85 results about "Interfacial polarization" patented technology

The invention discloses a frequency-domain dielectric theory-based evaluation method for evaluating the insulation aging state of the oiled paper of a transformer. According to the method, the transformer is cooled and short-circuited. Then the changing curve of the real part and the imaginary part of a complex dielectric constant along with the frequency is obtained via the domain spectrometry means based on the frequency-domain dielectric theory. After that, a polarized dual-relaxation model is adopted and the damage conditions of two principal polarization modes, namely the interfacial polarization and the ionic polarization, to an oiled paper insulating system can be respectively represented through the front and back portions of the model. Finally, characteristic parameters obtained through calculation are compared with the standard values of the characteristic parameters. Through the above five steps of the method, the state of the oiled paper insulating system of the transformer can be effectively diagnosed, so that the invention provides an advanced, lossless and non-destructive detection method. The method can be used for evaluating and diagnosing the insulating state of the oiled paper insulating system of an oil-immersed transformer that is put to use for a long time. Therefore, the safety operation of the power grid is ensured.

The invention discloses a preparation method of a graphene/Fe3O4/polyaniline ternary wave-absorbing composite material, and relates to the technical field of ternary composite conductive material production. The method is characterized in that a process using aniline monomer to directly reduce graphene oxide is used, and the coordination interaction of the graphene oxide and Fe3O4 is used to prepare the graphene/Fe3O4/polyaniline ternary composite material, so that the goal of greenization of the nano composite material preparation and compounding and refinement of the wave-absorbing material structure can be realized. In the composite material, polyaniline organically wraps the surface of the compound of Fe3O4 and graphene to form a specific layer-by-layer assembled structure. The specific surface area is greatly increased by the laminated graphene sheets, and more interfacial polarization and interfaces are caused by the layered structure and the core-shell structure. The prepared ternary composite material is capable of realizing impedance matching and is beneficial to the attenuation effect of electromagnetic waves by the additional interfacial polarization and multiple interfaces caused by the layer-by-layer assembled structure.

Disclosed herein is a polymer-ceramic dielectric composition. The dielectric composition comprises a polymer and a ceramic dispersed in the polymer wherein the ceramic is composed of a material having a perovskite structure represented by ABO₃ and a metal oxide dopant and has an electrically charged surface. According to the dielectric composition, the surface of the ceramic is electrically charged to induce space-charge polarization (or interfacial polarization) at the polymer/ceramic interface, resulting in an increase in dielectric constant. Since the dielectric composition has a high dielectric constant particularly in a low-frequency range, it can be suitably used to produce decoupling capacitors. Further disclosed are a capacitor and a printed circuit board that use the dielectric composition.

The invention relates to a heating modified MXene/ferroferric oxide composite wave-absorbing material and a preparation method thereof. Magnetic ferroferric oxide particles (Fe3O4) are grown in situ on the surface of a two-dimensional material MXene (Ti3C2Tx), and the MXene is heated in a tubular furnace to be partially oxidized into titanium dioxide (TiO2) to finally obtain the layered compositematerial. MXene and TiO2 are dielectric loss wave-absorbing materials, and Fe3O4 is a magnetic loss wave-absorbing material, so that the obtained composite material can synergistically absorb electromagnetic waves through dielectric loss and magnetic loss mechanisms, and the wave-absorbing effect is enhanced. Meanwhile, the composite material has a layered structure, so that electromagnetic wavescan be subjected to multiple interlayer reflection in the composite material and are more easily absorbed by the composite material. And finally, the impedance matching of MXene is improved by Fe3O4 and TiO2, the interfacial polarization of the composite material is enhanced by the multi-component structure, and the wave absorbing effect of the composite material is further enhanced.

The invention discloses a nano-particle composite wave-absorbing material with a double-shell microstructure so as to solve the defect that absorption frequency bands of the current wave absorbing materials are narrow. The nano-particle composite wave-absorbing material is characterized in that the composite wave-absorbing material is in a double-shell microstructure, an external shell is made of dielectric oxides, an internal shell is made of carbon, and an inner core is made of ferromagnetic materials. The nano-particle composite wave-absorbing material has the advantages that gradual impedance gradation is generated through the structural change of dielectric oxide shell-carbon shell-magnetic metal particle core, so that electromagnetic waves can maximumly transmit into the material, and the reflection of the electromagnetic waves is lowered; besides, the characteristics of resistance loss, dielectric loss and magnetic loss of the composite material, and ample interfacial polarization in the double-shell microstructure are utilized, so that the electromagnetic waves entering into the interior of the material rapidly attenuate. The composite material has the advantages of small density and wide frequency bands. The composite material has a wide application prospect in electromagnetic shielding, electrorheological fluids, functional coatings and the like.

