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1.
《Ceramics International》2022,48(7):9495-9505
Effects of dopants with different valences on the densification behavior and phase composition of a ZrO2–SiO2 nanocrystalline glass-ceramic (NCGC) during pressureless sintering were investigated in this study. The raw powder of Ca2+, La3+, Ce4+ and Ta5+ ions doped ZrO2–SiO2 (referred to as Ca-ZS, La-ZS, Ce-ZS, Ta-ZS, respectively) and pure ZrO2–SiO2 (PZS) sample were synthesized by sol-gel method, followed by pressureless sintering. Compared with the PZS sample, doping of Ca2+ and La3+ ions significantly promoted the densification of the NCGCs. The “densification promotion” effect was attributed to the formation of oxygen vacancies and the decrease of SiO2 viscosity due to doping of aliovalent cations. The dopants with various valences showed significant effects on the phase compositions of the NCGCs during sintering. Doping of Ca2+ ion accelerated the reaction kinetics between ZrO2 nanocrystallites and amorphous SiO2 to yield ZrSiO4. The La3+ ion acted as destabilizer of t-ZrO2, which resulted in a rapid tetragonal (t) to monoclinic (m) ZrO2 phase transformation during sintering, while in the Ta5+ and Ce4+ ions doped sample, the phase transformation occurred gradually. All the doping ions increased the lattice parameters and the volume of t-ZrO2 unit cell, while the effects of the doping ions on the lattice parameters of m-ZrO2 unit cell were more complex. 相似文献
2.
《International Journal of Hydrogen Energy》2020,45(24):13365-13375
A new proton conductor based on 1H-1,2,3-triazole doped nanocrystalline cellulose (2.66 CNC-Tri) has been synthesized for possible use as an electrolyte in proton exchange membrane (PEM) cells. The physicochemical properties of 2.66 CNC-Tri were determined and compared with those of imidazole-doped nanocrystalline (1.17 CNC-Im) and pure nanocrystalline cellulose (CNC). The composites were obtained in the form of a film and their synthesis proceeded under vacuum. The maximum conductivity of 2.66 CNC-Tri was measured to be 0.1 × 10−4 S/m at 175 °C and that of 1.17 CNC-Im to be 1.6 × 10−2 S/m at 155 °C, in the anhydrous state. The composite 2.66 CNC-Tri, compared to 1.17 CNC-Im, has much better thermal properties manifested as stability of the matrix and durability of the heterocyclic molecule. The lifetimes of 2.66 CNC-Tri fulfills the requirements of the U.S. Department of Energy for the minimum lifetimes of a PEM based fuel cell for cars. 相似文献
3.
《Journal of the European Ceramic Society》2020,40(13):4396-4402
The response of nanocrystalline silicon carbide (nc-SiC) to nanoindentation is investigated using molecular dynamics (MD) simulation. It is found that the hardness of the nc-SiC decreases with decreasing grain size, showing an inverse Hall-Petch relationship. The behavior is primarily attributed to the reduced number of intact covalent bonds with grain refinement. Dislocation nucleation and growth in nc-SiC are strongly suppressed by the grain boundaries (GBs). In addition to the dislocation region in the grains, the indentation-induced amorphization of nanograins proceeds preferentially from the GBs, leading to grain shrinkage until the grains are fully amorphized. The results provide an improved understanding of the mechanical properties in nc-SiC and other nanostructured covalent materials. 相似文献
4.
《Ceramics International》2020,46(5):5645-5648
Nanocrystalline silicon carbide (3C–SiC) particles have been irradiated by neutron flux (2 × 1013 n∙cm−2s−1) up to 5 h at the TRIGA Mark II type research reactor. At the present work, thermal properties of nanocrystalline 3C–SiC are comparatively investigated before and after neutron irradiation at the 300 K < T < 1300 K ranges. Simultaneously, the DSC (Scanning Calorimetry), TGA (Thermogravimetric Analysis) and DTG (Differential Thermogravimetric Analysis) experiments were conducted from 300 K up to 1300 K. Oxidation mechanism of nanocrystalline 3C–SiC particles have been theoretically and experimentally studied before and after neutron irradiation. The kinetics of mass and heat flux were analysed at the heating and cooling processes using DSC spectroscopy. 相似文献
5.
《International Journal of Hydrogen Energy》2020,45(7):4653-4672
Current challenge for researchers worldwide is to construct a reliable, efficient, and affordable medium that can store hydrogen reversibly at ambient temperature and pressure for on-board applications. Carbon nanotubes (CNTs) and their composites are considered as leading source of solid-state reversible hydrogen storage medium owing to its unique characteristics including high surface area, nanoporous structure, tuneable properties, low mass density, cage like structure, chemical stability, dissociation of hydrogen molecule, and easy synthesis method. Nanocrystalline metal or metal oxide or hydride is doped/embedded into pristine CNTs via in-situ reduction, wetness impregnation, high-energy ball milling and sputtering method. Characterization techniques of pristine and composites are utilized to study morphological, thermal, qualitative, quantative, and elemental analysis. Nanocomposite hydrogen uptake capacity is frequently measured by volumetric and gravimetric methods. Multifold enhancement of hydrogen storage of composites compared to pristine CNTs is attributed to activation, acidification, purification, ball milling and spillover of physisorbed hydrogen by metal catalyst onto CNTs via spillover mechanism. Hydrogen uptake of CNTs and composites follow monotonous dependence on hydrogen pressure. Composites not only present high hydrogen uptake as compared to pristine CNTs but also shows significant cyclic stability upon successive adsorption–desorption cycles. 相似文献
6.
