Physical Modeling and Electrodynamic Characterization of Dielectric Slurries by Impedance Spectroscopy (Part II)

Electrical characterization of dielectric slurries, as 0–3 composite systems, can provide valuable information on the dielectric properties of suspended particles. A new approach developed in our laboratory is based on impedance spectroscopy measurements of the slurries containing dispersed dielectric powders. Dielectric constants of the particles are determined through analysis of the low-frequency section of the impedance spectra. It was shown previously that this approach allows accurate and reliable measurement of dielectric constant of particles (ɛ: ∼100–2000) using host liquids (ɛ: ∼10–65). This study addresses the validation of this new method with physical model experiments using millimeter-sized sintered BaTiO₃ model samples suspended in the liquid. Impedance spectra of barium titanate powder slurries were compared with the spectra of the model samples containing macroscopic cubes prepared by sintering of the same starting powder. This comparison shows a good agreement between the impedance spectra of powder and bulk BaTiO₃ and validates the reliability of the new method to determine the dielectric constant of particulate materials.     

Impedance Analysis of Dielectric Nanoparticles Enabled via a Self‐Assembled Monolayer

Impedance spectroscopy has been shown to be a powerful tool to investigate the dielectric characteristics of powders suspended in suitable liquids. The electrical and dielectrical contributions of different components of the slurry can be extracted from the impedance spectra through measurement of frequency‐dependent relaxations. However, for ferroelectric powders that possess innate surface conductivity, such as BaTiO₃, nanoparticles have sufficient conductivity to exclude low‐frequency fields that preclude impedance characterization of the particle core. In this work, the slurry technique is shown to be effective for dielectric characterization of not only micrometer‐sized particles through equivalent circuit modeling but also applicable to nanometer size dielectric particles upon remediating the conductive surface defect. Application of a self‐assembled monolayer (SAM) onto the nanoparticle as a surface passivation layer reduces the surface conductivity, stabilizes the nanoparticles to dissolution, and allows a reproducible measurement and modeling of the nanoparticle dielectric characteristics including nanoparticle permittivity. The dielectric permittivity of surface passivated, ~40 nm diameter barium titanate particles was measured to be ε_r ~ 135.     

Fundamentals of Impedance Spectral Analysis Applied to Determine Permittivity of Dielectric Particles

It is demonstrated that the permittivity (dielectric constant) of powders suspended in suitable liquids can be determined by impedance spectroscopy techniques. A prior knowledge on the solids loading of particles in the slurry, the permittivity, and the electrical conductivity of the liquid is not required to determine the permittivity of particles by this technique. Some theoretical considerations of this method supported with experimental studies are described toward understanding of the physical phenomena involved with the characterization of slurries, which implemented to determine the permittivity of particulate materials.     

Emulsion polymerized polyaniline synthesized with dodecylbenzene-sulfonic acid and its electrorheological characteristics: Temperature effect

Dodecylbenzene-sulfonic acid (DBSA)-doped polyaniline (PANI) was prepared by emulsion polymerization, where DBSA was used as both an emulsifier and a dopant. The chemical structure and morphology of the DBSA were examined via FT-IR and SEM, respectively. Electrorheological (ER) properties of DBSA-doped PANI particles dispersed in silicone oil were studied under different operating temperatures and an applied electric field. Shear stress data as a function of shear rate fitted quite well with the Cho-Choi-Jhon (CCJ) shear stress model. Both deduced static and dynamic yield stresses were found to be collapsed into a universal scaling function. Furthermore, the Cole-Cole plot and the dielectric spectra gave relaxation times of the ER systems for different operating temperatures of dielectric measurements, confirming the correlation of dielectric properties with ER performance.     

Fabrication,characterization, and thermal property evaluation of silver nanofluids

Silver nanoparticles were successfully prepared in two different solvents using a microwave heating technique, with various irradiation times. The silver nanoparticles were dispersed in polar liquids (distilled water and ethylene glycol) without any other reducing agent, in the presence of the stabilizer polyvinylpyrrolidone (PVP). The optical properties, thermal properties, and morphology of the synthesized silver particles were characterized using ultraviolet-visible spectroscopy, photopyroelectric technique, and transmission electron microscopy. It was found that for the both solvents, the effect of microwave irradiation was mainly on the particles distribution, rather than the size, which enabled to make stable and homogeneous silver nanofluids. The individual spherical nanostructure of self-assembled nanoparticles has been formed during microwave irradiation. Ethylene glycol solution, due to its special properties, such as high dielectric loss, high molecular weight, and high boiling point, can serve as a good solvent for microwave heating and is found to be a more suitable medium than the distilled water. A photopyroelectric technique was carried out to measure thermal diffusivity of the samples. The precision and accuracy of this technique was established by comparing the measured thermal diffusivity of the distilled water and ethylene glycol with values reported in the literature. The thermal diffusivity ratio of the silver nanofluids increased up to 1.15 and 1.25 for distilled water and ethylene glycol, respectively.     

