- Pb0.5 + xMg xZr2 – x(PO4)3(x = 0, 0.5) Phosphates: Structure and Thermodynamic Properties
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Abstract—Crystalline Pb0.5 + xMgxZr2 – x(PO4)3 (x = 0, 0.5) phosphates of NaZr2(PO4)3 (NZP) structural type were synthesized. The heat capacity of Pb0.5Zr2(PO4)3 was measured by adiabatic vacuum and differential scanning calorimetry (DSC) within the temperature range 8–660 K. The studied phosphates were found to experience a reversible phase transition in the region 256–426 K. According to the results of Rietveld structural study, this transition occurred due to an increase in disorder of lead cation positions in cavities of the NZP structure. The measurements of PbMg0.5Zr1.5(PO4)3 heat capacity in the temperature range 195–660 K showed that it experienced a similar phase transition at 255–315 K. Based on the measured experimental data, the thermodynamic functions of Pb0.5Zr2(PO4)3, such as Cp 0(T) [H0(T) – H0(0)], S0(T), and [G0(T) – H0(0)] were calculated for the temperature range 0–660 K. The standard formation enthalpy of Pb0.5Zr2(PO4)3 was determined at 298.15 K.
- Asabina, E. A.,Kovalsky, A. M.,Markin, A. V.,Mayorov, P. A.,Pet’kov, V. I.,Smirnova, N. N.
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- Differential thermal analysis under quasi-isothermal, quasi-isobaric conditions (Q-DTA): Part III. Mechanism of congruent and incongruent phase transformations of salt hydrates
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By using the "simultaneous Q-DTA, Q-TG measuring technique" elaborated recently, conditions near to the requirements of thermodynamics can be created, thus the "normalized" course of curves taken by this method, their characteristic temperatures or the va
- Paulik,Bessenyey-Paulik,Walther-Paulik
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- On the photophysics and speciation of actinide ion in MgAl2O4spinel using photoluminescence spectroscopy and first principle calculation: A case study with uranium
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Actinide chemistry is very interesting not from scientific perspective but also from technological importance. Elucidating the valence state and coordinating environment of actinide ion like uranium in technologically important magnesium aluminate spinel (MAS) is important to fully understand its hazardous and other harmful effect in human as well as environment. Magnesium aluminate spinel doped with 1.0?mol % of Uranium ion has been synthesized using citric acid assisted gel-combustion route at 800?°C. The as prepared powder is characterised using X-ray diffraction (XRD), time resolved photoluminescence spectroscopy (TRPLS) and density functional theory (DFT) calculations. Uranium is an interesting element because it exhibits multiple oxidation state and each one of them is having characteristics fluorescence behavior. TRPLS is used to investigate the oxidation state and coordination behavior of uranium in MgAl2O4. Indeed in our earlier work on undoped and lanthanide ion doped MAS; it was oberved that in undoped sample itself defect induced emission could be seen in visible region which was probed using DFT. Here on doping uranium in MAS; complete energy of host is transferred to uranium ion which is explained using DFT. From excitation and emission spectroscopy it was observed that uranium stabilizes in?+6 oxidation state in the form of UO22+ ion. Based on luminescence lifetime and its comparison with the emission profile of uranyl fluoride crystal it was inferred that majority of uranium is occupying relatively asymmetric MgO4polyhedra and minority substitutes AlO6. The site stability of the uranyl ion in MAS was also validated using DFT based first principle calculations. Time resolved emission shows the uranyl at Mg2+site differs from the one at Al3+site in terms of peak position and intensity.
- Gupta, Santosh K.,Pathak, Nimai,Ghosh,Kadam
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- Thermodynamic properties of potassium nitrate-magnesium nitrate compound [2KNO3·Mg(NO3)2]
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The Mg(NO3)2-KNO3 binary system phase diagram has a congruent melting compound, 2KNO3·Mg(NO 3)2. The thermodynamic properties for this compound are not available in the literature. In this study, the nitrate compound was synthesized and the melting point and heat capacity were determined using differential scanning calorimetry (DSC). Two endothermic peaks were observed at 404.8 K and 468.83 K corresponding to solid state transition and melting of the compound with the enthalpies of transitions as 2.71 kJ/mol and 20.73 kJ/mol, respectively. The heat capacity data as function of temperature are fit to polynomial function and thermodynamic properties like enthalpy, entropy and Gibbs energies of the compound as function of temperature are subsequently deduced.
- Reddy, Ramana G.,Wang, Tao,Mantha, Divakar
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- Differential thermal analysis under quasi-isothermal, quasi-isobaric conditions (Q-DTA): Part IV. Latent error in the determination of the decomposition heat of salt hydrates decomposing congruently and incongruently
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The authors disclosed by the simultaneous Q-DTA, Q-TG method a latent, till now not known error in determining the decomposition heat of salt hydrates decomposing congruently or incongruently. This error cannot be shown by the traditional calorimetric or thermoanalytical methods owing to overlapping of the processes taking part in the heat decomposition, it can only be detected and eliminated by applying the simultaneous Q-DTA, Q-TG method of very high resolution and selectivity. A calculation technique is elaborated for the elimination of this error.
- Paulik,Bessenyey-Paulik,Walther-Paulik
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- Synthesis of MgAl2O4 nanopowders
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A procedure has been developed for the synthesis of MgAl2O 4 nanopowders with a characteristic particle size of 10-40 nm. Translucent hydrous xerogels have been synthesized as precursors to MgAl 2O4. The synthesized magnesium aluminum spinel nanopowders are promising for the fabrication of optical ceramics.
