The Influence of Ag and Ag(In) Alloy on Y–Ba–Cu–O Equilibrium Diagram Around the Y-123 Superconducting Phase

We studied the chemical compatibility of Ag, Ag(In)alloy, Y₂BaCuO₅ (the so-called Y-211 green phase) and YBa₂Cu₃O_7–δ (Y-123) phase in order to check if better grain growth and alignment with minimum contamination were possible during the Y-123melt texturing. We demonstrate that the addition of silver to Y-123 always led to an enhanced texture. The typical microstructure of the composite Y-123 plus Y-211 (that is believed essential for high critical currents in these High Tc superconductors) was not disturbed by addition of silver up to 7.5 wt%, while higher concentrations of metal led to a degradation of the texture. DTA–TG analysis was used to investigate the influence of Ag and Ag(In) alloy on the Y–Ba–Cu–O equilibria around the Y-123 phase. We found a very unexpected thermal behaviour, similar to an eutectic equilibrium, when the silver concentration was increased to35 wt%. We believe that this effect was essentially due to the increasingly higher concentration of silver that could react with the secondary phases present in the melt. This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinetics and mechanism of the addition of 1,3-butadiene to cyclohexa-1,3-diene in the gas phase

The thermal reactions of 1,3-butadiene (BD) with cyclohexa-1,3-diene (CHD) have been studied in a static system between 437 and 526 K. The pressures of BD and CHD were varied from 61 to 397 torr and from 50 to 93 torr, respectively. The percentages of consumed BD and CHD were always kept lower than 14%. The reactions—in the order of importance—are All the reactions are homogeneous and of the first order with respect to the reagents. Their rate constants (in L/mol·s) are given by A thermochemical analysis of a biradical mechanism is in agreement with these results.     

Electron interactions and scaling relations for optical excitations in carbon nanotubes

Recent fluorescence spectroscopy experiments on single wall carbon nanotubes reveal substantial deviations of observed absorption and emission energies from predictions of noninteracting models of the electronic structure. Nonetheless, the data for nearly armchair nanotubes obey a nonlinear scaling relation as a function of the tube radius R. We show that these effects can be understood in a theory of large radius tubes, derived from the theory of two dimensional graphene where the Coulomb interaction leads to a logarithmic correction to the electronic self-energy and marginal Fermi liquid behavior. Interactions on length scales larger than the tube circumference lead to strong self-energy and excitonic effects that compete and nearly cancel so that the observed optical transitions are dominated by the graphene self-energy effects.     

Unconventional reactivity of epichlorohydrin in the presence of triphenylphosphine: isolation of ((1,4-dioxane-2,5-diyl)-bis-(methylene))-bis-(triphenylphosphonium) chloride

Research on Chemical Intermediates - The selective formation of the heterocyclic salt ((1,4-dioxane-2,5-diyl)-bis-(methylene))-bis-(triphenylphosphonium) chloride was observed when epichlorohydrin...     

Nano/microscale order affects the early stages of biofilm formation on metal surfaces

The adhesion of Pseudomonas fluorescens was studied on nano/microengineered surfaces. Results show that these bacteria formed well-defined aggregates on randomly oriented nanosized granular gold substrates. These aggregates consist of aligned ensembles of bacteria, with some of them strongly elongated. This kind of biological structure was not found on ordered engineered surfaces because bacterial alignment and cell-to-cell sticking were hindered. Importantly, differences in cell morphology, length, orientation, and flagellation were observed between bacteria attached on the ordered nano/microstructures and the randomly ordered surfaces. The implications of the results are related to the design of engineered surfaces to enhance (nanostructured filters) or inhibit (medical implants and industrial biofouling) bacterial colonization on the surfaces and to the biocontrol of soil ecosystems.     

Reaction-induced phase separation in polyethersulfone-modified epoxy-amine systems studied by temperature modulated differential scanning calorimetry

In epoxy-amine systems with a thermoplastic additive, the initially homogeneous reaction mixture can change into a multi-phase morphology as a result of the increase in molecular weight or network formation of the curing matrix. Temperature modulated DSC (TMDSC) allows the real-time monitoring of this reaction-induced phase separation. A linear polymerizing epoxy-amine (DGEBA–aniline) and a network-forming epoxy-amine (DGEBA–methylene dianiline), both with an amorphous engineering thermoplastic additive (polyethersulfone, PES), are used to illustrate the effects of phase separation on the signals of the TMDSC experiment. The non-reversing heat flow gives information about the reaction kinetics. The heat capacity signal also contains information about the reaction mechanism in combination with effects induced by the changing morphology and rheology such as phase separation and vitrification. In quasi-isothermal (partial cure) TMDSC experiments, the compositional changes resulting from the proceeding phase separation are shown by distinct stepwise heat capacity decreases. The heat flow phase signal is a sensitive indication of relaxation phenomena accompanying the effects of phase separation and vitrification. Non-isothermal (post-cure) TMDSC experiments provide additional real-time information on further reaction and phase separation, and on the effect of temperature on phase separation, giving support to an LCST phase diagram. They also allow measurement of the thermal properties of the in situ formed multi-phase materials.     

