IMPORTANCE OF THE DIELECTRIC PROPERTIES OF MATERIALS FOR MICROWAVE HEATING

In this paper, we show the importance of having a good knowledge of the dielectric properties of a material when it is intended to heat or dry this material by microwaves. We study the frequency, temperature and composition dependence of the dielectric permittivity in order to see how these dependences can affect the microwave heating process. We also study the non-uniform absorption of energy in a sample due to dielectric or conductive losses.     

Comprehensive study of electromagnetic wave absorption properties of GdMnO3-MoSe2 hybrid composites

Recently, the public does not avoid the use of RF/microwave communication and non-communication devices, which means they will be constantly exposed to radiation from those devices, which will worsen their health in the long term, as well as there will be interference and coupling effects between devices. In this paper, a novel and high-performance absorber material is created and analyzed. The microscopic and macroscopic properties of Gadolinium Manganite (GdMnO₃), Molybdenum Diselenide (MoSe₂), and three mixtures of GdMnO₃-MoSe₂ (GdMo) with 20, 30, and 40% filler loading were investigated. The procedure for producing the five materials was explained and described in detail. The mixture of GdMo with 20, 30, and 40 wt% filler loading has the features of GdMnO₃ and MoSe₂. For macroscopic analysis, the measured relative complex permittivity and permeability of the five synthesized materials are modeled using the Lorentz dispersion model. Among the five study materials, GdMo with 40 wt% filler loading shows the highest electric and magnetic losses with loss tangent, tan δ_e ≈ 0.228 and tan δ_m ≈ 0.38 where the absorption performance is better compared to its pristine components, namely GdMnO₃ and MoSe₂. Based on the transmission theory of metal plate backing materials, the GdMo with 40 wt% filler loading and thicknesses ranging from 0.0014 m to 0.0021 m, which is terminated by a metal plate on the back side, exhibited the optimum microwave absorption performance with a minimum reflection loss value better than ?20 dB at X-band operating frequency. Without a metal backing, a 0.008 m thickness of GdMo with 40 wt% can achieve reflection loss, RL of ?10 dB from 9.2 GHz to 12.4 GHz, and RL of ?20 dB from 11.1 GHz to 12.4 GHz.     

以β-Co(OH)2为前驱体合成LiCoO2的研究

在空气气氛下,以自制的结晶度高的-βCo(OH)2为前驱体,固相合成了锂离子电池正极材料LiCoO2。研究了反应预处理方式、研磨时间、锂源、锂钴初始摩尔比、煅烧温度和时间等合成条件对产品结构的影响。实验发现:以LiOH.H2O为锂源、锂钴初始摩尔比为1,采取混合研磨后压块的预处理方式有利于合成反应的进行。随研磨和煅烧时间的延长,产物的衍射峰强度增大,层状结构更完美。     

锂离子电池正极材料LiCoO_2的研究进展

概述锂离子电池正极材料锂钴氧的制备方法,包括固相反应法、溶胶-凝胶法、水热合成法、沉淀-冷冻法、喷雾干燥法、熔盐合成法和微波合成法。介绍了国内外通过不同离子的掺杂改性和表面修饰对L iCoO2电化学性能的影响,并对其发展方向做出了展望。     

应用平行短路板法快速测量微波介质材料的复介电常数

为了快速获得微波介质材料的介电参数,研究了复介电常数的测量方法。采用平行短路板法测量TE011和TE013模介质谐振器的谐振频率和有载Q值,用Matlab编程求解超越方程,从而直接得到材料的相对介电常数和介电损耗。并对四种材料的介电性能进行了测试,结果表明该方法具有快速简单的特点。     

碳纳米管材料低频电磁参数及吸波产热特性

微波的热利用技术促进了吸波材料的应用研究。碳纳米管（CNTs）是近年来新兴的强吸波材料,具有密度小、比表面积大、量子尺寸效应的特点。对碳纳米管吸波材料的复介电常数和复磁导率随碳纳米管含量的变化进行探究。在此基础上,以石蜡油为蓄热介质探究了碳纳米管材料在微波辐照下吸波产热特性。同轴传输法适用于小型样品的测量,具有误差小的优点,故采用此种方法作为测量电磁参数手段。对碳纳米管电磁参数测量实验结果表明,碳纳米管吸波材料在低频下对于微波能的损耗兼具电损耗和磁损耗。对碳纳米管吸波产热特性实验结果表明,碳纳米管是一种强吸波材料。     

Effect of B4C content and annealing on complex permittivity and microwave-absorption properties of B4C/Al2O3 coatings

