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Ianculescu A. Braileanu A. Pasuk I. Zaharescu M. 《Journal of Thermal Analysis and Calorimetry》2001,66(2):501-507
In this paper the influence of alkaline-earth admixtures on the synthesis of lanthanum chromites of La1–xMxCrO3 (x=0; 0.3; M=Ca, Sr, Ca+Sr) type was studied.
The formation mechanism as well as the phase composition evolution, under non-isothermal and isothermal conditions, were investigated
by thermal analysis and X-ray diffraction.
The structure of the compounds and of the solid solutions formed depends on the solute type by means of the structural distortion
induced. The crystallinity of the chromites obtained is obviously influenced by both the temperature and the thermal treatment
plateau.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
2.
Dan Donescu Sever Serban Lia Stanciu Ana Braileanu Maria Zaharescu 《Journal of Sol-Gel Science and Technology》2000,19(1-3):839-843
In the present work the sol-gel process in the ternary system VAc-VTES-TEOS was approached. The monomer that ensures the crosslinking of the obtained networks is VTES, which could react with VAc by free-radical polymerisation and with TEOS by hydrolysis-polycondensation. The early stage evolution of the process was monitored by gas chromatography coupled with mass spectrometry (GC-MS). The gels obtained were characterised by IR spectroscopy, DTA/TG analysis and DSC measurements. Important differences in the gelling process and in the properties of the obtained gels could be noticed, related to the presence of VAc and VTES in the reaction mixtures. The investigation allowed to establish the compositions and the experimental conditions in which gels with high degree of crosslinking could be obtained. 相似文献
3.
A. Braileanu M. Zaharescu D. CriŞan D. FĂtu E. Segal C. Danciulescu 《Journal of Thermal Analysis and Calorimetry》1996,47(2):569-575
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.The presence of Bi2O3 exerts a complex influence on the CaCO3 decomposition acting on the nucleation as well as on the diffusion of CO2. The decomposition of the samples with low Bi2O3 content follows the mechanism of a contracting sphere. A change from surface nucleation to bulk nucleation is recorded for higher amounts of Bi2O3. 相似文献
4.
Lavinia P. Curecheriu Liliana Mitoseriu Adelina Ianculescu Ana Braileanu 《Applied Physics A: Materials Science & Processing》2009,97(3):587-594
In the present paper, Pb(Mg1/3Nb2/3)O3 (PMN) ceramics prepared by the columbite method were investigated. The dielectric study indicates typical relaxor properties,
with a frequency dispersion in the range of 200–350 K. The relaxor-to-paraelectric phase transition was evidenced by the continuous
decrease of the local order parameter derived from the permittivity-temperature data. As a result of the critical behavior,
the main Raman modes show anomalies at: (i) ∼150 K; (ii) ∼220 K (i.e. close to the critical temperature reported for the field-induced
ferroelectric state in PMN single crystal); (iii) ∼260 K (i.e. the temperature of the permittivity maximum); (iv) ∼350 K (the
temperature for initiation of the cluster freezing process T
*); (v) ∼620 K (Burns temperature). The frequency split of the doublet at ∼605 and ∼500 cm−1 presents a critical behavior related to the local symmetry lowering and to the structure ordering due to a phase transformation
which takes place below T
*. The tunability in the paraelectric state was interpreted in terms of reorientation of the non-interacting nanopolar clusters
in a double-well potential. The temperature dependence of the nanopolar domain size also shows anomalies in the range of T
*. The size and dynamics of the polar nanodomains is essential in determining the functional properties of the Pb(Mg1/3Nb2/3)O3 relaxor. 相似文献
5.
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. 相似文献
6.
Ana Braileanu Maria Zaharescu D. Crişan E. Segal 《Journal of Thermal Analysis and Calorimetry》1997,49(3):1197-1205
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. 相似文献
7.
Badea Michaela Emandi Ana Marinescu Dana Cristurean Elena Olar Rodica Braileanu Ana Budrugeac P. Segal E. 《Journal of Thermal Analysis and Calorimetry》2003,72(2):525-531
this paper deals with the first investigation concerning the thermal stability of two 1-(2-benzothiazolyl)-3-methyl-4-azo-pyrazil-5-one
derivatives and their Cu(II) coordination compounds of type ((C4H9)4N)2[Cu(L)2]. The thermal decomposition steps were established.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
M. Zaharescu A. Jitianu A. Braileanu J. Madarász G. Pokol 《Journal of Thermal Analysis and Calorimetry》2001,64(2):689-696
It is well known that SiO2 -based inorganic-organic hybrid materials present significant differences due to the organic moieties bound to the inorganic
network and to the preparation conditions.
In the present work the ageing effect on the thermal stability of the SiO2 -based inorganic-organic hybrid materials prepared using tetraethoxysilan (TEOS), triethoxymethylsilan (MTEOS), triethoxyvinylsilan
(VTEOS), tetramethoxysilan (TMOS), trimethoxymethylsilan (MTMOS) and trimethoxyvinylsilan (VTMOS) was studied.
TG/DTA-MS was used to study the decomposition process of the materials. The structural modifications of the materials during
ageing were studied using spectral methods.
The gels obtained starting with more reactive alkoxides, of methoxy-type, present more complex structures and are less stable
during ageing.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
9.
Ianculescu A. Braileanu A. Zaharescu M. Pasuk I. Chirtop E. Popescu C. Segal E. 《Journal of Thermal Analysis and Calorimetry》2001,64(3):1001-1010
It is well known that the manganites-based solid solutions are interesting for their electric and magnetic properties. LaMnO3 exhibits a distorted perovskite structure due to Mn3+ ion, which determines the presence of the Jahn–Teller effect. Replacing La3+ host ions by cations of lower valence leads to the disappearance of this effect and changes the characteristics of these
materials.
Although the formation of manganites-based solid solutions has been intensively studied, there are some unelucidated aspects
concerning their formation mechanism, depending both on the precursors used and on the thermal treatment applied in order
to obtain suitable properties.
In this work the formation mechanism of La0.7M0.3MnO3 (M=Ca, Sr, Ca+Sr in equimolecular mixture) solid solutions, in isothermal and non-isothermal conditions, was studied. For this
purpose XRD, DTA/TG and spectral techniques were used. The solid solutions formation was found to be more dependent on the
Mn-precursors type than the thermal treatment conditions.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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