The invention provides a high-thermal-conductivity wave-absorbing graphene composite film prepared from polyimide (PI) films, and a preparation method of the graphene composite film. The preparation method comprises the steps that multiple layers of the PI films are stacked up; then carbonization and graphitization are carried out; and a wave-absorbing agent is added in the carbonization and graphitization process for composition, and thus the graphene composite film is obtained. The graphene composite film comprises graphene and the wave-absorbing agent scattered among graphene layers. The wave-absorbing agent is added in the process that the PI films are carbonized and graphitized to be transformed into the graphene, so that the wave-absorbing agent is scattered among the graphene layers; through the wave-absorbing agent, electromagnetic waves are converted into heat energy so as to be dissipated; through the special structure of the graphene and the effects such as interfacial polarization and electron relaxation polarization which are caused by composition of the graphene and the wave-absorbing agent, the electromagnetic waves are dissipated; and thus, the graphene composite film becomes an electromagnetic shielding material with multiple electromagnetic loss mechanisms. Meanwhile, the graphene composite film rapidly conducts heat outwards by the excellent thermal conductivity thereof, thereby having good heat dissipation performance.

The invention belongs to the field of composite material preparation, and relates to a preparation method for resin matrix composite materials, in particular to a preparation method for a microwave dielectric ceramic/resin bicontinuous composite material for a PCB substrate. The method aims at solving the technical problems that a ceramic/resin composite material obtained through an existing method has a low dielectric constant and large dielectric losses. The preparation method comprises the steps of 1, preparing a sizing agent; 2, preparing a porous ceramic green body with directional holes; 3, preparing a porous microwave dielectric ceramic preform body; 4, pouring resin at the temperature ranging from minus 20 DEG C to the normal temperature into a mold, conducting vacuumizing until the molten resin completely enters the porous microwave dielectric ceramic preform body, and conducting solidification to obtain the microwave dielectric ceramic/resin bicontinuous composite material. Due to the fact that the specific surface area of the porous microwave dielectric ceramic preform body is much smaller than the specific surface area of powder, interfacial polarization is lowered, and dielectric losses are lowered; in addition, the composite materials of different ceramic contents can be obtained according to the material requirement, and the dielectric constant is adjustable.

The invention discloses a magnetic carbon nanofiber aerogel wave-absorbing material, which includes carbon nanofibers and magnetic nanoparticles. The magnetic nanoparticles are dispersed on the carbonnanofibers. The carbon nanofibers are carbon nanofibers pyrolyzed by a biomass material, have fiber diameters of 30 to 50 nm and an aspect ratio of 1000 to 3000. The magnetic carbon nanofiber aerogelwave-absorbing material provided by the present invention has a high aspect ratio, and has a porous network structure formed therein by staggered fibers so as to contribute to the construction of a conductive network under low fillers, and obtain the best wave-absorbing performance under low fillers. Further, the porous network structure filled with low fillers and formed by the staggered fibersprovides the magnetic carbon nanofiber aerogel wave-absorbing material with light and flexible features, improves the application value of the wave-absorbing material. In addition, the wave-absorbingmaterial has strong interfacial polarization and magnetic loss so as to contribute to the loss of incident electromagnetic waves.