Impedance spectroscopy and conduction mechanism of magnetoelectric hexaferrite BaFe10.2Sc1.8O19

The dielectric relaxation and conduction properties of hexaferrite BaFe_10.2Sc_1.8O₁₉ (BFSO) ceramics have been investigated by impedance spectroscopy (1 Hz-2 GHz) at various temperatures (253-473 K). The frequency dependence of impedance and modulus spectra of BFSO shows that its dielectric responses are thermally activated. The scaling behaviors of impedance spectra indicate that the distribution of dielectric relaxation times in BFSO is temperature independent. The frequency-dependent conductivity spectra follow the universal-power-law at high temperatures but deviate slightly at low temperatures. An enormous increase in relaxation/conduction activation energies of BFSO above 413 K is also observed in both impedance and conductivity spectra. This indicates that at high temperatures, relaxation/conduction processes may be contributed mainly by the movable oxygen vacancies, whereas at low-temperature electron hopping dominates. The conductivity fitting results further suggest that electron/oxygen vacancy-related small polaron hopping should be the most probable conduction mechanism for BFSO.     

Hydrostatic Levitation of Particles in Electric and Magnetic Fields

Abstract

Nonhomogeneous magnetic and electric fields generate levitational forces in magnetic and dielectric liquids whereby particles are separated according to their specific gravity and magnetic and electric properties, respectively. The corresponding systems are called magnetohydrostatic separation and wet dielectric separation. These forces depend on the field intensity and gradient, and on properties of the liquid and the particles to be levitated. This paper deals with the potential application of electric fields as compared with that of the magnetic field. It is shown that unless special measures are taken, the electric field is inferior to such an extent that its application is not promising. In this context the influences of particle size and shape in both methods are discussed.     

Percolation in Borosilicate Glass Matrix Composites Containing Antimony‐Doped Tin Oxide Segregated Networks. Part II: Examination of Electrical Behavior Using Impedance Spectroscopy

Glass nanocomposites, fabricated using borosilicate glass microspheres and antimony tin oxide (ATO) nanoparticles, were previously reported to have formed segregated networks at the boundaries of the glass particles. This resulted in an electrically conducting composite at low volume fractions (~0.5–0.8 vol%) of ATO nanoparticles. The wide range of electrical response in these borosilicate glass composites containing networks of varying concentration of ATO was examined using impedance spectroscopy. The electrical resistance of these composites varied over a range of around 12 orders of magnitude and exhibited several different types of insulator and conductor behavior. The formation of the ATO network was identified and tracked by scanning electron microscopy images and energy dispersive X‐ray spectroscopy (EDS) scans. Detailed impedance spectroscopy analysis using all of the dielectric functions (impedance, permittivity, electric modulus, and admittance) was found to be an excellent method for detecting the development of the network and the effect that processing variables can have on its formation and the overall electrical properties of the nanocomposites.     

Dielectric impedance studies of poly(vinyl butyral)–cenosphere composite films

In the current study, amino silane functionalized cenosphere particles was used as a reinforcing filler in poly(vinyl butyral) matrix and were made by melt blending. The changes observed in the dielectric performance of the composite films with varying weight percentage of cenosphere particle in the matrix were investigated. The dielectric property and impedance spectroscopy were evaluated as a function of applied frequency in the range of 50 Hz to 5 MHz. It is observed that, because of orientation polarization of the PVB polymer, the permittivity and impedance decrease, whereas conductivity increases. Tangent loss graph indicates that the property of the matrix is associated with geometrical fill factor and the lowest quality factor. Therefore, above 10 kHz, these composites can be considered as dielectric loss‐less material. POLYM. COMPOS., 35:1636–1643, 2014. © 2013 Society of Plastics Engineers     

溶胶-凝胶一步烧结法合成巨介电常数材料CaCu3Ti4O12

通过溶胶-凝胶法合成了巨介电常数材料类钙钛矿型钛酸铜钙(CaCu3Ti4O12,CCTO)先驱物,采用一步烧结法得到纯度较高的CCTO材料。利用X射线衍射、扫描电子显微镜、介电性能测试和阻抗谱测试对样品进行了结构、微观形貌、介电-频率、阻抗谱等分析表征,并讨论了CCTO的微观电导机理和晶粒晶界的性质,计算了晶界活化能。结果表明,此法制备的CCTO样品具有较好的结晶质量、较高的纯度以及优良的介电性能。     

Studies on Silicon Containing Nano-hybrid Epoxy Coatings for the Protection of Corrosion and Bio-Fouling on Mild Steel

An epoxy nano-composite coating was developed using amine functionalized nZnO (in the amount of 2.5 %, 5.0 % and 7.5 wt %) as the dispersed phase and a commercially available epoxy resin as the matrix phase. The structural features of these materials were ascertained by FT-IR spectral studies. The anti-corrosive properties of the epoxy/nZnO hybrid coatings in comparison with a virgin coating were investigated by a salt spray test and electrochemical impedance spectroscopy technique. The surface morphology determined by SEM, indicates that nZnO particles were dispersed homogenously through the epoxy polymer matrix. The results showed improved antifouling and anticorrosive properties for epoxy-nZnO hybrid coatings.     

