The dielectric properties and dielectric mechanism of perovskite ceramic CLST/PTFE composites

Polytetrafluorethylene (PTFE) composites filled with perovskite (Ca,Li,Sm)TiO₃ (CLST) dielectric ceramic of various volume fractions filler up to 60% were prepared. The effects of volume fraction of ceramic filler on the microstructure and dielectric properties of the composites have been investigated. A comparative study of dielectric properties of experiment and modeling analysis has been carried out at high frequencies for the CLST/PTFE composites. The results indicate that both the dielectric constant and the dielectric loss increase with the filler. The CLST/PTFE composite with 40% ceramic has exhibited good dielectric properties: ε _r?=?7.92 (~10 GHz), tan δ?=?1.2?×?10^?3 (~10 GHz), and τ _f?=??45 ppm/°C. The dielectric properties are obviously better than most composites reported previously at high frequencies in the aspects of dielectric loss and thermal stability. The dielectric constant and dielectric loss of composites predicted by the Rother–Lichtenecker equation and the general mixing model are in good agreement with the experiment data when the volume fraction of ceramic is less than 40%. When the volume fraction of the ceramic is more than 40%, the deviation occurs. By introducing the correction factor, the theoretical values of the dielectric constant agrees well with the experimental values.     

MgTiO3 filled PTFE composites for microwave substrate applications

MgTiO₃ filled PTFE composite substrates were fabricated for microwave circuit applications. The filler content in the PTFE matrix was varied from 30 to 70 wt%. Low loss MgTiO₃ ceramic powder was prepared by the solid state ceramic route. The phase formation of MgTiO₃ was studied by powder X-ray diffraction analysis. Morphology of the composites and dispersion of filler in the PTFE matrix was studied using scanning electron microscopy. Microwave dielectric properties of the composites with respect to filler loading were measured by stripline resonator method using Vector Network Analyzer. Different theoretical modeling approaches were used to predict the dielectric constant of PTFE ceramic composites with respect to filler loading. The linear coefficient of thermal expansion of the composites was investigated. Moisture absorption of the composites was found out conforming to IPC-TM-650 2.6.2.     

Improved properties of PTFE composites filled with glass fiber modified by sol–gel method

PTFE/GF(glass fiber) composites are widely applied in high-frequency printed circuit board (PCB) substrate materials due to the excellent dielectric properties of PTFE and the low thermal expansion coefficient of GF. However, the poor interface compatibility between PTFE and GF affects the performance of the composite substrates. In this study, tetraethyl orthosilicate (TEOS) was used as the silicon source, and polydimethylsiloxane (PDMS) was the organic precursor to modify the surface of GF through the sol–gel method to promote the interface compatibility of GF and PTFE. The modified GF noted T-GF was filled in PTFE to prepare PTFE/T-GF composites. SEM, FTIR, XPS, and contact angle confirmed that organic–inorganic hybrids were successfully loaded on GF's surface. Moreover, compared with PTFE/GF and the conventional coupling agent modified GF filled PTFE composites, the PTFE/T-GF exhibited improved dielectric constant (2.305), decreased dielectric loss (9.08E^?4), higher bending strength (21.45 MPa) and bending modulus (522 MPa), better thermal conductivity (0.268 W/m*K) and lower CTE (70 ppm/°C), making it has promising application as the substrate materials for high frequency PCB.

     

B4C包覆ZTA颗粒增强铁基复合材料制备与性能

ZTA (ZrO₂增韧Al₂O₃)陶瓷颗粒表面包覆B₄C微粉,将其制备成蜂窝状结构陶瓷预制体。采用传统重力浇注工艺将陶瓷预制体与熔融的高铬铸铁(HCCI)金属溶液进行复合,获得ZTA陶瓷颗粒增强高铬铸铁基复合材料。对复合材料中ZTA陶瓷颗粒增强相与高铬铸铁基体之间的界面及复合材料的耐磨料磨损性能进行了研究。结果表明,ZTA陶瓷颗粒与高铬铸铁界面结合处形成了明显的过渡区域,界面过渡区域的存在提高了陶瓷颗粒与金属基体的结合,从而提升了复合材料的整体稳定性能。同时,三体磨料磨损试验表明该复合材料的耐磨料磨损性能是高铬铸铁的3.5倍左右。     

Preparation and microwave characterization of BaWO<Subscript>4</Subscript> filled polytetrafluoroethylene laminates for microwave substrate applications

