Bi2O3对K2O–B2O3–SrO–Al2O3–Nb2O5–SiO2玻璃陶瓷介电储能性能的影响

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...     

Ternary phase relations in CeO2–DyO1.5–ZrO2 system

The present work explores the sub-solidus phase relations in the CeO₂–DyO_1.5–ZrO₂ ternary system. About 80 compositions in Zr_1−xDy_xO_2−x/2, Ce_1−xDy_xO_2−x/2, (Ce_0.8Zr_0.2)_1−xDy_xO_2−x/2, Zr_1−x(Ce_0.2Dy_0.8)_xO_2−0.4x, Ce_x(Dy_0.5Zr_0.5)_1−xO_1.75+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.     

Multiferroic ceramics in BaO–Y2O3–Fe2O3–Nb2O5 system

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.     

Composite wasteform based on SiO2–PbO–CaO–ZrO2–TiO2–(B2O3–K2O) parent glass with zircon as the second component

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.     

多组元BaO–SrO–CaO–MgO–Al2O3–2SiO2环境障涂层的制备与抗CaO–MgO–Al2O3–SiO2腐蚀性能

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Ba_0.3Sr_0.3Ca_0.35Mg_0.05Al₂Si₂O₈ (B_0.3S_0.3C_0.35M_0.05AS)单相多组元陶瓷材料。在 1 250、1 300 ℃和 1 350 ℃对 B_0.3S_0.3C_0.35M_0.05AS 进行 CMAS 腐蚀实验,相比于 Ba_0.5Sr_0.5Al     

Study of AC electrical properties of V2O5–P2O5–B2O3–Dy2O3 glasses

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 (T_g) and peak temperature of crystallization (T_c) 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.     

Eutectic crystallization in the UO2–Al2O3–HfO2 ceramic phase diagram

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.     

Crystallization behavior and properties of K2O–CaO–Al2O3–SiO2 glass-ceramics

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 (E_α) 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.     

Porous SiO2–TiO2–ZrO2 Obtained from Polymeric Systems Prepared by the Sol–Gel Process

An experimental strategy was developed to obtain Si–Ti–Zr transparent sols via the sol-gel process. The chelating agents isoeugenol (2-methoxy-4-propenylphenol, isoH), salicylaldehyde (2-hydroxybenzaldehyde, salH), and itaconic anhydride (2-methylenesuccinic anhydride, anhH) were employed separately to stabilize monomeric Ti and Zr precursors, in order to control their chemical reactivity, avoiding precipitation. In all cases a prehydrolyzed tetraethyl orthosilicate (TEOS) sol was the Si source. The sols were polymerized at room temperature (293 K) to obtain gels and these were dried and calcined at 873 K in air. The radial distribution functions (RDF) of the gels were obtained at room temperature. The solids were studied by scanning electron microscopy (SEM). The porosity and surface area of solids were determined by N₂ adsorption. The surface area results obtained range between 83–198 m²/g. The average pore diameters are 1.44–1.61 nm.     

The influence of In2O3 on electrical characteristics of iron mixed Li2O–PbO–B2O3–SiO2–Bi2O3 multi-component glass system

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, σ_ac, 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%.     

Crystallographic characterization of silicon nitride ceramics sintered with Y2O3–Al2O3 or E2O3–Al2O3 additions

Silicon nitride ceramics were sintered using Y₂O₃–Al₂O₃ or E₂O₃–Al₂O₃ (E₂O₃ denotes a mixed oxide of Y₂O₃ and rare-earth oxides) as sintering additives. The intergranular phases formed after sintering was investigated using high-resolution X-ray diffraction (HRXRD). The use of synchrotron radiation enabled high angular resolution and a high signal to background ratio. Besides the appearance of β-Si₃N₄ phase the intergranular phases Y₃Al₅O₁₂ (YAG) and Y₂SiO₅ were identified in both samples. The refinement of the structural parameters by the Rietveld method indicated similar crystalline structure of β-Si₃N₄ for both systems used as sintering additive. On the other hand, the intergranular phases Y₃Al₅O₁₂ and Y₂SiO₅ shown a decrease of the lattice parameters, when E₂O₃ was used as additive, indicating the formation of solid solutions of E₃Al₅O₁₂ and E₂SiO₅, respectively.     

In vitro bioactivity of glass–ceramics of the CaMgSi2O6–CaSiO3–Ca5(PO4)3F–Na2SiO3 system with TiO2 or ZnO additives

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).     

