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1.
随着电力电子系统的不断发展,高功率脉冲电容器的需求增多。电介质电容器因具有放电功率大、充放电速度快及性能稳定等优点,在电力系统、电子器件、脉冲电源等方面发挥着重要作用,广泛应用于民用领域及军事领域。通过熔融压延制备玻璃基体,采用可控结晶工艺研究了不同含量的Bi2O3 (x=0.0%、1.0%、2.0%、4.0%,摩尔分数)对K2O–B2O3–Sr O–Al2O3–Nb2O5–SiO2玻璃陶瓷物相演化、微观结构、介电和储能性能的影响。在该玻璃陶瓷中,KSr2Nb5O15为主要析出晶相,当Bi2O3的加入量为x=2.0%(摩尔分数)时,热处理温度为950℃时,玻璃陶瓷样品的储能密度最大可达到1.27 J/cm3,室温下介电常数可达342,是热处... 相似文献
2.
Multiferroic ceramics in BaO–Y2O3–Fe2O3–Nb2O5 system were synthesized and their dielectric, ferroelectric and magnetic properties were evaluated. XRD results showed that the ceramic composite consists of a major phase of tetragonal tungsten bronze structured Ba2YFeNb4O15, and minor phases of monoclinic YNbO4 and hexagonal Ba3Fe2Nb6O21. Three dielectric relaxations were observed in the temperature range from 125 to 575 K. The relaxor dielectric behavior in the temperature range from 125 to 350 K was attributed to the random occupation of Fe3+ and Nb5+ ions at B site of the tungsten bronze structure. The electrode polarization and the inhomogeneous structure contributed to the high-temperature and middle-temperature dielectric relaxations, respectively. Both the ferroelectric hysteresis loop and the magnetic hysteresis loop were measured, which suggested that the synthesized ceramic composite was a promising candidate of multiferroics. 相似文献
3.
采用固相法制备不同摩尔 Ba、Sr、Ca、Mg 配比的 Ba O–Sr O–Ca O–Mg O–Al2O3–SiO2 (BSCMAS)陶瓷材料,研究多组元陶瓷的制备工艺、显微结构及其抗 CMAS 腐蚀性能。结果表明:通过调控 MgO 的含量,在 1 400 ℃条件下制备了Ba0.3Sr0.3Ca0.35Mg0.05Al2Si2O8 (B0.3S0.3C0.35M0.05AS)单相多组元陶瓷材料。在 1 250、1 300 ℃和 1 350 ℃对 B0.3S0.3C0.35M0.05AS 进行 CMAS 腐蚀实验,相比于 Ba0.5Sr0.5Al 相似文献
4.
Many different types of glass and ceramic wasteforms have been investigated for nuclear waste immobilization. This study deals with synthesizing composite wasteforms based on a parent glass belonging to the SiO2–PbO–CaO–ZrO2–TiO2–(B2O3–K2O) system with the use of zircon as a second component. The fabrication involves powder mixing, pressing and pressureless sintering. The processing conditions were investigated so as to achieve the highest density and the best sintering temperature for different amounts of zircon, i.e. 5, 10 and 15 wt%. The sintered products were studied by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM); as well as ICP-MAS for leaching experiments. The most promising composite containing zirkelite and titanite crystals in a lead-rich glassy matrix was obtained at 700 °C for 10 wt% zircon. 相似文献
5.
In order to obtain high-strength anorthite glass-ceramics, K2O–CaO–Al2O3–SiO2 quaternary glass and relevant glass-ceramics were prepared and investigated. The results show that anorthite along with kalsilite or leucite was precipitated from the parent glass. Kalsilite crystals were formed firstly and then converted into leucite through reacting with SiO2 in the glass phase. The morphology of the crystals was dependent on the heat-treatment temperature. Column crystals were transformed into fine granular grains when the sintering temperature changed from 900 °C to 1100 °C. The activation energy (Eα) and avrami constant (n) were also calculated as 463.81 KJ/mol and 3.74 respectively, indicating that bulk nucleation and three-dimensional crystal growth were the dominating mechanisms in the temperature range 1000–1100 °C. The maximum value of the flexural strength for the glass-ceramics containing leucite was 248 MPa and the coefficient of thermal expansion (CTE) was in the range 5.69~11.94×10−6 K−1. The leucite is the main reason for the high CTEs and high flexural strength of glass-ceramics. 相似文献
6.
