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Subject: search.filters.subject.Crystallization

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Now showing 1 - 9 of 9
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    Structural and electrical transport studies in CuI substituted AgI-oxysalt glass-ceramic nanocomposites formed during crystallization
    (NISCAIR, 2013-05) Dalvi, Anshuman
    Electrical transport in CuIxAgI1-x-Ag2O-V2O5 glassy system has been studied for temperatures Tg ≤ T ≤ Tc. The XRD and DSC results suggest multiple crystallizations in this system. The electrical conductivity-temperature cycles are obtained for all the compositions and the conductivity behaviour for T ≥ Tc is explained using a crystallite by pass model.
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    Crystallization in Li2SO4–Li2O–P2O5 glassy ionic system: An assessment through electrical transport
    (Elsevier, 2014-10) Dalvi, Anshuman
    The electrical transport during the crystallization of ternary Li2SO4–Li2O–P2O5 glassy ionic system reveals interesting results. Electrical conductivity isotherms recorded at the crystallization temperature are found to be of immense importance, especially, in the understanding of phase transformation. The electrical conductivity falls rapidly during crystallization of LiPO3 compound and saturates at its completion. Such studies on conductivity isotherms further confirm the suppression of crystallization with addition of Li2SO4 in the glass matrix. A systematic variation of the Cole–Cole plots and conductivity spectra during crystallization further suggests a slow and predetermined process of glass–ceramic formation. The mechanism of electrical transport during crystallization is also explained using a crystallite bypass model. It is further revealed that the samples remain purely ionic during and after crystallization.
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    Electrical transport in Li2SO4-Li2O-B2O3 glass-ceramic composites
    (NISCAIR, 2013-05) Dalvi, Anshuman
    Lithium ion conducting glass-ceramic composites have been synthesized in Li2SO4-Li2O-B2O3 system by annealing the glass above its crystallization temperature. The electrical, structural and thermal characterization of these glass-ceramics reveals interesting results. The conductivity of the glass-ceramic increases with Li2SO4 content and exhibits a maximum of ~ 10-4 at 200°C
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    Thermal stability and crystallization kinetics in superionic glasses using electrical conductivity–temperature cycles
    (AKJournals, 2010-12) Dalvi, Anshuman
    The present work demonstrates application of electrical conductivity (σ)–temperature (T) cycles to investigate thermal properties viz., crystallization and glass transition kinetics in AgI–Ag2O–V2O5–MoO3 superionic glasses. The σ–T cycles are carefully performed at various heating rates, viz., 0.5, 1, 3, 5, and 7 K/min. The conductivity in Ag+ ion conducting glasses exhibit anomalous deviation from Arrhenius behavior near glass transition temperature (Tg) followed by a drastic fall at crystallization (Tc). The temperature corresponding to maximum rate of crystallization (Tp) is obtained from the derivative of σ–1/T plots. With increasing heating rates, the characteristic temperatures (Tg, Tp) are found to be shifting monotonically toward higher temperatures. Thus, activation energy of structural relaxation Es, crystallization Ec and other thermal stability parameters have been obtained from σ–T cycles using Kissinger equation and Moynihan formulation. For a comparative study, these kinetics parameters have also been calculated from differential scanning calorimetry plots. The parameters obtained from both the methods are found to be comparable within experimental error.
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    Electrical transport and crystallization in Cu+ ion substituted AgI–Ag2O–V2O5 glassy superionic system
    (Elsevier, 2010-01) Dalvi, Anshuman
    A new glassy solid electrolyte system CuxAg1 − xI–Ag2O–V2O5 has been synthesized. The structural, thermal and electrical properties of the samples have been investigated. The glassy nature of the samples is confirmed by X-Ray diffraction and Differential Scanning Calorimetry studies. The electrical conductivity of these samples increases with CuI content and approaches a maximum value of ∼ 10−2 Ω− 1 cm− 1 for x = 0.35 at room temperature. Ionic mobility measurements suggest that enhancement in the conductivity with Cu+ ion substitution may be attributed to increase in the mobility of Ag+ ions. The electrical conductivity versus temperature cycles carried out at well-controlled heating rate above Tg and Tc reveal interesting thermal properties. For lower CuI content samples conductivity exhibits anomalous rise above Tg and subsequent fall at Tc. It is also found that CuI addition into AgI–Ag2O–V2O5 matrix reduces the extent of crystallization.
