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81.
Xiaojing Cheng Qian Gou Jiagang Wu Xiaopeng Wang Binyu Zhang Dingquan Xiao Jianguo Zhu Xiangjian Wang Xiaojie Lou 《Ceramics International》2014
A new phase boundary with rhombohedral–orthorhombic and orthorhombic–tetragonal phase boundaries is designed in (K0.48Na0.52)NbO3 by adding Bi0.5(Na0.7K0.2Li0.1)0.5ZrO3 (BNKLZ), where Zr4+ and (BNKL)2+ are respectively used to improve the temperature of a rhombohedral phase and to decrease the temperature of an orthorhombic–tetragonal phase coexistence. These ceramics endure several continuous phase transitions with increasing BNKLZ content, i.e., an orthorhombic phase (0≤x<0.03), orthorhombic–tetragonal phases (x=0.03), orthorhombic–tetragonal and rhombohedral–orthorhombic (O–T and R–O) phase existence (0.03<x≤0.05), a rhombohedral phase (0.05<x≤0.07). The ceramics with O–T and R–O have a better piezoelectric behavior as compared with other phases because of more polarization states, enhanced εr and Pr, and a dense microstructure. Moreover, piezoelectric properties could be further optimized by modifying their sintering and poling temperatures. As a result, the construction of O–T and R–O phase coexistence benefits the improvement of piezoelectric properties in KNN-based ceramics. 相似文献
82.
《Journal of the European Ceramic Society》2014,34(3):739-744
Alumina-matrix eutectic in situ composite ceramics present excellent high-temperature mechanical properties, which have been considered as promising next-generation ultra-high temperature structural materials. A modified laser surface processing is developed to in situ fabricate highly-dense Al2O3/YAG bulk nanoeutectic ceramics with large size and homogeneous three-dimensional network of nanoeutectic microstructure by introducing two-side remelting and high-temperature preheating. The crack and porosity are avoided, and the eutectic structure achieves a good continuous growth between two solidified layers. The eutectic phases show sharp interface bonding with a defined orientation relationship. The dislocations and crack deflection at high-density phase interfaces importantly contribute to the enhanced fracture toughness. 相似文献
83.
《Ceramics International》2020,46(5):6174-6181
The ZrO2 alloying effect is widely used to optimize the thermo-mechanical properties of potential thermal barrier coatings. In this study, dense x mol% ZrO2-Gd3NbO7 with C2221 space group were manufactured via a solid-state reaction. The crystalline structure was determined through X-ray diffraction and Raman spectroscopy, when the surface morphology was observed by scanning electron microscopy. ZrO2-Gd3NbO7 had identical orthorhombic crystal structures, and there was no second phase. The crystalline structure of ZrO2-Gd3NbO7 shrunk with the increasing ZrO2 content as indicated by XRD and Raman results. The heat capacity and thermal diffusivity of ZrO2-Gd3NbO7 were 0.31–0.43 J g−1 K−1 (25–900 °C) and 0.25–0.70 mm2/s (25–900 °C), respectively. It was found that ZrO2-Gd3NbO7 had much lower thermal conductivity (1.21–1.82 W m−1 K−1, 25–900 °C) than YSZ (2.50–3.00 W m−1 K−1) and La2Zr2O7 (1.50–2.00 W m−1 K−1). The thermal expansion coefficients (TECs) were higher than 10.60 × 10−6 K−1 (1200 °C), which were better than that of YSZ (10.00 × 10−6 K−1) and La2Zr2O7 (9.00 × 10−6 K−1). The mechanical properties of Gd3NbO7 change little with the increasing ZrO2 content, Vickers hardness was about 10 GPa, and Young's modulus was about 190 GPa, which was lower than YSZ (240 GPa). Compared with previous work about alloying effects, much lower thermal conductivity was obtained. Due to the high melting point, high hardness, low Young's modulus, ultralow thermal conductivity and high TECs, it is believed that ZrO2-Gd3NbO7 is promising TBCs candidate. 相似文献
84.