The B₄C/Al₂O₃ coatings were fabricated by air plasma spraying technology, and their complex permittivity and microwave absorption properties in the X-band were investigated before and after annealing (500 °C/2 h). Both the real and imaginary parts of the complex permittivity of the coatings decreased after annealing, which can be attributed to the weakening of polarization relaxation intensity and the reduction of electrical conductivity caused by the escape of carbon atoms. In addition, the density of B₄C/Al₂O₃ coatings decreased from 3.01 to 2.16 g/cm³ with increasing B₄C content. The B₄C/Al₂O₃ coatings exhibit a minimum reflection loss (RL) value of ?39.58 dB and the effective absorption bandwidth (RL＜?10 dB, EAB) covers 1.9 GHz at a thickness of 1.6 mm. After annealing, the above coatings still had an EAB of 1 GHz. Therefore, the B₄C/Al₂O₃ coatings can be considered as a promising microwave-absorption candidate with good high-temperature microwave-absorbing performance and low density.     

Frequency dispersion characteristics of the complex permittivity of the epoxy-carbon black composites

The effects of frequency, volume fraction of carbon black, and porosity on the complex permittivity of the epoxy-carbon black composites were investigated and the frequency dispersion behavior model for the complex permittivity was proposed. In the epoxy-carbon black composites, the frequency dispersion behaviors of the complex permittivity changed from relaxation spectrum to resonance spectrum with increasing the amount of carbon black. The complex permittivity of the composites increased with decreasing the porosity. Comparing the complex permittivity of the composites filled with 2 vol % of carbon black with the values obtained from three types of previously reported model equations, the relaxation behavior coincided with the Havriliak-Negami model. The damping and asymmetrical factor values were increased with increasing porosity in the composites. The empirical equation proposed here was useful in describing the complex permittivity of the composites of > 3 vol % carbon black with resonance type. The damping factor (γ) decreased as the filler content increased, but the asymmetrical factor (κ) increased reversely. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 363–369, 1998     

丙酮溶解分离废旧锂离子电池中金属的方法

根据粘结剂PDVF的性质,选择使用极性较小且较廉价的丙酮溶解PDVF粘结剂,分离正极材料和集流体铝片,并优化出最佳分离条件。实验表明废旧锂电池正极材料在丙酮溶剂中配比为30mL／g、50℃下搅拌100min的联合作用下与集流体铝片分离效果最好。本实验丙酮和铝片均可回收再利用,节约试剂和成本,是一种经济环保的绿色技术。     

废旧手机电池回收制备 LiCoO2电极材料

首次提出采用混合溶剂（N－甲基吡咯烷酮（NMP）和N,N－二甲基甲酰胺（DMF）（1：1）]回收废旧手机电池,制备LiCoO2电极材料的方法。结果表明：用有机混合溶剂较采用单一有机溶剂NMP或DMF的提取效率好。提取效率提高13．2％～21．1％。在上述混合溶剂中100℃浸提1 h,盐酸80℃浸取1 h,氢氧化钠溶液沉淀,沉淀物经马福炉高温（700℃）煅烧7 h即可制得具有较好电化学性能的LiCoO2,可用作手机电池的主要正极材料。     

微螺旋炭纤维的微波电磁参数及其环氧复合材料的吸波性能研究

采用化学气相沉积法制备了微螺旋炭纤维(CMCs),研究了其在频率为8.2￣12.4GHz范围内的微波介电特性;以环氧树脂为胶粘剂制备了CMCs/环氧复合吸波涂层,并对其吸波性能进行了研究。结果表明,随着CMCs含量的增加,复介电参数实部ε′、虚部ε″和介电损耗tanδ均有所增加,当CMCs含量为1%￣5%时,ε″和tanδ增幅很小;当CMCs含量为10%时,两者增幅显著增大。ε′表现出高频减小的趋势,同时tanδ表现出高频增大的趋势,这些均有利于实现高频吸波。磁损耗tanξ较小且CMCs含量对其影响不明显。CMCs/环氧复合吸波涂层的反射率随着CMCs含量的增加而明显减小,表现出高频衰减略有增加的趋势,同时出现多吸收峰,这有利于实现宽频吸波。     

微波介质复介电常数的带状线法测量

采用工作波型为TEM的带状线谐振方法 ,对研制的PTFE/陶瓷 /微纤维为主要组成的多元复合微波介质系列基板的复介电常数进行了测量 ,结果表明 :对薄片状大面积基板采用带状线方法测试可以获得高精度且一致性好的数据。对微波频率下相对介电常数与介质损耗的机制及带状线测试产生的误差因素进行了探讨分析     