Phase pure BaWO₄ ceramic filler has been prepared through solid state ceramic route. Planar BaWO₄ filled Polytetrafluoroethylene (PTFE) composite substrates were fabricated through Sigma Mixing (SM), Extrusion (E), Calendering (C) followed by Hot pressing (H) (SMECH) processes. Morphology and filler distribution of the composites were analyzed using particle size analysis and scanning electron microscopy. The effect of BaWO₄ ceramic filler content on the dielectric properties of the composites was measured at microwave frequency using X-band waveguide cavity perturbation technique. Optimum BaWO₄ filler loading in the PTFE matrix has been found out as 74 wt%. The moisture absorption characteristics of the composite samples were ascertained as per IPC-TM-650 2.6.2.1 method. PTFE/BaWO₄ composite exhibits a dielectric constant of 4.3 and a loss tangent of 0.004 at optimum filler loading.     

Magnetic and dielectric properties of Ni0.8Zn0.2Fe2O4/HDPE composites for high-frequency application

A low loss high-frequency magnetic composite with Ni_0.8Zn_0.2Fe₂O₄ (NZO) ultrafine particles embedded in a high density polyethylene (HDPE) matrix was fabricated by using a simple low-temperature hot-pressing technique. The magnetic and dielectric properties of the as-prepared composites were investigated in details. The results indicate that as the volume of the ceramic fillers increase, the permittivity, permeability, dielectric and magnetic loss of the composite all increase. The cut-off frequencies of the composites are all above 1 GHz. Because of the low resistivity of NZO, the dielectric losses of the composites are big and decrease with frequency below 100 MHz. Good frequency stabilities of the permittivities and permeabilities, and low dielectric and magnetic losses within the measurement range have been observed. For the composite containing 30 vol% NZO, the permittivity, dielectric loss, permeability and magnetic loss are 3.7, 0.0025, 2.2 and 0.002 at 100 MHz, respectively.     

基于界面结构调控硅粒子/聚偏氟乙烯复合材料介电性能

为降低硅粒子/聚偏氟乙烯(Si/PVDF)复合材料体系的介电损耗(tanδ)及提高其击穿强度(E_b),采用高温氧化及聚苯乙烯(PS)包覆法,制备出两种分别具有SiO₂单壳及SiO₂@PS双壳的Si@SiO₂和Si@SiO₂@PS核壳结构粒子。采用FTIR、XRD和TEM分析测试了核壳粒子的壳层结构。分析测试证明,Si粒子表面存在SiO₂和PS壳层。结果表明,相比未改性Si/PVDF复合材料,SiO₂外壳显著降低和抑制了Si@SiO₂/PVDF复合材料的tanδ和漏导电流;PS层改进了Si/PVDF复合材料的界面相容性,促进其在基体中均匀分散。双壳结构Si@SiO₂@PS/PVDF复合材料呈现出最低tanδ和最高E_b。Si@SiO₂/PVDF和Si@SiO₂@PS/PVDF复合材料介电性能的改善归因于Si表面SiO₂及SiO₂@PS绝缘界面层有效阻止了半导体Si粒子间的直接接触,极大抑制了损耗。此外,Si/PVDF复合材料相界面缺陷减少及界面相容性改善均有效降低了局部电场畸变,提高了体系的E_b。Si@SiO₂@PS/PVDF复合材料在1 kHz下介电常数高达48,tanδ低至0.07,E_b约为6 kV/mm,在微电子器件及电力设备领域具有潜在的应用价值。      

The dielectric and thermal properties of Mn-doped (1 − x) ZrTi2O6–xZnNb2O6 filled PTFE composites

High dielectric constant and low loss (1 ? x) ZrTi₂O₆–xZnNb₂O₆ ceramic fillers have been prepared by the conventional solid-state reaction technique. Ceramic filled polytetrafluoroethylene (PTFE) microwave composite substrates were fabricated through the hot-pressing process. The microwave dielectric properties of (1 ? x) ZrTi₂O₆–xZnNb₂O₆/PTFE composites were measured using stripline resonator method. The relative dielectric constant (ε _r) and loss tangent (tan δ) of the composites increase with an increase of x in the (1 ? x) ZrTi₂O₆–xZnNb₂O₆ ceramic at an optimum filler loading of 46vol%. As the x in the (1 ? x) ZrTi₂O₆–xZnNb₂O₆ ceramic increase, the coefficient of thermal expansion and temperature coefficient of dielectric constant decrease. 0.55ZrTi₂O₆–0.45ZnNb₂O₆ filled PTFE composite exhibits a dielectric constant of 7.32 with a loss tangent of 0.0015 (10 GHz) and a temperature coefficient of dielectric constant of ?84 ppm/^oC at an optimum filler loading of 46 vol%.     