The AC conductivity of glass samples of composition 60V2O5–5P2O5–(35−x)B2O3–xDy2O3, 0.4≤x≤1.2 has been analyzed. The samples were prepared by the usual melt-quench technique. The prepared compounds were analyzed by X-ray diffraction (XRD) and thermo gravimetric–differential thermal analysis (TG/DTA). The activation energies were evaluated using glass transition temperature (Tg) and peak temperature of crystallization (Tc) from TG/DTA. The dependence of activation energy on composition was discussed. The electrical conductance and capacitance were measured over a frequency range of 20 Hz to 1 MHz and a temperature range of 303–473 K; these reveal semiconducting features based predominantly on an ionic mechanism. The dielectric and complex-impedance response of the sample is discussed. The relaxation time was found to increase with increasing temperature. Jonscher's universal power law is applied to discuss the conductivity. The electrode polarization was found to be negligible and confirmed from electrical modulus. 相似文献
7.
Glasses of the composition 19Li2O–20PbO–20B2O3–30SiO2–(10−x) Bi2O3–1Fe2O3: xIn2O3 with six values of x (0 to 5.0) were synthesized. Dielectric properties viz., dielectric constant, ε′(ω), loss, tan δ, ac conductivity, σac, electric modulus, M(ω) over wide ranges of frequency and temperature and also dielectric break down strength have been studied as a function of In2O3 concentration. The temperature dispersion of real part of dielectric constant, ε′(ω) has been analyzed using space charge polarization model. The dielectric loss (and also the electric moduli) variation with frequency and temperature exhibited relaxation effects and these effects were attributed to the divalent iron ion complexes. The ac conductivity exhibited maximal effect, whereas the activation energy for the conductivity demonstrated minimal magnitude at about 1.0 mol% of In2O3. The conductivity mechanism is understood due to the polaronic transfer between Fe2+ and Fe3+ ions. The low temperature ac conductivity mechanism is explained following the quantum mechanical tunneling model. Spectroscopic studies viz., optical absorption and ESR spectra have revealed that the redox ratio (Fe2+/Fe3+) is maximal when the concentration of In2O3 is ~1.0 mol%. The higher values of dielectric parameters observed at 1.0 mol% of In2O3 are attributed to the presence of iron ions largely in divalent state and act as modifiers. The analysis of these results together with spectroscopic studies has indicated that when In2O3 is present in the glass matrix in higher concentrations (more than 1.0 mol%) iron ions predominantly exist in trivalent state, occupy substitutional positions and make the glass more rigid. Such enhanced rigidity of the network is causing the decrease of dielectric parameters with the concentration of In2O3. Finally it is concluded that In2O3 mostly participate in the glass network in octahedral positions and make act as reducing agent (for iron ions) in the studied glass matrix when its concentration is ≤1.0 mol%. 相似文献
8.
The mechanochemical behavior of TiO2–B2O3–Mg–Al quaternary system to synthesize various composite nanopowders was studied. A mixture of boron oxide and titanium dioxide powders along with different amounts of magnesium and aluminum was milled using a high-energy planetary ball mill to persuade necessary conditions for the occurrence of a mechanically induced self-sustaining reaction (MSR). Results showed that the formation of composite nanopowders was influenced strongly by the reducing agents content. In the absence of Al (100 wt% Mg), TiB2 nanopowder was formed after 34 min of milling. In the presence of x wt% Mg–y wt% Al (x=40 and 70; y=100−x), mechanical activation was completed after 37–40 min which caused the formation of TiB2–MgFe0.6Al1.4O4 composite nanopowders. In the case of 10 wt% Mg–90 wt% Al, a ternary nanocomposite (TiB2–MgAl2O4–Al2O3) was produced after 43 min of milling. Besides, Al2O3–TiB2 nanocomposite was formed after 90 min of milling in the absence of Mg (100 wt% Al). From the SEM images, mechanochemical process reached a steady state after short milling times where the particles have become homogenized in size and shape. The reaction mechanism steps were proposed to clarify the reactions occurring during mechanochemical process. 相似文献
9.
Based on local raw materials, a range of LiZnMg aluminosilicate glasses were prepared to investigate the influence of TiO2, Cr2O3, and ZrO2 on the crystallization behaviour and thermal expansion characteristics. Differential thermal analysis showed that the crystallization propensity increases in the order TiO2 > Cr2O3 > ZrO2. Virgilite, β-spodumene ss, gahnite, enstatite and cristobalite were formed in the prepared glass-ceramics. The microstructure of glass-ceramic samples showed growths of rounded and subrounded grains in the base sample, whereas, somewhat rod-like and accumulated growths appeared in samples containing ZrO2. However, a rather homogeneous texture of accumulated growths was developed in glass-ceramics containing TiO2 and Cr2O3. The coefficient of thermal expansion of parent glasses was sensitive to the type of nucleating agent added (Cr2O3 > TiO2 > ZrO2) varying from 24.8 × 10−7 to 65.1 × 10−7 °C−1 being almost unchanged with the heat-treatment. The microhardness values of glass-ceramic samples were in the 763–779 kg/mm2 range. 相似文献
10.
