Dielectric Properties Of Composites Research Articles

Structural and dielectric properties of multiferroic (1-x)(0.675PMN-0.325PT)/(x)CoFe2O4 particulate composites obtained by microwave sintering

ABSTRACTThis paper discusses the effect of microwave-assisted sintering on the microstructural and physical characteristics of (1-x)Pb(Mg1/3Nb2/3)0.675Ti0.325O3/(x)CoFe2O4 ceramic particulate composites. Ceramic powders were prepared by the one-step method, employing the modified Pechini route. The microstructure analysis confirmed that the ceramics were well sintered, without phase interdiffusion, although grain size distribution of the ferrite phase becomes bimodal as ferrite phase concentration increased. The dielectric constant and dc electrical resistivity were found to decrease with increasing ferrite concentration, given that the dielectric properties of composites are a combined property of the constituent phases and are generally governed by the logarithmic mixture rule.

Technology and dielectric properties of the PLZT-NZF composites

ABSTRACTThe aims of the study were to design and obtain ferroelectric-ferromagnetic ceramic composites based on ferrite powder and PLZT powder. The synthesis of the composition of the PLZT material of chemical formula Pb0.98La0.02(Zr0.90Ti0.10)0.995O3 was carried out by conventional technology. The composite constituted 90% of PLZT powder and 10% of ferrite powder (Ni0.64Zn0.36Fe2O4).The article presents the technology and the results of a XRD measurement, a microstructure and the dielectric properties of the composite samples. This type of multiferroic materials and ferroelectric-ferrimagnetic composites can be used to develop a new class of transducers/sensors integrating electro-magnetic interaction in a single device.

Measurement of dielectric properties of polymer matrix composites developed from cow bone powder

This research was focused on determining the dielectric properties of composite materials developed from carbonized and uncarbonized agrowaste (cow bone) material. The uncarbonized materials were washed, air dried, and part of the materials were carbonized at a temperature of 750 °C after which they were milled into powder and sieved into sieve grades of 150, 300, and 600 μm. The cow bone particles were varied from 40 to 60 wt%. A mineralogical analysis carried out by the X-ray diffractometer revealed that the carbonized and uncarbonized bone particles contain the following elements: O, Na, Mg, Al, Si, Ca, and C. Surface morphology of the carbonized and uncarbonized particles as revealed by the SEM confirmed the particles to be regular and solid in nature. The TGA/DTA analysis shows that the carbonized particles were more thermally stable than the uncarbonized particles were. The dielectric strength, dielectric constant, and water absorption capacity were determined. The effect of carbonization on the abovementioned properties was studied and used as criteria for the evaluation of the composites. The results shows that smaller particles and weight percentage have the best properties: example at the 40 wt% of 150 μm, the dielectric strength for the CCB and UCB are 217.96 and 510.84 Kv/mm, respectively. The same trend was observed in all the compositions and all the particle sizes. Better enhancement of property was obtained for the composites with lower wt% and smaller particle sizes compared to the higher wt% and bigger particle-sized composites. The significant factors (main and interaction) were identified by analysis of variance technique. The Cube and 3D graphs show the estimated response surface for the composite properties as a function of sample condition, wt%, and particle size. It is also evident from the results that the actual experimental values are in close proximity with the predicted values.

Piezo, ferro and dielectric properties of ceramic-polymer composites of 0-3 connectivity

ABSTRACTFerroelectric PZT-PVDF composites (0–3 connectivity) of specific dimensions were made utilizing a hot press technique. Linear variation in the experimental density of the pellets made from 0.1 to 0.8 PZT volume fraction was observed. The surface morphology of the composite has been micro-graphed using SEM. The variation of the dielectric properties of the composites on PZT volume fractions is reported and analyzed. It is observed that there was an increment in dielectric constant (ϵr) with an increase in temperature and volume fractions. The piezoelectric strain coefficient (d33) increases with an increase in the volume fraction and voltage coefficient (g33) were calculated. Comparisons were made with the Furukawa model to ϵr and d33. The remnant polarization and coercive field were analyzed from the hysteresis plots.

