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Particulate matter of 0.3 μm in diameter (PM0.3) poses a serious threat to the environment and human beings. Ultrathin and -light nanofibrous filters with excellent filtration properties can significantly prevent the detrimental effects of these particles. Here, we develop free-standing polyamide PA-66 ultrafine nanofiber papers for PM0.3 filtration using effective and scalable blow and electro-blow spinning techniques. The smallest average fiber diameter is 61.7 nm, which is 2-3 orders of magnitude smaller than that of conventional textiles. Poly(ethylene terephthalate) nonwovens are selected to fabricate free-standing nanofiber papers of various polymers, including polyamide, poly(methyl methacrylate), poly(vinylpyrrolidone), and poly(ethylene oxide) owing to the smooth surfaces of the nonwovens. This underlying principle can be used to create similar free-standing nanofiber papers from other commodity polymers in the future. Mechanisms of capturing particulate matter with different nanofiber morphologies are discussed. Salt and oil particulates are used to characterize the filtration properties. PA-66 papers are promising reusable filters owing to their mechanical particle-capture mechanism. The blow-spun PA-66 papers show filtration performance of 98.75% efficiency and a pressure drop of 125.44 Pa owing to the "slip" effect caused by the ultrasmall diameter. In the electro-blow spinning process, a supplementary voltage supply is conducive to separating nanofiber bundles into random-oriented nanofibers. Electro-blown spun papers possess an ultrahigh efficiency of 99.99% with a reduced areal density of 0.9 g m-2. These PA-66 papers can be used in a variety of applications, such as reusable personal protective equipment, industrial waste gas treatment, and central ventilation purification systems.

With the development of the preparation methods of low dimensional materials, one-dimensional (1D) nanomaterials present enormous benefits in hydrogen sensing area. This work reviews the up-to-date research progress of 1D nanomaterials in the field of hydrogen gas sensing and its three routes via material, morphology and post-treatment to enhanced sensing performances. Besides, the mechanism of hydrogen gas sensing, the differences of enhancement effect between material synthesis, morphology control and post-treatment schemes are analyzed. Finally, the prospects and challenges of 1D nanomaterials in hydrogen gas sensing are discussed and outlooked.

In this paper, a novel hybrid structure of Pd doped ZnO/SnO2 heterojunction nanofibers with hexagonal ZnO columns was one step synthesized from electrospun precursor nanofibers. Due to the synergistic effect of hexagonal ZnO, SnO2 and Pd, the structure exhibited excellent hydrogen (H2) gas sensing properties. At low-temperature of 120 °C, the response (Ra/Rg) to 100 ppm H2 gas exceeded 160, the response/recovery time was only 20 s and 6 s respectively and the limit of detection was only 0.5 ppm. Meanwhile, it also had good selectivity for H2 gas and excellent linearity. In addition, the materials were characterized by XRD, FESEM, HRTEM, XPS, and the synthesis mechanism and gas sensing mechanism were proposed.

Seeking economical, efficient and stable catalysts to ameliorate the slow kinetics of oxygen reduction in cathode of proton exchange membrane fuel cells is still a great challenge. Herein, we design and synthesize an advanced Pd-based catalyst, where small palladium-phosphorus nanoparticles (Pd3P NPs) with ~ 5.2 wt% Pd loading are embedded in three-dimensional (3D) bubble-like nitrogen, phosphorus co-doped carbon (NPC) film (Pd3P@NPC). The resultant catalyst delivers markedly enhancive catalytic performance in comparison with commercial Pt/C, Pd/C, Pd3P and NPC toward ORR, benefiting from the specific 3D porous structure, nano-size effect and the electronic interaction between Pd3P NPs and NPC. Specifically, the half-wave potential of Pd3P@NPC (0.885 V) is 36 mV higher than that of commercial Pt/C, and the mass activity of Pd3P@NPC is 1.112 mA $${\mathrm{\mu g}}_{\mathrm{Pd}}^{-1}$$ at 0.85 V, which is 8.18-fold and 11.96-fold enhancement in regard to that of commercial Pt/C and Pd/C, respectively. It is interesting to note that the as-prepared Pd3P@NPC also maintains a predominant stability after 40,000 potential sweeping cycles. This new catalyst is expected to enlarge the species of 3D Pd-based composites such as palladium carbide, palladium nitride and palladium sulfide on heteroatoms doped carbon substrate for ORR.

In this paper, the pollution flashover performance of a superhydrophobic surface with different coating strategies are studied. The results show that a superhydrophobic coating is effective in preventing pollution flashover under high voltage. The superhydrophobic coatings show increased pollution flashover voltage when compared to room temperature vulcanized silicone rubber and to an uncoated glass substrate. A novel suppression mechanism of the superhydrophobic coating is proposed which is driven by the electrostatic force produced by the applied voltage. The coalesced slippery slurry droplets and the expanded dry area on the superhydrophobic surface contributes to increased flashover voltage on the superhydrophobic surface. The superhydrophobic coating promises to be a prospective application in anti-pollution performance of insulators.

