Study of the effect of Mn and Cu in Fe–Mn–Al–C–Cu alloys by ICEMS and XRD

Experimental analysis of magnetic and structural properties of Fe–Mn–Al–C–Cu alloys with compositions Fe _x Mn_0.915???x Al_0.075C_0.01 (series A) and Fe _x Mn_0.912???x Al_0.075C_0.01Cu_0.003 (series B), 0.500?≤?x?≤?0.800, in steps of 0.050 is presented and discussed. The analysis was performed by integral conversion electrons Mössbauer spectrometry and X-ray diffraction at room temperature. The results suggest, for both series of alloys, that for the highest Mn content, samples exhibit an antiferromagnetic behavior, typical of the FCC or austenite FeMn phase rich in Mn; for those of low Mn content, the coexistence of paramagnetic austenite, typical of the FeMn alloy poor in Mn, a ferromagnetic BCC or ferrite phases can be observed, while for the lowest Mn content, only ferromagnetic (FM) phase tends to prevail. The FM phase is associated to the BCC FeMnAl as was corroborated by X-ray diffraction. The samples with the highest Mn content, the influence of Cu addition is to reduce the mean hyperfine field and to stabilize the antiferromagnetic behavior.     

Olefin Cyclopropanation by Radical Carbene Transfer Reactions Promoted by Cobalt(II)/Porphyrinates: Active‐Metal‐Template Synthesis of [2]Rotaxanes

A Co^II/porphyrinate‐based macrocycle in the presence of a 3,5‐diphenylpyridine axial ligand functions as an endotopic ligand to direct the assembly of [2]rotaxanes from diazo and styrene half‐threads, by radical‐carbene‐transfer reactions, in excellent 95 % yield. The method reported herein applies the active‐metal‐template strategy to include radical‐type activation of ligands by the metal‐template ion during the organometallic process which ultimately yields the mechanical bond. A careful quantitative analysis of the product distribution afforded from the rotaxane self‐assembly reaction shows that the Co^II/porphyrinate subunit is still active after formation of the mechanical bond and, upon coordination of an additional diazo half‐thread derivative, promotes a novel intercomponent C?H insertion reaction to yield a new rotaxane‐like species. This unexpected intercomponent C?H insertion illustrates the distinct reactivity brought to the Co^II/porphyrinate catalyst by the mechanical bond.     

Pore Characterization Methodology by Means of Capillary Sorption Tests

In this study, a methodology is proposed for obtaining information about the porous structure of materials by analysing data supplied by a hydric absorption test. A model of vertical cylindrical pores is used for studying the variation of absorbed mass versus time. The proposed methodology requires an estimation of the numerical interval in which the radius distribution must be calculated and a minimum amount of experimental data. The experimental tests are developed with a system, designed and built in our laboratory, that allows capture the amount of data necessary to use the calculus methodology proposed. This methodology is based on the derivative of normalized mass in relation to the square root of time of the capillary absorption tests. The simplicity and low cost, in many cases, of the capillary absorption tests compared to other experimental techniques such as mercury porosimetry or SEM, make it feasible to design a simple methodology to obtain valuable information about the structure of a porous material, pore size distribution, and tortuosity factor.     

Gas-phase reactions of lithium dimethylaminoborohydride and related species

[reaction: see text] Ab initio and density functional theory (DFT) calculations were used to examine the mechanisms of reduction and amination of chloromethane by lithium dimethylaminoborohydride (LAB) in the gas phase. For comparison, the amination of chloromethane by lithium dimethylamide and the reduction by borane, diborane, and borohydride ions were also examined. The reduction of chloromethane by LAB occurred most readily from a conformation that allowed coordination of the lithium atom to the chloride leaving group, and the most favorable amination pathway occurred by a backside attack of the nitrogen nucleophile on chloromethane.     

A microwave-assisted and heteropolyacids-catalysed cyclocondensation reaction for the synthesis of 4(3H)-quinazolinones

We have investigated a microwave-assisted synthesis of 4(3H)-quinazolinones by condensation of anthranilic acid, orthoesters (or formic acid) and substituted anilines,using Keggin-type heteropolyacids (H(3)PW(12)O(40).13H(2)O, H(4)SiW(12)O(40).13H(2)O,H(4)SiMo(12)O(40).13H(2)O or H(3)PMo(12)O(40).13H(2)O) as catalysts. We found that the the use of H(3)PW(12)O(40).13H(2)O acid coupled to microwave irradiation allows a solvent-free, rapid (approximately 13min) and high-yielding reaction.     

Langmuir-Blodgett films of diazobenzene molecules

Langmuir-Blodgett (LB) films from diazobenzene Sudan III have been investigated using surface potential measurements as a function of number of layers and deposition pressures, with the surface potential data being related to molecular dipole moments obtained from theoretical electronic structure calculations. The surface potential increased with the number of layers for SIII LB films, and then tended to saturate. Results from density functional theory (DFT) and UV-vis spectroscopy indicated that the increase is due to addition of layers with oriented molecular dipoles, with the saturation tendency being attributed to a decrease in the amount of material deposited in each layer. The surface potential increased with the surface pressure used for deposition, probably owing to a higher contribution from the vertical component of the dipole moment as a closer molecular packing, which is associated with decreasing conformational entropy, was reached.     

Electrostatic layer-by-layer deposition and electrochemical characterization of thin films composed of MnO2 nanoparticles in a room-temperature ionic liquid

Thin films of MnO(2) nanoparticles were grown using the layer-by-layer method with poly(diallyldimetylammonium) as the intercalated layer. The film growth was followed by UV-vis, electrochemical quartz crystal microbalance (EQCM), and atomic force microscopy. Linear growth due to electrostatic immobilization of layers was observed up to 30 bilayers, but electrical connectivity was maintained only for 12 MnO(2)/PPDA bilayers. The electrochemical characterization of this film in 1-butyl-2,3-dimethyl-imidazolium (BMMI) bis(trifluoromethanesulfonyl)imide (TFSI) (BMMITFSI) with and without addition of a lithium salt indicated a higher electrochemical response of the nanostructured electrode in the lithium-containing electrolyte. On the basis of EQCM experiments, it was possible to confirm that the charge compensation process is achieved mainly by the TFSI anion at short times (<2 s) and by BMMI and lithium cations at longer times. The fact that large ions like TFSI and BMMI participate in the electroneutrality is attributed to the redox reaction that occurs at the superficial sites and to the high concentration of these species compared to that of lithium cations.     

Ramanspektroskopische Untersuchungen an PCl5 II. Das System PCl5—ZrCl4

Raman spectra of some solid and molten PCl₅–ZrCl₄ mixtures have been recorded. ZrCl₆ ^2– complex ions accompanied by at least one more chlorozirconate species are present in the solid as well as in the melt. The newRaman frequencies are attributed to ZrCl₅ ^–, which fundamentals are given and assignment is proposed to be analogous to TiCl₅ ^–. The presence of ZrCl₆ ^2– and ZrCl₅ ^– can be explained by the equilibrium ZrCl₆ ^2–+PCl₄ ⁺ZrCl₅ ^–+PCl₅.

     

Analysis of geological standards with PIXE and PIGE technioues applications to volcanic rocks

Geological standards are analyzed using PIXE and PIGE techniques. The concentrations of up to 26 elements are determined and compared with those obtained by other methods. PIXE and PIGE techniques are also applied to different volcanic rock samples. Their sensitivity, accuracy, and speed of data collection and reduction, are of great interest in the study of volcanic phenomena.