Niduterpenoids A (1) and B (2), two sesterterpenoids with a highly congested hexacyclic 5/5/5/5/3/5 carbon skeleton but no unsaturated functional group, were isolated from Aspergillus nidulans. Their structures were determined by a combination of spectroscopic data and single-crystal X-ray diffraction analyses. Compounds 1 and 2 present the first examples of sesterterpenoids with a hexacyclic carbon ring system. Compound 1 showed no cytotoxicity but abolished 17-estradiol-induced cell proliferation (IC 50 = 11.42 ± 0.85 μM).
Because of the dilemma that the current industrial Cu enhancement methods lead to a significant decline in conductivity and ductility, Cu matrix composites reinforced by oriented multi-walled carbon nanotubes (MWCNTs) were prepared through sintering, hot extrusion, and cold drawing. Before sintering, Ni, Cu, and Ni&Cu coatings were electroless plated on MWCNTs as the intermediate transition layer, and then they were mixed with Cu powder through a nitrogen bubbling assisted ultrasonic process. By analyzing the composition, microstructure, and formation mechanism of the interface between MWCNTs and the matrix, the influence and mechanism of the interface on the mechanical properties, conductivity, and ductility of the composites were explored. The results indicated that MWCNTs maintained a highly dispersed and highly consistent orientation in the Cu matrix. The coating on Ni@CNT was the densest, continuous, and complete. The Ni@CNTs/Cu composite had the greatest effect, while the Cu composite reinforced by MWCNT without coating had the smallest reduction in elongation and conductivity. The comprehensive performance of the Cu@CNTs/Cu composite was the most balanced, with an ultimate tensile strength that reached 373 MPa, while the ductility and conductivity were not excessively reduced. The axial electrical and thermal conductivity were 79.9 IACS % (International Annealed Copper Standard) and 376 W/mK, respectively.
The effects of electroless coatings on the microstructure and composition of the interface between multi-walled carbon nanotubes (MWCNTs) and a Cu matrix and the mechanical properties and wear behavior of the resulting copper matrix composites were investigated. Ni and Cu coatings were electrolessly plated on MWCNTs and mixed subsequently with copper powder. Then copper matrix composites were prepared by sintering, hot extrusion and cold drawing processes. The results showed that MWCNTs were straight, long, uniformly dispersed and aligned in the composites. The Ni coating is more continuous, dense and complete than a Cu coating. The tensile strength, compressive strength, microhardness and tribological properties of Ni@MWCNTs/Cu composite along the drawing direction were enhanced most. The ultimate tensile strength and compressive strength were 381 MPa and 463 MPa, respectively. The friction coefficient and wear rate were reduced by 59% and 77%, respectively, compared with pure Cu samples. This study provides a new insight into the regulation of tribological properties of composites by their interface.
In view of the poor weldability of electrodes in resistance spot welding (RSW) of galvanized steel sheets, the life of oriented multi-walled carbon nanotubes reinforced Cu matrix composites (Cu@MWCNTs/Cu) electrodes was studied, in which Cu coated multi-walled carbon nanotubes (MWCNTs) are arranged along the flow direction of working electric/force. By analyzing the macro/microscopic morphology, microstructure, hardness, texture and composition of the failed composite electrodes and the commercially CuCrZr electrode, the mechanism of the weldability enhancement and failure of electrodes was discussed. The results show that the life of Cu@ MWCNTs/Cu electrodes (2150 welds) is 3 times longer than that of CuCrZr electrode (600 welds), and the degradation rate is much slower. The hardness of Cu@MWCNTs/Cu electrodes is 30-40Hv higher. The content of recrystallized and recovery grains of Cu@MWCNTs/Cu electrodes is less. This is due to the pinning effect of MWCNTs, and straight and long MWCNTs are arranged along the electrical/force direction. These improve the hardness, mechanical properties, conductivity, and resistance to thermal deformation, cracking, and pitting of Cu@MWCNTs/Cu electrodes, which effectively slows down the failure rate and makes the spot welding life of Cu@MWCNTs/Cu electrodes longer. This work provides a new idea for the application of CNTs/Cu composites.
Cu matrix composites reinforced by Multi-walled Carbon Nanotubes (MWCNTs) were prepared aiming to enhance the mechanical performance of Cu through MWCNTs while preserving its excellent axial conductivity. The microscopic structure, mechanical performance and electroconductivity of the composites were characterized, and the related mechanism was discussed. MWCNTs dispersed uniformly in Cu matrix and arranged in the direction of drawing. The composites showed obvious orthogonal anisotropy. The mechanical properties of the composites increased with the content of MWCNTs. The composite with 10vol.% MWCNTs has the best strength and hardness, which was better than most of data in the literature. However, the highest enhancement efficiency of 3vol.%-MWCNTs/Cu composite was the highest. The main enhancement mechanism was load transmission effects and dislocation. The electroconductivity and thermal conductivity of 5vol.%-MWCNTs/Cu composite parallel to the drawing direction reached the maximum value. The main strengthening mechanism was that Ni-Cu coating on MWCNTs leads to strong interface combination between MWCNTs and Cu, which promotes the electron-phonon coupling and reduces electron or phonon scattering at the interface.
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