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2022 ◽  
Vol 3 (1) ◽  
pp. 53-62
Author(s):  
Hari Chandra Nayak ◽  
Shivendra Singh Parmar ◽  
Rajendra Prasad Kumhar ◽  
Shailendra Rajput

In this article, the dielectric properties of poly (9-vinylcarbazole) (PVK) and ferrocene-doped PVK thin films are studied. The thin films were grown by the isothermal solution casting technique. Dielectric properties of grown films were studied as function of ferrocene concentration, frequency, and temperature. The relative permittivity (ε′) is increased with increasing ferrocene percentage (~1%) due to the free charge carriers. The relative permittivity decreases for higher ferrocene percentage (~2%). However, the relative permittivity of PVK and ferrocene-doped PVK samples remains almost constant for studied temperature range (313–413 K). The frequency dependence of tan δ for all samples is studied. The frequency dependence of dielectric parameter exhibits frequency dispersion behavior, which suggests all types of polarization present in the lower frequency range. The loss tangent (tanδ) values are larger at higher temperatures in the low frequency region. However, the tan δ values at different temperatures are almost similar in the high frequency region. It is observed that the relative permittivity is maximum, dielectric loss is minimum, and AC conductivity is minimum for 1% ferrocene doped PVK as compared to pure PVK and 2% ferrocene doped PVK samples.


Materials ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 564
Author(s):  
Beate Capraro ◽  
Manuel Heidenreich ◽  
Jörg Töpfer

We have studied the sintering behavior of CT708 LTCC tapes with large CTE of 10.6 ppm/K. This low-k dielectric LTCC material is a quartz-based glass ceramic composite system with partial crystallization of celsian upon firing. The shrinkage, densification and dielectric properties were examined using different heating rates and a sintering temperature of 900 °C. The maximum shrinkage rate is at 836 °C (for a heating rate of 2 K/min) with a sintering density of 95% and a permittivity of ε’ = 5.9 and tan δ = 0.0004 (at 1 GHz). Due to their similar shrinkage and thermal expansion properties, CT708 tapes may be cofired with functional ceramic layers. As an example, we report on cofiring of a multilayer laminate of CT708 and a Sc-substituted hexagonal ferrite for applications as integrated microwave circulator components. This demonstrates the feasibility of cofiring of functional ceramic tapes and tailored LTCC tapes and documents the potential for the realization of complex LTCC multilayer architectures.


2022 ◽  
Author(s):  
Ahmed M. Abdel Hakeem ◽  
E.M.M. Ibrahim ◽  
Hazem Mahmoud Ali ◽  
M. M. Abd El-Raheem ◽  
Adel Hamazaoui ◽  
...  

Abstract M-type hexaferrite SrCrxFe12-xO19 compounds doped with Cr (x=0, 1, 2, 3 and 4 at.%) were prepared by microwave digestion system. X-ray diffraction was used to study the structure and crystallization of the samples. The samples are found to have a hexagonal phase, SrFe12O19, as a main phase at 2Θ ≈ 33.144° and 35.618° for x = 0 and 1 respectively, and 32.451° and 34.295° for x ≥ 2. The Rietveld refined parameters such as the lattice parameters (a=b, c), direct and indirect cell volume, crystallite size and microstrain were investigated. TEM and SEM results showed that the samples have hexagonal shape and grain sizes range from 126 nm to 379 nm. Magnetization, M, as a function of the applied magnetic field, H, was obtained from the hysteresis loop. The coercive field, HC , saturation, Ms and remnant, Mr , magnetization and squareness ration, Mr/Ms , were extracted from the hysteresis loop results. These results revealed that HC is inversely proportional with the grains size of the samples but directly proportional with Cr-doping values candidating these compounds to be used in computer hard disk memories applications. M values are inversely proportional with Cr-doping values. The variation of conductivity, σ, impedance, Z, dielectric constant, ε, dielectric loss factor, tan δ and dissipation factor as functions of both AC frequency, F(Hz) and Cr-doping, x, were investigated. The maximum value of the dissipation factor was at x=2 which equals 8.05x109 m/F when F = 2x105 Hz. The impedance of the samples behaved as a capacitor reactance that makes our compounds candidate for many crucial dielectric applications.


Author(s):  
Takuma Nishimura ◽  
Tsukasa Katayama ◽  
Shishin Mo ◽  
Akira Chikamatsu ◽  
Tetsuya Hasegawa

Layered perovskite nickelates have recently emerged as materials with colossal dielectric permittivity. However, they exhibit relatively high values of loss tangent (tan δ) owing to insufficient electric insulation; thus, lowering...