Permittivity Properties of Nickel Zinc Ferrite-Oil Palm Empty Fruit Bunch-Polycaprolactone Composite

The dielectric properties of composites based on nickel-zinc-ferrite (NZF) filler can be improved by the addition of various types of materials. Amongst others, ferrite–polymer composites have been subjected to wide range of research, due to their extensive applications: electromagnetic interference shielding, microwave absorption, electrodes and sensors. In this study, Ni0.5Zn0.5Fe2O4 (NZF) was prepared via conventional solid-state method. While NZF–OPEFB-PCL composite has been prepared via the mechanical milling mode and then characterized by X-ray powder diffraction. Dielectric properties of the composite, such as dielectric constant, loss factor and loss tangent were measured at different filler percentage over a wide range of frequency (0.20MHz-20GHz). An open ended coaxial probe connected to a vector network analyzer (VNA) was utilized for the evaluation of dielectric properties for materials and composites under test at the room temperature. Both dielectric constant and loss factor values increased due to the filler increment in the polymer matrix, where the composition of 15% NZF gives the extreme permittivity value at the used microwave frequency. Furthermore, the obtained results confirmed that dielectric properties of the composite can be controlled by the proper loading and the wise filler choosing. The adjusted properties support the purpose of polymer composite materials for microwave and communicational applications.

Relationship between dielectric properties and nanoparticle dispersion of nano-SiO2/epoxy composite

Polymer nanocomposites have advantage over traditional materials in electrical properties from the standpoint of dielectrics and electrical insulation. The influences of nanoparticle dispersion in the matrix, which is mainly caused by different preparation methods, on the dielectric properties of composites have been given in the past work. In order to investigate the relationship between the dispersion of nanoparticles in the matrix and the dielectric properties of composites, nano-SiO2/epoxy composites are prepared by different methods. Nano-SiO2 is first modified by silane coupling agent to obtain nano-SiO2 powder and nano-SiO2 dispersing liquid, then unmodified and modified nano-SiO2 powder are mixed into epoxy by mechanical mixing method, and the modified nano-SiO2 dispersing liquid is mixed into epoxy by bubble mixing method to prepare nano-SiO2/epoxy composites. The amounts of nano-SiO2 content in the composites are 2 wt%, 3 wt%, 4 wt%, 5 wt% and 6 wt%, respectively. Breakdown strength and corona-resistance characteristics of the composites are tested. The results show that with the increase of the nano-SiO2 content, the breakdown strength and corona-resistance of nano-SiO2/epoxy composites increase. The maximal breakdown strength appears in the composites with 5 wt% nano-SiO2. This appearance accords with percolation theory. The composites prepared by bubble mixing method have better breakdown strengths and corona-resistances than the composites prepared by mechanical mixing method. The scanning electron microscope images of the nano-SiO2/epoxy composites are analyzed by Image J software to obtain the information about the nanoparticle number in the special grid. Morisita's index is used to characterize the dispersion of nano-SiO2 in the matrix quantitatively. It is concluded that the composites prepared by bubble mixing method have better dispersion than those prepared by mechanical mixing method. Compared with the unmodified nano-SiO2, modified one has good dispersion in the composite because of the improved compatibility between the nanoparticles and the matrix. Based on the role that nano-SiO2 particles block discharge from developing in the composite, the better dispersion means that there are more nanoparticles and more barriers on the discharge path. Meanwhile, the better dispersion also means that more interface areas form between nano-SiO2 and matrix. The shallower traps supplied by the interface area will contribute less energy when current carriers jump into and out off the traps. So the better the dispersion of nano-SiO2 in the matrix, the superior the breakdown strength and corona-resistance of the composites are.

Acoustic and dielectric properties of 0–3 bismuth sodium titanate-bismuth potassium titanate-barium titanate/cement composites

ABSTRACTThe lead-free piezoelectric ceramic-cement composites made from bismuth sodium titanate-bismuth potassium titanate-barium titanate (BNBK) ceramic particle and Portland cement (PC) are developed for smart structure applications. The acoustic and dielectric properties of composites were investigated. The 30–60 vol% gave the optimal BNBK content for an acoustic impedance match between 0–3 connectivity BNBK-PC composites and structure materials, i.e. concrete. Parallel, cube and series models were also compared to the dielectric measurement results and the experimental values were found to fit closest to that of the cube model. The dielectric properties of composites were also found to depend on the frequency tested.

