The effect of Ni/Cu-coating residuals on the magnetic properties and microstructures of samarium–cobalt (SmCo5) magnets was studied. SmCo5 magnets with 0.0, 0.5, 1.0, 2.0, 3.0 and 4.0 wt.% of added ...Ni/Cu (85 wt.% Ni/15 wt.% Cu) were prepared using a conventional sintering route. The magnetic properties of the magnets were found to be consistent up to 2 wt.% Ni/Cu. Any further increase in the Ni/Cu content resulted in a significant reduction in the magnetic properties, to lower than values that would be commercially acceptable. SEM/EDS studies showed that two major phases, i.e., the SmCo5 matrix phase and Sm2O3 were present in all the sintered SmCo5 magnets. The presence of Sm2Co7 as a minor phase fraction was detected in the sintered SmCo5 magnets containing up to 2 wt.% Ni/Cu. A 2 wt.% Ni/Cu addition to magnets resulted in the presence of two new phases with compositions close to SmCo and Sm2Co17 in addition to SmCo5 and Sm2O3 as major phases in the SEM-observed microstructure. These newly formed phases are present in small fractions and are presumably homogenously distributed at the grain boundaries of the magnets. As they are known to act as nucleation sites for reverse magnetic domains, they effectively reduce the intrinsic grain boundary magnetic strength, leading to a drop in the coercivity. We concluded that the sintered SmCo5 magnets could be recycled with up to 2 wt.% Ni/Cu as a residual from the coating under our sintering and heat treatment conditions.
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The electrochemical polymerization of polyaniline (PANI) was studied using correlative measurements of electrochemistry and UV-vis spectroscopy, i.e., spectroelectrochemistry. The ...electropolymerization of PANI was performed in an acidic medium (1 M HCl) containing 0.1 M aniline with cyclic voltammetry (CV) in a potential window from −0.3 to 1 V and a 50 mV s−1 scan rate. At the same time, UV-vis absorbance spectra in the wavelength range from 200 to 900 nm were measured for every 10 mV change in the CV. The CV results show the oxidation of the monomer at a high positive potential (0.9 V vs Ag), the continuous growth of the PANI film and the transformation between the three best-known forms of PANI redox in the potential range between −0.3 V and 1 V. In parallel, the spectroscopic study confirmed the formation of PANI oxidation. The spectroscopic results showed the formation of the final conductive PANI product (emeraldine salt) due to the absorbance of the formed charge carriers (polarons, bipolarons) during the polymerization. The correlative electrochemical/spectroscopy study gave an additional dimension to the PANI polymerization mechanism, where not only was the oxidation the lead type of reaction, but the reduction was also found to play an important role.
In present work, we report on the enhanced electrocatalytic activity of formaldehyde oxidation in alkaline media for modified Ni nanowires (NWs)-based electrodes. Electrochemically deposited Ni NWs ...composed of metallic Ni and surface NiO were modified in KOH via cyclic voltammetry using different scan rates (10, 200 and 400 mV s−1) in order to transform an inactive NiO to the surface-catalytic-active structurally disordered β-NiOOH/β-Ni(OH)2. Various characterisations (XRD and FT-IR) and calculations based on the electric charge were performed to understand the surface transformations which were found to be scan-rate dependant. The cyclic voltammetry results and kinetic parameters (Tafel plot) of formaldehyde oxidation revealed the superior electrocatalytic activity of the Ni-NW-electrode modified at 200 mV s−1. The enhanced electrocatalytic performance, i.e., decreased onset overpotential by 400 mV when compared to Ni-based electrocatalysts, of this electrode was attributed to the thickness of structurally disordered the Ni–NiOOH/Ni(OH)2 and composite layered structure that enables the electron injection to reduce the NiOOH work function and thus promote the catalysis of formaldehyde oxidation. The proposed technique provides advances with a novel synthesis strategy for the preparation of highly active, structurally disordered β-Ni(OH)2/β-NiOOH redox systems on the surface of Ni-based nanostructured electrocatalysts for HCHO oxidation.
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•TRE-lean jet-milled Nd-Fe-B powders can be consolidated to full density with SPS.•The rapid non-equilibrium SPS hinders the grain growth during the sintering step.•The electrical effects associated ...with the SPS govern the microstructure formation.•A post-SPS thermal treatment is necessary for the final hard-magnetic properties.
