Narrow Results

Different pretreatment methods for electroless nickel and cobalt plating are demonstrated and compared in the present investigation. The surface morphologies of the nickel or cobalt deposits are investigated by scanning electron microscopy (SEM), and the chemical compositions of the coatings are analyzed by energy-dispersive X-ray spectroscopy (EDX). Method of single-step pretreatment is selected as the optimized method for electroless nickel plating process, while improved two-step sensitization-activation and single-step pretreatment methods can be selected for electroless cobalt plating. It can be found that the content of free Co is much lower compared to electroless Ni plating.

The Ni–Zn–P alloy coating has excellent physical and chemical properties that have been exploited for various industrial applications. Using sodium citrate as a complexing agent and lactic acid as a stabilizer, the effects of temperature and pH on the deposition rate and corrosion resistance of electroless plated Ni–Zn–P coating were studied. The results indicated that, when the temperature was 85${}^{\circ }$C, a good deposition rate was obtained with stable plating solution. pH value of 9.0 is preferred for the coating process by considering the stability of plating bath and deposition rate. The Ni–Zn–P alloy coating deposited with plating temperature of 85${}^{\circ }$C and bath pH of 9.0 has good quality, and a uniform and smooth surface texture without porosity.

Low phosphorus electroless Ni-P alloy coating has many advantages over medium and high phosphorus electroless Ni-P alloy coatings because of its special microstructure and composition, which can meet more special performance requirements. In addition, reducing the plating temperature can reduce energy consumption. The preparation process of electroless Ni-P plating at medium temperature and low-P was studied by single factor and orthogonal experiment. The results show that electroless Ni-P alloy coatings with 4–6% P can be obtained at 60–80${}^{\circ }$C and pH=5–6. The hardness, deposition rate and corrosion resistance of the coating were also evaluated.

W–Cu ultrafine/nanocomposite powders have high sintering activity, so ultrafine/nanotechnology of W–Cu composite powders is one of the main methods to obtain fully dense, high-performance W–Cu composite materials. Cu-coated ultrafine W composite powders were synthesized by ultrasonic-assisted electroless plating process with non-noble metal activation pretreatment at room temperature in this paper. The growth mechanism of Cu layers and surface morphologies and composition of initial ultrafine W powders, pretreated W powders and Cu-coated W powders were analyzed by field emission scanning electron microscopy (FE-SEM), and energy dispersion spectrometry (EDS). The results show that the uniformly Cu coated W composite powder is successfully synthesized without conventional sensitization and activation steps by ultrasonic-assisted electroless plating at room temperature. The Cu layers on the ultrafine W powders had cell structure with dense, uniform distribution. The growth mechanism of Cu layers appears as follows: the surfaces of pretreated W powders appear linear-like and lamellar-like surface defects which act as activated sites. The reactants in the plating solution were adsorbed on catalytic activity surfaces of powders and happened oxidation–reduction reaction. The growth and aggregation mechanisms of Cu particles after nucleation are stripy Cu-cells grew up, bend, bifurcated, and aggregated, then wounding into a cellular structure, like "wrapping wool clusters" in the life. Finally, Cu cells grow up and merge into a layer.

CoFeB nanotubes were fabricated by electroless plating in magnetic field using anodized aluminum oxide template, and the structural and magnetic properties of CoFeB nanotubes were investigated. It is found that some nano-scale particles form on the wall of nanotubes. Both coercivity ratio and squareness ratio of out-of-plane to in-plane are significantly changed by the applied magnetic field during electroless plating, which indicates that directional ordering in amorphous CoFeB nanotubes are achieved during electroless plating under magnetic field. The results show that the applied field impacts the magnetic anisotropy of amorphous nanotubes. The anisotropy is stronger with the magnitude of applied field increasing.

Thin nanocrystalline Cu films (< 1 μm) are deposited on a glass substrate using an improved electroless plating technique. The deposition course of the Cu film is illustrated by the variation of surface morphology with different deposition time. The results show that a more uniform and continuous nanocrystalline Cu film with very small nodules can be formed on a glass substrate at the deposition time over 1 min. The roles of SDBS as an additive in the bath are also discussed. According to the relation of the film thickness and the deposition time, it is obvious that the film thickness nearly linearly varies with the deposition time in the present work. An enhanced (111) texture with the diffraction intensity ratio (I₍₁₁₁₎/I₍₂₀₀₎) of about 4.0 and the very fine grain size of 15–28 nm determined by X-ray results has been observed. The variations of the resistivity show that it is strongly affected by the film thickness and grain size.

