Polyacrylonitrile-based FeCo/C nanocomposites: Preparation and magnetic properties

Metal–carbon nanocomposites that represent FeCo alloy nanoparticles uniformly distributed over the carbon matrix, were prepared by the IR pyrolysis of precursors comprising polyacrylonitrile (PAN), iron acetylacetonate, and cobalt acetate (the metal ratio in the precursors was Fe: Co = 1: 1, 3: 1). The composition of FeCo alloy nanoparticles satisfies the tailored ratio Fe: Co. The FeCo phase is formed at synthesis temperatures in the range 500–600°С; at T ≤ 500°С only FCC-Co-base solid solutions are observed. The nanocomposites prepared at T ≥ 600°С simultaneously contain FeCo intermetallic nanoparticles and an insignificant amount of a FCC-Co phase or a cobalt-base solid solution phase. The saturation magnetization of FeCo/C metal–carbon nanocomposites is determined by the mean nanoparticle size and the alloy composition, and ranges from 36 to 64 (A m²)/kg (when Fe: Co = 1: 1) and from 35 to 52 (A m²)/kg (when Fe: Co = 3: 1) at synthesis temperatures in the range 600–800°С.     

纳米晶Ni-Mo-Co合金镀层的结构与析氢行为

电沉积;结构;纳米晶Ni-Mo-Co合金镀层的结构与析氢行为     

低温熔盐中电沉积Sm-Co合金膜及其磁性能

在353 K的尿素-乙酰胺-NaBr-KBr熔体中, 用恒电位电解法在Cu基片上制备了Sm-Co合金膜. 利用循环伏安法研究了熔体的电化学行为. 电化学实验结果表明, 在Pt电极上, Co(II)+2e→Co(0)是一步完全的不可逆反应; 测得CoCl2-尿素-乙酰胺-NaBr-KBr熔体中, Co(II)在Pt电极上的传递系数α=0.31, 扩散系数D0=4.78×10^-5 cm2·s-1; Sm(III)难以单独沉积, 但能被Co(II)诱导共沉积, 在不同阴极电位下制备出不同Sm含量的非晶合金膜. 用等离子发射光谱仪(ICP)检测薄膜成分, 用SEM观察了薄膜的表面形貌结构, 用XRD和振动样品磁强计(VSM)分析样品退火前后的晶相和磁性能变化特征. 结果表明, 在923 K进行退火30 s后Sm-Co薄膜由非晶转变为多晶结构, 并以hcp晶相结构为主; 退火和Sm含量对Sm-Co合金膜的磁性能有重要的影响.     

Anomalous codeposition of cobalt and ruthenium from chloride–sulfate baths

Codeposition of Ru and Co was studied at room temperature and at 50 °C with various Ru³⁺ and Co²⁺ concentrations in the electrolyte. The codeposition of Co and Ru proved to be anomalous since no pure Ru could be obtained in the presence of Co²⁺ in the electrolyte, but a significant Co incorporation into the deposit was detected at potentials where the deposition of pure Co was not possible. The composition of the deposits varied monotonously with the change of the concentration ratio of Co²⁺ and Ru³⁺. The deposition of Ru was much hindered, and the current efficiency was a few percent only when the molar fraction of Co in the deposit was low. Continuous deposits could be obtained only when the molar fraction of Co in the deposit was at least 40 at.%. The deposit morphology was related to the molar fraction of Co in the deposit. The X-ray diffractograms are in conformity with a hexagonal close-packed alloy and indicate the formation of nanocrystalline deposits. Two-pulse plating did not lead to a multilayer but to a Co-rich alloy. Magnetoresistance of the samples decreased with increasing Ru content.     

FeCo2(CO)7(μ3-S)(O[P(SCH2)2]2)的合成与晶体结构

许多化学工作者对单齿膦配体（ＰＰｈ３,ＰＢｕｎ３,ＰＥｔ２Ｐｈ,Ｐ（ＯＥｔ）３,Ｐ（ＯＣ６Ｈ５）３）与母体簇合物ＦｅＣｏ２（ＣＯ）９（μ３－Ｓ）的取代反应进行过详细研究［１－３］,但对双齿膦配体与母体簇合物的取代反应研究报导较少．Ａｉｍｅ［４］合成了含双齿膦配体的簇合物ＦｅＣｏ２（ＣＯ）７（μ３－Ｓ）（Ｐｈ２ＰＣＨ２ＰＰｈ２）,并用１３ＣＮＭＲ和ＩＲ光谱方法对其结构进行了表征．到目前为止,含双齿膦配体的该类簇合物的晶体与分子结构还未见报导．ＲｏｓａｎｎａＲｏｓｓｅｔｔｉ［２］通过研究母体簇合物与…     