- Kuznetsov,Fedorov,Voronov,Osiko
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- Enhancement of upconversion emission and temperature sensing of paramagnetic Gd2Mo3O9: Er3+/Yb3+ phosphor via Li+/Mg2+ co-doping
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Herein, enhancement of upconversion emission and temperature sensing in Li+/Mg2+ co-doped Gd2Mo3O9: Er3+/Yb3+ is reported. The upconversion emission enhancement of 53 and 21 time
- Sinha, Shriya,Mondal, Ashok,Kumar, Kaushal,Swart
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- Preparation of MgO nanoparticles
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MgO nanoparticles have been prepared via hydroxide precipitation from aqueous solutions, followed by the thermal decomposition of the hydroxide. The nanoparticles inherit the platelike shape from the hydroxide and break into isometric particles upon signi
- Fedorov,Tkachenko,Kuznetsov,Voronov,Lavrishchev
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- Lead magnesium niobate-lead titanate fibres by a modified sol-gel method
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Lead magnesium niobate-lead titanate (PMN-PT) ceramic fibres with the nominal composition of 0.65Pb(Mg1/3Nb2/3)O 3-0.35PbTiO3 have been fabricated by a modified sol-gel method. Due to the difficulty of dissolving the magnesium component, the mixed oxide method was used together with the traditional sol-gel method. To obtain crack-free fibres, pyrolysis was carried out at a very slow heating rate under specific atmosphere to control the organic burnout. The thermal and microstructural properties were investigated using thermogravimetric analysis, scanning electron microscopy and X-ray diffraction. The optimum sintering temperature is 1200°C and yields a fibre with a final diameter of around 100 μm. A single PMN-PT fibre has been poled and its electrical properties were measured. The properties of the fibre are found to be better than that of a ceramic disc.
- Lam, Kwok-Ho,Li, Kun,Chan, Helen Lai-Wa
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- Enhanced photoredox chemistry in surface-modified Mg2TiO4 nano-powders with bidentate benzene derivatives
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Magnesium-orthotitanate (Mg2TiO4) nano-powder was synthesized using a Pechini-type polymerized complex route. Microstructural characterization involving transmission electron microscopy, X-ray diffraction analysis and nitrogen adsorption-desorption isotherms indicated that well-crystallized Mg2TiO4 nanoparticles are small in size (about 10 nm) with large specific surface area (72 m2 g-1). The surface modification of Mg2TiO4 nano-powders with 5-amino salicylic acid and catechol induced a significant shift of absorption to the visible spectral region due to charge transfer complex formation. It should be emphasized that tunable optical properties of Mg2TiO4 nano-powders have never been reported in the literature. Degradation reactions of an organic dye (crystal violet) were used to test the photocatalytic ability of pristine and surface-modified Mg2TiO4 nano-powders under illumination in different spectral regions. Excitation with UV light indicated, for the first time, photocatalytic ability of Mg2TiO4. Also, improved photocatalytic performance of surface-modified Mg2TiO4 nano-powders was found in comparison to unmodified ones.
- Medi?, Mina M.,Vasi?, Marija,Zarubica, Aleksandra R.,Trandafilovi?, Lidija V.,Dra?i?, Goran,Drami?anin, Miroslav D.,Nedeljkovi?, Jovan M.
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- Metal-organic phase-change materials for thermal energy storage
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The development of materials that reversibly store high densities of thermal energy is critical to the more efficient and sustainable utilization of energy. Herein, we investigate metal-organic compounds as a new class of solid-liquid phase-change materials (PCMs) for thermal energy storage. Specifically, we show that isostructural series of divalent metal amide complexes featuring extended hydrogen bond networks can undergo tunable, high-enthalpy melting transitions over a wide temperature range. Moreover, these coordination compounds provide a powerful platform to explore the specific factors that contribute to the energy density and entropy of metal-organic PCMs. Through a systematic analysis of the structural and thermochemical properties of these compounds, we investigated the influence of coordination bonds, hydrogen-bond networks, neutral organic ligands, and outer-sphere anions on their phase-change thermodynamics. In particular, we identify the importance of high densities of coordination bonds and hydrogen bonds to achieving a high PCM energy density, and we show how metal-dependent changes to the local coordination environment during melting impact the entropy and enthalpy of metal-organic PCMs. These results highlight the potential of manipulating order-disorder phase transitions in metal-organic materials for thermal energy storage.
- McGillicuddy, Ryan D.,Thapa, Surendra,Wenny, Malia B.,Gonzalez, Miguel I.,Mason, Jarad A.
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supporting information
p. 19170 - 19180
(2020/12/01)
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- Process for the production of mixed alcohols
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A process for producing a mixed alcohol by contacting a synthesis gas with a catalyst, wherein the catalyst is a solid substance prepared by: calcining a mixture of (A) a zinc compound, (B) a compound of at least one metal selected from iron, cobalt,
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- Infrared Spectra and Structure of Solutions of Magnesium Nitrate in Acetonitrile
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Ion solvation and association in acetonitrile solutions of magnesium nitrate have been studied by i.r. spectroscopy.
- Perelygin, I. S.,Klimchuk, M. A.,Beloborodova, N. N.
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p. 1703 - 1705
(2007/10/02)
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