CF3I gas mixtures have attracted considerable attention as potential environmentally-friendly alternatives to SF6 gas,owing to their excellent insulating performance.This paper attempts to study the CF3I ternary gas m...CF3I gas mixtures have attracted considerable attention as potential environmentally-friendly alternatives to SF6 gas,owing to their excellent insulating performance.This paper attempts to study the CF3I ternary gas mixtures with c-C4F8 and buffer gases N2 and CO2 by considering dielectric strength from electron transport parameters based on the Boltzmann method and synergistic effect analysis,compared with SF6 gas mixtures.The results confirm that the critical electric field strength of CF3I/c-C4F8/70%CO2 is greater than that of 30%SF6/70%CO2 when the CF3I content is greater than 17%.Moreover,a higher content of c-C4F8 decreases the sensitivity of gas mixtures to an electric field,and this phenomenon is more obvious in CF3I/c-C4F8/CO2 gas mixtures.The synergistic effects for CF3I/c-C4F8/70%N2 were most obvious when the c-C4F8 content was approximately 20%,and for CF3I/c-C4F8/70%CO2 when the c-C4F8 content was approximately 10%.On the basis of this research,CF3I/c-C4F8/70%N2 shows better insulation performance when the c-C4F8 content is in the15%–20%range.For CF3I/c-C4F8/70%CO2,when the c-C4F8 content is in the 10%–15%range,the gas mixtures have excellent performance.Hence,these gas systems might be used as alternative gas mixtures to SF6 in high-voltage equipment.展开更多
We calculated the uniform dielectric breakdown field strength of residual 30% CF3I/CO2 gas mixtures during the arc extinction process over the temperature range 300-3500 K at 0.1 MPa. The limiting reduced field streng...We calculated the uniform dielectric breakdown field strength of residual 30% CF3I/CO2 gas mixtures during the arc extinction process over the temperature range 300-3500 K at 0.1 MPa. The limiting reduced field strengths are decided by a balance of electron generation and loss based on chemical reactions estimated by the electron energy distribution function （EEDF）, which employs the Boltzmann equation method with two-term expanding approximation in the steady-state Townsend （SST） condition. During the insulation recovery phase, the hot CF3I/CO2 gas mixtures have maximum dielectric strength at a temperature of about 1500 K. At room temperature 300 K, the electric strength after arc extinction （90.3 Td, 1 Td=10-21 V.m2） is only 38% of the original value before arc （234.9 Td）. The adverse insulation recovery ability of CF3I/CO2 gas mixtures in arc extinction hinders its application in electric circuit breakers and other switchgears as an arc quenching and insulating medium.展开更多
The dynamics of negative surface discharges in c-C_(4)F_(8)/CF_(3)I/CO_(2) gas mixture is investigated here with a 2D fuid model.The distributions of ion concentration,electric field strength and photon flux during th...The dynamics of negative surface discharges in c-C_(4)F_(8)/CF_(3)I/CO_(2) gas mixture is investigated here with a 2D fuid model.The distributions of ion concentration,electric field strength and photon flux during the propagation of the streamer are obtained by solving the drift-diffusion equations of particles and Poisson's equation,and the photon flux variation function during the propagation is also fitted.It is found that the streamer branches occur when the streamer transitions from the upper surface of the insulator to the side surface,and then when the streamer approaches the plane electrode,the photon flux will increase significantly.On this basis,the positive and negative surface discharge models are compared in terms of streamer characteristics,particle characteristics and streamer branches.It is found that the streamer has a higher electron concentration and electric field in the positive model.The streamer develops“floating”in the positive surface discharge,while it is close to the surface of the insulator in the negative model.In addition,the negative streamer branch has a wider width and develops further.展开更多
Cr3 C2-NiCr particles were injected into the melted surface of Q235 low carbon steel to make a surface metal matrix composite （MMC） layer by gas tungsten are melt injection （GTAMI） process. Hardness of the surface...Cr3 C2-NiCr particles were injected into the melted surface of Q235 low carbon steel to make a surface metal matrix composite （MMC） layer by gas tungsten are melt injection （GTAMI） process. Hardness of the surface MMC layer was tested. Wear resistance of the surface MMC was investigated with a ball-on-disk dry sliding setup. Microstrnetures of the surface MMC layer and morphology of the worn surfaces were investigated with scanning electron microscopy （SEM）. The results showed that the hardness of the MMC was as high as 1 960. 7 HV. Wear loss of the upper part of the MMC layer is onlyO. 8% of that of the substrate under the dry sliding condition given. Wear loss of the bottom part is 2. 5 % of that of the substrate.展开更多