Online optical and dielectric monitoring of anisotropic epoxy/BaTiO3 composite formation tailored by dielectrophoresis

Anisotropic composites can be obtained by applying an alternating (ac) electric field, forming particle chains in its direction. The control of the particle chains will directly impact the final properties of the composite. Nevertheless, up to now the monitoring of the particle chain formation has only been made by direct optical or post-curing observations. A new technique for the monitoring of the particle dielectrophoretic alignment is proposed, based on the online measurement of the dielectric permittivity. Epoxy/barium titanate (BaTiO3) composites, in the range of 0.25 vol% to 20 vol% of BaTiO3 microparticles, are cured while an ac field (600 Vrms mm−1) is applied. The ac current magnitude and the phase shift angle are measured to determine the dielectric properties of the composite. The same experiment is achieved under optical microscope observation for 0.25 vol% to correlate the changes of the composite dielectric properties to the particle chain formation. As a result, the permittivity variations can be correlated to the particle chains formation and to their growth.

Towards suppressing loss tangent: Effect of polydopamine coating layers on dielectric properties of core–shell barium titanate filled polyvinylidene fluoride composites

Barium titanate (BT) particles coated with different thickness of polydopamine (PDA) layers were incorporated into polyvinylidene fluoride (PVDF) to investigate influence of PDA coating layers on dielectric properties of composites. It is found that PDA coating layers not only effectively improved the interfacial interaction between BT particles and matrix but also significantly affected dielectric properties. PVDF composites loaded with modified BT exhibits superior dielectric properties in comparison with unmodified BT. Interfacial polarization is substantially suppressed because the catechol groups of PDA are able to constrain the mobility of nomadic charge carriers and ionizable hydroxyl groups on surface of BT particles. As a result, dependency of dielectric constant on frequency attenuates and tan δ is lowered to below 0.050 (1 kHz). The effect of suppression on tan δ tends to be more prominent as the thickness of PDA coating layer increases. The tan δ derived from ionic relaxation polarization is also constrained due to the chelation of PDA catechol groups with migrated cations. The as-prepared composites possess high dielectric constant and ultralow tan δ, making them promising for the industrial application as embedded capacitors.

Enhanced dielectric properties of polyamide 11/multi‐walled carbon nanotubes composites

ABSTRACTComposites with multi‐walled carbon nanotubes (MWNTs) involved in polyamide 11 (PA11) were prepared via a conventional melt blending method. The structure, morphology, crystallization behavior, electrical, and dielectric properties of composites were investigated. The results demonstrated that the dispersed uniformly MWNTs favored the formation of α crystal of PA11 when the composites were quenched from melt. The dielectric constant of composites was dependent on the electric field frequency and MWNTs content, and the highest value of dielectric constant was as high as 350 for the composite with 1.21 vol % MWNTs at 103 Hz, accompanied by a low dielectric loss. The enhanced dielectric properties could be interpreted by the formation of abundant nanocapacitors within the composites and the interfacial polarization effect resulting from accumulation of charge carriers at the internal interfaces between MWNTs and PA11. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42642.

Novel organic–inorganic composites with high thermal conductivity for electronic packaging applications: A key issue review

Significant progress has been made recently in developing the organic–inorganic composites with high thermal conductivity, low dielectric constant, and dielectric loss, for applications in the electronic packaging and substrates. Many studies have shown that some polymers filled with high thermal conductivity and low dielectric loss ceramics are suitable for electronic packaging for device encapsulation. Until now, extensive attentions have been paid to the preparation of polymeric composites with high thermal conductivity and low dielectric loss for the application in electronic packaging. In contrast, the thermal conductivities of these dielectric materials are still not high enough and that might restrict their serviceable range. Herein, we briefly reviewed recent progress in this field and introduced a kind of novel composites with surface insulation modified metal aluminum cores to form multilayer coating structures as fillers in polyimide matrix for electronic applications. This structure can significantly improve the thermal conductivity and dielectric properties of composites and give some insights into the effects of modified fillers of composite materials. Such multilayer core–shell structures should have great potentials for the improvement of nanoparticle‐based fillers and applications of electronic packaging. POLYM. COMPOS., 38:803–813, 2017. © 2015 Society of Plastics Engineers

Dielectric Properties of Composites Based on Polyvinyl Alcohol with Ferroelectric Inclusions

The results of dielectric measurements for composites based on polyvinyl alcohol with ferroelectric inclusions are presented. The maxima shift in the temperature dependence of the capacitance at high temperatures compared to the bulk crystals is shown. Capacitance increase is observed in all the composites as compared with bulk materials. The study of emission properties of the composite polyvinyl alcohol – sodium nitrite revealed emission activity for all samples. The studies point to possibility of creating a ferroelectric state in the polymer-based composites with ferroelectric inclusions and maintaining this state to temperatures tens of degrees above the Curie temperature of bulk samples.

