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Journal of Thermal Analysis and Calorimetry
Authors: Alessandra Bianco, Ilaria Cacciotti, Mariangela Lombardi, Laura Montanaro, and G. Gusmano

Abstract  

Hydroxyapatite (HA) nanopowders were synthesised following two different precipitation routes: (a) from calcium nitrate and diammonium hydrogen phosphate solutions and (b) from calcium hydroxide suspension and phosphoric acid solution. The influence of precipitation process, concentration, and synthesis temperature on HA particle size and morphology, phase composition, thermal stability, and sintering behaviour was investigated by means of: thermogravimetry and differential thermal analysis (TG-DTA), induced coupled plasma–atomic emission spectroscopy (ICP-AES), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), electron microscopy (TEM, SEM) and dilatometry.

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Lithium cobaltate LiCoO 2 and Li-Mn oxides nanopowders are synthesized by plasma chemical method in RF-IC plasma flow. Plasma forming gases are air or nitrogen, additionally air is used as oxidizing and quenching gas. As-synthesized and annealed in air nanopowders are investigated by powder XRD, BET, DTA/TGA, SEM, TEM methods and wet chemical analysis; lattice parameters are estimated by the programme SCANIX. Evaporation of initial powder mixtures Li 2 CO 3 +Co with Li/Co molar ratio 1:1 or Li 2 CO 3 +(Mn 2 O 3 +MnO 2 ) with various Li/Mn molar ratios, subsequent quenching and condensation of products results in obtaining of nanopowders with SSA of 13-23 m 2 /g and average particle size of 67-95 nm. After synthesis nanopowders contain admixtures of lithium nitrate hydrate LiNO 3 ·nH 2 O by-phase because of plasma flow composition and air environment. After heat-treating at 600-1000°C pure LiCoO 2 , LiMn 2 O 4 spinel, Li 2 MnO 3 , LiMn 2 O 4 +Li 2 MnO 3 are formed with good crystallinity and average particle size of 70-240 nm. Prepared nanopowders can be applied as cathode materials for Li-ion batteries with appropriate electrochemical properties for high discharge rate.

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Abstract  

Aluminum (Al) nanopowders with mean diameter of about 50 nm and passivated by alumina (Al2O3) coatings were prepared by an evaporation route: laser heating evaporation. Thermal properties of the nanopowders were investigated by simultaneous thermogravimetric-differential thermal analysis (TG-DTA) in dry oxygen environment, using a series of heating rates (5, 10, 20, 30, 50 and 90°C min−1) from room temperature to 1200°C. With the heating rates rise, the onset and peak temperatures of the oxidation rise, and the conversion degree of Al to Al2O3 varies. However, the specific heat release keeps relatively invariant and has an average value of 18.1 kJ g−1. So the specific heat release is the intrinsic characteristic of Al nanopowders, which can represent the ability of energy release.

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Journal of Thermal Analysis and Calorimetry
Authors: M. Crişan, Ana Brăileanu, M. Răileanu, D. Crişan, V. Teodorescu, R. Bîrjega, V. Marinescu, J. Madarász, and G. Pokol

Abstract  

Pure TiO2 and S-doped TiO2 sol–gel nanopowders were prepared by controlled hydrolysis-condensation of titanium alkoxides. The influence of different Ti-alkoxides (tetraethyl-, tetraisopropyl- and tetrabutyl-orthotitanate) used in obtaining TiO2 porous materials in similar conditions (water/alkoxide ratio, solvent/alkoxide ratio, pH and temperature of reaction) has been investigated. The relationship between the synthesis conditions and the properties of titania nanosized powders, such as thermal stability, phase composition, crystallinity, morphology and size of particles, BET surface area and the influence of dopant was investigated. The nature of the alkyl group strongly influences the main characteristics of the obtained oxide powders, fact which is pointed out by thermal analysis, X-ray diffraction, TEM and BET surface area measurements.

