Preparation and Thermal Shock Resistance of Mullite Ceramics for High Temperature Solar Thermal Storage

Mullite thermal storage ceramics were prepared by low-cost calcined bauxite and kaolin.The phase composition,microstructure,high temperature resistance and thermophysical properties were characterized by modern testing techniques.The experimental results indicate that sample A3(bauxite/kaolin ratio of 5:5)sintered at 1620℃has the optimum comprehensive properties,with bulk density of 2.83 g·cm^(-3)and bending strength of 155.44 MPa.After 30 thermal shocks(1000℃-room temperature,air cooling),the bending strength of sample A3 increases to 166.15 MPa with an enhancement rate of 6.89%,the corresponding thermal conductivity and specific heat capacity are 3.54 W·(m·K)^(-1)and 1.39 kJ·(kg·K)^(-1)at 800℃,and the thermal storage density is 1096 kJ·kg^(-1)(25-800 mullite ceramics;sintering properties;high-temperature thermal storage;thermal shock resistance).Mullite forms a dense and continuous interlaced network microstructure,which endows the samples high thermal storage density and high bending strength,but the decrease of bauxite/kaolin ratio leads to the decrease of mullite content,which reduces the properties of the samples.

Influence of Composition on Properties of Medium Temperature Sintering (Ba,Sr)TiO_3 Series Capacitor Ceramics

The influence of the composition （Yb2O3, MgO, CeO2, Li2CO3） on the dielectric properties of medium temperature sintering （Ba, Sr）TiO3 （BST） series capacitor ceramics was investigated by means of conventional technology process and orthogonal design experiments. The major secondary influencing factors and the influencing tendency of various factor＇s levels for the dielectric properties of BST ceramics were obtained. The optimum formula for maximum dielectric constant （ε） and for minimum dielectric loss （tanδ） was obtained under the experimental conditions. The BST ceramics with optimum comprehensive properties was obtained by means of orthogonal design experiments, with the sintering temperature at 1200 ℃, the dielectric constant 5239, the dielectric loss 0.0097, withstand electric voltage over 6 MV·m^-1, capacitance temperature changing ence of various components on the providing the basis for preparation rate （△C/C） - 75.67%, and suited for Y5V character. The mechanism of the infludielectric properties of medium temperature sintering BST ceramics was studied, thus of multilayer capacitor ceramics and single-chip capacitor ceramics.

Application of response surface method for optimal transfer conditions of multi-layer ceramic capacitor alignment system

The multi-layer ceramic capacitor (MLCC) alignment system aims at the inter-process automation between the first and the second plastic processes.As a result of testing performance verification of MLCC alignment system,the average alignment rates are 95% for 3216 chip,88.5% for 2012 chip and 90.8% for 3818 chip.The MLCC alignment system can be accepted for practical use because the average manual alignment is just 80%.In other words,the developed MLCC alignment system has been upgraded to a great extent,compared with manual alignment.Based on the successfully developed MLCC alignment system,the optimal transfer conditions have been explored by using RSM.The simulations using ADAMS has been performed according to the cube model of CCD.By using MiniTAB,the model of response surface has been established based on the simulation results.The optimal conditions resulted from the response optimization tool of MiniTAB has been verified by being assigned to the prototype of MLCC alignment system.

Side-Chain-Type Polyimide-Cu Complexes with Suppressed Activation Energy of Relaxation for Advanced High-Temperature Capacitor

