Search results for "synthesis"
showing 10 items of 2844 documents
Enhancement of self-sustaining reaction by mechanical activation: case of an FeSi system
1999
Mechanical high energy ball milling of an Fe2Si elemental powders mixture was used to activate a self sustaining combustion reaction or so-called self-propagating high-temperature synthesis (SHS) to form iron disilicide, a reaction for which the thermodynamic criterion is not favorable. A complete characterization of the milled powders before reaction was performed with energy dispersive X-ray spectrometry, specific surface measurements and X-ray diffraction profile analysis. Thermal and structural information describing the combustion front initiated by heating up a sample to 400°C in a Fe‐Si system is communicated. In order to isolate the phases involved in the gasless reaction, a time-re…
Time-resolved XRD experiments for a fine description of mechanisms induced during reactive sintering
2005
The control of Mechanically Activated Field Activated Pressure Assisted Synthesis hereafter called the MAFAPAS process is the main objective to be achieved for producing nanostructure materials with a controlled consolidation level. Consequently, it was essential to develop characterization tools "in situ" such as the Time Resolved X-ray Diffraction (TRXRD), with an X-ray synchrotron beam (H10, LURE Orsay) coupled to an infrared thermography to study simultaneously structural transformations and thermal evolutions. From the 2003 experiments, we took the opportunity to modify the sample-holder in order to reproduce the better synthesis conditions of the MAFAPAS process, but without the conso…
In situ synchrotron characterization of mechanically activated self-propagating high-temperature synthesis applied in Mo–Si system
1999
Abstract An original experiment was designed to monitor structural and thermal evolutions during the MASHS (Mechanically Activated Self-propagating High-temperature Synthesis) process in the Mo–Si system. Time-Resolved X-Ray Diffraction (TRXRD) coupled with an infrared imaging technique was performed to study, in situ, the formation of the α-MoSi2 phase in the combustion front. Despite a temporal resolution of 50 ms between two consecutive diffractograms, no intermediate phase was observed during the passage of the combustion front. The only reaction responsible for the self-sustentation is Mo+2Si→MoSi2 in the primary zone inside the combustion wave. The mechanical activation was found to i…
Simultaneous IR and time-resolved X-ray diffraction measurements for studying self-sustained reactions.
1998
Self-propagating high-temperature synthesis provides an attractive practical method for producing advanced materials such as ceramics, composites and intermetallics. This kind of reaction has been investigated in situ using time-resolved X-ray diffraction, with an X-ray synchrotron beam (D43 beamline, LURE, Orsay) coupled to simultaneous IR thermography to study structural transformations and thermal evolution. With short acquisition times (30 ms per pattern) it has been possible to observe several steps before obtaining compounds. Two different compound formations have been described: (i) the different steps of reaction, aluminium melting, subsequent temperature increase and fast reaction …
Super resolved optical system for objects with finite sizes using circular gratings
2015
We present a real time all optical super resolution method for exceeding the diffraction limit of an imaging system which has a circular aperture. The resolution improvement is obtained using two fixed circular gratings which are placed in predetermined positions. The circular gratings generate synthetic circular duplications of the aperture, thus they are the proper choice for a circular aperture optical system. The method is applicable for both spatially coherent and incoherent illuminations, as well as for white light illumination. The resolution improvement is achieved by limiting the object field of view. The proposed method is presented analytically, demonstrated via numerical simulat…
Synthesis and comparison of the antiinflammatory activity of manoalide and cacospongionolide B analogues.
1998
We have synthesized analogues of two naturally occurring antiinflammatory marine compounds, manoalide and cacospongionolide B, containing a pyranofuranone moiety which is considered the pharmacophoric group. The two compounds, and hence their analogues, differ in the presence or absence in the dihydropyran ring of an hemiacetal function which was considered essential to irreversibly inactivate phospholipase A 2 (PLA 2 ). The two series of compounds were tested for their inhibitory effects on secretory PLA 2 belonging to the groups I, II, and III, and the activities were found to be similar in both series, irrespective of the presence or absence of the additional hemiacetal function. In addi…
Electrochemical synthesis of 2-arylimino-4,5-di(2-furyl)-1,3-dioxoles and (E)-1,2-di(2-furyl)vinylene bis(N-arylchloroformimidates). HF and B3LYP com…
2009
Abstract Cathodic reductions of 2,2′-furils in the presence of N-arylcarbonimidoyl dichlorides lead to 2-arylimino-4,5-di(2-furyl)-1,3-dioxoles in high yields, along with minor amounts of (E)-1,2-di(2-furyl)vinylene bis(N-arylchloroformimidates). HF and B3LYP density functional theory methods have been applied to the determination of molecular geometries and to study the topomerization mechanism of aryliminodioxoles. The molecular structure of (E)-1,2-di(2-furyl)vinylene bis[N-(2-chloro-4-methylphenyl)chloroformimidate] has been determined by X-ray crystallography and compared with the calculated structure.
Control over the oxidative reactivity of metalloporphyrins. Efficient electrosynthesis of meso,meso-linked zinc porphyrin dimer.
2011
The electrochemical oxidation of zinc(II) 5,15-p-ditolyl-10-phenylporphyrin at its first oxidation potential leads to the formation of the corresponding meso-meso porphyrin dimer as the main product. The number of electrons abstracted, the addition of the hindered base 2,6-lutidine as well as operating in DMF, instead of a CH(2)Cl(2)/CH(3)CN mixture are the key parameters to obtain high yields of the desired coupling product. Indeed, when the electrolyses are carried out in the CH(2)Cl(2)/CH(3)CN mixture, the unexpected zinc(II) 5-chloro-10,20-p-ditolyl-15-phenyl porphyrin is produced as a by-product, the chlorine atom originating from the CH(2)Cl(2) solvent. The monomer and the dimer are c…
Enzymatic esterification of bicyclic meso-diols derived from 1,4-bis(hydroxymethyl)furan. An enantioselective Diels–Alder reaction equivalent
1998
Abstract meso -Diols derived from the Diels–Alder adduct 1,4-bis(hydroxymethyl)furan/dimethyl acetylenedicarboxylate can be enantioselectively monoacetylated under CRL or PSL catalysis with very good yields and moderate to excellent ees. (+)-Monoacetates are always preferentially formed in the reactions catalyzed by CRL, and their (−)-enantiomers are the main products in the acetylations under PSL catalysis. Absolute configurations have been determined by X-ray analysis of a single crystal of an ( R )-α-methoxyphenylacetyl derivative.
Catalytic Enantioselective Addition of Me2Zn to Isatins
2017
Chiral α-hydroxyamide L5 derived from (S)-(+)-mandelic acid catalyzes the enantioselective addition of dimethylzinc to isatins affording the corresponding chiral 3-hydroxy-3-methyl-2-oxindoles with good yields and er up to 90:10. Furthermore, several chemical transformations were performed with the 3-hydroxy-2-oxindoles obtained.