Search

Abstract: Transformer oil-based nanofluids (NFs) with TiO2 semiconductive nanoparticles (SNFs) exhibit substantially higher AC breakdown voltage than that of pure transformer oils at variable relative humidity from 20% to 80%. Charge accumulation and decay characteristics of pure oils and SNFs were measured by the pulse electroacoustic technique (PEA). It reveals that SNFs have more uniform internal electric fields and higher charge decay rate compared to pure oils under high relative humidity. It is confirmed by the test results of electrophoresis and thermally stimulated current (TSC) that the nanoparticles adsorb water molecules at the nanoparticle–oil interface, giving rise to the higher shallow trap density and resulting in better charge transport in SNFs. [Copyright &y& Elsevier]

Abstract: Well-crystalline ZnO nanorods were synthesized by a simple solution route employing dodecyl benzene sulfonic acid sodium salt (DBS) as a modifying agent. ZnO gas sensors were fabricated from ZnO nanorods with an average diameter of around 95nm and their gas-sensing properties were investigated. It was found that the sensors based on ZnO nanorods exhibit high responses and good selectivities to benzene and ethanol gas. Our results indicate that ZnO sensors will be promising candidates for practical detectors for dilute benzene and ethanol, respectively. [Copyright &y& Elsevier]

Abstract: Optical properties of ZnO star-shaped nanostructures grown by wet chemical solution method were investigated by using Raman scattering and temperature-dependent photoluminescence. High intensity of Raman mode with narrow FWHM of 9cm−1 appearing at 436cm−1 indicates the good quality of ZnO wurtzitic structure. Temperature-dependent ultraviolet photoluminescence was studied over the temperature range from 78 to 293K. At low-temperatures and low-excitation intensities, the dominant spontaneous emissions are due to radiative recombination of excitons bound to donors and one longitudinal optical phonon assistant free exciton A. Finally, only the first-order longitudinal–optical phonon replica of the A free exciton recombination was observed at room temperature. The exciton emission behaviour, including excitonic energy, intensity and line width dependents on the temperature and excitation intensities are discussed. The deep-level emission band is barely observable both at room temperature and at cryogenic temperature measurements. [Copyright &y& Elsevier]

Dolostone reservoirs are crucial for global oil and gas storage, holding a significant portion of hydrocarbon reserves within carbonate formations. Understanding the chemical mechanism of dolomite dissolution with organic acids and associated porosity development in these reservoirs is vital for optimizing hydrocarbon recovery. In this work, two sets of simulation experiments are designed to understand the controls of temperature and ionic effects on porosity enhancement during the dissolution of dolomite with acetic acid. In specific, we discovered a three-step reaction process between dolomite and acetic acid, involving acetic acid dissolution in water, acetic acid dissociation, and dolomite dissolution. Burial environments with higher temperatures reduce the degree of acetic acid dissociation, leading to a corresponding decrease in dolomite dissolution in acetic acid solutions. The presence of salt ions in the solution influences the reaction process, with magnesium chloride (MgCl 2) having the most significant enhancing effect on dolomite dissolution, followed by sodium chloride (NaCl), while calcium chloride (CaCl 2) has a limited impact. Sodium sulfate (Na 2 SO 4) enhances dolomite dissolution at lower temperatures; however, at higher temperatures (>100 °C), it may reduce dolomite dissolution due to the precipitation of CaSO 4. Despite a relatively short open-flow time, episodic burial dissolution of dolomite by acetic acid fluids under overburden pressure leads to a "net increase" in the reservoir space and enhances its connectivity attributes. During burial diagenesis, geological forces episodically drive organic acid fluids to the dolomite reservoir, predominantly dissolving dolomite along pre-existing pore development zones and geological interfaces, exhibiting inheritance, episodicity, and localization characteristics. Overall, this study provides insights into the dissolution and diagenetic processes of dolomite in the presence under acetic acids, from the point of dissolution simulation experiments. Collectively, these findings enhance our understanding of pore-system evolution and fluid-rock interactions in deep carbonate reservoirs. • Simulations reveal temperature and ions' effects on dolomite porosity in acetic acid. • Higher temperatures reduce acetic acid dissociation and dolomite dissolution. • Nonlinear response of dolomite dissolution under Na 2 SO 4 -contained acid with temperature. • Episodic acetic acid-dolomite dissolution enhances reservoir space and connection. [ABSTRACT FROM AUTHOR]