The burgeoning growth of the new energy vehicles and aviation industry has escalated the need for energy storage capacitors capable of stable operation in harsh environments.The advent of metal-polyimide complexes has illuminated a novel approach for preparing tem perature-resistant capacitors.However,the general application of these metal-polyimide com plexes is impeded by the high dielectric loss and low breakdown strength,consequences of main-chain coordination and excessive metal ions content.Herein,our study proposes a novel polyimideCu complex material(POP-Cu)predicated on side-chain-type pyridine-Cu coordination,utilizing the structural backbone PMDA-ODA of mature commercial PI(Kapton)with reliable performance.Owing to the high degree of freedom afforded by the side chain with suppressed relaxation activation energy and the long-range electron delocalization formed by d-πcoordination,the dielectric constant of this material containing merely 2.7 mol%Cu increases from 3.25(POPI)to 5.58,while maintaining a remarkably low dielectric loss of 0.0066.Meanwhile,this material exhibits a substantial DC breakdown strength of 436.2 MV·m^(-1)and a high energy density of 5.42 J·cm^(-3),coupled with superior mechanical and thermal properties.Even at 150℃,it retains over 90%of its room-temperature energy density,demon strating notable dielectric stability under high temperatures.These attributes underscore its promising application for capacitors operating in harsh environments.

Boosting ultra-wide temperature dielectric stability of multilayer ceramic capacitor through tailoring the combination types of polar nanoregions

With the rapid development of space exploration and new energy vehicles,it is urgent to build ultra-wide temperature multilayer ceramic capacitors(UWT MLCCs)to match electronic circuits that can withstand harsh environmental conditions.Relaxor ferroelectrics with diffuse phase transition feature are potential dielectrics for the construction of UWT MLCCs.However,how to ensure high dielectric constant together with low dielectric loss in the wide temperature region is still a big challenge.Here,the above difficulties are addressed by tailoring the combination types of polar nanoregions(PNRs)in the(1-x)(0.8Na_(0.5)Bi_(0.5)TiO_(3)-0.2K_(0.5)Bi_(0.5)TiO_(3))-xNaTaO3(NBT-KBT-xNT)system.Compared with PNRS types of P4bm+R3c and P4bm+Pbnm,the combination type of P4bm+Pbnm+R3c PNRs in NBT-KBT-0.31NT is the most beneficial to obtain comprehensive excellent dielectric performance because it can balance the relationship between high dielectric constant and temperature stability over a wide temperature region.Further,by optimizing the laminating pressure and co-firing temperature to realize a tight interfacial structure between the dielectric layer and the Pt inner electrode,a record-high dielectric constant(er=(907%±15%))together with low dielectric loss(tan δ≤0.025)is achieved over an ultra-wide range from-61℃ to 306℃ for NBT-KBT-0.31 NT MLCC,demonstrating that tailoring the combination types of PNRs is a powerful strategy in designing UWT MLCC dielectrics.

Dopant Behaviours of Sm_2O_3 on Microstructure and Properties of Barium Zirconium Titanate Ceramics

The effect of Sm 2O 3 dopant on the sintering characteristics and dielectric properties of barium zirconium titanate ceramics (BaZr x Ti 1- x O 3) was investigated. It is shown that trace amount of Sm 2O 3 can greatly affect the grain growth and densification of barium zirconium titanate ceramics during sintering. At the same time, the dielectric peak at high temperature shifts to lower temperature and that at low temperature shifts to higher temperature. The two dielectric peaks overlap with each other when the Sm 2O 3 dopant content varies from 0 25% to 1%, and the maximum relative dielectric constant is greatly enhanced. These effects may be attributed to the substitution actions of the rare earth element in perovskite lattice. At the doping content of 0 75%, the dielectric constant maximum of 23570 can be obtained. By adopting some proper additives, an excellent Y5V dielective material is obtained, and the room temperature properties are as follows: relative dielectric constant ε RT ≥23,000, dielectric loss tgδ≤0 0075 and the breakdown strength under alternating field E b≥5 kV·mm -1 .

Effect of SiO_2 addition on the dielectric properties and microstructure of BaTiO_3-based ceramics in reducing sintering

The effect of SiO2 doping on the sintering behavior, microstructure, and dielectric properties of BaTiO3-based ceramics has been investigated. Silica was added to the BaTiO3-based powder prepared by the solid state method with 0.075mol%, 0.15mol%, and 0.3mol%, respectively. The SiO2-doped BaTiO3-based ceramic with high density and uniform grain size were obtained, which were sintered in reducing atmosphere. A scanning electron microscope, X-ray diffraction, and LCR meter were used to determine the microstructure as well as the dielectric properties. SiO2 can form a liquid phase belonging to the ternary system of BaO-TiO2-SiO2, leading to the formation of BaTiO3 ceramics with high density at a lower sintering temperature. The SiO2-doped BaTiO3-based ceramics can be sintered to a theoretical density higher than 95% at 1220℃ with a soaking time of 2 h. The dielectric constants of the sample with 0.15mol% SiO2 addition sintered at 1220℃ is about 9000. Doping with a small amount of silica can improve the sintering and dielectric properties of BaTiO3-based ceramics.

