膨胀石墨基纳米镍、铁、钴化学镀制备复合吸波材料

为了获得薄、轻、宽、强等性能理想的吸波材料,采用化学镀的方法在膨胀石墨表面镀覆纳米镍、镍钴、镍铁钴,制备了复合吸波材料。SEM和EDS分析证实,膨胀石墨表面镍层、镍钴层、镍铁钴层的镀覆厚度约为70～150 nm。采用HP8722ES矢量网络分析仪测量了复合吸波材料在2～18 GHz内的复介电常数(ε=ε’-jε")和复磁导率(μ=μ’-jμ")。用吸收屏理论公式计算了反射率损耗(R.L)、匹配频段(fm)及匹配厚度(dm)。结果表明,当dm=0.3 mm时,镀覆镍铁钴层的复合吸波材料最低的反射损耗达-28 dB,对应的fm=13.5 GHz,R.L<-10 dB时频宽达7.5 GHz。本法制备的复合吸波材料符合"轻、薄、宽、强"的现代要求。

Co/Ni多层膜的热处理研究

采用磁控溅射方法制备了Co/Ni多层膜并做了热处理,测量了系列样品的结构、磁性和磁电阻。受热处理条件等因素影响,多层膜的层间磁性耦合性质发生变化,电阻率下降,而其各向异性磁电阻的数值没有一致的变化趋势。讨论了磁性层织构和界面对多层膜的磁性与各向异性磁电阻效应的影响。

Effect of Co content on electrodeposition mechanism and mechanical properties of electrodeposited Ni-Co alloy

Ni–Co coatings with various cobalt contents were electrodeposited from modified Watts bath. The effect of cobalt content on electrodeposition mechanism of the coatings was studied by electro-chemical impedance spectroscopy method （EIS）. Surface morphology and crystallographic structure of the coatings were investigated by means of SEM and XRD. Mechanical properties of the coatings were determined using Vickers microhardness and tensile tests. It was found that with increasing the Co2＋ions in electroplating bath, the charge transfer resistance （Rct）of Ni-Co film increased whereas the Warburg impedence decreased. This may be due to enhancement in coverage of cathode surface by Co（OH）2 and higher diffusion rate of metal ions towards cathode surface, respectively. Also, with increasing the cobalt content in the bath, cobalt content in the alloy coating increased anomalously and （111） texture consolidated gradually. With increasing the cobalt content up to 45% in alloy coating, the grain size decreased and consequently, hardness and strength of the alloy increased. Further enhancement of cobalt content up to 55% led to a little decrease in hardness and strength. The maximum ductility was observed for Ni-25%Co coating due to relatively small grain size and compact structure.

Effect of sodium lauryl sulphate on microstructure, corrosion resistance and microhardness of electrodeposition of Ni-Co3O4 composite coatings

Ni?Co3O4 composite coatings were electrodeposited on mild steel surface from a Watts-type bath in the presence of sodium lauryl sulfate(SLS).The dispersed Co3O4 particles in the presence of SLS have a greater tendency to move towards cathode and get incorporated in the coating.SLS modifies chemical composition,surface morphology and microstructure of the Ni?Co3O4 composite coating.The developed composite coating exhibits higher corrosion resistance and microhardness than the pure nickel coating.The loadings of bath solution with different concentrations of Co3O4 particles in the presence of SLS provide hydrophobic nature to the coating surface,which is much effective in enhancing the corrosion resistance of Ni?Co3O4 composite coating.The agglomeration of Co3O4 particles(>3 g/L)under high bath load condition develops defects and dislocation on the coating surface,which results in lower corrosion resistance of the deposit.The mechanical properties of the hydrophobic coatings were assessed by the linear abrasion test.

