Growth and real time corrosion resistance monitoring of lead decanoate coatings

Lead is very susceptible to corrosion in the presence of organic acids and humidity. A potential countermeasure is to apply a lead carboxylate coating by immersing the metal in a sodium carboxylate solution/suspension. In this work we report on the degree of surface coverage and the corrosion resistance of a lead decanoate Pb(C₁₀)₂ coating as a function of treatment time. Results show that the surface coverage reaches 91% after 15 min and about 100% after 1 h in a 0.05 M sodium decanoate solution. The corrosion resistance, as indicated by electrochemical impedance spectroscopy, continues to increase even after 6 h of immersion. In addition, we show that in the case of planar transport, a diffusion layer of 17 mm thickness exists, wherein the sodium decanoate concentration drops linearly from its bulk value to almost zero at the solid/surface interface.     

Phonon coupling in inelastic atom-surface scattering

Inelastic scattering of a thermal He beam from a LiF surface has been observed in terms of velocity and intensity distributions as a function of scattering angle. The results allow a correlation with theoretical predictions assuming single Rayleigh phonon coupling for both phonon creation and annihilation processes. A marked decrease of inelastic intensities with momentum or energy transfer is demonstrated, which depends strongly on the temperature of the scattering surface.     

Multi-element model for the simulation of inductively coupled plasmas: Effects of helium addition to the central gas stream

A model for an atmospheric pressure inductively coupled plasma (ICP) is developed which allows rather easy extension to a variable number of species and ionisation degrees. This encompasses an easy calculation of transport parameters for mixtures, ionisation and heat capacity. The ICP is modeled in an axisymmetric geometry, taking into account the gas streaming into a flowing ambient gas. A mixture of argon and helium is applied in the injector gas stream as it is often done in laser ablation ICP spectrometry. The results show a strong influence of the added helium on the center of the ICP, which is important for chemical analysis. The length of the central channel is significantly increased and the temperature inside is significantly higher than in the case of pure argon. This means that higher gas volume flow rates can be applied by addition of helium compared to the use of pure argon. This has the advantage that the gas velocity in the transport system towards the ICP can be increased, which allows shorter washout-times. Consequently, shorter measurement times can be achieved, e.g. for spatial mapping analyses in laser ablation ICP spectrometry. Furthermore, the higher temperature and the longer effective plasma length will increase the maximum size of droplets or particles injected into the ICP that are completely evaporated at the detection site. Thus, we expect an increase of the analytical performance of the ICP by helium addition to the injector gas.     

The electrochemical detection of Ru(II) in a methyl methacrylate solution

This article describes the voltammetric behaviour of RuCl₂(PPh₃)₃ in a methyl methacrylate (MMA) solution. Acquiring this type of information is only possible when the ohmic resistance can be kept sufficiently low. Therefore, the conductivity study of pure methyl methacrylate and a tetrabutylammonium tetrafluoroborate (TBABF₄) methyl methacrylate solution has been described as well. Impedance measurements show an increase in conductivity by adding TBABF₄, while a conductometric curve illustrates the presence of ion pairs, triple ions and quadrupoles depending on the TBABF₄ concentration. The conductivity of a 0.1 mol L⁻¹ TBABF₄-MMA solution (formation of charged triple ions) was high enough to perform electrochemical experiments and a calibration curve could be obtained. The ability of obtaining relevant electrochemical data in low conducting media opens up new perspectives, especially for electroanalytical purposes used to monitor polymer reactions, more specific atom transfer radical polymerization (ATRP) reactions. This method employs a redox process with transition metal complexes in which a halogen ion is transferred reversibly between the transition metal and the polymer chain end. The dynamic equilibrium can be monitored by measuring the ruthenium concentration.     

Hybrid Monte Carlo — Fluid model for studying the effects of nitrogen addition to argon glow discharges

A computer model is developed for describing argon/nitrogen glow discharges. The species taken into account in the model include electrons, Ar atoms in the ground state and in the 4s metastable levels, N₂ molecules in the ground state and in six different electronically excited levels, N atoms, Ar⁺ ions, N⁺, N₂⁺, N₃⁺ and N₄⁺ ions. The fast electrons are simulated with a Monte Carlo model, whereas all other species are treated in a fluid model. 74 different chemical reactions are considered in the model. The calculation results include the densities of all the different plasma species, as well as information on their production and loss processes. The effect of different N₂ additions, in the range between 0.1 and 10%, is investigated.     

Theoretical simulation and experimental validation of inverse quasi-one-dimensional steady and unsteady glottal flow models

In physical modeling of phonation, the pressure drop along the glottal constriction is classically assessed with the glottal geometry and the subglottal pressure as known input parameters. Application of physical modeling to study phonation abnormalities and pathologies requires input parameters related to in vivo measurable quantities commonly corresponding to the physical model output parameters. Therefore, the current research presents the inversion of some popular simplified flow models in order to estimate the subglottal pressure, the glottal constriction area, or the separation coefficient inherent to the simplified flow modeling for steady and unsteady flow conditions. The inverse models are firstly validated against direct simulations and secondly against in vitro measurements performed for different configurations of rigid vocal fold replicas mounted in a suitable experimental setup. The influence of the pressure corrections related to viscosity and flow unsteadiness on the flow modeling is quantified. The inversion of one-dimensional glottal flow models including the major viscous effects can predict the main flow quantities with respect to the in vitro measurements. However, the inverse model accuracy is strongly dependent on the pertinence of the direct flow modeling. The choice of the separation coefficient is preponderant to obtain pressure predictions relevant to the experimental data.     

Microstructural characterisation of five simulated archaeological copper alloys using light microscopy, scanning electron microscopy, energy dispersive X-ray microanalysis and secondary ion mass spectrometry

This paper describes the microstructural characterisation of five simulated archaeological copper alloys, produced by modern powder technology. The chemical composition of the examined bronzes covers the major families of archaeological bronzes from antiquity until the Roman period. Light microscopy (LM), energy dispersive X-ray microanalysis (EDX), scanning electron microscopy (SEM) as well as two- and three-dimensional secondary ion mass spectrometry (SIMS) have been used to describe the main properties of the alloys. The results show a heterogeneous microstructure on a micrometer scale, formed by metallic and non-metallic phases. The latter are conglomerates of oxides or sulphides of major or minor elements.     

PHOTOPHYSICAL BEHAVIOUR OF NEW PYRROLOCOUMARIN DERIVATIVES

Abstract— The photophysical behaviour of new pyrrolocoumarins with different substituents on the nitrogen are reported. The photophysical properties of these pyrrolocoumarins are generally in agreement with those of the psoralens: a strong absorption (240–400 nm), a weak fluorescence (400–680 nm) characterized by a short singlet lifetime, and a rather strong phosphorescence at 77 K (480–600 nm). The absorption and fluorescence properties were investigated in several solvents. The shift of the fluorescence maximum is interpreted on the basis of the solvatochromic parameters π*, α and β. The triplet-triplet absorption spectra also depend on the nature of the solvent, while the triplet excited state has a lifetime of a few microseconds at room temperature (concentration 2.5 × 10⁻⁴ M ). Some absorption and fluorescence characteristics of the 4',5'-dihydropyrrolocoumarins, which are suitable models for the 4',5'-monoadducts to pyrrolocoumarins are reported.