Influence of a cationic surfactant in the properties of cobalt-nickel electrodeposits

The effect of a cationic surfactant, dodecyltrimethylammonium chloride (DTAC) on CoNi electrodeposition process has been analysed. CoNi electrodeposition is greatly modified by the presence of the cationic surfactant in the bath. The DTAC modifies the initial stages of the deposition process and enhances the cobalt percentage in the deposits. Structure and morphology of the deposits are also modified, as the manner that magnetic properties of the electrodeposited films were affected as a consequence of the structural change. The presence of the surfactant in the bath causes changes on the CoNi structure from face-centred cubic (fcc) to close-packed hexagonal (hcp). DTAC incorporation into the deposits is a function of its concentration in the bath. Thus, it is important to be careful with the effects caused by the surfactant on deposits when it assists the particles insertion.     

Morphology, structure and magnetic properties of cobalt–nickel films obtained from acidic electrolytes containing glycine

This paper focuses on the development and optimization of electroplated cobalt–nickel (CoNi) alloys for use in biomedical microdevices. CoNi films were electrodeposited from glycine-containing electrolyte solutions at acidic pH. The influence of pH (2.5–5), temperature (55 and 80 °C), current density (from −5 to −40 mA cm⁻²), glycine concentration (0.5 and 1 mol dm⁻³) and the nature of the metal salts (chlorides or sulphates) on the composition and the magnetic properties of the films were systematically analyzed. The cobalt content varied between 50 and 83 wt% depending on the applied conditions. As a result, deposits showed variable morphologies, different structures (either hexagonal close-packed (hcp) or mixed hcp and face-centered cubic phases) and tunable magnetic properties, ranging from semi-hard (18.51 kA m⁻¹, i.e. 233 Oe) to very soft (1.43 kA m⁻¹, i.e. 18 Oe). To understand the role of glycine in this system, a comparison of the electrochemical processes, and the structural and magnetic properties is made for samples produced in glycine-containing and glycine-free baths.     

Electrodeposition of magnetic CoPd thin films: Influence of plating condition

The manufacture and properties evaluation of Co-based thin film alloys are extensively studied because of their magnetic properties that make them a critical element in many different applications and devices. Therefore the electrodeposition of CoPd alloy thin films was studied from a chloride bath containing glycine as additive. The cobalt content in the CoPd deposits varied from 6.4 to 94.0 at% by controlling the pH and [Co²⁺]/[Pd²⁺] ratio in the bath. Current efficiencies were independent of the solution pH and bath composition. The morphology of the deposits depended on the applied current density: current densities higher than 50 mA cm⁻² resulted in deposits with a typical cauliflower morphology. For current densities lower than 25 mA cm⁻² cracks was observed. The XRD measurements showed that all CoPd alloys were amorphous. The magnetic properties for CoPd alloys revealed that the coercivity (H_c) values ranged from 84 up to 555 Oe and the magnetic saturation (M_s) from 0 to 1.73 T.     

Electrodeposition of nickel-BN composite coatings

Electrodeposition of nickel-boron nitride (Ni-BN) composites is carried out from a sulfamate bath containing up to 10 g/l of dispersed boron nitride particles with size 0.5 μm. Microhardness and wear resistance of the composites are investigated. Both the properties are influenced by the amount of incorporated boron nitride particles. Commercial surfactant containing alkyl-dimethyl-benzyl-ammonium saccharinate is used to stabilize the electrolyte: the effects on mechanical properties and structure of the electrodeposits are investigated. Morphology of the coatings and the effects of codeposited particles on metal matrix structure are reported.     

