Boris A. Gurovich; Denis A. Kuleshov; Dmitriy A. Maltsev; Oleg K. Chugunov; Alexey S. Frolov; Yaroslav I. Shtrombakh
Abstract
The operation of nuclear graphite in graphite-moderated reactors is accompanied by its properties degradation under the influence of neutron irradiation, which limits their service life. In this connection, it is of interest to identify the mechanisms that determine the properties degradation of graphite ...
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The operation of nuclear graphite in graphite-moderated reactors is accompanied by its properties degradation under the influence of neutron irradiation, which limits their service life. In this connection, it is of interest to identify the mechanisms that determine the properties degradation of graphite materials at various operational stages of operating RBMK power reactors.
Rajat K. Saha; Eeshankur Saikia;Mrinal K. Debanath
Abstract
In this study, we report the synthesis and optical properties of flower-shaped ZnO which is fabricated successfully using polyvinylpyrrolidone (PVP) as capping agent by wet chemical method at temperature 60 0 C. The structures and morphologies of flower-shaped ZnO is characterized by X-ray diffraction ...
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In this study, we report the synthesis and optical properties of flower-shaped ZnO which is fabricated successfully using polyvinylpyrrolidone (PVP) as capping agent by wet chemical method at temperature 60 0 C. The structures and morphologies of flower-shaped ZnO is characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM) for nonlinear dynamical study of the system of particles. The studies of SEM and TEM have confirmed flower-shaped structure of the ZnO. The UV-vis absorption spectroscopy of the synthesized sample indicates the presence of blue shift. FTIR analysis shows the characteristic absorption of the Zn-O bond. It has been observed in room temperature photoluminescence (PL) spectroscopy of the sample exhibits emission peaks at near band edge (NBE) along with a weak blue emission peak. It is found from the present study that the phenomenon of flower-like microstructure is based on the size and shape of the particles as well as their aggregated forms. Moreover, their optical properties predict the factors responsible in inhibiting microorganisms for which it may lead to some biological applications.
Miloš Janeček; Peter Minárik; Tomáš Krajňák; Kristína Bartha; Josef Straskuy; Jakub Cizek
Abstract
Mg22Gd alloy was processed by high pressure torsion (HPT) at room temperature and the pressure of 2 GPa. A series of specimens with different number of rotations N (N = 0-15) was prepared from the initial coarse grained as cast material. Mechanical properties were investigated by microhardness mapping. ...
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Mg22Gd alloy was processed by high pressure torsion (HPT) at room temperature and the pressure of 2 GPa. A series of specimens with different number of rotations N (N = 0-15) was prepared from the initial coarse grained as cast material. Mechanical properties were investigated by microhardness mapping. The microhardness was found to increase with increasing strain imposed by HPT and tend to saturate at about HV = 145. The microstructure (phase morphology and composition, etc.) evolution with strain was investigated by scanning electron microscopy and EDS. High Gd content in the alloy resulted in the precipitation of stable Mg5Gd phase. This phase exhibited apparently higher hardness than the magnesium matrix. During straining the phase was continuously fragmented and only tiny particles were found in heavily strained material. Electron back scatter diffraction (EBSD) and automated crystallographic orientation mapping in transmission electron (ACOM-TEM) were employed to characterize the fragmentation of the grain structure. HPT was found to result in strong grain refinement by the factor of approximately 1000. The dislocation density was determined by positron annihilation spectroscopy. Significant twinning was found in the initial stages of HPT straining. At high strains twin formation was suppressed and only dislocation storage in the material occurs.
Divyanshu Bhatnagar; Ratnamala Chatterjee
Abstract
BaBiO3 (BBO) particles were successfully synthesized through solid-state route, to provide better understanding of its transport properties, which is not well studied yet. X-ray diffraction (XRD) measurement confirmed that the particles were crystallized with monoclinic structure in single phase. The ...
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BaBiO3 (BBO) particles were successfully synthesized through solid-state route, to provide better understanding of its transport properties, which is not well studied yet. X-ray diffraction (XRD) measurement confirmed that the particles were crystallized with monoclinic structure in single phase. The Raman spectrum of BBO sample revealed the existence of two different Bi sites (the octahedral BiO6/3 and the triangular pyramidal BiO4/2 cluster). Subsequently, the observation of low resolution and lattice scale imaging through high resolution transmission electron microscope (HRTEM) indicated the formation of monoclinic BBO particles of size ~ 50-60 nm. The ring pattern obtained from selected area electron diffraction (SAED) inveterate polycrystalline nature of the sample and calculated structural parameters well harmonized with XRD results. As expected, BBO showed semiconducting behavior with resistivity of ~ 3.8 kΩ-cm at room temperature along with an excellent NTC (negative temperature coefficient) thermistor characteristic. The dielectric measurements and impedance spectroscopy studies reveal that BBO exhibit two typical characteristics, i.e., diffuse phase transition and frequency dependent dielectric maxima, of relaxor oxides; with negative dielectric constant above 550 K.