《Ceramics International》2020,46(12):20038-20044
Double perovskite La2MnNiO6 nanoparticles (approximately 30 nm in diameter) were synthesized using a modified sol-gel method followed by a firing process and used as promising electrode materials for oxygen evolution reactions (OERs). The phase purity of the nanoparticles was verified using X-ray diffraction and Raman spectroscopy measurements. La2MnNiO6 nanoparticles crystallize in a monoclinic structure (P21/n space group) with refined lattice parameters of a = 5.461(5) Å, b = 5.512(3) Å, c = 7.760(5) Å, and β = 90.10(2)°. The elemental composition, particle size, size distribution, and surface area of the La2MnNiO6 nanoparticles were also investigated. La2MnNiO6 nanoparticles are ferromagnetic in nature and exhibit hysteresis with a saturation magnetization value of approximately 9 emu/g. La2MnNiO6 nanoparticles exhibit highly efficient electro-catalytic activity for OERs with a low onset over-potential (approximately 65 mV) and low Tafel slope values (120 mV/dec) in alkaline media. The over-potential of La2MnNiO6 nanoparticles at a current density of 10 mA/cm2 is in good agreement with the reported over-potential (ƞ10) of double perovskites, commercial Pt/C and IrO2 electro-catalysts for promoting OERs. 相似文献
7.
《Ceramics International》2022,48(2):2281-2288
Understanding the phase regulation mechanism of BaTiO3 synthesized by a hydrothermal method is a complicated and challenging task. Here, we successfully prepared cubic and tetragonal BaTiO3 single nanocrystals by changing the ratio of water and ethanol in the solvent. We confirm that the BaTiO3 phase is mainly affected by the hydroxylation process due to the reaction with solvent. In particular, ethanol can be catalytically oxidized by titanium atoms, cause BaTiO3 hydroxylation and promote the formation of a cubic phase. In the mixed solution of ethanol and water, the hydroxylation process is suppressed, which facilitates the formation of the tetragonal phase. The relationship framework between the solvent ratio, phase structure and hydroxyl defects of BaTiO3 is established. Tetragonal BaTiO3 with fewer hydroxyl defects can promote charge transfer and surface reaction after polarization, thereby enhancing their photoelectric catalytic performance. This work provides references for the controllable synthesis of ferroelectric nanocrystals by hydrothermal methods and new insight for the utilization of polarization in photoelectrocatalysis applications. 相似文献
8.
本文以芦荟叶提取液为还原剂和稳定剂,成功地制备了小粒径、球状的金纳米粒子。在这种方法中,简单的芦荟叶提取液和金源混合,没有使用有毒试剂,因此该方法是一种生态友好的合成纳米金的方法。混合溶液的颜色从浅黄色变到紫色,表明生成了纳米金粒子。采用紫外-可见吸收光谱(UV-vis)、激光粒径分析仪(DLS)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、傅里叶变换红外光谱(FT-IR)、X-射线衍射(XRD)等方法对合成的纳米金粒子进行了表征和性能测试。紫外-可见光谱的吸收峰再次表明金纳米颗粒的形成。XRD分析表明所生成的纳米我金具有高度结晶性。TEM和SEM表明纳米金颗粒呈球形,粒径分布在20 nm到60 nm之间。FT-IR证实了金纳米粒子提取物所保护,使其不发生团聚和氧化。论文研究了反应温度、氯金酸溶液和提取物的用量对纳米金粒径的影响。结果表明,这些参数在金纳米粒子的合成中起着重要的作用。 相似文献
9.
《Materials Science & Technology》2013,29(8):1303-1308
AbstractBulk nanocrystalline Fe3Al based materials with 5, 10 and 15 wt-%Mo were prepared by aluminothermic reaction. The microstructure and mechanical properties of the materials were investigated. It was shown that the materials consisted of a nanocrystalline matrix phase that was composed of Fe, Al and Mo and a little Al2O3 contamination phase. The nanocrystalline phase had a disordered bcc crystal structure. Average grain sizes of the nanocrystalline phase of the materials with 5, 10 and 15 wt-%Mo were 19, 31 and 24 nm respectively and that of the material with 5 wt-%Mo was the smallest. The materials with 10 and 15 wt-%Mo exhibited brittle behaviour in compression, whereas the material with 5 wt-%Mo had a large plastic deformation. The material with 5 wt-%Mo had the highest bending strength and the lowest compressive yield strength. 相似文献
10.
An energy balance method to calculate the initiation of crack at triple junctions in nanocrystalline materials with the finest grains is developed. In the steady state of crack initiation, work done by an applied stress is considered to be dissipated as heat by specific rotational deformation, grain boundary sliding and diffusion. The stress field at crack tips, the energies of rotational deformation, grain boundary sliding and grain boundary diffusion are calculated. The analysis demonstrates that the existence of finest grains will lead to enhanced local fracture toughness. 相似文献