The invention belongs to the technical field of preparation of composites and relates to the preparation of lightweight porous structural microwave-absorbing material, in particular to a preparation method of lightweight porous nickel ferrite/carbon aerogel wave-absorbing material, comprising: extracting fibers from waste pericarps, lyophilizing, carbonizing at high temperature to obtain carbon aerogel, subjecting the carbon aerogel to hydrothermal reaction with nickel ferrite nano crystal at 150-200 DEG C for 7-16 h, and compositing. The wave-absorbing material prepared herein features largespecific surface area, small density, large porosity, good conductivity and good magnetism at the premise of retaining nickel ferrite magnetic effect, is capable of greatly absorbing electromagnetic wave under wide frequency by means of resistance loss, electromagnetic loss, interfacial polarization loss and multi-step reflecting absorption, has a minimum reflection loss of -20 dB to -50 dB duringuse, and has effective wave-absorbing bandwidth of 2 dB to 4 dB. The lightweight porous nickel ferrite/carbon aerogel wave-absorbing material prepared herein is widely applicable to radar hiding, electromagnetic interference shielding, microwave dark rooms and other fields, and has the advantages of wide range of source and low cost.

The invention provides a preparation method for a dielectric material with a high dielectric constant. The preparation method comprises the steps of uniformly mixing a thermosetting resin prepolymer,a curing agent, a thermoplastic polymer and a solvent, then, adding an inorganic filler and a dispersant, carrying out further uniform mixing, then, coating a substrate with the mixture, carrying outbaking and curing, and removing the solvent through volatilization. The thermosetting resin prepolymer cures, the compatibility of the thermoplastic polymer in the thermosetting resin becomes poor along with the curing of the thermosetting resin and is separated out from a continuous phase of the thermosetting resin to form a non-uniform two-phase structure and a microphase separating system, theinterface is polarized, and thus, the dielectric constant can be greatly increased.

The invention discloses a light-emitting diode epitaxial wafer and a manufacturing method thereof, which belong to the technical field of semiconductors. The epitaxial wafer comprises a substrate, a buffer layer, an un-doped gallium nitride layer, an N-type gallium nitride layer, a multi-quantum well layer, an electron barrier layer and a P-type gallium nitride layer, wherein the multi-quantum well layer comprises multiple quantum wells and multiple quantum barriers; the multiple quantum wells and the multiple quantum barriers are arranged in an alternately-stacked mode; the quantum well is an indium gallium nitride layer; the multi-quantum well layer also comprises at least one graphene film layer; each graphene film layer is arranged between the quantum well and the adjacent quantum barrier respectively; and when the number of graphene film layers is larger than one, at least one quantum well or at least one quantum barrier is arranged between adjacent two graphene film layers. The effective doping of indium in the quantum well can be improved, high temperature can be adopted to grow the quantum well, the quantum well growth quality is improved, interfacial polarization is improved, and the light-emitting efficiency of the light-emitting diode is improved.

The invention relates to the technical field of nano-compositing, and aims to provide a high-dielectric-constant full-organic composite hydrophobic material and a preparation method thereof. The high-dielectric-constant full-organic composite hydrophobic material is prepared in the mode that polydimethylsiloxane and poly (vinylidene fluoride-trifluoroethylene) which serve as a matrix and polystyrene microspheres serving as a filling material are blended and spin-coated; and in the matrix, the mass ratio of the polydimethylsiloxane to the poly (vinylidene fluoride-trifluoroethylene) is 2 to 3,and the filling material accounts for 5-30 wt% of the total mass of the full-organic composite hydrophobic material. The interfacial polarization effect can be enhanced by adding the nano polystyrenemicrospheres into the polymer matrix, the micro-rough surface is constructed, the dielectric constant of a composite is increased, and the excellent hydrophobic performance is kept. The preparation technology is simple, and operability and repeatability of the method are high. By adjusting the adding content of PS, dielectric performance, hydrophobic performance and the like of the composite can be adjusted and controlled, and meanwhile, the flexibility performance is good due to pure organic matter compounding.

The invention relates to the technical field of nanocomposite materials and aims to provide a silicon dioxide/magnesium oxide/polymer dielectric and hydrophobic composite material and a preparation method. The dielectric and hydrophobic material is prepared from polymethyl methacrylate as a polymer matrix and magnesium oxide coated with a silicon dioxide shell as a filling material by blending andtape casting, wherein the filling material accounts for 10%-40% of the total mass of the dielectric and hydrophobic material and adopts silicon dioxide as the shell and flaky magnesium oxide as the core. The silicon dioxide/magnesium oxide/polymer dielectric and hydrophobic composite material and the preparation method have the following advantages: interfacial interaction areas between inorganicparticles as well as between the inorganic particles and a polymer can be increased, the interfacial polarization effect is enhanced, the dielectric constant of the composite material is increased, and the surface hydrophobicity is improved. The preparation process is simple, and the method is high in operability and repeatability. Dielectric, thermal and hydrophobic properties of the composite material can be regulated and controlled by regulating the adding content of inorganic filler, and the composite material can be applied to manufacturing of capacitors, electrowetting displays and other devices and has broad development prospect.

