Fe_3O_4磁性纳米颗粒的制备及性能表征

以Fe_2(SO_4)_3·6H_2O,FeSO_4·4H_2O和NH_3·H_2O为原料,采用化学共沉淀法制备Fe_3O_4磁性纳米颗粒,并通过XRD、FTIR、TEM和VSM手段,研究了反应温度对其结构、形貌和磁性能的影响。结果表明:制备的Fe_3O_4磁性纳米颗粒表面包裹了一层有机物质,呈球形,大小均匀,平均粒径在13nm左右,分散性好,饱和磁化强度Ms最大值可达53.38A·m~2·kg~(–1),且反应温度70℃时其磁性能最佳。     

CoFe_2O_4纳米颗粒的共沉淀法制备及其磁性能

采用共沉淀法制备了CoFe2O4纳米颗粒,运用XRD、TEM和VSM测试手段,研究了煅烧温度对CoFe2O4的结构、形貌以及磁性能的影响。结果表明:CoFe2O4纳米颗粒的粒径大小均匀;煅烧前与经200℃和600℃煅烧的CoFe2O4纳米颗粒晶粒度分别约为15,20和30nm;CoFe2O4纳米颗粒的粒径、Ms、Mr和Hc随着煅烧温度的升高而增大。当煅烧温度为600℃时,Ms约为67A·m2·kg–1,Hc为4.67×107A·m–1。     

双金属合金纳米颗粒的原位透射电镜研究

实时监测双金属合金纳米颗粒在合成过程及工作条件下,形貌、组成、结构等的动态演变,有助于理解其合成及催化机理,从而实现高性能双金属合金的合理设计、调控与合成。虽然相较于原位谱学技术,原位透射电镜的能量分辨率和精确度不高,但其可以在热、电等外场作用下实时观测和分析气相或液相环境中样品的微观结构、组成及形貌的动态变化,且空间分辨率可以达到纳米甚至原子量级,是重要的结构分析技术。本文简要归纳原位透射电镜在双金属合金纳米颗粒方面的应用研究,并探讨未来研究的挑战与机遇。     

水热法制备CoxMn1-xFe2O4纳米磁性粉体及磁性研究

用水热法成功合成了CoxMn1-xFe2O4纳米磁性颗粒粉体。样品物相用X射线衍射仪表征,形貌通过透射电镜(TEM)观测。CoxMn1-xFe2O4纳米粉体的平均尺寸和晶格常数从XRD计算得到,CoxMn1-xFe2O4纳米颗粒的晶格常数随着Co2+含量的增加而变小。所得样品的磁性用振动样品磁强计(VSM)测试,结果表明,所制备的CoxMn1-xFe2O4粉体在室温下的铁磁性、饱和磁化强度和矫顽力随着Co2+含量的增加而变大。     

钴-铂双金属纳米颗粒的制备和特征描述

CoPt3纳米颗粒是用NaBH4作为还原剂采用二阶法来合成的。纳米颗粒通过热重分析法（TG）、差热分析法（DTA）、傅立叶红外变换法（FT-IR）、扫描电子显微镜（TEM）、X射线衍射仪（XRD）来表征。分光镜的研究显示纳米颗粒采用平均颗粒大小为2．6纳米的面心立方（FCC）晶体结构。超导量子干涉器研究显示合成的纳米颗粒在室温下具有超顺磁性，同时在温度为1．85K时也具有铁磁性，还伴随有9800e的矫顽力。试样在500℃时退火引起颗粒尺寸的增加和矫顽力的减小。     

铝硅合金表面纳米颗粒的原子力显微镜观察

利用原子力显微镜首次观察到２００℃磁控溅射铝硅合金表面存在纳米颗粒，经测量，此纳米颗粒直径约２０ｎｍ、高１ｎｍ。根据此纳米颗粒的分布，讨论了磁控溅射薄的生长机理，同时，还讨论了此纳米颗粒对半导体工艺的影响。     

纳米三氧化二砷磁性脂质体的制备及表征

作为具有磁定位功能的靶向给药系统，磁性纳米脂质体在外加磁场的作用下有良好的载药靶向能力及特有的局部热疗作用，从而显示出良好的应用前景。三氧化二砷治疗急性白血病已取得了显著的临床效果，许多学者尝试用As2O3治疗多种实体瘤，发现它具有抑制肿瘤生长及诱导凋亡的作用。但由     

