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.     

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.     

Influence of lubricant filling on the dry sliding wear behaviors of hybrid PTFE/Nomex fabric composite

To improve the antiwear property and load carrying capacity of hybrid PTFE/Nomex fabric/phenolic composites, graphene and graphene oxide (GO) had been synthesized and were employed as fillers, together with graphite. Sliding wear tests show that the wear rates of filler-reinforced PTFE/Nomex fabric composites were reduced greatly when compared to unfilled fabric composite. Besides, it was found that the 2 wt% GO filled PTFE/Nomex fabric composites exhibited the optimal tribological properties. It was proposed that the self-lubrication of GO, the favorable interface stability of the composite, and the uniform transfer film on the counterpart pin contributed together to the reinforced tribological property of GO filled PTFE/Nomex fabric composite. We also investigated the influence of filler content, applied load, sliding speed, and tensile and bonding strength on the tribological properties of PTFE/Nomex fabric composites.     

硅线石填充双马来酰亚胺摩擦学性能的研究

用Ｍ－２００型试验机在干摩擦条件下考察了硅线石单独填充双马来酰亚胺（ＢＭＩ）和硅线石与聚四氟乙烯（ＰＴＦＥ）共同填充ＢＭＩ两类复合材料的摩擦学特性。结果表明，适量的Ｓａ能降低ＢＭＩ的摩擦系数和磨损量，但会在对偶件上造成划伤，ＰＴＦＥ与Ｓａ共同填充ＢＭＩ，不仅能进一步降低复合材料的μ和磨损量，而且能有效地抑制对偶件上的划伤，经过分析，Ｓａ填充ＢＭＩ的复合材料，对磨时其表面较高的粗糙度和Ｓａ硬粒子友承     

Preparation and characterization of cordierite filled PTFE laminates for microwave substrate applications

Phase pure cordierite (2MgO · 2Al₂O₃ · 5SiO₂) powder was prepared through solid state ceramic route. Silane coated cordierite powder was filled in the PTFE matrix through SMECH process comprising of sigma mixing, extrusion, calendering, followed by hot pressing, to fabricate flexible microwave substrates. Filling fraction of cordierite in the PTFE matrix was varied from 10 to 70 wt% and its effects on density, dielectric properties, coefficient of thermal expansion and water absorption were investigated. The morphology and filler distribution of the filled composite were studied by SEM. Waveguide cavity perturbation technique was employed to measure the dielectric properties of the composites at X-band (8.2–12.4 GHz). Dielectric constant and loss tangent were found increasing with filler loading from 10 wt% (ε _r′ = 2.17, tan δ = 0.0007) to 60 wt% (ε _r′ = 3.17, tan δ = 0.0034).     

埃洛石-玻纤/聚四氟乙烯复合材料的摩擦磨损热膨胀及力学性能

采用冷压成型烧结工艺制备出玻璃纤维（GF）和埃洛石（HNTs）填充的聚四氟乙烯（PTFE）复合材料。研究了填料类型及不同配比的填料对PTFE复合材料的界面、摩擦学性能、线膨胀系数及力学性能的影响。结果表明:适量填充HNTs可以提升GF/PTFE复合材料的摩擦磨损、热膨胀及力学性能。填充2.0%HNTs时的HNTs-GF/PTFE复合材料比GF/PTFE复合材料的磨损率降低32.7%,高温时HNTs-GF/PTFE复合材料的线膨胀系数（CTE）比纯PTFE降低近2个数量级,断裂伸长率、拉伸强度和弯曲强度分别提高40.0%、2.3%和7.1%。      

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）。     

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.     

The tribological behavior of nanometer and micrometer TiO2 particle-filled polytetrafluoroethylene/polyimide

The friction and wear properties of micrometer and nanometer TiO₂ particle-filled polytetrafluoroethylene (PTFE)/polyimide (PI) composites were studied in this paper. The effect of filler contents (0.5%, 1%, 1.5%, 2%, 3%, 5% and 7 vol.%) on the tribological properties was examined. The transfer films and the worn surfaces of the PTFE/PI composites filled with micrometer and nanometer TiO₂ particles were investigated by using a scanning electron microscope (SEM). Experimental results show that anti-wear properties of the PTFE/PI composites can be improved greatly by filling nanometer TiO₂ particles. The wear rate of 1.5% nanometer TiO₂ filled composite is the lowest, which is about 52% lower than that of PTFE/PI. In the case of micrometer TiO₂ filler, the friction coefficient and wear rates increase with increasing filler volume fractions under identical test conditions. It was also found that the wear mechanism of micrometer TiO₂ particle-filled PTFE/PI is mainly severe adhesion and abrasive wear, while that of nanometer TiO₂ particle-filled PTFE/PI is mainly slight abrasive wear.     