Bradha Madhavan; Anuradha Ashok
Abstract
The present work highlights a series of perovskites La0.8A0.2TiO3-δ, (where A= Ba, Ca, Sr), which includes a high dielectric constant, a low dielectric loss over a wide temperature, in a frequency range of 30 MHZ. Undoped and A-site doped LaTiO3-δ (with Ba 2+ , Sr 2+ and Ca 2+ ) perovskites ...
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The present work highlights a series of perovskites La0.8A0.2TiO3-δ, (where A= Ba, Ca, Sr), which includes a high dielectric constant, a low dielectric loss over a wide temperature, in a frequency range of 30 MHZ. Undoped and A-site doped LaTiO3-δ (with Ba 2+ , Sr 2+ and Ca 2+ ) perovskites were synthesised by solid state reaction method (ball milling). The perovskite phase formation of the milled precursor powders under thermal treatments was investigated by thermogravimetry/differential scanning calorimetry (TG/DSC). Structural analysis of the phase pure sintered pellets revealed an orthorhombic crystal structure for all perovskites. Surface morphology of the sintered pellets exposed the presence of nanosized grains. The oxidation states of La 3+ and Ti 3+ ions have been confirmed using X-ray Photoelectron Spectroscopy (XPS). The dielectric spectral analysis reveals that dielectric properties of the perovskites depend on temperature and frequency. Among the dopants Sr is found to be the most effective in increasing the dielectric properties of LaTiO3-δ. This makes it suitable as a high dielectric material for making capacitors operating at higher frequencies.
Rajni Verma; Bhanu Mantri; Avanish Kumar Srivastava
Abstract
In the present study, ZnO and TiO2 nanostructures of different size have been synthesized in high yield with excellent repeatability by simple, economical and environmentally benign chemical route. ZnO quantum dots and nanorods of tuned aspect ratio were evolved by optimising the reaction conditions ...
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In the present study, ZnO and TiO2 nanostructures of different size have been synthesized in high yield with excellent repeatability by simple, economical and environmentally benign chemical route. ZnO quantum dots and nanorods of tuned aspect ratio were evolved by optimising the reaction conditions such as by varying solvent composition, precursor concentration and by using different additives. On the other hand, the synthesis of brookite, the rare phase, anatase and rutile, the stable phases of TiO2 were also achieved by just varying the annealing temperature from 400 to 615 °C. The obtained nanostructures were rationalized by various characterization techniques such as XRD, FTIR, Raman, SEM, HR- TEM, UV-Vis and PL. The Phase formation and structure determination were identified by using XRD, FTIR and Raman Spectra, SEM and HR-TEM were performed to determine the morphology and particle size. The aspect ratio was calculated to be in the range of 3.2-9.4 in case of ZnO NRs, and particle size was found to be 2-5 nm for ZnO QDs of wurtzite phase and ~ 10 nm for TiO2 (anatase phase) NPs, respectively. The UV-Vis optical absorption spectrum demonstrates the band gap value of 3.60, 4.02 and 3.40 eV for ZnO NRs, QDs and TiO2 NPs respectively. The UV-Vis optical absorption spectrum demonstrates the band gap and room temperature PL spectra illustrates about the various defects present in the sample. Various chemical reactions and mechanism involved in producing these nanostructures are dealt in detail. The future prospective of these metal oxide nanostructures lie in photocatalysis, sensors and biomedical applications.
P. Jegadeesan; S. Amirthapandian; Kitheri Joseph; C. David; B.K. Panigrahi; K.V. G Kutty
Abstract
Iron phosphate glass (IPG) is considered as a suitable matrix for the immobilization of nuclear waste containing higher concentration of Cs, rare earth, Mo and Cr. The central issue, while disposing nuclear waste in glass matrices, is the damage in glass matrices due to the ballistic processes caused ...
