Enhanced electromagnetic shielding property of cf/mullite composites fabricated by spark plasma sintering

Aiming to prepare high-performance electromagnetic interference (EMI) shielding materials, chopped carbon fibers were incorporated into mullite ceramic matrix via rapid prototyping process of spark plasma sintering (SPS). Results indicate that C_f/mullite composites with only 1 wt% of carbon fibers exhibit highest shielding effectiveness (SE_T) over 40 dB at a small thickness of 2.0 mm, showing great advantages both in terms of performance and thickness compared with many mature carbon/ceramic composites. The high EMI shielding properties mainly depend on two mechanisms of absorption and reflection in this present work. The enhanced absorption and reflection of electromagnetic wave are ascribed to the promotional electrical conductivity arising from the formation of conductive network by introduction of carbon fibers. Regarding enhanced electrical conductivity, notable intensified interfacial polarization on a large number of interfaces between mullite matrix and carbon fibers is also the key factor to the improved absorption, which makes absorption play a dominant role in the significant improvement of EMI SE_T. The C_f/mullite composites with excellent EMI shielding properties and thin thickness show great potential application as EMI materials.     

Degradation behavior of Ta2O5 stacks and its dependence on the gate electrode

Response of 8 nm Ta₂O₅ stacks with Al and Au gate electrodes to voltage stress at room temperature and at 100 °C is investigated. Stress-induced leakage current (SILC) reveals significant gate dependence and distinct difference to SILC in SiO₂. The mechanisms for SILC generation and stress degradation are discussed. Unlike SiO₂, pre-existing traps and positive charge build-up are recognized as a key factor for generation of SILC in Ta₂O₅ stacks.     

A practical test of a γ–γ coincidence measurement setup for PGAA

A second cold-neutron beam experimental station has been built as part of the renewal of our prompt gamma activation analysis facility at the Budapest Research Reactor. This new station has been instrumented for neutron-induced prompt gamma-ray spectroscopy, involving γ–γ coincidence measurements. The γ–γ coincidence arrangement is introduced briefly, and its usage is illustrated with a practical example of the inactive tracer method for samples from glass furnace.     

Preparation and characterization of an Al2O3–ZrO2 nanocomposite,Part I: Powder synthesis and transformation behavior during fracture

An alumina–zirconia composite containing 5 mol% zirconia was prepared by following a wet interaction process in aqueous medium via the sol–gel route. The formed hydrogel which was aged for proper growth and orientation at room temperature, was then dried at a low temperature to minimize agglomeration. The sol–gel derived precursor powder was properly characterized through determination of surface area, particle size and thermal analysis. The sintering behavior was studied by compacting the nano-powder through cold isostatic pressing where maximum densification of 98.4% was achieved at 1550 °C. During Vickers indentation using a 5 kg load, cracks were propagating around the grain boundaries and fractured the ZrO₂ particles, which was associated with t-ZrO₂ to m-ZrO₂ transformation. Sintering was studied in the absence of a mineraliser.     

Magnetic properties and loss separation mechanism of FeSi soft magnetic composites with in situ NiZn-ferrite coating

Journal of Materials Science: Materials in Electronics - The soft magnetic performances including frequency-dependent permeability, core loss, and DC-bias properties of the Fe-6.5 wt.%Si (FeSi)...     

Porous (Ce0.2Zr0.2Ti0.2Sn0.2Ca0.2)O2-δ high-entropy ceramics with both high strength and low thermal conductivity

Single-phase (Ce_0.2Zr_0.2Ti_0.2Sn_0.2Ca_0.2)O_2-δ porous high-entropy ceramics have been in-situ fabricated by foam-gelcasting-freeze drying method at different temperatures. The microstructure, phase composition, and properties of the obtained ceramics were investigated. The results indicate that compared with other porous ceramics reported in the literatures, this type of ceramics exhibits excellent performance. The sample prepared at 1350 °C shows high porosity (88.6 %), low thermal conductivity (0.023 W m^-1 K^-1), and high compressive strength (1.48 MPa). The current study suggests that porous (Ce_0.2Zr_0.2Ti_0.2Sn_0.2Ca_0.2)O_2-δ high entropy ceramics are promising candidates for thermal insulation applications.     

