Mechanical and tribological properties of graphene nanoplatelets-reinforced titanium composites fabricated by powder metallurgy

Titanium matrix composite reinforced by graphene nanoplatelets(GNPs)was fabricated via powder metallurgy route.Hot isostatic pressing and hot extrusion were used to consolidate the mixed powder of GNPs and TC4 titanium(Ti)alloy.The microstructures,mechanical properties and sliding wear performance of Ti/GNPs composite had been researched to evaluate the rein forcing effect of GNPs on tita nium matrix.Microstructure observation indicates that GNPs could restrain grai n growth slightly in titanium matrix.Titanium matrix and graphene exhibit a clean and firm interface formed by means of metallurgical bonding on atomic scale.Compared with the monolithic titanium alloy,the composite with 1.2 vol.%GNPs exhibits significantly improved elastic modulus and strength.The sliding wear test shows that there is an obvious enhancement in the tribological performance of Ti/GNPs composite with 1.2 vol.%GNPs.The results of this work indicate that GNP is an efficient reinforcenient material in titanium matrix.The strengthening mechanism including precipitates strengthening,load transfer and grain refinement mechanism of GNPs in titanium matrix was discussed.A modified shear-lag model was used to analyze the reinforcement contribution of the stress transfer mechanism.The calculation shows that the stress load mechanism constitutes the main strengthening mechanism in Ti/GNPs composite.

De novo synthesis of bifunctional conjugated microporous polymers for synergistic coordination mediated uranium entrapment

This work reports a de novo synthesis of novel bifunctional conjugated microporous polymers(CMPs)exhibiting a synergistic-effect involved coordination behavior to uranium.It is highlighted that the synthetic strategy enables the engineering of the coordination environment within amidoxime functionalized CMP frameworks by specifically introducing ortho-substituted amino functionalities,enhancing the affinity to uranyl ions via forming synergistic complexes.The CMPs exhibit high Brunauer-Emmett-Teller(BET)surface area,well-developed three-dimensional(3D)networks with hierarchical porosity,and favorable chemical and thermal stability because of the covalently cross-linked structure.Compared with the amino-free counterparts,the adsorption capacity of bifunctional CMPs was increased by almost 70%,from 105 to 174 mg/g,indicating evidently enhanced binding ability to uranium.Moreover,new insights into coordination mechanism were obtained by in-depth X-ray photoelectron spectroscopy(XPS)analysis and density functional theory(DFT)calculation,suggesting a dominant role of the oxime ligands forming a 1:1 metal ions/ligands(M/L)coordination model with uranyl ions while demonstrating the synergistic engagement of the amino functionalities via direct binding to uranium center and hydrogen-bonding involved secondary-sphere interaction.This work sheds light on the underlying principles of ortho-substituted functionalities directed synergistic effect to promote the coordination of amidoxime with uranyl ions.And the synthetic strategy established here would enable the task-specific development of more novel CMP-based functional materials for broadened applications.