With the commencement of high voltage alternating current (HVAC) and high voltage direct current (HVDC), the demands on insulating reliability of power transformer is getting more and more imperative. The mineral oil (MO/TO) in conjunction with paper is the main insulation components in oil-immersed transformers; their insulation properties play a significant role in the safe and stable operation of power transformers. To strengthen the insulation level of ultra-high voltage transformer and to reduce its size and weight, it is imminent to enhance the insulating performance of transformer oil and oil-impregnated cellulose. Recently, a unique novel effort of suspension of nanoparticles (NPs) into mineral oil (MO) has been carried out and the results have exhibited improved insulation characteristics of transformer oil. The Al 2 O 3 nanoparticles with favorable features were prepared in our lab to develop transformer oil/paper insulation system with better insulation performance. The transformer oil-based nanofluids (NFs) were prepared with nanorod shape, oleic acid (OA) surface modification and 0.8 g/L concentration of NPs. The pressboards were cut into the desired sizes (85 mm.55 mm). The thickness of the pressboards was 2 mm applied in flashover tests. The prepared pressboards were put into an oven at 105 °C for almost 48 h to carry out the hot air drying operation. Then they were put in the vacuum drying at 85 °C for 48 h. The impregnated pressboards were prepared by impregnating them into dried oil and NF under vacuum beneath 1 kPa at 80 °C for almost 48 h to obtain the oil-impregnated pressboard (OIP) and nanofluid-impregnated pressboard (NIP) respectively. Additionally, the prepared insulation system samples of liquid (MO and NFs) and solid (OIPs, NIPs) were thermally aged at 130 °C for 30 days. The effect of alumina NPs on thermal aging of transformer oil and pressboard were also investigated. The results showed that Al 2 O 3 NPs can slow down the aging of oil and pressboard. The average AC and positive LI BDV of aged NFs was 11% higher than aged MOs. The average LI creeping FOVs of NIPs were 6% higher than OIPs. Additionally, average AC creeping FOVs of NIPs were 8% higher than that of OIPs. The enhancement in insulating performance of aged NFs and NIPs as compared to MO and OIPs is interpreted in light of electron traps theory. • Nanoparticles have the potential to influence the breakdown performance of oil/paper insulation system. • Suspension of Al2O3 nanoparticles may slow down the aging process of the oil/paper insulation system. • The enhancement in insulting performance of oil/paper insulation system may be interpreted in light of electron traps theory. [ABSTRACT FROM AUTHOR]

Abstract: An icephobic surface is always desirable for high voltage overhead transmission lines to reduce ice formation on their aluminum surface, especially in a low temperature and high humidity environment. This work studied the effects of two hydrophobic coatings when applied on aluminum surfaces under cold and raining conditions in an artificial climatic chamber. Compared with bare hydrophilic aluminum surfaces, the aluminum surfaces coated with hydrophobic room temperature vulcanized silicone rubber (RTV SR) did resist ice formation but was covered by a layer of ice after 30min of spraying supercooled water. However, a superhydrophobic coating can largely prevent ice formation on the surface except a few ice growth spots at a working temperature of −6°C. Furthermore, such coating keeps average water contact angles larger than 150° even at a working temperature of −10°C. This highly icephobic performance of the above samples is mainly attributed to the superhydrophobic property of the coating, which was obtained on micronanoscale structured aluminum surfaces after the low surface-energy stearic acid treatment. [Copyright &y& Elsevier]

Four-electron process and the interference of Cl- make sluggish kinetics on oxygen evolution reaction (OER) for seawater electrolysis. Herein, NiFe LDH grown on NiFe-foam with CeO 2 modification and (W 2 O 7)2- intercalation was synthesized by one-step hydrothermal method. It only needs 353.8 and 386.7 mV to achieve a large current density of 1000 mA·cm−2 in 1 M KOH and alkaline natural seawater, respectively. The catalytic material can stand 100 h with a retention of 98.1% at 1000 mA·cm−2 in alkaline natural seawater. Experiments and theoretical calculations confirm that the state-of-the-art OER activity comes from the introduced CeO 2 with optimized adsorption energy of intermediates. The improved stability and selectivity in seawater can be ascribed to the preferential adsorption of Ni and Fe with higher valence on OH- based on hard and soft acid based (HSAB) principle by (W 2 O 7)2- intercalation. This work provides a viable approach to develop efficient catalytic material for large-current seawater electrolysis. NiFe LDH nanosheets with (W 2 O 7)2- intercalation and CeO 2 modification show state-of-the-art large-current seawater-electrooxidation performance contributed partially from introduced CeO 2 adjusting adsorption energy of intermediates during OER process, partially from preferential adsorption of OH- on metal active sites based on hard and soft acid based (HSAB) principle by (W 2 O 7)2- intercalation. [Display omitted] • NiFe LDH nanosheets with (W 2 O 7)2- intercalation and CeO 2 modification have been successfully synthesized. • It only needs an overpotential of 386.7 mV to achieve 1000 mA cm−2 in alkaline natural seawater electrocatalysis. • (W 2 O 7)2- intercalation enhances OH- selectivity and CeO 2 modification optimizes adsorption energy towards OER intermediates. [ABSTRACT FROM AUTHOR]

