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991.
《Ceramics International》2020,46(3):3236-3241
Chemical doping is an indispensable tool to tailor the properties of the commercial piezoelectric materials. However, a high piezoelectric coefficient with enhanced thermal stability is rarely achieved by one dopant in some high-performance ferroelectrics, e.g., the recently discovered eco-friendly (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 (BCZT) ceramics. In order to optimize the piezoelectric property in BCZT system by a simple way, we investigated the doping effect of Fe3+, Nb5+ and Bi3+ cations in BCZT ceramics respectively. The results indicate that only Nb5+-doped BCZT ceramics display a combination of large piezoelectric coefficient and enhanced thermal stability, compared with others. Moreover, the established phase diagrams and in-situ transmission electron microscope (TEM) observations reveal that such optimized piezoelectric properties after Nb5+ doping originates from (i) the low polarization anisotropy near the ambient tetragonal (T)-orthorhombic (O) phase transition and (ii) the easy domain wall motion of persistent miniaturized ferroelectric domains upon heating. 相似文献
992.
《Ceramics International》2020,46(8):12275-12281
Alumina and zirconia ceramic particles exhibit high hardness and excellent wear resistance at high temperature, and hence are used as ceramic reinforcement phases in some plasma sprayed coatings. In this study, the interface evolution of a zirconia/alumina eutectic ceramic and the phase transition of zirconia in a plasma-sprayed coating were investigated. Scanning electron microscopy and transmission electron microscopy combined with focused-ion beam and energy dispersive X-ray were used to analyze the microstructure and composition of the ceramic interface. The results showed that the eutectic ceramic particles consisted of alumina (outer) and columnar zirconia (inner) before and after the plasma spraying process. The inner zirconia part showed the martensitic transformation of t-type zirconia to stripe-like m-type zirconia. After the plasma spraying, the interface between alumina and zirconia changed significantly, which formed a new oxide layer. The phase transition mechanism in the ceramic particle and oxide layer formation mechanism at the alumina/zirconia interface were investigated. 相似文献
993.
《Ceramics International》2020,46(1):381-390
Ce-doped TiO2 thin films were synthesized by sol-gel dip coating route to evaluate the effect of Ce doping percentage on properties of TiO2. X-ray diffraction spectra revealed both anatase and brookite phases, and Ce doping favours the anatase–brookite transformation of TiO2 films. The optical constants of the thin films were achieved by evaluating spectroscopic UV-VIS-NIR spectrophotometry data. The band gap of the Ce doped TiO2 was reduced from ~3.93 eV to ~3.79 eV with an increase in Ce doping percentage. All films have shown ferromagnetic behaviors which increase with the increase in Ce content due to enhancement in the bound magnetic polaron. Higher Ce doping increases the oxygen vacancies and saturation magnetization. Boost magnetic properties stem from the generation of the interaction between the Ce ion and an oxygen vacancy. The study showed that the antimicrobial activity of Ce doped TiO2 is ineffective. Hence doping of Ce can modify the properties of TiO2 and are used in LEDs, magneto-optical devices and solar cells. 相似文献
994.
《Journal of the European Ceramic Society》2020,40(4):1217-1222
Lead-free (K0.5Na0.5)NbO3-based (KNN) piezoceramics featuring a polymorphic phase boundary (PPB) between the orthorhombic and tetragonal phases at room temperature are reported to possess high piezoelectric properties but with inferior cycling stability, while the ceramics with a single tetragonal phase show improved cycling stability but with lower piezoelectric coefficients. In this work, electric biasing in-situ transmission electron microscopy (TEM) study is conducted on two KNN-based compositions, which are respectively at and off PPB. Our observations reveal the distinctive domain responses in these two ceramics under cyclic fields. The higher domain wall density in the poled KNN at PPB contributes to the high piezoelectric properties. Upon cycling, however, a new microstructure feature, “domain intersection”, is directly observed in this PPB composition. In comparison, the off-PPB KNN ceramic develops large domains during poling, which experience much less extent of disruption during cycling. Our comparative study provides the basis for understanding the relation between phase composition and piezoelectric performance. 相似文献
995.
《Journal of the European Ceramic Society》2020,40(1):71-77
A novel (1-x)Na0.5Bi0.5TiO3-xBaHfO3 (abbreviated as (1-x)NBT-xBH) transparent ceramic was fabricated by the solid state reaction method. X-ray diffraction analysis showed that NBT-based transparent ceramics exhibit a cubic-like perovskite structure and the solid solubility of BH in NBT reached to 0.15. The Landau-Devonshire theory and I-E curves revealed that the transition between the antiferroelectric like phase and the ferroelectric phase deeply relies on the variation of composition and free energy. One sample (x = 0.15) was found to show a high dielectric constant (˜2418±10%) over the temperature range 57–400 °C. These ceramics also exhibited a high discharge energy density (Wd) of 2.1 J/cm3 and a high maximum polarization Pm of 34 μC/cm2 under relatively low electric fields which were less than 175 kV/cm. There was also high transparency in the visible spectra (more than 0.5) when the sample thickness was 250 μm. 相似文献
996.
