin films

      J J B Prasad K V Reddy

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      The study of lateral diffusion in thin metallic films is important from the application point of view, especially in electromigration reliability studies. Lateral self diffusion in cobalt thin films is studied using a non-destructive tracer scanning method. Neutron irradiation is employed to make a well-defined radioactive (60Co) region in the middle of a continuous cobalt thin film stripe of width 3 mm. The experimental data are fitted to the appropriate solution of the diffusion equations by means of a non-linear least square fitting procedure using a computer. The diffusion experiments are conducted in the temperature range 300–600°C in argon atmosphere. This thin film data are compared with the diffusion data available on bulk cobalt. The activation energy for surface diffusion obtained (0·14 eV) is very much smaller than the reported activation energy for grain boundary diffusion in cobalt.

    • X-ray diffraction study of cation interdiffusion in mixed UO2-PuO2 compacts

      Ravi Verma P R Roy

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      Cation interdiffusion kinetics in mixed oxide (UO2 + PuO2) compacts is studied using x-ray powder diffraction technique. A profile deconvolution method based on Fourier analysis is developed and used to characterise the degree of homogenisation in the sintered compacts. A concentric core-shell diffusion model in which UO2 constitutes a solute core enveloped by PuO2, acting as solvent, is adopted. The radial diffusion equation is solved for appropriate boundary conditions to yield a relationship between the annealing time and the degree of homogenisation. This relationship is used to estimate the interdiffusion coefficients at various temperatures.

    • A computer simulation of LiKSO4

      S L Chaplot K R Rao

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      Molecular-dynamics computer-simulation of an ionic molecular solid LiKSO4 has been carried out at 300 and 1000 K using the atom-atom potentials obtained from lattice dynamical studies. We observe hopping of lithium ions to interstitial positions which is related to reorientations of sulphate tetrahedra.

    • Simulation of polymer systems

      S L Narasimhan P S Goyal B A Dasannacharya

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      The present paper describes an algorithm which can generate, even on a small computer, arbitrarily long polymer chains, making sure that the configurations generated do not suffer from boundary effects. This has been achieved by employing the concept of a window, which is an analogue of virtual memory scheme. The algorithm has been tested for the case of dilute polymer solution.

    • Calculation of solute-vacancy binding energy in dilute fcc and bcc alloys by diffusion

      D D Pruthi

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      Due to excess charge of the solute with respect to solvent, the free energy of vacancy formation and migration in the neighbourhood of the solute will change. This results in a change in the solvent diffusivity. A relation for the solute vacancy binding energy for fcc and bcc lattices using enhancement factor has been derived considering the solute vacancy interactions to be limited to first neighbour and neglecting the changes in the solvent correlation factor.

    • Preparation and characterisation of Cd3P2, a II–V group compound semiconductor

      D R Rao V Bagulasankrithyan R A Tewari

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      Cadmium phosphide (α-Cd3P2) a II3–V2 compound semiconductor has been prepared by C/H2 reduction of cadmium phosphate. The reduction process is conducted at 550°C allowing the reaction to continue for 4 to 5 hr. The material always gets deposited on the walls of the quartz tube at different zones, which after analysis is found to contain, depending upon the location of the zone, Cd3P2, CdP2 and other cadmium rich phosphides. The resistivity of the pressed samples are of the order of 3 × 10−4Θ-cm. Optical absorption spectra of thin films, obtained by thermal evaporation on glass substrates, have exhibited broad bands around 620 nm.

    • Characterization of deep levels in semi-insulating gallium arsenide

      Y N Mohapatra N Balasubramanyam Vikram Kumar

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      Two traps with activation energies ofEc – 0·47 eV andEv + 0·79 eV have been detected in semi-insulating GaAs:Cr through optical transient current spectroscopy (otcs) in the temperature range 300–450 K. The latter trap gives rise to rising current transients which result in a negative peak in theotcs spectrum. The theoretical expressions for current transients have been derived.

    • Electrical, electromechanical and thermal properties of thin tellurium films

      S Sampath Kolluri V Ramanaiah

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      Thin films of tellurium of wide range of thicknesses have been deposited by vacuum evaporation and their electrical properties such as electrical resistivity and temperature coefficient of resistance have been measured. The suitability of these films for possible use as strain gauges has been studied and their strain resistivity behaviour is presented. The thermal conductivity of these films have been determined and these results are presented alongwith. An interesting phenomenon has been noticed. In all these effects an extraordinary behaviour is observed at a specific thickness. This smears out with an increase in the thickness of the film. These effects are explained in terms of size effects in thin films.

    • Radiation-induced modification of polyurethane with hydroxyethyl methacrylate: blood compatibility

      Chandra P Sharma

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      An attempt is made to develop the hydrophilic grafting of polyether urethane urea with hydroxyethyl methacrylate (hema) using60Coγ-irradiation for achieving optimum hydrophilic/hydrophobic property needed towards blood compatibility. Contact angle method and platelet adhesion from calf’s blood are used to determine the suitability of these modified surfaces.

    • Fig tree sap: antithrombogenicity on nylon surfaces

      Chandra P Sharma M K Sheela Vikram Chandrasekhar

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      An effort is made to study the anti-thrombogenic property of the latex of fig tree by immobilizing its components on nylon surface. It is also evaluated, how such surfaces may effect the blood compatibility by investigating variations in surface energy parameters, plasma recalcification time and platelet adhesion using calf’s blood.

    • Trypsinated (immobilized) nylon surfaces: antithrombogenicity

      Chandra P Sharma Geetha Kurian M K Sheela

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      An attempt is made to immobilize low molecular weight trypsin on nylon surface and to evaluate how such surfaces affect blood compatibility by investigating variations in surface energy parameters, plasma recalcification time and platelet adhesion using calf’s blood.

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