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11.
《Journal of the European Ceramic Society》2005,25(9):1603-1610
In a recent work [Basu, B., Lee, J. H. and Kim, D. Y., Development of WC-ZrO2 nanocomposites by spark plasma sintering. J. Am. Ceram. Soc. 2004 87(2), 317–319], the processing of ultrahard WC–ZrO2 nanocomposites using spark plasma sintering is reported. In the present work, we investigate the processing and properties of WC–6 wt.% ZrO2 composites, densified by pressureless sintering route. The densification of the WC–ZrO2 composites was performed in the temperature range of 1500–1700 °C with varying time (1–3 h) in vacuum. The experimental results indicate that significantly high hardness of 22–23 GPa and moderate fracture toughness of ∼5 MPa m1/2 can be obtained with 2 mol% Y–stabilized ZrO2 sinter-additive, sintered at 1600 °C for 3 h. Furthermore, the friction and wear behavior of optimized WC–ZrO2 composite is investigated on a fretting mode I wear tester. The tribological results reveal that a moderate coefficient of friction in the range from 0.15 to 0.5 can be achieved with the optimised composite. A transition in friction and wear with load is noted. The dominant mechanisms of material removal are tribochemical wear and spalling of tribolayer. 相似文献
12.
《Journal of the European Ceramic Society》2006,26(10-11):1957-1960
The structure evolution, sintering behavior and microwave dielectric properties of La(2−x)/3Nax(Mg1/2W1/2)O3 (x = 0–0.5) were investigated in this paper. The X-ray diffraction (XRD) results show that all samples exhibit single phase, and the structure changed from orthorhombic when 0 ≤ x < 0.3 to monoclinic phase when 0.3 ≤ x ≤ 0.5. The size and ordering degree of A/B-site domains decrease with the increase in x value. The sintering temperature of the Na-doped samples increased compared to the pure La2/3(Mg1/2W1/2)O3 (LMW) due to the estimated decrease in the concentration of A-site vacancies. The addition of Na+ ion does not affect the dielectric permittivity greatly. The Q × f value decreases with the increase in x value, although the estimated concentration of A-site vacancies decreases with increasing x, which may be ascribed to the decrease of A/B-site ordering and domain size with the increase in x. The temperature coefficient of resonant frequency changed from negative values into positive values with the increase in x value. 相似文献
13.
《Ceramics International》2019,45(10):13179-13186
Pb-free piezoceramics of K0.5Na0.5Nb1-xSbxO3 + 1 mol% CuO are synthesized via a solid-state reaction. Furthermore, the transformation of hardening to softening behaviors induced by Sb substitution is exhibited and the corresponding microscopic mechanism is proposed. The CuO-doped K0.5Na0.5NbO3 ceramic without adding Sb exhibits extremely hardening characteristics (i.e., ultrahigh Qm of ∼2426, low tanδ of 0.32%, and pinched ferroelectric hysteresis loop) due to the formation of defect combinations ( and ). Whereas, the addition of Sb dramatically reduces the levels of defect combinations, leading to obviously softening properties (d33 > 210 pC N−1, kp > 40%, low Qm, and normal single P-E hysteresis loop). Our results indicate that the decrease of defect combinations with Sb addition should be responsible for the hardening-softening transformation of piezoelectricity and ferroelectricity in CuO-doped K0.5Na0.5Nb1-xSbxO3 piezoceramics. 相似文献
14.
15.
Ca3Co4O9 ceramics were prepared using the sol-gel process with ordinary pressing sintering and their thermoelectric properties were
measured from room temperature to 673 K. The experimental results show that single phase Ca3Co4O9 can be fabricated at 750–900 °C in different citrate acid molar proportions for 0.2–1.0. For all the oxides, both the Seebeck
coefficients S and the electrical conductivities κ increase with the increasing temperature. The Seebeck coefficients S are all positive. The thermal conductivities k increase with the increasing temperature also and the lattice thermal conductivity
κ
l plays an important role to the thermal conductivity κ. The citrate acid molar proportions have a large influence on the particle sizes, which influences the thermoelectric properties
of the ceramics. The figure of merit increases with the increasing temperature and reaches 4.5×10−5 K−1 at 573 K for the sample in the citrate acid molar proportion of 0.46. 相似文献
16.
In this paper, ZnCo2O4 was deposited on nickel substrate by electrophoretic deposition (EPD) method as electrocatalyst for the oxygen evolution reaction. The effect of electrophoresis variables including the deposition time, the applied voltages was discussed. XRD, SEM, and electrochemical measurement techniques were used to characterize the deposit and ZnCo2O4/Ni electrode. Compared with the ZnCo2O4 electrode prepared by nitrate decomposition method, the electrophoretic ZnCo2O4 electrodes exhibit better electrocatalytic properties and higher mechanical stability. And the electrode prepared at 10 V for 5 min has the best electrocatalytic properties with the overpotential of only 0.203 V at current density of 100 mA cm−2. 相似文献
17.
