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Insights on mechanical and morphological metal hydride powder characteristics during hydrogen interaction and stress mitigation strategies for hydrogen storage vessels
No full textInterstitial metal hydride alloys exhibit significant volume changes between the hydrogenated and dehydrogenated states during cycling, resulting in macroscopic stresses in powder beds that must be considered in tank design. Interactions are complex, and these stresses are primarily influenced by the local particle size distribution (PSD) and packing density. This study examines radial expansion forces in vertical storage containers using AB 2 - type hydride alloys and synchrotron-radiation micro-computed tomography (SRμCT). Up to 50 cycles, progressive particle decrepitation occurs, with densification in the lower layers reaching a 91% packing density. This results in local pressures of up to 605 bar in the hydrogenated state. A new empirical equation links packing density to exponentially increasing stress. Experiments have shown that optimized PSDs can reduce stress by up to 45% and increase storage capacity by 87% within the same tank volume
High Granularity Scintillator Tiles for the High Luminosity Upgrade of the CMS Endcap Calorimeter
No full textThe High Granularity Calorimeter (HGCAL) will replace the existing Calorimeter Endcaps of the CMS detector as part of the upgrade program for HL-LHC. Proposed for the High Luminosity era, HGCAL’s design addresses its challenges by taking advantage of the radiation tolerance of silicon sensors and advances in the fields of mechanical and electrical engineering. Two main areas of the calorimeter – the electromagnetic and the hadronic sections – are made up of interchanging layers of dense absorber and active sensor. In addition, each active layer is further divided into smaller segments, making the whole structure a highly granular imaging calorimeter. Active layers of the whole electromagnetic section and part of the hadronic section consist of silicon cells smaller than 1 cm. The rest of the calorimeter is constructed using small scintillator tiles (4 – 30cm) coupled to silicon photo-multipliers – the SiPM-on-tile technology. The two sections make up more than 6 million cells, which are small enough to provide good signal-to-noise ratio throughout the detector’s lifetime. The HGCAL will be operated at -30°C to keep the electronics noise sufficiently low. The fine segmentation provides the ability for reconstruction of narrow jets and pile-up rejection, further aided by the timing capabilities of the silicon sensors. The SiPM-on-tile technology is a cost effective method to achieve high granularity in the region of the detector, where the estimated radiation levels do not exceed a fluence of 8x10 neq/cm. For this region, 280 000 scintillator tiles are being produced, characterized and assembled into the sensitive layer units – tile modules – in the collaborative efforts of US and German institutes. Tile module production is ongoing and estimated to be complete at the end of 2026. In the talk, general design, as well as the status of production of the SiPM-on-tile components will be discussed
RE-doped zinc-silicate glass-ceramics (RE = Ho, Tm, Yb) based on ZnSiO with enhanced photo- and radioluminescence properties
No full textThe photoluminescence and radioluminescence investigation of zinc-silicate glass-ceramics doped with Ho3+ or Tm3+ ions, co-doped with Yb3+ ions, and containing Zn2SiO4 (willemite) crystalline phase are presented. The precursor glasses were prepared by traditional melt-quenching, the glass-ceramics were prepared by controlled heat treatment of the glass. The structure of the resulting glass-ceramics was determined by X-Ray Diffraction and Transmission Electron Microscopy, which confirmed the crystallization of Zn2SiO4. The glass-ceramics were analyzed with respect to the photoluminescence properties of Tm3+ and Ho3+ ions. The glass exhibited typical emissions around 2 μm stemming from the Ho3+ or Tm3+ ions, and the intensity of the emission was increased by up to 350 % for Ho3+/Yb3+ and 280 % for or Tm3+/Yb3+ by the crystallization. The virgin glasses exhibited longest values of lifetime of 1.596 ms for Ho3+/Yb3+-doped samples, and 0.877 ms for Tm3+/Yb3+-doped samples. The crystallization of Zn2SiO4 crystalline phase resulted in radioluminescence around 350 nm after the X-ray excitation. The radioluminescence lifetime of samples containing Zn2SiO4 was approximately 30 ns. Although no obvious interaction between the rare earth ions and Zn2SiO4 was observed, the very fast response makes the materials an interesting choice for scintillation devices
femto-PIXAR: a self-supervised neural network method for reconstructing femtosecond X-ray free electron laser pulses
