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1.
Xiaolei Su Xiaoqin Liu Yan Jia Junbo Wang Jie Xu Xinhai He Chong Fu Songtao Liu Jing Zheng 《Journal of Materials Science: Materials in Electronics》2013,24(12):4974-4979
Fe-doped ZnO powder has been synthesized by coprecipitation method under different synthesized temperature, using zinc nitrate as the staring material, urea as the precipitator, and ferric nitrate as the doping source, respectively. The prepared powders have been characterized by XRD and SEM. Results show that when the synthesized temperature is below 700 °C the prepared powders are ZnO(Fe) solid solution powders and the ZnFe2O4 impurity phase appeared for the Fe-doped ZnO powder synthesized at 700 °C. The electric permittivities in the frequency range of 8.2–12.4 GHz and average infrared emissivity at the waveband range of 8–14 μm of prepared powders have been determined. The real part and imaginary part of electric permittivities of prepared powders have increased firstly and then decreased with increasing synthesized temperature. The average infrared emissivity has presented the opposite changing trend. 相似文献
2.
Xiaolei Su) Jie Xu) Zhimin Li) Junbo Wang) Xinhai He) Chong Fu) Wancheng Zhou) ) College of Mechanical & Electronic Engineering Xi an Polytechnic University Xi an China ) School of Technical Physics Xidian University Xi an China ) State Key Laboratory of Solidification Processing Northwestern Polytechnical University Xi an China 《材料科学技术学报》2011,(5):421-425
The SiC powders by Al or N doping have been synthesized by combustion synthesis, using Al powder and NH4Cl powder as the dopants and polytetra?uoroethylene as the chemical activator. Characterization by X-ray diffraction, Raman spectrometer, scanning electron microscopy and energy dispersive spectrometer demonstrates the formation of Al doped SiC, N doped SiC and the Al and N co-doped SiC solid solution powders, respectively. The electric permittivities of prepared powders have been determined in the frequency range of 8.2-12.4 GHz. It indicates that the electric permittivities of the prepared SiC powders have been improved by the pure Al or N doping and decrease by the Al and N co-doping. The paper presents a method to adjust dielectric property of SiC powders in the GHz range. 相似文献
3.
4.
Xiaolei Su Fa Luo Yan Jia Junbo Wang Jie Xu Xinhai He Chong Fu Songtao Liu 《Journal of Materials Science: Materials in Electronics》2014,25(11):5101-5106
Al-doped SnO2 powders have been prepared by coprecipitation method at 550 °C, using tin chloride (SnCl4·5H2O) as the raw material, ammonium hydroxide (NH3·H2O) as the precipitator, and aluminum nitrate (Al(NO3)3·9H2O) as the doping source, respectively. The microstructure of the prepared powders has been characterized by X-ray diffraction and scanning electron microscope, respectively. Results show that the prepared powders were Sn(1?x)AlxO2 (x = 0, 0.03, 0.06, and 0.09) solid solution powders and the lattice constant decreased with increasing Al doping content. The electromagnetic property in the frequency range of 8.2–12.4 GHz of prepared powders has been determined. The real part (ε′) and imaginary part (ε″) of permittivity of prepared powders increased with increasing Al doping content. There was little change of real part (μ′) and imaginary part (μ″) of permeability of prepared powders. The electromagnetic loss mechanism has been discussed. 相似文献
5.
Samarjit Singh Ankur Sinha Raj Hemant Zunke Abhishek Kumar Dharmendra Singh 《Advanced Powder Technology》2018,29(9):2019-2026
The present work has been focused on designing an efficient and cost-effective double layer microwave absorber in 8.2–12.4?GHz frequency range. For the same, Cu particles were dispersed in SiC to achieve enhanced microwave absorption by combining the excellent dielectric characteristics of SiC with highly conductive Cu. Cu dispersed SiC composites were prepared by dispersing various weight fractions of Cu particles in the SiC matrix using planetary ball mill. The Cu dispersion in SiC yielded excellent relative complex permittivity values translating into a decrease in the reflection loss (RL) values of dispersed composites as compared to the pristine counterpart. The minimum RL of ?17.18?dB has been observed for 2?wt% Cu dispersed SiC composite at 11.81?GHz with a thickness of 1.3?mm and bandwidth corresponding to ?10?dB is 1.77?GHz. Genetic algorithm approach has been implemented to design double layer microwave absorber to further enhance the microwave absorption of the prepared composites for realizing a cost-effective solution. The optimum double layer results show the RL of ?32.16?dB at 11.05?GHz with 1.67?mm total thickness and bandwidth corresponding to ?10?dB is 2.35?GHz. 相似文献
6.
