An eco-friendly tandem tosylation/Ferrier N-glycosylation of amines catalyzed by Er(OTf)3 in 2-MeTHF

Er(OTf)₃ in 2-MeTHF provides a new and eco-friendly process for Ferrier glycosylation of sulfonamides and amino acids with various N-nucleophiles.The stereoselective synthesis of 2,3-unsaturated-N-pseudoglycals was carried out with 3,4,6-tri-O-acetyl-d-glucal and different nucleophiles affording good results in a short time.     

Poly(ε-caprolactone) modified by functional groups: Preparation and chemical–physical investigation

Functionalization of polymers is a particular relevant approach in the field of biodegradable polymers, where modifications are often required to allow these materials to replace more conventional, not biodegradable polymers in a wider range of applications. This article will report on functionalization of poly(ε-caprolactone) with unsaturated monomers bearing either anhydride groups (PCL-g-(MA-GMA)) or tertiary amines (PCL-g-DMAEA), obtained through radical grafting in a Brabender mixer. Crystallization kinetics parameters have been determined with several techniques (rheology, optical microscopy and differential scanning calorimetry) and the results obtained are in good agreement. It was observed that the crystallization rate significantly increases in the case of the modified polymers.     

fs Laser surface nano-structuring of high refractory ceramics to enhance solar radiation absorbance

The surface and structural modification of titanium (Ti) has been explored after the interaction of ultrashort laser pulses with the surface target. The targets were exposed by femtosecond Ti: Sapphire laser pulses in liquid (ethanol) and dry (air) environment. In order to explore the effect of pulse energy, the targets were exposed to 1,000 succeeding pulses for various pulse energies ranging from 200 to 500 μJ for pulse duration of 25 fs. SEM analyses were performed for central as well as the peripheral ablated areas of the target. It was found that in the case of ethanol (both for central and peripheral ablated areas) there is a grain growth along with nanoscale pores and dots when the target was irradiated for 200 μJ. For intermediate energies (300–400 μJ), grains of 1–2 μm with distinct boundaries are formed in the central ablated area. Whereas in the peripheral ablated area, laser-induced periodic surface structures (LIPSS) and globules are grown. For the highest pulse energy (500 μJ), distinct grains are observed for both regions. However, in the peripheral area the grains are of bigger size with cracks along the boundaries. In case of ablation in air, in the center of ablated areas, island-like structures with multiple ablative layer or LIPSS and nanoscale spheres are observed both for lower and intermediate pulse energies. For the highest pulse energy only nanoscale LIPSS could be observed. For ablation in air at the peripheral areas, well-defined, laser-induced periodic surface structures are observed for all pulse energies. Raman spectroscopy reveals that the liquid (ethanol) environment forms the carbonyl compounds with the metal and induces C–C stretching vibration, whereas in case of air, hydroxo complexes are formed. It has been found that surface treatment of Ti with ultrashort (25 fs) laser radiation in ethanol environment allows the growth of particular surface structures in the form of grains and simultaneously induces changes in its chemical composition.     

An Inverse Problem for a Nonlinear Diffusion-Convection Equation

A method for constructing the Dirichlet-to-Neumann map for a nonlinear diffusion-convection equation is presented. The problem is reduced to the solution of a nonlinear integral equation in one independent variable. Existence and uniqueness of the solution may be proven for small times via a contraction mapping technique.     

A new crystal form of the NSAID dexketoprofen

Dexketoprofen [(2S)‐2‐(3‐benzoylphenyl)propanoic acid], C₁₆H₁₄O₃, is the S‐enantiomer of ketoprofen, a nonsteroidal anti‐inflammatory drug (NSAID) that has analgesic, antipyretic and anti‐inflammatory properties, and finds applications for the short‐term treatment of mild to moderate pain. A new crystalline phase of dexketoprofen is reported. Its solid‐state structure was determined by single‐crystal X‐ray diffraction (SCXRD). The molecular structure of the two independent molecules found in the asymmetric unit of this new phase ( DXKP‐β ) were compared to those of the already known crystal form of dexketoprofen ( DXKP‐α ) and with the S‐enantiomer of the racemic compound. The three different conformers of dexketoprofen found in DXKP‐α and DXKP‐β were then investigated by computational methods. The optimized structures are very close to the corresponding starting geometries and do not differ significantly in energy. The crystal packing of DXKP‐β was studied by means of Hirshfeld surface (HS) analysis; interaction energies were also calculated. A comparison with DXKP‐α shows close similarities between the two crystal forms, i.e. in both cases, molecules assemble through the catemer O—H…O synthon of the carboxylic acid stabilized by additional C—H…O contacts and, accordingly, the interaction energies, as well as the contributions to the HS area, are very similar. Finally, the thermal behaviour of the two polymorphs of dexketoprofen was assessed by means of XRD (both from single crystal and microcrystalline powder) and differential scanning calorimetry (DSC); both crystal forms are stable under the experimental conditions adopted (air, 300–350 K for DXKP‐α and 300–340 K DXKP‐β ) and no solid–solid phase transition occurs between the two crystal forms in the investigated temperature range (from 100 K up to ca 350 K).     

