Polyaniline (PANI) is a conducting polymer, widely used in gas-sensing applications. Due to its classification as a semiconductor, PANI is also used to detect reducing ammonia gas (NH
), which is a ...well-known and studied topic. However, easier, cheaper and more straightforward procedures for sensor fabrication are still the subject of much research. In the presented work, we describe a novel, more controllable, synthesis approach to creating NH
PANI-based receptor elements. The PANI was electrochemically deposited via cyclic voltammetry (CV) on screen-printed electrodes (SPEs). The morphology, composition and surface of the deposited PANI layer on the Au electrode were characterised with electron microscopy, Fourier-transform infrared spectroscopy and profilometry. Prior to the gas-chamber measurement, the SPE was suitably modified by Au sputtering the individual connections between the three-electrode system, thus showing a feasible way of converting a conventional three-electrode electrochemical SPE system into a two-electrode NH
-gas detecting system. The feasibility of the gas measurements' characterisation was improved using the gas analyser. The gas-sensing ability of the PANI-Au-SPE was studied in the range 32-1100 ppb of NH
, and the sensor performed well in terms of repeatability, reproducibility and sensitivity.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
A sustainable solution for the global construction industry can be partial substitution of Ordinary Portland Cement (OPC) by use of supplementary cementitious materials (SCMs) sourced from industrial ...end-of-life (EOL) products that contain calcareous, siliceous and aluminous materials. Candidate EOL materials include fly ash (FA), silica fume (SF), natural pozzolanic materials like sugarcane bagasse ash (SBA), palm oil fuel ash (POFA), rice husk ash (RHA), mine tailings, marble dust, construction and demolition debris (CDD). Studies have revealed these materials to be cementitious and/or pozzolanic in nature. Their use as SCMs would decrease the amount of cement used in the production of concrete, decreasing carbon emissions associated with cement production. In addition to cement substitution, EOL products as SCMs have also served as coarse and also fine aggregates in the production of eco-friendly concretes.
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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.
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•Micro-nonuniform heating during FAST was experimentally verified for Nd-Fe-B system.•Local overheating due to the Joule effect leads to formation of α-Fe phase.•Matrix phase decomposition can be prevented by decreasing the current in the sample.•Nonequilibrium microstructure formation influences the densification kinetics.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
With Liquid-Cell Transmission Electron Microscopy (LCTEM) we can observe the kinetic processes taking place in nanoscale materials that are in a solvated environment. However, the beam-driven solvent ...radiolysis, which results from the microscope's high-energy electron beam, can dramatically influence the dynamics of the system. Recent research suggests that radical-induced redox chemistry can be used to investigate the various redox-driven dynamics for a wide range of functional nanomaterials. In view of this, the interplay between the formation of various highly reactive radiolysis species and the nanomaterials under investigation needs to be quantified in order to formulate new strategies for nanomaterials research. We have developed a comprehensive radiolysis model by using the electron-dose rate, the temperature of the solvent, the H
2
and O
2
gas saturation concentrations and the pH values as the key variables. These improved kinetic models make it possible to simulate the material's specific radical-induced redox reactions. As in the case of the Au model system, the kinetic models are presented using Temperature/Dose-rate Redox potential (TDR) diagrams, which indicate the equilibrium Au
0
/Au
+
concentration ratios that are directly related to the temperature-/dose-rate-dependent precipitation or dissolution regions of the Au nanoparticles. Our radiolysis and radical-induced redox models were successfully verified using previously reported data from low-dose experiments with γ radiation and experimentally
via
TDR-dependent LCTEM. The presented study represents a holistic approach to the radical-induced redox chemistry in LCTEM, including the complex kinetics of the radiolysis species and their influence on the redox chemistry of the materials under investigation, which are represented here by Au nanoparticles.
A holistically described radical-induced redox chemistry modelling allows for a direct assessment of the
in situ
experiments inside a liquid-cell TEM.
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The consumption of critical raw materials, especially those in permanent magnets of Nd–Fe–B and Sm–Co-type, has significantly grown in the past decade. With predictions on further electrification ...growing exponentially the demand for these materials will even increase. This implies that efforts in assuring sustainability must involve recycling from secondary resources. In recent years the electrochemical approaches in recycling have been extensively investigated and applied owing to their advantages of high efficiency and selectivity, easy operation, low energy consumption, and environmental friendliness. In this paper, we investigate the Sm
2
(Co,Fe,Cu,Zr)
17
permanent magnet leaching process using the anodic oxidation to be paired with the metal deposition on the cathode. Linear sweep voltammetry was performed from − 0.15 to 1 V versus Pt quasi reference electrode that indicated current peaks that would correspond to some preferential leaching of the crystal phases contained in the magnet. The latter was confirmed using the SEM/EDXS analysis. The continuous leaching of the Sm
2
(Co,Fe,Cu,Zr)
17
magnet was performed at a direct current density of 2, 4 and 8 mA cm
−2
at the time period of 0–240, 240–480 and 480–720 min, respectively. The ICP-MS results confirmed the leaching of all the metals from the original Sm
2
(Co,Fe,Cu,Zr)
17
permanent magnet. The concentration of Sm
3+
, Cu
2+
, Fe
2+
and Zr
2+
increases linearly along with the leaching time. Reversely the concentration of Co
2+
decreases linearly due to its consumption by electrodeposition of Co, Fe and Cu on the cathode. The presented paired electrochemical process could serve as a starting point for the recycling and recovery of critical raw materials without any acid usage and waste generation.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In this study, we introduce a novel approach using correlative analysis techniques to unravel detailed insights into the environmental influences on crystal growth. Tabular and bipyramidal wulfenite ...samples from the Mežica mine in north-eastern Slovenia were analysed to combine the morphological aspects of crystal growth with the atomic-resolution reconstruction of the positions of lead (Pb) and molybdenum (Mo) atoms in the parent crystal lattice. These combined data also allow us to present the formation mechanism that enables the development of bipyramidal or tabular morphologies in wulfenite. The bipyramidal and tabular crystals are chemically pure wulfenite (PbMoO
), as confirmed by various advanced diffraction and spectroscopy techniques. However, each habit includes multiple inclusions, mostly consisting of carbonates, Pb-Fe oxides, Pb oxides and, more rarely, Pb vanadate (descloizite). The differences in the morphologies can be attributed to compositional changes during precipitation from a meteoric solution and thus, we propose a growth mechanism consisting of three different phases of growth. This innovative approach emphasises the importance of understanding the origin of crystal habits, as can help to decipher how external influences can affect the crystal structure and its surface, leading to the dissolution of preferred surfaces and the selective release of Pb and Mo.