No full textX-ray free electron lasers (X-FELs) produce ultrafast pulses in a wide range of lasing configurations, supporting a wide variety of scientific applications, including structural biology, materials science, and atomic and molecular physics. Shot-by-shot characterization of the X-FEL pulses is crucial for the analysis of experiments as well as for tuning the X-FEL performance. However, for the weak pulses found in advanced configurations, e.g., those needed for monochromatic, two-pulse studies of quantum materials, there is no current method for reliably resolving pulse profiles. Here, we show that an interpretable neural network (NN) model can reconstruct the individual pulse power profiles for sub-picosecond pulse separation without the need for simulations. Using experimental data from low-signal X-FEL pulse pairs, we demonstrate a NN can learn the pulse characteristics on a shot-by-shot basis when conventional methods fail. This new method enables the characterization of weak pulses—a condition expected to dominate future experimental configurations such as at the Linac Coherent Light Source-II—and opens the door to a wide range of new experiments
Understanding the reaction-induced restructuring of CoO species in silicalite-1 to control selectivity in non-oxidative dehydrogenation of propane
No full textNon-oxidative dehydrogenation of propane (PDH) is an important route for large-scale on purpose propene production. Although cobalt-based catalysts are promising alternatives to currently used platinum- or chromium oxide-based catalysts, their further developments are hindered by the uncertainties related to the kind of the active sites involved in the desired and side reactions. To contribute to closing such a gap, we systematically investigate the role of oxidized CoOx and metallic Co0 species in the PDH reaction over catalysts based in Silicalite-1 with supported CoOx species differing in their redox properties. C3H8 pulse experiments with sub-millisecond and second resolution at pulse sizes of about 13 and 2200 nmol, respectively, combined with in-depth catalyst characterization and PDH tests at different propane conversions enabled us to understand how the reaction-induced reduction of CoOx affects product selectivity. Propane readily reacts with CoOx to yield propene, carbon oxides and water. The formed Co0 species show high activity to coking and cracking reactions. However, if the size of such species is below 2 nm, these undesired reactions are significantly hindered due to the coverage of the active sites by carbon-containing species. The remaining uncovered surface Co0 sites selectively dehydrogenate propane to propene. The best-performing catalyst showed higher activity than a commercial-like K-CrOx/Al2O3 and operated durable in a series of 10 dehydrogenation/regeneration cycles under industrial relevant conditions. The space time yield of propene formation of 0.97 kg·h–1·kgcat–1 was achieved at 550 °C, 52% equilibrium propane conversion and 95% propene selectivity
Pressure-tuning ferroelectric relaxation process in BaFeO
No full textLow-energy ferroelectric photocurrent switches hold promise for optoelectronic devices and digital logic gates. Pressure, a clean and efficient method for microstructure tuning, can significantly affect the polarization photocurrent relaxation process. Upon negative poling, the photocurrent switching in a narrow bandgap ferroelectric BaFeO single crystal from a negative direction to a positive direction during polarization photocurrent relaxation was observed under pressure. Notably, this photocurrent switching time is boosted up by more than ten folds, from 0.2 to 5 GPa, followed by a slow reduction to around 20 GPa. The very low pressure (0.2 GPa) that induces the PPR process and the tuned by slight lattice distortions highlight the feasibility of environmental pressure control of PPR in ferroelectric materials for practical applications. This pressure-induced behavior arises from the coupled effect of the ferroelectric remanent field and micro-ferroelectric domain relaxation process after the external poling electric field is removed. The broad range of switching times under pressure allows one to precisely control the photoelectric switch applications
Increase in the count rates of ground-based cosmic-ray detectors caused by the heliomagnetic disturbance on 5 November 2023
No full textThis letter presents a rare physical phenomenon associated with solar activity, manifesting in anomalies within neutron, electron, and gamma-ray fluxes in the atmosphere. Conventionally, the Earth’s magnetic-field disturbances reduce cosmic-ray intensity reaching the surface.However, a temporary surge in cosmic-ray flux occurs intermittently known as the magnetosphericeffect (ME). Our observations reveal that this effect predominantly induces a count rate increasein particle detectors positioned at middle latitudes on mountaintops. On November 5, 2023, a2–3% increase in neutron monitors at mountain altitudes and up to 5% increase in thin plasticscintillators registering electrons and gamma rays was observed. This flux escalation coincidedwith a southward orientation of the interplanetary magnetic field. Importantly, we present, forthe first time, the energy spectrum of the Magnetospheric Effect observed at two mountaintops:Aragats and Zugspitze. Simulations of low-energy proton interactions in the terrestrial atmosphere affirm the augmentation of low-energy cosmic rays. Protons, typically restricted by thegeomagnetic cutoff, reached the Earth’s atmosphere, generating detectable particle showers onthe Earth’s surface. To sum up, 1) we measure an increase in the count rate of magnetosphericorigin using particle detectors located at mountain altitudes and middle latitudes; 2) for the firsttime, we measured the energy spectra of the particle fluxes during the magnetospheric effect withspectrometers located on Mount Aragats and Zugspitze; 3) particle flux enhancement coincideswith the depletion of the horizontal component of the geomagnetic field; 4) we explain why themagnetospheric effect was observed at mountain altitudes and not at sea level