In this study, ZnO–SnO2 heterojunction nanofibers were fabricated using electrospinning and treated by Ar plasma. The post treatment demonstrated the ability to regulate adsorbed oxygen of nanofibers and thus affecting the gas sensing performance. The results revealed that the gas sensing performances increased with the increase of plasma treatment time at first, then showed a downward trend. The setting for the best H2 gas performance was 20 min of plasma treatment, under which the response of the sample was 80% higher and the response time was two thirds shorter than those of the untreated sample. The explanation can be that appropriate plasma treatment can increase the oxygen vacancy on the surface of heterojunction nanofibers as well as the resistance modulation range in the air; however, excessive plasma treatment can result in the reduction of the resistance modulation range in the air by reducing the metal oxide to metal.

Pd-doped SnO2 nanofibres were prepared by electrospinning and magnetron sputtering. It was found that the efficiency of gas sensing properties in these fibres depends primarily on the density of oxygen vacancies, which can be regulated by plasma treatment. We demonstrated that moderate plasma treatment can increase the oxygen vacancy as well as improve the gas sensing performance of SnO2. However, excessive plasma treatment led to the production of other substances that deteriorated the gas sensing performance. Furthermore, the best results for hydrogen gas sensing were obtained when the nanofibres were subjected to plasma treatment for 1 min. The fabricated material demonstrated a response of more than 53 for 500 ppm hydrogen at the optimum temperature (130 °C), which is a significant improvement as compared to sensors without plasma treatment. Evidently, plasma treatment is an effective method to further enhance the sensing properties of the fabricated nanofibres.

It is well-known that the high-performance polymeric dielectric films used for high-voltage DC capacitors should have outstanding capabilities in terms of electrical and mechanical properties in order to face harsh operating conditions. Many factors limit the ability of these thin films to face different and growing stresses according to modern electrical requirements. Microstructure properties, additives, impurities, defects formed during manufacturing as well as applied stress types significantly affect the performance of dielectric films and their operational lifetime. This paper presents a comprehensive review of the factors which affect the ageing, degradation and breakdown of metallised polypropylene (PP) capacitors films. The effects of microstructure, surface morphological properties, mechanical properties and defects on the reliability of biaxially oriented polypropylene films (BOPP) are studied. In addition, the phenomena affecting dielectric performance and ageing mechanisms which are induced by electrical, thermal and electrothermal stresses are discussed.

In this paper, we present the synthesis of novel three-dimensional SnO2/MoS2 nanocomposites via electrospinning combined with a hydrothermal method and their application to CH4 gas detection. Morphological characterization proved that the flower-like MoS2 structures were successfully connected to the surface of porous SnO2 nanofibers. The CH4 gas-sensing test results indicated that the gas-sensing properties of SnO2/MoS2 nanocomposites were better than those of pure MoS2; the SnO2/MoS2 nanocomposites exhibited lower optimal operation temperature and higher gas response. Such excellent performance is mainly attributable to the special hierarchical structure and the existence of n–n junctions between SnO2 and MoS2.

High-stability triester insulation oil derived from the trimethylolpropane esters (TME) was synthesized by esterifying saturated fatty acids and trimethylolpropane (TMP). The TME oil shows higher AC breakdown voltage (Vb, 72.6 kV/2.5 mm) than that of FR3 (65 kV/2.5 mm). TME oil is readily biodegradable whose biodegradation is 82.2% after 28 days. Pressurized differential scanning calorimetry (PDSC) was applied to measure oxidation onset temperature (OOT) of TME oil for initial evaluating the oxidation stability. Due to the elimination of the carbon-carbon double bonds and β-H, the OOT of the TME oil without antioxidants is approximately 25°C higher than that of FR3. To evaluate the realistic performance of the TME oil, the effect of transformer materials on the aging behavior was investigated. The effect of transformer materials on the thermal aging of TME oil and mineral oil (MO) is less than that of FR3. Although the moisture content and acid value in TME oil induced by aging are higher than those in MO. These acids and moisture do not cause obvious degradation of breakdown voltage and dielectric loss factor, which may be attributed to the high moisture solubility in it.

Epoxy resin is widely used in DC converter valves, DC bushings, and gas-insulated switches due to its excellent insulation and mechanical properties. Since epoxy resin demonstrates low thermal conductivity and toughness, epoxy resin-impregnated power equipment exhibits poor heat dissipation capability and is easy to crack under mechanical stress. Therefore, research on epoxy resins with high thermal conductivity has received extensive research attention. In this article, a directional freezing method is used to build a thermally conductive network with polyimide and boron nitride nanosheets (BNNS) as the skeleton. The thermally conductive network is immersed in the epoxy resin to improve the thermal conductivity of the epoxy resin matrix. The microstructure of PI/BNNS aerogel and epoxy resin/polyimide interpenetrating networks (IPNs) was observed under the electron microscope. The thermal conductivity and dielectric properties of the composite material were tested. The directional growth of ice crystals contributes to the highly orientated tubular pores in the IPNs aerogel. The BNNS aligned along with the polyimide effectively improves the thermal conductivity of the epoxy resin, reaching a thermal conductivity of 0.745W·m−1·K−1, which is 5 times compared to pure epoxy resin with the BNNS content of 15wt%.

