以南方高湿度地区某500 k V交流线路复合绝缘子大面积发热事故为背景,选取7支绝缘子样品,测量表面灰密(non-soluble material deposit density,NSDD)/盐密(equivalent salt deposit density,ESDD)、憎水性;在高压试验大厅悬挂绝缘子进...以南方高湿度地区某500 k V交流线路复合绝缘子大面积发热事故为背景,选取7支绝缘子样品,测量表面灰密(non-soluble material deposit density,NSDD)/盐密(equivalent salt deposit density,ESDD)、憎水性;在高压试验大厅悬挂绝缘子进行加压试验,利用紫外仪和红外仪进行观察,研究绝缘子的发热特性;解剖绝缘子,结合X射线光电子能谱(X ray electron energy spectrum,XPS)分析材料的理化特性,排除局部放电造成端部异常温升的可能性;做硅橡胶和芯棒样品吸水性试验,分析老化绝缘子的受潮特性;测量受潮硅橡胶的介电常数和电阻率;基于有限元分析软件Ansoft对硅橡胶受潮后的绝缘子进行仿真,研究硅橡胶受潮对电场分布的影响。得出结论:运行一段时间后,交界面良好的绝缘子在硅橡胶受潮后电场分布改变,导致护套端部电场强度升高,从而导致局部的极化损耗增加,出现局部温升。增大的电场也会影响材料的微观结构,使得材料老化加速。最后,针对复合绝缘子受潮后温升,提出防范措施。展开更多
以7年生烟富3/M26/平邑甜茶为试材,采用^(15)N同位素示踪技术,研究不同供氮水平[低氮(100 kg N·hm^(-2),N_(100))、中氮(200 kg N·hm^(-2),N_(200))和高氮(300 kg N·hm^(-2),N_(300))]对烟富3/M26/平邑甜茶^(15)N-尿素...以7年生烟富3/M26/平邑甜茶为试材,采用^(15)N同位素示踪技术,研究不同供氮水平[低氮(100 kg N·hm^(-2),N_(100))、中氮(200 kg N·hm^(-2),N_(200))和高氮(300 kg N·hm^(-2),N_(300))]对烟富3/M26/平邑甜茶^(15)N-尿素吸收、利用、损失及产量和品质的影响.结果表明:不同供氮水平植株的生长状况及氮素吸收、利用和损失特性差异显著.N_(200)处理植株叶绿素含量(SPAD)、光合速率(Pn)、叶片全氮含量和生物量显著高于N_(100)和N_(300)处理,植株根冠比也显著增加.不同供氮水平下植株各器官对氮的吸收能力(Ndff值)存在显著差异,各测定时期果实(花)、叶片、一年生枝、多年生枝和中心干的Ndff值均为N_(100)>N_(200)>N_(300);而根的Ndff值在盛花期和春梢缓长期为N_(100)>N_(200)>N_(300),在秋梢生长期、果实膨大期和果实成熟期为N_(200)>N_(100)>N_(300).在果实成熟期,N_(200)处理^(15)N肥料利用率为23.6%,显著高于N_(100)(16.3%)和N_(300)处理(14.4%),而^(15)N损失率为56.4%,显著低于N_(100)(60.6%)和N_(300)处理(66.1%).不同供氮水平植株的平均单果质量、单株产量、可溶性固形物、硬度、可溶性糖、可滴定酸、糖酸比均存在显著差异,且均以N_(200)处理最高,其次是N_(300)处理,N_(100)处理最低.展开更多
The development of microwave absorption materials(MAMs) is a considerable important topic because our living space is crowed with electromagnetic wave which threatens human’s health.And MAMs are also used in radar st...The development of microwave absorption materials(MAMs) is a considerable important topic because our living space is crowed with electromagnetic wave which threatens human’s health.And MAMs are also used in radar stealth for protecting the weapons from being detected.Many nanomaterials were studied as MAMs,but not all of them have the satisfactory performance.Recently,metal-organic frameworks(MOFs) have attracted tremendous attention owing to their tunable chemical structures,diverse properties,large specific surface area and uniform pore distribution.MOF can transform to porous carbon(PC) which is decorated with metal species at appropriate pyrolysis temperature.However,the loss mechanism of pure MOF-derived PC is often relatively simple.In order to further improve the MA performance,the MOFs coupled with other loss materials are a widely studied method.In this review,we summarize the theories of MA,the progress of different MOF-derived PC-based MAMs,tunable chemical structures incorporated with dielectric loss or magnetic loss materials.The different MA performance and mechanisms are discussed in detail.Finally,the shortcomings,challenges and perspectives of MOF-derived PC-based MAMs are also presented.We hope this review could provide a new insight to design and fabricate MOF-derived PC-based MAMs with better fundamental understanding and practical application.展开更多