Magnetic properties of nanocrystalline CoPt electrodeposited films. Influence of P incorporation

Platinum-rich CoPt films have been electrodeposited with the aim of preparing hard magnetic films on silicon-based substrates without the need for subsequent annealing. Electrodeposition conditions have permitted the crystalline structure of the films to be controlled. Pt percentages of up to 60–65 wt.% have been attained while maintaining the hexagonal Co phase, leading to CoPt films with moderate coercivity and good corrosion resistance. However, when low deposition potentials were used, CoPt films with higher Pt percentages were obtained, but in this case, the films exhibited an fcc structure, having lower coercivity and less corrosion resistance. The presence of hypophosphite in the solution limited the platinum percentage in the deposited CoPtP films, but an hexagonal close-packed (hcp) structure was always observed in this case. The incorporation of P into the deposits led to increases in both the coercivity of the films and the corrosion resistance of the coatings, with respect to pure CoPt. The highest coercivity was obtained for hcp CoPtP deposits with 40 wt.% of Pt.     

Effect of nano-Al2O3 particles and of the Co concentration on the corrosion behavior of electrodeposited Ni–Co alloys

Incorporation of nano-Al₂O₃ particles into a Ni–Co alloy by electrodeposition influences the corrosion properties, morphology, and structure of the layers. The resistance against corrosion of Ni–Co/Al₂O₃ composite films deposited on stainless steel was investigated in a 0.1-M NaCl solution by potentiodynamic polarization. The presence of nanoparticles improves the corrosion resistance of Ni–Co/nano-Al₂O₃ deposits when compared to pure Ni–Co alloy. Moreover, by increasing the pH of the electrodeposition bath and the content of Co in the alloy, the resistance against corrosion is furthermore improved. The morphology of the deposits before and after their corrosion was analyzed by scanning electron microscopy. The presence of the embedded alumina particles in the Ni–Co alloys was one of the key factors that limited further propagation of corrosion on the metallic surface. Preferential corrosion attack, in the form of a pitting corrosion, was located mainly at the grain boundaries.     

Synthesis of air stable FeCo/C alloy nanoparticles by decomposing a mixture of the corresponding metal-acetyl acetonates under their autogenic pressure

A mixture of Fe(AcAc)(2) and Co(AcAC)(2) was thermolyzed in a closed cell under the autogenic pressure of the reactants. The nature of the products was temperature dependent. The reaction is a one-stage, simple, efficient, and solvent-free method to prepare FeCo alloy nanoparticles protected by a carbon shell. Particle sizes of 60-150 were obtained covered by a carbon layer of 3-4 nm. The air stability of these particles is also demonstrated.     

Correlation between magnetic properties of electrodeposited Co(P) and NH4Cl concentrations in the electrolyte

The effect of ammonium chloride on the electrodeposition process and resulting magnetic properties of Co(P) alloy films was investigated. It was observed that the magnetic properties of the films varied extensively with the ammonium chloride contents in the solution. Cyclic voltammetry was employed as an electroanalytical technique to characterize the variation of interfacial polarization at different electrolyte compositions. In addition, microstructural characterization of electrodeposited Co(P) thin films by transmission electron microscopy revealed a significant increase in both grain size and preferred orientation of Co(P) grains with ammonium chloride contents. Results of characterizations indicated that the addition of ammonium chloride controlled the kinetics of electrocrystallization of Co(P) by modifying the charge transfer process and thus gave rise to increased grain size and preferred orientation in the Co(P) thin films. These microstructural features provide reasonable explanation on the variation of the magnetic properties of electrodeposited Co(P) films with the amount of ammonium chloride in the solution.     

Length-controllable catalyzing-synthesis and length-corresponding properties of FeCo/Pt nanorods

Newly designed magnetic-alloy/noble-metal FeCo/Pt nanorods have been first reported and fabricated through a length-controllable catalyzing-synthesis process in which the growth of FeCo nanorods was induced on Pt nanotips. The length of FeCo/Pt nanorods depends on the number of platinum nanotips. The proposed synthesis mechanism was corroborated by scanning electron microscopy, transition electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. With the decrease of Fe content in Fe(x)Co(96-x)/Pt(4) nanoalloys from 77 to 15, the morphology changes from nanorods with different lengths to nanoparticles. The analysis of the magnetic hysteresis loops indicated that the magnetic saturation and coercivity were strongly dependent on the length of the nanorods in which maximum saturation magnetization and minimum coercivity were obtained for Fe(77)Co(19)/Pt(4) nanorods with the length of ～2.5 μm. In particular, FeCo/Pt exhibited length-dependent reactivity towards 1,1,2,2-tetrachloroethane, and Fe(77)Co(19)/Pt(4) nanorods with the length of ～2.5 μm yielded the greatest dechlorination rate. Moreover, Pt can enhance the dechlorination of 1,1,2,2-tetrachloroethane.     

