ZrB 2 -SiC coatings with varied porous structures were deposited on SiC fiber tows using the sol-gel method and cured at 1400 ℃ in vacuum. Tensile strength of the coated SiC fibers were much lower than that of the uncoated fibers. The bimodal distribution in the Weibull plot of the coated SiC fibers demonstrated that the fracture of the coated fiber can be attributed to two types of defects: the porous structure of the coating and the fiber defects. Detailed morphology and microstructure characterization of the coating and fiber combined with strength calculation were carried out to investigate the individual contribution of the fiber defects and the porous coating layer respectively. The results revealed that apart from the fiber damage during the coating process the porous structure of the fiber coating has a non-negligible effect on the fiber strength, presumably due to a relatively strong bonding between the fiber and coating.
The structural stability of supported metal nanoparticles determines the activity and longevity of heterogeneous catalysts. Unfortunately, the chemical/thermal working environment inevitably accelerates metal sintering to larger crystallites that leads to the degradation of catalytic performance. Here, we demonstrate that the distribution of defects in carbon support as an inherent parameter plays a crucial role in catalyst sintering. Based on in-situ transmission electron microscopy studies, the strong metal-support interaction between platinum (Pt) nanoparticles and defect-rich graphene nanoflakes largely suppresses metal sintering up to 700 °C. Particularly, the optimal carbon support can be achieved in the annealing process, in which the mass transfer and charge transport can be enhanced by accurately manipulating the distribution of defects in carbon matrix and graphitization degree. It is worth noting that the screened Pt/GNs-300 exhibits impressive oxygen reduction reaction performance with high half-wave potential (0.91 V), mass activity (108.1 A g –1 Pt ) and excellent stability. By its ascendancy in ORR, the Pt/GNs-300 exhibits a high open-circuit voltage of 1.41 V and a maximum power density of 198.6 mW cm −2 in Zn-air battery, implying its brilliant practicability. This work paves a pathway for achieving sinter-resistant metal-loaded catalysts in energy electrocatalysis.
Jianning Liu,Dongyan Zhang,Yangxi Yan,Zhimin Li,Fei Li,Sen Yang
Acceptor doping is a common method for hardening modified piezoelectric ceramics. The mechanism through which the hardening effect can be improved has been widely studied and verified. However, the effect of defects caused by different valence states of the B-site ions on the properties of multicomponent piezoelectric ceramics remains to be discussed. Therefore, in this work, a novel Pb(Ni 1/3 Nb 2/3 )O 3 –Pb(In 1/2 Nb 1/2 )O 3 –Pb(Mn 1/3 Nb 1/2 )–PbTiO 3 quaternary hard ceramic with excellent performance is prepared and studied. The interaction between grain-boundary defects and defect dipoles is proposed to be the mechanism behind the observed excellent performance. It is found that different types of defects improve the hardening effect in various ways. These results can provide a theoretical basis for the preparation of multicomponent piezoelectric ceramics with better properties.
Jinze Lyu,Junxian Gao,Min Zhang,Yanhong Wang,Dandan Hu,Juan Yi,Junbo Zhong,Ji Li,Shuo Wang
The distribution of bulk and surface defects significantly affects the separation and injection of photogenerated charge carriers. In this study, we provide a strategy of SiO 2 -shell-enhanced F modification to optimize the distribution of bulk and surface defects. The effects of SiO 2 coating and F modification on the physical structure, the separation behavior of photogenerated charge carriers, and the photocatalytic activity of P25 were studied by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, surface photovoltage spectroscopy, and toluene degradation experiments. Results showed that the removal rate of toluene over SiO 2 -F-modified P25 was significantly higher than those over P25 and F modified P25. The SiO 2 -shell-enhanced F modification simultaneously increased the content of surface Ti 3+ and reduced the bulk defects, thereby enhancing the separation of charge carriers. Furthermore, F doped at surface exerted a strong catalytic effect on the removal of toluene, whereas F doped in lattice caused the recombination of photogenerated charge carriers. The SiO 2 coating and calcination treatment significantly increased the amount of F ions doped at TiO 2 surface and inhibited F doping in lattice.
危险品化学品经营许可证（带存储）