• Issue front cover thumbnail

      Volume 32, Issue 4

      August 2009,   pages  369-463

    • Mobility activation in thermally deposited CdSe thin films

      Kangkan Sarmah Ranjan Sarma

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      Effect of illumination on mobility has been studied from the photocurrent decay characteristics of thermally evaporated CdSe thin films deposited on suitably cleaned glass substrate held at elevated substrate temperatures. The study indicates that the mobilities of the carriers of different trap levels are activated due to the energy of incident illumination, which results in the existence of two distinct trap levels. In each trap depth the energy of the trap increases linearly. It infers that there is a linear distribution of traps of different energies below the conduction band.

    • Fabrication and thermal stability studies of polyamide 66 containing triaryl phosphine oxide

      Xiaofeng Yang Qiaoling Li Zhiping Chen Hongli Han

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      An intrinsically halogen-free flame retardant polyamide 66 (FR-PA66) was fabricated successfully by two-step polymerization reaction with adipic acid hexamethylene salt (AH salt) and bis(4-carboxyphenyl) phenyl phosphine oxide (BCPPO) as raw materials. The structure, combustion properties and thermal stability were characterized by means of intrinsic viscosity, Fourier transform infrared spectroscopy (FTIR), combustion testing, differential scanning calorimetry (DSC), thermogravimetric analysis (TG) and scanning electron microscope (SEM). Experiments show that BCPPO have excellent copolymerization properties with AH salt. And incorporation of triaryl phosphine oxide (TPO) did not transform the crystal phase structure of PA66. During fabrication of FR-PA66, melt polymerization time exhibits more surprising influence on intrinsic viscosity than aqueous solution polymerization time. The LOI value of FR-PA66 with 9 wt% TPO reaches 27.2, and corresponding UL94 rating reaches V-0. Improved thermo-stability of FR-PA66 can be attributed to both forming of compact char protective layer and further consolidation effect of 𝑃/𝑁 synergistic system.

    • Effect of sintering condition on properties of Cr-doped Pb0.95Sr0.05 (Zr0.53Ti0.47)O3 ceramics

      J Costa Marrero A Suárez-Gómez J Saniger Blesa F Calderón-Piñar

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      The effects of sintering temperature (𝑇sinter) and sintering time (𝑡sinter) were investigated for Pb0.95Sr0.05(Zr0.53Ti0.47)O3 + 𝑥%wtCr2O3 system to determine the optimum regimen of sintering. The study was performed by determining the following parameters: relative density (ρrel) and sintering rate ($\dot{\varepsilon}_{\rho}$). The grain size was diminished when small amounts of Cr2O3 were added to system and was enhanced when the sintering temperature and time was increased. The dielectric constant becomes maximum and the electric loss becomes minimum with the sintering temperature of 1290°C. The optimum regimen of sintering is 𝑇sinter = 1290°C during 70 min. The piezoelectric properties for the optimum regimen of sintering were studied.

    • Influence of seeding on crystallization behaviour of BaNaB9O15 glasses

      Rahul Vaish K B R Varma

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      Transparent BaNaB9O15 (BNBO) glasses were fabricated via the conventional melt-quenching technique. X-ray powder diffraction (XRD) followed by differential scanning calorimetric (DSC) studies confirmed the amorphous and glassy nature of the as-quenched samples, respectively. The effect of seeding on the crystallization of BNBO glasses was studied by non-isothermal DSC method and was modeled using the Johnson–Mehl–Avrami and Ozawa equations. The activation energy for seeded glasses decreased with the increase in fraction of crystallization. The values for the onset of crystallization and Avrami exponent were found to be lower for seeded samples which were associated with the heterogeneous nucleation and epitaxial processes.

    • Effect of high thermal expansion glass infiltration on mechanical properties of alumina–zirconia composite

      A Balakrishnan B B Panigrahi K P Sanosh Min-Cheol Chu T N Kim Seong-Jai Cho

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      This work studies the effect on the mechanical properties of alumina-10 wt% zirconia (3 mol% yttria stabilized) composite by infiltrating glass of a higher thermal expansion (soda lime glass) on the surface at high temperature. The glass improved the strength of composite at room temperature as well as at high temperature. This could be attributed to the drastic drop in the coefficient of thermal expansion due to the compositional change in the soda lime glass during infiltration. There was a significant improvement in the Weibull modulus after glass infiltration. Glass infiltrated samples showed better thermal shock resistance. The magnitude of strength increment was found to be in the order of the surface residual stress generated by thermo-elastic properties mismatch between the composite and the penetrated glass.