Graphene sheets segregated by barium titanate for polyvinylidene fluoride composites with high dielectric constant and ultralow loss tangent

In this paper, we report a unique method to develop polyvinylidene fluoride (PVDF) composites with high dielectric constant and low loss tangent by loading relatively low content of graphene-encapsulated barium titanate (BT) hybrid fillers. BT particles encapsulated with graphene oxide (BT-GO) were prepared via electrostatic self-assembly and subsequent chemical reduction resulted in BT-RGO particles. SEM morphology revealed that RGO sheets were segregated by BT particles. The hybrid fillers have two advantages for tuning dielectric properties: loading extremely low content of RGO can be exactly controlled and individual RGO sheets segregated by BT particles would prevent leakage current. As a result, PVDF composites filled with BT-RGO displayed improved dielectric properties before percolative behavior occurred. Composites filled with 30 vol% BT-RGO have a dielectric constant and loss tangent (tan δ) value of 67.5 and 0.060 (1 kHz), respectively. By contrast, dielectric constant and tan δ of composites filled with 30 vol% BT-GO and BT were 57.7 and 38.3, 0.076 and 0.042 (1 kHz), respectively. The improvement of dielectric constant is attributable to the formation of microcapacitors by highly conductive RGO sheets segregated by BT particles. Meanwhile, the distance between adjacent RGO sheets is large enough to prevent leakage current from tunneling conductance, by which tan δ is remarkably constrained. The composites could achieve excellent dielectric properties by loading relatively low amount of ceramic fillers, which indicates that this method can be used as guideline for reduce the usage amount of ceramic fillers.     

Effects of coupling agent on the preparation and dielectric properties of novel polymer–ceramic composites for embedded passive applications

The study was carried out to investigate the effects of silane coupling agent, γ-aminopropyl triethoxy silane (KH-550), on the preparation and dielectric properties of Barium titanate (BaTiO₃)/Bisphenol-A dicyanate (2,2′-bis (4-cyanatophenyl) isopropylidene)(BADCy) composites for embedded passive implications. It was found that KH-550 accelerated the polymerization of BADCy and was beneficial to improve the compatibility between BaTiO₃ particles and BADCy matrix. The dielectric constant (ε) and dielectric loss (tanδ) both increased at first and then decreased with the increase of the KH-550 content. With the increase of the frequency, the variation ranges of the dielectric constant and dielectric loss of these composites were not obvious since the dielectric properties of cyanate ester were stable at various frequencies.     

Effects of the treatment of attapulgite and filler contents on tensile properties of PTFE and attapulgite reinforced fabric composites

Epoxy based fabric composites containing attapulgite (ATP) and polytetrafluoroethylene (PTFE) were prepared. Effects of the treatment of ATP, content of ATP and relative content of ATP and PTFE on tensile properties of the fabric composites were investigated. The results showed that the treatment of ATP resulted in the formation of the covalent link between the treated ATP nanorods and the epoxy matrix, which enhanced the tensile properties of the matrix. Also, the fiber–matrix adhesion was improved due to the high surface energy of the ATP nanorods. Thus, the tensile properties of the fabric composites increased due to the above reasons. 16% was the critical overall content of the fillers, exceeding which the fillers had a strong tendency to agglomerate lowering the tensile strength. ATP:PTFE = 1:1 was the optimal relative content ratio, at which ATP and PTFE acted synergisticly to further improve the tensile properties of the fabric composites.     

新型硅橡胶基压阻敏感复合材料制备及其性能研究

以多壁碳纳米管(MWNT)和纳米二氧化硅作为助填料,采用三辊研磨机制备了(MWNT-SiO2)/RTV复合材料,研究其压阻和介电性能.结果表明,纳米SiO2经KH570改性,其在基体中分散性及界面结合提高;(MWNT-SiO2)/RTV复合材料压力敏感性增强,当外界压力为150N时,含5％二氧化硅的复合材料相对电阻是M...     