Synthesis and characterization of MgAl2O4–ZrO2 composites

Different types of dense 5–97% ZrO₂–MgAl₂O₄ composites have been prepared using a MgAl₂O₄ spinel obtained by calcining a stoichiometric mixture of aluminium tri-hydroxide and caustic MgO at 1300 °C for 1 h, and a commercial yttria partially stabilized zirconia (YPSZ) powder as starting raw materials by sintering at various temperatures ranging from 1500 to 1650 °C for 2 h. The characteristics of the MgAl₂O₄ spinel, the YPSZ powder and the various sintered products were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), BET surface area, particle size analysis, Archimedes principle, and Vickers indentation method. Characterization results revealed that the YPSZ addition increases the sintering ability, fracture toughness and hardness of MgAl₂O₄ spinel, whereas, the MgAl₂O₄ spinel hampered the sintering ability of YPSZ when sintered at elevated temperatures. A 20-wt.% YPSZ was found to be sufficient to increase the hardness and fracture toughness of MgAl₂O₄ spinel from 406 to 1314 Hv and 2.5 to 3.45 MPa m^1/2, respectively, when sintered at 1600 °C for 2 h.     

Phase stability and hot corrosion behavior of ZrO2–Ta2O5 compound in Na2SO4–V2O5 mixtures at elevated temperatures

For thermal barrier coating (TBC) applications, yttria stabilized zirconia (YSZ) is susceptible to hot corrosion. This paper examines the hot corrosion performance of ZrO₂/Ta₂O₅ compounds. Different compositions of ZrO₂–Ta₂O₅ samples in the presence of molten mixture of Na₂SO₄+V₂O₅ at 1100 °C were tested. The compositions were selected to form tetragonal and orthorhombic phases of zirconium-tantalum oxides. Results show that orthorhombic zirconium-tantalum oxide is more stable, both thermally and chemically in Na₂SO₄+V₂O₅ media at 1100 °C, and shows a better hot corrosion resistance than the tetragonal phase.     

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.     

电熔镁砂在CaO–Al2O3–SiO2熔渣中的溶解行为

作为镁质耐火材料的重要原料，电熔镁砂在低密度高强钢精炼用CaO–Al₂O₃–SiO₂系熔渣中的溶解是影响炉衬使用寿命及钢质量的重要因素。本工作采用高温激光共聚焦显微观测系统研究了1 600℃下镁砂在该熔渣中的溶解行为，探究了镁砂颗粒的形状、质量及熔渣CaO和SiO₂质量分数比(即C/S)对其溶解行为的影响。结果表明：镁砂主要形状对其溶解速率影响较小；溶解速率随质量增大呈近线性下降，随C/S的增加而先降低后增加；镁砂颗粒的溶解曲线受质量影响更大，其溶解模型n值分别对应1/2、2/3、3/5，这为深入理解镁质耐火材料的渣蚀行为和提质优化提供指导。     

Depolarization temperature and piezoelectric properties of (Bi1/2Na1/2)TiO3–(Bi1/2Li1/2)TiO3–(Bi1/2K1/2)TiO3 lead-free piezoelectric ceramics

The phase transition temperature and piezoelectric properties of x(Bi_1/2Na_1/2)TiO₃–y(Bi_1/2Li_1/2)TiO₃–z(Bi_1/2K_1/2)TiO₃ [x + y + z = 1] (abbreviated as BNLKT100y–100z) ceramics were investigated. BNLKT100y–100z ceramics were prepared by conventional ceramic fabrication. The depolarization temperature T_d was determined by the temperature dependence of the dielectric and piezoelectric properties. This study focuses on the effect of Li¹⁺ and K¹⁺ ions on T_d and the piezoelectric properties of BNT ceramics. BNLKT100y–100z (y = 0–0.08) has a morphotropic phase boundary (MPB) between rhombohedral and tetragonal phases at z = 0.18–0.20, and high piezoelectric properties were obtained at the MPB composition. The piezoelectric constant d₃₃ increased with increasing y; however, T_d decreased above y = 0.06. The d₃₃ and T_d values of BNLKT4-20 and BNLKT8-20 were 176 pC/N and 171 °C, and 190 pC/N and 115 °C, respectively.     

Effect of different nucleation catalysts on the crystallization of Li2O–ZnO–MgO–Al2O3–SiO2 glasses

Based on local raw materials, a range of LiZnMg aluminosilicate glasses were prepared to investigate the influence of TiO₂, Cr₂O_3, 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.     

Densification and microwave dielectric properties of CaO–B2O3–SiO2 system glass–ceramics

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.     

低温热压制备高硬度、高韧性Si3N4–SiCw–ZrB2陶瓷

通常低温热压烧结的Si₃N₄陶瓷具有较高的硬度和较低的断裂韧性;而高温热压烧结的Si₃N₄陶瓷具有较低的硬度和较高的断裂韧性。为了获得高硬度、高韧性Si₃N₄陶瓷,添加20%SiC_w（SiC晶须,体积分数）和2.5%ZrB2,在1 500℃低温热压制备了Si₃N₄基陶瓷,开展其相组成、致密度、显微结构和力学性能研究,并与1 800℃高温热压烧结Si₃N₄进行了对比研究。结果表明：SiC_w的引入阻碍了Si₃N₄低温致密化,致密度从97.9%降低到92.9%,Vickers硬度从20.5 GPa降低到16.4 GPa,断裂韧性从2.9 MPa·m^1/2增加到3.4 MPa·m^1/2。同步引入SiC_w和ZrB₂