• O P Shrivastava

      Articles written in Bulletin of Materials Science

    • Cation exchange applications of synthetic tobermorite for the immobilization and solidification of cesium and strontium in cement matrix

      O P Shrivastava Rashmi Shrivastava

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      Immobilization and solidification of hazardous cations like Cs137 and Sr90 are required while handling the radioactive waste of nuclear power plants. Efforts are on to find a fail proof method of safe disposal of nuclear wastes. In this context, various materials like borosilicate glass, zeolites, cements and synthetic rocks have been tried by several workers. This communication deals with the synthesis, characterization, cesium uptake capacity and leaching behaviour of synthetic alumina-substituted calcium silicate hydroxy hydrate, which are close to that obtained for the natural mineral,11 Å tobermorite. The synthetic mineral show cation selectivity for Cs+ in presence of500–1000 times concentrated solutions of Na+, K+, Mg+, Ca2+, Ba2+ and Sr2+. Although the ordinary portland cement (OPC) which is often used in waste management operations alone holds negligible amounts of Cs+ and Sr2+, the addition of alumina-substituted tobermorite to OPC enhances the retention power of cement matrix by drastically lowering the leach rate of cations

    • Solid state synthesis and structural refinement of polycrystalline La𝑥Ca1-𝑥TiO3 ceramic powder

      O P Shrivastava Narendra Kumar I B Sharma

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      Perovskite structure based ceramic precursors have a characteristic property of substitution in the ``A" site of the ABO3 structure. This makes them a potential material for nuclear waste management in synthetic rock (SYNROC) technology. In order to simulate the mechanism of rare earth fixation in perovskite, La𝑥 Ca1-𝑥TiO3 (where 𝑥 = 0.05) has been synthesized through ceramic route by taking calculated quantities of oxides of Ca, Ti and La as starting materials. Solid state synthesis has been carried out by repeated pelletizing and sintering the finely powdered oxide mixture in a muffle furnace at 1050°C. The ceramic phase has been characterized by its powder diffraction pattern. Step analysis data has been used to determine the structure of solid solution of lanthanum substituted calcium titanate. The SEM and EDAX analyses also confirm that the CaTiO3 can act as a host for lanthanum. X-ray data has been interpreted using CRYSFIRE and POWDERCELL softwares. The ℎ, 𝑘, 𝑙 values for different lattice planes have been generated from the experimental data. The lanthanum substituted perovskite crystallizes in orthorhombic symmetry with space group 𝑃 𝑛 𝑚 𝑎 (#62). Following unit cell parameters have been calculated: 𝑎 = 5.410, 𝑏 = 7.631, 𝑐 = 5.382. The calculated and observed values of corresponding intensities, 2𝜃, and density show good agreement. GSAS based calculation for bond distances Ti–O, Ca–O, La–O and bond angles Ti–O–Ca, Ca–O–Ca, La–O–Ti have been reported.

    • Structure refinement of polycrystalline orthorhombic yttrium substituted calcium titanate: Ca1−𝑥Y𝑥TiO3+𝛿 (𝑥 = 0.1–0.3)

      Rashmi Chourasia O P Shrivastava

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      The perovskite ceramic phases with composition Ca1−𝑥Y𝑥TiO3+𝛿 (where 𝑥 = 0.1, 0.2 and 0.3; hereafter CYT-10, CYT-20 and CYT-30) have been synthesized by solid state reaction at 1050°C. The structure refinement using general structure analysis system (GSAS) software converges to satisfactory profile indicators such as Rietveld parameters: Rp, Rwp, RF2 and goodness of fit. The title phases crystallize at room temperature in the space group 𝑃𝑏𝑛𝑚 (#62) with 𝑎 = 5.3741(4) Å, 𝑏 = 5.4300(4) Å, 𝑐 = 7.6229(5) Å and 𝑍 = 4. Major interatomic distances, bond angles and structure factors have been calculated from the step analysis data of the compound. The crystal morphology has been examined by scanning electron microscopy. Energy dispersive X-ray (EDX) analysis of the specimens show that yttrium enters into the structural framework of CaTiO3. The particle size of the ceramic phases along major reflection planes ranges between 12 and 40 nm. The polyhedral (CaO8 and TiO6) distortions and valence calculations from bond strength data are also reported.

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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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