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Abstract

The scientific interest for the Bi2O3-PbO system has increased due to the importance of the PbO in the high-T c superconducting phase formation in the Bi2O3-SrO-CaO-CuO system. Also Bi2O3-PbO system contains compounds with some specific semiconductor and dielectric properties and Bi2O3-based solid solutions are well known as high oxygen ion conductors.

Previously, several low melting defined compounds have been identified in the system: 6Bi2O3·PbO; 3Bi2O3·2PbO; 4Bi2O3·5PbO; 4Bi2O3·6PbO and Bi2O3·3PbO.

This work deals with the phase formation and thermal stability of these compounds. Under non-isothermal conditions, in all mixtures regardless of the Bi2O3/PbO ratio, the compound 6Bi2O3·PbO is preferentially formed, followed by the compound 4Bi2O3·5PbO. The formation of the compound 4Bi2O3·6PbO was not confirmed while the formation of the compound Bi2O3

3PbO occurs through a complex mechanism which includes an intermediate step in which a solid solution with the litharge structure was identified. Under isothermal conditions in the same temperature range the tendency to form the stoichiometric compounds increases. All compounds form, decompose and melt at temperatures between 530–780°C.

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Journal of Thermal Analysis and Calorimetry
Authors:
János Madarász
,
Ana Brăileanu
,
Maria Crişan
,
Malina Răileanu
, and
György Pokol

Abstract  

Thermal decomposition of an amorphous precursor for S-doped titania (TiO2) nanopowders, prepared by controlled sol–gel hydrolysis–condensation of titanium(IV) tetraethoxide and thiourea in aqueous ethanol, has been studied up to 800 °C in flowing air. Simultaneous thermogravimetric and differential thermal analysis coupled online with quadrupole mass spectrometer (TG/DTA-MS) and FTIR spectrometric gas cell (TG-FTIR) have been applied for analysis of released gases (EGA) and their evolution dynamics in order to explore and simulate thermal annealing processes of fabrication techniques of the aimed S:TiO2 photocatalysts with photocatalytic activities under visible light. The precursor sample prepared with thiourea, released first water endothermically from room temperature to 190 °C, carbonyl sulfide (COS) from 120 to 240 °C in two stages, ammonia (NH3) from 170 to 350 °C in three steps, and organic mater (probably ether and ethylene) between 140 and 230 °C. The evolution of CO2, H2O and SO2, as oxidation products, occurs between 180 and 240 °C, accompanied by exothermic DTA peaks at 190 and 235 °C. Some small mass gain occurs before the following exothermic heat effect at 500 °C, which is probably due to the simultaneous burning out of residual carbonaceous and sulphureous species, and transformation of amorphous titania into anatase. The oxidative process is accompanied by evolution of CO2 and SO2. Anatase, which formed also in the exothermic peak at 500 °C, mainly keeps its structure, since only 10% of rutile formation is detected below or at 800 °C by XRD. Meanwhile, from 500 °C, a final burning off organics is also indicated by continuous CO2 evolution and small exothermic effects.

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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. Feder
,
Maria Popescu
,
E. Segal
,
N. Dragoe
,
D. Crisan
, and
N. Dragan

The solid-state reaction between SrCO3 and α-FeOOH was investigated by means of thermal analysis, X-ray diffraction, electron microscopy and magnetic measurements. The high reactivity of this mixture is discussed in comparison with that of the mixture of SrCO3 and α-Fe2O3.

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