Permittivity and tan delta characteristics of epoxy nanocomposites in the frequency range of 1 MHz-1 GHz

To achieve a compact and reliable design of electrical equipment for the present day requirements, there is an urgent need for better and smart insulating materials and in this respect, the reported enhancements in dielectric properties obtained for polymer nanocomposites seems to be very encouraging. To further understand the dielectric behavior of polymer nanocomposites, this experimental work reports the trends of dielectric permittivities and tan delta (loss tangent) of epoxy nanocomposites with single nano-fillers of Al₂O₃ and TiO₂at low filler concentrations (0.1%, 0.5%, 1% & 5%) over a frequency range of 1 MHz-1 GHz. Results show that the nanocomposites demonstrate some very different dielectric characteristics when compared to those for polymer microcomposites. Unlike the usual expectations of increasing permittivity with increasing filler concentration in polymer microcomposites, it has been seen that up to a certain nano-filler concentration and depending on the permittivity of the nano-filler, the permittivities of the epoxy nanocomposites are less than that of the unfilled epoxy at all the measured frequencies. This suggests that there is a very strong dependence of the filler concentration and nano-filler permittivity on the final permittivity of the nanocomposites at all these frequencies. But, in the case of tan delta behavior in nanocomposites, significant effects of filler concentrations were not observed with both Al₂O₃ and TiO₂ fillers. Tan delta values in nanocomposites with Al₂O₃ fillers are found to be marginally lower at all filler concentrations when compared with the value for unfilled epoxy. But, in TiO_2Oepoxy nanocomposites, although the variations in tan delta are not significant with respect to unfilled epoxy, some interesting trends are observed with respect to the frequencies of measurement.     

碳纳米管填充的高介电常数聚合物基复合电介质材料

介绍了碳纳米管电性能及其功能化改性、以及利用碳纳米管掺杂聚合物制备柔性高介电常数复合材料的研究现状,发现化学气相沉积法得到的多壁碳纳米管(MWNT)在化学处理前后形成的聚合物基复合材料具有明显不同的分散特性和介电性能.相对于微米级球形导电颗粒填充的复合材料,一维尺度碳纳米管填充的复合材料具有明显低得多的渗流阈值,低渗流阈值可以明显保持聚合物基体优良的机械性能.期望在这一领域从工程电介质的角度做深入的研究工作,以发现碳纳米管在聚合物基复合材料领域所表现出的新特性、新现象.     

Effect of filler concentration on electrical conductivity andultralow-frequency dielectric properties

The effect of filler concentration on the dielectric properties in the ultralow-frequency region and on the electrical conductivity was studied for ethylene propylene rubber. First, we investigated the relation between the electrical conductivity and filler concentration: as the volume fraction of fillers q_a increased, the conductivity decreased in the low filler concentration region but increased abruptly in the high filler concentration region. The decrease and increase in conductivity can be explained with the action of carrier traps at the interface between EPR and fillers and with the formation of highly conductive paths of filler across the sample, respectively. Secondly, we studied the dielectric properties in the ultralow-frequency region which was obtained from the discharge current. As q_a increased, the relaxation time decreased in the low filler concentration region and then rose in the high filler concentration region. The polarization in the high filler concentration region can be explained by two-layer interfacial polarization between filler and rubber     

Dielectric properties of epoxy nanocomposites

The dielectric properties of epoxy nanocomposites with insulating nano-fillers, viz., TiO₂, ZnO and AI₂O₃ were investigated at low filler concentrations by weight. Epoxy nanocomposite samples with a good dispersion of nanoparticles in the epoxy matrix were prepared and experiments were performed to measure the dielectric permittivity and tan delta (400 Hz-1 MHz), dc volume resistivity and ac dielectric strength. At very low nanoparticle loadings, results demonstrate some interesting dielectric behaviors for nanocomposites and some of the electrical properties are found to be unique and advantageous for use in several existing and potential electrical systems. The nanocomposite dielectric properties are analyzed in detail with respect to different experimental parameters like frequency (for permittivity/tan delta), filler size, filler concentration and filler permittivity. In addition, epoxy microcomposites for the same systems were synthesized and their dielectric properties were compared to the results already obtained for nanocomposites. The interesting dielectric characteristics for epoxy based nanodielectric systems are attributed to the large volume fraction of interfaces in the bulk of the material and the ensuing interactions between the charged nanoparticle surface and the epoxy chains.     

