Dielectric Properties Of Materials Research Articles

Preparation and properties of silicate inorganic external wall insulation materials based on heat storage

In this article, the foaming slurry after the reaction of silicate inorganic gelling material sodium silicate and foaming agent azodicamide is taken as the main investigation object, and the mechanism of bubble nucleation and the effect of physical parameters such as temperature, time, viscosity and surface tension on the structure of bubble pores are analyzed. As well as the influence of processing technology such as foiling temperature, heating rate, holding time and various kinds of modifiers on the structure and properties of the material, the appropriate processing technology conditions and modifiers are screened out, and an inorganic foiling insulation material with light weight, high strength, heat preservation, fire prevention, no pollution, low cost, simple process and easy to use is prepared. The experimental results show that, although the properties of the prepared material are better with the increase of azodicarbonamide (ADC) content and viscosity, the maximum amount of ADC added is only 1%. When the ADC content in the system is greater than 1%, the foaming slurry will appear gel, which is not conducive to the late high temperature foaming and the uniformity of the final product. Therefore, the optimal amount of ADC is 1% of the mass of sodium silicate.

Optimizing impedance matching by a dual-carbon Co-regulation strategy of Co3O4@rGO/celery stalks derived carbon composites for excellent microwave absorption

• Co 3 O 4 @rGO/CDC composites with different mass ratios of rGO:CDC were prepared. • S13 (weight ratio for rGO:CDC is 1:3) composite showed best microwave absorption performance. • It showed RL min value of -84.3dB and the widest effective bandwidth of 4.5 GHz. • Better impedance matching can be obtained by tuning the CDC ratio. Both macroscopic composition and microstructure should be considered for reasonable microwave absorbent designing. In this study, Co 3 O 4 @reduced graphene oxide (rGO)/Celery stalks derived carbon (CDC) was prepared by loading Co 3 O 4 particles into rGO and biomass-derived carbon mixture through oxidation precipitation. By changing the mass ratio of rGO to CDC, the dielectric and impedance matching properties of the composites can be easily regulated. The RL min value of Co 3 O 4 @rGO/CDC 13 composite (weight ratio for rGO: CDC is 1:3) reaches –84.3 dB with a thickness of 4.6 mm, and the widest effective bandwidth can be obtained at 4.5 GHz with a matching thickness of 2.8 mm. The Co 3 O 4 @rGO/CDC 13 composite with multiple components (Co 3 O 4 , CDC, rGO) and 3D net structure produces magnetic/dielectric loss combinations, interfacial polarization, and multiple reflections and scattering, and the CDC with half tube and half sheet structure is conducive to the optimization of impedance matching. The strategy of co-regulating dielectric properties of materials with double carbon provides a novel pathway for the preparation of lightweight, low-cost, and high-performance absorbers.

Analysis of the Research of Packages of Materials for Military Uniforms

The article presents an analysis of the results of a study of the physical and mechanical properties of packages of materials of various compositions for soldiers ' uniforms . The relevance of the article is as follows : currently , one of the urgent problems is the inconsistency of uniforms with consumer requirements , the insufficiency of domestic , high-quality , affordable uniforms for military personnel , the lack of research in Kazakhstan on the production of thermal insulation , including non-woven materials . The production of nonwovens occupies a special place among the branches of the textile industry , since the specific properties of these materials allow not only their widespread use as substitutes for fabrics , knitwear , but also to create canvases with fundamentally new properties . Therefore , non-woven materials from domestic raw materials were presented as thermal insulation materials when processing products for soldiers . The purpose of the article is to study the properties of a package of materials for designing uniforms for military personnel . A feature of using the proposed technology in the development of several variants of a new material for the widespread use of domestic raw materials is the production of non-woven material based on a combination of camel and sheep wool by needle method . Experimental researches of the properties of nonwoven insulation materials were carried out using standard methods in laboratory conditions .

