Search

Transformer oil-based nanofluid-impregnated pressboard (NIP) with TiO 2 nanoparticles has been previously shown to exhibit substantially higher AC breakdown strength than that of pure oil-impregnated pressboard (OIP). In this study, OIP and NIP with TiO 2 nanoparticles were prepared and experiments on DC breakdown strength of were performed. It was found that NIP possesses higher resistance to DC breakdown strength than that of OIP. To reveal the working mechanism, a pulsed electro acoustic (PEA) device was used to measure the space charge accumulation and dissipation characteristics in OIP and NIP. The results show that the density of deep level traps in NIP is visibly reduced owing to the addition of TiO 2 nanoparticles and homopolar space charge accumulation on both sides of NIP is suppressed. Moreover, the charges injected from electrodes into NIP under DC voltage is also restrained owing to the increase of the Schottky potential barrier. Thus, the DC breakdown performance of NIP is considerably improved. [ABSTRACT FROM AUTHOR]

Polarization and traps determine the electrical property of oil-paper insulation, but most attention has been paid to the modification of insulating oil with nanoparticles, so there are is little research about oil-impregnated paper, and the origin for performance variation is not understood yet. In this paper, spherical nanoscale titanium dioxide was prepared by the hydrolysis method and nanofluid-impregnated paper (NP) was fabricated through oil-impregnation. The frequency domain spectrum was measured for polarization analysis, and both thermally stimulated depolarization current (TSDC) and isothermal surface potential decay (ISPD) methods were used to reveal trap parameters. Results show that NP's low frequency permittivity is much larger, and another peak appears in the spectrum even though the content of nanoparticles is very low. With the addition of TiO2 nanoparticles, TSDC's amplitude and peak temperature increase, and the trap energy becomes shallower. TiO2 nanoparticles' strong polarization and high activation energy contribute to NP's larger interface polarization intensity and activation energy. Furthermore, because of oxygen vacancies, TiO2 nanoparticles offer a transfer site for holes and electrons to escape from deep traps; thus, the trap energy is greatly reduced. [ABSTRACT FROM AUTHOR]

All-inorganic perovskite quantum dots (PeQDs) have aroused great research interest in white light-emitting diodes (WLED) due to their excellent optoelectronic properties, but the poor stability, caused by dynamically binding long-chain capping ligands, hinders their future practical applications. To address this issue, here, we exploit short-chain butyric acid (BA) to replace long-chain oleic acid (OA) as capping ligand of CsPbX3 PeQDs by a hot-injection method. The addition of BA not only makes the morphology of CsPbBr3 PeQDs uniform and improves the crystallinity but also effectively suppresses nonradiative recombination, achieving a near unit photoluminescence quantum yield of 96%. The BA capped CsPbBr3 PeQDs exhibit high stability up to 180 d stored in ambient environment and also significantly improved resistance against polar solvent, ultra-violet lamp irradiation, and heat, which is rationalized by the strong binding capacity and shortened distance of BA to the PeQDs through ab initio calculations. Furthermore, by combining green-emission CsPbBr3 and red-emission CsPbBr0.8I2.2 PeQDs with blue GaN chip, we achieved WLEDs with excellent luminous properties, showing their great potential in practical application of wide-color-gamut display and lighting. [ABSTRACT FROM AUTHOR]

Nanoparticles have exhibited great potential in improving insulating property of liquid and solid dielectrics. To explore their modification mechanism on transformer oil-impregnated pressboards, TiO2 nanoparticles with different diameters of 5nm, 10nm, and 15nm were synthesized and used to prepare transformer oil-based nanofluids. The creeping flashover characteristics of both pure oil-impregnated paperboards (OPs) and nanofluid-impregnated pressboards (NPs) were examined under lightning impulse and AC voltages. It was found that the creeping flashover property of NPs is significantly improved with the decreasing of nanoparticle size. Especially, it is enhanced by 2.44 times under positive lighting impulse as nanoparticle size reduced from 15 nm to 5 nm. The results of space charge decay and trap characteristics reveal the decrease of nanoparticle size can lower trap depth and greatly enhance the space charge dissipation rate, leading to more uniform electric field distribution at the interface between nanofluid and pressboards and higher creeping flashover property. [ABSTRACT FROM AUTHOR]

