In order to clarify the effect of PbO addition on the formation steps of the superconducting phases in the system Bi2O3−SrO−CaO−CuO, a study of solid-state reactions under non-isothermal conditions, in the PbO−MO (M=Ca, Sr, Ca+Sr) system has been carried out.
Results suggest that the reactivity of the components in the system containing PbO and CaO is much higher than in the system
containing SrO. The Ca2PbO4 compound is formed first even in the system whereM=Ca+Sr. It is confirmed that Ca2PbO4 systems containing PbO.
Authors:Adelina Ianculescu, Ana Brăileanu, M. Crişan, P. Budrugeac, N. Drăgan, G. Voicu, D. Crişan and V. Marinescu
In order to obtain pure and fine BaTiO3
powders with controlled morphology, sol-precipitation methods involving the
use of titanium iso-propoxide and of two different barium sources, i.e. barium
nitrate and barium acetate, were proposed in this work. The thermal behaviour
of the synthesized gels and the X-ray diffraction data obtained for the oxide
powders pointed out that, by using Ba(NO3)2
as barium source, the decomposition process was completed at lower temperature
(750C) and was accompanied by a more pronounced tendency to obtain a
single phase BaTiO3 composition, by comparison with
the synthesis where barium acetate was used as raw material (1100C).
Scanning electron microscopy investigations emphasized the effect of the nature
of barium source and synthesis conditions on the morphology of the oxide powders,
as well as on the microstructure of the related ceramics.
Authors:Ana Brăileanu, M. Răileanu, M. Crişan, D. Crişan, R. Bîrjega, V. Marinescu, J. Madarász and G. Pokol
Two series of nanocomposites
from the FexOy–SiO2
system, containing 20 mass% iron oxide were prepared by the alkoxide route
of the sol–gel method, in the absence and presence of catalyst. The
silica gel has been obtained using tetraethoxysilane. The iron(III) nitrate
nonahydrate has been used as iron oxides source. The samples have been prepared
in identical conditions, differing only by the gelation times, induced by
different surface of evaporation/volume (S/V) ratios of sol let to gelify. Thermal analysis
data have established the thermal treatments conditions of the prepared samples
and were correlated with X-ray diffraction, IR spectroscopy and TEM results,
in order to accomplish a complete structural characterization. The correlation
between the structural modifications of the FexOy–SiO2
nanocomposites and different conditions of drying has been established.
Authors:M. Popa, J. Calderon-Moreno, D. Crisan and M. Zaharescu
This work introduces results obtained during the preparation of a Bi-based material with superconducting properties by oxalate
The influence of Fe presence on the precursors thermal stability and on the superconducting phases formation mechanism are
presented. The thermal decomposition and the stability in air of FeC2O42H2O and also of the components mixture were studied by DTA/TG. It was evidenced that iron oxalate decomposes at the lowest temperature
compared to the decomposition temperatures of the individual oxalates.
XRD, IR and TEM/ED studies were approached to investigate the individual oxalates and the mixture coprecipitates for the high-Tc superconducting material synthesis.
Authors:Ana Braileanu, Maria Zaharescu, D. Crişan and E. Segal
The scientific interest for the Bi2O3-PbO system has increased due to the importance of the PbO in the high-Tc 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.
Authors:A. Brăileanu, M. Zaharescu, D. Crişan and E. Segal
Following our previous research, this work is dedicated to the study of phase formation in the subsolidus domain of the Bi2O3-PbO-CaO system.
Former investigations performed by DTA/TGA and XRD have pointed out that under non-isothermal conditions only the formation
of binary compounds occurs. Under such conditions these compounds could be non-equilibrium phases.
In order to establish the conditions of formation of equilibrium phases, a study of the Bi2O3-PbO-CaO system, in isothermal conditions, was carried out. The results obtained in isothermal conditions have confirmed the
presence of Bi2O3-rich solid solutions and Ca2PbO4 as main equilibrium phases. An attempt to represent the phase relations of the mentioned system at 700C should be equally
Authors:Maria Crişan, Ana Brăileanu, D. Crişan, Mălina Răileanu, N. Drăgan, Diana Mardare, V. Teodorescu, Adelina Ianculescu, Ruxandra Bîrjega and M. Dumitru
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.
Authors:M. Crişan, Ana Brăileanu, M. Răileanu, D. Crişan, V. Teodorescu, R. Bîrjega, V. Marinescu, J. Madarász and G. Pokol
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.
Authors:A. Braileanu, M. Zaharescu, D. CriŞan, D. FĂtu, E. Segal and C. Danciulescu
Former studies concerning the formation of the compounds in the pseudobinary systems of Bi2O3-MO type (M =Ca, Sr, Ca+Sr) have shown that the reaction which occurs with the highest rate is that between Bi2O3 and CaO. In the present work CaCO3 was used as CaO source. We carried out an investigation of the thermal decomposition of CaCO3 in the presence of Bi2O3 in comparison with the decomposition of pure CaCO3.