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    Effect of conditional glass former variation on electrical transport in Li2O–P2O5 glassy and glass-ceramic ionic system
    (Elsevier, 2014-10) Dalvi, Anshuman
    Giving emphasis to electrical transport in the thermally unstable region, a conditional glass former based system 50Li2O–(50-x)P2O5–xMoO3 is investigated. Though glass forming region is narrow, the electrical conductivity exhibits significant rise up to x ≤ 15 mol%. Scanning electron microscopy investigations suggest existence of tiny crystallites well separated by glass tissues for higher MoO3 content samples. It is therefore revealed that addition of MoO3 improves the thermal stability. Electronic conductivity in this system is found to be fairly low and suggests phonon assisted polaron hopping. Electrical conductivity is found to be comparable to glass and glass-ceramic samples.
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    A comparative study of crystallization kinetics between conventionally melt quenched and mechanochemically synthesized AgI–Ag2O–CrO3 superionic system
    (Elsevier, 2003-10) Dalvi, Anshuman
    Non-isothermal crystallization kinetics in conventionally melt quenched versus mechanochemically synthesized amorphous AgI–Ag2O–CrO3 superionic solids is discussed. The quenched as well as ball-milled samples exhibit glass (Tg) and multiple amorphous⇒crystalline (Tc) transitions. Tg as well as Tc are found to increase monotonically with heating rate. The activation energy for structural relaxation (Es) obtained using Moynihan equation is found to be higher for ball-milled samples that eventually suggests the relatively rigid and highly viscous structure of milled samples. The activation energy associated with nucleation and growth (Ec) is obtained using Matusita–Sakka equation and its higher value confirms the higher rate of crystallization in ball-milled samples. The values of Tc–Tg and the enthalpy of phase transformation (ΔH) are also found higher for the ball-milled samples that confirm their comparatively high thermal stability. The electrical conductivity near the crystallization temperatures is studied as a function of time and temperature and these results confirm the presence of amorphous⇒crystalline transition temperatures in the ball-milled as well as in the melt-quenched samples.
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    Electrical transport in Li2SO4–Li2O–P2O5 ionic glasses and glass–ceramic composites: A comparative study
    (Elsevier, 2013-05) Dalvi, Anshuman
    A comparative investigation carried out between glasses and glass–ceramics, in the system (Li2SO4)x–(LiPO3)1 − x, reveals interesting results. The conventionally melt-quenched compositions for x ≤ 60 mol% were found to be purely glassy in nature. The glass–ceramic composites obtained by crystallization of the glassy samples were found to be composed of fine nanocrystallites of LiPO3 and Li2SO4 embedded in the glass matrix. The electrical conductivity, in both glasses as well as glass–ceramics, increases with Li2SO4 content and found to be maximum for a composition with 60 mol% of Li2SO4. Scaling of the conductivity spectra reveals that the relaxation dynamics of Li+ ions is independent of temperature and composition for glasses as well as glass–ceramics. Further, the cyclic voltammetry investigations suggest a relatively better stability of glass–ceramic samples at least up to 300 °C.
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    Modeling Polymer Crystallization Kinetics in the Meltblowing Process
    (ACS, 2020-12-06) Ghosal, Arkaprovo
    A novel model of the crystallization process in meltblowing process is proposed and implemented in numerical simulations. The spinline crystallization is studied using numerical solutions of the system of coupled quasi-one-dimensional equations describing the dynamics of multiple polymer jets moving in the surrounding high-speed air. Cooling, crystallization, and solidification accompany three-dimensional motion of polymer jets resulting in their vigorous stretching by the air flux including the aerodynamically driven bending/flapping. The numerical solutions predict distribution of the degree of crystallinity in polymer jets in flight, as well as in the laydown formed on the collecting screen, with the three-dimensional structure of the laydown being fully reconstructed. The effect of the collector screen temperature, die-to-collector distance (DCD), and the activation energy of the viscous flow in the polymer melt on the laydown features is studied in detail.