Yun Shuai Peng Zhang Xiaoyun Guo Xinyan Wang Zhengliang Huang Yao Yang Jingyuan Sun Meng Li Yan Jiang Jiong Ma Jingdai Wang Yongrong Yang 《American Institute of Chemical Engineers》2020,66(1):e16778
Three gas–liquid dispersion states including flooding, loading, and complete dispersion are observed sequentially in a jet bubbling reactor with an increase of the liquid jet velocity at the nozzle outlet (uj). The gas–liquid dispersion states are identified through the slope (k) of the curve of fluctuation distribution index (FI) versus uj as follows: (a) under the flooding, k = 0; (b) under the loading, k > 0; (c) under the complete dispersion, k < 0. In particular, the uj at the transition points from flooding to loading and from loading to complete dispersion are referred to flooding jet velocity (ujf, the transition point between k = 0 and k > 0) and complete dispersion jet velocity (ujcd, the transition point from k > 0 to k < 0), respectively. The average relative deviations of the uj at the transition points obtained through the acoustic emission measurement and visual observation are less than 5%. 相似文献
997.
Dariusz Kajewski Irena Jankowska-Sumara Jae-Hyeon Ko Jeong W. Lee Rafał Sitko Andrzej Majchrowski Annette Bussmann-Holder Krystian Roleder 《Journal of the American Ceramic Society》2020,103(6):3657-3666
Micro-Raman light scattering experiments on PbZrO3 (PZO) single crystal doped with Nb5+ have been investigated. Special attention was paid to the paraelectric (PE) phase in which nominally forbidden first-order Raman spectra were detected at temperatures far above the phase transition TC. Complex Raman spectra were observed in the vicinity of three structural phase transitions. These results mainly from the coexistence of phases with different symmetries in a wide temperature range below TC. The Raman measurements have been compared with dielectric and optical observations and proved that polar nanoregions in a centrosymmetric lattice appear well above TC. It was shown that doping ABO3 perovskites with heterovalent ions like Nb5+ unbalances charge neutrality of the lattice and strongly extends the temperature range of polar regions. The investigations performed point out that in the PE matrix the interaction between electrons and lattice vibrations, as recently suggested for pure PZO, plays an important role. 相似文献
998.
A fractionation system is an essential unit in the hydrocracking process. Its optimal operation is challenging because of the complexity in the structure of the distillation tower and composition of the stream. In addition, the series-parallel structure between the distillation towers of different techniques aggravates the coupling and complexity of the hydrocracking fractionation system (HFS). This, in turn, increases the time complexity of the optimization problem. In this paper, a rigorous mechanism model of an actual HFS is first applied to describe the operating conditions of the HFS. Then, an improved state transition algorithm (STA) with a staged evaluation strategy is proposed to solve the above problem. To overcome problems caused by the series-parallel structure of HFS, the model is divided into multiple stages for evaluation by mechanism analysis. Furthermore, several typical convergence estimation criteria are introduced to reduce unnecessary model calculations. To solve time-consuming problems associated with HFS optimization, the adaptive change operator is used to improve the search function of the original algorithm and two performance criteria are presented to reduce the optimization time. The proposed algorithm is successfully applied to the operational parameter optimization problem of HFS with a multi-fractionator series-parallel structure. The experimental results indicated that the staged evaluation strategy improved the fast convergence probability of the HFS mechanism model and reduced unnecessary calculations, whereas the improved algorithm increased accuracy and significantly decreased optimization time. 相似文献
999.
Carboxylated-terminated liquid acrylonitrile rubber (CTBN) and epoxy resin (JEF-0211) were coreacted with cyanate ester (CE) to form CTBN/EP/CE ternary resin systems. Further, the ternary resin system was applied as prepreg for carbon fiber composites with vacuum bag degassing molding process. CTBN/EP/CE ternary shape memory polymer (SMP) exhibited relatively high tensile strength, Young's modulus, impact strength, and excellent shape memory properties. Compared with CTBN/EP/CE ternary SMP, CTBN/EP/CE carbon fiber composites showed much higher mechanical properties, such as their tensile strength and Young's modulus were high to 570 MPa and 36.7 GPa, respectively. Furthermore, CTBN/EP/CE carbon fiber composites exhibited good shape memory properties, their shape fixity ratio and shape recovery ratio were more than 95% after 30 times repeating shape memory tests. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48756. 相似文献
1000.
Anouar El Magri Khalil El Mabrouk Sébastien Vaudreuil Hicham Chibane Mohamed Ebn Touhami 《应用聚合物科学杂志》2020,137(37):49087
Many processing parameters can be adjusted to optimize the fused filament fabrication (FFF) process, a popular and widely used additive manufacturing techniques for plastic materials. Among those easily adjusted parameters are the nozzle temperature, printing speed, raster orientation, and layer thicknesses. Using poly(ether ether ketone) (PEEK) as the base material, a design of experiments analysis was performed on the main FFF parameters. A response surface methodology was applied to analyze the results and to maximize the output responses. Results have shown that the nozzle temperature is the most influential parameter on tensile properties and the crystallinity degree of printed PEEK by FFF process. Parts produced with optimized FFF parameters were then subjected to an annealing treatment to induce a relaxation of residual stress and to enhance crystallinity. The best properties for 3D printed PEEK parts were achieved with annealed parts prepared at 400°C with a printing speed of 30 mm/s, 0.15 mm layer thickness and raster orientation of [0°/15°/−15°]. The resulting parts have mechanical properties comparable to those of injected PEEK. 相似文献