Filler effect of low loss dielectricity in printed circuit board material

Dielectric properties of low-loss dielectric materials are investigated with variation of silica filler which is known to be general filler in PCB composite. With comparison of dielectric losses of various filler materials in use of BCB resin, it could be known that crystalline cristobalite was superior to other crystalline or amorphous silica-base materials and reduced dielectric losses in the composite with resin. And dielectric properties of composite with the variation of filler quantity showed that amorphous silica and quartz increased dielectric loss as their quantities increased, while cristobalite increased little. As quantity of crystalline cristobalite phase increases in cristobalite/quartz intermediates, dissipation factor decreases.     

SF6断路器喷口用复合PTFE电气性能的研究

高压SF6断路器喷口用聚四氟乙烯(PTFE)的粒径、填料的种类、粒径和添加量,对复合PTFE介电性能和耐电弧烧蚀性能都有着明显影响。应用正交设计软件设计了多种因素、每种因素不同水平组合的试验方案,研究了添加Al2O3, BN,MoS2的复合PTFE的电气性能受多种因素影响的变化规律。结果表明,添加无机填料能有效提高喷口材料耐电弧烧蚀性能,当填料种类不同时,复合FTFE的电弧烧蚀量依次为:复合MoS2的PTFE烧蚀量>复合Al2O,的PTFE烧蚀量> 复合BN的PTFE烧蚀量:复合PTFE相对介电常数随填料添加量的增加而增大,随温度的升高而减小;介质损耗角正切随填料的增加及温度的升高而增大。应用正交设计软件的分析功能,对电弧烧蚀试验结果进行了分析,得出填料添加量对烧蚀量的影响最为显著,其次为填料粒径,再次为填料粒径和PTFE粒径的交互作用。     

Low loss flexible SrTiO<Subscript>3</Subscript>/POE dielectric composites for microwave application

Flexible, high dielectric constant and low dielectric loss composites for microwave application fabricated with SrTiO₃ (STO) ceramic filler dispersed inside a thermoplastic polyolefin elastomer (POE) polymer matrix have been studied in this paper. The dielectric property and the mechanical property of STO/POE composites filled with different volume fraction of ceramic filler were investigated. The results indicated that with the increase volume fraction of ceramic filler, both the permittivity and the dielectric loss of composites increased. Good frequency stability within a wide range was observed in all the samples. For the composites containing 40 vol% STO, the composites has a tensile strength of 2.75 MPa with an elongation of about 90% at break value. The permittivity and the dielectric loss of the composites were 11.0 and 0.01 in microwave frequency, respectively. A microstrip transmission line on the composites containing 40 vol% STO as a microwave substrate is designed and measured after bending at different angles, meanwhile the transmission coefficients of the microstrip transmission line were unchanged when bending angle is less than 60°. This indicates that the STO/POE composites have the promising characteristics for potential applications in microwave substrate, flexible dielectric waveguide and related flexible microwave devices.     

Dielectric relaxation properties of filled ethylene propylenerubber

Thermally stimulated discharge currents and time domain dielectric spectroscopy were employed to characterize the behavior of clay-filled ethylene propylene rubber. Measurements were made on samples with different clay concentrations and particle sizes. The main effect of the clay filler on the electrical properties is on interfacial polarization which occurs at the clay polymer interface. The experimental results are sensitive to the shape of the clay particles. A few results indicate that other mechanisms also affect the electrical behavior of this material     

复合导电高分子材料微观网络结构及导电行为仿真分析

导电填料的形貌、尺寸、材料特性及导电填料之间、导电填料与基体之间的相互作用等因素,均能对复合导电高分子材料的导电行为产生重要的影响。为此,通过建立球状导电填料填充的复合导电高分子材料微观结构模型,利用Matlab计算软件,仿真分析了复合导电高分子材料的导电行为即渗流现象,研究了导电填料的粒径大小和体积分数对复合导电高分子材料导电特性的影响。研究结果表明,该仿真模型能够从整体上反映复合导电高分子材料的导电特性,并能推广到其他形貌的导电填料的情况以及三维领域。     

复合电介质介电性能有限元仿真

以聚合物基体添加具有非线性填料非线性复合电介质为研究对象,利用编程实现填料颗粒在基料中随机分布和基于蒙特卡洛(MC)模拟的模型随机构建,并通过三维有限元数值分析软件求得不同电压激励下的响应电流.采用时域最小二乘法对仿真得到的总电流进行分解并获得材料的宏观介电参数与电场强度的关系.结果表明:填料在空间的随机分布导致复合材...     

