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91.
Chencheng Wang Feng Chen Yuanzheng Tang Xiao Chen Junchao Qian Zhigang Chen 《Ceramics International》2018,44(6):5834-5841
Biologically structured carbon/cerium dioxide materials are synthesized by biological templates. The microscopic morphology, structure and the effects of different oxidation temperatures on materials are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) ultraviolet-visible light spectrum (UV–Vis) and X-ray Photoelectron Spectroscopy (XPS). Moreover, by splitting water under visible light irradiation, the hydrogen production is measured to test the photocatalytic property of these materials. The results show that materials made with bamboo biological templates which are immersed in 0.1 mol L?1 of cerium nitrate solution, then carbonizated in nitrogen (700 °C) and oxidized in air (500–600 °C), can obtain the biological structure of bamboo leaves. The product is in the composition of hybrid multilayer membrane, which one is carbon membrane form plant cell carbonation and another is ceria membrane by nanoparticle self assembly. The best oxidation temperature is 550 °C and the band gap of carbon/cerium dioxide materials synthesized at this optimum oxidation temperature could be reduced to 2.75 eV. After exposure to visible light for 6 h, the optimal hydrogen production is about 302 μmol g?1, which is much higher than that of pure CeO2. 相似文献
92.
The focus of this work is to prepare polyvinyl alcohol (PVA) thin film reinforced by green synthesized zirconia nanoparticles. In order to do so, firstly, zirconia nanoparticles were synthesized by the rosemary extract-assisted sol-gel process as both template and stabilizing agents. The results showed that the as-obtained sample with zirconium salt to rosemary extract ratio of 1:4 had a semi-spherical morphology with the mean particle size of 12–17?nm. This nanoparticle was added as reinforcement with different ratios to the polyvinyl alcohol matrix. The mechanical property of the as-prepared nanocomposites revealed that the elastic modulus of 1?wt% ZrO2-PVA sample was about 5.5 times higher than pure PVA thin film. 相似文献
93.
Pure Na0.5Bi0.5TiO3 (NBT), donor W6+ doped NBT (NBTW), acceptor Ni2+ doped NBT (NBTNi), as well as donor W6+ and acceptor Ni2+ codoped NBT (NBTWNi) polycrystalline films are fabricated on indium tin oxide (ITO)/glass substrates via a chemical solution deposition method. The roles of aliovalent-ion substitution on the crystallinity, ferroelectric and dielectric properties of NBT film are mainly investigated. With the introduction of aliovalent-ion, the surface of the doped film becomes more uniform and the leakage current is reduced. Well saturated polarization-electric field (P-E) loops can be observed in W6+ and Ni2+ codoped NBT film due to its lowest leakage currents compared to those of other films. Also, the effect of voltage and frequency on the capacitance-voltage (C-V) curve and the dielectric tunability for the NBTWNi film is discussed. The ferroelectric and dielectric properties are largely improved in NBTWNi film, which can be ascribed to the synergetic effect of high-valence W6+ and low-valence Ni2+ ions. The cooperation between the acceptor and donor cations can effectively eliminate the mobile oxygen vacancies in NBT films. 相似文献
94.
Chemical liquid vapor deposition (CLVD) is a rapid preparation method, but it is rarely involved in fabrication of C/C-UHTCs composites and its technology parameters are hardly discussed. In the present study, C/C-ZrC samples were prepared by CLVD process, and the effects of thermal gradient on the deposition behavior, microstructure and properties were investigated. Results exhibited the density, ZrC content and uniformity of the composites increased as the thermal gradient decreased from 30.4 to 9.8?°C/mm, indicating the deposition behavior was improved gradually. When the thermal gradient was 30.4?°C/mm, the deposition behavior of the specimen was poor, which resulted in the high porosity, small numbers of ZrC blocks and uneven distribution. Therefore, the specimen had a low flexural strength with brittle fracture and poor ablation resistance. As the thermal gradient decrease to 9.8?°C/mm, there was an excellent deposition in the composites, and the composites possessed large amounts of ZrC particles and their dispersion were improved remarkably. In this case, the composites displayed a non-brittle fracture with high strength, and the linear and mass ablation rates were reduced, which indicated an improvement of anti-ablation property. Nevertheless, the deposition was deteriorated evidently when the thermal gradient reached to 0?°C/mm. The density, ZrC content and uniformity of the sample became poor, leading to the decline of mechanical property and ablation resistance. 相似文献
95.
96.
