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《Ceramics International》2020,46(1):678-684
Lightweight MgAl2O4 spinel ceramic foams with high mechanical strength and good dielectric properties were prepared with a direct foam-gelcasting method using MgAl2O4 and TiO2 (rutile phase, as sintering aid) powders. The effects of calcination temperature and foam volume on bulk density, apparent porosity, and on the mechanical and dielectric properties of the ceramic foams were investigated. Tailored porosity (75.14–82.46%), pore size (10–200 μm), dielectric constant (1.66–2.05), and compressive strength (4.0–14.3 MPa), were obtained based on the change of the foam volume in the foamed slurries, and the calcination temperature of porous ceramics. The compressive strength and dielectric constant of the as-manufactured spinel foam with a porosity of ~75.14% was as high as 14.3 MPa and 2.05, respectively. The spinel ceramic foam which had a porosity of 81.84% was prepared with a foam volume of 350 mL and a sintering temperature of 1500 °C, and exhibited heterogeneous pore structures, whereby large and open spherical cells involved in small circular windows on the internal walls with a mean pore size of ~66.26 μm and a grain size of ~8 μm. The experimental dielectric constant matches well with that calculated by the modified Bruggeman model. The dependence of the mechanical strength on the relative density can be represented by the Gibson and Ashby model. The fitted index values of the power relationship were 3.504 and 3.533, compared to the theoretical value of 1.5. The ceramic foam can potentially become a new type of electromagnetic wave-transmitting radome material due to its low dielectric constant (1.66–2.05) and dielectric loss (0.0026–0.006) values. 相似文献
3.
Xiaomin Meng Bo Peng Longjiao Yao Yadong Wang Shuang Feng Qi Ge Majid Shaker 《International Journal of Applied Ceramic Technology》2023,20(4):2331-2340
In this paper, the electron beam vacuum coating method was used to coat a SiO2 film on an MgAl2O4 spinel substrate. The thickness of the coating was aimed to be 925 nm based on the physics of the antireflection coatings. Atomic force microscope images revealed that the coated silica was 880 nm thick, which is close to the aimed theoretical thickness and had 2.11 nm roughness. It could enhance the transparency of the spinel substrate by being coated on it. The infrared transmittance of the sample coated with SiO2 film in the range of 3700 nm-4800 nm was measured by a Fourier transform infrared spectrometer and reached 92.5% to 78.5%, which was about 2%–4% higher than that of MgAl2O4 spinel. In addition, it was discovered that the bonding force between the coating and the substrate is determined to be about 200 MPa. The results of this study can be used for further precise design and production of antireflection coatings on the transparent materials that need more transparency. 相似文献
4.
Zhuo Wang Haonan Chen Chun Wang Tian Wang Yujia Xiao Wenwen Nian 《Journal of the European Ceramic Society》2018,38(16):5402-5410
Pure phase of Ba0.94Bi0.04(Fe0.5Nb0.5)O3 (BBFN) nano-particles were obtained by chemical co-precipitation method. The core-shell structure of BBFN@SiO2 and BBFN@SiO2/Al2O3 particles and the target ceramics were successfully prepared by aqueous chemical coating approach. The microstructures and dielectric properties of BBFN@SiO2 and BBFN@SiO2/Al2O3 were studied. Both the BBFN@SiO2 and BBFN@SiO2/Al2O3 samples show significantly decreased dielectric loss and good frequency and temperature stability on relative permittivity. Compared to the rapid decline of relative permittivity of BBFN@SiO2, the synergistic effect of SiO2 and Al2O3 in BBFN@SiO2/Al2O3 ceramics made the relative permittivity of which remains a relatively high level with very low dielectric loss, making it more suitable in colossal permittivity applications. Based on the impedance analysis, the grain boundary effect and IBLC models play the important role for the improvement of dielectric properties of BBFN@SiO2/Al2O3 samples. 相似文献
5.