Effect of coupling agent on the thermal and dielectric properties of PTFE/Sm2Si2O7 composites

The present study investigates the dielectric and thermal properties of PTFE/Sm₂Si₂O₇ composites. The composites were prepared by powder processing technique followed by hot pressing. The variation of the dielectric properties with filler content (0–0.5 V_f) was studied at 1 MHz and 9 GHz. The filler surface was chemically modified using phenyl trimethoxy silane (PTMS) as a coupling agent. The microstructural study using scanning electron microscopy (SEM) showed that the particles were well dispersed in the matrix when coupled with PTMS. The surface modification led to an improvement in the dielectric properties. The PTFE filled with 0.4 V_f silane treated Sm₂Si₂O₇ composite showed a low dielectric loss of 0.0054 and slightly higher relative permittivity of 3.92 when compared with the untreated composite of the same composition. The experimental values of relative permittivities were compared with the theoretical predictions and the Effective Medium Theory was found to agree well even for higher content of silane treated filler. It was found that the addition of silane coupling agent is very effective in improving the thermal properties of the PTFE/Sm₂Si₂O₇ composites.     

Preparation and dielectric properties of surface modified TiO2/PEN composite films with high thermal stability and flexibility

A series of surface modified titanium dioxide (TiO₂)/polyarylene ether nitriles (PEN) composite films with different modified TiO₂ contents were prepared by solution casting method combined with ultrasonic dispersion technology. TiO₂ particles were successfully surface modified by PEN–COOH polymer previously, which was confirmed by transmission electron microscopy, Fourier transform infrared spectroscopy and thermogravimetric analysis. Besides, SEM images of composite films revealed that the interfacial adhesion between surface modified TiO₂ particles and the PEN matrix was effectively improved because of their common cyano groups and similar structure units. Furthermore, thermal, mechanical and dielectric characterizations showed that the composite films possess excellent thermal properties and flexibility as well as good dielectric properties, their glass transition temperatures were as high as 223?°C and the initial decomposition temperatures were all above 480?°C. In addition, it was found that the tensile strength of modified TiO₂/PEN composites was better than raw TiO₂/PEN composites. More importantly, the dielectric constant of composite films increases linearly with increment of the surface modified TiO₂ particles content. When the mass fraction of modified TiO₂ particles reached 40?%, the dielectric constant of the composite film increased to 7.9 (1?kHz), while the dielectric loss is just 0.028 (1?kHz).     

Preparation of high k expanded graphite/CaCuTi4O12/cyanate ester composites with low dielectric loss through controlling the interfacial action between conductors and ceramics

New composites with high dielectric constant and low dielectric loss, based on expanded graphite (EG), CaCuTi₄O₁₂ (sCCTO) and cyanate ester (CE) resin, were developed by controlling the interaction between EG and sCCTO. Difference from EG, surface modified EG (mEG) has an additional strong chemical interaction with sCCTO, this not only improves the dispersion of fillers, but also enhances the filler-matrix interfacial adhesion, leading to different micro-structures and dielectric properties. Specifically, the percolation thresholds of mEG/sCCTO/CE and EG/sCCTO/CE composites are 3.45 vol% and 2.86 vol%, respectively. When the loading of conductors approaches the percolation threshold, mEG/sCCTO/CE composite has much higher dielectric constant and lower dielectric loss than EG/sCCTO/CE composite. The nature behind these attractive data was revealed by building an equivalent circuit.     

复配偶联剂对SiO_2/聚四氟乙烯复合材料性能的影响

制备了不同组分配比的氨丙基三乙氧基硅烷(KH550)-苯基三甲氧基硅烷(Z6124)复配偶联剂(KH550-Z6124)改性SiO2/聚四氟乙烯(PTFE)复合材料,系统地研究了KH550-Z6124组分配比对复合材料介电性能、吸水率和导热性能的影响。采用Lichtenecker模型计算了SiO2/PTFE复合材料的介电常数和介电损耗理论值,并与实验值进行对比。结果表明:当KH550、Z6124的含量(以SiO2的质量为基准)分别为0.3wt%和1.7wt%时,KH550-Z6124改性SiO2/PTFE复合材料的介电损耗由Z6124改性SiO2/PTFE复合材料的1.7×10-3降低至1.0×10-3,吸水率由0.082 6wt%降低至0.020 3wt%,导热率提高66%;SEM形貌分析发现KH550-Z6124改性SiO2颗粒在PTFE基体中均匀分散,界面连接更紧密;KH550-Z6124改性SiO2/PTFE复合材料的介电常数和介电损耗实验值更接近其理论值。     