Charge-Sensitive Technique for Deformation Processes’ Study

Surface charge can be used as an information parameter about the change in the state of the material under the action of mechanical stresses. The aim of the work was to develop methods for studying deformation processes in metallic and polymeric materials using a charge-sensitive method.Experimental studies of deformation processes under tensile, compressive and impact loads were carried out on samples of various materials: aluminum alloy of AMg2 grade, steel of grade 08PS, high-pressure polyethylene of grade 12203-250 and samples of composite materials based on it, F4 polytetrafluoroethylene. As a research method, the analysis of changes in the relative values of the surface electron work function in the case of metals and the surface electrostatic potential in the case of polymers and composite materials is used. A scanning modification of a charge-sensitive probe is used as a measuring instrument.The results of experimental studies of materials in a stress-strain state demonstrate the high efficiency of the proposed method. The research methodology makes it possible to detect local changes in the surface potential of the material in the area of deformations, which are not detected on a macroscopic scale using standard methods. The results obtained can serve as a basis for the development of new methods and techniques for studying the mechanical properties of both metals and dielectric materials.

Point Defect Stability and Dielectric Properties of Graphene-Like Monolayer Materials

Atomically thin two-dimensional (2D) materials have attracted tremendous interest and shown great potential in various research areas of modern nanotechnology. Here, we systematically study a category of 2D families, namely, graphene-like monolayer monoxides, monochlorides, and mononitrides (GLMMs), by virtue of density functional theory and density functional perturbation theory. First, the stability of different native point defects in GLMMs is investigated energetically, and the results show that most vacancy defects, especially the neutral nonmetal atom vacancies, possess high formation energy, manifesting their outstanding structural stability and high resistance to vacancy formation during the preparation process. The ab initio molecular dynamics also confirm the thermal stability of these GLMMs with and without defects. Subsequently, their dielectric properties are explored by the effective dielectric model (EDM) and 2D electronic polarizability simultaneously for comparison. It is found that most GLMMs possess far higher out-of-plane dielectric constants than h-BN, behaving as promising monolayer materials for device applications. Moreover, 2D electronic polarizability is proven to exhibit a significant advantage in evaluating the dielectric property of 2D materials with an atomically thin layer over the EDM method, owing to the sensitivity of the EDM on the layer thickness. All theoretical calculation results provide a comprehensive prediction of the atomic structures and dielectric properties of GLMMs, aiming to facilitate the synthesis and further application of such novel 2D materials.

All-Aerosol-Jet-Printed Carbon Nanotube Transistor with Cross-Linked Polymer Dielectrics.

The printability of reliable gate dielectrics and their influence on the stability of the device are some of the primary concerns regarding the practical application of printed transistors. Major ongoing research is focusing on the structural properties of dielectric materials and deposition parameters to reduce interface charge traps and hysteresis caused by the dielectric-semiconductor interface and dielectric bulk. This research focuses on improving the dielectric properties of a printed polymer material, cross-linked polyvinyl phenol (crPVP), by optimizing the cross-linking parameters as well as the aerosol jet printability. These improvements were then applied to the fabrication of completely printed carbon nanotube (CNT)-based thin-film transistors (TFT) to reduce the gate threshold voltage (Vth) and hysteresis in Vth during device operation. Finally, a fully aerosol-jet-printed CNT device was demonstrated using a 2:1 weight ratio of PVP with the cross-linker poly(melamine-co-formaldehyde) methylated (PMF) in crPVP as the dielectric material. This device shows significantly less hysteresis and can be operated at a gate threshold voltage as low as -4.8 V with an on/off ratio of more than 104.

Dedication to Professor Jūras Banys

This year, on 30 December, is the 60th anniversary of the outstanding physicist, Vilnius University professor, academician, president of the Lithuanian Academy of Sciences Jūras Banys. J. Banys graduated with honours from the Faculty of Physics of Vilnius University in 1985, defended his doctoral thesis in 1990. In 1989–1990, he worked at a professor Mike Glazer’s laboratory at the University of Oxford (UK), studying the structural properties of ferroelectric crystals using X-ray diffraction methods. In 1993–1995, after receiving Alexander von Humboldt scholarship, he worked at the University of Leipzig, where he studied the local dynamics of phase transitions using electron paramagnetic spectroscopy. After returning to his Alma Mater, J. Banys took charge of the Laboratory of Microwave Spectroscopy, turning it into a modern centre for the study of the dielectric properties of ferroelectric materials. Over the years, he assembled here a group of highly qualified scientists who perform scientific experiments using unique materials developed in well-known foreign and Lithuanian laboratories. In 2000, J. Banys successfully defended his habilitation thesis, and in 2003 the title of Vilnius University professor was awarded to him.