Developing electromagnetic(EM) wave absorbing materials with low reflection coefficient and optimal operating frequency band is urgently needed on account of the increasingly serious EM pollution. However, the applica...Developing electromagnetic(EM) wave absorbing materials with low reflection coefficient and optimal operating frequency band is urgently needed on account of the increasingly serious EM pollution. However, the applications of common EM absorbing materials are encumbered by poor high-temperature stability, poor oxidation resistance, narrow absorption bandwidth or high density. Herein, the strong EM absorption capability and wide efficient absorption bandwidth of high entropy ceramics are reported for the first time, which are designed by a combination of the novel high entropy(HE) rare earth silicide carbides/rare earth oxides(RE3 Si2 C2/RE2 O3). Three HE powders, i.e., HERSC-1(HE(Tm0.2 Y0.2 Dy0.2 Gd0.2 Tb0.2)3 Si2 C2),HERSC-2 HE(Tm0.2 Y0.2 Dy0.2 Gd0.2 Tb0.2)3 Si2 C2/HE(Tm0.2 Y0.2 Dy0.2 Gd0.2 Tb0.2)2 O3) and HERSC-3(HE(Tm0.2 Y0.2 Dy0.2 Gd0.2 Tb0.2)3 Si2 C2/HE(Tm0.2 Y0.2 Dy0.2 Gd0.2 Tb0.2)2 O3), are synthesized. Although HERSC-1 exhibits a limited absorption effect(the minimum reflection loss(RLmin) is-11.6 d B at 3.4 mm) and a relatively narrow effective absorption bandwidth(EAB) of 1.7 GHz, the optimal absorption RLminvalue and EAB of HERSC-2 and HERSC-3 are-40.7 d B(at 2.9 mm), 3.4 GHz and-50.9 d B(at 2.0 mm), 4.5 GHz,respectively, demonstrating strong microwave absorption capability and wide absorption bandwidth.Considering the better stability, low density and strong EM absorption effect, HE ceramics are promising as a new type of EM absorbing materials.展开更多
Two-dimensional(2D)transition metal carbide MXene-based materials hold great potentials applied for new electromagnetic wave(EMW)absorbers.However,the application of MXenes in the field of electromagnetic wave absorpt...Two-dimensional(2D)transition metal carbide MXene-based materials hold great potentials applied for new electromagnetic wave(EMW)absorbers.However,the application of MXenes in the field of electromagnetic wave absorption(EMA)is limited by the disadvantages of poor impedance matching,single loss mechanism,and easy oxidation.In this work,MoO_(3)/TiO_(2)/Mo_(2)TiC_(2)T_(x)hybrids were prepared by the annealing-treated Mo_(2)TiC_(2)T_(x)MXene and uniform MoO_(3)and TiO_(2)oxides in-situ grew on Mo_(2)TiC_(2)T_(x)layers.At the annealing temperature of 300℃,the minimum reflection loss(RLmin)value of MoO_(3)/TiO_(2)/Mo_(2)TiC_(2)T_(x)reaches-30.76 dB(2.3 mm)at 10.18 GHz with a significantly broadening effective absorption bandwidth(EAB)of 8.6 GHz(1.8 mm).The in-situ generated oxides creating numerous defects and heterogeneous interfaces enhance dipolar and interfacial polarizations and optimize the impedance matching of Mo_(2)TiC_(2)T_(x).Considering the excellent overall performance,the MoO_(3)/TiO_(2)/Mo_(2)TiC_(2)T_(x)hybrids can be a promising candidate for EMA.展开更多
Developing a flexible,light-weight and effective electromagnetic(EM)absorber remains challenging despite being on increasing demand as more wearable devices and portable electronics are commercialized.Herein,we report...Developing a flexible,light-weight and effective electromagnetic(EM)absorber remains challenging despite being on increasing demand as more wearable devices and portable electronics are commercialized.Herein,we report a flexible and lightweight hybrid paper by a facile vacuumfiltration-induced self-assembly process,in which cotton-derived carbon fibers serve as flexible skeletons,compactly surrounded by other microwave-attenuating