BN表面沉积纳米Sn对BN/环氧树脂复合材料导热绝缘性能的影响

采用液相还原法,制备了BN表面沉积纳米Sn粒子(BN-Sn NPs)杂化材料,用于环氧树脂(EP)的导热绝缘填料。BN-Sn NPs表面纳米Sn的粒径和熔点分别为10~30 nm 和166.5~195.3℃。BN表面沉积纳米Sn后,粉体Zeta电位及压片的导热系数增加,EP滴在压片表面的接触角降低。在BN-Sn NPs/EP复合材料固化过程中,BN-Sn NPs表面纳米Sn熔融烧结,有利于填料相互桥联在一起,降低接触热阻,并改善界面性能,从而提高BN-Sn NPs/EP复合材料的导热系数。当填料体积含量为30vol%时,BN-Sn NPs/EP复合材料的导热系数达1.61 W(m·K)?1,比未改性BN/EP复合材料的导热系数(1.08 W(m·K)?1)提高了近50%。Monte Carlo法模拟表明,BN和BN-Sn NPs在EP基体中的接触热阻(R_c)分别为6.1×106 K·W?1和3.7×106 K·W?1。与未改性BN/EP复合材料相比,BN-Sn NPs/EP复合材料的介质损耗增加,介电强度及体积电阻率降低,但仍具有良好电绝缘性能。      

Investigation of thermal conductivity and dielectric properties of LDPE-matrix composites filled with hybrid filler of hollow glass microspheres and nitride particles

The hybrid filler of hollow glass microspheres (HGM) and nitride particles was filled into low-density polyethylene (LDPE) matrix via powder mixing and then hot pressing technology to obtain the composites with higher thermal conductivity as well as lower dielectric constant (D_k) and loss (D_f). The effects of surface modification of nitride particles and HGMs as well as volume ratio between them on the thermal conductivity and dielectric properties at 1 MHz of the composites were first investigated. The results indicate that the surface modification of the filler has a beneficial effect on thermal conductivity and dielectric properties of the composites due to the good interfacial adhesion between the filler and matrix. An optimal volume ratio of nitride particles to HGMs of 1:1 is determined on the basis of overall performance of the composites. The thermal conductivity as well as dielectric properties at 1 MHz and microwave frequency of the composites made from surface-modified fillers with the optimal nitride to HGM volume ratio were investigated as a function of the total volume fraction of hybrid filler. It is found that the thermal conductivity increases with filler volume fraction, and it is mainly related to the type of nitride particle other than HGM. The D_k values at 1 MHz and microwave frequency show an increasing trend with filler volume fraction and depend largely on the types of both nitride particles and HGMs. The D_f values at 1 MHz or quality factor (Q × f) at microwave frequency show an increasing or decreasing trend with filler volume fraction and also depend on the types of both nitride particle and HGM. Finally, optimal type of HGM and nitride particles as well as corresponding thermal conductivity and dielectric properties is obtained. SEM observations show that the hybrid filler particles are agglomerated around the LDPE matrix particles, and within the agglomerates the smaller-sized nitride particles in the hybrid filler can easily form thermally conductive networks to make the composites with high thermal conductivity. At the same time, the increase of the value D_k of the composites is restricted due to the presence of HGMs.     

木塑复合材料的界面改性方法

表面有机化改性是提高木质填料(木纤维或木粉)的分散程度和增强其与聚合物基体界面相互作用的重要手段。对于木塑复合材料而言,木质填料与树脂基体的界面粘接程度是有效传递载荷、提高力学性能、降低吸水率和提高尺寸稳定性的关键因素。针对国内外木塑复合材料的研发现状,本文主要概述了木质填料的表面处理方法及其对木塑复合材料性能的影响。     

低损耗ZrTi2O6填充PTFE复合基板性能

采用热压成型工艺,制备了一种低损耗ZrTi₂O₆陶瓷填充聚四氟乙烯（PTFE）的新型微波复合基板材料。采用介质谐振器法研究了ZrTi₂O₆/PTFE复合材料的微波介电性能（8~12 GHz）。结果表明,ZrTi₂O₆/PTFE复合材料的相对介电常数（ε _r）和介电损耗（tanδ）随着ZrTi₂O₆陶瓷体积分数（0~46%）的增加而增大,介电常数实验值与Lichtenecker模型预测值最吻合。ZrTi₂O₆/PTFE复合材料的热膨胀系数和介电常数温度系数随着ZrTi₂O₆陶瓷体积分数的增加而减小。46%的ZrTi₂O₆为较优填料比例,ZrTi₂O₆/PTFE的相对介电常数为7.42,介电损耗为0.0022（10 GHz）。