Search Results (147)

Non-stoichiometric high-entropy carbides (Nb_0.2Ta_0.2Ti_0.2W_0.2Zr_0.2)C_x (x = 0.71–0.85) nanoscale powders were prepared using oxides and carbon as raw materials via carbothermal reduction. The (Nb_0.2Ta_0.2Ti_0.2W_0.2Zr_0.2)C_0.73 synthesized at 1700 °C exhibited a grain size of approximately 400 nm, an oxygen content of 0.3 wt.%, and uniform nanoscale distribution of the five metal elements. After ball milling, (Nb_0.2Ta_0.2Ti_0.2W_0.2Zr_0.2)C_0.73 powder was sintered by spark plasma sintering to produce high-entropy ceramics with a relative density of 98.1% and an average particle size of about 5.3 μm. The Vickers hardness, nano-hardness, Young’s modulus, and fracture toughness were 17.6 GPa, 29.1 GPa, 514 GPa, and 5.3 MPa·m^1/2, respectively. The thermal conductivity of the ceramic at room-temperature was as low as 8.5 W/m·K. Full article

A novel amorphous Hf-MOFs precursor was successfully synthesized and converted into HfC nanoparticles via one-step pyrolysis. The effects of metal/ligand molar ratios, solvent types, and pyrolysis temperature were systematically studied. High-purity spherical HfC nanoparticles (44.30 ± 9.63 nm) were obtained at 1500 °C using a 1.5:1 metal/ligand molar ratio with mixed anhydrous ethanol/deionized water solvents. At a pyrolysis temperature of 1700 °C, the as-synthesized HfC nanoparticles possessed an exceptionally low oxygen content of 0.76%, alongside a carbon content of 6.42% that almost perfectly matches the theoretical value of stoichiometric HfC. The formation mechanism involving Hf-O-C coordination and carbothermal reduction was clarified. Additive-free HfC ceramics were fabricated using the as-synthesized HfC nanoparticles via spark plasma sintering (1950 °C, 30 MPa, 20 min). The resulting ceramics exhibited a relative density of 96.7% and a Vickers hardness of 20.2 GPa, both of which are significantly superior to those of ceramics sintered from commercial HfC powders under identical conditions (95.8% and 17.8 GPa, respectively). This work provides a promising and feasible pathway for the preparation of other high-quality ultra-high temperature hafnium-based carbide powders and ceramics. Full article

Silver-coated copper (Cu@Ag) core–shell nanoparticles are promising interconnect materials for electronic packaging due to their high conductivity, oxidation resistance, and reduced use of precious metals. However, the key factors governing their sintering behavior and mechanical performance are not fully understood. In this study, molecular dynamics simulations were performed to examine the effects of sintering pressure (300–700 MPa), temperature (500–700 K), particle size, and silver shell thickness on atomic diffusion, microstructural evolution, and mechanical properties. Results show that higher pressure improves particle contact, accelerates densification, and strengthens interfacial bonding, with optimal performance achieved at 600–700 MPa. Elevated temperatures enhance atomic mobility, promoting neck growth and pore elimination, with the most active diffusion observed between 650 K and 700 K. Particle size and shell thickness also affect sintering: the Ag6Cu3 configuration exhibits the highest atomic mobility and a balanced combination of strength and ductility. Moderately thick silver shells facilitate surface diffusion and interfacial interdiffusion, while mechanisms such as the Kirkendall effect and local plastic relaxation reduce defect density, yielding stable sintered structures. These findings provide atomic-scale insights into the sintering mechanisms of Cu@Ag nanoparticle solder pastes and offer guidance for optimizing processing parameters in high-performance electronic packaging applications. Full article

Printed electronics have emerged as a versatile manufacturing platform for next-generation biosensors, enabling on-demand and low-cost fabrication of functional devices on flexible, stretchable, and unconventional substrates. One major challenge in this field lies in the sintering of printed features, as conventional high-temperature processing is incompatible with polymeric substrates and thermally sensitive biological components. Low-temperature sintering inks, typically processed below 200 °C or even at room temperature, have become a critical enabling technology for bio-integrated electronics. This review provides an overview of the current state-of-the-art and key challenges associated with low-temperature sintering inks for printed bioelectronics. We discuss inks based on metal nanoparticles, metal–organic decomposition precursors, metal oxides, chalcogenides, and hybrid material systems. The emphasis is on how ink chemistry, ligand selection, and precursor structure govern rheology, stability, and sintering behavior. In addition, key low-temperature sintering and curing strategies, including thermal, photonic, laser, plasma, microwave, and chemical sintering, are compared in terms of energy delivery, densification mechanisms, and substrate compatibility. Finally, we outline emerging directions towards low temperature and room-temperature sintering inks, and sustainable biobased ink formulations, and discuss their applications for wearable, implantable, and soft biosensing platforms. Full article

