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Abstract: We report the synthesis of a ceria-based catalyst support containing embedded magnetic iron–oxide nanoparticles (IONPs) that enable heating under a high-frequency alternating magnetic field. The ≈11 nm IONPs, synthesized by co-precipitation of Fe2+/Fe3+ ions at room temperature, were coarsened to ≈18 nm through subsequent hydrothermal treatment at 120 ◦C and then coated with a ≈2 nm silica layer. The catalyst support was prepared by depositing nanocrystalline ceria (CeO2) onto the IONPs via controlled precipitation of Ce3+ ions in the presence of hexamethylenetetramine (HMTA) in aqueous suspension. When deposited directly on the iron oxide, ceria formed small agglomerates of ≈10 nm octahedral nanocrystallites, whereas deposition on silicacoated IONPs produced a homogeneous 3–6 nm-thick shell composed of ≈3 nm globular crystallites. Special attention was given to elucidating the mechanism of shell formation. The magnetic catalyst was obtained by precipitating Ru nanoparticles (1–2 nm) onto the ceria support. Morpho-structural characterization was performed by XRD, TEM, and aberration-corrected STEM. Static and dynamic magnetization measurements at room temperature were used to assess the magnetic and heating performance. At low field amplitudes (<15 mT), catalysts prepared with IONPs of both sizes exhibited similar specific absorption rates, whereas at higher amplitudes the larger IONPs demonstrated superior heating efficiency. The catalytic performance was demonstrated in the magnetically heated hydrogenation of the bio-based compound 5-(hydroxymethyl)furfural to 2,5-bis (hydroxymethyl)furan, showing high activity, 100 % selectivity, and excellent stability upon recycling.
Keywords: nanotechnology, catalyst synthesis, ceria, magnetic nanoparticles, catalysis by magnetic heating, biomass valorisation, transmission electron microscopy
Published in DiRROS: 14.01.2026; Views: 25; Downloads: 10
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Keywords: waste glass, porous materials, heating microscope, recycled materials, sintering
Published in DiRROS: 03.10.2025; Views: 452; Downloads: 158
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Abstract: Delivery of electrical energy for sensing or therapeutic purposes often involves electrochemical phenomena at the electrode-electrolyte solution interface. Release of gaseous bubbles that accompanies delivery of pulsed electric fields to tissues in applications such as electrochemotherapy of tumours and irreversible electroporation or pulsed field ablation in cardiac electrophysiology needs to be understood and characterized. We present an in vitro study using pulsed field delivery into saline, employing multiple different treatment protocols, two electrode geometries (pair of needles and a modified RF catheter), and two imaging systems to elucidate the complex relationship between the electrical treatment protocol, temperature changes at and around the electrodes, and gas release due to pulse delivery. Our primary objective was to identify the key parameters responsible for bubble formation and to highlight the importance of the treatment parameters and their interplay – ranging from the temperature to appropriate choice of electrode geometry, and, most importantly, to the choice of the treatment protocol. We found that bubbles originating from electrochemical reactions are more prevalent in monophasic pulsing protocols, whereas in high frequency biphasic pulsing protocols the bubbles are mainly caused by boiling of the medium. Degassing of liquid due to lower solubility of gasses at elevated temperatures does seems to play a role, though a minor one. We also observed that bubbles caused by boiling collapse very rapidly, whereas electrochemically produced bubbles or those produced through degassing appear to have longer lifetimes. Therefore, the treatment protocols most suited to minimizing gas release are biphasic trains of short (▫$\mu$▫s) pulses with a significant inter-pulse delay (i.e. low duty cycle) to prevent excessive heating. Moreover, electrodes must be designed to avoid high local current densities. Our findings have broad implications extending from lab-on-achip cell electroporation devices to intracorporeal pulsed field applications in the cardiovascular system, particularly pulsed field ablation procedures.
Keywords: pulsed field ablation, gas release, electrochemistry, Joule heating, water phase transition
Published in DiRROS: 10.04.2025; Views: 619; Downloads: 341
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Abstract: This research study investigates the effect of different heating and cooling regimes on the effective cross-section of timber elements exposed to natural fires. An advanced calculation method based on a 1D finite-difference heat transfer model and effective thermo-physical properties is adopted to analyse the heat penetration and the consequent reduction in mechanical properties. In particular, the research focuses on the evolution and penetration speed of the char depth (300 ◦C isotherm) and zero-strength layer (determined through in-depth temperatures and reduced mechanical properties). Results reveal how the char depth mainly develops during the heating phase, with non-negligible contributions from the cooling phase. In contrast, the zero-strength layer increases throughout the whole fire exposure, particularly during cooling and, possibly, after the end of the cooling phase. In general, the heating phase contributes about 2/3 to the total effective char depth, while the cooling phase about 1/3. The most challenging conditions were found for the fires of the longest durations (heating and overall), corresponding to low ventilation and high fuel load density conditions. The study emphasises the necessity of incorporating the cooling phase in performance-based methodologies for fire-safe timber structures to avoid under-estimating heat penetration effects.
Keywords: timber structures, fire safety, charring, zero-strength layer, natural fire, heating, cooling, structural fire engineering, performance-based design
Published in DiRROS: 22.11.2024; Views: 866; Downloads: 805
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Abstract: Shallow geothermal energy (SGE) is a renewable energy that could contribute to the decarbonatization of the heating and cooling sector. SGE is predominantly harnessed through ground source heat pump (GSHP) systems. The choice of which type of GSHP system depends on various factors. Understanding these factors is crucial for optimizing the efficiency of GSHP systems and fostering their implementation. In this paper, we have analysed the spatial distribution of GSHPs in Slovenia. We identified 1073 groundwater and 1122 ground-coupled heat pump systems with a total heat pump capacity of almost 30 MW. We quantitatively assessed the influence of geological, hydrogeological, and climate conditions on their spatial distribution. Using the χ2 test and information value method, we identified hydrogeological conditions as the most influential factor for the GSHP systems’ spatial distribution. We also performed the spatial analysis of geological and hydrogeological data in 22 European countries, including Slovenia. We collected the reported numbers of installed GSHP units in 2020 and were able to distinguish the shares of groundwater and ground-coupled heat pump systems for 12 of these countries. The analysis showed that ground-coupled heat pumps predominate in most countries, even if the natural conditions are favourable for groundwater heat pumps.
Keywords: shallow geothermal energy, renewable heating and cooling, ground-source heat pump, spatial distribution, natural condition
Published in DiRROS: 19.03.2024; Views: 1449; Downloads: 465
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