Materials ◽  
2021 ◽  
Vol 14 (24) ◽  
pp. 7649
Author(s):  
Muhammad I. Qureshi ◽  
Basit Qureshi

In this experimental investigation, hydrophobic silane-grafted fumed nano-silica was employed in transformer oil to formulate nanofluids (NFs). A cold-air atmosphere-pressure plasma reactor working on the principle of dielectric barrier discharge was designed and utilized to functionalize the surface of these nanoparticles. A field emission scanning electron microscope (FE-SEM) coupled with energy-dispersive X-ray (EDX) module and Fourier transform infrared (FTIR) spectroscopy were used to scan surface features of new and plasma-treated nanoparticles. The study revealed considerable changes in the surface chemistry of nanoparticles, which led to good dispersibility and stability of nanofluids. The measurements of AC breakdown voltages (AC-BDV) of nanofluids so prepared were conducted according to IEC-Std 60156, and a significant improvement in the dielectric strength was achieved. A statistical analysis of these results was performed using Weibull probabilistic law. At a 5% probability of failure, modified nanofluid remarkably exhibited a 60% increase in breakdown voltage. The dielectric properties such as variation of εr and tan δ in temperature of up to 70 °C were measured and compared with untreated fluid. Results exhibit an increase in tan δ and a slight decrease in permittivity of nanofluids. The analysis also revealed that while unpolar silane coating of NPs increased the breakdown strength, the polar-amino-silane-coated NPs in oil resulted in a drastic reduction. Details of this antagonistic trend are elaborated in this paper.


Author(s):  
Mohammed Iqbal Shueb ◽  
Mohd Edeerozey Abd Manaf ◽  
Mahathir Mohamed ◽  
Noraiham Mohamad ◽  
Jeeferie Abd Razak ◽  
...  

Thermal behaviour of graphene nanoplatelets (GNP) reinforced nylon 66 nanocomposites were investigated using differential calorimetric scanning (DSC), thermogravimetric analyzer (TGA) and dynamic mechanical analysis (DMA). The influence of low content GNP on thermal properties of GNP/nylon 66 nanocomposites was studied for low GNP content (0.3, 0.5 and 1.0 wt%). DSC results indicate that addition of GNP increases crystallization temperature and degree of crystallinity of the nanocomposites. Thermal stability and mass loss were studied through TGA analysis. The results show that thermal stability and weight loss of GNP/nylon 66 nanocomposites slightly improve with the GNP addition with an increase in the onset of degradation temperature as much as 10 °C. DMA analysis shows that GNP in the nylon 66 matrix act similar to plasticizer; it decreases the storage modulus and glass transition temperatures of the nanocomposites. GNP addition also reduces tan δ indicating an improvement in the damping property of the nanocomposites. Overall, this study concludes that a minimal amount of 0.3 wt% of GNP is effective in improving the thermal properties of nylon 66 composites.


Forests ◽  
2021 ◽  
Vol 12 (12) ◽  
pp. 1654
Author(s):  
Xiaoyi Chen ◽  
Liping Deng ◽  
Xin Wei ◽  
Mingpeng Li ◽  
Ge Wang ◽  
...  

Bamboo has natural damping properties, but, due to the obvious gradient differences in bamboo walls, the damping properties of different layers may vary. Using bamboo slivers as the research object, this study investigated the underlying mechanism of the effect of microstructural and chemical components on the damping properties (η, damping ratio) of bamboo using the resonance and nonresonance methods. The damping ratio decreased on L3 (inner layer), L2 (middle layer), and L1 (outer layer) due to lower microfibril angles, increased crystallinity of cellulose, and decreased hemicellulose content. All of these limited the motion of the bamboo’s molecular chains. The damping ratio successively increased in the oven-dried, air-dried, and water saturated states because water acted as a plasticizer. The damping ratio of L1, in the oven-dried state, was slightly higher than that of the air-dried state because L1 had the lowest water content. This allowed less water to escape during drying, which intensified the molecular distortion. The initial tan δ (tangent of the loss angle) decreased successively on the L3, L2, and L1 layers of the bamboo, and the tan δ of L3 was lower than that of L2 due to changes in the temperature sensitivity of hemicellulose.