A study of polymer-modified mortars by the AC impedance technique

Cement mortar can be regarded as a composite consisting of the cement paste, fine aggregate, and the interfacial transition zone (ITZ). In this paper, the formation and development of the ITZ of polymer-modified mortar (PMM) was studied by alternating current impedance spectroscopy (ACIS). The test results showed that the AC impedance spectra of the PMMs had the following characteristics: (1) the AC impedance spectra of the fresh PMMs were almost parallel to the imaginary axis; (2) The AC impedance spectra of the hardened PMMs showed a high-frequency part not connected to the intermediate frequency part. This characteristic was maintained over a rather long period, and then obvious changes appeared in the AC impedance spectra. The age at which the impedance spectra of the mortars changed appeared to shorten with an increase of the sand volume fractions (SVFs). These characteristics of the AC impedance spectra of the PMMs were related to the close contact, the packing, and the formation of a mechanically rigid film of the polymer particles.     

EIS法研究3种配套涂层体系的腐蚀电化学行为

采用电化学阻抗谱(EIS)研究了由水性无机富锌底漆、环氧中间漆和氯化橡胶面漆3种涂料配套而成的3种不同涂层体系在3.5%NaCl溶液中的电化学腐蚀行为,考察了氯化橡胶面漆、水性无机富锌底漆／氯化橡胶面漆、水性无机富锌底漆／环氧中间漆／氯化橡胶面漆这3种涂层体系的阻抗谱在浸泡过程中的演化并据此比较了3种涂层体系的防护性能。结果表明,两涂层体系的防护性能比单涂层的还要差,三复合涂层体系的防护性能最好。根据涂层腐蚀电化学阻抗谱特征推测,中间漆在三复合涂层体系中起到了使底漆和面漆结合更加紧密的桥梁作用。     

Structural and dielectric properties of CuO nanoparticles

The DC conduction and dielectric behaviour of copper oxide nanoparticles prepared by sol-gel method and sintered at 950 °C were studied in the temperature range of 200–526 K. The formation of single phase monoclinic CuO was confirmed by x-ray diffraction. Chemical composition of the CuO ceramic was investigated with X-ray photoelectron spectroscopy (XPS) technique. Although XRD analysis shows the formation of single phase CuO, XPS spectra revealed the presence of Cu³⁺ and Cu²⁺. Deviation from linearity ln (σ_DC) vs. 1/T plot at ~390 K was observed, which indicates that DC conduction in the CuO pellet is dominated by two different conduction mechanisms. The results obtained on AC conductivity indicate that AC conduction mechanism could be well explained by the multihopping model at low frequencies, while high frequency AC conductivity data can be described by small polaron tunnelling model. The dielectric relaxation mechanism in the CuO pellet was studied by impedance spectroscopy. It was found that while dielectric constant is an increasing function of temperature, it decreases with increasing frequency. The obtained impedance spectra indicated that the grain boundary effects and intergranular activities play a crucial role on the dielectric relaxation processes.     

石墨纸-BaTiO_3/PI一体化复合薄膜的制备及研究

聚合物复合薄膜超级电容器因其可实现大面积制备、性能可靠等优点,引起了能源领域的广泛关注。如何实现导电层与介电层的一体化加工制备,是叠片式薄膜超级电容器的重要研究方向。本文介绍了以溶液混合法制备的钛酸钡/聚酰亚胺复合薄膜作为介电材料,以石墨纸作为电极材料以及复合薄膜的载体,利用提拉法制备石墨纸-钛酸钡/聚酰亚胺一体化复合薄膜,实现导电层与介电层直接成型的一体化制备过程。利用红外(FT-IR)、扫描电镜(SEM)、EIS和LCR电桥仪对复合薄膜进行表征分析。实验结果表明聚酰亚胺亚胺化完全,钛酸钡在复合薄膜中分散良好,复合薄膜的介电损耗非常小,很好地满足了高介电材料的应用要求。     

Water sorption and diffusional properties of a cured epoxy resin measured using alternating ionic liquids/aqueous electrolytes in electrochemical impedance spectroscopy

