Zhu Li-qun

Fabrication of Nanostructured Electroforming Copper Layer by Means of an Ultrasonic-assisted Mechanical Treatment

Abstract Electroformed copper layer with nanostructure is obtained using a subsequent mechanical treatment under the conditions of ultrasonic vibration according to the demand of high performance material in aeronautics. The microstructure of the electroformed copper layer is observed by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The tensile strength is evaluated with a tensile tester. It is found that bulk crystal of electroformed coppers surface layer is changed to nanocrystals (about 10 nm in size) after the ultrasonic-assisted mechanical treatment (UMT) but the whole monocrystalline structure still remains. The tensile strength exhibited by the new copper layer is two times better than the regular electroformed copper layer, while the fracture strain remains constant. In addition, the strengthening mechanism of UMT process is proved to be dislocation strengthening mechanism.

Synthesis of metallic silicide fullerenes and the characteristics thereof by mass spectrometry

Direct current arc discharge is used for the study on the synthesis of metallofullerenes (MFs) to discover whether there exist metallic silicide fullerenes and silicon fullerenes. The resultant components are isolated by the multistage high-performance liquid chromatography (HPLC) and analyzed with the Time-of-Flight (TOF) mass spectrometry. Results show that there exist fullerenes such as SiC69, YSi2C64, YSi2C78, Y3Si2C78 as well as Y2Si2C90 which are structurally similar to (Y2C2)@C82.Direct current arc discharge is used for the study on the synthesis of metallofullerenes (MFs) to discover whether there exist metallic silicide fullerenes and silicon fullerenes. The resultant components are isolated by the multistage high-performance liquid chromatography (HPLC) and analyzed with the Time-of-Flight (TOF) mass spectrometry. Results show that there exist fullerenes such as SiC69, YSi2C64, YSi2C78, Y3Si2C78 as well as Y2Si2C90 which are structurally similar to (Y2C2)@C82.

Effect of Cathodic Hydrogen Evolution on the Coercivity and Thermal Stability of Sintered NdFeB Magnets

Abstract The effect of cathodic hydrogen evolution on coercivity and thermal stability was investigated in sintered NdFeB magnets. The magnetic properties, phase structure and morphology were studied by SQUID-VSM, DSC, XRD, TEM and SEM. After cathodic hydrogen evolution, the Hcj decreases from 1034.8 kA·m−1 to 963.16 kA·m−1. The temperature coefficient α declines from −0.253%·°C−1 to −0.3229%·°C−1, and the β declines from −0.7518%·°C−1 to −0.7738%·°C−1. A mechanism was proposed to explain the results. In the process of cathodic hydrogen evolution, some of the generated hydrogen atoms react with the Nd2Fe14B phase and Nd-rich phase, forming Nd2Fe14BHx and NdHx, respectively. The formation of NdHx causes a volume expansion, which results in intergranular cracks and stress. X-ray diffraction and morphology characterization confirms the presence of these defects. These defects would significantly promote the nucleation of reverse magnetic domains, and further decline the coercivity and thermal stability of magnets.