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Iron phosphate glass (IPG) is considered as a suitable matrix for the immobilization of nuclear waste containing higher concentration of Cs, rare earth, Mo and Cr. The central issue, while disposing nuclear waste in glass matrices, is the damage in glass matrices due to the ballistic processes caused by atomic displacements due to α-particles and the recoiling of heavy nuclei resulting from actinide decay. Ion irradiation produces similar kind of damage, and hence the samples are irradiated with 4 MeV O + (self) ion. The microstructural studies were carried out using transmission electron microscopy (TEM) for as-prepared, annealed and ion irradiated samples. It is observed that ion irradiation in IPG leads to the formation of nanocrystals with different phases containing Fe, P and O. Thermally activated crystallization process is ruled out based on the non-equilibrium experimental conditions. In the present experiments, stress driven crystallization mechanism was invoked. The stress, around the ion track formed during ion irradiation, is larger than the yield strength of the glass and hence, the surrounding matrix undergoes substantial deformation resulting in the formation of shear bands. Nucleation of nanocrystals is driven by the stress in the vicinity of the shear bands.
Punita Srivastava;Kedar Singh
Abstract
We have developed successfully the synthesis of highly yielded CdSe nanoparticles (NPs) at 60 0C by solvothermal route in which the cadmium and selenium precursors have been dissolved in deionized water, ethylene glycol and hydrazine hydrate. This route is very facile, inexpensive and less hazardous ...
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We have developed successfully the synthesis of highly yielded CdSe nanoparticles (NPs) at 60 0C by solvothermal route in which the cadmium and selenium precursors have been dissolved in deionized water, ethylene glycol and hydrazine hydrate. This route is very facile, inexpensive and less hazardous and ensures almost complete yield of the precursors. The powder product was well characterized by powder X- ray diffraction (XRD), Transmission electron microscopy (TEM), Scanning electron microscopy (SEM), UV-Vis spectroscopy, Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR) .It is investigated that as synthesized powder has a hexagonal (Wurtzite) structure of CdSe with diameters of the particles are in the range of 10-15 nm. The formation mechanism is also discussed.
V. K. Sharma; M. Najim; G. D. Varma
Abstract
We report on the effect of different gaseous environments (air, argon and Ar/H2) on the structural and magnetic properties of Zn0.98Co0.02O synthesized by the solid state reaction route. We have also studied the effect of different annealing times and temperatures on the as synthesized samples. M-H curves ...
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We report on the effect of different gaseous environments (air, argon and Ar/H2) on the structural and magnetic properties of Zn0.98Co0.02O synthesized by the solid state reaction route. We have also studied the effect of different annealing times and temperatures on the as synthesized samples. M-H curves of the air sintered and the argon annealed samples show paramagnetic behavior whereas the samples annealed in the hydrogenated argon (Ar/H2) environment exhibit ferromagnetic property at room temperature. Based on the structural and magnetic properties it has been found that Co metal clusters are responsible for the observed room temperature ferromagnetism (RTFM) in the hydrogenated samples.
Mandeep Singh; Manish Kumar; Frantisek Stipanek; Pavel Ulbrich; Pavel Svoboda; Eva Santava; M.L. Singla
Abstract
We have synthesized nickel nanoparticles using nickel chloride as a precursor in ethanol using PVP (Poly Vinyl Pyrrolidone) as a surfactant and hydrazine hydrate as reducing agent at 60 °C in a facile manner. The structural analysis showed that particles are face-centered cubic and monodisperse within ...
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We have synthesized nickel nanoparticles using nickel chloride as a precursor in ethanol using PVP (Poly Vinyl Pyrrolidone) as a surfactant and hydrazine hydrate as reducing agent at 60 °C in a facile manner. The structural analysis showed that particles are face-centered cubic and monodisperse within the PVP matrix with average size about 3 nm. The magnetic analysis shows the superparamagnetism of the single-domain nickel nanoparticles with the blocking temperature (Tb) exists around 14 K with clear hysteretic effect observation below this blocking temperature.
A. K. Srivastava; M. Deepa; K. N. Sood; E. Erdem; R. A. Eichel
Abstract
Novel growth morphologies of sharp needle-shaped tetrapods and coexistent tetrapods and nanowires of ZnO have been prepared by sublimation of pure Zn utilizing a simple solid – catalyst free - vapor mechanism at the temperatures of 950 and 1100 ºC respectively. These striking differences in ...
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Novel growth morphologies of sharp needle-shaped tetrapods and coexistent tetrapods and nanowires of ZnO have been prepared by sublimation of pure Zn utilizing a simple solid – catalyst free - vapor mechanism at the temperatures of 950 and 1100 ºC respectively. These striking differences in these microscopic objects, which evolved at two different process temperatures, were deduced from electron paramagnetic resonance and Raman spectra thereby revealing the role of microstructures, defects and oxygen vacancies in ZnO at lattice scale, which are receptive for luminescence, and electrochemical activity of this functional oxide.
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