    • Application of new tool material for electrical discharge machining (EDM)

      A K Khanra L C Pathak M M Godkhindi

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      In EDM, Cu and graphite are commonly used as tool materials. The poor wear resistance is the drawback of these tools. In the current study, an attempt has been made to develop a ZrB2–Cu composite as an EDM tool material to overcome this problem. Initially, the ZrB2 powder is prepared by self-propagating high-temperature synthesis (SHS) technique and synthesized powder is mixed with different amounts of Cu powder. Dense composite is developed by a pressureless sintering at 1250°C. The composites are tested as tool material at different EDM process parameters during machining of mild steel. The ZrB2–40 wt% Cu composite shows highest metal removal rate (MRR) with significant tool removal rate (TRR) than other composites. The performance of ZrB2–40 wt% Cu composite is compared to conventional Cu tool. The composite shows higher MRR with less TRR than Cu tool but it shows more average surface roughness and diameteral overcut than Cu tool.

    • in situ templating synthesis of conic Ba0.5Sr0.5Co0.8Fe0.2O3–𝛿 perovskite at elevated temperature

      Wei Zhou Ran Ran Zongping Shao Wanqin Jin

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      Conic Ba0.5Sr0.5Co0.8Fe0.2O3–𝛿 (BSCF) functional composite oxide was synthesized via a simple in situ templating process. The treatment of the solid precursor with concentrated nitric acid resulted in the mismatch of ionic radius at 𝐴-site and 𝐵-site of the ABO3 perovskite, due to the oxidation of cobalt/iron ions, and the formation of Ba0.5Sr0.5(NO3)2 solid solution. Therefore, instead of the direct formation of BSCF oxide, an intermediate phase of Ba0.5Sr0.5CoO3 (BSC) in hexagonal lattice structure and with conic particle shape was preferentially formed during calcination at low temperature. BSCF perovskite was then produced by the in situ templating of BSC with iron diffusing into the BSC lattice during calcination at high temperature. Wellcrystallized BSCF particles in conic shape were obtained by the calcination of the nitric acid treated precursor at 900°C.

    • Discontinuous precipitation in copper base alloys

      K T Kashyap

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      Discontinuous precipitation (DP) is associated with grain boundary migration in the wake of which alternate plates of the precipitate and the depleted matrix form. Some copper base alloys show DP while others do not. In this paper the misfit strain parameter, 𝜂, has been calculated and predicted that if 100 𝜂 > ± 0.1, DP is observed. This criterion points to diffusional coherency strain theory to be the operative mechanism for DP.

    • Recrystallization microstructure modelling from superimposed deformed microstructure on microstructure model

      Prantik Mukhopadhyay

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      The recovered cold rolled microstructure obtained from orientation image microstructure of Al–4%Mg–0.5%Mn alloy (AA5182 alloy) was superimposed on the grid of cellular automata based microstructure model. The Taylor factors of deformed/cold rolled orientations were considered as the driving force for recrystallization. The local development of recrystallized microstructure and texture were simulated with orientation dependent grain boundary mobility and compared with the experimental results.

    • Preparation and characterization studies of metaborates, Cu1–𝑥M𝑥B2O4 (M = Ni, Co and Mn; 𝑥 = 0, 0.1 and 0.5)

      N Anantharamulu B Vijaya Kumar V Rama Devi T Sarojini Ch Anjaneyulu M Vithal

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      Copper metaborates of Cu1–𝑥M𝑥B2O4 (M = Ni, Co and Mn; 𝑥 = 0, 0.1 and 0.5) compositions are prepared using B2O3 flux. Powder XRD studies showed them all to belong to the tetragonal system with space group $I\bar{4}2$𝑑. Their infrared spectra exhibit characteristic vibrational bands of BO4 tetrahedron. The room temperature powder electron spin resonance (ESR) spectrum of copper metaborate gave a single peak at g ≈ 2.15. The diffuse reflectance spectra (DRS) of Cu1–𝑥M𝑥B2O4 (M = Ni, Co and Mn; 𝑥 = 0, 0.1 and 0.5) are consistent with ligand to metal ion charge transfer and square planar symmetry of Cu2+ ion. The ligand field parameters 𝐷𝑞xy, 𝐷s and 𝐷t are obtained.