This study examines the influence of sintering temperature on the structural and transport properties of GdBa₂Cu₃O₇ (Gd123) superconductors prepared from nano-sized precursors via the co-precipitation method. The metal-oxalate precursor (average particle size < 50 nm) was calcined at 900 °C for 12 h, and then the prepared pellets were sintered under an oxygen atmosphere in the range of 920–950 °C for 15 h. All samples showed metallic properties and a sharp superconducting transition. Critical temperatures T_C(R=0) were 94–95 K, with higher sintering temperatures steadily boosting critical current density. X-ray diffraction confirmed orthorhombic Gd123 as the dominant phase, with its phase fraction increasing from 92% to 99.8% as the sintering temperature increased. SEM micrographs showed large, densely packed grains, with higher sintering temperatures promoting improved grain connectivity and reduced porosity. The sample sintered at 950 °C exhibited the most favorable transport performance, attributed to enhanced intergranular coupling and the presence of nanoscale secondary phases acting as effective flux-pinning centers. Overall, these results demonstrate that careful control of sintering temperature can significantly optimize the microstructure and superconducting properties of Gd123 materials, supporting their advancement for practical electrical and magnetic applications. Full article

This study reports the fabrication of copper-based metal matrix composites reinforced with a combination of micro- and nano-sized titanium carbide (TiC) particles using the powder metallurgy route. The micro-TiC content was maintained at 5 wt.%, while the nano-TiC addition was systematically varied between 1 and 3 wt.% in increments of 1 wt.%. The consolidation of the blends was achieved by uniaxial compaction at 500 MPa, followed by sintering in a nitrogen atmosphere at 750–900 °C for 2 h. Tribological assessment under dry sliding conditions was performed using a pin-on-disk apparatus. Structural and microstructural examinations using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS) confirmed a uniform incorporation of the reinforcements within the Cu matrix. The incorporation of nano-TiC up to 2 wt.% significantly enhanced density, hardness, and wear resistance, after which a marginal decline was observed. SEM analysis of worn surfaces revealed that adhesive wear, abrasion, and delamination were the primary wear mechanisms. To better understand the relationship between processing conditions and material responses, response surface methodology (RSM) was employed. The developed models for density, hardness, and wear loss showed good agreement with the experimental results, with confirmatory tests yielding errors of 1.59%, 2.06%, and 2%, respectively, thereby validating the approach’s reliability. Full article

This work presents results on laser-induced fabrication of metal and oxide structures on glass substrates. The Laser-Induced Reverse Transfer (LIRT) technique is applied using Zn and Sn, sintered ZnO and SnO₂, and oxide composite targets. The processing is performed by nanosecond pulses of a Nd:YAG laser system operated at wavelength of 1064 nm. Detailed analyses of the deposited material morphology, composition and structure are presented, as the role of the processing conditions is revealed. It is found that at the applied conditions of using up to five laser pulses, the deposited material is composed of a nanostructured film covered in microsized nanoparticle clusters or droplets. The use of metal targets leads to formation of structures composed of metal and oxide phases. The adhesion test shows that part of the deposited material is stably adhered to the substrate surface. It is demonstrated that the deposited materials can be used as resistive gas sensors with sensitivity to NH₃, CO, ethanol, acetone and N₂O, at concentrations of 30 ppm. The ability of the method to deposit composite structures that consist of a mixture of both investigated oxides is also demonstrated. Full article

Dry reforming of methane (DRM) is a promising method for turning two major greenhouse gases, CO₂ and CH₄, into syngas (H₂ + CO). This syngas has the right H₂/CO ratio for making valuable chemicals and liquid fuels. However, there are significant challenges that make it tough to implement commercially. One big issue is that the process requires a lot of energy because it is highly endothermic, needing temperatures over 700 °C. This high heat can quickly deactivate the catalyst due to carbon build-up (coking) and the thermal sintering of metal nanoparticles. Researchers increasingly recognize mechanochemistry—a non-thermal, solid-state technique employing mechanical force to drive chemical transformations—as a sustainable, solvent-free strategy to address these DRM challenges. This mini-review critically assesses the dual role of mechanochemistry in advancing DRM. First, we examine its established role in creating advanced catalysts at lower temperatures. Here, mechanochemical methods help produce well-dispersed nanoparticles, enhance strong interactions between metal and support, and develop bimetallic alloys that resist coke formation and show great stability. Second, we delve into the exciting possibility of using mechanochemistry to directly engage in the DRM reaction at near-ambient temperatures, which marks a major shift from traditional thermocatalysis. Lastly, we discuss the key challenges ahead, like scalability and understanding the mechanisms involved, while also outlining future directions for research to fully harness mechanochemistry for converting greenhouse gases sustainably. Full article