Nanostructured magnetic CoNiP electrodeposits: structure-property relationships

Magnetic CoNiP thin film alloys were electrodeposited from chloride baths. The effects of solution composition, solution pH and film thickness on the magnetic properties, microstructure and phases of electrodeposited CoNiP films were investigated. Solution pH and NaH₂PO₂ concentration significantly influenced the magnetic properties of CoNiP deposits. These films when deposited from solutions of pH <2.25 exhibited soft magnetic properties, whereas from solutions of pH >2.25, hard magnetic deposits (H_C,⊥≈2000 Oe and H_C,//≈1000 Oe) were obtained. X-ray diffraction revealed hcp structure consisting of nanocrystalline grains (∼50 nm) with preferred (002) planes as deposit P content and solution pH increased.     

Study of the mechanical and structural properties of Zn–Ni–Co ternary alloy electroplating

Ternary zinc–nickel–cobalt alloys were electrodeposited on steel substrates from sulfate bath by direct current. Microstructural and mechanical properties of Zn–Ni–Co ternary alloy coatings were investigated and contrasted with the characteristics of Zn–Ni and Zn–Co alloy coatings. It was found that the obtained Zn–Ni–Co alloy exhibited more preferred surface morphology and mechanical properties as compared to the other alloy coatings electroplated at the same conditions. X-ray diffraction studies showed that the deposits of Zn–Ni–Co alloy coatings consisted of Zn, ZnNi₃, and ZnCo₁₃ phases. The structure, surface morphology, and surface topography of the deposited alloys were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray microanalysis (EDS), and atomic force microscopy (AFM). In addition, hardness, elasticity modulus, and adhesion strength of coated alloys were measured with dynamic ultra-microhardness (DUH) and Scratch tester.     

Effects of 2-buthyne-1,4-diol additive on electrodeposited Ni films from a Watts-type bath

Structures of Ni films electrodeposited from a Watts-type bath containing 2-buthyne-1,4-diol (BD) were investigated using SEM, cross-sectional SIM, XRD measurement with a pole profiling technique and electrochemical methods for controlling properties of Ni electrodeposits. Preferred orientation of Ni electrodeposits was assigned to potential domains for electrodeposition. Preferred orientation in the higher potential region was (1 1 0) or (1 0 0), that in the middle potential region were (1 1 1) and (3 1 1), and that in the lower potential region was (1 0 0). The growing axis of Ni electrodeposits seems to agree with the speculation from Pangarov's model based on the two-dimensional nuclei theory in the lower overpotential region in which the dominant growing plane is fundamentally determined by crystallization overpotential related to supersaturation of adatom, although the growth axes of Ni deposits do not always agree with the preferred orientation. For example, preferred orientation of (1 1 0) was assigned to growing (1 1 1) plane which tilts at 55° to the substrate. Adsorption of BD affects the structure and morphology of electrodeposits via an inhibitory effect related to its surface coverage depending on surface orientation, growth rate and BD concentration in the plating bath.     

The effect of pulse reversal on morphology of cobalt hard gold

The impact of pulsed reverse current on cobalt hard gold electrodeposition from a cyanide bath is presented. The reversed current results in a significant change in the morphology of electrodeposits, improvement of the overall current efficiency, and reduction of deposit porosity. With longer pulses, hemispherical surface features are generated, while larger grains result from shorter pulse widths. The porosity of the plated samples is found to decrease compared with results at the same time-average plating rate obtained from dc or on–off pulse plating.     

Magnetic properties of nanocrystalline iron group thin film alloys electrodeposited from sulfate and chloride baths

Systematic studies of iron group binary (NiCo and CoFe) and ternary (CoNiFe) thin film alloys relating their magnetic properties with film composition, grain size and the corresponding crystal structure were investigated. Anions influence current efficiencies, magnetic properties, surface morphology and phases of electrodeposited films. Higher current efficiencies in chloride baths compared to sulfate baths were observed for CoFe, NiCo and CoNiFe alloys. The higher deposition current efficiencies in chloride baths were attributed to a catalytic effect. Anion types in CoFe and CoNiFe thin film alloys influenced the microstructures and the resulting magnetic properties (coercivity and squareness). The microstructures of NiCo alloys depend on the deposit Co contents rather than anion types. The surface morphologies of CoFe, NiCo and CoNiFe thin films were independent of anion types. CoFe deposits exhibited relatively smooth surface morphology and turned into fine crystallites with increasing solution Fe⁺² concentration. NiCo deposits showed very smooth surface morphology. CoNiFe deposits had the surface morphology of polyhedral crystallites. The deposit Fe content in CoFe electrodeposits linearly increased with increasing solution Fe⁺² concentration for both chloride and sulfate baths. Similar linear behavior of deposit Co contents was observed in NiCo electrodeposits.     