Recycling of organic residues to produce insulation composites: A review

The building sector accounts for high energy consumption, and increasing the energy efficiency of buildings is considered a key measure to meet the climate goals worldwide. Even though there are various residual biomass streams available that show good thermal insulation properties, most applied thermal insulation materials are of mineral or synthetic polymer basis and non-biodegradable. To foster the application of bio-based thermal insulation materials, the aim of this study was an investigation of bio-composite- and mycelium-based boards and mats currently available or under research and their thermal insulation properties. The focus was laid on the treatment of various biomasses using fungi to enhance their application in the building sector as well as their thermal insulation properties. The different materials were compared regarding density, thermal conductivity, specific heat capacity, water vapour resistance, water absorption, fire performance, and mechanical properties. This work provides the basis for selecting residual biomass streams to produce case-specific thermal insulation materials. • Biomasses were highlighted for production of thermal insulation materials • Properties of insulation materials have been clarified • Possibilities to improve properties have been shown • Mycelium-based composites are particularly interesting as insulation materials

Analysis of High-Temperature Wideband Dielectric Properties of ATH-Filled Silicone Rubber Used for On-Site Insulation of Bare Overhead Conductors

Due to its excellent electrical and mechanical properties, and easy to cure at room temperature, room temperature vulcanizing silicone rubber is currently used in the on-site insulation of bare overhead conductors in the distribution system. The dielectric properties of silicone rubber materials have a great impact on power loss, which is vital to the transmission lines. Therefore, in this article, the dielectric properties of silicone rubber with the addition of different aluminum hydroxide contents are investigated by broadband dielectric spectroscopy in wide broadband range and wide temperature ranges, and the influence of aluminum hydroxide filler on the dielectric response is analyzed using a modified Cole–Cole model which takes the low-frequency dispersion process into account. It is found that the relationship of the dc conductivity and the low-frequency dispersion strength with temperature follows the Arrhenius equation law. The low-frequency dielectric response is influenced by dipoles’ polarization and electrode polarization. Moreover, the relaxation time decreases with the increase in temperature, and its mechanism can be revealed by the double-well model. The characteristic parameters obtained in this article can provide a reference for on-site insulating of bare overhead conductors.

Basic research on the microwave dielectric properties of ammonium hexachlororuthenate(Ⅳ) via Ru doping

Exploring the dielectric properties of ammonium hexachlororuthenate(Ⅳ) (N0), the five mixtures (N0/Ru) of N0 mixed with different Ru ratios, and ruthenium (Ru) is fundamental to the application with microwave technology rather than traditional technology to the thermal decomposition self-reduction of N0. In this work, the microwave dielectric properties of N0, N2, N4, N6, N8 N10, and Ru were determined using a resonant cavity perturbation approach, and the pyrolysis reduction features of N0 were thoroughly analyzed using thermogravimetric mass spectrometry. Results showed that the dielectric characteristics of N0 and N0/Ru with temperature were similar, it risen, then decreased, and eventually gone up significantly as temperature increased, showing outstanding sensitivity to microwaves. The change pattern was primarily linked to the thermal decomposition self-reduction N0 to Ru with releasing HCl, NH3 and N2. Meanwhile, the dielectric properties commonness of N0 and N0/Ru with bulk density increasing stably, with amazing reactivity to microwaves, which the tendency was mainly driven by the rise quantity of materials and Ru particles per unit volume. Likewise, the heating characteristics well matched with the dielectric properties of mixes and raw materials, and the self-reduction process at inert condition can be separated into two stages: raw material pyrolysis and intermediates reduction, which can be explained as the fact that (NH3)4Ru3Cl12 is formed between 301.7 °C and 372.7 °C, and it is further reduced into Ru between 372.7 °C and 430 °C. This work sheds light on a novel process for producing Ru using microwave heating N0, and emphasis the common feasibility of microwave absorbers can successfully improve microwave absorption performance of compounds.

