1. Anisotropy limitations in additive manufacturing with material extrusionBenjamin Podmiljšak, Matej Komelj, Anubhav Vishwakarma, Petra Jenuš, Sašo Šturm, Kristina Žužek Rožman, 2026, izvirni znanstveni članek 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: 569; Prenosov: 275
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2. Unravelling the intricacies of micro-nonuniform heating in field-assisted sintering of multiphase metallic microstructuresTomaž Tomše, Benjamin Podmiljšak, Lavinia Scherf, Reto Kessler, Spomenka Kobe, Andraž Kocjan, Sašo Šturm, Kristina Žužek Rožman, 2024, izvirni znanstveni članek 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: 984; Prenosov: 328
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3. A rapid thermal-radiation-assisted sintering strategy for Nd-Fe-B-type magnetsTomaž Tomše, Aljaž Iveković, Andraž Kocjan, Sašo Šturm, Kristina Žužek Rožman, 2024, izvirni znanstveni članek Povzetek: The green transition has spiked demand for high-performance sintered Nd-Fe-B permanent magnets, necessitating advanced powder consolidation technologies to enhance production efficiency. This study explores the rapid sintering methodology for an Nd-Fe-B powder using a radiation-assisted sintering approach. The case study material is an industrially used powder, prepared through strip-casting, hydrogen decrepitation, and jet milling, with a mean particle size of 5.5 µm. The powder is sintered to full density in a modified Spark Plasma Sintering furnace, achieving pressureless conditions and eliminating electrical currents in the sample to preserve grain alignment and prevent decomposition of the hard-magnetic phase. Fully-dense samples are obtained with heating rates ranging from 10 to 200 °C/min and up to 5 minutes of dwell time at 1100 °C. Rapid heating results in grain size and microstructure comparable to conventionally sintered magnets prepared from the same powder, without compromising magnetic performance after post-sinter annealing at 520 °C for 120 minutes. This sintering method contributes to a novel strategy for optimizing magnet production by utilizing efficient thermal-radiation heat transfer. The combination of rapid heating and pressureless sintering drastically reduces heat-up and dwell times, providing a fundamental advantage over slow conventional sintering.
Ključne besede: rapid sintering, finite-element modeling
Objavljeno v DiRROS: 28.03.2025; Ogledov: 1551; Prenosov: 359
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4. IoT electrochemical sensor with integrated ▫$Ni(OH)_2–Ni$▫ nanowires for detecting formaldehyde in tap waterŠpela Trafela, Abhilash Krishnamurthy, Kristina Žagar, Urška Kavčič, Igor Karlovits, Beno Klopčič, Sašo Šturm, Kristina Žužek Rožman, 2023, izvirni znanstveni članek 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: 1934; Prenosov: 1536
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