Su Xiaolei Zhou Wancheng Li Zhimin Luo Fa Du Hongliang Zhu Dongmei 《Materials Research Bulletin》2009,44(4):880-883
The SiC(B) solid solution powders were synthesized via combustion reaction of Si/C system in Ar atmosphere, using boron powder as the dopant and polytetrafluoroethylene as the chemical activator, which were investigated by X-ray diffraction (XRD), scanning electronic microscope (SEM) and Raman spectra. Results show that the prepared powders are C-enriched SiC with C antisites and sp2 carbon defects in which the sp2 carbon is transformed to the sp3 carbon due to boron doping. The electric permittivities of the prepared powders were determined in the frequency range of 8.2-12.4 GHz. The dielectric real part ?′ and dielectric loss tan δ of undoped powder have maximum values (?′ = 5.5-5.3, tan δ = 0.23-0.20), and decrease with increasing boron content. The mechanism of dielectric loss by doping has been discussed. 相似文献
7.
纳米Si/C/N复相粉体的制备及其在不同基体中的微波介电特性 总被引:1,自引:1,他引:0
以六甲基二硅胺烷((Me3Si)2NH)(Me:CH3)为原料,用双反应室激光气相合成纳米粉体装置制备了纳米Si/C/N复相粉体.研究了纳米Si/C/N复相粉体在不同基体中8.2~12.4GHz的微波介电特性,纳米粉体介电常数的实部(ε’)和虚部(ε”)随频率增大而减小,介电损耗(tgδ=ε”/ε’)较高·纳米Si/C/N复相粉体中的SiC微晶固溶了大量的N原子,在纳米Si/C/N复相粉体中形成大量的带电缺陷;极化弛豫是吸收电磁波的主要原因. 相似文献
8.
Si3N4-SiC composite ceramics were fabricated by chemical vapor infiltration using porous Si3N4 ceramic as preform. The average grain size of SiC was 30 nm. Relationship between SiC content and relative complex permittivity of Si3N4-SiC within the frequency range of 8.2-12.4 GHz (X-band) was investigated. The average real part of relative complex permittivity ε of Si3N4-SiC increased from 3.7 to 14.9 and the relative imaginary part ε increased from 0.017 to 13.4 when the content of SiC increased from 0 to 10 vol.%. The Si3N4-SiC ceramic with 3 vol.% SiC achieved a reflection loss below 10 dB (90% absorption) at 8.6-11.4 GHz, and the minimum value was 27.1 dB at 9.8 GHz when the sample thickness was 2.5 mm. The excellent microwave absorbing abilities of Si3N4-SiC ceramic were attributed to the interfacial polarization at interface between Si3N4 and SiC and at grain boundary between SiC nanocrystals. 相似文献
9.
Xiaolei Su ) Wancheng Zhou) Zhimin Li) Fa Luo) Dongmei Zhu) ) State Key Laboratory of Solidification Processing Northwestern Polytechnical University Xi an China ) College of Mechanical & Electronic Engineering Xi an Polytechnic University Xi an China ) School of Technical Physics Xidian University Xi an China 《材料科学技术学报》2009,25(3)
The nonstoichiometric β-SiC powders were synthesized via combustion reaction of Si and C system in a 0.1 MPa nitrogen atmosphere, using Teflon as the chemical activator. The prepared powders were invistigated by XRD and Raman spectra. The results indicates that the cell parameters of all the prepared β-SiC powder are smaller than the standard value of β-SiC because of generation of CSi defects. The complex permittivity of prepared products was carried out in the frequency range of 8.2-12.4 GHz. It shows tha... 相似文献
10.
The nonstoichiometric β-SiC powders were synthesized via combustion reaction of Si and C system in a 0.1 MPa nitrogen atmosphere, using Teflon as the chemical activator. The prepared powders were invistigated by XRD and Raman spectra. The results indicates that the cell parameters of all the prepared β-SiC powder
are smaller than the standard value of β-SiC because of generation of CSi defects. The complex permittivity of prepared products was carried out in the frequency range of 8.2−12.4 GHz. It shows that the dielectric property of prepared β-SiC powder decrease with increasing PTFE content. The effect of CSi defects on dielectric property of -SiC powder has been discussed. 相似文献
11.