Strontium niobate SrNb2O6 has been synthesized by columbite solid-state reaction method and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and temperature as well as frequency dependence of dielectric and impedance study. XRD analysis indicates single phase formation of the compound with ∼180 nm crystallite size. Study of SEM micrographs pointed out that prepared material has good sinterability and enough density with homogeneous grain distribution. It was found that the magnitude of relative dielectric constant (?r) was relatively high with low dielectric loss compared with reported columbite compounds. Impedance spectroscopy was used to characterize the electrical behavior of the compound. AC impedance spectrum results indicate that the relaxation mechanism of the material is temperature dependent and has bulk and grain boundary contribution in different temperature ranges. 相似文献
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《Ceramics International》2017,43(14):11116-11122
Experimental phase equilibrium data for the Cu-O-Al2O3-MgO system is required to improve the performance of MgAl2O4-containing refractories and slagging in non-ferrous smelting. In this work, the phase relations of MgAl2O4 in the Cu-O-Al2O3-MgO system were studied experimentally in air within a temperature range of 1100–1400 °C using the equilibration and quenching method. The chemical compositions of the phases in the quenched samples were determined using electron probe microanalysis (EPMA). Less than 1 wt% of Al2O3 or MgO were found in the oxide liquid phase, whereas the solid MgAl2O4 and MgO phases contained up to 23 wt% and 30 wt% of ‘Cu2O’, respectively. Discrepancies between these results and the corresponding calculated values generated by the MTDATA 6.0 software and Mtox database Version 8.2 ranged from 3 wt% to 19 wt%. The results of this work indicate that the MgAl2O4 spinel is chemically stable in the presence of a CuOx-rich liquid under the conditions studied. 相似文献
7.
《Ceramics International》2016,42(16):18215-18222
Porous MgAl2O4 ceramics were prepared via a low cost foam-gelcasting route using MgAl2O4 powders as the main raw material, ammonium polyacrylate as a dispersant, a small amount of modified carboxymethyl cellulose as a gelling agent, and TH-IV polymer as a foaming agent. The effects of additive's content, solid loading and gelling temperature on slurry's rheological behavior were investigated, and microstructures and properties of as-prepared porous MgAl2O4 ceramics examined. Based on the results, the roles played by the foaming agent in the cases of porosity, pore structure, pore size, mechanical properties and thermal conductivity were clarified. Porosity and pore sizes of as-prepared porous MgAl2O4 ceramics increased with increasing the foaming agent from 0.05 to 0.6 vol%. Porous MgAl2O4 ceramics with porosity of 75.1% and average pore size of 266 µm exhibited a compressive strength as high as 12.5±0.8 MPa and thermal conductivity as low as 0.24 W/(m K) (at 473 K). 相似文献
8.
Hidehiro Yoshida Roy Johnson Mantravadi Krishna Mohan 《Journal of the American Ceramic Society》2017,100(2):554-562
The sintering behavior of commercially available MgAl2O4 spinel was investigated under DC electric field in a range of 0 and 1000 V/cm. Flash‐sintering results in densification close to theoretical density at 1410°C under the DC field of 1000 V/cm, in comparison to the higher sintering temperature of 1650°C in case of conventional sintering. It was observed that the fields less than 750 V/cm had no significant effect on the densification behavior. An abrupt increase in power dissipation was observed corresponding to the occurrence of the flash event. A significant enhancement in grain size was observed in case of flash‐sintered dense spinel samples. The gradual increase in the specimen conductivity observed in the electric field‐assisted sintering (FAST) regime led to Joule heating within the specimen. The increased specimen temperature triggered further increment of current and Joule heating, resulting in the immediate densification. 相似文献
9.
C.R. Mariappan P. Kumar A. Kumar S. Indris H. Ehrenberg G. Vijaya Prakash R. Jose 《Ceramics International》2018,44(13):15509-15516
We report on the ion transport properties of Li1+xZr2-xYx(PO4)3 (0.05?≤ x?≤?0.2) NASICON type nanocrystalline compounds prepared through a Pechini-type polymerizable complex method. Structural properties were characterized by means of powder X-ray diffraction, Raman spectroscopy and electron microscopy with selected area electron diffraction. Impedance spectroscopy was utilised to investigate the lithium ion transport properties. Y3+ doped LiZr2(PO4)3 compounds showed stabilized rhombohedral structure with enhanced total ionic conductivity at 30?°C from 2.87?×?10?7 S?cm?1 to 0.65?×?10?5 S?cm?1 for x=0.05 to 0.20 respectively. The activation energies of Li1+xZr2-xYx(PO4)3 show a decreasing trend from 0.45?eV to 0.35?eV with increasing x from 0.05 to 0.20. The total conductivity of these compounds is thermally activated, with activation energies and pre-exponential factors following the Meyer-Neldel rule. The tanδ peak position shifts to the high-frequency side with increasing yttrium content. Scaling in AC conductivity spectra shows that the electrical relaxation mechanisms are independent of temperature. 相似文献
10.