Enhanced dielectric performance of three phase percolative composites based on thermoplastic-ceramic composites and surface modified carbon nanotube

Three-phase composites were prepared by embedding CaCu3Ti4O12(CCTO) nanoparticles and Multiwalled Carbon Nanotube (MWNT) into polyimide (PI) matrix via in-situ polymerization. The dependences of electric and dielectric properties of the resultant composites on volume fractions of filler and frequency were investigated. The dielectric permittivity of PI/CCTO-surface modified MWNT (MWNT-S) composite reached as high as 252 at 100 Hz at 0.1 vol. % filler (MWNT-S), which is about 63 times higher than that of pure PI. Also the dielectric loss is only 0.02 at 100 Hz. The results are in good agreement with the percolation theory. It is shown that embedding high aspect ratio MWNT-S in PI/CCTO composites is an effective means to enhance the dielectric permittivity and reduce the percolation threshold. The dielectric properties of the composites will meet the practical requirements for the application in high dielectric constant capacitors and high energy density materials.

Facile Preparation and Origin of High-kCarbon Nanotube/Poly(Ether Imide)/Bismaleimide Composites through Controlling the Location and Distribution of Carbon Nanotubes

The morphology (location and distribution) of conductive fillers in conductive filler/polymer nanocomposites has a decisive influence on dielectric properties of a composite, so with the same components, how to facilely control the morphology of nanofillers, build its relationship with dielectric properties of the composite, and clearly reveal the origin behind are still interesting challenges. Herein, a fixed loading (0.4 wt %) of multiwalled carbon nanotubes (MWCNTs) was embodied into an incompatible poly(ether imide) (PEI)/bismaleimide (BD) system to prepare a series of composites (0.4MWCNT/PEI/BD). As the PEI content increases, the structure of composite successively changes from sea-island to cocontinuous phase and phase inversion. More interestingly, MWCNTs prefer to selectively distribute in the BD phase, tend to enrich around the PEI dense zone, and arrange normally to the radius of the PEI sphere zone, so the morphology of MWCNTs and thus dielectric properties of composites can be facilely controlled. The dielectric constant and loss of 0.4MWCNT/PEI/BD composite with 10 wt % PEI are about 4.5 and 0.1 times the values of 0.4MWCNT/BD composite, respectively, overcoming the critical problem of available conductive filler/polymer composites. Different equivalent circuits were built for these composites, revealing the origin behind the method developed herein for controlling unique dielectric properties of 0.4MWCNT/PEI/BD composites.

Study on Relationship between Carbon Black and Dielectric Properties of Tire Rubber in UHF Band

In UHF band, the effects of carbon black component on the dielectric properties of rubber composites are studied through experiments. The results show that the content of the carbon black have great effects on the dielectric properties of the composite rubber. The higher content of the carbon black in the rubber composite, the larger the permittivity and dielectric loss tangent. At the same time, the operating frequencies also have great influence on the dielectric properties of the rubber composite. In the UHF band, the permittivity and the dielectric loss tangent of the rubber composites decrease with frequency increasing.

Ternary graphite nanosheet/copper phthalocyanine/sulfonated poly(aryl ether ketone) dielectric percolative composites: preparation, micromorphologies and dielectric properties

A phthalocyanine layer was coated on the surface of acidified graphite nanosheets for improving the dielectric properties of composites.

Effect of Magnetic Field Treatment on Dielectric Properties of LDPE Composites with Carbon Nanotube and Nanographite

Magnetic phenomenon is one of the most fundamental phenomena of substances. All substances possess strong or weak magnetic property, and have different responds to external magnetic field. Development of high performance materials by using external magnetic field is an important research field of material science. In this study, a static magnetic field is applied during thermoforming processing of low density polyethylene (LDPE)/carbon nanotube (CNT), LDPE/nanographite composites. The effect of magnetic field treatment on dielectric property of these composites is investigated. Experimental results indicate that CNT and nanographite orientate in melted LDPE under the magnetic field. The electrical conductance, the dielectric constant and the dielectric loss angular tangent value of LDPE/CNT and LDPE/ nanographite composites along the magnetic field direction all increase.

