Darja Feizpour

Binder architecture governs liquid-phase sintering and mechanical response in tungsten heavy alloys. Three 92 wt.% tungsten heavy alloys with Ni-Co-Fe-Al-Ti, Ni-Fe-Al, and Ni-free Co-Fe-Ti binders, designated W-NCFAT, W-NFA, and W-CFT, were produced by elemental powder milling, cold isostatic pressing, liquid-phase sintering at 1425 and 1455 °C under a controlled vacuum-H2-Ar atmosphere sequence, and vacuum dehydrogenation. Densification, tungsten grain morphology, binder continuity, elemental partitioning, contiguity, hardness, and compressive behavior were compared under identical processing conditions. The Ni-containing alloys reached 95.8–97.0% relative density and developed rounded tungsten grains separated by continuous metallic binder regions. W-CFT increased from 78.1% relative density at 1425 °C to 90.4% at 1455 °C, but retained substantial porosity, incomplete grain spheroidization, and discontinuous binder regions. W-NCFAT showed the highest hardness and reached a peak true compressive stress of 1255.4 MPa under quasi-static loading. W-NFA showed a lower peak stress but sustained a final true strain of 0.589 and a higher deformation energy density. In a representative split Hopkinson pressure bar test at approximately 2 × 10³ s⁻¹, W-NFA reached a converted true stress of 1020.7 MPa and remained intact to a final true strain of 0.344, whereas W-NCFAT reached 832.9 MPa at 0.065 before rapid load loss and fragmentation. EDS and XRD indicated continuous Ni-containing metallic binders, discrete Al/Ti-enriched oxygen-bearing constituents, dominant BCC tungsten, and weak reflections consistent with an FCC binder. For the investigated compositions and processing conditions, effective Al/Ti-containing binder performance was associated with sufficient Ni-assisted liquid-phase activity.

Gold nanoparticles (AuNPs) are used in cosmetic formulations due to their physicochemical stability and potential skin benefits. Despite their popularity, the possibility of skin absorption raises concerns about their safety. This feature is especially important for higher concentrations of smaller AuNPs. To overcome this problem we produced larger AuNPs with a diameter of 75.24 ± 16.12 nm using an optimised ultrasonic spray pyrolysis (USP) method. Upon stabilisation with polyvinylpyrrolidone (PVP), the AuNPs were incorporated into a multicomponent cosmetic cream at a low concentration (25 ppm). Physicochemical characterisation of the AuNPs, both in the dried state and within the cream, showed a predominantly spherical and irregular morphology, as well as good dispersion and colloidal stability. The AuNPs were integrated into the cream formulation well, showing no structural, colour, or fragrance changes in the cream matrix. The biocompatibility of the AuNPs cream was evaluated thoroughly using a battery of in vitro tests. The dermal absorption assay using human skin in Franz diffusion cells (OECD TG 428) demonstrated no penetration of AuNPs through the skin. The caffeine control confirmed assay sensitivity. The viability studies, as assessed using L929 mouse fibroblast cells, U937 human monocytic cells and human peripheral blood mononuclear cells (PBMCs), did not show the cytotoxic effect of AuNPs, even at high concentrations. Genotoxicity was not detected in the stimulated PBMCs using the cytokinesis-block micronucleus assay (OECD TG 487). However, the U-SENS™ assay (OECD TG 442E) indicated a positive reaction, most probably due to the presence of sensitising components in the cream`s formulation. When the AuNPs were tested separately the result was negative. In conclusion, our results are consistent with a favourable safety profile of the tested AuNPs-containing cream under the evaluated conditions. However, quantitative dose-bridging and margin-of-safety analysis are needed to substantiate product safety further for real-world use.

Gold nanoparticles (AuNPs) were synthesised using ultrasonic spray pyrolysis (USP) with the addition of polyvinylpyrrolidone (PVP) as a stabilising agent and subsequently dried via lyophilisation. The resulting dried AuNPs were redispersed in ethanol and homogenised to ensure uniform dispersion. This AuNP dispersion was then deposited onto a ceramic substrate—aluminum oxide (Al₂O₃)—using plasma jet printing. Comprehensive characterisation of the dispersion, AuNPs, and the resulting printed lines was performed using the following methods: inductively coupled plasma optical emission spectroscopy (ICP-OES), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDS), ultraviolet-visible spectroscopy (UV-Vis), dynamic light scattering (DLS), measurements of dispersion viscosity and printed line roughness. ICP-OES confirmed consistent gold content in the AuNP dispersion, while the SEM and EDS analyses revealed predominantly spherical AuNPs with minimal aggregation and similar size distributions. TEM, SAED, and STEM/EDS confirmed that the crystalline structure and elemental composition of the AuNPs had diverse morphologies and strong gold signals. The UV-Vis, DLS, and zeta potential measurements indicated moderate colloidal stability, and thermogravimetric analysis (TGA) verified the AuNPs dispersion’s composition. The AuNP dispersion exhibited thixotropic behaviour favourable for printing applications, while confocal microscopy confirmed smooth, uniform printed traces, with an average surface line roughness of 1.65 µm. The successful use of plasma printing with the AuNP dispersion highlights its potential for functional material applications in electronics.

