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Structural evolution of ZrV2O7: supercell persistence revealing local and global structure duality
No full textIn the AM2O7 family of negative thermal expansion materials (NTE), evidence of supercell at room temperature was reported following the Völlenke et al. discovery of missed superlattice due to the apparent linearity of the M-O-M bond in GeP2O7. Korthuis et al. and Khosrovani et al. demonstrated it to be true for cubic ZrV2O7 as well. It was concluded that at room temperature, the structure consists of 27 'subcells' with bent M2O7 groups that appear to form a linear configuration due to refinement of averaged position. However, around 100 °C, the transition to the “parent” cell was reported, where the cell volume increases, and the M-O-M angles are constrained by the Pa-3 space group symmetry to be 180°.
We followed structural changes in the ZrV2O7 at high temperatures to demonstrate partial disorder within the crystal, local and global structural duality and supercell persistence at high temperatures. Total scattering measurements and Pair Distribution Function (PDF) analysis revealed that the experimental pattern cannot be fitted with the “parent structure” model, and only the 3×3×3 supercell model can correspond to local and global structures throughout the full 25-700 °C temperature range.
We also show how short and long-range order within the crystal changes when approaching the phase transition, which might indicate the existence of coherent structural domains that evolve between order and disorder with increasing temperature. We further hypothesize how this can be related to the negative thermal expansion mechanism and the interpretation of structure solutions presenting data from high-temperature X-ray absorption fine structure (XAFS) and Transmission Electron Microscopy (TEM) measurements
Simulation of wood pyrolysis with component-based mechanism
No full textThis paper presents a comprehensive fire simulation study that models the pyrolysis process of beech wood using kinetic parameters with the Fire Dynamics Simulator (FDS). The kinetic methodology is based on the application of these kinetic parameters to govern the underlying pyrolysis reactions. The primary objective was to numerically model the pyrolysis process for beech wood using both single-component (single-step, single reaction scheme) and multi-component (single-step, multi-reaction scheme) kinetic reaction schemes. The accuracy of the numerical model was validated by comparing FDS simulation results with experimental data obtained from thermogravimetric analysis (TGA) and cone calorimeter tests. This approach aids in identifying reliable kinetic reaction input parameters for modelling wood fires. A case study was included to demonstrate the implementation of the kinetic reaction schemes. Numerical results from the TGA simulations for the small-scale pure cellulose test using the single-component approach exhibit consistency with the experimental data. Furthermore, the results demonstrated that the multi-component approach more accurately replicates the shape of the experimental curve for beech wood compared to the single-component approach. However, discrepancies in the tail regions of the curves obtained from the FDS simulations showed the need for further improvement in the modelling approach, particularly regarding the exclusion of char oxidation reactions, which needs to be investigated further
Room-Temperature Co-Precipitation Synthesis of Magnetite Nanoparticles and Application as Electrocatalytic Platform for Agricultural Pesticides Sensing in Water
No full textThis work presents a straightforward room-temperature co-precipitation method for the synthesis of magnetite nanoparticles (Fe3O4NPs) and application as electrocatalytic material for the simultaneous determination of diuron (DR) and thiabendazole (TBZ) pesticides in water for the first time. The Fe3O4NPs were synthesized using an aqueous-based approach and immobilized onto a glassy carbon electrode (GCE) surface. Comprehensive characterization using Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray, cyclic voltammetry (CV), and electrochemical impedance spectroscopy have confirmed the successful formation of well-crystallized Fe3O4NPs with an average crystallinity size of 61.62 nm. Electrochemical studies demonstrated strong electrostatic interactions between GCE/Fe3O4NPs and [Ru(NH3)6]3+. The electrochemical behavior of both pesticides were established by CV, while sensing parameters were optimized through differential pulse voltammetry. Under optimal conditions, the sensor achieved detection limits of 0.398 and 0.480 μM for DR and TBZ, respectively, with good selectivity and reproducibility. The practical utility of the sensor was successfully demonstrated through analysis of real water samples, offering a cost-effective solution for environmental monitoring applications
Thermal cycling of YAG infiltration and plasma sprayed coatings as environmental barrier coating on ceramic heat shields for use in hydrogen operating gas turbines
No full textEnvironmental barrier coatings (EBC) are intended to protect alumina ceramic tiles in hot water vapor conditions, enabling gas turbines to operate with higher hydrogen content or even pure hydrogen. For these operating conditions, yttrium aluminum garnet (YAG) promises the highest protection against hydrolysis, which can be applied via atmospheric plasmaspraying (APS). To enhance the protection efficiency, the coating is combined with a prior infiltration of the base material. The obtained design acts as in-depth protection even if the coating exhibits cracks
Temperature-Induced Phase Transitions of Vivianite: In Situ Analysis of a Redox-Driven Crystallization
No full textWe document a solid-state, temperature-dependent (25−700 °C), multistage redox transformation of crystalline ferrous iron phosphate, vivianite (Fe3(PO4)2·8H2O). Under anoxic conditions, vivianite breaks down at T > 250 °C into an anhydrous, amorphous intermediate Fe3(PO4)2 phase, yet the bulk shape and morphology of the starting vivianite crystals were retained. This amorphous intermediate phase remained stable until T > 500 °C, after which a redox-dependent crystallization into two different minerals was observed. Under anoxic conditions, the amorphous ferrous intermediate (Fe3(PO4)2) transformed into the crystalline ferrous phosphate (graftonite, (Fe2+)3(PO4)2), while under oxic conditions it crystallized into a ferric phosphate (rodolicoite, Fe3+PO4). Graftonite formation occurs via an exothermic molar enthalpy (ΔHcryst) of −16.7 ± 0.2 kJ mol−1. Rietveld refinements of the two crystalline endmembers (vivianite and graftonite) revealed a unit cell volume decrease of ∼3.1% during the transformation, which was observed by in situ electron microscopic observations as an overall shrinking of the initial vivianite crystals. Despite volume loss and bubble-like features, the original vivianite shape was preserved, indicating a solid-state pseudomorphic transformation. Ex situ XRD and TEM-EELS analyses confirmed the ferrous-to-ferric oxidation, forming rodolicoite, through changes in the Fe geometry and oxidation state
Weathering Campaigns in the North Sea for an Offshore Power-to-X Project
No full textThe poster contributes to the assessment of corrosivity in offshore atmospheric exposure environments according to DIN EN ISO 9224 for unalloyed steel, zinc, copper and aluminium. Studies on corrosivity from an offshore wind turbine and a distribution platform in the North Sea are presented. The results show that the corrosivity of unalloyed steel is mostly dependent on the altitude of exposure and whether it is inside or outside
Acoustic Ion Manipulation (AIM)
No full textThe precise control of gaseous ions is a cornerstone in ion-based spectrometry and other disciplines such as materials processing. Traditional high-pressure ion optics rely on electrostatic and magnetic fields that often demand the use of intense electric fields, radio frequency activation, complex geometrical arrangements, or partially transmissive grids. Consequently, the efficiencies of such devices tend to be low or they require large footprints, as ion motions under ambient conditions are governed aerodynamically by collisions and fluid dynamics. However, from a different perspective and holistic reasoning, the limitations posed by collisions, aerodynamics, and other factors that hinder ion control in the open-air suggested an innovative direction for ion manipulation.
