The effect of TiN deposition time on the field-emission performance coated on ZnO nanorod arrays

ZnO nanorod arrays (NRs) with a large number of sharp tips and uniform shapes were grown on the carbon cloth (CC) by a simple hydrothermal method. Titanium nitride (TiN) nanoparticles with various thicknesses were deposited on the ZnO NRs by magnetron sputtering to obtain ZnO/TiN core-shell arrays. Field emission (FE) performance of ZnO NRs show close dependence on TiN coating thickness. The turn-on field first decreases and then increases with increasing TiN coating thickness from 60 nm to 300 nm. The arrays with a design architecture can strike a balance between increased emission sites and limited field shielding effects. ZnO/TiN240 core-shell NRs have the lower turn-on electric field at 0.79 V/μm and the higher current densities at 9.39 mA/cm². The field enhancement factor (β) of ZnO/TiN240 is about 3.2 times that of the bare ZnO NRs. On the other hand, the electrochemical properties were improved due to the formation of core-shell heterojunction on the ZnO/TiN interface and porous structure, which makes the ion and charge transport more convenient. Hence, this work not only revealed that the ZnO/TiN core-shell structure exhibited excellent improvement in both FE and supercapacitors applications, but also that growing arrays on CC was expected to achieve flexible display.     

Microstructure induced ultra-high energy storage density coupled with rapid discharge properties in lead-free Ba0.9Ca0.1Ti0.9Zr0.1O3–SrNb2O6 ceramics

Novel lead-free (1-x)Ba_0·9Ca_0·1Ti_0·9Zr_0·1O₃-xSrNb₂O₆ ceramics were synthesized via a two-step high energy ball milling process. The evolution of microstructural properties, phase transformation, and energy storage characteristics was comprehensively investigated to assess the applicability of material in multi-layered ceramic capacitors. The substitution of SrNb₂O₆ (SNO) in Ba_0·9Ca_0·1Ti_0·9Zr_0·1O₃ (BTCZ) has resulted in substantial improvement in materials density along with a small increase in the grain size of the synthesized ceramic. A thorough microstructural investigation indicates an excellent dispersibility and compatibility between BTCZ and SNO phases. With an increase in SNO substitution, a transition from typical ferroelectric to relaxor ferroelectric has been observed, which has led to a significantly slimmer ferroelectric loop along with frequency dispersive dielectric properties. The optimized composition (i.e., x = 0.10) exhibits an ultra-high recoverable energy density of 2.68 J/cm³ along with a moderately high energy efficiency of 83.4%. Further, SNO substituted samples have also shown an enhancement in breakdown strength. The improvement in energy storage performance and breakdown strength of SNO substituted BTCZ composites are mainly attributed to relatively homogeneous grain morphology, optimum grain size, microstructural density, and improved grain boundary interface.     

Fabrication and properties of 3D printed zirconia scaffold coated with calcium silicate/hydroxyapatite

The scaffold of bone repair needs a variety of material combinations to meet its intended performance; a typical single material such as zirconia has excellent mechanical properties, while hydroxyapatite and calcium silicate are bioactive materials with different degradation rates. In this paper, porous zirconia scaffolds were fabricated using 3D printing technology. The surface of the scaffold was coated by dipping with different contents of calcium silicate and hydroxyapatite to improve the biological activity and mechanical properties. Mechanical tests show that the coating material can effectively fill the pores of the porous scaffold, increasing its compressive strength by an average of 55%. The simulated body fluid (SBF) test showed that the higher calcium silicate in the coating increased the degradation rate. Cell experiments showed that the coated scaffolds exhibited good cytocompatibility and were beneficial to the proliferation and differentiation of cells. In conclusion, coated scaffolds have potential applications in the field of bone repair.     

