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排序方式: 共有9424条查询结果,搜索用时 15 毫秒
41.
《Journal of the European Ceramic Society》2022,42(4):1354-1361
Core–rim structures were observed as common features in Y-α-SiAlON ceramics hot-pressed between 1550?1950 °C. We found most dopants were taken into α’-rims, and a transition layer grown first on α-cores from liquid-phase over-saturated with metal solutes. Elongated β’-grain were formed as minor phase with α’- or AlN-cores thus only after the α’ matrix had consumed up all Y solutes, revealing that the α’ → β’ transformation is controlled by the transient liquid-phase and similar defects and dangling bonds could be detected in both SiAlON phases by cathodoluminescence. Quantitative assessment of Ym/3Si12?(m+n)Alm+nOnN16?n demonstrates the multiphase evolution, initiated by over-saturation of Y solutes at low temperatures thus retaining α-phase as cores to lower the infra-red transmittance, dictated by homogenization of Al solutes at higher temperature. The elimination of those phase boundaries leads to better dopant and sintering design for achieving transparent and high-performance SiAlON ceramics. 相似文献
42.
《Ceramics International》2022,48(16):23241-23248
In this work, a two-step solid-state reaction method is used to prepare the 0.55 Pb(Ni1/3Nb2/3)O3-0.135PbZrO3-0.315PbTiO3/xSnO2 (PNN-PZT/xSnO2) ceramics. The influences of SnO2 on the crystalline structure, electromechanical properties, and temperature stability of PNN-PZT ceramics were studied in detail. The results demonstrate that the Sn4+ ions are successfully introduced into the PNN-PZT crystalline lattice and substitute B-site Ni2+ and Zr4+. The x = 0.0025 ceramic with the coexistence of rhombohedral, tetragonal, and pseudocubic phases exhibits the optimized comprehensive properties: the quasi-static piezoelectric constant d33, large-signal d33*, electromechanical coupling coefficients kp and kt, free dielectric constant εr, and mechanical quality factor Qm are 1123 pC/N, 1250 p.m./V, 0.63, 0.54, 9529, and 57, respectively. Meanwhile, the Curie temperature for this composition is 103 °C, almost maintaining the same level as the PNN-PZT matrix. After annealing at 75 °C, the retained d33 of x = 0.0025 ceramic is as high as 975 pC/N, superior to the PNN-PZT matrix (retained d33 ≈ 873 pC/N). Our results provide a promising piezoelectric material for board bandwidth, high sensitivity, and miniaturized medical ultrasonic transducers applications. 相似文献
43.
《Ceramics International》2022,48(9):12790-12799
The ablation behavior of high-entropy ceramics (HECs) was investigated in this study using an oxyacetylene flame at 2000 °C. Spark plasma sintering was used to construct a dense HEC (TiZrHfNbTa)C with a 20 vol% of SiC addition (HEC-20SiC). The densification of HEC-20SiC can be improved to a certain extent by adding SiC particles, increasing the hardness of HEC-20SiC to up to 24.6 GPa, and the crack deflection observed through the addition of SiC particles were considered to be the strengthening and toughening mechanisms. After ablation, Hf6Ta2O17, Ti5.1Ta4.9O20, Nb2Zr6O17, TaZr2.75O8, and SiO2 can be detected on an ablated surface and HEC-20SiC possesses the minimum mass ablation rate (?1.9 mg s?1) and line ablation rate (2.1 μm s?1) among the comparative ceramics. On the one hand, the SiC phase forms gaseous CO, CO2, and SiO as well as viscous SiO2 during ablation and some part of the heat can be dissipated by the evaporation of gaseous CO, CO2, and SiO; further, pore defects can be healed by viscous SiO2, thus inhibiting the diffusion of reactive oxygen species. On the other hand, the HEC phase with a lattice-distortion caused by single-phase solid-solution can effectively inhibit the invasion of reactive oxygen species and the outward migration of metal atoms. The invasion rate of reactive oxygen is considered to be the main step during HEC-20SiC ablation, and it is believed that higher principal component HECs can improve ablation performance even further. 相似文献
44.
《Ceramics International》2022,48(8):10885-10894
Lead-free bismuth sodium titanate-strontium titanate (NBT-ST) dielectric ceramic materials have been extensively investigated energy storage materials because of their relaxor characteristics. In this study, four different lanthanide elements were introduced into the ferroelectric NBT-ST ceramic to improve their relaxor properties. The introduction of the lanthanide resulted in an increase in disorder at location A within the perovskite lattice and improved relaxor characteristics, leading to a stored energy density of more than 3.5 J/cm3. In particular, an ultrahigh recoverable stored energy density of 4.94 J/cm3 and efficiency of 88.45% were achieved at 440 kV/cm when the NBT-ST ceramic was modified with neodymium. The modified ceramic also exhibited good thermal stability in the range of 30–120 °C, as well as a fast discharge time of ~153 ns, indicating that Nd-incorporated NBT-ST is a promising candidate for electrical energy storage ceramic. 相似文献
45.