Background. Previous studies have shown that alkannin has anticancer, anti-inflammatory, and antibacterial effects. However, the effect of alkannin in the development of ovarian cancer (OC) remains unknown. Therefore, this study aims to elucidate the function of alkannin in OC progression. Methods. RT-qPCR and western blot analysis were used to measure mRNA and protein expression. Cell viability and metastasis were detected by the CCK-8 assay, flow cytometry analysis, and transwell assay. Results. Alkannin had no cytotoxicity toward normal ovarian cells, but alkannin can inhibit cell proliferation and induce apoptosis in OC cells. In addition, alkannin inhibited cell migration and invasion and blocked EMT in OC. Besides, upregulation of miR-4461 was found in OC tissues and cells, which was regulated by alkannin. More importantly, miR-4461 can inverse the effects of alkannin on cell viability and metastasis in OC cells. Conclusion. Alkannin restrains cell viability, metastasis, and EMT in OC by downregulating miR-4461 expression.

Levofloxacin (LEV) is a broad-spectrum quinolone antibiotic and widely used for human and veterinary treatment. Overuse of LEV leads to its frequent occurrence in the water environment. In this study, the transformation characteristics of LEV in water during the simulated chlorination disinfection treatment were explored. Fifteen major transformation products (TPs) of LEV were identified, and their plausible formation pathways were proposed. The reaction pathways were strongly dependent on pH condition, and LEV removal was relevant to free available chlorine (FAC) dose. Antibacterial activity of chlorination system was dramatically declined when FAC was more than 3-equivalent (eq) due to the elimination of antibacterial related functional groups. Genotoxicity of chlorination system increased more than 3 times at 0.5-eq of FAC and then decreased with increasing FAC dose, which were in accordance with the relative concentration of toxic TPs estimated by QSAR model. These results implied that the combination of bioassay, QSAR computation and chemical analysis would be an efficient method to screen toxic TPs under chlorination treatment. It is anticipated that the results of this study can provide reference for optimizing operational parameters for water disinfection treatment, and for scientifically evaluating the potential risk of quinolone antibiotics.

The room temperature vulcanized silicone rubber has been widely used in the electric transmission line. However, the accumulated surface charge leads to the flashover, and degradation limits its development. In this paper, room temperature vulcanized silicone rubbers with a rough surface are prepared via a polymer emulsion template method. The wettability, surface potential decay characteristics, and electrical traps distribution of the samples are investigated. The results show that the rough room temperature vulcanized silicone rubber presents a better hydrophobicity with the increases of the addition of nonsolvent. Besides, the rough room temperature vulcanized silicone rubber with higher addition of nonsolvent performs lower initial surface potential, and the surface potential on it decays faster. Additionally, the addition of the nonsolvent contributes to reducing the trap energy level of the room temperature vulcanized silicone rubber. The rough surface is beneficial to suppress the surface charge accumulation on the room temperature vulcanized silicone rubber.

The effects of C=C, ester and &beta, H groups on the ionization potential (IP) and electron affinity (EA) of molecules in natural ester insulation oil were investigated by density functional theory (DFT). The major contribution to the highest occupied molecular orbital (HOMO) comes from the carbon atoms adjacent to C=C. Thus, the IPs of triglycerides decrease as the number of C=C double bonds increases. The C=C in alkanes may also lower the IP. However, the &beta, H in triglycerides has little effect on the IP, and C=C and &beta, H have only a small effect on the EAs of the triglycerides because of the major contributions of atoms near the ester group in triglycerides to the lowest unoccupied molecular orbital (LUMO). This study calculated the IPs of 53 kinds of molecules in FR3, which are significantly lower compared with those of molecules in mineral oil (MO) and trimethylolpropane triester without C=C. However, the lightning impulse breakdown voltage (LI Vb) of trimethylolpropane triester is still significantly lower than that of MO at the large gap. Therefore, the transition from slow to fast streamers under low lighting impulse voltage is determined by the ester group rather than by C=C and &beta, H. The ester group may attract more electrons, impacting itself more compared to alkane in MO and facilitating the transition from slow to fast streamers.

A new method, which involves the addition of alkaline Al 2 O 3 (3 wt%) and activated clay (5 wt%) as adsorbents for homogeneous synthetic trimethylolpropane triesters (TME), is reported here to not only improve electrical properties but also to shed light on future volume production. The results show that the acid value and the dielectric loss of TME oil is successfully reduced and meets IEC 61099. The viscosity of TME approaches that of mineral oil (MO) for transformers. In addition, TME oil with antioxidants exhibits fairly good oxidation stability that is evidenced by a notably high oxidation onset temperature of 226°C, which is 39 K and 14 K higher than that of commercial natural ester oil (NEO) (187°C) and MO (212°C), respectively. Furthermore, compared with the AC breakdown voltage (V b ) of NEO (65.3 kV) and MO (70.4 kV), the TME oil has a higher V b =73.2 kV. Besides, the positive lightning impulse (LI) V b and streamer behavior of TME at small gaps are comparable to those of MO and NEO. However, the negative LI V b of TME and NEO are significantly lower than that of MO owing to the combined field variation towards the plane electrode which will facilitate the propagation of the streamer. Therefore, additives without oxygen, fluorine and chlorine should be given priority when they are used to improve the properties of insulation oil.