Gold nanoparticles (AuNPs) were synthesised using ultrasonic spray pyrolysis (USP) with the addition of polyvinylpyrrolidone (PVP) as a stabilising agent and subsequently dried via lyophilisation. The resulting dried AuNPs were redispersed in ethanol, and homogenised to ensure uniform dispersion. This AuNPs` dispersion was then deposited onto a ceramic substrate (Al2O3) using plasma jet printing. Comprehensive characterisation of the dispersion, AuNPs and the resulting printed line were performed using: ICP-OES, SEM/TEM/EDS, UV-Vis, DLS, measurements of dispersion viscosity and printed line roughness. ICP-OES confirmed consistent gold content in the AuNPs` dispersion, while the SEM and EDS analyses revealed predominantly spherical AuNPs with minimal aggregation and similar size distributions. TEM, SAED, and STEM/EDS confirmed the crystalline structure and elemental composition of the AuNPs, with diverse morphologies and strong gold signals. The UV-VIS, DLS, and zeta potential measurements indicated moderate colloidal stability, and TGA verified the AuNPs dispersion’s composition. The AuNPs` dispersion exhibited thixotropic behaviour favourable for printing applications, while confocal microscopy confirmed smooth, uniform printed traces, with an average surface line roughness of 1.65 µm. The successful use of plasma printing with the AuNPs` dispersion highlights its potential for functional material applications in electronics.

The coupled processes of coprecipitation and ultrasonic spray pyrolysis (USP) were used to synthesize Fe₃O₄-Au hybrid nanostructures. The first coprecipitation method enabled the synthesis of Fe₃O₄ nanoparticles by mixing iron salts’ ions (Fe²⁺ and Fe³⁺) and ammonia as the base, and USP was used as the coating process of the Fe₃O₄ nanoparticles with Au. The formatted hybrid nanostructures consist of Fe₃O₄ nanoparticles that have Au on their surface in the form of gold nanoparticles (AuNPs). AuNPs have a crystalline structure and range in size from 10 to 200 nm. Additional characterization techniques, including ICP-OES, TEM, SEM, EDS, DLS, zeta potential, and room temperature magnetic hysteresis loops, were used to determine the chemical, physical, and magnetic properties of the Fe₃O₄ nanoparticles and hybrid nanostructures. It was found that USP produces separate AuNPs too (not just on the Fe₃O₄ surface), suggesting a bimodal formation of AuNPs. The zeta potential of the Fe₃O₄ nanoparticles showed poor stability (−15 mV), indicating a high tendency to aggregate, and the zeta potential of the hybrid nanostructures was also very low (≅0), which, comparatively means even worse stability. The saturation magnetization of the Fe₃O₄ nanoparticles was 35 emu/g, which is relatively lower than that of bulk Fe₃O₄, while the saturation magnetization of the hybrid nanostructures was significantly lower (0.1 emu/g) compared to the Fe₃O₄ nanoparticles.

Magnetic nanoparticles coated with gold nanoparticles are hybrid nanostructures combining the magnetic properties of iron oxide with the optical and chemical versatility of gold. The iron oxide core gives the nanoparticles magnetic functionality, which is useful in magnetic resonance imaging (MRI), targeted drug delivery, and hyperthermia treatment. The gold coating enhances biocompatibility, provides resistance to oxidation, and allows for surface functionalisation with biomolecules for targeted applications. This combination makes these nanoparticles ideal for a range of biomedical applications, including diagnostics, therapeutics, and imaging, due to their magnetic, optical, and chemical properties. Transmission electron microscopy, dynamic light scattering, zeta potential and magnetisation of nanoparticles are key techniques that provide a comprehensive understanding of the nanoparticles’ size, structure, optical properties and magnetic behaviour, which are important factors for determining their potential use in various applications.

The magnetocaloric effect (MCE) is currently intensively investigated in various rare earths (RE)-containing magnetic solids, not only for developing appropriate magnetocaloric materials (MCMs) for cryogenic magnetic cooling but also for deepening our understanding into the inherent physical properties of these materials. Here, we provide a systematic experimental investigation into a series of new RE₂CuTiO₆ (RE = Dy, Ho, Er) double-perovskite (DP) oxides regarding the structural and magnetic properties, especially for their cryogenic MCE and magnetic-phase transition (MPT). All of these RE₂CuTiO₆ oxides crystallize in a B-site-ordered hexagonal DP-type structure with the symmetry of the crystallographic space group P6̅m2. These DP oxides exhibit magnetic ordering, with MPT temperatures of approximately 2.7, 2.2, and 2.7 K for Dy₂CuTiO₆, Ho₂CuTiO₆, and Er₂CuTiO₆, respectively. The magnetocaloric performances of the RE₂CuTiO₆ DP oxides were characterized by the peak values of magnetic entropy change, the temperature-averaged magnetic entropy change (5K-lift), and relative cooling powers. These magnetocaloric parameters were deduced to be 18.7/17.9 J/kgK and 298.2 J/kg for Dy₂CuTiO₆, 12.5/12.2 J/kgK and 273.9 J/kg for Ho₂CuTiO₆, and 13.8/12.9 J/kgK and 188.4 J/kg for Er₂CuTiO₆ under a magnetic field change of 0-5 T. These values are comparable to those of most reported RE-containing magnetocaloric materials, indicating that these RE₂CuTiO₆ DP oxides are promising candidates for cryogenic magnetic cooling applications.