The invention relates to a nanometer composite material technology and aims to provide a titanium dioxide/polymer composite dielectric hydrophobic material and a preparation method thereof. The dielectric hydrophobic material is prepared by taking polydimethylsiloxane as a polymer matrix and taking titanium dioxide nanowire as a filling material through a blending and spin-coating process, whereinthe filling material accounts for 5 to 30 percent of the total mass of the dielectric hydrophobic material. In the titanium dioxide nanowire prepared by a hydrothermal method, the diameter is about 100 nanometers and the length is about 8 microns. A composite film with uniformly dispersed titanium dioxide can be prepared by applying the titanium dioxide nanowire to a solution blending and spin-coating process. The titanium dioxide nanowire with high length-to-diameter ratio can increase the interaction area of the inorganic filler/polymer interface, the interfacial polarization effect is enhanced, the dielectric constant of the composite material is increased, and low dielectric loss and excellent surface hydrophobic performance are maintained. The preparation process is simple and the method is high in operability and high in repeatability.

The present invention discloses a triiron tetraoxide/polypyrrole/polyaniline nanometer complex and a preparation method thereof, wherein the triiron tetraoxide/polypyrrole/polyaniline nanometer complex comprises a triiron tetraoxide core layer, a polypyrrole layer wrapped around the periphery of the triiron tetraoxide core layer, and a polyaniline layer wrapped around the periphery of the polypyrrole layer. According to the present invention, the triiron tetraoxide (Fe3O4)/polypyrrole (PPy)/polyaniline (PANI) nanometer complex has excellent microwave absorbing ability, and is superior to the existing similar complexes in the prior art; and the large-scale electric conduction network is established in the system by introducing the multilayer electric conduction polymer so as to substantially reduce the resistivity, and the interfacial polarization is introduced through the wrapping between different mediums so as to improve the impedance matching, such that the wave absorbing effect of the system is substantially enhanced.

The invention relates to the field of polymer composite materials, in particular to a polypropylene/ nickel plated glass fiber/ titanium dioxide composite material and a preparation method thereof. The composite material is prepared from 85.0-92.0% of polypropylene, 7-14.0% of nickel plated glass fibers and 0.5-1.0vol% of titanium dioxide. According to the polypropylene/ nickel plated glass fiber/ titanium dioxide composite material, the titanium dioxide and the nickel plated glass fibers serve as binary filler for conducting functional improvement on polypropylene; the structural features that the glass fibers are large in length-diameter, and lap joint is easy to conduct are utilized, continuous distribution and network construction of a wrapping nickel layer in the polypropylene are achieved, a conductive path is formed under an extremely low metallic nickel content, and the electric conduction performance is provided for the polypropylene; meanwhile the characteristics of high dielectric constants and dipolar polarization effect of the titanium dioxide are utilized, nanometer TiO<2> particles are added to a polymer, electromagnetic waves are attenuated through the interfacial polarization action, and the electromagnetic shielding property of the composite material is improved.

The invention relates to the technical field of power cable aging evaluation, and particularly discloses a nuclear-grade power cable aging degree diagnosis method. The method specifically comprises the following steps: 1, carrying out a polarization-depolarization current test on a to-be-diagnosed cable to obtain a polarization current and a depolarization current of the to-be-diagnosed cable; 2,acquiring the interfacial polarization charge quantity of the cable to be diagnosed; and 3, obtaining an aging degree diagnosis result of the cable according to the interface polarization charge quantity. According to the method, the characteristic that the more serious the aging is, the more obvious the interfacial polarization phenomenon is can be utilized, so that the overall aging condition ofcable insulation is judged, meanwhile, no damage is caused to the insulation due to lower test voltage, the degree of influence of irradiation aging factors on the state of XLPE insulation is evaluated, and the aging degree of the XLPE insulation is analyzed.

