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Povzetek: Electrochemical nucleation and growth are traditionally described by classical atom-by-atom deposition models, yet the nanoscale dynamics governing phase formation at electrochemical interfaces remain poorly understood. Here, we directly visualize copper electrodeposition on glassy carbon by combining in situ electrochemical liquid-cell transmission electron microscopy (EC-TEM) with cyclic voltammetry, enabling direct correlation between global electrochemical signals and particle-resolved structural dynamics. Real-time imaging reveals that nanoparticle formation proceeds through a complex interplay of classical and non-classical pathways. Beyond radial and dendritic growth, we observe a range of particle-level processes, including mobility, coalescence, ripening-like mass exchange, and discrete relocation events, reflecting coupled transport and morphological transformation at the nanoscale. Quantitative tracking of individual nanoparticles reveals localized mass-transfer processes, including near one-to-one ripening dynamics and particle–particle interactions that redistribute material without producing a clear signature in the voltammetric response. These findings demonstrate that processes such as ripening, coalescence, and structural rearrangements can proceed without a discernible signature in the global electrochemical response. By bridging in situ nanoscale imaging with electrochemical analysis, this work provides direct mechanistic insight into early-stage electrochemical phase formation and highlights the dynamic nature of metal growth at electrochemical interfaces.
Objavljeno v DiRROS: 02.09.2026; Ogledov: 124; Prenosov: 87
Celotno besedilo (2,82 MB)
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Povzetek: High-entropy alloys (HEAs) offer opportunities to discover new functional materials with combination of properties not reached in other classes of materials. Here we report a detailed investigation of the structure, magnetic and magnetocaloric properties of some high entropy materials in the FeMnNiGeSi quinary system. Our findings indicate the persistence of partial chemical ordering, with transition metal atoms and metalloids preferentially occupying specific crystallographic sites. This ordering is further supported by ab initio total energy calculation. In turn, the magnetic moment - carried out mainly by Fe and Mn - exhibits a strong dependence on the crystallographic sites occupied by these magnetic atoms. By exploring the chemical landscape, we observed highly non-linear magnetic behavior upon Mn doping, resulting in an isothermal entropy change (ΔSm) as high as 35 Jkg−1K−1 in 5 T, while the transition temperature can be tuned in the range from 160 to 263 K, approaching room temperature. These outstanding performances suggest that rare-earth free high entropy materials can rival conventional magnetocaloric materials. Additionally, we find that the first-order magnetostructural transition can evolve into a second-order magnetic transition through chemical tuning. This opens the possibility of discovering similar materials near the boundary between first- and second-order transitions, with vanishing hysteresis - potentially addressing their mechanical instability issue.
Ključne besede: high-entropy alloys, magnetocaloric properties
Objavljeno v DiRROS: 04.06.2026; Ogledov: 275; Prenosov: 315
Celotno besedilo (6,90 MB)
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Povzetek: Achieving anisotropy in additively manufactured composites is essential for high-performance functional materials but remains challenging in fused filament fabrication (FFF). This study investigates a field-assisted FFF approach using strontium hexaferrite (SrFe12O19)–polyphenylene sulfide (PPS) composites, in which particle alignment is induced by processing on top of a high-strength neodymium–iron–boron (Nd–Fe–B) magnet. Two configurations were compared: (i) a continuous setup, where the growing printed material remains in direct contact with the magnet and can act as a flux-guiding core, and (ii) a spacer-based setup, where non-magnetic spacers separate the print from the field source. Structural, functional (magnetic) measurements and finite element simulations (FEMM) were used to quantify the evolution of anisotropy as a function of build height. In the continuous configuration, particle alignment—and thus macroscopic anisotropy—remains high up to about 20 mm, with 0.90, and then gradually declines while still being detectable at 57.5 mm. Spacer-printed samples lose anisotropy much earlier, with approaching isotropic values (∼0.5) beyond 20–25 mm. Simulations reproduce these trends and show that previously deposited material acts as a flux-guiding path, sustaining a predominantly uniaxial field with height. The results define practical limits for static-field alignment in material-extrusion processing and provide geometry-dependent design rules for scalable fabrication of anisotropic ceramic–polymer composites. The findings are relevant for materials and process design in applications where controlled anisotropy is required over centimetre-scale dimensions.
Objavljeno v DiRROS: 11.02.2026; Ogledov: 806; Prenosov: 470
Celotno besedilo (8,61 MB)
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Povzetek: Micro-nonuniform heating in the field-assisted sintering (FAST) of electrically conductive powders has been a topic of discussion in the materials science community. Microstructural specifics, such as neck formation at low consolidation temperatures and density variations, have previously been ascribed to local overheating at the particle-particle contacts due to the Joule effect. However, recent theoretical modelling studies suggest that the very fast diffusion of heat within the micron-sized particles prevents the overheating, thereby challenging the conventional understanding of FAST-related heating effects. To provide a new experimental perspective on the local overheating and underscore its pivotal role in controlling the microstructure formation, we have studied the phase transformations in a Nd-Fe-B-type multiphase metallic powder during FAST. The formation of the α-Fe phase, following the peritectic decomposition of the Nd2Fe14B matrix phase expected at ≈1180 ◦C (TPER), was observed for FAST temperatures (TFAST) below TPER. A correlation between the electric current and the final phase composition, which can only be explained by considering the local overheating effect, was established. We showed that the formation of the α-Fe phase at TFAST < TPER can be mitigated by (i) decreasing the electric current through the sample, which is achieved by lowering the heating rate from 100 to 10 ◦C/min or by using electrically highly conductive pressing tools (WC) and a non-conductive coating (BN), or by (ii) interparticle necking achieved through a thermal pre-treatment of the powder compact that decreases the overall resistance. Our findings emphasize the criticality of the electric current modulation to minimize any undesired phase transformation, paving the way for future developments in rapid, FAST-based strategies aimed at refining the microstructures and tailoring the properties of multiphase metallic materials
Objavljeno v DiRROS: 28.03.2025; Ogledov: 1126; Prenosov: 408
Celotno besedilo (4,68 MB)

Povzetek: Simple, low-cost methods for sensing volatile organic compounds that leave no trace and do not have a detrimental effect on the environment are able to protect communities from the impacts of contaminants in water supplies. This paper reports the development of a portable, autonomous, Internet of Things (IoT) electrochemical sensor for detecting formaldehyde in tap water. The sensor is assembled from electronics, i.e., a custom-designed sensor platform and developed HCHO detection system based on Ni(OH)2–Ni nanowires (NWs) and synthetic-paper-based, screen-printed electrodes (pSPEs). The sensor platform, consisting of the IoT technology, a Wi-Fi communication system, and a miniaturized potentiostat can be easily connected to the Ni(OH)2–Ni NWs and pSPEs via a three-terminal electrode. The custom-made sensor, which has a detection capability of 0.8 µM/24 ppb, was tested for an amperometric determination of the HCHO in deionized (DI) and tap-water-based alkaline electrolytes. This promising concept of an electrochemical IoT sensor that is easy to operate, rapid, and affordable (it is considerably cheaper than any lab-grade potentiostat) could lead to the straightforward detection of HCHO in tap water.
Ključne besede: formaldehyde, electrochemical sensor, nickel, tap water
Objavljeno v DiRROS: 06.06.2023; Ogledov: 2108; Prenosov: 1647
Celotno besedilo (2,65 MB)
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