• Volume 14, Issue 1

      February 1991,   pages  1-91

    • Announcements

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    • Effect of indium concentration on the internal oxidation of a silver-tin alloy

      A Verma T R Anantharaman

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      The investigation reported here was undertaken to study the beneficial influence of indium on the internal oxidation behaviour of silver-tin alloys in the context of electrical contact material development. Five compositions of varying indium content, namely Ag-6Sn-xIn (x = 2·0, 2·5, 3·0, 3·5, 4·0 wt%) were prepared and internally oxidized at different temperatures and oxygen pressure. The kinetics of internal oxidation was studied and an attempt made to correlate the same with microstructure.

    • Ordered structures in ternary hcp alloys

      Ashok Kumar Singh Shrikant Lele

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      A study of ordered structures in ternary hcp alloys has been undertaken. For this, the hcp structure has been divided into several sublattices and used to generate ordered structures with three types of atoms. Nine ground-state ordered structures have been identified on the basis of maximum or minimum number ofAB, BC andCA bonds. Complete crystallographic details about these structures have been worked out. In an alternate approach, ordered ternary structures were obtained by populating 8 types of sublattices (which generate Ti3Al structure) with three types of atoms. Thus, fortyeight ordered structures were found. For each structure, complete structural details have also been worked out, some of which are reported. Configurational energy of each structure has been calculated using pairwise interactions up to third neighbour distances. To gain insight regarding low-energy structures, some assumptions were utilized to reduce the number of independent parameters in the energy expressions and their consequences explored. Two types of degenerate situations have been observed. One type of degeneracy occurs for ideal hcp alloys where only first neighbour interactions are considered. Another degenerate situation occurs for non-ideal hcp alloys where interactions are considered up to third neighbour distances.

    • Thermomechanical ageing (TMA) of 2014 aluminium alloy for aerospace applications

      S Singh D B Goel

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      Various thermomechanical ageing (TMA) treatments for 2014 Al-alloy have been developed which include partial peak ageing, warm rolling and further ageing to peak hardness at 160°C. Electron microscopic studies reveal that the TMA treatments affect substantially the ageing characteristics. The TMA-Ib treatment yields finestϑ′ needles having longitudinal dimensions of ∼400 Å. TMA treatment leads to precipitate-dislocation network of different magnitudes. Among the TMA treatments, the TMA IIb treatment results in thickest precipitate-dislocation tangles. In addition toϑ′, two types of dispersoids Al4CuMg5Si4 and Al12 (Fe, Mn)3Si have been observed. The density or concentration of these dispersoids is drastically reduced due to TMA treatments. Thus an optimum TMA treatment i.e. TMA-IIb has been developed which results in a significant improvement in the mechanical properties of 2014 Al-alloy.

    • Photoabsorption and energy band gap of amorphous Se alloy films

      S C K Misra T P Sharma

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      Amorphous selenium alloy films have been found to exhibit excellent photosensitive properties from 300 to 700 nm. These films constitute the essential part of xerographic photoreceptors. Optical absorption, energy band gap and X-ray structural analysis of Se85 Te15 and Se85 As15 films are reported. The effect of annealing on these parameters has also been indicated.

    • Effects of insulating layer on the performance of thin film electroluminescent devices

      M K Jayaraj C P G Vallabhan

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      Thin film electroluminescent devices were fabricated with active layer of ZnS:Mn and different insulators viz Sm2O3, Eu2O3, Na3A1F6, MgF2, CeO2 and SiO in MIS and MISIM structure. The threshold voltage for light emission in AC thin film electroluminescent devices of MIS and MISIM structures is found to depend on the dielectric properties of insulating materials. The observed threshold voltage for these devices and its variations for devices with different insulators are explained using the equivalent circuit for the device and the dielectric properties of the insulting material used for the preparation of device. Variation of threshold voltage with operating time is also studied for some of the devices.

    • Variations of interlayer structure in CuxS/CdS bilayer thin film with annealing of CdS: an ellipsometric study

      K P Vijayakumar

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      Irregularities at the interface in CuxS/CdS thin films can be controlled by annealing CdS film prior to chemiplating. The interlayer formed on CdS films annealed at 200°C is comparatively smooth. In CdS films annealed at higher temperatures, the interlayer is rather thick and the CdS intrusions into this layer are thin. An ellipsometric technique is used for this study and the effective medium theory which is utilized to interpret the results is based on the difference in reaction rate in the grains as well as grain boundaries during chemiplating.

    • Measurement of ultrasonic wave velocity in a solid under gas pressures up to 0·4 GPa

      C Divakar A K Singh

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      A set-up is described for the measurement of longitudinal and transverse wave velocities in a solid under gas pressures up to 0·4 GPa. To check the performance of the set-up, the elastic constants of Se and As2Se3 glasses and their pressure derivatives were obtained from the wave velocity data and compared with the data available in the literature.

    • Electrical conductivity of doped ZnS

      S V Sharma R J Singh

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      The electrical conductivity of doped ZnS with different impurities (Mn, Fe, Co, Ni and Cu) of various concentrations has been measured to verify the existence of ladder-like levels of ‘killers’ of luminescence. Attempts have been made to ascertain the separation between the valence band of the host ZnS and the ground state of the acceptor impurities and also to investigate the effect of various concentrations of impurities on the electrical conductivity of doped ZnS.

    • Curing of visible light-activated dental restorative composites

      S N Pal R Vowles D F Williams

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      FTIR spectroscopy and microhardness measurements were employed to follow the degree of curing of visible light activated dental composites. The observed dependence of curing on grade and shade of the materials, exposure time and depth from the light exposed surface have been discussed. Immediately after curing, it was found that direct correlation of microhardness values with that of double bond conversion estimated by FTIR technique could not be established.

    • Effect of annealing on crystal size in pure Mysore silk fibres

      R Somashekar R Gopalkrishna Urs

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      Wide angle X-ray diffraction studies of pure Mysore silk fibres, annealed at various temperatures at different periods of time were carried out to evaluate crystal size and lattice distortion parameters as these determine the properties of silk fibres.

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