Effect of Co addition on microstructural and mechanical properties of WC–B4C–SiC composites

In this study, the effect of Co addition on microstructural and mechanical properties of WC-B₄C–SiC composites sintered by spark plasma sintering (SPS) method was investigated. For this purpose, three batches of WC-B₄C–SiC with different contents of Co (10 vol%, 15 vol%, and 20 Vol %) were sintered at 1400 °C. The results of X-ray diffraction (XRD) analysis of the samples indicated the formation of W₂B₅, W₃CoB₃ as well as the remained C phases and unreacted SiC phase. It was observed that by increasing the Co content, the amount of W₂B₅ phase reduces and W₃CoB₃ and C contents increase. Therefore, W₂B₅ peaks were not detected in the sample containing 20vol% Co. Relative density values above 97% were obtained for all the composites. However, a decrease was observed in relative density by increasing the Co content in the composites. The highest flexural strength (510 ± 42 MPa), fracture toughness (10.34 ± 0.82 MPa m^1/2), and hardness (20.63 ± 0.75 GPa) were also obtained for the sample containing 10vol% Co compared to the other samples. In addition, Transgranular fracture of SiC as well as pulling out of W₃CoB₃ and W₂B₅ particles were observed in the fracture surface micrographs of the samples. The presence of micro-cracks in the SiC grains, fracture of W₃CoB₃ grains, and crack deflection was reported as dominant toughening mechanisms.     

Development and characterisation of microporous biomimetic scaffolds loaded with magnetic nanoparticles as bone repairing material

Fine-tuning of the scaffolds structural features for bone tissue engineering can be an efficient approach to regulate the specific response of the osteoblasts. Here, we loaded magnetic nanoparticles aka superparamagnetic iron oxide nanoparticles (SPIONs) into 3D composite scaffolds based on biological macromolecules (chitosan, collagen, hyaluronic acid) and calcium phosphates for potential applications in bone regeneration, using a biomimetic approach. We assessed the effects of organic (chitosan/collagen/hyaluronic acid) and inorganic (calcium phosphates, SPIONs) phase over the final features of the magnetic scaffolds (MS). Mechanical properties, magnetic susceptibility and biological fluids retention are strongly dependent on the final composition of MS and within the recommended range for application in bone regeneration. The MS architecture/pore size can be made bespoken through changes of the final organic/inorganic ratio. The scaffolds undertake mild degradation as the presence of inorganic components hinders the enzyme catalytic activity. In vitro studies indicated that osteoblasts (SaOS-2) on MS9 had similar cell behaviour activity in comparison with the TCP control. In vivo data showed an evident development of integration and resorption of the MS composites with low inflammation activity. Current findings suggest that the combination of SPIONs into 3D composite scaffolds can be a promising toolkit for bone regeneration.     

Effect of environmental pressure on the microstructure of YSZ thermal barrier coating via suspension plasma spraying

Suspension plasma spraying (SPS) as a potential technique to prepare thermal barrier coatings (TBCs) has been attracting more and more attention. However, most reports on SPS were carried out in the atmosphere. Given the unique features of in-flight particles and plasma jets under low pressure, the resulting coatings are expected to be different from those under atmospheric pressure. In this article, yttria-stabilized zirconia (YSZ) thermal barrier coatings were prepared using suspension plasma spraying under different environmental pressures. The results show that as the environmental pressure decreased, the column-like structural coating turned into a vertical crack segmented structure, as well as a dramatic decrease in surface roughness. More nanoparticle agglomerates were formed in the coating under lower environmental pressures. The real porosity of the coating increased with a decrease in environmental pressure.     

Ir-Pt/C composite with high metal loading as a high-performance anti-reversal anode catalyst for proton exchange membrane fuel cells

Voltage reversal induced by hydrogen starvation can severely corrode the anode catalyst support and deteriorate the performance of proton exchange membrane fuel cells. A material-based strategy is the inclusion of an oxygen evolution reaction catalyst (e.g., IrO₂) in the anode to promote water electrolysis over harmful carbon corrosion. In this work, an Ir-Pt/C composite catalyst with high metal loading is prepared. The membrane-electrode-assembly (MEA) with 80 wt% Ir-Pt(1:2)/C shows a first reversal time (FRT) of up to 20 hours, which is about ten times that of MEA with 50 wt% Ir-Pt(1:2)/C does. Furthermore, the MEA with 80 wt% Ir-Pt(1:2)/C exhibits a minimum cell voltage loss of 6 mV@1 A/cm² when the FRT is terminated in 2 hours, in which the MEA with 50 wt% Ir-Pt(1:2)/C exhibits a voltage loss of 105 mV@1 A/cm². Further physicochemical and electrochemical characterizations demonstrate that the destruction of anode catalyst layer caused by the voltage reversal process is alleviated by the use of the composite catalyst with high metal loading. Hence, our results reveal that the combination of OER catalyst on the Pt/C with high metal loading is a promising approach to alleviate the degradation of anode catalyst layer during the voltage reversal process for PEMFCs.     