    • Growth and characterization of pure and doped NLO L-arginine acetate single crystals

      P Praveen Kumar V Manivannan P Sagayaraj J Madhavan

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      Single crystals of pure, Cu2+ and Mg2+ doped L-arginine acetate (LAA) were grown successfully by slow evaporation technique. In order to improve the device characteristics of LAA crystals, metal dopants of Cu2+ and Mg2+ were incorporated into the parent crystals. The grown pure and doped crystals were confirmed by X-ray powder diffraction studies. The pure and doped crystals were characterized by Fourier transform Raman (FT–Raman) and thermal studies. Absorptions of these grown crystals were analysed using UV–Vis–NIR studies, and it was found that these crystals possess minimum absorption in the entire visible region. Nonlinear optical studies of pure and doped crystals were carried out and it reveals that the dopants have increased the efficiency of LAA crystals.

    • Radiation from a current sheet at the interface between a conventional medium and anisotropic negative refractive medium

      Yuan You

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      In this paper we investigate the radiation from a current sheet at the interface between semiinfinite isotropic positive refractive medium and anisotropic negative refractive medium. The distribution of the electric and magnetic fields in two regions and Poynting vectors associated with propagating and evanescent waves are calculated. The reasons for the singularity of the electric or magnetic field are briefly provided if the waves are evanescent in two media.

    • Synthesis, structural and ferromagnetic properties of La1–𝑥K𝑥MnO3 (0.0≤ 𝑥 0.25) phases by solution combustion method

      C Shivakumara Manjunath B Bellakki

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      We describe the solution combustion synthesis and characterization of La1–𝑥K𝑥MnO3 (0.0 ≤ 𝑥 ≤ 0.25) perovskite phases, which is a low temperature initiated, rapid route to prepare metal oxides. As-synthesized compounds are amorphous in nature; crystallinity was observed on heating at 800°C for 5 min. Structural parameters were determined by the Rietveld refinement method using powder XRD data. Parent LaMnO3 compound crystallizes in the orthorhombic structure (space group 𝑃𝑏𝑛𝑚, No. 62). Potassium substituted compounds were crystallized with rhombohedral symmetry (space group 𝑅–3c, No. 167). The ratio of the Mn3+/Mn4+ was determined by the iodometric titration. The Fourier transform infrared spectrum (FT–IR) shows two absorption bands for Mn–O stretching vibration (𝜈s mode), Mn–O–Mn deformation vibration (𝜈b mode) around 600 cm-1 and 400 cm-1 for the compositions, 𝑥 = 0.0, 0.05 and 0.10. Four-probe electrical resistivity measurements reveal a composition controlled metal to insulator transition (𝑇M–I}}$), the maximum 𝑇M–I was observed for the composition La0.85K0.15MnO3 at 287 K. Room temperature vibrating sample magnetometer data indicate that for the composition up to 𝑥 = 0.10, the compounds are paramagnetic whereas composition with 𝑥 = 0.15, 0.20 and 0.25 show magnetic moments of 27, 29 and 30 emu/g, respectively.

    • Investigation of tribological and mechanical properties of metal bearings

      Bekir Sadik Ünlü

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      Copper, aluminum and tin–lead based alloys are widely used as journal bearing materials in tribological applications. Bronze and brass are widely used as journal bearing materials for copper based alloys. Zamacs find applications as journal bearing materials for zinc based alloys, while duralumines are chosen as journal bearing materials for aluminum based alloys. In addition, white metals are widely used as journal bearing materials for tin–lead based alloys. These alloys ensure properties expected from journal bearings. In this study, tribological and mechanical properties of these journal bearings manufactured by metals were investigated. SAE 1050 steel shaft was used as counter abrader. Experiments were carried out in every 30 min for a total of 150 min by using radial journal bearing wear test rig.

    • Estimation of scattering from a moist rough surface with spheroidal dust particles

      Mukesh Kumar

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      The scattering from moisture rough surface with spheroidal dust particles having surface with spheroidal dust particles has recently received much attention. In part due to the recent prediction and observation of the spheroidal dust particles in rough surfaces under elastic wave by the Kirchhoff scattering model and scalar approximation with slope. Our analysis shows that the scattering depends on the moisture (2–4.5%) with spheroidal dust particles. At slightly moisture rough surface the dielectric properties increase with change in field amplitude in a rough surface with spheroidal dust particles.

    • Sintering behaviour of spinel–alumina composites

      Soumen Pal A K Bandyopadhyay P G Pal S Mukherjee B N Samaddar

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