This article adds more information to the problem of natural ester use as an electroinsulating fluid in cellulose paper-oil systems, e.g., for use in power transformers. An accelerated thermal aging (120, 140 and 160 °C) of samples consisting of cellulose paper (transformerboard), a treated natural ester (filtered, basic Al2O3, 0.53% DBPC), a copper plate and moisture was studied. Research was especially focused on the impact of moisture on the aging of the above system. Samples with three different oil moisture levels (80, 143 and 305 ppm water content) were subjected to thermal aging to display the change in a selection of properties (tanδ, acid number, water content). For a study of the polarization effects, broadband dielectric spectroscopy (BDS) was performed to observe the complex permittivity and conductivity dependencies on the temperature and frequency (±30 °C, 0.01-107 Hz). Havriliak-Negami (H-N) diagrams were used to further understand the results. The degradation products during thermal aging were recognized by Fourier transform infrared (FT-IR) spectroscopy. Hydrolysis and hydrogenation occurred in the insulating system with a natural ester aged by elevated temperatures, which is in contrast to CO2 formation in the case of electric aging. The results showed an increase in the acid number, dissipation factor, and number of hydrolysis and hydrogenation products. Furthermore, changes in polarization were observed as a consequence of the thermal aging of paper-natural ester insulation system with the presence of copper and moisture.

The life expectancy of a transformer is closely related to the ageing state of its paper insulation. This paper presents novel markers for ageing characterization of paper insulation in oil-filled transformers based on the dispersion staining colors of cellulose fibres. Accelerated thermal ageing experiments were performed for oil-paper specimens at 120 and 130 °C to obtain aged oil-paper samples of different ageing degrees. The average degree of polymerization (DP), crystallinity index, and refractive index of insulation paper were measured; the experimental results show that an increase in refractive index of insulation paper was observed with the increase of ageing degree. Meanwhile, the dispersion staining colors of cellulose fibres in oil were observed using dispersion staining method; the experimental results show that the refractive index of cellulose fibres detached from insulation paper increases with the increment of ageing degree of insulation paper. Finally, two ageing markers—that is, the primary color ratio-based ratio of blue to red and the primary color ratio-based Mahalanobis distance were presented. Their relationship with DP and ageing time of insulation paper were obtained, and were compared with the corresponding relationship with 2-furaldehyde (2-FAL) and carbon oxides. The proposed ageing markers demonstrate an advantage over 2-FAL and carbon oxides and show potential in ageing state evaluation and residual life prediction of paper insulation in transformers.

Metal particles, such as copper and iron, not only reduce the breakdown voltage but also accelerate the oxidation of insulating oils. The effects of metal particles on the dielectric properties of mineral and natural ester insulating oils were investigated in this work. The experimental results indicate that the AC and impulse breakdown voltages of the insulating oil decrease with the increase of the size and the quantity of the metal particles. The positive breakdown voltages V b+ of insulating oils decrease moderately in the beginning, while the particles quantity increases to a certain extent, the V b+ decreases significantly. In comparison, the metal particles always reduce the negative impulse breakdown voltage V b− significantly. The effect of the copper particles on the insulating oils is slightly greater than that of the iron particles due to their higher conductivity. The permittivity of contaminated insulating oils increases quasi-linearly with the concentration of copper particles. Improved models considering the polarization of the surface oxidation layer of copper particles were proposed, and the calculated data were in good agreement with the measured permittivity of the contaminated insulating oil.

A method of determining high fluence rate for D-T neutron source by using two long counters is introduced. One long counter contains a BF3 proportional counter, and a response of 1.1 cm2 is determined by calibration. The other long counter contains a gamma compensated boron neutron ionization chamber, and a response of 2.06e-5 cm2 is determined by comparing with the results of long counter containing BF3 proportional counter. By appropriately arranging the two long counters, fluence measurements are performed at the high intensity D-T neutron generator (HINEG). The results of the experimental characterization to the long counter are presented at this paper.

Vegetable oils, mainly composed of triacylglycerol molecules, have been widely studied as new insulation materials in the recent years. In this work, we study the electronic properties of various triacylglycerol molecules with different degree of unsaturation by density functional theory (DFT). The ionization potential (IP), electron affinity (EA), and electron trap are estimated by theoretical analysis and experiments. The results show that the C atoms of cis C C double bond make the primary contribution to the highest occupied molecular orbital (HOMO) of unsaturated triacylglycerol molecule; the IPs of fully unsaturated triacylglycerol molecules are almost confined to the narrow ranges from 7.30 to 7.45 eV in gas-phase and from 6.77 to 6.84 eV in liquid-phase correspond to LnLnLn and OOO molecules, respectively; the atoms of ester group and neighboring atoms make the primary contribution to the lowest unoccupied molecular orbital (LUMO) of both saturated and unsaturated triacylglycerol molecules; the EAs of triacylglycerol molecules are confined to the narrow ranges from −0.34 to −0.18 eV and the chemical trap is estimated to be 0–0.16 eV; the total trap is 0.32–0.36 eV. The IP distribution character and shallow trap feature maybe the main causes that vegetable oils demonstrate a low resistance against the fast streamers. The work can provide theoretical basis to molecular modification for performance improvement of vegetable insulating oils.