Electrical performance of RTV silicone rubber coatings

The role played by two major constituents in a room temperature vulcanized (RTV) silicone rubber coating, namely, the inorganic alumina trihydrate (ATH) filler and the silicone polymer, on the coating's electrical performance was examined. The principal variable in the RTV silicone rubber coatings evaluated was the different weight fraction of the silicone polymer and ATH inorganic filler normally used for improving the tracking and erosion resistance. Other formulation details were essentially the same in the cured rubber. The coatings were spray coated on glazed porcelain rods and subjected to accelerated aging in a salt fog chamber. The changes produced by accelerated aging on the contamination withstand capability, leakage current suppression and erosion resistance were determined and correlated with the ratio of polymer to inorganic filler in the coating. It is shown that critical aspects of electrical performance necessary for satisfactory service operation such as contamination withstand capability before flashover and leakage current suppression are superior for the coating with a relatively high ratio of polymer to inorganic filler in comparison to the coatings with a relatively low ratio of polymer to inorganic filler. While all the coatings showed a high erosion resistance under mild discharge activity, the erosion resistance was found to be superior for the formulations with high inorganic filler under conditions of intensive surface discharge activity     

聚合物基复合薄膜的高温储能性能研究进展

聚合物薄膜电容器具有功率密度大、安全性高、绝缘性好等优点而被广泛应用在工程领域。近年来,随着新能源交通、清洁能源并网、油气开采等领域对具有优异高温储能特性的介电薄膜电容器需求日益增加,高温、高电场等极限条件下介质薄膜电容器的储能受到越来越多的关注,相关研究已成为电工材料领域的研究热点。该文总结近年来有关聚合物基复合薄膜的高温储能研究进展。首先,介绍决定电介质材料高温储能特性的关键参数,分析高温、高电场对相关参数的影响规律;其次,梳理基于不同空间层次设计的聚合物薄膜高温储能特性优化研究现状,从分子结构、微观结构、介观结构3个方面总结高温储能性能的调控方法;最后,对进一步提升聚合物薄膜的高温储能性能做出展望。     

Structural Changes in EPDM Subjected to Ageing in High Voltage Transmission Lines

This work presents a study of the structural changes in aged EPDM (ethylene-propylene-diene monomer) from outdoor high voltage transmission lines. Samples were taken from failed and non-failed insulators after up to ten years in service on a 33 kV line. Infrared absorption, hydrophobicity index, dynamical mechanical analysis (DMA) and dielectric relaxation (DR) were employed as experimental techniques. The same experimental techniques were also applied to new samples of EPDM that were subjected to high electric fields (up to 14 kV/mm) for several hours. Results from DMA and DR techniques are in good agreement and, together with previous results from neutron irradiation techniques, suggest that the experimental data obtained from outdoor-aged and laboratory tested samples may be explained by a decrease in the degree of crystallinity due to the interaction between electrical and mechanical effects in the dielectric. The proposed model is based on the disentanglement of the crystallites by forces originated in the interaction of the electric field with the polar groups located in the amorphous phase of the polymer matrix. An alternative explanation, based on a relaxation process appearing at the interfaces between the filler (ATH) and the polymer matrix conflicts with several experimental results presented in this work.     

凝胶聚合物PVDF-HFP电解质膜的性能研究

锂离子电池由于形状多样化、灵活性及轻便等优点而用于商业化生产,满足微型电子工业的需要,而偏氟乙烯和六氟丙烯的共聚物PVDF-HFP由于较高的电导率,较好的机械强度和热稳定性,优良的界面特性和电化学性能而被认为是最受欢迎的一种聚合物电解质。主要综述了PVDF-HFP固体电解质的组成、制备方法和进展,讨论了PVDF-HFP电解质的改性措施:填料改性、增塑剂改性、共聚共混改性及聚合物改性。对今后的发展方向作了简单展望。     

Effects of various oxide fillers on physical and dielectric properties of calcium aluminoborosilicate-based dielectrics