Bismuth calcium titanate (BiCa0.5Ti0.5O3) ceramic, fabricated by a ceramic processing technique, has been characterized using a variety of experimental techniques. Analysis of basic crystal structure using X-ray diffraction data exhibits the orthorhombic system. Measurements and detailed analysis of some electrical parameters (i.e.,dielectric constant, loss tangent (energy loss), electrical impedance and modulus, conductivity, etc.) of Bi(Ca0.5Ti0.5)O3 in a wide range of frequency (103–106 Hz) and temperature (30–500 °C) have provided some interesting and useful data and results on structure–properties relationship, conduction mechanism, etc.The role of interface, space charge polarization and Maxwell–Wagner dielectric relaxation in getting high dielectric constant of the material at low frequencies and high temperatures has been discussed. Study of temperature dependence of Nyquist plots clearly shows the contributions of grains in resistive and capacitive properties of the material. The frequency of the applied electric field and temperature strongly affect the dielectric (permittivity and dissipation of energy) and electrical (impedance, electrical modulus and conductivity) characteristics of the material. 相似文献
11.
《Ceramics International》2020,46(11):19046-19051
In the present work, MgAl2-x(Mg0·5Ti0.5)xO4 (x = 0.02, 0.04, 0.06, 0.08, 0.10) solid solutions were synthesized via the traditional solid-state reaction route. The valence state of Ti ions, crystal structural characteristics, and microwave dielectric properties were discussed. A solid solution with spinel structure was revealed by the Rietveld refinement results. The partial substitution of (Mg0·5Ti0.5)3+ for Al3+ lowered the sintering temperature and improved the Q × f value of MgAl2O4 ceramic. The MgAl2-x(Mg0·5Ti0.5)xO4 solid solutions with x = 0.06 can be well sintered at 1425 °C in an oxygen atmosphere for 8 h and exhibits excellent microwave dielectric properties with εr = 9.1, Q × f = 98,000 GHz, τf = −61.36 ppm/°C. The sintering temperature of MgAl1·94(Mg0·5Ti0.5)0.06O4 microwave dielectric ceramics was approximately 200 °C lower than that of conventional MgAl2O4 ceramics. 相似文献
12.
《Journal of the European Ceramic Society》2017,37(10):3417-3424
Samples of transparent polycrystalline spinel with average grain size varying from 0.14 to 170 μm were prepared by different sintering approaches. The effect of grain size on the flexural strength, hardness and Hugoniot elastic limit (impact loading) was investigated. It was found that values of hardness divided by three for samples with grain size in the 0.14–15 μm range were almost equal to the dynamic yield strength values, estimated based on the Hugoniot elastic limit. This led to the assumption that the onset of inelastic deformation at the Hugoniot elastic limit was brittle rather than ductile. The observed departure of the dynamic yield strength from the hardness divided by three value for ceramics with grain size >15 μm was associated with either impact-induced shear banding or twinning. The feasibility of such banding/twinning intervention in initiating inelastic deformation in the spinel is supported by the values of apparent Hall-Petch coefficients in the corresponding grain size domains. 相似文献
13.
用一步碳热还原法制备了Li3V2-xCux(PO4)3/C(x=0.00、0.02、0.05、0.08、0.10、0.15)复合正极材料,并研究了掺杂对材料结构、微观形貌、充放电性能的影响。结果表明掺杂少量铜(Ⅱ)不会影响材料Li3V2(PO4)3的基本结构,但会在Li3V2(PO4)3中形成电子缺陷,提高晶体内部原子的无序化程度,降低极化和电荷转移电阻。从而改善材料的电化学性能。Li3V1.98Cu0.02(PO4)3/C的10 C放电容量比Li3V2(PO4)3/C提高了20 mA.h/g,具有较好的倍率性能。 相似文献
14.