Electrodeposition of Compositionally Modulated Zinc-cobalt Alloy Multilayer Coatings

The effects of pulse parameters on the cobalt content, surface morphologies and grain size of Zn-Co alloy deposits were studied using a pulse plating technique with a square-wave current containing reverse pulse. Average current density and reverse anodic current density amongst the variables investigated have very strong effects on the cobalt content in the Zn-Co alloy deposits. Grain size, surface appearance and internal stress in the deposit were improved significantly by introducing the reverse current. Varieties of Zn-Co alloy compositionally modulated multilayer (CMM) coatings with large differences in cobalt contents for different sublayers were electrodeposited by designing corresponding waveforms using a computer-aided pulse plater and characterized in terms of surface morphologies. Cross-sectional morphologies of the Zn-Co alloy CMM coatings, examined using field emission gun scanning electron microscopy (FEGSEM), confirmed the layered structure.

Electroless Co-Zn Surface-Modified Nickel Hydroxide as an Active Material for Pasted Nickel Electrodes

Chemically precipitated β type nickel hydroxide powder was surface modified by electroless deposition of Co Zn coatings,and physical properties of both the modified and unmodified nickel hydroxide were characterized by scanning electron microscopy (SEM), specific surface area (BET), X ray diffraction (XRD) and X ray photoelectron spectroscopy (XPS). It has been found that Co and Zn components of the surface electroless coatings exist in the oxidized state. Electrochemical performances of pasted nickel electrodes using the modified nickel hydroxide as an active material were investigated, and compared with those of the electrodes prepared with the unmodified nickel hydroxide. Charge/discharge tests show that the modified nickel hydroxide electrodes exhibit better performances in the charge efficiency, specific discharge capacity and active material utilization. Their resistance to swelling with cycling is also superior to that of the unmodified nickel hydroxide electrodes. Cyclic voltammetric (CV) studies indicate that the modified electrodes have a higher electrochemical activity, and the porous pasted nickel electrodes have some distinguished CV characteristics in comparison with those of the thin film nickel electrodes.

Electrodeposition of Ni-Co-Fe_2O_3 composite coatings

Ni-Co-Fe2O3 composite coatings were electrodeposited using cetyltrimethylammonium bromide(CTAB)-modified Watt's nickel bath with Fe2O3 particles dispersed in it.The effects of the plating parameters on the chemical composition,structural and morphological characteristics of the electrodeposited Ni-Co-Fe2O3 composite coatings were investigated by energy dispersive X-ray(EDS) spectroscopy,X-ray diffractometry(XRD) and scanning electron microscopy(SEM).The results reveal that Fe2O3 particles can be codeposited in the Ni-Co matrix.The codeposition of Fe2O3 particles with Ni-Co is favoured at high Fe2O3 particle concentration and medium stirring,and the deposition of Co is favoured at high concentration of CTAB.Moreover,the study of the textural perfection of the deposits reveals that the presence of particles leads to the worsening of the quality of the observed <220> preferred orientation.Composites with high concentration of embedded particles exhibit a preferred crystal orientation of <111>.The more the embedded Fe2O3 particles in the metallic matrix,the smaller the sizes of the crystallite for the composite deposits.

An Ostwald ripening route towards Ni-rich layered cathode material with cobalt-rich surface for lithium ion battery

An Ostwald ripening-based route is proposed to prepare Ni-rich layered cathodes with Co-rich surface for li- thium-ion batteries （LIBs）. Commercially available Nio.aCo0.1 Mn0.8（OH）2 and spray pyrolysis derived porous Co304 are used as mixed precursors. During the lithiation reaction process under high-temperature, the porous Co304 microspheres scatter primary particles and spontaneously redeposit on the surface of Ni-rich spheres according to Ostwald ripening mechanism, forming the Ni-rich materials with Co-rich outer layers. When evaluated as cathode for LIBs, the resultant material shows ability to inhibit the cation disorder, relieves the phase transition from H2 to H3 and diminishes side re- actions between the electrolyte and Ni-rich cathode material. As a result, the obtained material with Co-rich outer layers exhibits much more improved cycle and rate performance than the material without Co-rich outer layers. Particularly, NCM-Co-1 （molar ratio of Nio.sCo0.1Mn0.1（OH）2/Co3Oa is 60：1） delivers a reversible capacity of 159.2 mA h g-1 with 90.5% capacity retention after 200 cycles at 1 C. This strategy pro- rides a general and efficient way to produce gradient sub- stances and to address the surface problems of Ni-rich cathode materials.