Wireless contactless pressure measurement of an LC passive pressure sensor with a novel antenna for high-temperature applications

In this paper, a novel antenna is proposed for high-temperature testing, which can make the high-temperature pressure characteristics of a wireless passive ceramic pressure sensor demonstrated at up to a temperature of 600℃. The design parameters of the antenna are similar to those of the sensor, which will increase the coupling strength between the sensor and testing antenna. The antenna is fabricated in thick film integrated technology, and the properties of the alumina ceramic and silver ensure the feasibility of the antenna in high-temperature environments. The sensor, coupled with the ceramic antenna, is investigated using a high-temperature pressure testing platform. The experimental measurement results show that the pressure signal in a harsh environment can be detected by the frequency diversity of the sensor.

Superior energy storage efficiency through tailoring relaxor behavior and band energy gap in KNN-based ferroelectric ceramic capacitors

With the increasing demand of high-power and pulsed power electronic devices,environmental-friendly potassium sodium niobate((Na_(0.5)K_(0.5))NbO_(3),KNN)ceramic-based capacitors have attracted much attention in recent years owning to the boosted energy storage density(W_(rec)).Nevertheless,the dielectric loss also increases as the external electric field increases,which will generate much dissipated energy and raise the temperature of ceramic capacitors.Thus,an effective strategy is proposed to enhance the energy storage efficiency(η)via tailoring relaxor behavior and bad gap energy in the ferroelectric 0.9(Na_(0.5)K_(0.5))-NbO_(3)-0.1Bi(Zn_(2/3)(Nb_(x)Ta_(1−x))1/3)O_(3) ceramics.On the one hand,the more diverse ions in the B-sites owing to introducing the Ta could further disturb the long-range ferroelectric polar order to form the short−range polar nanoregions(PNRs),resulting in the highη.On the other hand,the introduction of Ta ions could boost the intrinsic band energy gap and thus improve the Eb.As a result,high Wrec of 3.29 J/cm^(3) and ultrahighηof 90.1%at the high external electric field of 310 kV/cm are achieved in x=0.5 sample.These results reveal that the KNN-based ceramics are promising lead-free candidate for high-power electronic devices.

Influence of doped Ag^+ on multifunction characteristics in SrTiO_3 ceramics

SrTiO 3 capacitor varistor multifunction ceramics is fabricated by a single sintering process. The research is carried out, mainly aimed at the influence of the doped Ag + on multifunction characteristics in SrTiO 3 ceramics and its mechanism. The results show that the density of grain boundary acceptor state increases effectively due to the fact that Sr 2+ on grain surface is substituted by doped Ag distributing at grain boundary in form of Ag + during the course of oxidizing annealing, which is proposed to be the fundamental reason for understanding the significant difference of both the dielectric properties and varistor properties in SrTiO 3 ceramics samples with various Ag + contents.

Dielectric Properties and Structure of Yb_2O_3-Doped (Ba,Sr)TiO_3 Ceramics

The effect of Yb2O3 doping amount on the dielectric properties of (Ba, Sr)TiO3 (BST) series capacitor ceramics prepared using solid state reaction method were studied. With the increasing of Yb2O3 doping amount, the dielectric constant(ε) of materials increased, the dielectric loss(tanδ) of materials decreased to minimum when w(Yb2O3) was 0.9%. The BST ceramics with high ε(10000), low tanδ(0.0213) and high DC breakdown voltage(7.2 kV·mm-1) were obtained. The influence of Yb2O3 doping amount on the structure of BST ceramics was studied by means of X-ray diffraction(XRD) and scanning electron microscope. The influencing mechanism of Yb2O3 on the dielectric properties of BST ceramics was studied. The results showed that Yb2O3 doping influenced the properties and structure of BST ceramics by means of forming defect solid solution, but did not influence crystal grain size,the crystal phase was single perovskite structure, did not influence XRD data of BST and did not improve capacitance temperature property greatly, but increase dielectric constant greatly. These results provided the basis for Yb2O3-doped BST series capacitor ceramics.