components(reduced graphene oxide and Fe3O4@C nanowires).Owing to its unique architecture and synergy of the three components,the asprepared hybrid paper exhibits flexible and lightweight features as well as superb microwave absorption performance.Maximum absorption intensity with reflection loss as low as-63 dB can be achieved,and its broadest frequency absorption bandwidth of 5.8 GHz almost covers the entire Ku band.Such a hybrid paper is promising to cope with ever-increasing EM interference.The work also paves the way to develop low-cost and flexible EM wave absorber from biomass through a facile method.展开更多
文摘以南方高湿度地区某500 k V交流线路复合绝缘子大面积发热事故为背景,选取7支绝缘子样品,测量表面灰密(non-soluble material deposit density,NSDD)/盐密(equivalent salt deposit density,ESDD)、憎水性;在高压试验大厅悬挂绝缘子进行加压试验,利用紫外仪和红外仪进行观察,研究绝缘子的发热特性;解剖绝缘子,结合X射线光电子能谱(X ray electron energy spectrum,XPS)分析材料的理化特性,排除局部放电造成端部异常温升的可能性;做硅橡胶和芯棒样品吸水性试验,分析老化绝缘子的受潮特性;测量受潮硅橡胶的介电常数和电阻率;基于有限元分析软件Ansoft对硅橡胶受潮后的绝缘子进行仿真,研究硅橡胶受潮对电场分布的影响。得出结论:运行一段时间后,交界面良好的绝缘子在硅橡胶受潮后电场分布改变,导致护套端部电场强度升高,从而导致局部的极化损耗增加,出现局部温升。增大的电场也会影响材料的微观结构,使得材料老化加速。最后,针对复合绝缘子受潮后温升,提出防范措施。
文摘以7年生烟富3/M26/平邑甜茶为试材,采用^(15)N同位素示踪技术,研究不同供氮水平[低氮(100 kg N·hm^(-2),N_(100))、中氮(200 kg N·hm^(-2),N_(200))和高氮(300 kg N·hm^(-2),N_(300))]对烟富3/M26/平邑甜茶^(15)N-尿素吸收、利用、损失及产量和品质的影响.结果表明:不同供氮水平植株的生长状况及氮素吸收、利用和损失特性差异显著.N_(200)处理植株叶绿素含量(SPAD)、光合速率(Pn)、叶片全氮含量和生物量显著高于N_(100)和N_(300)处理,植株根冠比也显著增加.不同供氮水平下植株各器官对氮的吸收能力(Ndff值)存在显著差异,各测定时期果实(花)、叶片、一年生枝、多年生枝和中心干的Ndff值均为N_(100)>N_(200)>N_(300);而根的Ndff值在盛花期和春梢缓长期为N_(100)>N_(200)>N_(300),在秋梢生长期、果实膨大期和果实成熟期为N_(200)>N_(100)>N_(300).在果实成熟期,N_(200)处理^(15)N肥料利用率为23.6%,显著高于N_(100)(16.3%)和N_(300)处理(14.4%),而^(15)N损失率为56.4%,显著低于N_(100)(60.6%)和N_(300)处理(66.1%).不同供氮水平植株的平均单果质量、单株产量、可溶性固形物、硬度、可溶性糖、可滴定酸、糖酸比均存在显著差异,且均以N_(200)处理最高,其次是N_(300)处理,N_(100)处理最低.
基金financial support from Ministry of Science and Technology of China(MoST,2016YFA0200200)the National Natural Science Foundation of China(NSFC,21875114,51373078,and 51422304)NSF of Tianjin City(15JCYBJC17700)。
文摘The development of microwave absorption materials(MAMs) is a considerable important topic because our living space is crowed with electromagnetic wave which threatens human’s health.And MAMs are also used in radar stealth for protecting the weapons from being detected.Many nanomaterials were studied as MAMs,but not all of them have the satisfactory performance.Recently,metal-organic frameworks(MOFs) have attracted tremendous attention owing to their tunable chemical structures,diverse properties,large specific surface area and uniform pore distribution.MOF can transform to porous carbon(PC) which is decorated with metal species at appropriate pyrolysis temperature.However,the loss mechanism of pure MOF-derived PC is often relatively simple.In order to further improve the MA performance,the MOFs coupled with other loss materials are a widely studied method.In this review,we summarize the theories of MA,the progress of different MOF-derived PC-based MAMs,tunable chemical structures incorporated with dielectric loss or magnetic loss materials.The different MA performance and mechanisms are discussed in detail.Finally,the shortcomings,challenges and perspectives of MOF-derived PC-based MAMs are also presented.We hope this review could provide a new insight to design and fabricate MOF-derived PC-based MAMs with better fundamental understanding and practical application.