宁波材料所在硬磁纳米颗粒的绿色和宏量制备方面取得进展CSCD

磁性纳米颗粒在催化、生物医用、磁记录以及高性能永磁体等领域都具有重要的应用前景。在这些应用以及相关研究中,纳米颗粒的尺寸、形貌对磁性及其相关性能影响至关重要,因此如何探索出一种简便的纳米颗粒的合成方法具有重要意义。在各种磁性纳米材料中,     

高密存储介质磁性纳米颗粒薄膜与纳米超晶格结构研究进展(英文)

钴基合金和铁基合金磁性纳米颗粒薄膜和纳米超晶格结构,由于具有较高的矫顽力和各向异性能,较小的粒子尺寸分布和能形成“单域”结构等特性,从而成为颇有潜力的高密存储介质。最近几年,人们竞相研究其制备方法,其中主要包括真空淀积法、液相化学合成法和离子注入法等,采用各种措施来提高存储介质的热稳定性和其他磁学性能,并取得巨大进展。     

磁控溅射和热氧化法制备ZnO纳米颗粒

利用射频磁控共溅射技术在Si(111)衬底上沉积金属锌／二氧化硅基质(Zn/SiO2)复合薄膜。在空气中600℃退火60min，从SiO2基质中析出的金属Zn被空气中O2氧化生成了ZnO纳米颗粒，并形成了SiO2多孔网络结构。用X射线衍射(XRD)、扫描电子显微镜(SEM)和光致发光谱(PL)对样品的组成、结构、表面形貌及发光特性进行了分析。结果表明，生成的ZnO纳米颗粒为六角纤锌矿结构，呈近椭圆形，平均尺寸在65nm左右。在280nm光激发下，有较强的370nm近带边激子跃迁紫外光发射和峰位在460nm处较弱的蓝色发光。     

Using the DFT to synthesize bivariate orthogonal white noise series

The discrete Fourier transform (DFT) is used to generate bivariate orthogonal series in the form of bivariate random-phase multisine series. The properties of those series are presented. The concept of N/2-lag white series is introduced as series whose ad function coincides with the ac function of white noise for lags 0, 1, ..., N/2-1. It is shown how to turn bivariate orthogonal multisine series into corresponding bivariate orthogonal N/2-lag white series and into asymptotically Gaussian bivariate orthogonal white series. The main part of the algorithm for generating such series via DFT is presented. The spectral, correlation, and Gaussian properties of the introduced series are illustrated by three numerical examples     

A facile thermal-treatment route to synthesize the semiconductor CdO nanoparticles and effect of calcination

In this research, a thermal treatment method was used to synthesize cadmium oxide nanoparticles. The metal precursor, cadmium nitrate and a capping agent were dissolved in deionized water, which later was dried and crushed into powder. The powder underwent calcination treatment of 500, 550, 600, and 650 °C to crystallize the nanoparticles and to remove organic compounds. The structural studies of CdO nanoparticles have been carried out using EDAX, FTIR, XRD, SEM and TEM. The FTIR and XRD spectra showed that the crystalline structure formation of metal oxide nanoparticles has only occurred after been exposed to calcination. The optical properties which were determined using a UV–vis spectrophotometer showed a decrease in the band gap with increasing calcination temperature. These results prove that the thermal treatment method is a simple technique that can produce pure metal oxide nanoparticles with no other chemicals added.     

Ecodesigns and applications for noble metal nanoparticles by ultrasound process

Ecodesigns for nano-sized noble metal particles were investigated by a new liquid-solid (metal oxide-alcohol) system. We have reduced noble metal oxides as low-emission starting materials by ultrasound and tried to fabricate various noble metal nanoparticles (Ag, Au, Pt, Pd) at room temperature, Noble metal oxides were investigated during decomposition. These reductions are ecologically clean, because many noble metal oxides are not toxic, and during decomposition, O/sub 2/ is evolved. By choosing suitable conditions, it is reasonable to expect that this simple sonochemical process can be extended to obtain nano-sized metal particles.     

激光熔覆金属陶瓷复合合金层的组织与性能研究

介绍了用大功率CO2激光束在45#钢表面进行的金属陶瓷复合合金TiC-WC-Co的熔覆处理,对熔覆样品的显微组织和性能进行了测试和分析,同时对熔覆层形成的机理作了初步讨论.     