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In this review article, we focus on the relationship between permanent magnets and the electric motor, as this relationship has not been covered in a review paper before. With the increasing focus on ...battery research, other parts of the electric system have been neglected. To make electrification a smooth transition, as has been promised by governing bodies, we need to understand and improve the electric motor and its main component, the magnet. Today's review papers cover only the engineering perspective of the electric motor or the material-science perspective of the magnetic material, but not both together, which is a crucial part of understanding the needs of electric-motor design and the possibilities that a magnet can give them. We review the road that leads to today's state-of-the-art in electric motors and magnet design and give possible future roads to tackle the obstacles ahead and reach the goals of a fully electric transportation system. With new technologies now available, like additive manufacturing and artificial intelligence, electric motor designers have not yet exploited the possibilities the new freedom of design brings. New out-of-the-box designs will have to emerge to realize the full potential of the new technology. We also focus on the rare-earth crisis and how future price fluctuations can be avoided. Recycling plays a huge role in this, and developing a self-sustained circular economy will be critical, but the road to it is still very steep, as ongoing projects show.
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The green transition initiatives and exploitation of renewable energy sources require the sustainable development of rare earth (RE)-based permanent magnets prominent technologies like wind turbine ...generators and electric vehicles. The recycling of RE-based permanent magnets is necessary for the future supply of critical rare-earth elements. The short-loop recycling strategies to directly reprocess Nd-Fe-B magnet waste are economically attractive and practical alternatives to conventional hydro- and pyrometallurgical processes. This study focuses on the development of a procedure to extract the (Nd, Pr)2Fe14B hard-magnetic phase from sintered Nd-Fe-B magnets. The extraction is achieved through preferential chemical leaching of the secondary, RE-rich phases using 1 M citric acid. Before the acid treatment, the magnets were pulverized through hydrogen decrepitation (HD) to increase the material’s surface-to-volume ratio. The as-pulverized Nd-Fe-B powder was subsequently exposed to a 1 M citric acid solution. The effect of leaching time (5–120 min) on the phase composition and magnetic properties was studied. The results of the microstructural (SEM) and compositional (ICP-MS) analyses and the study of thermal degassing profiles revealed that the RE-rich phase is preferentially leached within 5–15 min of reaction time. Leaching of the secondary phases from the magnet’s multi-phase microstructure is governed by the negative electrochemical potential of Nd and Pr. The extraction of (Nd, Pr)2Fe14B grains by the proposed acid leaching approach is compatible with the existing hydrogen processing of magnetic scrap (HPMS) technologies. The use of mild organic acid as a leaching medium makes the leaching process environmentally friendly, as the leaching medium can be easily neutralized after the reaction is completed.
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Rare earth element (REE)‐based metals and alloys are generally synthesized by molten‐salt electrolysis which is an energy‐intensive approach. Previous attempts to deposit alloys of rare earths from ...solutions at mild temperatures have met with little success. Excitingly, in this investigation we were able to electrodeposit Nd−Fe from the 1‐ethyl‐3‐methylimidizolium dicyanamide (EMIMDCA) ionic liquid (IL) at 110 °C. We observed that NdIII cannot be reduced independently, although it can be co‐deposited inductively on a Cu substrate with the addition of FeII. The transmission electron microscopy (TEM) analysis combined with electron‐energy‐loss spectroscopy (EELS) verified that NdIII is reduced to Nd0 during the electrodeposition process. The TEM/EELS was also able to confirm that the deposition of the Nd−Fe starts with the sole deposition of Fe, followed by the co‐deposition of Nd−Fe. This is in agreement with transition‐state theory, which has the iron initially reduced to an activated state (Fe*), where it is able to catalyse the reduction of the rare earth from NdIII to Nd0. This new insight into the electrodeposition process brings us a very important step closer to being able to recycle rare earths efficiently and even to realise electrodeposited rare‐earth‐based permanent‐magnet thin films at a mild temperature, thus giving us a sustainable, green‐chemistry approach that provides a genuine alternative to high‐temperature molten‐salt electrolysis.
Induced co‐deposition mechanism of rare earth element (REE) ‐transition metal (TM) describes the role of the activated state of TM which catalyzes the reduction of REEIII to REE0. The results highlight the theoretical model for REE‐TM co‐deposition and provide a novel mechanistic insight. The realization of electrodeposited Nd−Fe‐based thin films at a mild temperature exhibits a sustainable, green‐chemistry approach compared to molten‐salt electrolysis.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
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