《Ceramics International》2020,46(13):21211-21215
A ternary solid solution of Bi0.5Na0.5TiO3–Bi0.5K0.5TiO3–Bi(Mg2/3Ta1/3)O3 (BNKT-xBMT) lead-free electroceramics was synthesized by a solid-state reactive sintering technique. The electrostrain, dielectric, and ferroelectric properties as well as the impedance characteristics and the microstructure were systematically assessed. With the increase of BMT, the BNKT-xBMT ceramics gradually transformed from non-ergodic relaxor phase to ergodic relaxor phase, manifested as the ferroelectric-to-relaxor temperature (TF-R) shifts towards below room temperature. Additionally, the ferroelectric hysteresis curves became pinched, and the strain curve changed from butterfly-shaped into sprout-shaped. At the ergodic relaxor composition of x = 0.04, a large electrostrain value (S = 0.4%; under an electric field of 60 kV/cm, d33* = 632 pm/V) was achieved, which is mainly attributed to the electric-field-induced transition from the ergodic relaxor phase to the ferroelectric phase. 相似文献
85.
《Ceramics International》2020,46(2):2116-2121
Zn0.95V0.05O ceramics, elaborated from milled ZnO and V2O5 nanopowders, were sintered at 900, 1000 and 1100 °C for 1, 2, 4, 6, 10 and 14 h. The growth kinetics was studied identifying the grain growth exponent, the activation energy and the pre-exponential factor. The high V2O5 concentration allowed a rapid grain growth at 900 °C only at the very first stages (t < 1 h). Meanwhile, at temperatures of 1000 and 1100 °C, the grain growth was extremely fast with a growth exponent of 0.72. The magnetic properties of the samples indicate that ferromagnetism exist in all samples in different magnitudes depending on the sintering conditions. In particular, the maximum magnetization was obtained on the sample sintered at 1100 °C for 14 h, despite the reduction of V concentration. Additionally, secondary paramagnetic phases were detected in the samples sintered at lower temperatures and shorter sintering times. 相似文献
86.
《Ceramics International》2020,46(11):19228-19231
As a promising high-temperature ceramic, aluminum silicon carbide (Al4SiC4) has attracted much attention. Al4SiC4 is usually synthesized at high temperatures with a long reaction time in an electric furnace. Self-propagating high-temperature synthesis (SHS) is a promising technique for rapid synthesis. In this study, Al4SiC4 was prepared by the SHS method from a mixture of silicon, aluminum and carbon black with the addition of poly(tetrafluoroethylene) (PTFE) as an exothermic promoter. The experimental results showed that the use of a high-pressure Ar atmosphere could retain the gaseous materials in the pellet mixture, and the PTFE additive promoted the formation of silicon carbide. In addition, the oxide layer present on the surface of silicon particles inhibited the reaction between silicon and carbon. As a result, high-purity Al4SiC4 could be synthesized from aluminum, silicon, and carbon black with 15 wt% PTFE under 1.0 MPa Ar atmosphere in several seconds by the SHS method. 相似文献
87.
MOF assisted synthesis of a Ho2O3/CNT nanocomposite photocatalyst for organic pollutants degradation
《Ceramics International》2020,46(11):19084-19091
In this work, a holmium oxide (Ho2O3/CNT) photocatalysts were successfully synthesized through a MOF assisted route for the first time. The effects of the morphology and purity on the photocatalytic behavior of the products, were investigated by determining various physicochemical properties. The Ho2O3/CNT nanocomposite was systematically analyzed by powder X-ray diffraction (P-XRD), transmission electron microscopy (TEM), ultraviolet–visible diffuse reflectance spectroscopy (UV–vis DRS), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy studies. The Ho2O3 derived from a MOF assisted synthetic route using Ho(NO3)3·5H2O and terephthalic acid with a 1:1 M ratio at a temperature of 750 °C for 3 h prove the most advantageous, 98% degradation of 20 mg/L aqueous tetracycline pollutant was observed within 60 min. The elevated photocatalytic activity was mainly attributable to the unique synthetic route, improved crystallinity, wide UV-light absorption rate and excellent adsorption capabilities of CNT, as well as enhanced oxygen deficiency. The photocatalytic results confirm that the Ho2O3/CNT nanocomposite is an efficient photocatalyst for the degradation of toxic tetracycline pollutant and is thus suitable for use in environmental remediation. 相似文献
88.