It is essential to develop a methanol gas sensor with high selectivity and low working temperature for human health and environmental monitoring.In this work,a blend of PEDOT:PSS and Ti3C2Tx with the mass ratio of 4:1...It is essential to develop a methanol gas sensor with high selectivity and low working temperature for human health and environmental monitoring.In this work,a blend of PEDOT:PSS and Ti3C2Tx with the mass ratio of 4:1 is used to fabricate a methanol gas sensor.It possesses a high response ratio of the largest response and the second largest response(5.54)and an enhanced response compared to pure PEDOT:PSS and pure Ti3C2Tx tested at room temperature.These findings may pave the way towards design of the MXenes based high-performance gas-sensing materials in the future.展开更多
As a powerful non-destructive and label-free detection technology,surface-enhanced Raman scattering(SERS)has been widely used in environmental-pollutant detection,biological-tissue sensing,molecular fingerprint analys...As a powerful non-destructive and label-free detection technology,surface-enhanced Raman scattering(SERS)has been widely used in environmental-pollutant detection,biological-tissue sensing,molecular fingerprint analysis and so on.Different from the traditional SERS substrates represented by noble metals and semiconductors,herein,we report a new highly sensitive SERS substrate material with high stability,biocompatibility,and low cost,namely nucleusfree two-dimensional electron gas(2DEG)Ti3C2 monolayer nanosheets.The highly crystalline monolayer Ti3C2 nanosheets with clean surface are synthesized by an improved chemical exfoliation and microwave heating method.The unique structure of nucleus-free-2DEG in Ti3C2 monolayer provides an ideal transport channel without nuclear scattering,which makes the highly crystalline monolayer Ti3C2 nanosheets achieve a Raman enhanced factor of 3.82×108 and a 10-11 level detection limit for typical environmental pollutants such as azo dyes,trichlorophenol,and bisphenol A.Singlemolecule imaging is also realized on the surface of the Ti3C2 monolayers,which may be the first time that approximate single-molecule imaging has been achieved on a non-noblemetal SERS substrates.Preliminary toxicological experiments show that the cytotoxicity of this material is very low.Considering the facile synthesis,high biocompatibility,low cost and high chemical stability of carbide nanosheets,these Ti3C2 monolayer nanosheets show significant promise for the design and fabrication of flexible SERS substrates for the sensing of trace substances with ultrahigh sensitivity.展开更多
基金supported by National Natural Science Foundation of China(No.51337006)。
文摘CF3I gas mixtures have attracted considerable attention as potential environmentally-friendly alternatives to SF6 gas,owing to their excellent insulating performance.This paper attempts to study the CF3I ternary gas mixtures with c-C4F8 and buffer gases N2 and CO2 by considering dielectric strength from electron transport parameters based on the Boltzmann method and synergistic effect analysis,compared with SF6 gas mixtures.The results confirm that the critical electric field strength of CF3I/c-C4F8/70%CO2 is greater than that of 30%SF6/70%CO2 when the CF3I content is greater than 17%.Moreover,a higher content of c-C4F8 decreases the sensitivity of gas mixtures to an electric field,and this phenomenon is more obvious in CF3I/c-C4F8/CO2 gas mixtures.The synergistic effects for CF3I/c-C4F8/70%N2 were most obvious when the c-C4F8 content was approximately 20%,and for CF3I/c-C4F8/70%CO2 when the c-C4F8 content was approximately 10%.On the basis of this research,CF3I/c-C4F8/70%N2 shows better insulation performance when the c-C4F8 content is in the15%–20%range.For CF3I/c-C4F8/70%CO2,when the c-C4F8 content is in the 10%–15%range,the gas mixtures have excellent performance.Hence,these gas systems might be used as alternative gas mixtures to SF6 in high-voltage equipment.
基金supported by National Natural Science Foundation of China(No.10875093)
文摘We calculated the uniform dielectric breakdown field strength of residual 30% CF3I/CO2 gas mixtures during the arc extinction process over the temperature range 300-3500 K at 0.1 MPa. The limiting reduced field strengths are decided by a balance of electron generation and loss based on chemical reactions estimated by the electron energy distribution function （EEDF）, which employs the Boltzmann equation method with two-term expanding approximation in the steady-state Townsend （SST） condition. During the insulation recovery phase, the hot CF3I/CO2 gas mixtures have maximum dielectric strength at a temperature of about 1500 K. At room temperature 300 K, the electric strength after arc extinction （90.3 Td, 1 Td=10-21 V.m2） is only 38% of the original value before arc （234.9 Td）. The adverse insulation recovery ability of CF3I/CO2 gas mixtures in arc extinction hinders its application in electric circuit breakers and other switchgears as an arc quenching and insulating medium.