Lin Chen Jun Guo Yuke Zhu Mingyu Hu Jing Feng 《Journal of the American Ceramic Society》2021,104(1):404-412
The features of crystal structures, thermo-mechanical properties and their dominant mechanisms of weberites RE3NbO7 were studied as high-temperature oxides. We concentrated on connections between structures and thermo-mechanical properties, the influences of bond lengths, lattice distortion degrees and microstructures on these properties were estimated. The shortening of bond length and increment of bonding strength would lead to the increase of mechanical properties. The Vickers hardness (4.5-7.8 GPa) and toughness (0.5-1.6 MPa·m1/2) of weberites RE3NbO7 are enhanced by grain refinement and increment of bond strength, while crystal structures, bond lengths, and lattice distortion degrees influenced their Young's modulus (100-170 GPa). Nano-indentation was applied to test the influence of microstructures on modulus and hardness. The dominant mechanisms for mechanical properties and thermal conductivity were proposed, which was conducive to properties tailoring and engineering applications of weberites RE3NbO7 oxides. 相似文献
46.
Jun Wang Fushuo Wu Ruoan Zou Yueshu Wu Mengdi Gan Jing Feng Xiaoyu Chong 《Journal of the American Ceramic Society》2021,104(11):5873-5882
In this study, high-entropy rare-earth tantalate ceramics (Y0.2Ce0.2Sm0.2Gd0.2Dy0.2)TaO4 ((5RE0.2)TaO4) have been successfully fabricated. The possibility of formation of (5RE0.2)TaO4 was verified via first-principles calculations. In addition, the phase structure, ferroelastic toughening mechanism, thermophysical, and mechanical properties were systematically investigated. The (5RE0.2)TaO4 ceramics have lower phonon thermal conductivity (1.2–2.6 W·m–1·K–1) in the entire temperature range than that of RETaO4 and YSZ. (5RE0.2)TaO4 has a higher fracture toughness and lower brittleness index than YSZ. The thermal expansion coefficients of (5RE0.2)TaO4 are as high as 10.3 × 10-6 K–1 at 1200°C and Young's modulus is 66–189 GPa, and thus, (5RE0.2)TaO4 possesses great potential for application in thermal barrier coatings (TBCs). 相似文献
47.
《Ceramics International》2021,47(23):32641-32647
Multi-components and equimolar rare earth monosilicates, (Y1/3Dy1/3Er1/3)2SiO5, (Y1/3Dy1/3Lu1/3)2SiO5, (Y1/4Dy1/4Ho1/4Er1/4)2SiO5 and (Yb1/4Dy1/4Ho1/4Er1/4)2SiO5, were prepared by solid-state reactions and the following hot-pressing. Dense microstructures with uniform elemental distributions were obtained for all samples. These investigated multi-components monosilicates exhibit low thermal conductivities and similar coefficients of thermal expansion with SiC. Moreover, they exhibit high corrosion resistances in 1400 °C water vapor, especially, four-components (Y1/4Dy1/4Ho1/4Er1/4)2SiO5 and (Yb1/4Dy1/4Ho1/4Er1/4)2SiO5 experienced almost invariable weights after small weight losses during the initial 0.5 h. All those results indicate that multi-components rare earth monosilicates are promising candidates of environmental barrier coatings for SiC/SiC composites. 相似文献
48.
以铅玻璃与粉煤灰为原料,通过协同熔炼制备了微晶玻璃。通过XRD和SEM等手段研究了不同烧结时间下微晶玻璃的物相组成及显微结构,测定了微晶玻璃的密度、吸水率、维氏硬度和化学抗性。结果表明: 延长烧结时间对含铅玻璃加入量为40%(FG40)、50%(FG50)样品的晶相类型和晶化程度有影响,而对含铅玻璃加入量为60%(FG60)、70%(FG70)和80%(FG80)样品的影响较小。随着烧结时间延长,样品晶化程度提高,晶体长大,玻璃相减少。适宜的含铅玻璃加入量为50%~70%,对应的FG50、FG60、FG70样品最佳烧结时间分别为4 h、3 h、3 h。 相似文献
49.
Ziming Cai Peizhong Feng Chaoqiong Zhu Xiaohui Wang 《Journal of the European Ceramic Society》2021,41(4):2533-2538
Dielectric breakdown is a fundamental issue for ferroelectric ceramics. In this work, a phase-field method is introduced to study the breakdown behavior of ferroelectric ceramics with pores randomly distributed. Effects of the position and the size of pores on the breakdown behavior are analyzed. Results indicate that the position of pores, for example in grains or at grain boundaries, has a significant influence on the breakdown strength of ferroelectric ceramics. The nominal breakdown strength of ferroelectric ceramics with 2 % pores at grain boundaries is almost 50 % higher than 2 % pores in grains. Further, for ferroelectric ceramics with a certain porosity, the smaller the pore size, the higher the breakdown strength. As the nominal pore size decreases from 2.5 to 1, the nominal breakdown strength is enhanced from 0.73 to 1.16. Such results agree well with the widely accepted Gerson-Marshall model and previously published experimental observations. 相似文献
50.
With this contribution,as a comment to the publication in Journal of Mate rials Science&Technology 44(2020)54,reporting giant dielectric response,structural characterization and numerical simulations in Sr_(1-1.5 x)Bi_xTiO3ceramics,we show that the re ported results are rather contradicting and not well analysed,while the suggested mechanism for the giant permittivity response is not valid or doubtful and has to be reconsidered.Moreover,many details and data are missing making impossible not only to call the obtained results very suitable for practical application but even to reproduce them. 相似文献