2021 ◽  
Vol 43 (4) ◽  
pp. 268-279
Author(s):  
L.V. KARABANOVA ◽  
◽  
L.A. HONCHAROVA ◽  
N.V. BABKINA ◽  
◽  
...  

A series of the nanocomposites based on a multicomponent polymer matrix consisting of polyurethane and poly(hydroxypropyl methacrylate) and 1,2-propanediolysobutyl polyhedral oligomeric silsesquioxane (1,2-propanediolysobutyl-POSS), used as a functionalized nanofiller, was synthesized. The polymer matrix was formed on the principle of interpenetrating polymer networks (IPNs). The influence of 1,2-propanediolysobutyl-POSS amount on the thermodynamics of polymer components of the matrix interactions and on the dynamic mechanical properties of the created nanocomposites was studied. With purpose of the thermodynamic parameters interactions calculations the isothermal sorption of methylene chloride vapour by samples was investigated. The methylene chloride vapour sorption by the samples was studied using a vacuum installation and a McBain balance. By calculations of the thermodynamic parameters of PU and PHPMA interactions was shown that the free energy of PU and PHPMA mixing was positive. The introduction of 1-3 wt % of POSS lead to further phase separation in semi-IPNs. This is due to concentration of POSS particles in the PU’s nanodomains. The increasing of POSS content up to 5-10 wt % lead to compatibi-lization in semi-IPNs. These is due to concentration of POSS nanoparticles not only in the PU’s nanodomains but also in the interphase region of semi-IPN. The dynamic mechanical properties of the created nanocomposites were investigated and the degree of polymer components segregation was calculated. It was shown that there are two peaks of tan δ (PU and PHPMA) in the nanocom-posites. The introduction of 1-3 wt % of POSS lead to increasing of tan δ peak of PHPMA and to deepening of the bridge between two peaks (PU and PHPMA). At the same time the degree of polymer components of the matrix segregation became higher. This means the further phase separation in semi-IPNs. Increasing of 1,2-propanediolysobutyl-POSS amount up to 5-10% leads to the concentration of the nanofiller not only in the nanodomains of PU, but also in the interfacial layers. This leads to a change in the free energy of polymer components mixing, which becomes negative. At the same time the degree of polymer components of the matrix segregation became significantly reduced. These means that the process of compatibilization took part in the semi-IPNs.


Author(s):  
A. AlGhamdi ◽  

In this work, design of a reconfigurable metasurface using all-dielectric materials is presented. An elliptical all-dielectric microfluidic-based metasurface is designed using Rogers RO3210 substrate (ε = 10.2 and tan δ = 0.03). The substrate is covered with microfluidic channel which is filled with five various AgTiTe2, Cu2S, Te.5 Se.5, CuTSe2 and Cu3SbSe4. semiconductor alloys. The reflection and transmission characteristics of the designed metasurface are analyzed in the frequency range of 20-30 GHz using COMSOL Multiphysics software. The results demonstrate that change in the semiconductor alloy in the microfluidic channel various the dynamic transmission and reflection characteristics of the metasurface and thus depicts a reconfigurable operation of the proposed design.


2021 ◽  
Author(s):  
Pradeep Lall ◽  
Madhu Kasturi ◽  
Haotian Wu ◽  
Jeff Suhling ◽  
Edward Davis

Abstract Automotive underhood electronics may be exposed to high temperature in the neighborhood of 100°C–200°C. Property evolution may impact reliability and accuracy of predictive models to assure desired use life. In this paper, evolution of properties of two underfill material properties are studied using DMA (Dynamic Mechanical Analyzer). The underfills are exposed to three different operational temperatures in the range of 100°C to 140°C for the measurements. The dynamic mechanical properties such as storage modulus (E′), loss modulus (E″), tangent delta (tan δ), and respective glass transition temperatures (Tg) are studied using DMA. Study of viscoelastic behavior of underfills is achieved by performing TTS (time-temperature superposition) experiments at 7 discrete frequencies 0.1, 0.21, 0.46, 1, 2.15, 4.64, and 10 Hz using DMA in three-point bend mode. From the selected reference temperatures, the master curves were constructed for storage moduli, loss moduli and tan delta as a function of frequency using TTS results. Using the WLF (Williams-Landel-Ferry) equation, the shift factors as a function of temperature were determined along the frequency axis. The relaxation modulus as a function of temperature and time can be obtained using the master curves of storage and loss moduli. A simple and detailed procedure has been established to find the Prony series constants.


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