• A K Srivastava

      Articles written in Bulletin of Materials Science

    • 50 MeV lithium ion beam irradiation effects in poly vinylidene fluoride (PVDF) polymer

      A K Srivastava H S Virk

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      Irradiation effects of 50 MeV7Li+3 ion beam induced in bulk PVDF polymer have been studied with respect to their optical, chemical, structural and electrical behaviour by using UV-visible, FT-IR spectroscopy, XRD technique and electrical frequency response using LCR bridge. The ion fluences ranging from 1.27 X 1011 to 2.15 X 1013 ions cm-2 have been used to study dose effects of irradiation in PVDF. The recorded UV-visible spectra clearly shows five characteristic peaks at 315, 325, 360, 425 and 600 nm. Due to irradiation, the optical absorption initially decreases but then increases with higher fluences. In the FT-IR spectra, no appreciable change has been observed after irradiation, indicating that this polymer is chemically stable. There is exponential increase in admittance with log of frequency but the effect of irradiation is not quite appreciable. The value of tan δ and relaxation frequency are changed appreciably due to irradiation. The diffraction pattern of PVDF indicates that this polymer is in semi-crystalline form; a decrease in the crystallinity and crystallite size has been observed due to irradiation

    • Physical and chemical response of 70 MeV carbon ion irradiated Kapton-H polymer

      H S Virk P S Chandi A K Srivastava

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      Physical and chemical responses of 70 MeV carbon ion irradiated Kapton-H polymer were studied by using UV-visible, FTIR and XRD techniques. The ion fluences ranging from 9.3 × 1011–9 × 1013 ions cm–2 were used. Recorded UV-visible spectra clearly showed a decrease in absorption initially with fluence, but for the higher fluences it showed a recovery characteristic. A decrease in band-gap energy of 0.07 eV was observed. The FTIR analysis indicated the high resistance to radiation induced degradation of polymer. The diffraction pattern of Kapton-H indicates that this polymer is semi-crystalline in its nature. In case of irradiated one, there was an average increase of crystallite size by 20%, but diffuse pattern indicates that there was a decrease in crystallinity, which may be attributed to the formation of complex structure induced by the cross-linking of the polymeric chains.

    • Effect of isochronal annealing on phase transformation studies of iron oxide nanoparticles

      Anjali J Deotale R V Nandedkar A K Sinha Anuj Upadhyay Puspen Mondal A K Srivastava S K Deb

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      The effect of isochronal annealing on the phase transformation in iron oxide nanoparticles is reported in this work. Iron oxide nanoparticles were successfully synthesized using an ash supported technique followed by annealing for 2 h at various temperatures between 300 and 700° C. It was observed using X-ray diffraction (XRD) and transmission electron microscopy (TEM) that as-grown samples have mixed phases of crystalline haematite (α-Fe2O3) and a minor phase of either maghemite (𝛾-Fe2O3) or magnetite (Fe3O4). On annealing, the minor phase transforms gradually to haematite. The phase transformation is complete at annealing temperature of 442° C as confirmed by differential scanning calorimetric (DSC) analysis. The unresolved phases in XRD were further analysed and confirmed to be maghemite from the X-ray absorption near edge structure (XANES) studies. The magnetic measurements showed that at room temperature nano-𝛼-Fe2O3 is weak ferromagnetic, and its magnetization is larger than the bulk value. The mixed phase sample shows higher value of magnetization because of the presence of ferromagnetic 𝛾-Fe2O3 phase.

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    • Dr Shanti Swarup Bhatnagar for Science and Technology

      Posted on October 12, 2020

      Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
      Chemical Sciences 2020

      Prof. Surajit Dhara — School of Physics, University of Hyderabad, Hyderabad
      Physical Sciences 2020

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      Posted on July 25, 2019

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