Chain-Like Semiconductive Fillers for Dielectric Enhancement and Loss Reduction of Polymer Composites.

Dielectric loss is a crucial factor in determining the long-term endurance for security and energy loss of dielectric composites. Here, chain-like semiconductive fibers of titanium oxide, indium, and niobium-doped titanium oxide are used for enhancing the complex dielectric properties of a polymer through composite construction, which involves significant interface enhancements. The chain-like fibers significantly enhance the dielectric constant owing to the special morphology of the fillers and their interfacial polarization, especially at higher temperatures. The dielectric loss and electrical conductivity of the composites are substantially reduced across the entire investigated temperature range, achieved by passivating the fiber surface with an alumina shell using atomic layer deposition. The as-deposited alumina shell transformed from an amorphous to a crystalline phase through thermal annealing results in a porous shell and more effective suppression of the loss tangent and electrical conductivity. A plausible mechanism for loss suppression is associated with carrier movement along the surface of the fibers and bulk, leading to a higher loss tangent. The alumina shell blocks the carrier transport path, particularly at the interfaces, resulting in a reduced interfacial polarization contribution and energy storage loss. This study provides a method for inhibiting dielectric loss by fabricating fillers with special surfaces.

Carbon Contamination Prevention during Spark Plasma Sintering.

Carbon contamination from graphite molds during spark plasma sintering (SPS) considerably affects the properties of the sintered materials, especially transparent ceramics. Herein, transparent Y3Al5O12 (YAG) ceramics were prepared via SPS using Mo and Ta foils, separately and in tandem, as protective barriers against carbon contamination. The effects of Ta and Mo foils on the transparency and microstructure of the ceramics, and their protection mechanisms were studied. Experimental results show that a reaction layer formed at the Ta-YAG interface with a YTaO4-Al2O3 eutectic composition suppresses carbon penetration into the ceramic, increasing its transparency. By contrast, Mo foils, when used as protective barriers, allow carbon diffusion into the ceramic, resulting in the formation of nonuniform microstructural features. However, it does not form a reactive layer and, hence, is removed easily from the YAG surface. Multilayered Ta-Mo barrier exhibits improved outcomes if the Ta thickness is more than ∼100 µm. This behavior is attributed to the interior diffusion-blocking mechanism of Ta. Similar optical performance was demonstrated by both approaches. The results prove that carbon contamination in SPS-derived samples can be effectively prevented. Additionally, this study reports on a novel strategy of bonding oxide ceramics to metals by adding a Ta layer at the joint interface.

Highly Transparent Polycrystalline MgO via Spark Plasma Sintering.

Optically transparent ceramics and MgO in particular are promising materials for a wide range of optical applications. This study introduces exceptionally highly transparent MgO ceramics produced via spark plasma sintering (SPS) at relatively low temperature and pressure by optimal incorporation of LiF as a sintering additive. The effect of LiF content on the microstructural and optical properties is presented with emphasis on its function as a densification aid and an agent for minimizing residual carbon contamination. Fully dense MgO discs, 20 mm in diameter and 2 mm thick, with ∼80% in-line transmission at 800 nm and >85% transmission in the infrared range (2-6 µm), are attained. These results demonstrate outstanding transparency in SPS polycrystalline MgO in the 800 nm range, only 7% below the theoretical value. In addition, this work strengthens our understanding of the LiF action mechanism during MgO sintering and its influence on texture development in the SPS-pressing direction. These findings pave the way for fabrication of large, fully dense samples with nearly theoretical transparency.

Composite Indium Tin Oxide Nanofibers with Embedded Hematite Nanoparticles for Photoelectrochemical Water Splitting.