Incorporating Cu into gold-based catalysts effectively reduced nanoparticle sintering and free carbonate accumulation, promoting long-term preservation of catalytic surface area over time. This study explores the catalytic activity of monometallic Au and bimetallic AuCu catalysts with varying Au:Cu atomic ratios (1:0.5, 1:1, and 1:1.5) that were synthesized on $\gamma$${\mathrm{-Al}}_2{\mathrm{O}}_3$ via sequential deposition–precipitation with urea. The catalysts were pretreated in either air or ${\mathrm{H}}_2$ and evaluated for CO oxidation activity and stability. A comprehensive characterization (EDS, BET, TEM, ${\mathrm{H}}_2$-TPR, ${\mathrm{O}}_2$-TPO, XPS, DRIFTS, and UV–Vis) was used to investigate particle size, metal oxidation states, and redox properties. Among all materials, the AuCu 1:1 catalyst exhibited the highest low-temperature CO conversion (>90% at 0 °C) and improved stability during 24 h tests, reflecting minimal nanoparticle sintering as confirmed by TEM analysis. In situ DRIFTS revealed that the presence of Cu⁺ and Cu²⁺ minimizes the accumulation of free carbonates (one of the main deactivation pathways in Au/$\gamma$${\mathrm{-Al}}_2{\mathrm{O}}_3$) while promoting the formation of reactive intermediates that facilitate ${\mathrm{CO}}_2$ production. Notably, air pretreatment at moderate temperature proved as effective as ${\mathrm{H}}_2$ pretreatment in activating both monometallic and bimetallic catalysts. These findings highlight the role of Cu as a structural and electronic promoter of gold, offering practical guidelines for designing durable, cost-effective catalysts for low-temperature CO oxidation on non-reducible supports. Full article

In recent years CO₂ reforming of methane has attracted great interest as it produces high CO/H₂ ratio syngas suitable for the synthesis of higher hydrocarbons and oxygenated derivatives since it is a way for disposing and recycling two greenhouse gases with high environmental impact, CH₄ and CO₂, and because it is regarded as a potential route to store and transmit energy due to its strong endothermic effect. Along with noble metals, all the group VIII metals except for osmium have been studied for catalytic CO₂ reforming of methane. It was found that the catalytic activity of Ni, though lower than those of Ru and Rh, was higher than the catalytic activities of Pt and Pd. Although noble metals have been proven to be insensitive to coke, the high cost and restricted availability limit their use in this process. It is therefore valuable to develop stable Ni-based catalysts. In this contribution, we show how their activity and coking resistivity are greatly related to the size and dispersion of Ni particles. Well-dispersed Ni nanoparticles were achieved by multistep impregnation on a mesoporous silica support, namely SBA-15, obtained through a sol-gel method, using acetate as a nickel precursor and keeping the Ni loading between 5% and 11%. Significant catalytic activity was obtained at temperatures as low as 450 °C, a temperature well below their deactivation temperature, i.e., 700 °C. For the pre-reduced samples, a CO₂ conversion higher than 99% was obtained at approximately 680 °C. As such, their deactivation by sintering and coke formation was prevented. To the best of our knowledge, no Ni-based catalysts with complete CO₂ conversion at temperatures lower than 800 °C have been reported so far. Full article

Residual-free eutectic Au80Sn20 soldering is still the dominant assembly technology for optoelectronic devices such as high-power lasers, LEDs, and photodiodes. Due to the high cost of gold, alternatives are desirable. This paper investigates the thermal performance of copper-based sintering for optoelectronic submodules on first and second level to obtain thermally efficient thin bondlines. Sintered interconnects obtained by a new particle-free copper ink, based on complexed copper salt, are compared with copper flake and silver nanoparticle sintered interconnects and benchmarked against AuSn solder interconnects. The copper ink is dispensed and predried at 130 °C to facilitate in situ generation of Cu nanoparticles by thermal decomposition of the metal salt before sintering. Submounts are then sintered at 275 °C for 15 min under nitrogen with 30 MPa pressure, forming uniform 2–5 µm copper layers achieving shear strengths above 31 MPa. Unpackaged LEDs are bonded on first level using the copper ink but applying only 10 MPa to avoid damaging the semiconductor dies. Thermal performance is evaluated via transient thermal analysis. Results show that copper ink interfaces approach the performance of thin AuSn joints and match silver interconnects at second level. However, at first level, AuSn and sintered interconnects of commercial silver and copper pastes remained superior due to the relative inhomogeneous thickness of the thin Cu copper layer after predrying, requiring higher bonding pressure to equalize surface inhomogeneities. Full article