The Mo as electron trapper and donor to modulate the electron of CoP2 in phosphating process

To prepare bifunctional electrocatalyst towards HER and OER is extremely important for promoting the development of electrochemical water splitting technology. Herein, the element doping method is employed to tune the electron environment of cobalt phosphide (CoP). The Mo-doped CoP supported on carbon cloth (CC) is constructed by solvothermal and annealing method. The effect of Mo on the electron modulation of CoP during different phosphating time was studied carefully. It is noted that the Mo play an important role in tuning the electron state of Co and P elements which can trap the electron and was reduced to low valence, then transfer the electron to Co and P. With increasing the phosphating time, the electron transfer phenomenon between Mo and CoP is obvious. Benefiting from the electron engineering of Mo, Co and P as well as thin and wrinkle sheets structure, the optimal electrocatalyst only requires 39 mV and 251 mV to deliver 10 mA cm⁻² for HER and OER, respectively. Also, as for the whole water splitting performance, it delivers 10 mA cm⁻² at cell voltage of 1.56 V. Importantly, Faraday efficiency of the optimal catalyst achieves 99.9% for HER due to the tuned electron state of Co and P, high ECSA and low R_ct.     

Effect of inserted baffles on hydrogen heterogeneous reaction in planar catalytic micro combustor

Heterogeneous reaction characteristics of premixed H₂/Air mixture are numerically investigated in micro combustor with coating platinum (Pt) catalyst on the inner wall. The well-designed combustor with the inserted baffle is committed to improving the transport of bulk species on the catalytic surface, therefore enhancing the fuel conversion ratio. A two-dimensional numerical model with detailed heterogeneous reaction mechanism is developed and verified. In this work, the numerical results reveal that the heterogeneous reaction rate and fuel conversion ratio are significantly improved in the combustor with inserted baffle. The velocity of gaseous mixture swiftly increases between the baffle and catalytic surface, resulting in the increasing adsorption-desorption of bulk species on the catalytic surface. The main influencing factors of inserted baffle body comprise of slit width between two ribs in the same row (W), rib length (L), distance between adjacent baffles row (D), number of baffle row (n) which are studied to obtain a set of optimized parameters of baffle in the well-designed combustor. The optimized parameters of the baffle are W = 0 mm, L = 0.4 mm, D = 4 mm and n = 4, which are employed in the combustor to obtain a high hydrogen conversion ratio. Moreover, the effect of different inlet velocities and equivalent ratios of the mixture on the heterogeneous reaction characteristics are carried out in the designed combustor. As the designed combustor performs well, and the improvement effect of the optimized baffle gradually increases together with the inlet velocity, particularly for high inlet velocity (7 m/s). The promotion effects of baffle in the designed combustor are presented when the rich and lean fuel are adopted at inlet velocity of 7 m/s. Finally, the relative parameters of this work can serve as a reference and guidance for the design of micro scale combustor.     

Quaternary Ti–Zr–Be–Ni bulk metallic glasses with large glass-forming ability

The glass-forming ability (GFA) of Ti–Zr–Be ternary alloys is dramatically improved by partially replacing Be with Ni. Centimeter-scale fully amorphous samples can be obtained in a wide Ni content range of 4 at.%–12 at.%. In particular, some of the developed Ti–Zr–Be–Ni alloys exhibit a critical diameter up to 20 mm, which is larger than that of other quaternary Ti-based bulk metallic glasses (BMGs). Moreover, Ni addition also enhances the yield strength and compressive plastic strain of Ti–Zr–Be alloys obviously. Based on the experimental results, the effect of substituting elements addition on the glass-forming ability of Ti–Zr–Be alloys has been systematically investigated and an empirical composition design method for the development of novel Ti-based BMGs with large GFA has been proposed.     

Synthesis and pyrolysis behavior of a soluble polymer precursor for ultra-fine zirconium carbide powders

A soluble polymer precursor for ultra-fine zirconium carbide (ZrC) was successfully synthesized using phenol and zirconium tetrachloride as carbon and zirconium sources, respectively. The pyrolysis behavior and structural evolution of the precursor were studied by Fourier transform infrared spectra (FTIR), differential scanning calorimetry, and thermal gravimetric analysis (DSC–TG). The microstructure and composition of the pyrolysis products were characterized by X-ray diffraction (XRD), laser Raman spectroscopy, scanning electron microscope (SEM) and element analysis. The results indicate that the obtained precursor for the ultra-fine ZrC could be a Zr–O–C chain polymer with phenol and acetylacetone as ligands. The pyrolysis products of the precursor mainly consist of intimately mixed amorphous carbon and tetragonal ZrO₂ (t-ZrO₂) in the temperature range of 300–1200 °C. When the pyrolysis temperature rises up to 1300 °C, the precursor starts to transform gradually into ZrC, accompanied by the formation of monoclinic ZrO₂ (m-ZrO₂). The carbothermal reduction reaction between ZrO₂ and carbon has been substantially completed at a relatively low temperature (1500 °C). The obtained ultra-fine ZrC powders exhibit as well-distributed near-spherical grains with sizes ranging from 50 to 100 nm. The amount of oxygen in the ZrC powders could be further reduced by increasing the pyrolysis temperature from 1500 to 1600 °C but unfortunately the obvious agglomeration of the ZrC grains will be induced.