The present work explores the sub-solidus phase relations in the CeO2–DyO1.5–ZrO2 ternary system. About 80 compositions in Zr1−xDyxO2−x/2, Ce1−xDyxO2−x/2, (Ce0.8Zr0.2)1−xDyxO2−x/2, Zr1−x(Ce0.2Dy0.8)xO2−0.4x, Cex(Dy0.5Zr0.5)1−xO1.75+x/4 systems, were synthesized and explored to investigate the phase fields in this ternary system. Detailed XRD analysis showed the existence of a variety of phase fields viz. Fluorite-type cubic, C-type cubic, biphasic fields containing both F-type and C-type phases as well as co-existence of two different fluorite type phases. A few compositions also showed the presence of monoclinic as well the tetragonal phases. The trends observed in cell parameter are found to be governed by the competing factors of average ionic radius and the repulsion between excess anions in the lattice due to the aliovalent substitution. This ternary system showed the existence of a very wide cubic phase field. This ternary phase relation has relevance to the inert matrix fuel concept. 相似文献
11.
坩埚耐火材料对钛合金熔炼的质量非常重要,为开发高性能新型坩埚材料,以工业Y2O3和Al2O3–MgO–CaO系粉末(AMC)为原料,制备出Y2O3–Al2O3–MgO–CaO系复合耐火材料,研究了烧结温度(1 500℃、1 600℃)和AMC含量(0、25%、50%、75%和100%,质量分数)对所制备耐火材料的物相组成、烧结性能(线收缩率、体积收缩率、显气孔率、体积密度)、常温耐压强度、抗热震性能和显微结构的影响。结果表明:相对于Y2O3和AMC材料,复合材料的性能均有所提高;提高烧结温度,其性能更佳;且随着AMC含量的提高,复合材料的线收缩率、体积收缩率、体积密度和常温耐压强度随之增大,显气孔率降低;当AMC的质量含量为75%时,1 500℃烧结3 h制得复合材料的综合性能最优,其显气孔率为4.37%,常温耐压强度为274.99 MPa,3次水冷热震后残余强度为16... 相似文献
12.
Glass–ceramic materials based on diopside [CaMgSi2O6]–wollastonite [CaSiO3]–fluoroapatite [Ca5(PO4)3F]–sodium silicate [Na2SiO3] system with TiO2 or ZnO additives were successfully prepared and examined in vitro, by using a simulated body fluid (SBF) solution, to be suitable for restorative dental and bone implant materials. In vitro bioactivity of the glass–ceramics was examined by using scanning electron microscopy equipped with energy dispersive X-ray detectors (EDAX–SEM) and inductive coupled plasma emission spectroscopy (ICP). 相似文献
13.
A thermodynamic calculation on co-deposition of ZrC–SiC from the ZrCl4–C3H6–MTS–H2–Ar system was performed using the FactSage thermochemical software and verification experiments were performed. The surface diagrams of condensed-phases in this system were expressed as functions of the deposition temperature, total pressure, reactant ratio of MTS/(MTS+C3H6) and ratio of H2/(ZrCl4+MTS+C3H6), and the composition of the products was determined by the diagram. The calculation results indicate that their yields strongly depend on the molar ratio of the injected reactants and temperature, and ZrC–SiC can be co-deposited under a proper condition. The experimental results show that ZrC–SiC coating was successfully co-deposited on graphite substrates and carbon fibers according to the thermodynamic calculation. 相似文献
14.
PbO–SrO–Na2O–Nb2O5–SiO2 glass–ceramics were prepared via roll-quenching followed by controlled crystallization from 700 °C to 900 °C. The effects of PbO and SrO contents on crystallization and dielectric properties were investigated. The results show that Pb2Nb2O7, Sr2Nb2O7 and their solid solutions crystallize at 700 °C, NaNbO3 is the primary phase at 800 °C, Pb2Nb2O7 disappears and PbNb2O6 forms at 900 °C. The dielectric properties of the glass–ceramics formed through controlled crystallization has a strong dependence on the phase compositions that were developed during heat treatment. The highest dielectric constants (∼600) are found in samples with 6.0 mol% SrO annealed at 900 °C for 3 h. The dielectric–temperature characteristics of the samples show stability over the range from −60 °C to 180 °C, except the sample without SrO heated at 900 °C. 相似文献
15.