微米和纳米SiO2改性聚四氟乙烯的摩擦磨损性能

使用超细及纳米SiO₂颗粒填充改性聚四氟乙烯塑料。测量其摩擦系数、磨损系数、结晶度,得到了填加量与复合材料摩擦系数、磨损系数和结晶度的关系曲线,并使用扫描电镜(SEM)对其表面形貌进行了分析。结果表明,无论微米或纳米SiO₂、表面处理后的纳米SiO₂,均使PTFE的摩擦系数有所提高,而耐磨损性能也有大幅度的提高。填充量小于6%时,填加未经偶联剂处理的纳米SiO₂的SiO₂/PTFE复合材料的磨损率降低98.5%;填充量大于6%以后,磨损率趋于稳定;填充量为6%时,摩擦系数仅从未加填料时的0.1提高为0.12。而偶联剂表面处理的纳米SiO₂复合材料的摩擦系数提高幅度最小。      

Study on the effects of nanoparticulates of SiC,Al2O3, and ZnO on the mechanical and tribological performance of epoxy-based nanocomposites

In this research work, mechanical and tribological characteristics of ortho cresol novalac epoxy (OCNE)-based nanocomposites filled with nanoparticulates of SiC, Al₂O_3, and ZnO have been investigated. Also, in these investigations, the influence of wear parameters such as applied normal load, sliding velocity, filler contents, and sliding distance have been explored. The experimental plan for four factors at three levels using face centered composite design (CCD) has been employed by the response surface methodology (RSM) technique. The friction and wear tests were carried out using a pin on disc wear test apparatus under dry sliding conditions. The hardness and flexural strength of nano ortho cresol novalac epoxy composites filled with nano (SiC, Al₂O_3, and ZnO) particulates increases with an increase in the filler contents. Whereas, the tensile strength of these nanocomposites increases with an increase in the filler contents from 1 to 2 wt%, and with a further increase in filler contents the tensile strength decreases. The results of the study also showed that (2 wt%) filler contents bring superior mechanical and tribological properties. The lowest coefficient of friction and specific wear rate were found with nano Al₂O₃-filled composites. Also, the wear mechanisms of these nanocomposites were studied using a scanning electron microscope (SEM) equipped with an EDS analyzer.     

An Experimental Investigation on the Fabrication and Testing of Mechanical Properties of Aluminum-Silica Gel Metal Matrix Composite

A metal matrix composite (MMC) was fabricated using Al as the base metal which was reinforced by a ceramic material silica gel. This article shows detail fabrication stages in the production of MMC. The properties were considered with regard to the saturation point of the reinforcement of silica gel into the metal matrix of Al-Si alloy which was found out experimentally. Here the improvement of the mechanical properties of Al-silica gel MMC composite were studied with respect to that of pure Al-Si alloy. Different tests were conducted to show the results. Conventional ingot metallurgy with infiltration technique using vortex method had been employed in the fabrication process. The test results show that there are improvements by 17.14%, 13.46%, 11.48%, and 18.18% on compressive strength, impact strength, Brinell hardness value, and Rockwell hardness no respectively of Al-silica gel MMC over the pure Al-Si alloy.     

TEOS surface modification of CLST ceramic particles for PTFE-based composites

PTFE-based ceramic-polymer dielectric composites have been widely researched in the communication field due to their good processing, wide range frequency and temperature stability and being able to provide tunable dielectric constant in a scale. In order to improve the compatibility between the ceramic fillers and polymer matrix without damage of dielectric properties, surface modifiers with less carbon remain are preferred. In this paper, tetraethylorthosilicate (TEOS) is employed as a surface modifier to improve the compatibility between the (Ca, Li, Sm)TiO₃ (CLST) ceramic and PTFE, and the dispersion of the ceramic particles in the matrix. FTIR, XPS and TEM results indicate that TEOS is coated on the ceramic particles successfully and forms a silica coating layer. The surface modification improves the dispersion of particles in PTFE and interface contact between the ceramic fillers and PTFE matrix. These improve the thermal stability and reduce the dielectric loss of the dielectric composites. The CLST/PTFE composite modified by TEOS exhibits a dielectric constant of 6.22 with dielectric loss just 0.0012 at microwave frequencies (around 10 GHz).     

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.     

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%.     