Combustion Synthesis of h-BN-SiC Ceramic Composites

The feasibility was demonstrated to fabricate h-BN-SiC ceramics through combustion synthesis of the mixture of boron carbide and silicon powders under 100 MPa nitrogen pressure. The mass fraction of BN and SiC in the combustion products were found to be 72 % and 28 % respectively. The thermodynamics of the synthesis reaction and the adiabatic combustion temperature were calculated on the theoretical ground. The bending strengths of the ceramics were measured to be 65.2 MPa at room temperature and 55 MPa at 1350℃ The phase composition and microstructure of the combustion products were identified by X-ray diffraction （XRD） and scanning electron microscopy （SEM）.

The multiscale modeling and data mining of high-temperature dielectrics of SiO_2/SiO_2 composites

The high temperature dielectrics of Quartz fiber-reinforced silicon dioxide ceramic （Si02/SiO2 ） composites were studied both theoretically and experimentally. A multi-scale theoretical model was developed based on the theory of dielectrics. It was realized to predict dielectric properties at higher temperature （ 〉 1200 ℃） by experimental data mining for correlative coefficients in model. The results show that the dielectrics of SiO2/SiO2, which were calculated with the theoretical model, were in agreement with experimental measured value.

Strength Acquisition Mechanism of High Temperature Resistant Materials Prepared by Waste Architectural Ceramics

In order to realize the large-scale and high-value utilization of waste architectural ceramics,high-temperature resistant materials based on waste architectural ceramics were prepared with sodium silicate as the binder,clay/bauxite and metakaolin/bauxite as coating materials,and the cold strength obtaining mechanism was explored.The phase composition,the microstructure and the mechanical properties of the high temperature resistant materials based on waste architectural ceramics were tested and analyzed.The results showed that when the heat treatment temperature was between 110-1000℃,the strength of the samples mainly came from the physical adhesion of sodium silicate and fine powder.When the temperature rose to 1100℃,the strength of the sample was improved since the internal low-melting-point components melted and promoted sintering.The addition of clay and bauxite can effectively enhance the flexural strength of the samples when the heat treatment temperature is 1000℃.When the heat treatment temperature rises from 900 to 1000℃,the flexural strength of the samples will be enhanced owing to the formation of silica alumina spinel and mullite from metakaolin.

The research of feet pressing energy collection and utilization device --based on piezoelectric ceramics

After people or vehicles press, piezoelectric ceramics can send a weak and unstable alternating current. According to this characteristic, we made feet pressing energy collection and utilization device based on piezoelectric ceramics. The two parts of this device includes energy storage and utilization. In terms of storage, the energy collection module, can deposit AC sent by piezoelectric ceramics in the super capacitor after rectification. In terms of utilization of energy, the device achieve a variety of usage： through the USB interface, it can supply power for different equipments, replace the mobile station of train stations and realize the function of saving the electricity as the night corridor induction lamp, combined with vibration module design and programmable timer. The whole structure is supported by an acrylic plate, which saves cost and have good durability. This device implements the storage and usage of idle feet pressing energy. In conclusion, it is helpful to provide a new idea for people＇ s low carbon lives and has a quite broad application prospect.

