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Anodic Oxide Films on Niobium and Tantalum in Different Aqueous Electrolytes and Their Impedance Characteristics

100%
Verma N., Singh K., Marí B., Mollar M., Jindal J.
Acta Physica Polonica A
|
2016
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vol. 129
|
issue 3
297-303
EN
The anodic oxide films were prepared on the niobium and tantalum in aqueous electrolyte mixtures containing 1 M CH₃COOH + 1 M H₃PO₄ or 1 M CH₃COOH + 1 vol.% HF or 1 M CH₃COOH + 1 M H₃PO₄ + 1 vol.% HF at 30 V for 30 min. The barrier films were obtained on both niobium and tantalum surfaces in all electrolyte mixtures except niobium oxide film formed in 1 M CH₃COOH + 1 vol.% HF which is porous in nature. The anodic oxide films were characterized by FESEM. Also, electrochemical impedance spectroscopy at open-circuit potential on Nb and Ta was applied and obtained data were analyzed by fitting with four different equivalent circuits.
2
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Thermoacoustical Excess Properties of Binary Liquid Mixtures - A Comparative Experimental and Theoretical Study

100%
Yasmin M., Singh K., Parveen S., Gupta M., Shukla J.
Acta Physica Polonica A
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2009
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vol. 115
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issue 5
890-900
EN
Specific heat ratio (γ), pseudo-Grüneisen parameter (Γ), heat capacity (C_p) and effective Debye temperature (θ_{D}) for binary system of tetrahydrofuran with o-cresol and methanol respectively, were calculated using the experimentally measured densities, velocities and viscosities of the pure liquids and their mixtures over the whole composition range and at T = 293, 303, 313 K. The excess pseudo-Grüneisen parameter (Γ ^{E}), excess molar isentropic compressibility (K_{s}^{E}) and excess acoustic impedance (Z^{E}) were also calculated. The excess deviation functions have been correlated using Redlich-Kister polynomial equation. The observed values of the excess parameters plotted against the mole fraction of tetrahydrofuran have been explained on the basis of intermolecular interaction suggesting strong interaction in tetrahydrofuran + o-cresol than in tetrahydrofuran + methanol. Partial molar isentropic compressibility at infinite dilution and their excess values were calculated for each component. Sanchez theory, Goldsach-Sarvas volume fraction statistics, Sudgen's relation, Flory-Patterson-Rastogi and Brock and Bird model were used with the Aurebach relation to compute theoretically the values of ultrasonic velocities at varying temperatures. The velocity deviations were estimated in terms of average percentage deviations. Internal pressure for both the systems were calculated theoretically and discussed on the basis of relative applicability of the models in theoretical estimations. The isothermal compressibility (k_T), for these binary mixtures were theoretically evaluated by using the Flory statistical theory and five hard sphere models and compared with the experimental values.
3
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Luminescence Properties of CaAl₂O₄:Eu³⁺, Gd³⁺ Phosphors Synthesized by Combustion Synthesis Method

100%
Verma N., Singh K., Marí B., Mollar M., Jindal J.
Acta Physica Polonica A
|
2017
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vol. 132
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issue 4
1261-1264
EN
CaAl₂O₄:Eu³⁺ (1 mol.%) co-doped with varying concentration of Gd³⁺ (1, 2, 5, and 10 mol.%) were prepared by combustion synthesis method at 600°C and further annealed at 1000°C. All the compositions were investigated for their structural and photoluminescence properties. It was observed that both states of europium i.e. Eu³⁺ and Eu²⁺ were present and ratio of these states changes on heating at 1000°C. The materials synthesized at 600°C showed high intense peak around 440 nm due to presence of Eu²⁺ and less intense peaks in the red region which were due to presence of Eu³⁺. On annealing the compounds at 1000°C, intensity of peak around 440 nm decreases and intensity of peaks in the red region increases significantly. The ⁵D₀ → ⁷F₃ transition due to Eu³⁺ at 657 nm appears as the highest intensity peak. All co-doped samples annealed at 1000°C showed the higher intensity than the mono doped sample which is due to energy transfer from the Gd³⁺ to Eu³⁺. The second rare-earth ion (Gd³⁺) acts as sensitizer and enhances the photoluminescence intensity. The X-ray diffraction spectra reveal the monoclinic phase of CaAl₂O₄ in all the samples which showed that Eu³⁺ and Gd³⁺ do not change the crystalline structure of calcium aluminate.
4
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Molecular Interaction Study of Binary Mixtures of THF with Methanol and o-Cresol - an Optical and Ultrasonic Study

86%
Parveen S., Singh S., Shukla D., Singh K., Gupta M., Shukla J.
Acta Physica Polonica A
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2009
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vol. 116
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issue 6
1011-1017
EN
The refractive indices, densities and ultrasonic velocities of binary liquid mixtures of tetrahydrofuran (THF) with methanol and o-cresol over the entire composition range have been measured at 293, 303 and 313 K. Refractive index, density and ultrasonic velocity data have been used to evaluate the molar refraction deviation ΔR_{m}, deviation in ultrasonic velocity Δu, excess internal pressure π_{i}^{E}, excess molar enthalpy H_{m}^{E} and excess free volume V_{f}^{E}. The computed results of ΔR_{m}, Δu, π_{i}^{E}, H_{m}^{E} and V_{f}^{E} were fitted to the Redlich-Kister polynomial equation. These results suggest that specific strong interactions are taking place in THF + o-cresol mixture while dispersive forces seem to be responsible for behaviour of THF + methanol mixture. Further, experimental refractive index and density data of these mixtures were also used to test the validity of the empirical/semi-empirical relations and models for refractive index and density, respectively.
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