Praseodymium induced symmetry switching and electrochemical characteristics of LaCoO nanostructures
No full textA comparative study of the crystal structures and electrochemical characteristics of bulk and nanoscale La1-xPrxCoO3 (x = 0, 0.3 and 0.6) perovskites is made using synchrotron x-ray diffraction, cyclic voltammetry, and galvanostatic charge/discharge methods. It is shown that the sol-gel synthesized nano structures and bulk LaCoO3 exhibit different crystal structures, viz., rhombohedral [a = b = 5.4401 Å, c = 13.134 Å (on hexagonal axes), Z = 6, R c] and monoclinic [am = 5.3865 Å, bm = 5.4482 Å, cm = 7.6365 Å, βm = 89.010°, Z = 4, I2/a], respectively. The evidence for CoO6 octahedra distortion in bulk LaCoO3 is also gathered from the three distinct Raman active modes at 518, 646, and 688 cm−1 emerging due to the Jahn-Teller effect, which, in-turn, reduces the crystal symmetry for achieving structure stabilization. This amounts to changes in Co–O bond lengths and Co–O–Co bond angles with promotion of t2g electron to eg level simultaneously for Co3+(3d6) to attain an intermediate spin state (S = 1) or higher. However, Pr-insertion induces phase transition to orthorhombic in both but with space group Pnma in nanostructures and equivalent Pbnm in bulk. The substitution effect on the specific capacitance (C) is opposite in nature, i.e., while ‘C’ decreases from 149 to 12 F/g in nano structures, it increases from 0.4 to 4 F/g in bulk with increase in Pr-content from x=0 to 0.6. A galvanostatic charge-discharge test of pristine nano LaCoO3 performed at a constant scan rate of 50 mVs−1 reveals electrode electrochemical stability by retaining 96 % of specific capacitance ∼82.5 F/g for 2000 cycles at least. The variation in the crystal structure and bond length and/or angle plays a key role in controlling the electrochemical performance of Pr-substituted LaCoO3 perovskites
Fabrication and deformation mechanism analysis of an AlCoCrFeNi/magnesium composite
No full textCompared to traditional ceramic reinforcements, metallic particles have emerged as effective reinforcements for simultaneously enhancing the strength and ductility of magnesium alloys. In this study, a high-entropy alloy (HEA) was introduced as a reinforcement, and a novel magnesium-based composite with 1.5 vol.% AlCoCrFeNi particles was fabricated using the thixomolding technology. The AlCoCrFeNi/AZ91D composite achieves a well-balanced combination of mechanical properties, with a yield strength of 182.8 MPa, an ultimate tensile strength of 280.3 MPa, and an elongation of 6.1 %. The deformation mechanisms of the composite were systematically analyzed through in-situ X-ray diffraction and full-field crystal plasticity (CP) simulation. The results reveal that the AlCoCrFeNi particles effectively bear the applied load throughout the entire deformation process, without cracking or interface debonding. The matrix/particle interface exhibits a distinct nanoscale production layer, which contributes to a strong interfacial bonding. The edges of the AlCoCrFeNi particles adjacent to the magnesium matrix undergo plastic slip, which helps accommodate interface heterogeneous deformation and improve ductility. According to the CP simulation, the von Mises stress in the AlCoCrFeNi particle interior is approximately 700 MPa, while it exceeds 1200 MPa at the edges. Higher stress at the particle interface and the soft interfacial layer fundamentally drive the plastic flow. Furthermore, the AlCoCrFeNi particles experience unidirectional or multidirectional compressive stress, which enhances particle toughness and inhibits cracking. This study proposes a new strategy for developing lightweight metal composites, leveraging the low density of magnesium alloys and the high strength of body-centered cubic HEA reinforcements
Probing the high radiation tolerance of minor actinide selective zirconium phosphonate sorbents
No full textMinor actinide (MA) selective materials that are resistant to radiation are necessary to enable separation of MAs from lanthanides in nuclear wastes. Zirconium(IV) phosphonates (ZrPs) are a class of amorphous coordination polymers with promising applications as a solid-phase sorbent for MA-lanthanide separations. In this study, a zirconium phosphonate sorbent (ZrPTP) that intramolecularly incorporates the MA-selective 2,6-bis(1,2,3-triazol-4-yl)pyridine (PTP) ligand was synthesised and evaluated for radiation tolerance with high energy electron irradiation to doses of 2 MGy. The MA sorption selectivity of ZrPTP before and after irradiation was compared using Am and Eu. ZrPTP demonstrated maintained selectivity for Am over Eu even after a 2 MGy dose. Synchrotron radiation characterisation techniques and solid-state NMR were employed to accurately assess the average local structure before and after irradiation, where minor amounts of Zr–O bonds, aliphatic C–H bonds, and triazole groups were broken, showcasing excellent radiation stability for doses up to 2 MGy. Our results demonstrate the importance of chemistry in ZrP coordination polymers maintaining not only selective separation properties, but also maintaining radiation stability as well