Physical and dielectric properties of LTCC (low temperature co-fired ceramics) materials based on a typical calcium aluminoborosilicate glass and various fillers such as Al₂O₃, BaTiO₃, CaTiO₃, TiO₂, ZrO₂, MgO and SiO₂ were investigated. Densification, crystallization and thermal and dielectric properties were found to strongly depend on the type of filler. The XRD patterns of Al₂O₃, BaTiO₃, CaTiO₃ and MgO samples demonstrated crystalline phases, CaAl₂Si₂O₈, BaAl₂Si₂O₈, CaTiSiO₅ and CaMgSi₂O₆, respectively, as a result of firing at 850 °C. For the sample containing CaTiO₃ filler, specifically, dielectric constant increased drastically to approximately 19.9. A high quality factor of >210 and a high TCE (temperature coefficient of expansion) of >8.5 ppm/°C were obtained for the composition containing MgO or SiO₂. Near zero TCF (temperature coefficient of frequency) was obtained for the samples containing TiO₂. The purpose of this work is to investigate the effects of various ceramic fillers on physical and dielectric properties and ultimately to provide the technical guidelines for the proper choice of filler in various LTCC systems.     

FEATURE ARTICLE Conducting Polymer Composites

Conducting polymer composites become increasingly important for technical applications. In this article, the resulting electrical properties of such materials are illustrated by a variety of experimental examples. It is shown that the combined mechanical, thermal and electrical interaction between the filler particles via their electrical contacts and the surrounding polymer host matrix are responsible for the properties of the composite material. A short review is given of the theoretical background for the understanding of the electrical transport in such materials. The arrangement of the filler particles and the resulting conductivity can be described either by percolation or by effective medium theories. It can also be related to different types of charge carrier transport processes depending on the internal composite structure. Special emphasis is given to the microstructure of the filler particles such as size, hardness, shape and their electrical and thermal conductivities. A detailed analysis of the physics of the contact spots and the temperature development during current flow at the contact is given. It is shown that the polymer matrix has a strong influence on the electrical conductivity due to its elastic properties and the response to external thermal and mechanical stimulation. Strong changes in the electrical conductivity of conducting polymer composites can be realized either by thermal stimuli, leading to a positive and negative temperature coefficient in resistivity, or by applying mechanical stress. By using nonlinear fillers an additional degree of functionality can be achieved with conducting polymers.     

聚合物/无机纳米复合电介质介电性能及其机理最新研究进展

聚合物/无机纳米复合电介质由于其优异的电、热、机械等性能而成为电介质领域研究的热点.本文综述了该领域的最新研究进展,涉及纳米电介质的结构特性和介电性能及其机理,重点阐述了纳米电介质的界面特性和电阻率、介电常数、介质损耗、击穿场强、耐电晕老化、电树枝老化、陷阱、空间电荷等介电特性及其对应的微观和介观机理,并展望了纳米电介...     

Effect of SiO<Subscript>2</Subscript> Addition to BaO-ZnO-B<Subscript>2</Subscript>O<Subscript>3</Subscript> Glass on Dielectric and Thermal Properties for Application to Barrier Ribs of Plasma Display Panels

The effect of SiO₂ addition to barium zinc borate (BaO-ZnO-B₂O₃, BZB) glass on dielectric and thermal expansion properties was investigated. When SiO₂ was added to the glass batch to form a SiO₂-BaO-ZnO-B₂O₃ (SBZB) glass, the dielectric constant decreased significantly from 15.5 to 9.9. When SiO₂ (quartz) was further added to the SBZB in the form of filler particles to yield ceramic filler-reinforced SBZB microcomposites, the dielectric constant was further decreased. The coefficient of thermal expansion (CTE) of SBZB was slightly lower than the allowable range, while the filler addition to SBZB correspondingly increased CTE to the allowable range. Thus, the addition of SiO₂ to BZB glass to form SBZB glass and further addition to SBZB in the form of ceramic filler were shown to be amenable ways to tailor the dielectric constant as well as CTE of the barrier rib glass for the PDP application.     

锂离子电池聚合物复合电解质研究介绍

本文介绍了固体粒子/聚合物复合电解质的研究情况，着重研究了固体粒子的加入对电解质性能的改善作用，并探讨了复合电解质的导电机理。     

On optimization of the design of metal-film segment capacitors

Results of the experimental studies of the electric properties of metallized polymer films for segment metal-film capacitors are presented. The optimization criteria for selection of the geometrical dimensions of insulating gaps between segments and metallized fuses are determined. The surface resistance of the metallized coating and the chemical structure of polymer films are found to influence the operation parameters of the segment capacitor dielectric.