Surface barrier layer effect in (In + Nb) co‐doped TiO2 ceramics: An alternative route to design low dielectric loss
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Theeranuch Nachaithong Pinit Kidkhunthod Prasit Thongbai Santi Maensiri 《Journal of the American Ceramic Society》2017,100(4):1452-1459
Giant dielectric permittivity (ε′) with low loss tangent (tanδ) was reported in (In + Nb) co‐doped TiO2 ceramics. Either of electron‐pinned defect‐dipole or internal barrier layer capacitor model was proposed to be the origin of this high dielectric performance. Here, we proposed an effectively alternative route for designing low‐tanδ in co‐doped TiO2 ceramics by creating a resistive outer surface layer. A pure rutile‐TiO2 phase with a dense microstructure and homogeneous dispersion of dopants was achieved in (In + Nb) co‐doped TiO2 ceramics prepared by a simple sol‐gel method. Two giant dielectric responses were observed in low‐ and high‐frequency ranges, corresponding to extremely high ε′≈106‐107 and large ε′≈104‐105, respectively. After annealing in air, a low‐frequency dielectric response disappeared and could be restored by removing the outer surface of the annealed sample, indicating the dominant electrode effect in the initial sample. Annealing can cause improved dielectric properties with a temperature‐ and frequency‐independent ε′ value of ≈1.9 × 104 and cause a decrease in tanδ from 0.1 to 0.035. High dielectric performance in (In0.5Nb0.5)xTi1?xO2 ceramics can be achieved by eliminating the electrode effect and forming a resistive outer surface layer. 相似文献
15.
《Ceramics International》2022,48(14):20245-20250
There has been extensive research on microwave dielectric materials considering their application in 5G and 6G communication technologies. In this study, the sintering temperature range of Mg2TiO4–CeO2 (MT-C) ceramics was broadened using a composite of CeO2 and Mg2TiO4 ceramics, and their microwave dielectric performance was stabilized. Low-loss MT-C composite ceramics were prepared using the solid-phase reaction method, and their microwave dielectric properties, microscopic morphologies, and phase structures were investigated. The proposed MT-C ceramics contained Mg2TiO4 and CeO2 phases; their average grain size was maintained at 2–4 μm in the sintering temperature range of 1275–1425 °C, and the samples were uniformly dense without porosity. The cross-distribution of Mg2TiO4 and CeO2 grains in the samples inhibited the growth of ceramic grains, providing uniform and dense surfaces. The dielectric loss of MT-C ceramics remained constant in the temperature range of 1300–1425 °C at 9 × 10?4 (8.45 ≤ f ≤ 8.75 GHz). As opposed to the base material, MT-C ceramics are advantageous owing to their wide sintering temperature range and the stable microwave dielectric properties, and there are suitable substrate materials for further industrial applications. 相似文献
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《Ceramics International》2021,47(21):29707-29711
This research aims to investigate the density, hardness, fracture toughness, and infrared and visible transmittance of spark plasma sintered (SPS) spinel discs fabricated through the powder injection molding (PIM) method. These properties were compared with the sample directly SPSed without the PIM process. For this purpose, initially, a feedstock was prepared with 80 wt% spinel nanopowder and 20 wt% binder. The results revealed that the hardness and fracture toughness of the SPSed spinel disc sintered at 1400 °C were greater than those of the spinel sample without PIM treatment. Also, for the PIMed sample and then SPSed sample, the level of infrared and visible transmittance was ~10% greater than for the SPSed spinel nanopowders. 相似文献
17.