基金the National Natural Science Foundation of China(No.62075045)。
文摘The dynamics of negative surface discharges in c-C_(4)F_(8)/CF_(3)I/CO_(2) gas mixture is investigated here with a 2D fuid model.The distributions of ion concentration,electric field strength and photon flux during the propagation of the streamer are obtained by solving the drift-diffusion equations of particles and Poisson's equation,and the photon flux variation function during the propagation is also fitted.It is found that the streamer branches occur when the streamer transitions from the upper surface of the insulator to the side surface,and then when the streamer approaches the plane electrode,the photon flux will increase significantly.On this basis,the positive and negative surface discharge models are compared in terms of streamer characteristics,particle characteristics and streamer branches.It is found that the streamer has a higher electron concentration and electric field in the positive model.The streamer develops“floating”in the positive surface discharge,while it is close to the surface of the insulator in the negative model.In addition,the negative streamer branch has a wider width and develops further.
文摘Cr3 C2-NiCr particles were injected into the melted surface of Q235 low carbon steel to make a surface metal matrix composite （MMC） layer by gas tungsten are melt injection （GTAMI） process. Hardness of the surface MMC layer was tested. Wear resistance of the surface MMC was investigated with a ball-on-disk dry sliding setup. Microstrnetures of the surface MMC layer and morphology of the worn surfaces were investigated with scanning electron microscopy （SEM）. The results showed that the hardness of the MMC was as high as 1 960. 7 HV. Wear loss of the upper part of the MMC layer is onlyO. 8% of that of the substrate under the dry sliding condition given. Wear loss of the bottom part is 2. 5 % of that of the substrate.
基金supported by the National Natural Science Foundation of China(No.51602035)State Scholarship Fund of China,Liaoning Provincial Natural Science Foundation of China(No.20180510036)the Fundamental Research Funds for the Central Universities(No.DUT19JC41)。
文摘It is essential to develop a methanol gas sensor with high selectivity and low working temperature for human health and environmental monitoring.In this work,a blend of PEDOT:PSS and Ti3C2Tx with the mass ratio of 4:1 is used to fabricate a methanol gas sensor.It possesses a high response ratio of the largest response and the second largest response(5.54)and an enhanced response compared to pure PEDOT:PSS and pure Ti3C2Tx tested at room temperature.These findings may pave the way towards design of the MXenes based high-performance gas-sensing materials in the future.
基金support from the Science Foundation of Chinese Academy of Inspection and Quarantine(2019JK004)the National Key Research and Development Program of China(2017YFF0210003)the high performance computing center of Qufu Normal University。
文摘As a powerful non-destructive and label-free detection technology,surface-enhanced Raman scattering(SERS)has been widely used in environmental-pollutant detection,biological-tissue sensing,molecular fingerprint analysis and so on.Different from the traditional SERS substrates represented by noble metals and semiconductors,herein,we report a new highly sensitive SERS substrate material with high stability,biocompatibility,and low cost,namely nucleusfree two-dimensional electron gas(2DEG)Ti3C2 monolayer nanosheets.The highly crystalline monolayer Ti3C2 nanosheets with clean surface are synthesized by an improved chemical exfoliation and microwave heating method.The unique structure of nucleus-free-2DEG in Ti3C2 monolayer provides an ideal transport channel without nuclear scattering,which makes the highly crystalline monolayer Ti3C2 nanosheets achieve a Raman enhanced factor of 3.82×108 and a 10-11 level detection limit for typical environmental pollutants such as azo dyes,trichlorophenol,and bisphenol A.Singlemolecule imaging is also realized on the surface of the Ti3C2 monolayers,which may be the first time that approximate single-molecule imaging has been achieved on a non-noblemetal SERS substrates.Preliminary toxicological experiments show that the cytotoxicity of this material is very low.Considering the facile synthesis,high biocompatibility,low cost and high chemical stability of carbide nanosheets,these Ti3C2 monolayer nanosheets show significant promise for the design and fabrication of flexible SERS substrates for the sensing of trace substances with ultrahigh sensitivity.