FeCo/C nanocomposites: Synthesis,magnetic and electromagnetic properties

FeCo alloy nanoparticles encapsulated in the carbon matrix of metal–carbon nanocomposites have been manufactured under IR heating. The size of FeCo nanoparticles have been found to be tailored by varying synthesis temperature and metal concentration. The saturation magnetization has been shown to increase as the synthesis temperature or metal concentration rises, with an attendant decrease in coercive force. The electromagnetic properties of FeCo/C nanocomposites have been studied. Complex magnetic permittivity measurements have shown that variation of the synthesis temperature or metal concentration can appreciably increase magnetic loss, which leads to a shift of the band of minimum electromagnetic reflectivity in the frequency range 3–12 GHz.     

Pulse Plating of Zn-Co Alloy Coatings

Pulse plating of Zn-Co alloys was studied using square pulse containing reverse current.The surface morphologies of Zn-Co alloy deposits were examined using scanning elecron microscopy （SEM）, and an attendant energy dispersive X-ray analyzer （EDA） was used to analyze the composition of Zn-Co alloy deposits. Results obtained showed that the average current density and reverse current density amongst all the variables investigated had very strong effects on the cobalt content and surface morphologies of Zn-Co alloy deposits. It is possible to elecrodeposit Zn-Co alloy coatings with a very wide cobalt content range of 10-90 wt% by modulating pulse parameters.     

An X-ray absorption spectroscopy investigation of the formation of FeCo alloy nanoparticles in Al2O3 xerogel and aerogel matrixes

Extended X-ray absorption fine structure and X-ray absorption near-edge structure techniques were used to study in detail the structural characteristics of FeCo-Al2O3 nanocomposite xerogels and aerogels. The formation of bcc FeCo alloy, which cannot be assessed unambiguously by X-ray diffraction, dispersed within the alumina matrix was evidenced in the final samples obtained by heat treatment at 800 degrees C in reducing atmosphere. Aerogel samples reduced below 800 degrees C still present a fraction of oxidized metal together with the bcc alloy. The investigation of the xerogels and aerogels calcined at increasing temperature indicates that Fe(III) and Co(II) ions are present and they are located in the tetrahedral sites of the spinel structure of the matrix (gamma-Al2O3); moreover, the precursor of the spinel is more ordered in the aerogel sample than the xerogel sample.     

担载四核羰基簇:FeCo~3(CO)~11PPh 在聚苯乙烯表面簇骼畸变的EXAFS研究

通过配体取人工将四核羰基簇FeCo~3(CO) 锚联在膦化的聚苯乙烯表面,获得担载簇FeCO~3(CO)~11PPh/poly,目的在于使簇骼结构偏离较高对称性,以考察锚联过程对簇结构的影响.本文以EXAFS(Extended x-ray Absorption Fine Struature)方法研究了担载样品的结构.结果显示担载簇与FeCO~3(CO)~11PPh 晶体具有相同的结构模式,尤其是膦配体确实与一Co原子相连接.EXAFS结果表明:(1)与FeCO~3(CO) (其簇骼具有三重对称结构)比较,锚联使Co-Fe键增长0.005nm;金属-金属及金属-桥联碳壳层Debye-Waller因子均增大约一倍而金属一端联碳壳层的值变化很小.说明金属-金属间实际键长值具有一较宽分布,因而其簇骼已偏离了三重对称结构;(2)与FeCO~3(CO)~11PPh 晶体的结构比较,Co-Fe键长长0.003nm而Co-Co键长则短约0.002nm.考虑到EXAFS分析只能给出平均键长值,因此认为,存在于FeCO~3(CO)~11PPh 晶体中的由于一个羰基被膦配体取代而引起的簇骼畸变,在锚联后被加剧.     

Structural characterization study of FeCo alloy nanoparticles in a highly porous aerogel silica matrix

A series of FeCo-SiO(2) nanocomposite aerogels having different FeCo loadings of 3, 5, and 8 wt % were prepared using a novel urea-assisted sol-gel route. The size of the nanoparticles, which was estimated using Scherrer analysis of the main peak of the x-ray diffraction pattern, varies from 3 to 8 nm. X-ray absorption fine structure (EXAFS) and x-ray absorption near edge structure (XANES) techniques at both Fe and Co K edges were used to investigate the structure of the FeCo nanoparticles. EXAFS and XANES show that FeCo nanoparticles have the typical bcc structure. Evidence of oxidation was observed in low FeCo content aerogels. Spatially resolved electron energy loss spectroscopy analysis suggests the formation of a passivation layer of predominantly iron oxide.     

