• Volume 8, Issue 1

      February 1986,   pages  1-89

    • Kinetics of electrophoretic deposition ofβ-alumina

      DU Krishna Rao AB Malage D Baral EC Subbarao

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      The equations describing electrophoretic deposition, proposed by Hamakar Avgustinik and coworkers, have been verified in the case ofβ-alumina suspended in isoamyl alcohol. The variation of electrophoretic yield with (i) concentration of suspension, (ii) extent of grinding the suspension, (iii) temperature of the suspension, and (iv) electrode separation was studied. The effect of addition of glycol monethyl ether was also investigated. The effect of various parameters on the electrical conductivity of the suspension, which in turn influences the yield, was noted.

    • Microstructural and dielectric behaviour of glass ceramics in the system PbO-BaO-TiO2-B2O3-SiO2

      OM Parkash Devendra Kumar R Rajgopalan

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      Glasses in the system PbO-BaO-TiO2-B2O3-SiO2 with and without P2O5 as nucleant have been prepared. The glass samples were ceramized based ondta studies. The ferroelectric phase crystallizing out has been found to be BaTiO3 fromxrd. The optical and scanning electron micrographs show the presence of BaTiO3 as major phase. In these glass ceramic samples, dielectric constant and dissipation factor are approximately constant with temperature and frequency upto the glass transition temperatureTg and thereafter increase sharply with temperature and finally level off. The addition of P2O5 as nucleant and molar ratio of (PbO + BaO) to TiO2 has marked influence on the dielectric behaviour and composition of ferroelectric phase crystallizing out.

    • Dielectric properties of the system Pb2 −xNdxLi0·5Nb1·5 O6+δ

      S G Phadnis M Subramanian R Rajan

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      The dielectric properties of the ceramic defect pyrochlore-structured system Pb2−xNdxLi0·5Nb1·5 O6+δ has been studied as a function of concentrationx, frequency and temperature. The results have been analyzed for relaxation process and conduction mechanism.

    • Surface morphology and properties of GaAs epilayers controlled by temperature difference method of liquid phase epitaxy

      Y K Su C C Wei S C Lu C C Chang

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      Epilayers of gallium arsenide were grown by using the steady-state temperature difference method of liquid phase epitaxy. The surface of grown layers was smooth and shiny. Carrier concentrations of films varying from 1016 to 1017 cm−3 could be obtained with good reproducibility. The surface morphology growth rate, carrier concentration and Hall mobility of the epilayers were studied. Several distinct types of surface features were also investigated and explained. A segregation coefficient for the net carrier concentration versus tin concentration in the growth melt was calculated as 1·84 × 10−4 at 700°C for (100) GaAs substrate. Thickness control for epilayers down to submicron can be obtained reproducibly.

    • Magnetic and mössbauer studies on ductile Fe-Cr-Co permanent magnet alloys

      V Chandrasekaran Ch Sreerama Murthy P Subrahmaniam G Venkateswarlu

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      Iron-chromium-cobalt alloys possess attractive magnetic properties combined with good formability and hence are identified as technologically important magnetic materials. Alloys with compositions Fe-28·9 Cr-15·6 Co and Fe-28·4 Cr-20·1Co (weight percent) have been studied. Heat-treatment parameters during thermomagnetic treatment viz temperature, time and external magnetic field were optimized with reference to magnetic properties. The fully treated anisotropic alloys develop remanence=11·5–12·0 kilo Gauss, coercivity=600–650 Oersted and energy product=4–4·5 million Gauss Oersted. Electron microscopic and Mössbauer spectroscopic techniques were used to identify the original and transformed phases. During the various stages of the development of the alloy, the changes in mechanical hardness were correlated with magnetic hardness.

    • Tunnelling of electrons from deep traps of MgO

      M N Bapat S Sivaraman

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      A new result on electron tunnelling from the deep traps of MgO, reported recently is discussed. The electrons from the 540 K trapping group are released spontaneously at 480 K. The proposed mechanism for electron tunnelling is discussed in the light of existing theories. The location of the peak in the isothermal decay is found to depend on (i) the extent of population of the source trap group; (ii) the availability of shallow trapping levels to the rushing electrons and (iii) the nature of traps.

      The glow curve experiment indicates that the isothermal decay after saturation excitation causes reduction in the thermoluminescence intensity of the 540 K peak.

    • Thermal expansion studies on As-Sb-Se glasses

      A Giridhar Sudha Mahadevan A K Singh

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      The results of measurement of thermal expansion coefficient from 50°C to the softening temperature on eight glass compositions of the As-Sb-Se system are presented. Measurements have been made on (As, Sb)40Se60 and AsxSb15Se85−x glasses at heating rates of 1°C/min and 5°C/min. The composition and temperature dependence of the thermal expansion coefficient is discussed in the light of results of other chalcogenide glasses.

    • X-ray line profile analysis of silver base Ag-Cd-In alloys

      S Venkat Reddy S V Suryanarayana

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      X-ray diffraction line profiles of five silver base ternary alloys in α-phase with varying atomic percentages of cadmium and indium were recorded in both cold-worked and annealed states of the samples. Detailed studies on the profiles involving peak shift, peak asymmetry and Fourier analysis of line shapes have been carried out to evaluate microstructural parameters such as deformation fault probabilities,rms strains and dislocation densities. It was found that the addition of indium has a marked effect in producing deformation fault probabilities in comparison to that of adding cadmium in ternary silver base alloys. Compound fault probability was found to be maximum for the alloy Ag-10Cd-15In.

    • Phase relations and activities in the Co-Ni-O system at 1373 K

      K T Jacob S Srikanth G N K Iyengar

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      The tie-lines delineating equilibria between CoO-NiO and Co-Ni solid solutions in the ternary Co-Ni-O system at 1373 K have been determined by electron microprobe andedax point count analysis of the oxide phase equilibrated with the alloy. The oxygen potentials corresponding to the tie-line compositions have been measured using a solid oxide galvanic cell with calcia-stabilized zirconia electrolyte and Ni + NiO reference electrode. Activities in the metallic and oxide solid solution have been derived using a new Gibbs-Duhem integration technique. Both phases exhibit small positive deviations from ideality; the values ofGE/X1X2 are 2640 J mol−1 for the metallic phase and 2870 J mol−1 for the oxide solid solution.

    • Effect of texture and grain size on the mechanical properties of warm-worked cadmium, zinc and zinc-0·35% aluminium alloy

      K Ratnaji Rao S Ranganathan D H Sastry

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      Changes in the grain size and crystallographic texture during warm working and their influence on the room temperature mechanical properties are investigated on Cd, Zn and a Zn-Al alloy. The yield strength increase in the early stages of working in extruded cadmium is accounted for based on the development of a basal texture while in rolled zinc and zinc alloy, the properties are affected more by the grain size. Cadmium exhibits ductile fracture at all extrusion ratios whereas the fracture mode in zinc and the alloy changes from cleavage at small rolling strains to ductile at higher deformation strains.

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