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Journal of Thermal Analysis and Calorimetry
Authors: Konstantin Gavrichev, Mikhail Ryumin, Alexander Tyurin, Andrey Khoroshilov, Larisa Mezentseva, Alexander Osipov, Valeriy Ugolkov, and Viktor Gusarov

Abstract  

Thermal behavior of LaPO4·nH2O and NdPO4·nH2O nanopowders from room temperature to 973 K was investigated by DSC, TA/DTG, ESM, and X-ray study. Mass loss due to the release of adsorbed and hydrate water was found in the range from 323 to 623 K. Phase transitions from hexagonal structure nanopowders to monoclinic one for bulk specimens were found above 873 K.

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Summary The size effect on the crystal structure including the chemical bonding nature has been investigated for several kinds of BaTiO3 nanopowder with the particle sizes down to 50 nm in diameter, by means of powder diffraction using high-energy synchrotron radiation. The Rietveld refinement reveals that the BaTiO3 nanopowder consists of tetragonal and cubic structure components at 300 K. The feature of coexistence can be illustrated by the core/shell model for the particle, in which the shell with a cubic structure covers the core with a tetragonal structure. The thickness of the cubic shell is almost constant irrespective of the particle sizes, and is estimated as approximately 8 nm. Hence, the critical particle-size, where the entire particle is covered with the cubic shell, is suggested as 16 nm. The charge density distributions of the BaTiO3 nanopowder in the cubic phase at 410 K are revealed by the maximum entropy method. Changes in the bonding electron density and the ionic valence expected are not observed clearly even in the 50 nm crystal compared with the bulk crystal.

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Journal of Thermal Analysis and Calorimetry
Authors: Maria Crişan, Ana Brăileanu, D. Crişan, Mălina Răileanu, N. Drăgan, Diana Mardare, V. Teodorescu, Adelina Ianculescu, Ruxandra Bîrjega, and M. Dumitru

Abstract  

Among the great number of sol-gel materials prepared, TiO2 holds one of the most important places due to its photocatalytic properties, both in the case of powders and coatings. Impurity doping is one of the typical approaches to extend the spectral response of a wide band gap semiconductor to visible light. This work has studied some un-doped and Pd-doped sol-gel TiO2 nanopowders, presenting various surface morphologies and structures. The obtained powders have been embedded in vitreous TiO2 matrices and the corresponding coatings have been prepared by dipping procedure, on glass substrates. The relationship between the synthesis conditions and the properties of titania nanosized materials, such as thermal stability, phase composition, crystallinity, morphology and size of particles, and the influence of dopant was investigated. The influence of Pd on TiO2 crystallization both for supported and unsupported materials was studied (lattice parameters, crystallite sizes, internal strains). The hydrophilic properties of the films were also connected with their structure, composition and surface morphology. The methods used for the characterization of the materials have been: simultaneous thermogravimetry and differential thermal analysis, powder X-ray diffraction, electron microscopy (TEM, SAED) and AFM.

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Journal of Thermal Analysis and Calorimetry
Authors: M. Bernardi, E. Antonelli, A. Lourenço, C. Feitosa, L. Maia, and A. Hernandes

Abstract  

The results reported here based on a study of BaTi1–xZrxO3 (x=0, 0.2 and 1) nanometric powders prepared by the modified Pechini method. The powder samples annealed from 600 to 1000C/2 h were characterized by thermogravimetric analysis (TG), differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The decomposition reactions of resins were studied using thermal analysis measurements. The barium titanate zirconate system presented just one orthorhombic phase. Furthermore, this study produced BaTiO3 powders with a tetragonal structure using shorter heat treatments and less expensive precursor materials than those required by the traditional methods.

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), isopropanol ( i PrOH, Merck), diethanolamine (DEA, Merck) and hydrochloric acid (HCl, Merck). All materials were used as received without further purification. TiO 2 nanopowder (Degussa P-25), containing 70 % anatase and 30 % rutile, was obtained from Degussa

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– 10724 . [4] Fu C. , Huo , M. , Cai , W. , Deng X. ( 2012 ) Preparation of bismuth ferrite nanopowders at different calcination temperatures

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