The protective quality of a coating is often measured by how long it delays the arrival of water to the substrate. The transport of water in, redistribution within, and eventually through a coating to the substrate has long been investigated through electrochemical impedance spectroscopy (EIS). EIS measurements employing alternating nonaqueous (room temperature ionic liquids, RTIL) and aqueous electrolytes elucidated the behavior of water within the coating. Diffusion coefficients could be measured and the redistribution of water into percolating paths identified. The use of RTIL alternating with aqueous electrolytes allows determination of intrinsic properties (water volume fraction at saturation and relative dielectric) and kinetic properties predicted by the Brasher Kingsbury formulation. This article focuses on the sensitivity of these intrinsic and kinetic properties to test duration in an unique experimental method.     

Study on corrosion electrochemical behavior of several different coating systems by EIS

Corrosion electrochemical behavior of chlorinated rubber top coating (single-layer), inorganic zinc-rich primer/chlorinated rubber top coating (double-layers) and inorganic zinc-rich primer/epoxy middle paste/chlorinated rubber top coating (tri-layers) in 3.5 wt% NaCl solution was studied by electrochemical impedance spectroscopy (EIS). A series of impedance spectra of the three coating systems during immersion were measured; and their protective properties were compared according to the spectra. The experimental results showed that, the protective properties of the double-layers coating system were even worse than that of the single-layer coating system; and the tri-layers coating system had the best protective properties in the three coating systems; epoxy middle paste had played a very important role for protective properties of the composite coating system.     

聚合物改性水泥砂浆界面过渡区的交流阻抗谱研究

水泥砂浆可视为由水泥浆体、细集料和水泥浆体－－休料界面过渡区（interfacial transition zone，简称ITZ）所组成，聚合物改性水泥砂浆中，较小的聚合物颗粒有利于休料表面的紧密堆积，用交流阻抗方法研究了不同砂子粒径和不同砂子体积分数的聚合物改性砂浆在不同龄期的表现，结果表明：交流阻抗方法是研究聚合物改性砂浆界面过渡区发展变化的一种新手段，聚合物改性砂浆的阻抗谱随龄期延长出现二次明显变化，这种特征分别与聚合物在砂浆界面过渡区的聚集、凝结、形成紧密堆积的颗粒结构以及聚合物颗粒相互扩散渗透，形成具有一定力学强度的过程有关。同时，聚合物在界面过渡区的成膜情况与砂子粒径及其体积分数有关，从而在交流抗谱上可以观察到相应的响应。     

Hydrogenation of Carbon Dioxide on Rh, Au and Au–Rh Bimetallic Clusters Supported on Titanate Nanotubes, Nanowires and TiO2

Supported gold, rhodium and bimetallic rhodium-core?Cgold-shell catalysts were prepared. The supports were TiO₂ as well as titanate nanotube and nanowire formed in the hydrothermal conversion of titania. The catalytic properties were tested in the CO₂ hydrogenation at 493?K. The amount and the reactivity of the surface carbonaceous deposit were determined by temperature-programmed reduction. The surfaces of the materials were characterized by X-ray photoelectron and low-energy ion scattering spectroscopy (LEIS). The surface forms during the catalytic reaction were identified by DRIFT spectroscopy. On the XP spectra of bimetallic catalysts the existence of highly dispersed gold particles could be observed besides the metallic form on all supports. Small Rh particles could also be identified on the titanate supports. LEIS spectra demonstrated that Rh-core?CAu-shell particles formed, since no scattering from Rh was detected. The main product of CO₂ hydrogenation was CH₄ on all catalysts. IR spectra revealed the existence of CO and formate species on the surface. In addition, a new band was observed around 1,770?cm^?1 which was assigned as tilted CO. It is bonded to Rh and interacts with a nearby the oxygen vacancy of the support. Agglomeration of highly dispersed Rh was observed on bimetallic samples induced by reaction or reactant.     

Low-Temperature Sintering and High-Strength Pb(Zr,Ti)O3-Matrix Composites Incorporating Silver Particles

Lead zirconate titanate based composites containing silver particles were fabricated from commercially available PZT and Ag₂O powder mixtures. Densification behavior and mechanical and dielectric properties were evaluated as a function of the volume fraction of silver. No unwanted reaction phases between the PZT matrix and silver could be detected in the X-ray diffraction analysis. The added silver particles were homogeneously dispersed in the matrix. The densification of PZT was substantially accelerated by the addition of silver particles. Mechanical properties, e.g., fracture toughness and fracture strength, were improved by the addition of silver particles. The relative dielectric constant also increased when the volume fraction of silver was increased. This observed enhancement in dielectric constant may be associated with the effective dielectric field developed by the existence of conducting silver particles.