Time-resolved photoelectron spectroscopy to probe ultrafast charge transfer and electron dynamics in solid surface systems and at metal-molecule interfaces

Photoelectron spectroscopy (PES) is a versatile tool, which provides insight into electronic structure and dynamics in condensed matter, surfaces, interfaces and molecules. The history of PES is briefly outlined and illustrated by current developments in the field of time-resolved PES. Our group's research is mostly aimed at studying ultrafast processes and associated lifetimes related to electronic excitation at solid surfaces.     

High-resolution and tandem mass spectrometry--the indispensable tools of the XXI century

Mass spectrometry-based qualitative and quantitative (bio)molecular analysis is a corner stone in the state-of-the-art pipelines in systems biology and environmental sciences. High-resolution and efficient tandem mass spectrometry methods and techniques are the essential analytical capabilities for the in-depth analysis of extremely complex mixtures of (bio)molecules of a very broad dynamic range of concentrations. Here, we briefly review the advantages and limitations of the current mass spectrometry with a focus on resolution, or resolving power, and methods of (bio)molecular fragmentation in the gas phase. We conclude with an outlook that considers possible avenues for further mass spectrometry-based method and technique development, indispensable for advancing the challenging real-life mass spectrometry applications in the XXI century.     

Limitations of quadrature-based moment methods for modeling inhomogeneous polydisperse fluidized powders

Computational fluid dynamics (CFD) is extensively used to investigate the behavior of dense fluidized suspensions. Often modelers assume that these are formed by few solid phases of particles with constant size. But real powders are continuously distributed over the particle size, and their distribution functions change continuously in time and space reflecting the physical and chemical phenomena occurring within the system. To account for this key feature, models have to include a population balance equation (PBE), which needs to be solved in place of or along with the customary fluid dynamic transport equations. The recently developed quadrature method of moments (QMOM) and direct quadrature method of moments (DQMOM) permit to solve PBEs in commercial CFD codes at relatively low computational cost. These methods, however, still need testing in the context of multiphase flows. Investigating a simple problem, namely the dynamics of two inert polydisperse fluidized suspensions initially segregated, we highlight an important limitation of these methods, which fail to properly model diffusion in real space. We explain where the problem originates and comment on a possible way to overcome it. To conclude the work, we discuss some simulations based on the original and revised formulations of the methods, describing how the code numerics affects the results.     

Evidence for Bulk Residual Stress Strengthening in Al2O3/SiC Nanocomposites

The fracture behavior of Al₂O₃/SiC nanocomposites has been studied as a function of the SiC volume fraction and compared to that of the pure Al₂O₃ matrix. A pronounced strengthening effect was only observed for materials with low SiC content (i.e., ≤10 vol%) although no evidence of concurrent toughening was found. Assessment of near-tip crack opening displacement (COD) could not experimentally substantiate significant occurrence of an elastic crack-bridging mechanism, in contrast with a recently proposed literature model. Quantitative fractography analysis indicated that transgranular crack propagation in Al₂O₃/SiC nanocomposites depends on the location of the SiC dispersoids within the matrix texture; the higher the fraction of transgranularly located dispersoids, the more transgranular the fracture mode. Experimental evidence of remarkably high residual stresses arising from thermal dilatation mismatch (upon cooling) between Al₂O₃ and SiC phases were obtained by fluorescence and Raman spectroscopy. A strengthening mechanism is invoked which merely arises from residual stress through strengthening of Al₂O₃ grain boundaries.     

Bulk Crystallization of Glasses Belonging to the Calcia—Zirconia—Silica System by Microwave Energy

This paper reports results that show the effect of microwave absorption on the bulk crystallization of two glasses in the CaO—ZrO₂—SiO₂ system. The glass samples were devitrified using either microwave or conventional heating, to compare the results obtained from the two different techniques. Remarkably different crystallization paths were observed, depending mostly on the composition of the glass. This observation was especially true when microwave heating was used, where the dielectric losses observed in silicate glasses are related to the ZrO₂ content. X-ray diffraction analysis was performed on the powdered samples, to determine the crystalline phases present. The microstructure and microanalysis results of these glass-ceramic compositions are presented and are related to the different ZrO₂ contents.     

An experimental investigation of Fischer–Tropsch synthesis over washcoated metallic structured supports

In principle, the application of monolithic catalysts to the Fischer–Tropsch synthesis can solve many of the problems related to the classical Fischer–Tropsch reactors, in particular concerning the necessity to operate with short diffusion distances and low pressure drops, preferably according to the ideal plug-flow behavior, while still maintaining a reasonable inventory of catalytic material in the reactor volume.The preparation of prototype cobalt-based catalysts, washcoated onto metallic structured supports with different geometries, is described herein, together with the evaluation of the catalytic properties of such systems in the Fischer–Tropsch synthesis at industrially relevant process conditions (220–235 °C, 20 bar, 2.1  mol_H2/mol_CO,  5000 cm³(STP)_CO+H2/h/g_cat). Comparative tests with the same catalyst in the powdered form were also carried out at the same process conditions.It was found that the structured catalysts maintained the activity and the selectivity of the original powdered catalyst, provided that the washcoat thickness is sufficiently thin.     

Crystallization and morphology of the trigonal form in random propene/1-pentene copolymers

The melting and crystallization behaviour of a series of isotactic propene/1-pentene random copolymers, with 1-pentene contents up to 50 mol%, was investigated by DSC and temperature resolved WAXD/SAXS. The role of the 1-pentene comonomer in the development of the trigonal modification (δ-form) of i-PP was studied and the results were compared with those reported in the literature for PP copolymers with 1-hexene. The crystallizing capability of the δ-form, which develops in the composition range between ca. 10 and 50 mol% of 1-pentene content, only slightly decreases with concentration of 1-pentene. This result is correlated with the limits imposed to cell expansion by the crystal density. The crystallinity degree calculated from the deconvolution of the WAXD patterns is in fair agreement with the results of the DSC analysis, from which the value of the melting enthalpy of the perfect i-PP δ-form has been estimated to be around 140 J/g. The crystallization kinetics of the trigonal modification is characterized by a composition-dependent induction time followed by a relatively fast development of structural order. The sharp WAXD reflections combined with the SAXS data suggest that, notwithstanding the intrinsic intrachain structural disorder, thin and wide lamellae characterize the morphology of the δ-form crystallites.     

Casting process and comparison of the properties of adapted load-sensitive magnesium alloys

Magnetic magnesium alloys can be utilized as a load sensitive material, in which the inverse magnetostrictive effect is used in order to measure the actual loads in structural components manufactured from such lightweight sensor alloys. To achieve a material which exhibits magnetic properties, Mg is alloyed with ferromagnetic materials like cobalt or samarium-cobalt. Alloying elements commonly used with Mg are utilized to improve the mechanical properties of these alloys, which however may have a slight negative impact on the magnetic sensitivity. In this work, two separate magnetic Mg alloys are compared, each with properties matched to the opposing requirements: (a) high load sensitivity and (b) satisfactory mechanical properties, respectively. The precipitation behavior of the ferromagnetic constituent Co in Mg together with other alloying elements is shown on the basis of SEM images. In addition, the dissolving behavior of the Co powder during the casting process of a binary Mg–Co alloy is investigated. Cyclic loading tests employing harmonic analyses of eddy current signals are utilized in order to verify the alloys’ sensory properties. The mechanical properties are investigated using tensile tests.