SiO2-TiO2/聚四氟乙烯复合材料的制备及热膨胀性能

为了使微波基板材料与Cu金属衬底的热膨胀性能匹配,对陶瓷/聚四氟乙烯（PTFE）微波复合基板材料的热膨胀性能进行了研究。采用湿法工艺制备了以SiO₂和TiO₂为填料的SiO₂-TiO₂/PTFE复合材料,研究了复合材料密度、填料粒度和填料体积分数对SiO₂-TiO₂/PTFE复合材料热膨胀性能的影响。结果表明,当SiO₂的体积分数由0增至40%（TiO₂ ：34%~26%）时,SiO₂-TiO₂/PTFE复合材料的线膨胀系数（CTE）由50.13×10^-6 K^-1减小至10.03×10^-6K^-1。陶瓷粉体粒径和复合材料密度减小会导致CTE减小。通过ROM、Turner和Kerner模型计算CTE发现,ROM和Kerner模型与实验数据较相符,而实验值与Turner模型预测值之间的差异随PTFE含量的升高而逐渐增大。     

界面层对复合材料强度的影响

本文对氧化铝(Al₂O₃),氟化钙(CaF₂)和玻璃微珠颗粒填充环氧基(双酚A类E-51-胺固化体系)复合材料的断裂和抗拉强度进行了研究,并考察了复合材科抗拉强度与填料体积分数的关系。复合材料中,从填料固体表面开始形成了有一定厚度的密界面层。界面层的强度性质对复合材料的强度有重要作用。得到了三种复合材料界面层的抗拉强度。并提出了颗粒填充复合材料抗拉强度的计算公式:σ_o=〔σ_mS_m+σ₁S₁a₁〕η计算结果和实验数据有较好的一致性。      

Composites of Poly(Acrylate) Copolymer filled with diatomaceous earth: morphology and mechanical behaviour

Failure mechanisms of poly(acrylate) (PA) copolymer system filled with a diatom filler have been studied. The natural diatom filler is characterised by the original skeletal structure which allows high "inner" porosity and thus matrix penetration inside the filler particles and agglomerates of various shapes in PA composite. High diatom filler crystallinity influences the matrix re-structurization by changing the intensity ratio of matrix amorphous halos indicating the increased composite film inhomogeneity. Interactions at the interface between diatom filler and PA copolymer matrix, specially for coarse cylindrical-shaped particles are low, showing low adhesion in the composite. We see composite weakening with the increased filler volume fraction, i.e. lowering the composite strength at break as a consequence of lower degree of interactions. On the other hand, the composite modulus and the yield strength increased as a result of matrix hardening due to the pronounced matrix penetration inside the porous diatom filler. The mechanisms of failure depend on the location with the lowest product of composite module and break energy. Because dewetting occurred, it is the product EG in the interfacial region between PA matrix and diatom filler particles that was relevant. The effects of filler characteristics, may be followed through an interaction coefficients calculated from a model equations. The numerical values of coefficients in the model are only comparative, but the relative values can be connected with changes at the interface. Electronic Publication     

稀土改性玻璃纤维对PTFE复合材料摩擦磨损性能的影响

分别用硅烷偶联剂SG-Si900(SGS)、含SG-Si900的稀土溶液(SGS/RES)和稀土溶液(RES)对玻璃纤维进行表面改性,考察了稀土改性玻璃纤维填充的PTFE复合材料在油润滑条件下的摩擦磨损性能,并用扫描电子显微镜(SEM)分析了磨损表面形貌.结果表明:与未经表面改性玻璃纤维填充的PTFE复合材料相比,经表面改性玻璃纤维填充的PTFE复合材料的减摩耐磨性能得到提高,以RES的作用最明显,SGS/RES次之,SGS第三;在油润滑条件下,稀土改性玻璃纤维填充的PTFE复合材料只出现了轻微磨损,这是由于玻璃纤维经稀土表面改性后极大地改善了玻璃纤维与PTFE基体之间的界面结合力,使稀土改性玻璃纤维填充的PTFE复合材料具有优异的摩擦磨损性能.     

Optimization of tribological parameters in abrasive wear mode of carbon-epoxy hybrid composites

Abrasive wear performance of fabric reinforced composites filled with functional fillers is influenced by the properties of the constituents. This work is focused on identifying the factors such as filler type, filler loading, grit size of SiC paper, normal applied load and sliding distance on two-body abrasive wear behaviour of the hybrid composites. Abrasive wear tests were carried on carbon fabric reinforced epoxy composite (C-E) filled with filler alumina (Al₂O₃) and molybdenum disulphide (MoS₂) separately in different proportions, using pin-on-disc apparatus. The experiments were planned according to Taguchi L18 orthogonal array by considering five factors, one at two levels and the remaining at three levels, affecting the abrasion process. Grey relational analysis (GRA) was employed to optimize the tribological parameters having multiple-response. Analysis of variance (ANOVA) was employed to determine the significance of factors influencing wear. Also, the comparative specific wear rates of all the composites under dry sliding and two-body abrasive wear were discussed. The analysis showed that the filler loading, grit size and filler type are the most significant factors in controlling the specific wear rate of the C-E composite. Optimal combination of the process parameters for multi performance characteristics of the composite under study is the set with filler type as MoS₂, filler loading of 10 wt.%, grit size 320, load of 15 N and sliding distance of 30 m. Further, the optimal parameter setting for minimum specific wear rate, coefficient of friction and maximum hardness were corroborated with the help of scanning electron micrographs.