Understanding on the hydrogen detection of plasma sprayed tin oxide/tungsten oxide (SnO2/WO3) sensor

The plasma spray technique was well proven in producing metal oxide based gas sensors in the last two decades using different powder feedstocks. However, limited research was made to fabricate hydrogen gas sensor from tin oxide layer coated over tungsten oxide layer. This paper attempts to interpret the hydrogen gas sensing performances of plasma sprayed coating derived by depositing tin oxide layer over tungsten oxide (SnO₂/WO₃) layer. Plasma sprayed SnO₂/WO₃ sensor showed maximum response of 90% at 150 °C in contrast to stand-alone WO₃ (89% at 350 °C) and stand-alone SnO₂ (89% at 250 °C). The lower operating temperature of SnO₂/WO₃ sensor without compromising gas response was attributed to the WO₃–SnO₂ hetero-junction. SnO₂/WO₃ sensor showed selective sensing towards hydrogen with respect to carbon monoxide and methane gases. This sensor also possessed repeatable characteristics after 39 days from the initial measurement. In a nut-shell, plasma spayed SnO₂/WO₃ sensor showed stability of base resistance, repeatability after successive response and recovery cycles, selective sensing towards 500 ppm H₂ with significant magnitude of gas response of 90%, response time of 35 s and recovery time of 269 s at a temperature of 150 °C.     

Completely eliminating the metal barrier cracks on Nafion for suppressing methanol crossover with anodic aluminum oxide substrates

Methanol crossover is one of the main challenges for direct methanol fuel cells (DMFCs). Depositing a metal barrier on Nafion can reduce the crossover but usually faces the metal cracking issues. This study presents a new composite membrane in which an anodic aluminum oxide (AAO) substrate is impregnated with a Nafion solution and then coated with a layer of Au. The AAO/Nafion/Au composite membrane shows an ideal metal crack-free surface. Higher and more stable voltage has been achieved for the cell with the membrane, indicating an effectively suppressed methanol-crossover. Results reveal that there is a tradeoff between suppressing the methanol crossover and increasing the ion transmission. By optimizing the membrane, it can not only suppress the methanol crossover but also enhance the output performance of DMFCs. The current density and power density of the cells can be enhanced by 59% and 52.85%, respectively, compared to the cell with a commercial Nafion 117. Overall, this work provides a new approach to designing crack-free membranes for DMFCs.     

High H2 selectivity with low coke formation for methanol steam reforming over Cu/Y1.5Ce0.84Ru0.04O4 catalyst in a microchannel plate reactor

The synthesized novel metal oxides Y_xCe_yRu_zO₄ (x = 1.5, y = 0.84, z = 0.04) which was produced by the sol-gel method was used as a support for Cu active metal on the surface of a microchannel plate reactor in the methanol steam reforming (MSR) process. The prepared catalysts were characterized by X-ray powder diffraction (XRD), BET surface area analysis (S_BET), energy-dispersive X-ray analysis (EDX), field-emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), temperature-programmed desorption (NH₃-TPD), and temperature-programmed reduction (H₂-TPR). High methanol conversion (99.5%) and H₂ selectivity (98.7%) and low CO selectivity (1.4%) were achieved for Cu/Y_xCe_yRu_zO₄ coated microchannel reactor at 250 °C. FE-SEM images and TGA curve of the spent catalyst displayed no coke formation on the surface of the catalyst after 32 h on stream at 300 °C. The low reduction temperature of Cu, high BET surface area, and high pore volume of the catalyst are considered imperative factors that cause a better dispersion of copper on the Y_1.5Ce_0.84Ru_0.04O₄ support.