Preparation and Dielectric Properties of the Three-phase Composites of Graphite Oxide/Barium Titanate/Epoxy Resin

Polymer-based dielectric composites have important applications in the fields of power engineering, mi- croelectronics and high-density packaging. In this study, graphite oxide was prepared through oxidizing nature graph- ite flakes with concentrated sulfuric acid and potassium permanganate. And graphite oxide/barium titanate/epoxy resin (GO/BT/ER) three-phase composites were prepared. Dielectric performance of the composites with varied GO loading amounts was investigated. The experimental results showed that the GO/BT/ER composites with low GO loading amount exhibited higher dielectric constant than that of BT/ER and the dielectric loss remained low. The dielectric constant of 3wt%GO/BT/ER composite was 42.6 and the dielectric loss was 0.043 (20℃, 1 kHz), while the dielectric constant of the BT/ER composites was 17.7. Therefore, the GO/BT/ER composites are promising candidates for the embedded dielectrics. Furthermore, the mechanism of graphite oxide on the dielectric properties of the composites also explored.

Tailoring of thermal and dielectric properties of LDPE-matrix composites by the volume fraction, density, and surface modification of hollow glass microsphere filler

Hollow glass microsphere (HGM) filled low-density polyethylene (LDPE) composites were prepared, and the effects of density, content, and surface modification of HGM on the thermal and dielectric properties of the composites were investigated. It is found that the thermal conductivity of the composites decreases with increasing HGM content or decreasing HGM density. At the same HGM content and density, the composites filled with suitable amount of silane coupling agent (KH570) modified HGM exhibit higher thermal conductivity than unmodified-HGM filled composites. The dielectric constant at 1MHz of the composites also decreases with increasing HGM content or decreasing HGM density, but their dielectric loss increases with increasing HGM content or increasing HGM density. By modifying the surface of HGM with suitable amount of KH570, the dielectric constant and loss at 1MHz of the composites can be decreased at the same time. The results of microwave dielectric properties of the composites indicate that the dielectric constant decreases with increasing HGM content or decreasing HGM density, the quality factor (Q×f) decreases with increasing HGM content or increasing HGM density, but both dielectric constant and quality factor are slightly affected by the surface modification of HGM. Due to lower intrinsic thermal conductivity and dielectric constant but higher dielectric loss of HGM than LDPE, the thermal conductivity and dielectric properties of the composites can be controlled with adding HGM and varying its volume fraction. The surface modification of HGM improves the interface contact between HGM and LDPE in the composites, which is confirmed by the SEM observation, and thus the heat conduction and dielectric properties at low frequency are improved. Based on calculated thermal conductivity and dielectric constant of HGM, the experimental trends of thermal conductivity and dielectric constant at 1MHz of the composites are analyzed by using different models, including typical models for particles-filled composites and special models developed for hollow microsphere filled composites. The results from suitable models show close correlation with the experimental values.

Effects of ZrO2interphase on mechanical and microwave absorbing properties of SiCf/SiC composites

Zirconia (ZrO2) coatings were successfully prepared on KD-II SiC fibers by sol–gel approach in zirconyl chloride and ethanol–water solution. Subsequent heat treatment at 1000 °C was done in vacuum. Phase composition and morphological characteristics of the ZrO2 coatings were investigated by XRD, FTIR, and SEM. The SiCf/SiC composites with ZrO2 coatings as interphase were fabricated by chemical vapor infiltration (CVI). The effects of ZrO2 interphase on the mechanical and dielectric properties of composites were studied. The results show that the flexural strength of SiCf/SiC composites with and without ZrO2 interphase are 261 and 103 MPa, respectively. It is demonstrated that ZrO2 interphase can effectively adjust the interfacial bonding strength and improve the mechanical properties of SiCf/SiC composites. In addition, both the real and imaginary parts of the complex permittivity (ϵ′ and ϵ″) of the SiCf/SiC composites with ZrO2 interphase are higher than those of without ZrO2 interphase. The effective absorbing bandwidth (below −10 dB) of SiCf/SiC composites with ZrO2 interphase is 1.6 GHz and the lowest reflection loss is −11.5 dB when the sample thickness is 2.7 mm.