《Journal of the European Ceramic Society》2020,40(4):1005-1013
Ar ion bombardment was conducted to modify the SiC surface microstructures, which had a vital effect on the interfacial microstructure and shear property of brazing joints. The amorphous layer with thickness of ∼120 nm was formed on the bombarded surface, accompanied with plenty of dislocations and twins beneath the amorphous layer. Reliable SiC/AgCu-Ti/SiC joints were brazed in vacuum at 900 °C for 10 min, and the interfacial microstructure was investigated by SEM, EDS and TEM in detail. When the ion bombarded SiC was used as substrates, the microstructure of brazing beam was optimized as SiC / Ti5Si3 + TiC mixed layer / Ag(s,s) + Cu(s,s) containing TiCu / Ti5Si3 + TiC mixed layer / SiC, in which the interfacial stratification was eliminated compared to the conventional SiC brazing. The shear strength was improved to 30.9 MPa with ion bombardment, which was ∼72.6 % higher than that of the original SiC joints without ion bombardment. The proposed Ar ion bombardment method provides a novel way to modify the brazability of ceramics. 相似文献
89.
《Journal of the European Ceramic Society》2020,40(4):1186-1190
Two melilite ceramics Sr2AGe2O7 (A = Mg, Zn) with low permittivity were prepared by a solid-state reaction method. The crystal structure and microstructure of the ceramics were characterized by X-ray diffraction, transmission electron microscopy, Raman spectroscopy, and scanning electron microscopy. Both ceramics crystallized in a single melilite structure with a tetragonal space group P-42m (113) and exhibited homogeneous microstructures. Optimum microwave dielectric properties with relative permittivity (εr) of 8.56, quality factor (Q × f) of 28,800 GHz, and temperature coefficient of resonance frequency (τf) of −70.5 ppm/°C were obtained in Sr2MgGe2O7 sintered at 1330 °C. Sr2ZnGe2O7 possessed εr of 8.81, Q × f of 35,700 GHz, and τf of −84.4 ppm/°C when sintered at 1290 °C. Thermal stability of resonance frequency was accessible when the negative τf values of Sr2AGe2O7 were adjusted after the formation of composite ceramics with CaTiO3. 相似文献
90.
Anton Polotai Julie Voak Jim Henry David Thoss Yi Yang Sanjay Chitale 《International Journal of Applied Ceramic Technology》2020,17(2):728-733
The need for electronics to operate at temperatures of 200°C and above continues to grow. These applications include avionics, aerospace, automotive, downhole drilling, mining, and many others. To satisfy this demand, a significant amount of research and development has been conducted. Despite the efforts, the number of new electronic components designed specifically for high-temperature operation is still relatively limited. In Low Temperature Co-fired Ceramic (LTCC) packages, LTCC materials are generally used as the host media for a number of pre-fabricated semiconductor components. As a result, reliability of the entire LTCC package largely depends on the performance of the least robust component. Ferro A6M-E and Ferro L8 are the two well-established and recognized LTCC dielectrics widely used for mid and high frequency LTCC applications, including several high reliability aerospace and defense applications that require demanding Mil-Spec qualifications. This study is our first attempt to characterize and understand basic high-temperature dielectric properties of these two commercial LTCC materials. The secondary objective is to initiate a dialogue in attempt to establish reliability requirements for LTCC packages dedicated for high-temperature operation. 相似文献