Weiling Xiao Peng Xiao Heng Luo Wei Zhou Yang Li 《Journal of Materials Science: Materials in Electronics》2014,25(9):4088-4094
Gelcasting was employed to fabricate Si3N4/SiC whisker (SiCw) composite ceramics, and the effects of heat-treatment temperature on the length-to-diameter ratio of the whiskers and SiCw content on microwave dielectric properties were studied. Compared with pure SiCw of spherical structure obtained at temperature of 1,750 °C(Ar), pure SiCw treated at 1,600 °C(Ar) showed rod-like structure, higher dielectric properties and more evenly distribution in Si3N4/SiCw composite ceramics. Both the real (ε′) and imaginary (ε″) permittivity of Si3N4/SiC whisker (SiCw) composite ceramics decreased with increasing frequency and increased as the whisker content raised owing to the interface and SiCw playing a role of dipole in the frequency range of 8.2–12.4 GHz. In addition, comparing the ceramics with lower content of SiCw, the reflectivity of the composite ceramics moved to a lower frequency; the maximum absorption peak reached ?22.4 dB at the whisker content of 15 wt%. 相似文献
12.
采用LAS玻璃粉末和激光诱导法制备的纳米SiC(N)粉体,通过热压烧结法制备了SiC(N)/LAS纳米陶瓷复合材料,研究了该复合材料在8.2~12.4GHz频率范围内的微波介电特性。结果表明,SiC(N)/LAS的介电常数主要受纳米SiC(N)粉体含量的控制,此外还与烧结温度有关。随着烧结温度的提高,复合材料介电常数和介电损耗均随之增大。SiC(N)/LAS对电磁波的损耗作用明显优于同体积分数的纳米SiC(N)与石蜡混合体,这与烧结过程中形成的碳界面有关。 相似文献
13.
Zhimin Li Wancheng ZhouFa Luo Yunxia HuangGuifang Li Xiaolei Su 《Materials Science and Engineering: B》2011,176(12):942-944
Nitrogen-doped SiC powders were synthesized by combustion synthesis using α-Si3N4 as solid nitrogen dopant. Results showed that β-SiC phases were produced and the introduction of α-Si3N4 resulted in the decrease of particle size of β-SiC powder. The complex permittivities of the undoped and doped samples were determined in the frequency range of 8.2-12.4 GHz. The real part ?′ and imaginary part ?″ of the complex permittivity of doped SiC powder were greatly increased compared to undoped one. The mechanism of nitrogen doping on increasing the complex permittivity of SiC has been discussed, indicating that NC defects contribute to higher permittivity. 相似文献
14.
Zhen Hu Wangzhao Lu Shan Tang Chenting Guo Yonggen Lu 《Fullerenes, Nanotubes and Carbon Nanostructures》2017,25(11):637-641
The pre-oxidized fibers were carbonized at the temperature ranging from 400 to 1300 °C for 1 h. The microwave absorption properties of carbon fibers (CFs) were examined in the frequency range of 2–18 GHz. It is found that the reflection loss characteristics are highly sensitive to the carbonization temperature. At a thickness of 2 mm, the CFs obtained at 710 °C exhibit the best microwave absorbing ability with a maximum reflection loss of ?22.9 dB at 15 GHz, and a bandwidth exceeding ?10 dB in the range 12.4–18 GHz. Results indicate that dielectric loss in cooperation with better matched characteristic impedance results in the excellent microwave absorption of CFs. Low temperature makes ?′ and ?″ too small to consume the energy of microwave, while over high temperature makes ?′ and ?″ too large to transmit the microwave into the CFs. 相似文献
15.
碳包覆铁纳米颗粒制备及电磁性能分析 总被引:5,自引:0,他引:5
以纤维素为基质,硝酸铁为金属颗粒前躯体,在氢气保护下进行控温炭化合成出准球形的碳包覆铁纳米颗粒.产物通过TEM、EDX和XRD表征呈核壳结构,粒径分布比较窄.通过波导法对所制备的碳包覆铁纳米颗粒进行吸波性能分析,采用矢量网络仪研究分析其在8.2~12.4GHz频率范围内的电磁性能. 相似文献
16.
To improve the dielectric properties of β-SiC powders, microwave synthesis was applied to produce SiC powders doped with different amounts of Al from fine powders of Si, C and Al under Ar atmosphere. The dielectric properties of the as-synthesized Al-doped SiC powders were investigated, and the mechanism of dielectric loss by doping has been discussed. The presence of Al influenced the formation of secondary phases (α-SiC and Al4SiC4) and the microstructure of the resultant powders. The produced powders form Al-SiC solid-solutions, which seemingly favor defect polarization loss effect in the high frequency region. This is consistent with the measurements of dielectric properties, which showed that doping of SiC with Al causes increase of permittivity, both real and imaginary parts, and loss tangent, within 8.2-12.4 GHz. The results show that SiC doped with 30% Al has the highest real part ?′ and imaginary part ?″ of permittivity and also loss tangent. 相似文献
17.