Junjun Chen Jian Chen Xiumin Yao Zhongming Chen Xuejian Liu Zhengren Huang 《Journal of the European Ceramic Society》2018,38(9):3083-3088
SiC/20?wt% ZrB2 composite ceramics were fabricated via pressureless solid phase sintering in argon atmosphere at different temperature. The effect of sintering temperature on microstructure, electrical properties and mechanical properties of SiC/ZrB2 ceramics was investigated. Electrical resistivity exhibits twice significant decreases with increasing sintering temperature. The first decrease from 1900?°C to 2000?°C is attributed to the obvious decrease of continuous pore channels in as-sintered materials. The second decrease from 2100?°C to 2200?°C results from the improvement of carbon crystallization and the disappearance of amorphous layers enveloping ZrB2 grains. Additionally, the increase of sintered density with increasing temperature caused greatly advance of flexural strength, elastic modulus and Vickers hardness. But excessive temperature is detrimental to flexural strength because of SiC grain growth. 相似文献
97.
Xueli Du Yuelong Wang Rongna Shi Zhiyong Mao Zhihao Yuan 《Journal of the European Ceramic Society》2018,38(10):3512-3517
The PbClxS1-x and Pb1-xBixS (x? =?0–0.05) bulks were fabricated with a facile method of hydrothermal synthesis and microwave sintering, and the effect of anionic and cationic donors on the thermoelectric performance of PbS was investigated. Although Cl? and Bi3+ both effectively improved the thermoelectric properties of n-type PbS, more excellent thermoelectric performance was obtained from Cl? doped samples because of higher electrical property and lower thermal conductivity at higher temperature (T? >?600?K). The thermoelectric figure of merit (ZT) reaches 1.04 for PbCl0.015S0.985 at 800?K and increases with temperature increasing without sign of saturation, which is probably the highest value ever reported for single-phase polycrystalline n-type PbS. The results also indicate that the hydrothermal synthesis and microwave sintering can realize anion doping as well as cation doping for n-type PbS at low cost, and PbS should be a robust alternative for PbTe thermoelectric materials. 相似文献
98.
研究了添加锥栗、马铃薯与绿豆回生抗性淀粉(RS3)对米淀粉的冻融稳定性与流变学性质的影响。结果表明:添加锥栗、马铃薯与绿豆RS3都能显著提高米淀粉凝胶的持水率,且冻融超过3次后,其影响的差别越来越显著。随着冻融次数增多,米淀粉凝胶中不易流动水明显降低、自由水显著增加;当冻融次数相同时,添加RS3可使米淀粉凝胶中不易流动水明显增多而自由水显著减少。添加锥栗、马铃薯和绿豆RS3后,米淀粉糊的黏性模量明显增加,而弹性模量的增加更加显著。在相同剪切速率下,添加锥栗、马铃薯和绿豆RS3可以使米淀粉糊的抗剪切强度大大增强。添加相同质量浓度的锥栗、马铃薯和绿豆RS3后,米淀粉糊的稠度系数都大大升高、流体指数和滞后环面积显著减小。 相似文献
99.
《Ceramics International》2020,46(14):22738-22744
(1-x) K0.5Na0.5NbO3 ~ xAl2O3 (x = 0, 0.2, 0.4, 0.6) ceramics were prepared via a traditional solid-state reaction method. The phase structure, micro-morphology, dielectric properties and electromagnetic properties of ceramic samples were studied and analyzed. Results indicate that all the samples are similar to K0.5Na0.5NbO3 (KNN) in perovskite structure. With the increase of Al2O3 content, the X-ray diffraction peaks move to a large angle region, suggesting the substitution of niobium ions by aluminium ions and the distortion of the KNN lattice with a new phase arising. With the increase of Al2O3 content the grain size reduces and the dielectric constant decrease, yielding to the decrease of the electromagnetic shielding performance of ceramic. When the x is 0.4, the minimum value of reflectivity of sample is −28 dB at the frequency of 11.6 GHz. It can be concluded that both the grain size and Al2O3 content can obviously affect the electromagnetic properties of ceramics, which can be easily turned through a multi-layer SiO2 heterojunction structure. 相似文献
100.
Dongdong Xia Xiaokui Yue Haowei Wen 《International Journal of Adaptive Control and Signal Processing》2020,34(12):1812-1830
A novel immersion and invariance (I&I) angular velocity observer is presented for the attitude tracking control of a rigid body with the lack of angular rate. Global exponential convergence of angular velocity estimate errors are guaranteed by an innovative filter design for the estimates' Euclidean norm. The proposed method requires fewer filter states compared with existing I&I angular velocity observer designs, which achieves a simpler closed-loop structure (dynamic reduction). The observer synthesis and convergence are independent of the control torque, which leads to much convenience in establishing “separation property” when combining a proportional-derivative attitude tracking controller driven by angular velocity estimates. A rigorous stability analysis is provided to ensure the (almost) global asymptotic convergence of the overall closed-loop tracking errors, and several numerical simulations are carried out to demonstrate the effectiveness of the combined implementation of proposed angular velocity observer and full-state feedback attitude tracking controller. 相似文献