Impact of Thickness and wt% on the Dielectric Properties of Sugarcane Bagasse and MWCNT Composite Material as Microwave Absorber

Impact of Thickness and wt% on the Dielectric Properties of Sugarcane Bagasse and MWCNT Composite Material as Microwave Absorber

Temperature dependent dielectric properties of GeTe-rich (GeTe)x(Sb2Te3)1−x glass

The dielectric properties of phase-change materials, which could switch between crystalline and amorphous states, determine the device performances in the electronic and optical applications. Here, we have systematically investigated the dielectric properties of amorphous (a-) Ge8Sb2Te11 thin films with temperature by two complementary methods, i.e., the AC electrical measurement (0.5–186 Hz) and the impedance spectroscopy (9 kHz–3 GHz). The characterization of dielectric behavior of a-Ge8Sb2Te11 at low frequencies approaching DC, as defined by the static dielectric constants (εst), is achieved by the measurement at very low temperature. The resulting εst of a-Ge8Sb2Te11 is much larger than its optical dielectric constant ε∞ at room temperature, which is mainly ascribed to the contribution of infrared active phonons at around tens of meV. The εst increases linearly by 16.5% from 5 to 300 K, due to more optical phonons activated at elevated temperatures. We also notice that εst shows little dependence on the frequency, and the total conductivity of a-Ge8Sb2Te11 extracted from impedance spectroscopies is frequency independent up to 10 MHz. Hence, no obvious dielectric relaxations are observed in a-Ge8Sb2Te11 below 10 MHz close to room temperature. In addition, the bandgap calculated from temperature dependence of the electrical conductivity is larger than that measured from the optical absorption edge by 11.5%.

Exploration of adulteration in common raw spices using antenna-based sensor

AbstractThe ability of food products to store and dissipate electromagnetic energy is determined by the material's dielectric properties. In relation to this phenomenon, a non-destructive technique is presented for food evaluation based on the shift in resonant frequency and reflection coefficient magnitude value of the proposed slot-loaded microstrip line-fed antenna-based sensor caused by the change in dielectric properties of the food material. In this work, a miniaturized antenna sensor of 10 × 10 mm2 size comprised of a dielectric substrate FR-4 with permittivity (εr) = 4.4 having ground plane at the bottom and a radiating element at the top is designed to operate at 13.3 GHz. Three samples of spices, i.e. red chilli powder, black pepper powder, and turmeric powder, are considered for quality monitoring whose relationship in terms of reflection coefficient, resonant frequency, and dielectric permittivity at 13.17, 12.61, and 13.09 GHz respectively is analyzed. Further, second-order polynomial model is derived to predict dielectric permittivity of the material under test with high accuracy. The experimental procedure of this proposed sensor is based upon the interaction of the sample food materials with the electromagnetic field owing to shift in resonant frequency as a function of dielectric permittivity of the samples. The proposed antenna sensor has a Q-factor of 409, showing significantly high sensitivity of 280 MHz with 98% accuracy and standard deviation less than the difference between unadulterated and adulterated values, giving resolution high enough to distinguish adulteration with an acceptable statistical accuracy.

Design of a high-efficient metamaterial X-band absorber composed of a dielectric cylinder combined with a thin magnetic cylinder unit

High-efficient microwave absorbers (MAs) with excellent absorption performance and lightweight characteristics have important applications in the military and civil. Here, we propose a dielectric-magnetic hybrid microwave absorber composed of a lattice of dielectric cylinders combined with thin magnetic cylinders backed by a perfect electrical conductor ground plane. The dielectric material that is designed as the dielectric cylinder is based on multi-walled carbon nanotubes-epoxy (MWCNT-EP). The MWCNT-EP is prepared and the S-parameters are measured by the standard transmission/reflection (T/R) method. The thin magnetic cylinder is based on a commercial magnetic material with a height of only 1 mm. With the coaction of magnetic loss and dielectric loss, the proposed microwave absorber’s reflection loss is less than −20 dB under normal incident with a total height of 5 mm in the X-band. Besides, the dielectric-magnetic microwave absorber can maintain good absorption performance with different incident angles and polarizations. In this work, we provide a method to combine the properties of magnetic and dielectric material to construct the MA with high-efficient absorption performance.