Yu Huang Liang Shu Suwei Zhang Zhen Zhou Yue-Yu-Shan Cheng Biaolin Peng Lisha Liu Yuanyuan Zhang Xuping Wang Jing-Feng Li 《Journal of the American Ceramic Society》2021,104(8):4119-4130
With the development of advanced electrical and electronic devices and the requirement of environmental protection, lead-free dielectric capacitors with excellent energy storage performance have aroused great attention. However, it is a great challenge to achieve both large energy storage density and high efficiency simultaneously in dielectric capacitors. This work investigates the energy storage performance of sol-gel-processed (K,Na)NbO3-based lead-free ferroelectric films on silicon substrates with compositions of 0.95(K0.49Na0.49Li0.02)(Nb0.8Ta0.2)O3-0.05CaZrO3-x mol% Mn (KNN-LT-CZ5-x mol% Mn). The appropriate amount of Mn-doping facilitates the coexistence of orthorhombic and tetragonal phases, suppresses the leakage current, and considerably enhances the breakdown strengths of KNN-LT-CZ5 films. Consequently, large recoverable energy storage density up to 64.6 J cm−3 with a high efficiency of 84.6% under an electric field of 3080 kV cm−1 are achieved in KNN-LT-CZ5-5 mol% Mn film. This, to the best of our knowledge, is superior to the majority of both the lead-based and lead-free films on silicon substrates and thus demonstrates great potentials of (K,Na)NbO3-based lead-free films as dielectric energy storage materials. 相似文献
18.
Rui Xu Jing Song Shijiao Zhao Lei Nie Changsheng Deng Shaochang Hao Xingyu Zhao Bing Liu Jingtao Ma 《Journal of the American Ceramic Society》2021,104(11):5489-5500
ZrO2 microspheres are widely used as a simulant of UO2 in the development of nuclear fuel. However, the cracking of ZrO2 microspheres prepared by internal gelation is still a challenge during drying and sintering processes. To address this issue, we designed and optimized the washing process for obtaining crack-free ZrO2 microspheres. Through thermogravimetric, infrared, Raman, BET, and SEM analysis, it is shown that the cracking of the microspheres is mainly related to the pores in microspheres. The washing solvent with low surface tension is used to reduce the effect of capillary force on pore shrinkage. Therefore, the optimal washing process was designed as trichloroethylene (TCE)—0.5 M NH3.H2O—Propylene glycol methyl ether (PM) and gel microspheres with a high specific surface area of 315.3 m2/g and pore volume of 0.4125 cm3/g were obtained. The characterizations also further showed that when the microspheres were dried and sintered, the water vapor and the decomposition gas of organic matter were completely released from the pores in the microspheres. Our new washing process could be directly extended for preparing crack-free ceramic microspheres by internal gelation. 相似文献
19.
《Journal of the European Ceramic Society》2021,41(16):239-246
The large shrinkage that ceramics undergo during sintering is a severe challenge for high-performance porous ceramics. In this study, we report a powder-based selective laser sintering (SLS) approach to prepare Al2O3 ceramic foams with near-zero shrinkage, high porosity, and outstanding strength. The ceramic foams consist of specific coral-like and hollow-sphere structures derived from the raw Al2O3/Al composite powders via reaction bonding (RB). A near-zero shrinkage of 0.91 ± 0.15 % and a high porosity of 73.7 ± 0.2 % can be achieved based on the Kirkendall effect during the oxidation of Al particles. Meanwhile, the reinforced sintering necks and robust bond-bridge connections between hollow-sphere and coral-like structures result in a remarkable bending strength of 7.37 ± 0.37 MPa. This measured strength is more than six times higher than other fabricated samples from spherical Al2O3 powders, and the comprehensive performance of ceramic foams prepared by this novel SLS/RB strategy is exceptionally remarkable versus that via conventional forming methods. 相似文献
20.
《Journal of the European Ceramic Society》2021,41(15):7662-7669
Piezoelectric energy harvesters (PEH) hold enormous potential for converting mechanical energy from our surrounding environment into electrical energy that can be used for powering portable electronics. Potassium sodium niobate (KNN) is one of the promising alternatives to replace lead-based piezoelectric materials. This work presents a cutting-edge demonstration of synthesis-function-device integration of piezoelectric nanofibers, where the morphology and the composition are engineered towards achieving high device output. We report a flexible nanogenerator based on electrospun Li and Ta-modified lead-free KNN nanofibers yielding a high voltage output of 5.6 V, which is around 9-fold higher than for the Mn-doped KNN nanofibers reported previously. The influence of Li and Ta-incorporation into the KNN lattice on the electromechanical coupling and the effect of a nanofiber morphology are investigated. The net-shaped KNN and Li and Ta-modified KNN nanofibers, synthesized by electrospinning of appropriate sols, maintain their structural integrity upon calcination and firing steps. The phase analysis (XRD) confirms the formation of single-phase (KNN) material. Li and Ta are found to be incorporated on the A and B-sites of the perovskite lattice, respectively. Piezo force microscopy data show the heat-treated nanofibers to exhibit multi-domain ferroelectric properties. 相似文献