In this study, high-yield biopolymer/ceramic hollow fibers were fabricated via a facile, modified polyol process in a spinneret setup, enabling the controlled adsorption of Cu²⁺ ions. Post sintering transformed these into catalytic copper-decorated carbon/ceramic (alumina) composite hollow fibers, with alginate serving as both a metal ion binder and a copper nanoparticle stabilizer. The resulting hollow fibers featured porous walls with a high surface area and were densely decorated with copper nanoparticles. Their structural and morphological characteristics were analyzed, and their NO reduction performance was assessed in a continuous flow configuration, where the gas stream passed through both the shell and lumen sides of a fiber bundle in a tangential flow mode. This study also examined the stability, longevity and regeneration potential of the catalytic fibers, including the mechanisms of deactivation and reactivation. Carbon content was found to be decisive for catalytic performance. High-carbon fibers exhibited a light-off temperature of 250 °C, maintained about 90% N₂ selectivity and sustained a consistently high NO reduction efficiency for over 300 h, even without reducing gases like CO. In contrast, low-carbon fibers displayed a higher light-off temperature of 350 °C and a reduced catalytic efficiency. The results indicate that carbon enhances both activity and selectivity, counterbalancing deactivation effects. Owing to their scalability, durability and effectiveness, these catalytic fibers and their corresponding bundle-type reactor configuration represent a promising technology for advanced NO abatement. Full article

Famatinite (Cu₃SbS₄) is an earth-abundant, nontoxic material with potential for thermoelectric energy generation applications. Herein, rapid, energy-efficient, and facile one-pot modified polyol synthesis was utilized to produce gram-scale quantities of phase-pure famatinite (Cu_2.7M_0.3SbS₄, M = Cu, Zn, Mn) nanoparticles (diameter 20–30 nm) with controllable and stoichiometric incorporation of transition metal dopants on the Cu-site. To produce pellets for thermoelectric characterization, the densification process by spark plasma sintering was optimized for individual samples based on thermal stability determined using differential scanning calorimetry and thermogravimetric analysis. Electronic transport properties of undoped and doped famatinite nanoparticles were studied from 225–575 K, and the thermoelectric power factor was calculated. This is the first time electronic transport properties of famatinite doped with Zn or Mn have been studied. All famatinite samples had similar resistivities (>0.8 mΩ·m) in the measured temperature range. However, the Mn-doped famatinite nanomaterials exhibited a thermoelectric power factor of 10.3 mW·m⁻¹·K⁻¹ at 575 K, which represented a significant increase relative to the undoped nanomaterials and Zn-doped nanomaterials engendered by an elevated Seebeck coefficient of ~220 µV·K⁻¹ at 575 K. Future investigations into optimizing the thermoelectric properties of Mn-doped famatinite nanomaterials are promising avenues of research for producing low-cost, environmentally friendly, high-performing thermoelectric materials. Full article

A ceramic–metal composite was synthesized using sol–gel and electrospinning methods to serve as a SERS substrate. The precursors used were tetraethyl orthosilicate, aluminum nitrate, and zirconium, and polyvinylpyrrolidone was added to electrospun nonwoven fibrous membranes. The membranes were sintered, decorated with silver nanoparticles. The enhancement substrates were made of fibers of cylindric morphology with an average diameter of approximately 190 nm, a smooth surface, and 9 nm spherical particles decorating the surface of the fibers. The enhancement capacity of the substrates was tested using pyridine, methyl orange, methylene blue, crystal violet, and Eriochrome black T at different concentrations with Raman spectroscopy to determine whether the size and complexity of the analyte has an impact on the enhancement capacity. Enhancement factors of 2.53 × 10², 3.06 × 10¹, 2.97 × 10³, 4.66 × 10³, and 1.45 × 10³ times were obtained for the signal of pyridine, methyl orange, methylene blue, crystal violet, and Eriochrome black T at concentrations of 1 nM. Full article

Objective: Fluoride is widely recognized for its preventive role against secondary caries. This systematic review aimed to evaluate how environmental and material factors influence fluoride ion release from metal-reinforced glass ionomer cements. Methods: A structured literature search was performed in March 2025 across PubMed, Scopus, and Web of Science databases. Search terms included combinations of fluoride release AND glass ionomer AND silver OR zinc OR strontium OR copper. The study selection process followed PRISMA 2020 guidelines and was organized using the PICO framework. Out of 281 initially identified records, 153 were screened based on titles and abstracts. After applying predefined eligibility criteria, 23 studies met the inclusion requirements and were included in the qualitative analysis. Results: Among the 23 included publications, 12 involved glass ionomers modified with silver, and 6 of these reported an increase in fluoride release. Seven studies focused on zinc-modified cements, and four examined materials reinforced with strontium. Conclusions: The addition of strontium, titanium oxide, silver nanoparticles, or zirconium oxide increases the release of fluoride ions, while sintered silver reduces it. There is a great discrepancy among researchers regarding the effect of the addition of zinc oxide and its appropriate amount in the glass ionomer material. Full article