Sintered Nd-Fe-B permanent magnets are the first choice for electro-mechanical devices that rely on hard-magnetic materials to provide strong magnetic fields in a variety of operating conditions. However, the limitations of conventional powder-metallurgy methods regarding the complexity of the magnet’s geometry restrict the design freedom for electrical motors. Here, we propose a spark-plasma-sintering (SPS) approach to the waste-free net-shape manufacture of anisotropic Nd-Fe-B magnets. We investigated the effect of the SPS parameters on the density, magnetic properties and microstructure of disc-shaped samples prepared from a rare-earth-lean jet-milled powder. The absence of a grain-boundary phase and the presence of α-Fe in the as-sintered samples were identified as the main factors hindering the development of the intrinsic coercivity. The observed microstructural features were correlated with electrical effects specific to the rapid, non-equilibrium SPS. A post-SPS thermal treatment was found to be necessary for achieving the hard-magnetic properties. Our findings pave the way towards developing an SPS-based sintering procedure with great potential for the manufacture of complex- and net-shape permanent magnets for high-performance electrical devices.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Highly ordered, Ni(OH)2Ni-nanowire-based receptor elements were electrochemically fabricated and tested for formaldehyde (HCHO) detection by monitoring their oxidation ability in alkaline media. In ...order to normalize the electrochemical output currents, the Ni nanowires' electrochemically active surface area was assessed using an oxalate-based method after the template was released. The electrochemical transformation of the Ni-nanowire surfaces to a Ni(OH)2/NiOOH redox couple was performed in 0.5-mol L−1 KOH using cyclic voltammetry at 200 mV s−1. The transformation was monitored for two cases: without KOH modification and with KOH-modified Ni nanowires. It was shown that the non-modified Ni nanowires possess a poor electrochemical response to HCHO oxidation, mainly due to the formation of a NiO surface layer. On the other hand, the modified Ni nanowires donated an electron to the HCHO oxidation reaction, resulting in high output-current densities, attributed to the thin Ni(OH)2/NiOOH layer, its amorphous state (TEM/SAED) and its small work function, due to electron doping from under the layered Ni. The modified Ni-nanowire-based electrodes had high sensitivity, reproducibility, selectivity and a low detection limit (0.8 μmol L−1). The developed HCHO Ni-nanowire-based electrodes’ characteristics surpass other Ni-based nanostructured electrodes and have limits of detection comparable to those achieved with noble metals.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Nd-Fe-B magnets with locally tailored magnetic properties can be prepared with SPS.•Consolidation temperature of ≈650 °C is favorable for co-sintering multiple melt-spun powders.•Nd-Dy-Fe-B powder’s ...coercivity (2075 kA/m) is preserved in a multicomponent magnet.•Interdiffusion between different Nd-Fe-B materials during sintering is hindered.•Reliable performance over a wide range of operating temperatures is ensured.
The magnetic properties of an Nd-Fe-B-type permanent magnet depend on the microstructure and the chemistry of the material. To compensate for unfavorable microstructural features, such as micron-sized grains of the hard-magnetic phase, the intrinsic coercivity is often enhanced by the addition of heavy-rare-earth elements, but these additions also reduce the magnetization. In some applications, like electro-mechanical devices, a high intrinsic coercivity is only required in certain regions of a magnet. In such cases, using magnets with locally tailored magnetic properties, i.e., multicomponent magnets, would enhance the magnet-containing device’s performance. Here, we propose a spark-plasma-sintering (SPS) approach to the manufacture of multicomponent Nd-Fe-B magnets. By exploiting the SPS-specific processing conditions, namely fast heating rates (100 °C/min) and low consolidation temperatures (≈670 °C), such magnets can be prepared directly from nanostructured melt-spun powders (the one-step SPS approach) or SPS-processed precursor magnets (the two-step SPS approach). Optimizing the SPS processing conditions prevents the grain coarsening related to the pre-existing microstructural inhomogeneities of the powders. The magnetic characterization reveals reliable performance over a wide range of operating temperatures. The high remanent magnetization of a heavy-rare-earth-free powder (Br = 0.82 T) and the high intrinsic coercivity of a powder containing 1.5 at. % Dy (Hci = 2075 kA/m) are preserved in a multicomponent magnet characterized by an abrupt change in magnetic properties close to the interface between the respective magnet parts.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Despite medical advances, skin-associated disorders continue to pose a unique challenge to physicians worldwide. Skin cancer is one of the most common forms of cancer, with more than one million new ...cases reported each year. Currently, surgical excision is its primary treatment; however, this can be impractical or even contradictory in certain situations. An interesting potential alternative could lie in topical treatment solutions. The goal of our study was to develop novel multilayer nanofilms consisting of a combination of polyhydroxyethyl methacrylate (PHEMA), polyhydroxypropyl methacrylate (PHPMA), sodium deoxycholate (NaDOC) with incorporated superparamagnetic iron-platinum nanoparticles (FePt NPs), and the potent anticancer drug (5-fluorouracil), for theranostic skin cancer treatment. All multilayer systems were prepared by spin-coating and characterised by atomic force microscopy, infrared spectroscopy, and contact angle measurement. The magnetic properties of the incorporated FePt NPs were evaluated using magnetisation measurement, while their size was determined using transmission electron microscopy (TEM). Drug release performance was tested in vitro, and formulation safety was evaluated on human-skin-derived fibroblasts. Finally, the efficacy for skin cancer treatment was tested on our own basal-cell carcinoma cell line.