基金financially supported by the National Natural Science Foundation of China(Nos.51672064 and 51972089)。
文摘Developing electromagnetic(EM) wave absorbing materials with low reflection coefficient and optimal operating frequency band is urgently needed on account of the increasingly serious EM pollution. However, the applications of common EM absorbing materials are encumbered by poor high-temperature stability, poor oxidation resistance, narrow absorption bandwidth or high density. Herein, the strong EM absorption capability and wide efficient absorption bandwidth of high entropy ceramics are reported for the first time, which are designed by a combination of the novel high entropy(HE) rare earth silicide carbides/rare earth oxides(RE3 Si2 C2/RE2 O3). Three HE powders, i.e., HERSC-1(HE(Tm0.2 Y0.2 Dy0.2 Gd0.2 Tb0.2)3 Si2 C2),HERSC-2 HE(Tm0.2 Y0.2 Dy0.2 Gd0.2 Tb0.2)3 Si2 C2/HE(Tm0.2 Y0.2 Dy0.2 Gd0.2 Tb0.2)2 O3) and HERSC-3(HE(Tm0.2 Y0.2 Dy0.2 Gd0.2 Tb0.2)3 Si2 C2/HE(Tm0.2 Y0.2 Dy0.2 Gd0.2 Tb0.2)2 O3), are synthesized. Although HERSC-1 exhibits a limited absorption effect(the minimum reflection loss(RLmin) is-11.6 d B at 3.4 mm) and a relatively narrow effective absorption bandwidth(EAB) of 1.7 GHz, the optimal absorption RLminvalue and EAB of HERSC-2 and HERSC-3 are-40.7 d B(at 2.9 mm), 3.4 GHz and-50.9 d B(at 2.0 mm), 4.5 GHz,respectively, demonstrating strong microwave absorption capability and wide absorption bandwidth.Considering the better stability, low density and strong EM absorption effect, HE ceramics are promising as a new type of EM absorbing materials.
基金This work was financially supported by the National Natural Science Foundation of China(Nos.U2004177 and U21A2064)Outstanding Youth Fund of Henan Province(No.212300410081)Support Plan for Scientific and Technological Innovation Talents in Colleges and Universities of Henan Province(No.22HASTIT001)。
文摘Two-dimensional(2D)transition metal carbide MXene-based materials hold great potentials applied for new electromagnetic wave(EMW)absorbers.However,the application of MXenes in the field of electromagnetic wave absorption(EMA)is limited by the disadvantages of poor impedance matching,single loss mechanism,and easy oxidation.In this work,MoO_(3)/TiO_(2)/Mo_(2)TiC_(2)T_(x)hybrids were prepared by the annealing-treated Mo_(2)TiC_(2)T_(x)MXene and uniform MoO_(3)and TiO_(2)oxides in-situ grew on Mo_(2)TiC_(2)T_(x)layers.At the annealing temperature of 300℃,the minimum reflection loss(RLmin)value of MoO_(3)/TiO_(2)/Mo_(2)TiC_(2)T_(x)reaches-30.76 dB(2.3 mm)at 10.18 GHz with a significantly broadening effective absorption bandwidth(EAB)of 8.6 GHz(1.8 mm).The in-situ generated oxides creating numerous defects and heterogeneous interfaces enhance dipolar and interfacial polarizations and optimize the impedance matching of Mo_(2)TiC_(2)T_(x).Considering the excellent overall performance,the MoO_(3)/TiO_(2)/Mo_(2)TiC_(2)T_(x)hybrids can be a promising candidate for EMA.
基金financial support from National Natural Science Foundation of China(No.:51971111)the National Research Foundation,Prime Minister’s Office,Singapore under its Campus for Research Excellence and Technological Enterprise(CREATE)program+2 种基金the Funding for Outstanding Doctoral Dissertation in NUAA(No.BCXJ17-07)Postgraduate Research&Practice Innovation of Jiangsu Province(KYCX17_0252)the Open Research Fund of Jiangsu Provincial Key Laboratory of Bionic Functional Materials。
文摘Developing a flexible,light-weight and effective electromagnetic(EM)absorber remains challenging despite being on increasing demand as more wearable devices and portable electronics are commercialized.Herein,we report a flexible and lightweight hybrid paper by a facile vacuumfiltration-induced self-assembly process,in which cotton-derived carbon fibers serve as flexible skeletons,compactly surrounded by other microwave-attenuating components(reduced graphene oxide and Fe3O4@C nanowires).Owing to its unique architecture and synergy of the three components,the asprepared hybrid paper exhibits flexible and lightweight features as well as superb microwave absorption performance.Maximum absorption intensity with reflection loss as low as-63 dB can be achieved,and its broadest frequency absorption bandwidth of 5.8 GHz almost covers the entire Ku band.Such a hybrid paper is promising to cope with ever-increasing EM interference.The work also paves the way to develop low-cost and flexible EM wave absorber from biomass through a facile method.