Nanocrystalline Ni–Co alloy coatings: electrodeposition using horizontal electrodes and corrosion resistance

Nanocrystalline Ni–Co alloy coatings containing 0–45 wt% Co were electrodeposited using horizontal electrodes in a modified Watts bath. Different techniques including scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, microindentation, and potentiodynamic polarization were used to characterize the alloy coatings. Properties of the alloy coatings were investigated as a function of the cobalt ion concentration (Co²⁺) in the bath. It was observed that the alloy codeposition exhibits anomalous behavior. Co content in the alloy coatings increases with increasing Co²⁺ in the bath and with electrolyte agitation. Morphology and grain size of alloy coatings are greatly affected by Co content. By increasing Co content, surface morphology of the alloy coatings changes from pyramidal to spherical. Microhardness of the alloy coatings increases with increasing Co content mainly due to decreasing grain size that follows the Hall–Petch relation. In addition, Ni–17 wt% Co alloy exhibits better corrosion resistance compared to pure Ni and other Ni–Co alloy coatings. The higher corrosion resistance of Ni–17 wt% Co coating is discussed based on its phase structure, grain size, and preferred orientation.     

Direct and pulse current electrodeposition of Ni–W–TiO2 nanocomposite coatings

Ni–W–TiO₂ nanocomposite coatings have been obtained on mild steel surface by direct current (DC) and pulse current (PC) electrodeposition from Watts bath containing an ammonical citrate complexing agent. The morphology of the coatings was explored by scanning electron microscopy (SEM), atomic force microscopy (AFM) and the composition of the electrodeposits was analyzed by energy dispersive X-ray analysis (EDX). Surface morphology studies revealed that Ni–W alloy surface was covered by long needle like crystals and Ni–W–TiO₂ composite coatings with smaller spherical sized grains. The coated surface contained 25.55% W and 5.55% Ti. XRD studies revealed that (111) plane was predominant in both Ni–W alloy deposits and Ni–W–TiO₂ composite coatings. The patterns of the electrodeposits confirmed only fcc frame work structure. Microhardness values increased with TiO₂ addition in the alloy. The corrosion resistance of Ni–W alloy deposit and TiO₂ incorporated coatings was evaluated by Potentiodynamic polarization studies in 3.5% NaCl solutions. Corrosion current densities decreased with TiO₂ inclusion in the alloy deposit. Electrochemical impedance studies revealed that the charge transfer resistance increased with TiO₂ inclusion in the alloy deposits while the double layer capacitance decreased. The PC composites coatings offer uniform surface, high microhardness and enhanced corrosion resistance than DC composites coatings.     

Electrodeposition of Co-Ni and Co-Ni-Cu systems in sulphate-citrate medium

Electrodeposition of Co-Ni and Co-Ni-Cu alloys was performed in a sulphate-citrate medium. Experimental electrodeposition parameters (pH, cobalt(II), nickel(II) and citrate concentrations) were varied in order to analyse their influence on the deposition. Anomalous Co-Ni codeposition occured in the citrate medium. High [Ni(II)]/[Co(II)] ratios (above 5) were suitable for the preparation of homogeneous magnetic Co-rich Co-Ni deposits of hexagonal close-packed (hcp) structure or face centred cubic (fcc) structure as a function of the deposition potential.The presence of very low copper(II) concentrations (<10⁻² mol dm⁻³) in the nickel-cobalt bath makes it possible to incorporate copper in the deposits in amounts ranging from 5 to 60% Cu, although uniform deposits are obtained only for low copper percentages. These ternary deposits are solid solutions with fcc structure and magnetic behaviour both dependent on the deposition potential.     