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•Electrodeposited Ni films were modified by potential cycling in KOH.•KOH modification increases the amount of structurally disordered Ni(OH)2/NiOOH.•The amount of structurally ...disordered Ni(OH)2/NiOOH influences the catalytic properties.•The KOH-modified Ni films provide better catalytic activity towards HCHO oxidation.
The main challenge with electrocatalysis is finding low-cost electrocatalysts that can work efficiently to oxidize the HCHO. Here, we propose a mechanism for the voltammetric formation of a highly active, structurally disordered β-Ni(OH)2/β-NiOOH redox pair on the surface of electrodeposited Ni thin films to achieve an extraordinary catalytic performance with respect to HCHO oxidation in alkaline media. We report electrochemical, XRD and FT-IR measurements on as-deposited and voltammetrically treated (i.e., KOH-modified) Ni thin films, and calculations based on the electrical charge to investigate the changes in the surface composition, crystal structure and related HCHO oxidation activity. We found that the KOH-modification process plays a crucial role in the formation of surface highly active, disordered β-Ni(OH)2/β-NiOOH. The KOH-modified Ni film with the largest amount of the structurally disordered β-Ni(OH)2/β-NiOOH resulted in improved catalytic performance, i.e., an onset overpotential reduced by 400 mV and a catalytic rate increased by 69 mV dec−1. The presented technique has a wide range of applications and provides advances with a novel design idea and a new synthesis strategy for the preparation of highly active, structurally disordered Ni(OH)2/NiOOH redox systems on the surface of Ni thin films and other Ni-based nanostructured electrocatalysts for HCHO oxidation.
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In a novel process to enhance the coercivity we have electrophoretically deposited DyF3 powder onto the surface of an as-sintered Nd–Fe–B magnet as the initial step in the grain-boundary diffusion ...process. After a conventional heat treatment at 850 and 500 °C the coercivities were higher than in the case of simple dipping after a typical 10 h, with Hci values exceeding 1600 kA/m for a 200 μm-thick deposited layer. The electrophoretic deposition (EPD) process is quick, easily controllable in terms of thickness and can be used to deposit the rare earth fluoride powder on the surface of complex and irregularly shaped magnets. Since the amount of deposited powder can be tailored to maximise the coercivity while minimising the quantity of expensive heavy rare earth there is no wasted powder, making the diffusion process, which takes place after the sintering process, more environmentally friendly and potentially cheaper than conventional dipping.
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► A novel technique to enhance coercivity via the GBDP. ► Controllable layer thickness for heavy rare earths. ► Maximised coercivity with minimum losses of material. ► Environmentally friendly and low-cost.
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Ammonia (NH3) present in biological fluids is biomarker for several disease states. In this work the well-known interaction between polyaniline (PANI) and NH3 was used for the fabrication of an ...amperometric sensory platform to detect aqueous NH3 at neutral i.e. biological pH. Understanding PANI's electrochemical synthesis and redox behaviour in acidic and neutral media was used to determine the NH3 detection mechanism. The latter is based on the PANI deprotonation reaction, NH4+ oxidation and follow-up PANI reduction and oxidation. Chronoamperometry was applied as an NH3-detection method in a 50 µL background electrolyte in which a 1 µL sample was injected, triggering instantaneous changes to the current. The sensory platform's detection limit, based on pure electrochemically synthesised PANI (PANIel) (24.64 µM), was reduced 17 times (1.44 µM) with the addition of 20 nm Au nanoparticles. This Au-decorated PANIel sensory platform showed excellent reversibility, reusability and the possibility for continuously cycled NH3 measurements, with a recovery rate of 90–99.5% for artificial saliva samples of different pHs. This demonstrates its suitability for more complex samples. The developed sensory platform presents potential from the industry point of view, as a base for an NH3 batch injection analysis and for preventive home medical self-care.
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