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排序方式: 共有2350条查询结果,搜索用时 15 毫秒
1.
《Intermetallics》2015
An equiatomic CoCrFeNiMn high-entropy alloy was synthesized by mechanical alloying (MA) and spark plasma sintering (SPS). During MA, a solid solution with refined microstructure of 10 nm which consists of a FCC phase and a BCC phase was formed. After SPS consolidation, only one FCC phase can be detected in the HEA bulks. The as-sintered bulks exhibit high compressive strength of 1987 MPa. An interesting magnetic transition associated with the structure coarsening and phase transformation was observed during SPS process. 相似文献
2.
《International Journal of Hydrogen Energy》2021,46(80):39645-39657
This article reported a series of g–C3N4–CNS (g-C3N4 and carbon nanosheets) composite carriers formed by the hydrothermal method, and then the ethylene glycol reduction method was used to anchor Pt nanoparticles on the g–C3N4–CNS carrier to form the Pt/g–C3N4–CNS catalysts. The electrochemical test for the electrocatalytic oxidation of methanol (MOR) shown that the Pt/20%g–C3N4–CNS catalyst has the best catalytic performance and stability. These Pt/g–C3N4–CNS catalysts were analyzed by TEM, XRD, XPS, and BET characterization. It is discovered that the amount of g-C3N4 greatly influenced the structure and chemical properties of Pt/CNS precursor. As the content of g-C3N4 increases, the content of pyridine nitrogen and pyrrole nitrogen also increases, and N species can enhance the interaction between Pt nanoparticles and CNS, promote Pt dispersion, and increase the specific surface area of the catalyst. Similarly, an excessive addition of g-C3N4 will cause a sharp decline in the conductivity of the catalyst, and then led to the decline of MOR activity. 相似文献
3.
《Ceramics International》2020,46(8):11846-11853
Cr2AlC and its composites containing α-Al2O3 (6.1 and 15.2 wt %) were prepared by hot pressing and their corrosion behaviors in air-saturated 3.5 wt % NaCl aqueous solution were investigated by electrochemical testing methods. It was revealed that the secondary phase of Al2O3 particles mainly distributed along grain boundaries of Cr2AlC matrix. The potentiodynamic polarization measurements showed that the corrosion current densities of these Cr2AlC composites were lower than that of the pure Cr2AlC. The Aluminum in Cr2AlC was prone to be attacked more easily. When immersed at open circuit potential (OCP), Al readily slipped out from Cr2AlC matrix into NaCl solution in the form of dissoluble species. But in the case of polarization, regardless of potentiostatic polarization or potentiodynamic polarization, more de-intercalated Al, reacted with the electrolyte to form corrosion products of Al2O3 and/or AlOOH and deposited on the sample surface. For Cr2AlC/α-Al2O3 composites, the presence of Al2O3 weakened the corrosion along grain boundaries by partly blocking the permeation of electrolyte and inhibiting the anodic dissolution process. 相似文献
4.
Shuangjian Li Xiaoqin Zhao Yulong An Duanduan Liu Huidi Zhou Jianmin Chen 《Ceramics International》2018,44(15):17864-17872
Thermal sprayed ceramic coatings have extensively been used in components to protect them against friction and wear. However, the poor lubricating ability severely limits their application. Herein, yttria-stabilized zirconia (YSZ)/MoS2 composite coatings were successfully fabricated on steel substrate with the combination of thermal spraying technology and hydrothermal reaction. Results show that the synthetic MoS2 powders are composed of numbers of ultra-thin sheets (about 7 ~ 8?nm), and the sheet has obvious lamellar structure. After vacuum impregnation and hydrothermal reaction, numbers of MoS2 powders, look like flowers, generate inside the plasma sprayed YSZ coating. Moreover, the growing point of the MoS2 flower is the intrinsic micro-pores of YSZ coating. The friction and wear tests under high vacuum environment indicate that the composite coating has an extremely long lifetime (>?100,000 cycles) and possesses a low friction coefficient less than 0.1, which is lower by about 0.15 times than that of YSZ coating. Meanwhile, the composite shows an extremely low wear rate (2.30?×?10?7 mm3 N?1 m?1) and causes slight wear damage to the counterpart. The excellent lubricant and wear-resistant ability are attributed to the formation of MoS2 transfer films and the ultra-smooth of the worn surfaces of hybrid coatings. 相似文献
5.
6.
《Catalysis communications》2008,9(3):431-436
Ion-exchanged Pd–ZSM-23 (1 wt% Pd) with Na form and H form was well characterized and examined in the hydrodehalogenation of bromobenzene. TPR and XPS results suggested that Pd species dispersed in the different location of ZSM-23. Catalytic test was successfully carried out in mild conditions, using hydrazine hydrate as the hydrogen donor, and no by-products were detected. Recycling test of Pd–NaZSM-23 showed that the catalytic performance did not decrease remarkably until four recycle runs. 相似文献
7.
8.
《Wear》2007,262(5-6):575-581
PM304 composite has been prepared by high-energy ball milling and powder metallurgy. The composition of the PM304 composite is the same as that of PS304, but the microstructure is quite different. The microstructure of PM304 composite was fine and dense, the size of self-lubricating particles in the composite was very small. The tribological properties of PM304 composites against Inconel X-750 were examined in the temperature range from room temperature to 800 °C. The friction coefficient of PM304 was ranged from 0.32 to 0.41. At room temperature, brittle fracture occurred on the worn surface. With the increase of temperature up to 200 °C, a protective layer consisting of fluorides and Ag existed on the worn surface and led to a low wear rate. The wear resistance of the PM304 was superior to that of the PS304 in the temperature range from room temperature to 650 °C. The improvement in wear resistance of the PM304 was discussed in the terms of its microstructural characteristics. 相似文献
9.
The epoxidation of β-ionone over the Pt/MCM-41 catalyst using molecular oxygen in the liquid phase had been studied. The results
indicated that the β-ionone was catalytically oxidized to 5,6-epoxy-β-ionone, 4-oxo-β-ionone, 4-hydroxy-β-ionone and dihydroactinidiolide
using molecular oxygen as the sole oxidant. The effects of solvent, content of Pt, reaction temperature and time on the catalytic
activity and product selectivity had also been investigated in detail. 相似文献
10.
《Diamond and Related Materials》2006,15(10):1720-1726
NiTi alloy has found wide application in the biomedical field due to its unique shape memory effect, superelasticity and biocompatibility. However, the materials are vulnerable to surface corrosion and the most serious issue is out-diffusion of toxic Ni ions from the substrate into body tissues and fluids. In this paper, NiTi alloys were coated with diamond-like carbon (DLC) fabricated by plasma immersion ion implantation and deposition (PIIID) to improve their corrosion resistance and blood compatibility without sacrificing their shape memory effect and superelasticity. The structure of the films and the depth profiles between the films and substrate were studied using Raman spectroscopy and XPS, respectively. The phase transformation temperature, superelasticity, anticorrosion behavior and Ni ions release of the coated and uncoated sample were investigated by DSC, tensile tests, potentiodynamic polarization and AAS, respectively. The hemocompatibilty of the coated and uncoated samples was measured using clotting time and platelet adhesion. The results shows that the films is DLC accompanying with the formation of the mixing layer, and the DLC films can markedly improve the corrosion resistance and the hemocompatibility, obviously increase the ratio of albumin-to-fibrinogen and effectively block the Ni ions release of the NiTi alloys without sacrificing its superelasticity and changing its phase transformation temperature. The research results suggest DLC films prepared by PIIID could improve the in vivo performance of NiTi alloys implanted into the human body. 相似文献