Optimal and heuristic algorithms to synthesize lattices of four-terminal switches

In this work, we study implementation of Boolean functions with nano-crossbar arrays where each crosspoint behaves as a four-terminal switch controlled by a Boolean literal. These types of arrays are commonly called as switching lattices. We propose optimal and heuristic algorithms that minimize lattice sizes to implement a given Boolean function. The algorithms are mainly constructed on a technique that finds Boolean functions of lattices having independent inputs. This technique works recursively by using transition matrices representing columns and rows of the lattice. It performs symbolic manipulation of Boolean literals as opposed to using truth tables that allows us to successfully find Boolean functions having up to 81 variables corresponding to a 9 × 9-lattice. With a Boolean function of a certain sized lattice, we check if a given function can be implemented with this lattice size by defining the problem as a satisfiability problem. This process is repeated until a desired solution is found. Additionally, we fix the previously proposed algorithm that is claimed to be optimal. The fixed version guarantees optimal sizes. Finally, we perform synthesis trials on standard benchmark circuits to evaluate the proposed algorithms by considering lattice sizes and runtimes in comparison with the recently proposed three algorithms.     

A circuital approach to estimate the magnetic field reduction ofnonferrous metal shields

The reduction of magnetic fields is a topic of concern to the electric utility industry and the electromagnetic compatibility community. One technique to reduce the magnetic fields is to use metal plates and enclosures for shielding, in addition, knowledge or the loading effect of a conducting structure in close proximity to power cables is needed for estimating power loss. Until now there has not been a simple and efficient method to calculate the low frequency magnetic shielding of, nor power loss caused by, two-dimensional shields. This paper presents a method for the rapid numerical estimation of the magnetic shielding efficiency and power loss of nonferrous metal structures. The method was validated analytically and experimentally     

CoSi合金的磁性和光学性质的第一性原理研究

采用第一性原理的局域自旋密度近似和在位库伦能修正(LSDA+U)的计算方法,结合广义梯度近似下的赝势平面波方法,计算了CoSi合金的磁性和光学性质。计算结果显示在费米能级附近,CoSi合金的上自旋能级与下自旋能级相互交叠,出现了明显的自旋极化现象,并且自旋态密度都穿过费米能级,表明CoSi合金具有金属特征。磁性计算结果表明CoSi合金具有铁磁性,磁性主要来源于Co原子3d轨道电子的贡献。特别是采用LSDA+U修正方法发现,当位库伦修正值增加到6.6eV时,CoSi合金体系的几何参数与实验值完全吻合,表明位库仑能U值的大小对CoSi合金的原子磁矩以及磁性原子的能级分布影响较大。同时,光学吸收谱计算结果表明,随着位库仑能U值的增大,CoSi合金的吸收峰在低能区发生红移,在高能区发生蓝移。以上结果表明,CoSi合金是一种很好的磁光导电材料。     

Using magnetic coupling to eliminate right half-plane zeros in boost converters

A dynamic analysis of the boost converter with an output filter reveals that magnetic coupling between inductors allows transfer of the zeros to the left half-plane of the control-to-output transfer function. Similar results requiring smaller magnetic components are obtained by combining magnetic coupling with damping of the output filter. The analysis is based on the application of the Routh-Hurtwitz's criterion to the numerator of the transfer function in order to derive the design conditions for the converter parameters. A design example illustrates the procedure, and experimental results verify the theoretical predictions. The application of these techniques will allow the design of high efficiency voltage boost-based regulators with dynamic behavior similar to buck-derived structures.     

Using a 77 K SQUID to measure magnetic fields for NDE

A bare HTS SQUID of commercial design was used in 77 K experiments concerning NDE. The SQUID was operated with flux-locked instrumentation to provide a noise floor of 80 pT/√Hz. The effective sensor area was measured to be approximately 70 μm² equivalent to an ideal point detector for NDE. The SQUID was used unshielded in a normal laboratory environment in a special purpose LN₂ cryostat positioned above a motorized computer-controlled scanning system. We measured magnetic fields associated with current flowing in wires and compared them with calculations. We also detected a simulated flaw in an aluminum plate using an eddy current technique and made a preliminary depth assessment by frequency sweeping. Although developments in electronic gradiometers and gradiometric SQUID's should make the use of single bare magnetometer SQUID's unnecessary, we show that these already have sufficient sensitivity for NDE research, even without flux-focusing washers or pick-up coils