短切导电纤维填充复合材料吸波性能

摘要：采用浇注工艺制备了短切导电纤维填充乙烯基酯树脂复合材料。研究了短切导电纤维含量的变化对复合材料电磁特性和吸波性能的影响,并对这种影响进行了理论分析;研究了复合材料厚度对吸波性能的影响。结果表明,在8～18 GHz频段内,随着短切导电纤维含量的增加,介电常数实部和虚部数值增大;在26.5～40 GHz频段内,短切导电纤维质量分数大于1%时,复合材料的介电常数实部和虚部随着频率的升高均呈下降趋势,表现出一定的频散特性。在8～18 GHz,26.5～40 GHz频段内,当短切导电纤维质量分数不大于5%时,复合材料的吸波性能随短切导电纤维含量的增加而增强,短切导电纤维质量分数为7%时,吸波性能反而降低;当短切导电纤维质量分数为5%时,在整个测试频段内,复合材料反射率小于-10?dB的有效带宽达到16.5 GHz,在10.3 GHz和29.8 GHz,复合材料各有一吸收峰,峰值均为-15?dB。随着复合材料厚度的增加,谐振峰向低频移动。     

正极材料钴酸锂的SEI膜研究

通过不同测定方法对SEI膜的形成过程和主要组分进行测定。通过循环伏安和阻抗测试,确定了正极材料钴酸锂的表面SEI膜在第一次循环过程中形成,其后随着循环次数的增加,其表面SEI膜变得更加致密,并且有利于锂离子通过,但其厚度不再增加;通过电镜分析同样确定了正极材料钴酸锂的表面SEI膜在第一次循环过程中形成,并且其厚度在10 nm以下;通过X射线光电子能谱分析（XPS）确定了正极材料钴酸锂的表面SEI膜的组成为氟化锂和有机锂化合物。     

聚苯胺包覆短碳纤维的制备及电磁性能研究

对短碳纤维(SCF)硝酸氧化处理后,采用聚苯胺原位氧化聚合法对其进行包覆改性,制备聚苯胺包覆改性SCF,以改善SCF的电磁性能.采用XPS、SEM对聚苯胺包覆的SCF进行了微观结构和形貌的分析,结果显示聚苯胺层包覆完整、致密,且聚苯胺和SCF表面之间存在化学键合作用.采用PNA-LN5230A微波网络测试仪测定了聚苯胺包覆SCF的电磁性能(复介电常数和复磁导率),并对2mm厚度下的吸收和反射损耗进行了分析,研究了以此为填料制备的涂膜的电磁屏蔽性能和导电性.结果表明,在50 MHz～2 GHz频率范围内,相对于未包聚改性的短碳纤维,导电聚苯胺/碳纤维(PASCF)的复介电常数实部和虚部都有所提高,磁损耗正切为O,为电损耗型材料,而不导电聚苯胺/碳纤维(NPASCF)的复介电常数实部和虚部都有所下降,而磁损耗止切高达O.09,显示出弱电磁性;采用Matlab 6.5软件进行屏蔽性能分析,导电聚苯胺包覆碳纤维的吸收损耗可达4.654 dB,不导电聚苯胺包覆碳纤维(NPASCF)的吸收损耗为1.105 dB:以PASCF为填料制备的涂膜表面电阻率为1.02 Ω·m-2,电磁屏蔽效能值约为17 dB,以NPASCF为填料制备的涂膜表面电阻率为2.32×1011Ω·m-2,电磁屏蔽效能值可达8 dB.     

Microwave absorption of M-type hexaferrite Ba1-xCaxFe12O19 (x ≤ 0.4) ceramics in 2.6–18 GHz

Ba_1-xCa_xFe₁₂O₁₉ (x?=?0.0, 0.1, 0.2, 0.3 and 0.4, BCFO) ceramics were prepared using high-temperature solid-state method and the effect of Ca²⁺ substitution was investigated. The grain size of BCFO ceramics sintered at 1250?°C for 2?h increases from 1?µm to 5?µm as Ca²⁺ added. The BCFO ceramics show a typical hard magnetic behavior with a maximum saturation magnetization (M_S) of 51.8?emu?g^?1 at x?=?0.2. The bandwidth of microwave reflection loss (RL) below ??10?dB (> 90.0% microwave absorption) is obtained in 7.60???9.8?GHz with the minimum RL ??30.8?dB at 8.5?GHz for x?=?0.2 (thickness 2.0?mm), which makes Ba_0.8Ca_0.2Fe₁₂O₁₉ ceramic a potential microwave absorption candidate.     

LiCoO2的制备及电化学性能研究

采用高温固相反应法在工业级别的设备上制备了一系列LiCoO2样品。运用SEM和XRD分析技术研究了样品微观形貌和晶相结构。将LiCoO2样品制成工作电极，组装了试验电池进行充放电循环测试。结果表明，不同原料来源对LiCoO2结构与电化学性能有一定的影响。烧结温度对LiCoO2晶相结构、晶化程度、结构致密性及稳定性有显著影响。在800℃和900℃条件下合成的LiCoO2都具有电化学活性，首次充电容量均大于130mA.h.g^-1。