The invention discloses a magnetoelectric aerogel. The aerogel is prepared from the following raw material components in percentage by mass: 15%-85% of CoFe2O4 and 15%-85% of rGO based on the total mass of a wave-absorbing material. A rod-like FeCo-MOF precursor is synthesized, and is subjected to gelation with graphene oxide, CoFe2O4/rGO composite aerogel is obtained through heat treatment in the atmosphere of nitrogen, argon or helium, and CoFe2O4 particles are embedded into a three-dimensional framework of reduced graphene oxide, so that the magnetic loss capacity of the material is improved, interface polarization relaxation loss is provided by an interface of the reduced graphene oxide, and the aerogel shows good microwave absorption performance. The prepared aerogel with the magnetic dielectric property has large reflection loss and absorption bandwidth, the preparation method is simple, raw materials are easy to obtain, and repeatability is good.

The invention provides a microwave absorbing material. The molecular formula of the microwave absorbing material is Bi(0-0.3)La(0.7-1)FeO3. The microwave absorbing material provided by the invention has multiple polarizations, which include space charge polarization, dipole polarization and interface polarization, the dielectric loss of the material is reduced, meanwhile, a large number of irregular micropores exist in the material, the pore size distribution is narrow, multiple reflection channels exist, when electromagnetic waves are emitted into the material, the electromagnetic waves are reflected and scattered multiple times in the material, larger electromagnetic wave attenuation is caused, and then the purposes of reducing the thickness of the material and achieving excellent wave absorbing performance are achieved. Experimental results show that the microwave absorbing material provided by the invention can absorb electromagnetic waves in a microwave band of 2-18GHz, the absorption efficiency is greater than 90%, and excellent microwave absorbing performance can be obtained within 1.6-2.0mm thickness.

The invention discloses a method for evaluating the oil paper insulation aging state of a converter transformer, which belongs to the technical field of converter transformer operation and maintenance. The method comprises the following steps of: obtaining polarization and depolarization current initial data of an oil paper insulation test sample through a micro-current sampling system; calculating an oil-paper composite insulation interface polarization attenuation current, performing differential transformation to obtain a time domain dielectric response function dielectric spectrum curve, extracting a double-peak branch polarization charge quantity Q (t), relaxation time tau n and a branch shape parameter alpha n, fitting main relaxation time and an oil-paper polymerization degree valueto obtain a fitting curve, obtaining the oil paper polymerization degree of the actual converter transformer according to the differential time domain spectrum main relaxation time of the actual converter transformer, and evaluating the aging state of the oil paper insulation structure of the converter transformer. The problem that a polarization depolarization current method cannot be directly and accurately used for evaluating the oil paper insulation aging degree of a complex transformer oil paper insulation system is solved.

The invention belongs to the technical field of gas sensors, and provides a hydrogen sensor of a gallium nitride-based high electron mobility transistor. A source electrode, a drain electrode and a Pd/Pt layer are respectively evaporated on the surface of a gallium nitride-based material. When hydrogen is adsorbed on a Pd/Pt layer and decomposed into hydrogen atoms to be transmitted to an interface, an electric field generated after the hydrogen atoms are subjected to interface polarization adsorption causes surface longitudinal charge change, then the two-dimensional electron gas concentration at a heterojunction interface is modulated, the output current of a source electrode and a drain electrode is changed, and therefore hydrogen concentration is tested. The preparation method is advantaged in that operation is simple, the prepared hydrogen sensor is good in stability, low in cost and the like, the prepared hydrogen sensor is good in quality, good performance can be kept, the hydrogen sensor can be tested in a loose humidity environment, and the output of the hydrogen sensor cannot be influenced. The preparation environment condition requirement is simple, and stable preparation can be realized.

The invention discloses a method for preparing a wave absorption material. The method comprises the following steps: preparing a graphene oxide dispersion liquid, preparing an intermediate state composite material, and performing material preparation. Due to effective compounding of graphene, tin dioxide and ferric oxide, the interfacial polarization property of the material is improved, under thesynergetic effect of magnetic consumption and dielectric consumption, the impedance matching and the attenuation matching of the composite material are improved, and furthermore the microwave absorption property of the material is improved.