电镀非晶态镍磷合金的研究

采用亚磷酸－镍盐体系制得光亮镍磷镀层,研究了镀液组成,电流密度,温度等对镀层性能和电流效率的影响,优选出分别获得最佳镀层耐蚀性,硬度和电流效率的工艺条件;分析了耐蚀非晶态镍磷合金镀层的形成原因,即在电镀过程中,镀层形成了类似Ｎｉ３Ｐ的稳定结构。     

Electrodeposition of Zn–SiC nanocomposite coatings

Zn–SiC composite coatings were obtained on mild steel substrate by electrodeposition technique with high-current efficiency. A slightly acidic chloride bath, containing SiC nanoparticles and gelatine as additive, was used. The electrodeposition was carried out under galvanostatic control with pulsed direct current; the effect of experimental parameters (temperature, average current density and particles concentration) on composition, morphology and structure of the deposit was studied. Coatings were characterized by means of scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffractometry and Vickers microhardness measurements. Zn–SiC electrodeposits with the best characteristics were obtained by performing electrodepositions at 45 °C, with 20 g L^?1 SiC in the bath and with average current density in the range 100–150 mA cm^?2. Under these experimental conditions, homogeneous and compact coatings, with low-grain size and SiC content ranging from 1.7 to 2.1 wt%, were found to be electrodeposited. Microhardness measurements showed for these deposits an increase of about 50 % with respect to those without nanoparticles obtained in the same experimental conditions.     

Electrochemical studies of zinc–cobalt alloy coatings deposited from alkaline baths containing glycine as complexing agent

Co-deposition of Zn–Co alloy coatings that were electrodeposited from weakly alkaline glycine solutions has been studied by cyclic voltammetry. Scanning electron microscopy (SEM), energy depressive spectroscopy (EDS), and X-ray diffraction (XRD) analyses were used to study surface morphology, chemical composition, and phase structure of the coatings. Corrosion behavior of the coatings was also studied using potentiodynamic polarization tests in 3.5 wt% NaCl solution. Cyclic voltammetry results showed that in Zn–Co deposition from an alkaline bath in the presence of glycine, cobalt deposited at a potential near to that of zinc together with successful co-deposition of Co and Zn. It was also shown that reduction–oxidation (redox) reactions of Zn–Co alloy deposits were quasi-reversible and resulted in deviation of electrodeposited alloys from the equilibrium phase diagrams. The corrosion resistance of the deposits was also highly influenced by the composition and morphology of the coatings. Overall, Zn–Co deposit containing 0.89 wt% Co showed that the highest corrosion resistance among the coatings that was due to its single phase structure and fine morphology.     

Preparation of hierarchical leaf-like cobalt and enhanced magnetic properties by a new low-temperature synthesis method

Hierarchical leaf-like cobalt materials have been synthesized by a simple method at relatively low temperature. The product was characterized by means of XRD, SEM, EDS, and VSM techniques. The effects of temperature and cobalt acetate amount on the final Co were investigated by a series of experiments. It was found that the temperature played an important role in the formation of such novel leaf-like cobalt. When the reaction temperature of the mixture was as low as 40–65 °C, the morphology of final products can be changed from fluffy like to leaf like hierarchical structures. The leaf-like cobalt possessed hexagonal close-packed (HCP) phase structure. The hierarchical leaf-like cobalt exhibited high saturation magnetization (M_s) of 151.6 emu/g and coercivity (H_c) of 158.5 Oe. The low temperature chemical reduction method is quite simple, it will provide possibility for large scale preparation of such leaf-like cobalt. Due to the specific structure and magnetic properties, these cobalt leafs are expected to have potential applications as candidates for microwave absorption and sensors.     