Foam-gelcasting preparation of porous Si C ceramic for high-temperature thermal insulation and infrared stealth

Porous SiC ceramics(PSCs)are promising lightweight and efficient thermal insulators that can evade infrared detection by reducing the surface temperature of the protected object,which plays a crucial role in the development of new military equipment.However,the controllable synthesis of PSCs with both hierarchical pore structure and thermal/mechanical stability remains challenging.In this work,such PSCs were prepared by a facile foam-gelcasting/solid-state reaction method,using silicon powders and glucose-derived carbon as starting materials.The favorable dispersibility and wettability of hydrophilic carbon microspheres and the in-situ formed SiC guarantee the highly porous structure(92.8%porosity),comparable bulk density(0.20 g·cm^(-3))and reasonable mechanical property of the product.The designed PSCs performed outstanding high-temperature performance,especially thermal insulation in both oxidizing and inert atmospheres.More importantly,the composite architecture of PSCs and low emissivity layer(Al foil)exhibited desirable infrared stealth property(at a temperature up to 1100℃),significantly extending the operating temperature range of thermal camouflage material.The unique combination of excellent properties would make PSCs a potential candidate material for future thermal protection and infrared stealth applications in an extreme environment.

Unusual local electric field concentration in multilayer ceramic capacitors

Local electric-field around multitype pores(dielectric pore,interface pore,electrode pore)in multilayer ceramic capacitors(MLCCs)was investigated using Kelvin probe force microscopy combined with the finite element simulation to understand the effect of pores on the electric reliability of MLCCs.Electricfield is found to be concentrated significantly in the vicinity of these pores and the strength of the local electric-field is 1.5e5.0 times of the nominal strength.Unexpectedly,the concentration degree of the pores in the inner electrode is much higher than that in the dielectrics and dielectric-electrode interfaces.Meanwhile,geometry orientations are found to have a remarkable influence on the local electric field strength.The pores act as an insulation degradation precursor via local electric,thermal center,and oxygen vacancies accumulation center.Such unusual local electric field concentration of multitype pores can provide new insights into the understanding of insulation degradation evolution,processing tailoring and design optimization for MLCCs.

高压陶瓷电容特性及在配网柱上开关的应用研究

电压传感器是深度融合型柱上开关的关键器件,其自身直接承受电压载荷,是深度融合柱上开关产品开发成败的关键。以无机物介质为载体的高压陶瓷电容器,具有体积小、容量大、寿命长的特点,尤其契合深度融合型固封极柱的结构特点和应用场景。文中首先分析了陶瓷电容器件特性,再结合深度融合柱上开关产品的具体应用场景,开发了基于高压陶瓷电容器的一二次融合柱上开关产品;相关研究表明,高压陶瓷电容器在配网领域应用具有相当潜力。

BaTiO_(3)基超薄层BME MLCC的可靠性机理

多层陶瓷电容器(Multilayer ceramic capacitors,MLCC)作为市场占有率最高的无源电子元器件,是基础电子元件产业中需要突破关键技术的重点产品之一,在汽车电子、5G通讯、电网调频、航空航天等领域有广泛的应用。在小型化、薄层化发展趋势下,MLCC的介质层厚度不断降低,单层介质在相同电压下的电场显著增大,尤其是中高压超薄层MLCC。因此,MLCC的可靠性愈发成为一项关键的产品质量指标。本文结合加速老化测试、高温阻抗谱、漏电流测试,系统研究超薄层MLCC的劣化机理,揭示抑制氧空位的迁移与富集是保证超薄层MLCC可靠性的重中之重。为此,应减小介质层内部的氧空位浓度,增大其迁移所需的激活能,提高界面肖特基势垒,从而提升超薄层MLCC的可靠性。本文的研究成果为超薄层MLCC介质材料的设计提供了有力指导。

陶瓷电容器在电力电子应用中的性能优化研究

笔者深入研究了陶瓷电容器在电力电子应用中的性能优化方法,以提高其在现代电子设备中的关键性能。从材料选择与优化、结构设计优化、温度稳定性改进、降低漏电流以及寿命和可靠性改进等多个方面探讨了相关方法。通过精心选择陶瓷材料、改进结构设计、控制漏电流和优化温度稳定性,可以显著提高陶瓷电容器的性能和可靠性,从而满足不断变化的电子设备需求,推动电力电子技术的不断进步。