The long non-coding RNA (lncRNA) NF-κB interaction lncRNA (NKILA) has been found to exert tumor suppressive effects in numerous types of carcinoma; however, the relationship between NKILA and cervical cancer (CC) remains largely unclear. The present study aimed to investigate the effects of NKILA on the proliferation and metastasis of CC cell lines, in addition to the related molecular mechanisms. Reverse transcription-quantitative PCR was used to detect the expression levels of NKILA in cancer tissues and cell lines. The constructed overexpression vector, pcDNA3.1NKILA, and its corresponding negative control sequence were transfected into CaSki cells and short hairpin RNA targeting NKILA and the corresponding negative control sequence were transfected into C-33A cells. Subsequently, the proliferative, migratory and invasive ability, as well as the process of epithelial-mesenchymal transition (EMT) of C-33 A and CaSki cells were analyzed by performing Cell Counting Kit-8, wound healing, Matrigel invasion and western blot assays, respectively. The expression levels of proteins were detected using western blot analysis. The expression levels of NKILA were decreased in CC tissues and CC cell lines (SiHa, C-33A, CaSki and HeLa) and the downregulation of NKILA expression using shRNA was observed to significantly increase the proliferation of CC cells. Conversely, the upregulation of NKILA inhibited the proliferation of CC cells, in addition to significantly inhibiting the migration and invasion of CaSki cells, whereas the knockdown of NKILA promoted the invasion of C-33A cells. Thus, it was hypothesized that NKILA may inhibit the migration and invasion of CC cells via regulation of EMT processes, which was reflected by the expression of ZO-1, E-cadherin, N-cadherin and Vimentin. Furthermore, the overexpression of NKILA significantly inhibited the activation of NF-κB in CaSki cells, whereas the knockdown of NKILA expression promoted the degradation of inhibitory protein-κB and promoted the transfer of p65 into the nucleus in C-33A cells. In conclusion, the results from the present study suggested that NKILA may be involved in the inhibition of migration and invasion in CC cells through regulating EMT processes, which may be related to its inhibition of NF-κB activation.

The trimethylolpropane esters (TME) based high performance electrical insulating oil was synthesized by esterification of the mixture of C 6 , C 8 and C 10 acids blend with trimethylolpropane (TMP). The electrical performance is significantly improved by a purpose-oriented purification process which is structured by washing with ultrapure water and absorption with molecular sieve. The obtained insulating oil shows much reduced viscosity (25.6 mm2/s) and much enhanced AC breakdown voltage (72.6 kV) comparing with the commercial natural ester insulating FR3® (38.9 mm2/s and 65 kV). The high performance of the insulating oil is also manifested by quite low pour point (-45°C) and relative high flash point (240°C). The remarkable oxidation stability of the insulating oil is metered by the oxidation induction temperature (OIT) 203°C which should be attributed to the elimination of C=C double bonds and $\beta$-H atoms.

Super-hydrophobic coatings have recently drawn considerable attention in research and applications towards self-cleaning materials. This paper presents experiments and analysis of water droplet behaviors on glass, silicone rubber, and super-hydrophobic surface in an ac electric field applied parallel to the surface. Experimental results show that a water droplet tends to move on a super-hydrophobic surface while it tends to stretch or deform on glass and silicone rubber surfaces. A physical model of the water droplet deformation and motion mechanism is presented. An electrostatic force acting as the domain driving force plays a key role in water droplet motion on super-hydrophobic surface. The electrostatic stress acting along the external profile of a water droplet cross section was simulated using a surface integral of the Maxwell stress tensor. The simulation for surfaces with different wetting properties are in good agreement with the experimental results. Super-hydrophobic coating demonstrates a prospective electric field enhanced self-cleaning property.

Nomex paper has been recognized as an excellent insulation material that was evidenced by its electrical properties and been widely used in high voltage insulation system such as dry-type transformers and oil-immersed transformers. Because of its high surface and volume resistivity, the surface charge accumulation on Nomex paper was difficult to dissipate, which was believed to have great influence on its electrical performance. Surface fluorination has been considered to be an effective approach to modify the surface of paper and to suppress the surface charge. To understand the influence of surface fluorination on surface charge characteristic of dry Nomex paper and oil-impregnated Nomex paper, Nomex T410 paper was fluorinated using a F 2 /N 2 mixture with duration of 15, 30 and 45 min. The oil-impregnated samples were prepared by impregnating the untreated and fluorinated Nomex paper in insulation oil. Attenuated total reflection infrared spectroscopy (ATR-IR, Bruker ALPHA) was used to characterize the surface chemical bond changing caused by fluorination. The surface potential decay characteristics were investigated. The ATR-IR spectra of untreated and fluorinated Nomex paper evidence that the C-Fx bonds were induced to Nomex surface by substitution for hydrogen atoms, accompanying with aromatic chain scission and ring opening reaction. The measured surface potential decay characteristics shows that both positive and negative potential decay were accelerated by surface fluorination. For both untreated and fluorinated Nomex paper, the surface potential decay of dry Nomex paper was faster than oil-impregnated Nomex paper. The surface trap energy and trap distribution of the samples were calculated by isothermal surface potential decay (ISPD) method. The result shows that the fluorination may shallow the traps by modify the chemical chain while the oil-impregnated samples had higher trap energy because some charges were trapped by the insulation oil.