[Display omitted] • Compositional regulation by introducing MoS 2 provides rich H adsorption sites. • Internal electronic regulation in heterostructure accelerates the RDS in OER process. • MnCo 2 S 4 @MoS 2 employed as a bifunctional catalyst for efficient hydrogen production. • Operating stably in industrial condition with structural reconstruction at the anode. • The electron redistribution and reaction pathways are explained by DFT calculations. It remains to be challenging to develop bifunctional catalysts for overall water splitting (OWS) with high activity and durability at large current density. In an attempt to overcome this bottleneck, unique MnCo 2 S 4 hexagonal stars covered with MoS 2 nanosheets were in-situ grown on nickel foam (NF) to obtain MnCo 2 S 4 @MoS 2 /NF heterostructure with optimized composition and local electronic structure in this work. When employed as a bifunctional catalyst, it only needs low overpotentials of 208 and 332 mV in 6.0 M KOH to drive 1000 mA cm−2 with small Tafel slopes of 56.8 and 75.6 mV dec-1 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. In addition, MnCo 2 S 4 @MoS 2 /NF showed remarkable stability in simulated industrial conditions, operating stably for 50 h at 1000 mA cm−2 without any attenuation for HER/OER. Thus, the MnCo 2 S 4 @MoS 2 /NF can function as a bifunctional electrocatalyst for OWS, only requiring 1.795 V to afford 1000 mA cm−2 with splendid stability. The improved performance is ascribed to dual electric and compositional regulation, which endow MnCo 2 S 4 @MoS 2 /NF with rich active sites and heterointerfaces, thereby promoting electron transfer and boosting the reaction kinetic. Furthermore, density functional theory (DFT) calculations reveal that the construction of heterostructure can help regulate intrinsic electronic structure, resulting in accelerated reaction kinetics. This work provides a reasonable and meaningful method for boosting industrial green hydrogen production. [ABSTRACT FROM AUTHOR]

The relationship between the permittivity of a two-phase porous composite material and its structure forms the basis for the adjustment and analysis of the permittivity of the porous material. However, existing calculation models exhibit significant errors at low frequencies. A wide-frequency equivalent model is proposed in this paper based on the geometrical structural characteristics of porous materials, considering the effects of interface polarization and dielectric relaxation process. The relationship between the two-phase porosity material and the dielectric response of its framework and filling medium in a wide-frequency range can be calculated. Furthermore, the modified Cole–Cole model is adopted to analyze the dielectric spectrum characteristics of cellulose and aramid, thereby exhibiting the effects of polar bonds in the molecular structure and impurity ions in the material on the polarization strength and polarization process. The results obtained from this study can provide key parameters and a basis for the analysis of the polarization process of two-phase combined porous materials and the design of low-permittivity insulating paper. [Display omitted] [ABSTRACT FROM AUTHOR]

Low-temperature preparation of efficient electron transport layer (ETL) can effectively expand the application of perovskite solar cells (PSCs). We herein introduce anatase TiO 2 nanoparticles (NPs) with an average diameter of 15 nm prepared by hydrothermal method and optimized with acetic acid (AA) as well as oleic acid (OA). The Ti3+ as well as Ti–OH signals indicate the surface defects of TiO 2 NPs investigated by X-ray photoelectron spectroscopic (XPS) are observed to be passivated by the modifiers through chelate or bridging pattern. Thus, when the modified NPs are dispersed into the precursor for spin-coating ETLs under 150 °C, higher power conversion efficiency (PCE) of 20.15% and 19.41% is achieved based on planar structured PSC using TiO 2 modified with AA and OA, respectively. The device stability is also considerably increased. Analyzed by photoluminescence and electrochemical impedance spectroscopies, the improved cell performance can be ascribed to the reduced charge transport resistance, enhanced electron extraction, and suppressed recombination behavior. We anticipate this facile approach of fabricating efficient TiO 2 ETLs can be further employed into PSCs commercialization. [ABSTRACT FROM AUTHOR]