Surface modifications of carbide ceramics induced by pulsed laser treatments

It is well known that sintered ceramics are very hard and difficult materials to process and machine by traditional methods. An easy and available solution seems to be a pulsed laser treatment, under appropriate experimental conditions (pulse duration and energy, radiation incidence angle, working atmospheres, etc.). In these experiments, in order to modify the structure and morphology of the surface, polycrystalline sintered SiC substrates were irradiated with an ArF (5=193 nm,h9=6.4 eV,F=30 ns) pulsed laser, at different fluences and at grazing incidence angle. Since it is well known that laser irradiation can produce both a dissociation of surface compounds and a high level of amorphisation (owing to very rapid cooling of melted material) different working atmospheres (Ar or O₂ or CH₄) and substrate heating (~700 °C) have been used, with the aim of confining and controlling any chemical and physical transformation produced by laser-material interaction. Morphological and structural modifications have been studied by SEM/EDAX microscopy. Surface chemistry has been analysed by Raman spectroscopy. Changes in surface roughness have also been quantified by AFM microscopy.     

Analysis of residual stresses in ternary electroconductive composites

Residual stresses in ceramic particle electroconductive composites were investigated by Raman microprobe spectroscopy and X-ray diffraction. The composites were ternary electroconductive ceramics in the system AlN+SiC+(ZrB₂,MoSi₂). Due to the poor definition of the reinforcing phase peaks, only the matrix residual stress could be evaluated by Raman spectroscopy, whilst the residual stress in the reinforcing phase was calculated by the equilibrium conditions. These calculated values were compared with those experimentally obtained by X-ray diffraction. The agreement between Raman and X-ray results was quite satisfactory. The values of residual stress calculated by the composite theory were in good agreement with those measured by Raman and X-ray diffraction for the MoSi₂-containing composite. For the ZrB₂-containing composite, the value calculated by the composite theory falls between the values measured by Raman and X-ray diffraction. PACS 81.05.Je; 87.64.Je; 87.64.Bx     

UV laser ablation of alumina ring faces for mechanical seal applications

Al₂O₃ seal ring faces were treated by KrF excimer laser irradiation. Surface characteristics induced by laser irradiation depend upon laser fluence, the number of laser pulses, the frequency and duration of the laser pulses, the rotation rate of the ring, and the processing atmosphere. Microstructural analyses of the surface and cross section of the laser-processed seal faces showed that, at low fluence (1.8 J/cm²), the surface is covered by scale due to the melting/resolidification processes. At high fluence (7.5 J/cm²), there is no continuous scaling on the surfaces. Material is removed by decomposition/vaporisation and the ablation depth is linearly dependent on the number of pulses; on the surface, a network of microcracks forms. The evolution of surface morphology and roughness is discussed with reference to composition, the microstructure and physical and optical properties of Al₂O₃, and laser processing parameters.     

Surface modification and oxidation kinetics of hot-pressed AlN–SiC–MoSi2 electroconductive ceramic composite

The effects of oxidation on the microstructural modification and on the electrical resistivity and mechanical strength of a hot-pressed AlN–SiC–MoSi₂ electroconductive ceramic composite were studied. The kinetic of the oxidation was also evaluated. After the oxidation at temperatures below 1000 °C samples do not gain weight, due to simultaneous formation of SiO₂ and evaporation of MoO₃ formed by the oxidation of MoSi₂. However, the AlN/SiC matrix disables the “pesting” phenomena and strength degradation, despite the fact that at these temperatures MoSi₂ oxidizes rapidly. At temperatures above 1000 °C, the composite gains weight due to protective mullite layer formation on the surface, that provides a good oxidation resistance for use at higher temperatures. The kinetics of the oxidation follows the parabolic law. The possible rate-controlling mechanism is the diffusion of oxygen through the mullite-rich surface oxide scale.     

On the toughening mechanisms of MoSi<Subscript>2</Subscript> reinforced Si<Subscript>3</Subscript>N<Subscript>4</Subscript> ceramics

The toughness increment occurring in Si₃N₄-based composites due to the addition of MoSi₂ particles was compared to the predictions of theoretical models based on the combination of residual stresses and crack deflection toughening mechanisms. A direct application of theoretical models led to a substantial discrepancy between predicted and observed values. For this reason, the basic parameters of the theoretical models were experimentally evaluated. The residual stresses were assessed by measuring the strain in the reinforcing particles by X-ray diffraction. Moreover, the MoSi₂ interparticle distance was calculated by image analysis and the crack paths were analyzed in order to check the actual extent of crack deflection. The overall toughness increase recalculated as the sum of the newly estimated values of residual stresses and crack deflection contributions, was shown to be in good agreement with the experimental results. PACS 81.05.Je; 81.40.Np