DSC-measurements show in a simple and convincing manner that the precipitation of the metastableS-phase in an Al-2.1% Cu-1.3% Mg alloy is enhanced in the presence of lattice defects (dislocation loops, helices, dislocations), but is little influenced by pre-existing GPB-zones.
Zusammenfassung DSC-Untersuchungen zeigen auf einfache und überzeugende Weise, da\ die Bildung der metastabilen S-Phase in einer Al-Cu-Mg-Legierung (Al-2.1%, Cu 1.3 %Mg) in Gegenwart von Gitterdefekten (Versetzungsringe, Wendeln, Versetzungen) gesteigert, aber durch vorherige GPB-Zonen nur wenig beeinflu\t wird.
We are greatly indebted to Centre de Recherches de Voreppe S. A. for the preparation of the alloy. 相似文献
The high-field 1H NMR spectra of 1,3-propanesultams (2), 2,4-butanesultams (3) and 2,4-dimethyl-1,3-butadienesultams (6) are reported. Comparison of 2,3 and 6 with 1,3-propanesultone (1) and 2,4-dimethyl-1,3-butadienesultone (5) reveals that the paramagnetic shift induced by the NH group is smaller than that induced by oxygen. NMR spectra at lower temperature show coupling effects with the NH proton. A half-chair conformation was deduced for 2,4-butanesultam from coupling constants and from a conformational analysis based on the R values, but a chair-chair interconversion could not be detected in the temperature range between 210 and 330 K. An unambiguous assignment was carried out for the methyl signals in the spectrum of 5 by homodecoupling experiments. 相似文献
The presence of small GP-zones in an Al-3 wt% Zn solid solution aged at temperatures below 80° is inferred from calorimetric reversion studies, although this composition lies outside the miscibility gap of the accepted phase diagram. The size of the zones is about 1 to 1.5 nm, as measured by high resolution electron microscopy.We are greatly indebted to the research staff in the electron microscopy laboratory of C.E.N.G. (Grenoble, France) for the use of a high resolution electron microscope. 相似文献
Today, plant extracts based on synthetic procedures have drawn consideration over conventional methods like physical and chemical procedures to synthesize nanomaterials. Green synthesis of nanomaterials has become an area of interest because of numerous advantages such as non-hazardous, economical, and feasible methods with a variety of applications in biomedicine, nanotechnology and nano-optoelectronics and as catalysts for various organic transformations. In this research, silver nanoparticles were deposited on the surface of nano-silica spheres by an in-situ reduction of Ag+ ions using an aqueous extract of Thymus kotschyanus aerial parts as a natural reducing and a capping agent. The result recorded from ultraviolet–visible (UV–Vis) spectrometer, Fourier transform infrared spectroscopy (FT-IR), thermal gravimetric analysis, scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDS) and X-ray powder diffraction supports the biosynthesis and characterization of Ag/SiO2 nanoparticles. The results indicated that the average size of Ag/SiO2 nanoparticles is 25–60 nm. The Ag/SiO2 nanoparticles act as an environmentally friendly heterogeneous catalyst in the synthesis of spirooxindoles via the three-component condensation reaction of isatins, activated methylene reagents, and 1,3-dicarbonyl compounds in aqueous media, and the desired products were obtained with yields ranging from 90 to 98%. The catalyst can be recovered easily and used repetitively without significant loss of catalytic activity.
11H-Indeno[1,2-b]quinoxalin-11-ones generated in situ from ninhydrin and various 1,2-phenylenediamines, catalysed by montmorillonite K10 under microwave irradiation, condense with 4-hydroxyproline to produce 11-(1H-pyrrol-1-yl)-11H-indeno[1,2-b]quinoxaline derivatives in good yields. 相似文献
A facile and chemoselective one-pot synthesis of stable phosphorus ylides containing a β-amino group has been developed via reaction of triphenylphosphine, dialkyl acetylenedicarboxylate and 1,2-phenylenediamine in the presence of phenol or 2-aminophenol on its own at ambient temperature. 相似文献
The kinetic study of competitive consecutive reactions presents difficulties owing to the complexity of the mathematical integration of differential equation systems. Many investigators adopted methods using graphs of experimental data to determine the kinetic constants of a reaction. We propose, in this work, a direct determination of these constants based on thermograms recorded with a Calvet conduction microcalorimeter using a computing program which includes numerical integration of differential equation systems, signal convolution with an experimental function of apparatus (to get rid of the inertness of the detector—recorder system) and the optimization of the adopted model parameters. We applied this exploitation process to the alkaline hydrolysis of some diester of diols or dicarboxylic acids in aqueous solution. 相似文献
The cis-configurated isocephem 26 as well as isodethiaoxacephems 21 and 33 were synthesized (Schemes 4 and 5). The key step involves chlorination of the corresponding carbanions of 23, 18 , and 31 with CF3SO2Cl followed by internal alkylation. β-Lactams 3, 21, 26 , and 33 were found to possess biological activity against several pathogenic microorganisms in vitro. Electronic activation of the lactam moiety in isodethiaoxacephem 33 remarkably enhanced its biological activity. 相似文献