Synergistic adsorption and advanced oxidation processes (AOPs) is being considered as an effective strategy to solve the poor catalytic performance and incomplete mineralization of pollutants currently faced by traditional AOPs and adsorption techniques. However, the poor adsorption-specificity/catalytic performance of catalyst needs to be improved. Herein, a daidzein imprinted defective Fe-MOF (Fe-MOF-DMIP) was successfully developed. Due to its enhanced hydrogen-bond/hydrophobic interaction and pore-filling effect, Fe-MOF-DMIP can selectively adsorb levofloxacin (Q max was 315.31 mg g−1). The acid-stability of Fe-MOF-DMIP in water was improved and pH can be expanded to 3–11. Attributed to the enhanced Fe cycle and mass transfer efficiency, Fe-MOF-DMIP could efficiently active H 2 O 2 /persulfate, resulting in the removal rate of levofloxacin reached 98.4%/82.4% (H 2 O 2 /persulfate). The synergistic mechanism of adsorption@degradation and degradation pathway were also expounded. This work provided a new strategy for developing multifunctional catalysts, and emphasized the importance of paying attention to the types of free radicals produced in AOPs. [Display omitted] • Introducing imprinting strategy greatly increased the adsorption selectivity of LEX. • Formed defects could enhanced Fe (III)/Fe (II) cycle and mass transfer efficiency. • Fe-MOF-DMIP exhibited enhanced pH (3−10) stability. • Synergy adsorption@degradation strategy significantly improved the removal of LEX. • Fe-MOF-DMIP show excellent RSE (69.3%) in PS activation. [ABSTRACT FROM AUTHOR]

Creeping flashover of mineral-oil-impregnated pressboard under impulse stress is a common insulating failure in oil-immersed transformers, arousing increasing attention. Recent studies have shown that the breakdown strength of transformer oil under positive lightning impulse voltage can be significantly improved through nanoparticles-based modification, and Fe3O4 has shown the best improvement in breakdown strength compared to other nanoparticles that have been used. This paper presents the creeping flashover characteristics of pure oil-impregnated pressboard (OIP) and nanofluid-impregnated pressboard (NIP) based on Fe3O4 nanoparticles under positive and negative lightning impulse voltages, respectively. It was found that NIP possessed higher resistance to creeping flashover than OIP. The relative permittivities of oil and oil-impregnated pressboard before and after nanoparticles-based modification were measured, and the results revealed that the addition of nanoparticles led to a better match in relative permittivity between oil and oil-impregnated pressboard, and a more uniform electric field distribution. Furthermore, the shallow trap density in NIP was obviously increased compared to that of OIP through the thermally stimulated depolarization current (TSDC), which promoted the dissipation of surface charges and weakened the distortion of the electric field. Therefore, the creeping flashover characteristics of oil-impregnated pressboard were greatly improved with Fe3O4 nanoparticles. [ABSTRACT FROM AUTHOR]

Abstract Laves phase segregation is a universal phenomenon in additive manufactured or as-cast Inconel 718 alloy, and the Laves phase usually degrades the mechanical properties of the matrix. In this work, nickel-based alloys designed with different Nb contents were successfully fabricated by laser metal deposition (LMD) via a dual-feed system, and the Laves phase distribution at the macro level was relatively uniform. The effects of Nb content on the microstructure, mechanical properties and surface potential of the as-received and heat-treated nickel-based alloys were investigated. The grain size of the as-received LMD nickel-based alloys decreased with the Nb content, and the Laves phase exhibited a universally higher nano-hardness but lower surface potential than the γ matrix. The nano-hardness of the Laves phase linearly increased, whereas the Volta potential decreased with the Nb content. The strength improvement for the as-received LMD nickel-based alloys with different Nb contents was equally attributed to grain refinement and enhancement of the Laves phase (both hardness and content), while the increase in the precipitate content (main γ″) as a function of Nb content contributed to the substantial improvement in hardness for the heat-treated LMD nickel-based alloys and the grain refinement strengthening effect was comparative minor after aging treatment. Graphical abstract Image 1 Highlights • Graded nickel-based alloys were fabricated one-time via a dual-feed system. • Nb content errors of the designed parts were all within 4%. • Strength improvement was attributed equally to grain refinement and Laves phase. • γ″ precipitation ascribed to the hardness improvement for heat-treated alloys. [ABSTRACT FROM AUTHOR]

Sulfur quantum dots (SQDs), as a novel metal-free fluorescent material, are getting increasingly tremendous attention in metal ion detection, especially for Fe3+, due to the merits of antimicrobial potential, low toxicity, and exciting optoelectronic properties. However, sensing mechanism of SQD based fluorescent probe for Fe3+ is not clear yet, and high sensitivity and large detection range remain a challenge. Here, we report the synthesis of hydrophilic SQDs as a fluorescent nanoprobe for Fe3+ via a fluorescent turn-off mode. We systematically studied the quenching mechanism by ultraviolet–visible absorption spectra, steady-state and time-resolved photoluminescent spectra, and temperature-dependent quenching constants. Results unclearly evidenced the quenching behavior to both inner filter effect and static quenching. Furthermore, the nanoprobe presents a large detection range from 2.5 to 700 μM and a limit of detection low to 53.6 nM, both of which are the record performance to our knowledge. At last, it shows high selectivity toward Fe3+ and presents no ionic strength effect in the range of investigation, which enables surprising results for Fe3+ detection in deionized water with interference ion and real water samples. [Display omitted] • A novel fluorescent nanoprobe based on sulfur quantum dots for Fe3+ was reported. • The nanoprobe delivers a record detection range and limit of detection. • The sensing mechanism is systematically studied and uncovered. • The nanoprobe shows high selectivity and results for Fe3+ in real water samples. [ABSTRACT FROM AUTHOR]