2∶17 型SmCo永磁材料的研究进展与展望

2∶17型SmCo永磁体自1977年问世以来,已有很大发展,其性能不断提高.因其具有优异的磁性能,在微波通讯技术、航空航天、国防工业、交通运输业等很多领域有着广泛的应用.最近又提出了最高工作温度大于400 ℃的永磁材料的要求,因2∶17型SmCo永磁体具有高的居里温度和较高的磁能积而成为首选材料.从1996年至今出现了2∶17型SmCo高温磁体的研究热潮,本文主要介绍了2∶17型SmCo永磁的发展过程、磁体的磁性能、制备工艺、应用情况及其发展趋势.     

Synthesis of superconductor MgCNi3 with carbon nanotubes

MgCNi3, an intermetallic compound superconductor with a cubic perovskite crystal structure, has been synthesized using fine Mg and Ni powders and carbon nanotubes （CNTs） as starting materials by the conventional powder metallurgy method. The composition, microstructure and superconductivity are characterized using x-ray diffraction （XRD）, energy dispersive x-ray （EDX） analysis, scanning electron microscopy （SEM）, and superconducting quantum interference device （SQUID） magnetometer. The results indicate that the phases of the synthesized samples are MgCNi3 （major phase） and traces of C and MgO. The MgCNi3 particle sizes range from several hundreds of nanometres to several micrometres. The onset superconducting transition temperature Tc of the MgCNi3 sample is about 7.2 K. The critical current density Jc is about 3.44 × 10^4 A/cm^2 calculated according to the Bean model from the magnetization hysteresis loop of the slab MgCNi3 sample at 5 K and zero applied field.     

不同温度下微波烧结Fe-Cu-C的性能

对微波烧结Fe-2Cu-0.6C粉末冶金材料进行探索性研究,研究不同烧结温度下微波烧结样品的性能和显微组织,并与相同温度下的常规烧结样品进行对比.研究结果表明:与常规烧结相比,微波烧结可得到较高的烧结密度以及较高的抗拉强度和伸长率,两者的洛氏硬度相当;微波烧结样品在1150℃时性能最佳,密度为7.20g/cm3,抗拉强度为413.90 MPa,洛氏硬度为HRB75;微波烧结样品具有良好的微观结构,即小的、近圆形且均匀分布的孔隙结构,从而也有利于获得细小的晶粒和较高的致密度;微波烧结与常规烧结相比,样品具有更多片状和粒状珠光体,能显著改善其性能.     

Electron field emission from single-walled carbon nanotube nonwoven

Field emission from single-walled carbon nanotube (SWNT) nonwoven has been investigated under high vacuum with different vacuum gaps. A low turn-on electric field of 1.05\,V/$\mu $m is required to reach an emission current density of 10 $\mu $A/cm$^{2}$. An emission current density of 10 mA/cm$^{2}$ is obtained at an operating electric field of 1.88\,V/$\mu $m. No current saturation is found even at an emission current of 5\,mA. With the vacuum gap increasing from 1 to 10 mm, the turn-on field decreases monotonically from 1.21 to 0.68\,V/$\mu $m, while the field amplification is augmented. The good field-emission behaviour is ascribed to the combined effects of the intrinsic field emission of SWNT and the waved topography of the nonwoven.     

Seed-mediated growth of gold nanoparticles using self-assembled monolayer of polystyrene microspheres as nanotemplate arrays

Arrays of noble metal nanoparticles show potential applications in (bio-)sensing, optical storage, surface-enhanced spectroscopy, and waveguides. For all such potential devices, controlling the size, morphology, and interparticle spacing of the nanoparticles is very important. Here, we combine seed-mediated growth with nanosphere lithography to study the controllable growth of gold nanoparticles (Au NPs), in which the self-assembly monolayer of polystyrene (PS) on a silicon surface is used to guide the modification of alkanesilanes and the subsequent adsorption of gold seeds; seed-mediated growth is applied to controlling the morphology and size of Au NPs. The size of adsorption region (determining the number of adsorbed gold seeds) is controlled by etching PS microspheres with oxygen plasma or annealing PS microspheres at the glass transition temperature. The size and morphology of the Au NPs are controlled by changing growth conditions. In such a way, we have achieved the dual control of the obtained Au NPs. Preliminary results show that this strategy holds a great promise. This approach can also be extended to a wide range of materials and substrates.     

Growth of aligned single-walled carbon nanotubes under ac electric fields through floating catalyst chemical vapour deposition

Through floating catalyst chemical vapour deposition(CVD) method,well-aligned isolated single-walled carbon nanotubes (SWCNTs) and their bundles were deposited on the metal electrodes patterned on the SiO₂/Si surface under ac electric fields at relatively low temperature(280℃). It was indicated that SWCNTs were effectively aligned under ac electric fields after they had just grown in the furnace.The time for a SWCNT to be aligned in the electric field and the effect of gas flow were estimated. Polarized Raman scattering was performed to characterize the aligned structure of SWCNTs. This method would be very useful for the controlled fabrication and preparation of SWCNTs in practical applications.     

Synthesis and characterization of axially periodic Zn2SnO4 dendritic nanostructures

Zn2SnO4 （ZTO） nanowires with a unique dendritic nanostructure were synthesized via a simple one-step thermal evaporation and condensation process. The morphology and microstructure of the ZTO nanodendrite have been investigated by means of field emission scanning electron microscopy （SEM）, x-ray diffraction （XRD） and high-resolution transmission electron microscopy （HRTEM）. SEM observation revealed the formation of branched nanostructures and showed that each branch exhibited a unique periodic structure formed by a row of overlaid rhombohedra of ZTO nanocrystals along the axis of the nanobranch. HRTEM studies displayed that the branches grew homoepitaxially as single-crystalline nanowires from the ZTO nanowire backbone. A possible growth model of the branched ZTO nanowires is discussed. To successfully prepare branched structures would provide an opportunity for both fundamental research and practical applications, such as three-dimensional nanoelectronics, and opto-electronic nanodevices.     

微米/纳米相结合的三维金属铝图案

利用光刻，反应离子刻蚀以及电化学阳极氧化技术在铝基底上构建出了微米纳米相结合的三维金属铝图案。首先在铝片的表面形成一层具有图案的二氧化硅阻碍层，阳极氧化过程中，在二氧化硅阻碍层之下会形成侧向生长的倾斜孔道和残留的金属铝微结构。形成机制可阐述为：由于表面二氧化硅阻碍层的存在造成局域电场方向的偏折，影响到反应过程中离子的输运，从而导致侧向倾斜孔的形成，而在远离阻碍层的区域孔道则会正常垂直表面向下生长。这种垂直与侧向阳极腐蚀的同时进行导致在二氧化硅阻碍层之下形成了金属铝微结构。     

W-Cu触头材料的微波烧结

采用微波烧结技术制备W-25Cu触头材料,并与常规烧结进行对比.结果表明:微波烧结升温速度快,周期短,能促进w-Cu材料的致密化:在适当条件下,微波烧结能获得相对密度达99.8%的w-Cu样品;微波烧结能改善W-Cu样品中两相分布的均匀性和w晶粒尺寸的一致性,但引起w晶粒的快速长大;Fe烧结助剂导致W-Cu材料显微组织均匀性变差,并引起晶粒进一步粗化;微波烧结技术能够应用于W-Cu材料的制备,在缩短生产周期、降低生产成本方面具有潜在优势.