Reactions de ligands derives de l'hydroxylamine et de l'hydrazine avec des oxocomplexes de molybdene (VI) et de tungstene (VI) : synthese et etude structurale de nouveaux organopolyoxometallates

SIGLECNRS T Bordereau / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

EPIDEMIOLOGIE DE LA CRYPTOSPORIDIOSE DES MAMMIFERES

NANTES-Ecole Nat.Vétérinaire (441092302) / SudocSudocFranceF

Fretting Characteristics of Rubber X-Ring Exposed to High-Pressure Gaseous Hydrogen

The rubber ring is an essential component of high-pressure hydrogen storage systems. However, the fretting damage can lead to the seal failure of the rubber ring, which may cause hydrogen leakage. Rubber X-ring has been proven to own excellent static sealing performance, while its fretting characteristics under high-pressure hydrogen remain unclear. In this study, a numerical model is developed to explore the fretting characteristics of the X-ring combined seal, in which the effect of hydrogen swelling is well considered. The stress distribution of the fretting seal and the effects of fretting amplitude, friction coefficient, hydrogen pressure, and pre-compression ratio on the fretting behavior of the X-ring are investigated. Moreover, the similarities and differences in the fretting performance of X-ring and O-ring under high-pressure hydrogen are discussed. It is shown that the evolution of the stress concentration zone inside the X-ring is closely linked to the cover’s drag direction and the wedge-ring’s blocking action. The X-ring enters the fretting cycle earlier with increased fretting amplitude, whereas the fretting period remains unchanged. Furthermore, increasing the hydrogen pressure and pre-compression ratio could enhance the fretting sealing performance. The friction coefficient and hydrogen pressure increase the possibility of failure due to cracks or elasticity. The fretting characteristics of the X-ring are superior to those of the O-ring, denoting that X-ring may be an alternative to the O-ring in the fretting seal structure. This work is of theoretical importance for the quantitative evaluation and reliable prevention of fretting damage to rubber rings and improving the safety of high-pressure hydrogen storage systems

Fretting Characteristics of Rubber X-Ring Exposed to High-Pressure Gaseous Hydrogen

The rubber ring is an essential component of high-pressure hydrogen storage systems. However, the fretting damage can lead to the seal failure of the rubber ring, which may cause hydrogen leakage. Rubber X-ring has been proven to own excellent static sealing performance, while its fretting characteristics under high-pressure hydrogen remain unclear. In this study, a numerical model is developed to explore the fretting characteristics of the X-ring combined seal, in which the effect of hydrogen swelling is well considered. The stress distribution of the fretting seal and the effects of fretting amplitude, friction coefficient, hydrogen pressure, and pre-compression ratio on the fretting behavior of the X-ring are investigated. Moreover, the similarities and differences in the fretting performance of X-ring and O-ring under high-pressure hydrogen are discussed. It is shown that the evolution of the stress concentration zone inside the X-ring is closely linked to the cover’s drag direction and the wedge-ring’s blocking action. The X-ring enters the fretting cycle earlier with increased fretting amplitude, whereas the fretting period remains unchanged. Furthermore, increasing the hydrogen pressure and pre-compression ratio could enhance the fretting sealing performance. The friction coefficient and hydrogen pressure increase the possibility of failure due to cracks or elasticity. The fretting characteristics of the X-ring are superior to those of the O-ring, denoting that X-ring may be an alternative to the O-ring in the fretting seal structure. This work is of theoretical importance for the quantitative evaluation and reliable prevention of fretting damage to rubber rings and improving the safety of high-pressure hydrogen storage systems

Preparation of Superhydrophobic Coating on Aluminum Alloy by Dip - Coating Method and Its Corrosion Resistance

For improving the corrosion resistance of aluminum alloy, a superhydrophobic coating was prepared on the surface of 6063 aluminum alloy by dip - coating method. The microscopic morphology, composition and roughness of the coating were analyzed by scanning electron microscope, energy dispersive spectrometer and 3D optical profiler. Meanwhile, the bonding performance of the coating to the substrate was evaluated by tape test, and the corrosion behavior of the coating was studied by electrochemical potentiodynamic scanning polarization curve and AC impedance spectroscopy. Results showed that the coating had a micro/nano structure and showed a superhydrophobic characteristic with a water contact angle up to 152.1°. The corrosion resistance of the coating was excellent in 3.5% NaCl solution. In comparison with the substrate, the corrosion potential of the coating shifted positively 407 mV, the corrosion current density decreased by three orders of magnitude, and the impedance modulus in the low - frequency region increased by seven orders of magnitude, indicating that the superhydrophobic coating could significantly improve the corrosion resistance of 6063 aluminum alloy

A Bibliometric and Visualized Overview of Hydrogen Embrittlement from 1997 to 2022

The mechanical properties of materials deteriorate when hydrogen embrittlement (HE) occurs, seriously threatening the reliability and durability of the hydrogen system. Therefore, it is important to summarize the status and development trends of research on HE. This study reviewed 6676 publications concerned with HE from 1997 to 2022 based on the Web of Science Core Collection. VOSviewer was used to conduct the bibliometric analysis and produce visualizations of the publications. The results showed that the number of publications on HE increased after 2007, especially between 2017 and 2019. Japan was the country with the highest numbers of productive authors and citations of publications, and the total number of citations of Japanese publications was 24,589. Kyushu University was the most influential university, and the total number of citations of Kyushu University publications was 7999. Akiyama was the most prolific and influential author, publishing 88 publications with a total of 2565 citations. The USA, South Korea and some European countries are also leading in HE research; these countries have published more than 200 publications. It was also found that the HE publications generally covered five topics: “Hydrogen embrittlement in different materials”, “Effect of hydrogen on mechanical properties of materials”, “Effect of alloying elements or microstructure on hydrogen embrittlement”, “Hydrogen transport”, and “Characteristics and mechanisms of hydrogen related failures”. Research hotspots included “Fracture failure behavior and analysis”, “Microstructure”, “Hydrogen diffusion and transport”, “Mechanical properties”, “Hydrogen resistance”, and so on. These covered the basic methods and purposes of HE research. Finally, the distribution of the main subject categories of the publications was determined, and these categories covered various topics and disciplines. This study establishes valuable reference information for the application and development of HE research and provides a convenient resource to help researchers and scholars understand the development trends and research directions in this field