In order to relieve the narrow processing window and poor material compatibility in practical applications as well as understand the microwave dielectric properties, investigation on the formulations of CaO/B2O3/SiO2 glasses on their structure, thermal properties, and microwave properties were performed in this study. Six glasses with different molar ratios of CaO/B2O3/SiO2 (designed as CBS-3, CBS-5, CBS-7, CBS-8, CBS-9, and CBS-10) were prepared and pulverized. Results indicate that most softening points of glasses are ranging from 680 to 710 °C. They were sintered at different temperatures to reach maximum densification. Among various glass formulations, CBS-9 glass–ceramic containing the largest amount of SiO2 has the lowest CTE. The dielectric constants can be divided into two groups including around 4–5 and 7–8, and the dielectric losses (tan δ) are all below 0.005 in the frequency of ≈10 GHz. The dielectric constants and dielectric losses are generally frequency dependent. For CBS-9 glass–ceramic, the dielectric constant and dielectric loss at 4.7 and 18.6 GHz are 4.13 and 0.0018, and 4.20 and 0.0063, respectively. 相似文献
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17.
为满足不断增长的高性能储能设备需求,亟需研发能量存储性能出众的电介质电容器。采用传统固相反应法制备了(1–x)(0.75Bi0.5K0.5TiO3–0.25BiFeO3)–xNa0.73Bi0.09NbO3(x=0~0.4)(简称BKT–BF–xNBN)样品。在380kV/cm电场下,样品表现出良好的储能性能,可实现可回收能量密度Wrec=4.23J/cm3和效率η=81.2%。NBN的引入对BKT基陶瓷的微观结构与弛豫性产生了显著影响,导致晶粒尺寸减小、陶瓷更加致密,并诱导促使极性纳米区域的形成。此外,样品还具有出色的充放电性能(放电时间t0.9<75ns,放电电流密度CD=757.9A/cm2,放电功率PD=94.7MW/cm3)。这些结果表明BKT–BF–xNBN无铅铁电... 相似文献
18.
In the frame of the Generation IV Sodium Fast Reactor (SFR) safety studies, a core catcher with a sacrificial material could be placed at the bottom of the nuclear reactor. Its role is to dilute the (U, Pu)O2 molten fuel in case of a hypothetical core meltdown accident. A Al2O3–HfO2 ceramic is a candidate for the sacrificial material. To understand how the molten fuel would mix with this sacrificial material, the UO2–Al2O3–HfO2 system was investigated at CEA Cadarache PLINIUS corium platform. The eutectic position of the UO2–Al2O3–HfO2 was determined: the eutectic temperature is 1728±22 °C (2001±22 K) and the eutectic composition is 30 wt% UO2–35 wt% Al2O3–35 wt% HfO2. Then, the pseudo-binary UO2–(50 wt% Al2O3–50 wt% HfO2) phase diagram has been proposed. 相似文献
19.
以发射蓝色荧光的Ui O–66–NH2和发射红色荧光的Eu–MOFs为荧光基团,构建了比率荧光探针(Ui O–66–NH2@Eu–MOFs),成功应用于环境水样中的微量PO43–的检测。将发射蓝色荧光UiO–66–NH2与发射红色荧光Eu–MOF结合,构建了测定环境水样中的微量PO43–的比率荧光探针。结果表明:当PO43–存在时,由于配体–金属电荷转移(LMCT)效应的减弱,导致UiO–66–NH2的荧光增强;另一方面,PO43–和Eu3+的强配位作用将阻止配体–金属的能量转移(LMET),破坏了“天线”效应并导致Eu–MOF的荧光猝灭,在最优条件下,F445/F633与PO43–在1~12μmol/L浓度范围内呈现... 相似文献
20.
CMAS (CaO–MgO–Al2O3–SiO2) resistance of Y2O3-stabilized ZrO2 thermal barrier coatings with Pt layers
Calcium–magnesium–alumina–silicate (CMAS) corrosion significantly affects the durability of thermal barrier coatings (TBCs). In this study, Y2O3 partially stabilized ZrO2 (YSZ) TBCs are produced by electron beam-physical vapor deposition, followed by deposition of a Pt layer on the coating surfaces to improve the CMAS resistance. After exposure to 1250 °C for 2 h, the YSZ TBCs were severely attacked by molten CMAS, whereas the Pt-covered coatings exhibited improved CMAS resistance. However, the Pt layers seemed to be easily destroyed by the molten CMAS. With increased heat duration, the Pt layers became thinner. After CMAS attack at 1250 °C for 8 h, only a small amount of Pt remained on the coating surfaces, leading to accelerated degradation of the coatings. To fully exploit the protectiveness of the Pt layers against CMAS attack, it is necessary to improve the thermal compatibility between the Pt layers and molten CMAS. 相似文献