Nonwoven Polypropylene(PP) electret film is widely used for filtration due to its excellent filtration performance resulting from the electrostatic attraction between electret fibers and impurities. In this work, nonwoven PP films were fluorinated in F 2 /N 2 mixture gas and isothermally crystallized in an oven with elevated temperature. A point-grid-plate electrode system was utilized to prepare the electret PP filtration films by corona charging. The results from Fourier-Transform Infrared (FTIR) spectrum and Scanning Electron Microscopy (SEM) evidenced that hydrogen atoms had been replaced by fluorine atoms in the surface of the PP fibers during the fluorination reaction. It was also found that the fluorination lead to increased roughness of the PP fibers. The initial surface potential of the fluorinated PP film after corona charging was slightly higher than that of the nonfluorinated film. However, the former one showed higher decay rate than the latter at 90°C. The isothermal crystallization on the fluorinated PP films significantly improved the charge stability. This should be attributed to the increase of the crystallinity and the density of deep traps introduced during isothermal crystallization. After filtration using the fluorinated and isothermally crystallized PP electret films, the relative permittivity $\varepsilon_{r}$ and the loss factor tan$\delta$ of the aged transformer oil decreased to a low level that was almost identical to the new transformer oil.

Vegetable insulating oils are gaining importance worldwide to be used in power transformers as an alternative to petroleum based mineral oils because of their biodegradable nature and higher fire points than conventional mineral oils. However, these oils (whether natural or synthetic esters) easily absorb moisture and hence tend to affect the dielectric and physiochemical properties of insulation oils. This paper presents the effect of moisture absorbed by commonly used rapeseed oil on its AC breakdown voltage. A mathematical relationship was developed between breakdown voltage and percentage moisture absorbed to access the values of BDV at any moisture level and this relationship holds good for any moisture content in the oil. Moreover, effect of suspended water molecules on breakdown voltage was simulated using COMSOL Multiphysics. Empirical relationship developed was tested and verified and can be used to find out the BDV of these oils as the percentage moisture increases.

Surface modification is an efficient approach to improve the dispersion of alumina nanoparticles. In addition, it is also useful for improving the electrical properties of polymer nanocomposites. In this work, alumina nanoparticles were treated by the saline coupling agent of γ-Aminopropyltriethoxysilane (KH550) to restrict the aggregation. The chemical bonding was examined by Fourier Transform Infrared Spectroscopy (FTIR). Experiment results confirmed that the chemical bond was formed between alumina and KH550 after modification. The modified epoxy/alumina has more traps which results in larger volume resistivity which is 2.22×1017Ω/cm when the alumina content is 1wt%. With increase of the filler concentration, e.g. 3 and 5 wt%, many over lapping interaction zones occur so that the effect of deep traps is gradually weakened and the effect of shallow traps is increased which resulting the decreased volume resistivity. The modified alumina/epoxy resin nanocomposite shows a higher AC breakdown strength as compare to unmodified nanocomposites.

Both the thermal faults and electrical faults may lead to hydrogen gas generation that dissolved in transformer oil. Diagnosis and early warning of transformer faults have been widely recognized by detecting the content change of dissolved hydrogen gas in the oil. This work aims to detect the change of hydrogen-gas content in transformer oil by using the surface acoustic wave (SAW) sensors. The sensing is recognized through the wavelength variation of SAW. The mass change of the sensitive layer due to the absorption of hydrogen-gas molecular is found to lead to significant changing of the SAW wavelength. By the controlled sputtering parameters, this work takes layer-structure optimized SnO 2 and Pd to build up the sensing layer. The hydrogen selectivity of Pd film, the sensitivity of the sensor is enhanced effectively by increasing the surface process of the bilayer sensitive film. The results indicate that the sensitivity of the processed sensor is 1.4 times as high as that before the processing.

Ageing assessment of paper insulation is important to safe operation, condition based maintenance, and replacement of power transformers. This paper investigated the effect of oil replacement (OR) upon ageing assessment of paper insulation based on dispersion staining colours of cellulose fibres in oil. Accelerated thermal ageing experiments were conducted for oil-paper specimens for different durations and OR was conducted at different ageing stages. Degree of polymerization (DP) of paper and 2-furaldehyde (2-FAL) in oil were measured, and the dispersion staining colours of cellulose fibres were observed. DP of paper was predicted using traditional ageing marker 2-FAL and proposed ageing marker, i.e., primary colour ratio based Mahalanobis distance (PCR-MD) of (r, b) points. Results show that OR has little effect on DP of paper while it can results in substantial loss of carbon oxides and 2-FAL in oil. The OR has limited effect on Mahalanobis distance of (r, b) points. The prediction errors of DP with ageing marker PCR-MD is smaller than those with 2-FAL, which implies that the proposed ageing marker PCR-MD can be applied to ageing assessment of paper insulation that undergoes OR with accepted error level.

Super-hydrophobic surfaces can be fabricated based on discarded silicone after arc exposure. Hydrophobicity, microstructural development, chemical composition, corrosive liquid resistance, and the microscopic process of contaminant elimination of the surface are presented. High temperature of the arc discharge plays a substantial role in the preservation of surface hydrophobicity.

The insulating performance of oil is vulnerable to particles especially the conductive particles. This paper investigated the influence of copper particles of micrometer size on the breakdown strength and frequency-dependent properties of vegetable oil. The AC breakdown voltage of contaminated vegetable oil with copper particles of different numbers (ranging from 103 to 106) was measured. The frequency-dependent dielectric properties including volume resistivity, relative permittivity and dissipation factor of the contaminated vegetable oil with copper particles of various volumetric concentrations (0.011%, 0.056% and 0.112%) were measured. Identical experiments were conducted with mineral oil for comparison. Results show that the AC breakdown voltage of vegetable oil decreases with the increase of copper particle concentration. The mineral oil exhibits a similar trend, but the influence of copper particles on the AC breakdown voltage of vegetable oil is less significant than that on mineral oil because of its greater viscosity. The relative permittivity and dissipation factor increase with increasing copper volumetric concentration while the volume resistivity decreases. The influence of copper particles on them is significant at low frequencies and this influence becomes inconspicuous as the frequency increases. Similar results were observed for mineral oil.