Synergistic strengthening mechanisms of mechanical activation-microwave reduction for selective lithium extraction from spent lithium batteries

Carbothermal reduction of cathode materials is an effective method to selectively extract lithium carbonate, both mechanical activation and microwave heating can enhance thermal reduction of mixed electrode materials. However, the mechanism of enhanced lithium extraction has not been fully revealed. This study attempts to uncover the synergistic strengthening mechanisms of mechanical activation-microwave reduction from the aspects of material structure, dielectric properties, reduction kinetics and lithium recovery rate. Mechanical activation induces amorphization and structural defects. The enhanced dielectric properties of materials and the induced hotspots/arc plasmas are also responsible for the enhancement of the reduction reaction. The average dissociation activation energy in the activated sample is 18.0 kJ·mol−1, which is 20.3 kJ·mol−1 lower than that of unactivated sample. The model-free method reveals that the carbothermic reduction process can be divided into three stages: (I) initial stage (α < 0.4(0.6)): the activation energy gradually decreases with the formation of strong microwave acceptor-reduction products; (II) transitional stage (0.4(0.6) < α < 0.7): the increase in mass transfer resistance leads to gradual increase in activation energy. Mechanical activation shortens the transitional reaction stage; (III) later reaction stage (α > 0.7), the decrease in activation energy may be attributed to the enhanced microwave absorption and CO reduction. The model-fitting method reveals that after mechanical activation, the reaction kinetic changes from reaction-order model to Ginstling-Brounshtein diffusion model. The optimized lithium extraction process parameters were: activation 300 rpm for 1.5 h, reduction temperature 550 °C. The research results can provide theoretical support for the enhanced extraction of cathode materials.

Research Progress of Polymers/Inorganic Nanocomposite Electrical Insulating Materials.

With the rapid development of power, energy, electronic information, rail transit, and aerospace industries, nanocomposite electrical insulating materials have been begun to be widely used as new materials. Polymer/inorganic nanocomposite dielectric materials possess excellent physical and mechanical properties. In addition, numerous unique properties, such as electricity, thermal, sound, light, and magnetic properties are exhibited by these materials. First, the macroscopic quantum tunneling effect, small-size effect, surface effect, and quantum-size effect of nanoparticles are introduced. There are a few anomalous changes in the physical and chemical properties of the matrix, which are caused by these effects. Second, the interaction mechanism between the nanoparticles and polymer matrix is introduced. These include infiltration adsorption theory, chemical bonding, diffusion theory, electrostatic theory, mechanical connection theory, deformation layer theory, and physical adsorption theory. The mechanism of action of the interface on the dielectric properties of the composites is summarized. These are the interface trap effect, interface barrier effect, and homogenization field strength effect. In addition, different interfacial structure models were used to analyze the specific properties of nanocomposite dielectric materials. Finally, the research status of the dielectric properties of nanocomposite dielectric materials in the electrical insulation field is introduced.

Tuning of dielectric and magnetic performance of graphene oxide via defect regulation by metal oxide nanoparticle for high temperature device

Graphene oxide (GO) is used as a dielectric material in device applications. However, relatively low dielectric constant, high loss, and low working temperature significantly constrain their widespread application. The electrical and magnetic properties of GO can be regulated by using different fillers. Here, we try to regulate the defects of Zinc Oxide ( ZnO) by doping Fe ions and then make composites with GO (GO@ZnO-Fe) towards the increment of the dielectric constant and reduce the loss of GO. The morphology and microstructure characterization of GO composites ensured the enhancement of interlayer cross-links and lateral bridging between the edges of adjacent GO sheets in the presence of ZnO and ZnO-Fe nanofillers. The layered structure of GO produced charge accumulation based on the Maxwell- Wagner (MW) polarization, and after compositing, with ZnO nanofillers, the dielectric constant of GO increases from 350 to 470. But the use of Fe doped ZnO nanofiller increased the maximum dielectric constant to∼ 2240 due to the synergic effect of ZnO and Fe ions. At the same time, the loss is also decreased simultaneously with increasing Fe doping (tanδ =96 for GO and 30 for composite). The dielectric surge occurs at different high temperatures for different composites of GO, and before the surge, the dielectric constants are thermally stable. The conductivity and magnetic properties of the composites increases compared to GO due to the presence of Fe2+/Fe3+ ions. The increase of Fe doping composites displayed thermally stable dielectric properties with a high dielectric constant (7100) and low loss over a broad temperature. Our work demonstrates an efficient method of tuning the dielectric, conductive and magnetic properties of GO-based materials that hold great potential in high-temperature electronic applications.