Our study introduces a novel method that employs low-power standing acoustic waves to effectively manipulate ion beams. We observe that ions distinctively prefer traveling through areas of static pressure within the acoustic field, identified as "nodes." In contrast, neutral gases are unaffected by the acoustic field structure and continue to move along a straight trajectory. We have named this method Acoustic Ion Manipulation (AIM). Initial studies demonstrated selective and efficient manipulations of ion with AIM, including gating, redirection, regional dispersion, and focusing. This technique broadens the scope of ion manipulation strategies at high pressures while enriching our fundamental understanding of ion-acoustic kinetics. The potential applications of this method are vast, promising significant advancements in the fields of analytical chemistry, environmental science, and beyond
Determingpeak tensile residual stresses in laser powder bed fusion using diffraction based analysis
No full textLaser powder bed fusion (PBF-LB) metal additive manufacturing process is well known to generate large residual stresses in a range of alloys due to the complex and localized thermal cycles. In general, these residual stresses are considered deleterious during manufacturing and subsequent service operation. In several alloy classes including austenitic stainless steels and nickel alloys, tensile residual stresses are generated with magnitudes equal to the yield strength of the processed material depending on geometry and process parameters, which can be located at surfaces/subsurface of a built structure. Knowledge of the magnitude and location of these peak tensile residual stresses is crucial for optimizing in-process or post process mitigation strategies, validating process models, and for consideration in structural integrity assessments. Several diffraction-based approaches have been demonstrated to characterize the magnitude and location of the maximum tensile residual stresses. These approaches include laboratory X-ray diffraction with electrolytic layer removal, energy dispersive synchrotron diffraction and neutron diffraction onPBF-LB prisms of several alloys, resolving the position and magnitude of the peak tensile residual stress. This work provides important considerations when determining these peak tensile residual stresses in newly developed alloys,novel processing strategies and when using more standard residual stress analysis methods
Realistische Simulation realer Röntgencomputertomografie-Systeme mit basisqualifizierter Simulationssoftware – CTSimU2
No full textDas Förderprojekt CTSimU2 baute auf den Ergebnissen des Projektes CTSimU auf. Dieses Vorprojekt erarbeitete ein (Basis-)Qualifizierungsframework für Simulationssoftwares zur Anwendung bei der Röntgen-CT für dimensionelle Messungen. Dabei stand die ausreichende physikalische Korrektheit der Durchstrahlungssimulation im Vordergrund. Für die realitätsnahe Simulation einer CT-Anlage in einer Simulationssoftware (Digitales Modell) ist jedoch nicht nur die Korrektheit der Simulationssoftware selbst, sondern auch die Güte der Parametrisierung des realen CT-Systems in der Simulationssoftware entscheidend – dies stellte den Ausgangspunkt dar. Die Parametrisierung eines CT-Systems in einer Simulationssoftware lässt sich in vier Schritte unterteilen: nach der Datenaufnahme am realen CT-System folgt die Auswertung der aufgenommenen Daten für die Generierung allgemeiner Parameterangaben. Als letztes folgte die Übertragung der Parameter in die spezifischen Simulationssoftwares und die Validierung der resultierenden Simulationsparameter. Die Methodik der Datenaufnahme am CT und die Auswertung der Daten wurde in einem Werkzeugkasten allgemein beschrieben. Der dritte Schritt, die Umsetzung der Parameter, war softwarespezifisch und wurde beispielhaft mit den vorhandenen Simulationssoftwares durchgeführt. Die Validierung der Parameter war standardisierbar und konnte durch den entwickelten Test geleistet werden, auf dessen Basis die ausreichend korrekte Simulation einer realen Anlage beurteilt werden konnte. Endresultat des Projektes war ein Richtlinienentwurf (z. B. VDI/VDE 2630) zu diesem Test, der einen informativen Annex zum Stand der Technik bezüglich der Möglichkeiten zur Parameterbestimmung enthält. Mit einer Simulationssoftware, die die Basisqualifizierung aus CTSimU bestanden hat und einen Parameterdatensatz für ein reales CT-System enthält, der den Test aus CTSimU2 bestanden hat, können realistische Simulationen dieses CT-Systems möglich sein