Natural ester has been widely studied as an alternative dielectric liquid to mineral oil in recent years. Unsaturated triacylglycerol molecules are the main components of natural ester; therefore, in this paper, we investigate the molecular structure and electronic properties of the triolein molecule, an oleic-type triacylglycerol molecule, as a representative component of natural ester oils. The effects of external electric fields at the electric field intensity related to streamer initiation and propagation on the bond lengths, dipole moment, total energy, infrared spectra, and orbital energy of the triolein molecule are investigated using density functional theory (DFT). In addition, the excitation energies, transition wavelengths, and oscillator strengths of the first eight excited states of the triolein molecule under external electric fields are calculated by time-dependent DFT. The results show that the bond lengths, dipole moments, total energy, and infrared spectra change obviously under external electric fields. With increasing external electric field intensity, the energy of the highest occupied molecular orbital increases, and the gap between that and the energy of the lowest unoccupied molecular orbital decreases, which make the molecule susceptible to excitation. The calculations contribute to an understanding of the causes behind the degradation of the insulation properties of natural ester oils.

We prepared an ethanol extract from Laminaria japonica, and obtained five fractions from the extract using various solvents. We investigated the antibacterial activities of the fractions against Clavibacter michiganensis subsp. sepedonicus (Spieckermann & Kotthoff) Davis et al., the causal agent of bacterial ring rot of potato (BRR). Among all the fractions, the petroleum ether fraction showed the strongest (P

In this paper, the porous NiO/SnO2 nanofibers were synthesized via the electrospinning method along with the carbonization process. The characterization results show that the pristine SnO2-based nanofibers can form porous structure with different grain size by carbonization. The hydrogen gas-sensing investigations indicate that the NiO/SnO2 sensor exhibits more prominent sensing properties than those of pure SnO2 sensor devices. Such enhanced performance is mainly attributed to the porous nanostructure, which can provide large active adsorption sites for surface reaction. Moreover, the existence of p-n heterojunctions between NiO and SnO2 also plays a key role in enhancing gas-sensing performances. Finally, the H2 sensing mechanism based on the NiO/SnO2 nanocomposite was proposed for developing high-performance gas sensor devices.

Polarisation processes and charge transport in polyvinylidene fluoride (PVDF) with a small amount (0.01–10 wt%) of the ionic liquid (IL) 1-ethyl-3-methylimidazolium nitrate ( $$\hbox {[EMIM]}^+[\hbox {NO}_3]^-$$ ) are investigated by means of dielectric spectroscopy. The response of PVDF that contains more than 0.01 wt% IL is dominated by a low-frequency relaxation which shows typical signatures of electrode polarisation. Furthermore, the $$\alpha _{{\rm a}}$$ relaxation, related to the glass transition, disappears for IL contents of more than 1 wt%, which indicates that the amorphous phase loses its glass-forming properties and undergoes structural changes. The DC conductivity is determined from the low-frequency limit of the AC conductivity and from the dielectric loss peak related to the electrode polarisation. DC conductivities of $$10^{-10}$$ to $$10^{-2}\,\hbox {S}/\hbox {m}$$ are obtained—increasing with IL content and temperature. The dependence of the DC conductivity on the IL content follows a power law with an exponent greater than one, indicating an increase in the ion mobility. The temperature dependence of the DC conductivity shows Vogel–Fulcher–Tammann behaviour, which implies that charge transport is coupled to polymer chain motion. Mobile ion densities and ion mobilities are calculated from the DC conductivity and the dielectric loss related to electrode polarisation, with the results that less than one per cent of the total ion concentration contributes to the conductivity and that the strong increase in conductivity with temperature is mainly caused by a strong increase in ion mobility. This leads to the conclusion that in particular the ion mobility must be reduced in order to decrease the DC conductivity.

This paper focuses on the space charge characteristics in TiO2/cross-linked polyethylene (XLPE) nanocomposites; the unmodified and modified by dimethyloctylsilane (MDOS) TiO2 nanoparticles were added to XLPE matrix with different mass concentrations (1 wt%, 3 wt%, and 5 wt%). The scanning electron microscope (SEM) showed that the MDOS coupling agent could improve the compatibility between TiO2 nanoparticles and XLPE matrix to some extent and reduce the agglomeration of TiO2 nanoparticles compared with unmodified TiO2 nanoparticles; the volume resistivity testing indicated that the volume resistivity of TiO2/XLPE nanocomposites was higher than Pure-XLPE and increased with the increase of filling concentrations. According to the pulsed electroacoustic (PEA) measurements, it was concluded that the space charge accumulation was suppressed by filling TiO2 nanoparticles and the distribution of electric field in samples was improved greatly. In addition, it was found that the injection of homocharge was more obvious in MDOS-TiO2/XLPE than that in UN-TiO2/XLPE and the homocharge injection decreased with the increase of filling concentration.