Electrodeposition of iron–palladium thin films

FePd thin films were electrodeposited from ammonium citrate complex baths. The effects of various electrodeposition and post heat treatment conditions including pH, current density, bath concentrations, substrates and annealing temperature on composition, material, and magnetic properties were systematically investigated. In these baths, the deposited iron content increased linearly with an increase in current density from 1 to 5 mA cm⁻² producing films with compositions extending from Fe₇Pd₉₃ to Fe₉₁Pd₉. Magnetic saturation (M_S) of electrodeposited FePd thin films linearly increased with increase in deposited iron content (i.e. 1.8 T for Fe₈₂Pd₁₈ and 0.1 T for Fe₁₉Pd₈₁) which is similar to its bulk counterparts. The effects of post-heat treatment on the phase and crystal structure of near equiatomic FePd electrodeposits (i.e. Fe₄₈Pd₅₂) was investigated by subjecting electrodeposits to different annealing temperatures from 400 to 600 °C under reducing environment. L1₀ FePd phase was formed from nanocrystalline FePd solid solution and the crystallinity improved with increasing annealing temperatures.     

共沉淀法制备M-型钡铁氧体

本文用共沉淀法,在不同的预烧温度下合成了Ti、Mn、Cu掺杂的M-型钡铁氧体,考察了在不同预烧条件下,铁氧体的形成情况,以及离子的掺杂对铁氧体的磁性能的影响。利用XRD、SEM、VSM对样品进行了表征。结果发现:在预烧温度为500℃条件下形成的掺杂态的铁氧体的形状呈现片状六角形,并且磁性能良好σs(23.27emu/g);jHc(3580Oe)。     

Unique magnetic properties and magnetization reversal process of CoFe2O4 nanotubes fabricated by electrospinning

CoFe(2)O(4) nanotubes have been directly fabricated by single-capillary spinneret electrospinning. The external diameter of the CoFe(2)O(4) nanotubes ranges from 60 nm to 160 nm. The morphology and structure characterizations show that individual CoFe(2)O(4) nanotubes are made of CoFe(2)O(4) nanocrystals stacking along the nanotubes with no preferred growth directions and these individual nanocrystals are single crystal with a cubic spinel structure. Each nanocrystal was shown to be a single magnetic domain. The magnetic measurements show that the coercivity (H(c)) of the CoFe(2)O(4) nanotubes decreases from 10?400 Oe at 5 K to 300 Oe at 360 K. The CoFe(2)O(4) nanotubes have a spin reorientation (SR) at 5 K, which is different from CoFe(2)O(4) nanorods and nanoparticles. Based on the observed morphology and crystal structure, a micromagnetic model, "chain-of-rings", is developed to interpret the magnetic behavior of the CoFe(2)O(4) nanotubes. The theoretical coercivity (534 Oe) is in good agreement with the experimental results (509 Oe). It is believed that our work should open a new route to prepare various magnetic ferrite nanotubes and is significant for expanding the application of CoFe(2)O(4) into the new fields.     

Ni纳米线阵列的电化学组装及磁性能研究

利用二次氧化法制备了多孔阳极氧化铝(AAO)模板,通过恒电位沉积法在模板内组装了Ni纳米线阵列。采用SEM、TEM、SAED、EDS和VSM等检测技术对填孔过程、阵列形貌、结构和磁性能进行了分析和表征。结果表明,Ni纳米线在纳米孔中的生长过程经历四个阶段,填孔终止时间控制在第三阶段。适宜AAO模板中Ni纳米线沉积的电位为-0.9 V,pH为3.5。Ni纳米线是沿着(111)方向生长的单晶结构。当外磁场平行或垂直Ni纳米线阵列时,在磁场强度周期变化下,测量纳米线阵列磁滞现象的闭合磁化曲线,Ni纳米线阵列在平行和垂直两个方向的磁性不同,剩余磁化强度Mr与饱和磁化强度Ms之比分别为0.282和0.055,其矫顽力是293 Oe、100 Oe。