Hematite is a classical photoanode material for photoelectrochemical water splitting due to its stability, performance, and low cost. However, the effect of particle size is still a question due to the charge transfer to the electrodes. In this work, we addressed this subject by the fabrication of a photoelectrode with hematite nanoparticles embedded in close contact with the electrode substrate. The nanoparticles were synthesized by a solvothermal method and colloidal stabilization with charged hydroxide molecules, and we were able to further use them to prepare electrodes for water photo-oxidation. Hematite nanoparticles were embedded within electrospun tin-doped indium oxide nanofibers. The fibrous layer acted as a current collector scaffold for the nanoparticles, supporting the effective transport of charge carriers. This method allows better contact of the nanoparticles with the substrate, and also, the fibrous scaffold increases the optical density of the photoelectrode. Electrodes based on nanofibers with embedded nanoparticles display significantly enhanced photoelectrochemical performance compared to their flat nanoparticle-based layer counterparts. This nanofiber architecture increases the photocurrent density and photon-to-current internal conversion efficiency by factors of 2 and 10, respectively.

Electrospun Anion-Conducting Ionomer Fibers-Effect of Humidity on Final Properties.

Anion-conducting ionomer-based nanofibers mats are prepared by electrospinning (ES) technique. Depending on the relative humidity (RH) during the ES process (RHES), ionomer nanofibers with different morphologies are obtained. The effect of relative humidity on the ionomer nanofibers morphology, ionic conductivity, and water uptake (WU) is studied. A branching effect in the ES fibers found to occur mostly at RHES < 30% is discussed. The anion conductivity and WU of the ionomer electrospun mats prepared at the lowest RHES are found to be higher than in those prepared at higher RHES. This effect can be ascribed to the large diameter of the ionomer fibers, which have a higher WU. Understanding the effect of RH during the ES process on ionomer-based fibers' properties is critical for the preparation of electrospun fiber mats for specific applications, such as electrochemical devices.

Electrospun Fe-Al-O Nanobelts for Selective CO2 Hydrogenation to Light Olefins.

Ceramic nanobelt catalysts consisting of Fe-Al-O spinel modified with potassium were synthesized for CO2 hydrogenation into hydrocarbons. Nanobelts and hollow nanofibers were produced utilizing the internal heat released by oxidation of the organic component within the fibers. This extremely fast and short heating facilitated crystallization of the desired phase, while maintaining small grains and a large surface area. We investigated the effects of mat thickness, composition, and heating rate on the final morphology. A general transformation mechanism for electrospun nanofibers that correlates for the first time the mat's thickness and the rate of oxidation during thermal treatment was proposed. The catalytic performance of carburized ceramic K/Fe-Al-O nanobelts was compared to the K/Fe-Al-O spinel powder. The electrospun catalyst showed a superior carbon dioxide conversion of 48% and a selectivity of 52% to light C2-C5 olefins, while the powder catalyst produced mainly C6+ hydrocarbons. Characterization of steady state catalytic materials by energy-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and N2-adsorption methods revealed that high olefin selectivity of the electrospun materials is related to a high extent of reduction of surface iron atoms because of more efficient interaction with the potassium promoter.

Lamellar-like Electrospun Mesoporous Ti-Al-O Nanofibers.

Ceramic oxides nanofibers are promising materials as catalysts, electrodes and functional materials. In this report, a unique lamellar-like mesoporous structure was realized for the first time in a new system based on titania and alumina. The final structure was found to be highly dependent on the process conditions which are outlined herein. In view of the similar architecture we recently obtained with Fe-Al-O fibers, the pore formation mechanism we outline herein is general and is applicable to additional systems.

The effect of roughness on biophysical stimuli at the bone-cartilage interface.

Numerical simulations are often used to investigate the effect of mechanical environment on fracture healing. Although these models exhibit biologically relevant mechanical parameters at the bone-callus interface, this interface is modelled as perfectly smooth when in fact it is rough. In this study, a macro-micro-two-scale finite element model was used to determine if roughness significantly alters calculated local mechanical parameters. An idealized fracture healing poroelastic model with a small micro-modelled sub-domain of cartilaginous callus adjacent to rough bone was subjected to cyclic loading. The shear stress, tangential fluid velocity, and pore pressure were investigated. With roughness similar to that at the growth plate, solid matrix shear stress differed substantially with interface roughness, whereas interstitial fluid velocity and pore pressure were only slightly affected. Hence, when modelling local micro-mechanical environments near hard-soft tissue interfaces, interface roughness should be considered.