As a new environmentally friendly liquid dielectric material, vegetable insulating oil has been widely used in oil-filled power equipment. In oil-filled power equipment, ageing, faults of overheating and discharge cause the decomposition of insulating oil and insulating paper, resulting in dissolved gases in oils. The diffusion behavior of dissolved gases in oils is helpful for evaluation of health state of oil-filled power equipment. In this study, the molecular dynamics simulation based on polymer consistent force field (PCFF) is adopted to analyze diffusion processes of dissolved gases in camellia insulating oils. The diffusion coefficients and free volume of dissolved gases including hydrocarbons, carbon oxides and hydrogen are calculated. The diffusion trajectory of dissolved gases in oils are also given. In addition, impacts of gas species and temperature on molecular diffusion coefficients of oils were also studied. Results quantitatively describe the diffusion behavior of gases with different molecular weight in the oils under various temperatures. The research provides theoretic support for further application of vegetable insulating oils in power equipment.As a new environmentally friendly liquid dielectric material, vegetable insulating oil has been widely used in oil-filled power equipment. In oil-filled power equipment, ageing, faults of overheating and discharge cause the decomposition of insulating oil and insulating paper, resulting in dissolved gases in oils. The diffusion behavior of dissolved gases in oils is helpful for evaluation of health state of oil-filled power equipment. In this study, the molecular dynamics simulation based on polymer consistent force field (PCFF) is adopted to analyze diffusion processes of dissolved gases in camellia insulating oils. The diffusion coefficients and free volume of dissolved gases including hydrocarbons, carbon oxides and hydrogen are calculated. The diffusion trajectory of dissolved gases in oils are also given. In addition, impacts of gas species and temperature on molecular diffusion coefficients of oils were also studied. Results quantitatively describe the diffusion behavior of gases with different mole...

Vegetable insulating oil may replace the mineral insulating oil used in large power transformers due to its extraordinary biodegradability and fire resistance. According to component analysis, 1-methylnaphthalene and eicosane are considered the typical molecules in mineral oil. Triolein and tristearin are considered the typical molecules in vegetable oil. The ionization potential (IP) and the variation of highest occupied molecular orbital (HOMO) of typical molecules under an external electric field are calculated using quantum chemistry methods. The calculation results show that the IP of the triolein molecule is comparable to that of the 1-methylnaphthalene molecule. The mechanisms of losing electrons are discussed, based on the analysis of HOMO composition. The insulation characteristics of the triolein and tristearin are more likely to be degraded under an external electric field than those of 1-methylnaphthalene and eicosane. Due to the fact that the number density of low IP molecules groups in vegetable oil is much greater than that in mineral oil, the polarity effect in vegetable oil is more obvious than that in mineral oil. This eventually leads to different streamer characteristics in vegetable oil and mineral oil under positive polarity and negative polarity.

The piezoelectricity of a pressure-treated cellular polypropylene (PP) (commercially available, trade name PQ50) film electret was studied by the measurement of direct-and inverse-piezoelectric d 33 coefficient. The sample expanded with optimal parameters has a quasi-static piezoelectric d 33 coefficient of more than 600 pC/N, which is about 40 times as high as that of polyvinylidene fluoride (PVDF). In addition, the hybrid multi-layer system, which properly combines single-layer cellular PP film electrets, shows a quasi-static piezoelectric sensitivity of as high as 2010 pC/N. This is around three times higher than that of well-known lead zirconate titanate (PZT) ceramics. The results are theoretically and technically helpful to promote the application of cellular PP film electrets.

Poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) is an aromatic polyester with molecular structure similar to that of poly(ethylene terephthalate)(PET). In this paper, the space charge storage ability and its stability in corona charged PEN were studied by measurement of surface potential decay under different storage conditions including different temperatures and relative humidities, and analysis of open circuit thermally stimulated discharge (TSD) current spectra and charge TSD curves. The comparison between the charge stability of PEN and PET was carried out. The results point out that the charge stability of PEN is markedly better than that of PET under different environmental conditions. By means of isothermal depolarization program, the space charge lifetimes (effective time constant) t at room temperature of positively and negatively charged PEN are estimated to be 90 y. The results offer theoretical and technical support for the use of PEN as the chip of high quality electret condenser microphone due to its excellent dielectric, mechanical and thermal properties.

In this paper, the electret properties of three types of castings prepared P(VDF-HFP) (poly(vinylidene fluoride-hexafluoropropylene)) copolymer films whose contents of HFP are 4.2, 4.7 and 5.9% are discussed. Experimental results point out that the copolymer film is a polar material, i.e. there exists both oriented dipoles and deposited space charge in the film after charging. Estimating polarizations at different charging fields based on analysis of charging current curves indicate a comparatively high polarization formed under the charging field above 200 MVm-1 for the copolymer film. The mechanically thermal stretching process not only increases the density of the oriented dipoles and deposited space charge but also improves the thermal stability of deposited space charge. However, the increase of HFP content in the copolymer has a negative impact on the density of oriented dipoles and deposited space charge. The measurements by means of laser doppler vibrometer show that the copolymer in which the HFP content is 4.2% and 4.7%, respectively has a notable converse piezoelectric coefficient as high as 140 pmV-1 and 130 pmV -1 . Dynamics of interaction of space charge with oriented dipoles for the copolymer with HFP content of 4.7% are investigated by means of isothermal surface potential decay at different temperatures. At the same time, pyroelectric effect of the copolymer is also discussed