Herein, we report a new strategy to effectively enhance the thermal conductivity of epoxy composites by constructing a three-dimensional thermally conductive network with 2D boron nitride nanosheets (BNNSs) and 0D boron nitride microspheres (BNMSs). In the composites, the BNMSs serve as the principal building blocks for constructing the thermally conductive network because of their large sizes, while the BNNSs are embedded within the interspaces of the BNMSs to improve the thermal pathway density. Experimental and finite element analysis reveals that the combined BNNSs and BNMSs (BNNSs/BNMSs) outperform individual BNNSs and BNMSs in terms of thermal conductivity enhancement. Notably, the BNNSs/BNMSs/epoxy composite with a filler loading of 30 wt % shows a thermal conductivity of 1.148 W m −1 K −1 , which is approximately 28.0 and 51.5% higher than the corresponding data for BNNSs/epoxy and BNMSs/epoxy composites, respectively, and five times that of pure epoxy. In addition, the BNNSs/ BNMSs/epoxy composites exhibit favorable dielectric properties, dynamic mechanical properties, and thermal stability simultaneously. The strategy described in this study provides guidance for optimizing the design of high-performance epoxy composites to meet the requirements of thermal management in modern electronic devices.
Two-dimensional boron nitride nanosheets (BNNSs) hold great promise as thermal management materials because of their ultrahigh thermal conductivity and wide band gap. However, the scalable exfoliation of hexagonal boron nitride (h-BN) into few-layered BNNSs remains a challenge. Herein, we proposed a novel tannic acid (TA)-assisted liquid-phase exfoliation approach to realize efficient exfoliation and functionalization of h-BN in an aqueous medium. This method gave rise to a high exfoliation yield of 42.2% and the resultant TA-functionalized BNNSs (BNNSs@TA) showed good dispersion in both water and organic liquids. Additionally, the BNNSs@TA can easily combine with poly(vinyl alcohol) (PVA) to give flexible free-standing composite films with an ultrahigh in-plane thermal conductivity of 70.3 W m −1 K −1 because of the enhanced intermolecular hydrogen bonds between the attached TA and PVA chains. This study provides a simple, environmentally friendly, and highly efficient approach to achieving the exfoliation of BNNSs and highlights the critical role of BNNS surface functionalization in determining the thermal conductivity of composite films.
Cellulosimicrobium cellulans CWS2, a novel strain capable of utilizing benzo(a)pyrene (BaP) as the sole carbon and energy source under nitrate-reducing conditions, was isolated from PAH-contaminated soil. Temperature and pH significantly affected BaP biodegradation, and the strain exhibited enhanced biodegradation ability at temperatures above 30 °C and between pH 7 and 10. The highest BaP removal rate (78.8%) was observed in 13 days when the initial BaP concentration was 10 mg/L, and the strain degraded BaP at constant rate even at a higher concentration (50 mg/L). Metal exposure experimental results illustrated that Cd(II) was the only metal ion that significantly inhibited biodegradation of BaP. The addition of 0.5 and 1.0 g/L glucose enhanced BaP biodegradation, while the addition of low-molecular-weight organic acids with stronger acidity reduced BaP removal rates during co-metabolic biodegradation. The addition of phenanthrene and pyrene, which were degraded to some extent by the strain, showed no distinct effect on BaP biodegradation. Gas chromatography–mass spectrometry (GC-MS) analysis revealed that the five rings of BaP opened, producing compounds with one to four rings which were more bioavailable. Thus, the strain exhibited strong BaP degradation capability and has great potential in the remediation of BaP-/PAH-contaminated environments.
A time-dependent 3D numerical model considering anode evaporation is developed for the high current vacuum arc (VA) under a realistic spatial magnetic field. The simulation work contains steady state 3D numerical simulation of high current VA considering anode evaporation at nine discrete moments of first half wave of 50 Hz AC current, transient numerical simulation of anode activity, and realistic spatial magnetic field calculation of commercial cup-shaped electrodes. In the simulation, contact opening and arc diffusion processes are also considered. Due to the effect of electrode slots, the simulation results of magnetic field and temperature of anode plate exhibit six leaves shape (SLS). During 6–8 ms, the strong evaporation of anode surface seriously influence the parameter distributions of VA. Ions emitted from anode penetrate into arc column and the axial velocity distribution on the anode side exhibits SLS. The ions emitted from anode surface have the same temperature with anode surface, which cool the arc plasma and lead to a relative low temperature area formed. The seriously evaporation of anode leads to the accumulation of ions near the anode, and then the current density is more uniform.
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