An EQCM study on the influence of saccharin on the corrosion properties of nanostructured cobalt and cobalt-iron alloy coatings

Nanostructured cobalt (Co) and cobalt-iron (CoFe) alloy coatings were electrodeposited from sulfate solutions in the presence and absence of saccharin. The effects of saccharin on the corrosion behavior of Co and CoFe alloy coatings were investigated using the electrochemical quartz crystal microbalance (EQCM) technique coupled with cyclic voltammetry (CV) measurements. Saccharin was added to the electrolyte as a grain refiner and brightener. Interestingly, opposite corrosion behaviors were found for all nanostructured coatings in 0.1 M H₂SO₄ and 0.1 M NaOH. The use of saccharin as an additive in the plating solution accelerated the anodic reaction for all deposits in acidic medium. The mass decreases while dissolution rate increased with higher saccharin concentration. Meanwhile, formation of a thick passive film on the Co electrode surface were enhanced while a hindering effect was observed for CoFe alloy coatings deposited in the presence of saccharin in alkaline solution. The anodic and cathodic curves obtained from potentiodynamic polarization experiments were also in agreement with the EQCM results.     

半导体Si上电沉积Cu-Co颗粒膜及其巨磁电阻效应

采用电化学沉积方法在半导体Si上制备Cu-Co金属颗粒膜. XRD测试结果表明制备态的薄膜形成了单相亚稳态面心合金结构, 薄膜经退火后, XRD谱图中出现了析出的纯金属Co的衍射峰, 这表明薄膜在退火过程中发生了相分离. TEM测试结果也进一步证实了磁性的Co颗粒从非磁性的铜基体中析出. 随着退火温度的增加, 颗粒膜巨磁电阻(GMR)效应不断增大, 当退火温度为450 ℃时, Co0.20Cu0.80薄膜的巨磁电阻效应达到最大, 磁阻率为8.21％. 之后, 磁阻率又随退火温度的升高而降低. 退火前后样品磁滞回线的变化表明薄膜中发生了从超顺磁性到铁磁性的转变, 矫顽力、剩余磁化强度和饱和磁化强度均随退火温度的增高而逐渐增大. 超顺磁性颗粒的作用导致了GMR－H与M－H曲线的不同.     

Interaction of O2, CO and CO2 with Co films

Metastable impact electron spectroscopy (MIES), ultraviolet photoelectron spectroscopy (UPS(HeI)) and x‐ray photoelectron spectroscopy (XPS) were applied to study the interaction of O₂, CO and CO₂ with Co films at room temperature. The films were produced on Si(100) surfaces under the in situ control of MIES, UPS and scanning tunnelling microscopy (STM). For O₂, dissociative adsorption takes place initially and then incorporation of oxygen starts at exposures of ～5 L. Comparison of the MIES and UPS spectra with those published for CoO shows that near‐stoichiometric CoO films can be obtained by co‐deposition of Co and O₂. The CO is adsorbed molecularly up to a maximum coverage of ～0.6 monolayer, with the C‐end pointing towards the surface. The CO₂ adsorption is dissociative, resulting in the formation of Co–CO bonds at the surface. The resulting oxygen atoms are mostly incorporated into the Co layer. For all studied molecules the interaction with Co is similar to that with Ni. Copyright © 2005 John Wiley & Sons, Ltd.     

Studies on Preparation of Co-Bi Alloy Films by Electrodeposition From Nonaqueous Medium

IntroductionSemimetallic bismuth is a material exhibitinginteresting magnetoresistance( MR) characteristicand finite- size effect,whose electronic propertiesare fundamentally different from those of commonmetals due to the complex and highly anisotropicFermi surface[1] .Recently,Bi has attracted ourmuch attention for its applications involving fieldand current sensing due to its extremely high mag-netoresistance( MR) relative to those reported forGMR and CMR materials.The large MR of Bia…     

Iron–cobalt and iron–cobalt–nickel nanowires deposited by means of cyclic voltammetry and pulse-reverse electroplating

Metal nanowires composed of Fe–Co and Fe–Co–Ni alloys were successfully prepared by means of cyclic voltammetry (CV) and pulse-reverse (PR) electroplating techniques from acidic metal chloride solutions. The anodic dissolution process in the CVs or in the reverse electroplating period was found to be the key factor influencing the formation of metal nanowires. The addition of nickel into the Fe–Co alloy was found to extend the diameter of these nanowires. The morphology and crystalline information of these alloy deposits prepared by CV and PR deposition techniques were obtained from the field-emission scanning electron microscopic (FE-SEM) photographs and X-ray diffraction (XRD) patterns, respectively.