Frequency-Dependent Dielectric Spectroscopy of Insulating Nanofluids Based on GTL Oil during Accelerated Thermal Aging

Improving the dielectric properties of liquid-insulating materials is a current problem in research into the insulation system of a power transformer. Modern optimization of insulating liquids involves the potential use of unique synthetic esters enriched with nanoparticles. This study presents the results of the dielectric response of liquefied gas-based (GTL) insulating liquids during accelerated thermal aging. The dielectric relaxation spectroscopy method was used in the frequency domain to point out power losses as an imaginary part of a complex electric modulus. The relaxation spectra express the validity of applying this complex dielectric parameter. The polarization processes of the base oil alternately change position in the low-frequency band during thermal aging. Fullerene nanofluid undergoes three phases of dielectric loss changes during thermal aging. In the case of magnetic nanofluid, the effect of electric double-layer polarization disappeared after 500 h of thermal aging. It was found that with the gradual increase in the thermal aging time, there is no gradual increase in the dielectric losses investigated in the measured frequency spectrum. This study shows that the concentration of the two types of nanoparticles independently causes a different dielectric response to an applied AC electric field in the GTL base fluid.

Ab Initio Study of H-Bond Dynamics in Three-Component Crystals Comprising (DABCOH+ )n Polycationic Chains.

In this work, the dynamic character of hydrogen-bond (H-bond) networks in two three-component crystals comprising polycationic chains was described. The first studied system was 1,4-diazabicyclo[2.2.2]octan-1-ium (DABCOH+ ) sulfamate monohydrate, known for its large negative linear compressibility. The second analyzed material was the newly obtained polar salt co-crystal: 1,4-diazabicyclo[2.2.2]octan-1-ium sulfamate urea. X-ray diffraction measurements enabled us to study the H-bond systems in both crystals using the graph set analysis. Obtained structures served as the initial models for Born-Oppenheimer molecular dynamics computations. A detailed study of intermolecular interactions and power spectra was conducted. The analysis of time and space correlations between the changes in H-bonds enabled the detection of proton transfer occurring in both systems at 300 K. Further study of those dynamic phenomena was done using the Energy Decomposition Analysis for selected trajectory fragments. Our work should improve the understanding of dielectric and ferroelectric properties of hybrid organic-inorganic materials.

A study on some physical and mechanical properties of molded thermal insulation materials produced from perlite and boric acid added forestry by-products

ABSTRACT The tree bark and cones are either burned or left in the forest. In both cases, it causes both environmental problems and a significant loss of economic potential. In this study, some physical and mechanical properties of molded thermal insulation materials produced from natural raw materials were investigated experimentally. In this context, 15 types of sandwich panel materials containing honeycomb-shaped core were produced from pine (Pinus brutia Ten.) bark and cones. The mean moisture content, density, compressive strength, tensile strength perpendicular to the surface, tensile strength parallel to the surface, and dimensional stability values of the materials were 10.6%, 269.717 kg/m3, 0.493.06 N/mm2, 0.011 N/mm2, 0.150 N/mm2 and −0.156%, −0.054%, 0.942%, respectively. According to the results, it was determined that the increase in particle size and perlite ratio in the materials produced from the bark decreased the density. Moreover, it was found that the particle size-moisture content relationship and the perlite ratio-moisture content relationship varied in the materials containing bark and cones, that the mechanical properties were higher in the materials containing cones, and that the dimensional stability did not show a regular change.