《Ceramics International》2022,48(17):24965-24978
YCr0.5Mn0.5O3(YCM)-CaCu3Ti4O12(CCTO) ceramics were prepared using a solid processing method, and their properties were studied. XRD measurements showed that all prepared ceramics had pure perovskite structures. With increasing YCM content, grain size in ceramics decreased, and the resistivity of materials was found to be very sensitive to grain size and grain size distribution. Moreover, ceramics had NTC characteristics, and values of ρ25, B25/75, and Ea ranged from 2.21 × 106–7.30 × 106 Ω cm, 5797–6300 K, and 0.5390–0.5800 eV, respectively. The presence of heterovalent ion pairs in samples suggested that conduction mechanism may have been related to electron hopping. Impedance spectroscopy results showed that excessive doping with YCM resulted in greater contribution from grains to overall resistance of the material. Temperature-dependent electrical relaxation behavior was dominated by short-range movement of charge carriers. 相似文献
18.
《Ceramics International》2023,49(19):30999-31005
Composite materials are emerging and have potential to revolutionize the modern technology. In this work, a series of tri-phase composite materials having the chemical formula; 0.8[(1-x) SrCoO2.29+xCr2FeO4] + 0.2PZT, is synthesized to explore their energy storage capability. In this series, SrCoO2.29 and Cr2FeO4 ceramics are synthesized by using a sol-gel auto-combustion process while PZT is prepared by the solid-state method. The XRD analysis confirmed the formation of cubic crystal structure of the SrCoO2.29 and Cr2FeO4 and the rhombohedral phase of PZT. The SEM images exhibited an increase in average grain size with the incorporation and increasing contents of Cr2FeO4. The presence of all constituting elements with the exact stoichiometric ratio is validated through EDX analysis. Wide-range frequency-dependent dielectric behavior showed a dramatic fall in dielectric constant with increasing frequency. A same frequency dependent behaviour of ε'' and tanδ is witnessed as that of ε'. The investigation of electric modulus reveals that in the low-frequency region it possesses a trivial value which became significantly large with the increase of frequency. The presence of a relaxation peak in the plot of the imaginary part of the electric modulus plays a decisive role to distinguish the small and large range hopping mechanism. The complex impedance analysis revealed different electroactivity of composite material in the different frequency domains which made them viable for advanced energy storage devices working in the vast frequency range. 相似文献
19.
Seok-Hyun Yoon Je-Hun Lee Doh-Yeon Kim Nong M. Hwang 《Journal of the American Ceramic Society》2003,86(1):88-92
Changes in the microstructure and dielectric properties with the variation of the donor/acceptor ratio in BaTiO3 ceramics were investigated. In donor-rich specimens, a liquid that appeared during sintering did not penetrate into grain boundaries. However, in the acceptor-rich specimens, the grains were separated by a liquid film during sintering. The much higher mobility of the liquid film than that of the grain boundaries was suggested to cause extensive grain growth in acceptor-rich BaTiO3 . The macroscopic homogenization of dopants because of grain growth in acceptor-rich specimens resulted in changes in the dielectric properties. 相似文献
20.
《Ceramics International》2020,46(9):13737-13742
Aiming to establish relationships between intrinsic structure factors and dielectric characteristics, a series of Li2Mg3Ti1-x(Al1/2Nb1/2)xO6 (x = 0.0, 0.04, 0.08, 0.12, 0.16, 0.20) ceramics were synthesized to investigate the influences of (Al1/2Nb1/2)4+ substitution on the dielectric properties of Li2Mg3TiO6 ceramics. The XRD and SEM results revealed that the pure rock salt phase (space group: Fm-3m) with a dense microstructure could be obtained with increasing the (Al1/2Nb1/2)4+ concentration, which is accompanied by an increase in the grain size from 11.69 to 22.81 μm. Meanwhile, some intrinsic factors, such as the average ionic polarizability, bond energy, packing fraction and lattice energy were calculated according to the complex chemical bond theory and refinement results. The unusual change in the dielectric constant (εr) was explained by the combined effects of the average ionic polarizability and relative density. The variation in the quality factor (Q × f) was ascribed to the packing fraction and lattice energy. The temperature coefficient of the resonant frequency (|τf|) reduced gradually with the increase in the octahedral bond energy, which enhanced the system thermal stability. Particularly, the Li2Mg3Ti0.92(Al1/2Nb1/2)0.08O6 sample exhibited outstanding dielectric characteristics:εr = 15.256, Q × f = 174,300 GHz and τf = −19.97 ppm/°C. 相似文献