In situ monitoring of reaction-induced phase separation with modulated temperature DSC

A linearly polymerizing and network forming epoxy-amine system, DGEBA-aniline and DGEBA-MDA, respectively, will be modified with 20 wt% and 50 wt% of a high-T_g thermoplastic poly(ether sulphone) (T_g=223°C), respectively, both showing LCST-type demixing behavior. Reaction-induced phase separation (RIPS) in these modified systems is studied using Modulated Temperature DSC (MTDSC) as an in situ tool. Phase separation in the linear system can be probed by vitrification of the PES-rich phase, occurring at a higher conversion than the actual cloud point from light scattering measurements. The negative slope of the cloud point curve in a temperature-conversion-transformation diagram unambiguously shows the LCST-type demixing behavior of this system, while the relation between the composition/glass transition of the PES-rich phase and the cure temperature is responsible for the positive slope of its vitrification line. Phase separation in the network forming system appears as reactivity increases at the cloud point due to the concentration of reactive groups. Different mixture compositions alter the ratio between the rate of phase separation and the rate of reaction, greatly affecting the morphology. Information about this in situ developed structure can be obtained from the heat capacity evolutions in non-isothermal post-cures.     

TMDSC and Dynamic Rheometry,Gelation, Vitrification and Autoacceleration in the Cure of an Unsaturated Polyester Resin

The free radical cross-linking copolymerization of an unsaturated polyester resin with styrene is studied in isothermal conditions using temperature modulated differential scanning calorimetry (TMDSC) and dynamic rheometry. The dynamic rheometry measurements show that gelation occurs at a conversion below 5%, while TMDSC measurements show that an important autoacceleration starts near 60% conversion, giving rise to a maximum cure rate closely before the (partial) vitrification of the system near 80%. This indicates that the autoacceleration is not due to the sharp increase in bulk viscosity at gelation, but rather to a change in molecular mobilities at higher conversion.This revised version was published online in November 2005 with corrections to the Cover Date.     

Operando soft X-ray microscope study of rechargeable Zn–air battery anodes in deep eutectic solvent electrolyte

Zn–air batteries are very promising devices for energy storage at high energy density due to their intrinsic safety, environmental friendliness, and low cost, but still, there are key issues to be solved to get to the industrial scale. One of the unsolved problems is the poor cyclability of batteries based on aqueous solvents that urges to consider nonaqueous solvents. Among different possible options are deep eutectic solvents, which are cost-effective and technologically relatively easy to implement. The present investigation reports for the first time an operando scanning soft X-ray microscope analysis of the Zn behaviour in a choline–chloride/urea deep eutectic solvents electrolyte during the cathodic and anodic phase formation processes taking place in battery charge and discharge, providing a platform for in-depth space–time dependent investigations of the chemistry of crystallites evolving during potential cycling. These operando measurements have been enabled by the construction of a novel wet cell, improving the design and filling protocol of earlier generation cells developed by authors. High-resolution soft X-ray microscope images were acquired in two modes: (a) dynamic mode at a fixed beam energy, allowing to follow morphology evolution under electrochemical control and (b) static mode for selected morphologies representative of characteristic Zn growth and dissolution steps.     

Impact of metalloporphyrin-based porous coordination polymers on catalytic activities for the oxidation of alkylbenzene

Seven metalloporphyrin-based porous coordination polymers: Fe^ш (TZP)Poly ( CP1 ), Co^II (TZP)Poly ( CP2 ), Ni^II (TZP)Poly ( CP3 ), Cu^II (TZP)Poly ( CP4 ), Zn^II (TZP)Poly ( CP5 ), Mn^II (TZP)Poly ( CP6 ), Pb^II (TZP)Poly ( CP7 ) (TZP = 5,10,15,20- tetrakis[4-(2,3,4,5-tetrazolylphenyl)] porphyrin) were prepared and characterized. CP1−CP7 are amorphous aggregation supported with lower crystallinity by scanning electron microscopy, Brunauer−Emmett−Teller and powder X-ray diffraction. These coordination polymers exhibit effective dye scavenging and catalytic activities toward the oxidation of alkylbenzene to ketones and can be reused by filtration with a slight decreasing of catalytic activities. Metal atoms metalloporphyrin polymers have a great influence on the catalytic activities of metalloporphyrin polymers.