Si/C/N纳米粉体的吸波特性研究 总被引:17,自引:0,他引:17
采用XRD研究了氮原子百分含量为11.61%的Si/C/N纳米粉体的相组成,并测定了粉体介电常数根据介电常数,分别优化设计了单层和双层的吸波徐层,设计的吸波涂层对8~18GHz范围的电磁波有较好的吸收作用.设计厚度为2.7mm的单层吸波涂层,在8~15GHz范围内反射率<-5dB设计厚度为2.8mm的双层吸波涂层,在8~18GHz频率范围内电磁波的反射率均<-5dB,反射率<-8dB的频带为6GHz.针对纳米粉体的吸波特性,提出了Si/C/N纳米粉体的吸波机理. 相似文献
18.
Esmail Kiani Amir S. H. Rozatian Mohammad H. Yousefi 《Journal of Superconductivity and Novel Magnetism》2013,26(3):733-738
M-type hexagonal ferrite powders, SrFe12?2x La x (Mn0.5Zr0.5) x O19 (x=0.0, 0.2, 0.4, 0.6, 0.8), have been synthesized by the coprecipitation method. The X-ray diffraction, field emission scanning electron microscope, vibrating sample magnetometer and vector network analyzer all were used to characterize the structure of the samples, their magnetic and microwave properties. The value of the saturation magnetization increased up to x=0.2 and then slowly decreased with increasing doping. A decreasing trend was observed in the value of coercivity with increasing substitution degree, and its value reached a minimum of 2420 Oe for x=0.6 and then increased with further increasing x. The relative complex permittivity and permeability of the composite powders were investigated in the X-band frequency range (8.2–12.4 GHz). 相似文献
19.
The present study aims to produce a light weight electromagnetic interference (EMI) shielding material from carbon nanofibers (CNFs)-based polysulfone (PSU) nanocomposites. EMI shielding effectiveness (EMI SE) was studied by analyzing the electromagnetic wave transmission, reflection, and absorption characteristics of nanocomposites. The electrical conductivity and EMI SE of the nanocomposite with different weight percentage of CNFs (3–10 wt%) were investigated at room temperature and the measurement of EMI SE was carried out in a frequency range of 8.2–12.4 GHz (X-band). The mechanism of EMI shielding of PSU/CNFs nanocomposite has been well explained by comparing the contribution of reflection and absorption to the total EMI SE. The state of dispersion of CNFs and PSU–CNFs interaction was studied by high resolution transmission electron microscopy and scanning electron microscopy. The thermal stability of nanocomposite studied from thermogravimetric analysis was increased after addition of CNFs to PSU matrix. Electrical conductivity of nanocomposite followed power law model of percolation theory having a percolation threshold Φc = 0.0079 vol% (0.9 wt%) and exponent t = 1.73. The EMI SE of nanocomposites with thickness of 1 mm was 19–45 decibel (dB) at 3–10 wt% CNFs loading. This high thermal stability and high EMI SE suggest the potential use of PSU/CNFs nanocomposite as effective lightweight EMI shielding material in different electronic applications. 相似文献
20.
《材料科学技术学报》2011,(7):607-614
The structure, magnetic and microwave-absorption properties of graphite-coated (Fe, Ni) alloy nanocapsules, synthesized by the arc-discharge method, have been studied. High-resolution transmission electron microscopy shows that the nanocapsules have a core/shell structure with (Fe, Ni) alloy as the core and graphite as the shell. All (Fe, Ni) alloy nanocapsules/paraffin composites show good microwave-absorption properties. The optimal reflection loss (RL) was found for (Fe70Ni30)/C nanocapsules/paraffin composites, being -47.84 dB at 14.6 GHz for an absorber thickness of 1.99 mm, while the RL values exceeding -10 dB were found in the 12.4- 17.4 GHz range, which almost covers the Ku band (12.4-18 GHz). For (Fe70Ni30)/C nanocapsules/paraffin composites, RL values can exceed -10 dB in the 11.4-18 GHz range with an absorber thickness of 1.91 mm, which cover the whole Ku band. 相似文献