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41.
Adelina Ianculescu Ana Brăileanu M. Crişan P. Budrugeac N. Drăgan G. Voicu D. Crişan V. E. Marinescu 《Journal of Thermal Analysis and Calorimetry》2007,88(1):251-260
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
(750°C) 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 (1100°C).
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. 相似文献
42.
43.
Fluorous gallic acid derivatives as versatile gelators. Self-assembly into nanosized fibers or balls
A new class of low molecular mass organogelators, the fluorous derivatives of gallic acid 1–3, is described. The gelation properties have been examined in a large variety of organic liquids. The corresponding analogs possessing alkyl instead of semiperfluoroalkyl chains (4–6) do not display any gelation properties, thus revealing the key role of perfluorinated chains in the aggregation/gelation process. Gels have been studied by scanning electron microscopy, revealing the presence of three-dimensional networks of nanosized fibers. In the case of an instable gel, SEM images showed that these elongated fibers curl up into nanoballs, failing to create the entangled network responsible for solvent entrapment. 相似文献
44.
A new compact near-field desktop-sized diode laser thermal-lens microscope for analysis in microfluidics was proposed. A novel beam-alignment and detection systems provided high signal stability and, along with reduced number of optical elements rendered the instrument portable. The detection of nonfluorescent model species (Fe(II)-bathophenanthroline chelate) in water showed good linearity in the range of 5 × 10(-9) to 1 × 10(-4) M, and the limit of detection was 3.5 × 10(-9) M, which corresponded to 3.5 × 10(-7) absorbance units and provided a 20-fold enhancement in sensitivity compared with existing schematic. 相似文献
45.
N. Glvez M. Moreno‐Maas R. M. Sebastin N. Serra E. Trepat A. Vallribera E. Molins 《Journal of heterocyclic chemistry》2000,37(4):895-905
Diastereoselective alkylations of acetoacetates of chiral inductors are reviewed. The formed products are starting materials for the preparation of enantiomerically pure amino acids, 4,4‐disub‐stituted 2‐pyrazolin‐5‐ones, and of oxazoles and pyrazoles incorporating the chiral inductors. 相似文献
46.
Michele Karoline Lima Daniela Martins Fernandes Marcela Fernandes Silva Mauro Luciano Baesso Antonio Medina Neto Gutierrez Rodriguês de Morais Celso Vataru Nakamura Angelo de Oliveira Caleare Ana Adelina Winkler Hechenleitner Edgardo Alfonso Gómez Pineda 《Journal of Sol-Gel Science and Technology》2014,72(2):301-309
Pure and Co-doped ZnO nanoparticles were synthesized with different cobalt levels (1–10 mol%) via adapted sol–gel method using water as solvent and characterized by X-ray diffraction, transmission electron microscopy, Raman spectroscopy and photoacoustic absorption spectroscopy. The results showed that all the samples have hexagonal wurtzite structure, with no evidence of any secondary phases until 10 mol% of the dopant. The average crystallite size of the samples was in the range of 25–50 nm, do not showing significant differences with the increase of the dopant level. However, the band gap energy of the nanoparticles decreases from 2.98 eV (pure ZnO) to 1.95 eV (10 mol% of Co). The photocatalytic activity of the samples was evaluated on the removal of methylene blue under visible light irradiation, which revealed an efficiency reduction by Co-doping ZnO. The antibacterial property was carried out indicating activity of the prepared samples against gram-positive bacteria. 相似文献
47.
An Alternative to the Classical α‐Arylation: The Transfer of an Intact 2‐Iodoaryl from ArI(O2CCF3)2 下载免费PDF全文
Dr. Zhiyu Jia Dr. Erik Gálvez Prof. Dr. Rosa María Sebastián Prof. Dr. Roser Pleixats Dr. Ángel Álvarez‐Larena Dr. Eddy Martin Prof. Dr. Adelina Vallribera Dr. Alexandr Shafir 《Angewandte Chemie (International ed. in English)》2014,53(42):11298-11301
The α‐arylation of carbonyl compounds is generally accomplished under basic conditions, both under metal catalysis and via aryl transfer from the diaryl λ3‐iodanes. Here, we describe an alternative metal‐free α‐arylation using ArI(O2CCF3)2 as the source of a 2‐iodoaryl group. The reaction is applicable to activated ketones, such as α‐cyanoketones, and works with substituted aryliodanes. This formal C? H functionalization reaction is thought to proceed through a [3,3] rearrangement of an iodonium enolate. The final α‐(2‐iodoaryl)ketones are versatile synthetic building blocks. 相似文献
48.
Marilene Elisa do Nascimento Patrícia Benedini Martelli Clascídia Aparecida Furtado Adelina P. Santos Luiz Fernando Cappa de Oliveira Honória de Fátima Gorgulho 《Mikrochimica acta》2011,173(3-4):485-493
A new composite electrode is described for anodic stripping voltammetry determination of Pb(II) at trace level in aqueous solution. The electrode is based on the use of multiwalled carbon nanotubes and Amberlite IR-120. The anodic stripping voltammograms depend, to a large extent, on the composition of the modified electrode and the preconcentration conditions. Under optimum conditions, the anodic peak current at around ?0.57 V is linearly related to the concentration of Pb(II) in the range from 9.6?×?10?8 to 1.7?×?10?6 mol L?1 (R?=?0.998). The detection limit is 2.1?×?10?8 mol L?1, and the relative standard deviation (RSD) at 0.24?×?10?6 mol L?1 is 1.7% (n?=?6). The modified electrode was applied to the determination of Pb(II) using the standard addition method; the results showed average relative recoveries of 95% for the samples analysed. Figure
A new composite electrode is described for anodic stripping voltammetry determination of Pb(II) at trace level in aqueous solution. The electrode is based on the use of MWCNT and Amberlite IR-120. The method showed a good linearity for 9.6?×?10?8 - 1.7?×?10?6 mol L?1 and detection limit of 2.1?×?10?8 mol L?1. 相似文献
49.
Feitosa E Alves FR Niemiec A Real Oliveira ME Castanheira EM Baptista AL 《Langmuir : the ACS journal of surfaces and colloids》2006,22(8):3579-3585
The thermotropic phase behavior of cationic liposomes in mixtures of two of the most investigated liposome-forming double-chain lipids, dioctadecyldimethylammonium bromide (DODAB) and didodecyldimethylammonium bromide (DDAB), was investigated by differential scanning calorimetry (DSC), turbidity, and Nile Red fluorescence. The dispersions were investigated at 1.0 mM total surfactant concentration and varying DODAB and DDAB concentrations. The gel to liquid-crystalline phase transition temperatures (Tm) of neat DDAB and DODAB in aqueous dispersions are around 16 and 43 degrees C, respectively, and we aim to investigate the Tm behavior for mixtures of these cationic lipids. Overall, DDAB reduces the Tm of DODAB, the transition temperature depending on the DDAB content, but the Tm of DDAB is roughly independent of the DODAB concentration. Both DSC and fluorescence measurements show that, within the mixture, at room temperature (ca. 22 degrees C), the DDAB-rich liposomes are in the liquid-crystalline state, whereas the DODAB-rich liposomes are in the gel state. DSC results point to a higher affinity of DDAB for DODAB liposomes than the reverse, resulting in two populations of mixed DDAB/DODAB liposomes with distinctive phase behavior. Fluorescence measurements also show that the presence of a small amount of DODAB in DDAB-rich liposomes causes a pronounced effect in Nile Red emission, due to the increase in liposome size, as inferred from turbidity results. 相似文献
50.
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