Surface modification of polytetrafluoroethylene (PTFE) films is done by exposing the films to a sodium naphthalenide (Na/naphtha) etchant, and esterification of 4,4'-azobis(4-cyanopentanoic acid) (ACP) with the hydroxyl groups covalently linked to the surface, followed by the surface-initiated free radical polymerization of 4-vinylpyridine (4 VP). The surface elemental composition and topography of the poly(4-vinylpyridine) (PVP) graft-functionalized PTFE surfaces (PTFE-g-PVP surfaces) were characterized by X-ray photoelectron spectroscopy (XPS), attenuated total reflectance (ATR) FTIR spectroscopy, and atomic force microscopy (AFM). Water contact angles on the pristine PTFE surface and PTFE-g-PVP surfaces were measured. The PVP brushes on the PTFE surface with well-preserved pyridine groups were used not only as the chemisorption sites for the palladium complexes (without the need for prior sensitization by SnCl₂) during the electroless plating of copper, but also as an adhesion promotion layer to enhance the adhesion of the electrolessly deposited copper to the PTFE surfaces. The T-peel adhesion strength of the electrolessly deposited copper to the PVP grafted PTFE (PTFE-g-PVP) surface could reach about 7.2 N/cm. This adhesion strength was much higher than that of the electrolessly deposited copper to the pristine or Na/naphtha-treated PTFE surface. Effects of the graft polymerization time and the activation time in the PdCl₂ solution on the T-peel adhesion strength of the electrolessly deposited copper (from the Sn-free process) to the PTFE-g-PVP surface were determined.

In order to investigate the electrochemical properties of Li/FeS cell, FeS powder was fabricated by using a high-energy ball milling method. Then, surface of FeS powder was coated with metallic nickel. Nickel coating was conducted by using electroless nickel plating method. Nickel chloride (NiCl₂ · 6H₂O) was used as the nickel ion source for electroless nickel plating. The effects of nickel coating on the electrochemical properties of FeS electrode for Li/FeS cell were investigated by CV measurement and charge/discharge tests. Then, cells for electrochemical tests were assembled by stacking a lithium anode, separator containing liquid electrolyte, and FeS cathode in turn. From the results, electroless nickel plated FeS electrode showed very high initial discharge capacity of 581 mAh/g-FeS. And also, it showed higher discharge capacity than that of bare FeS electrode until the 29th cycle. Therefore, it is found that metallic nickel gives beneficial effects on enhancing the electrical conductivity of FeS cathode material. 82.47.Cb.

Electroless plating has been considered as an effective approach to provide protection and enhancement for metallic materials with many excellent properties in engineering field. This paper begins with a brief introduction of the fundamental aspects underlying the technological principles and conventional process of electroless nickel–phosphorus (Ni–P) coatings. Then this paper discusses different electroless nickel plating, including binary plating, ternary composite plating and nickel plating with nanoparticles and rare earth, with the intention of improving the surface performance on steel substrate in recent years in detail. Based on different coating process, the varied features depending on the processing parameters are highlighted. Separately, diverse preparation techniques aiming at improvement of plating efficiency are summarized. Moreover, in view of the outstanding performance, such as corrosion resistance, abrasive resistance and fatigue resistance, this paper critically reviews the behaviors and features of various electroless coatings under different conditions.

In order to arrange directionally, multi-wall carbon nanotubes (MWCNTs) are functionalized with ferromagnetic cobalt on the surface via the electroless plating method. The uniform and continuous cobalt coating was received in pH $=$ 9 at 45${}^{\circ }$C for 30min. It is found that the hydroxyl and carbonyl groups could be successfully introduced on the surface of raw MWCNTs after treated in boiling nitric acid that would provide the active points for cobalt deposition. The diameters of the cobalt (Co)-coated MWCNTs increase to 20–50nm from 8–15nm of purified ones. As a result of nanoscale cobalt coating, MWCNTs show strong ferromagnetism at room temperature. The Co-coated MWCNT respond to magnetic field susceptibly in the distilled water and arrange themselves in the direction of the applied magnetic field up to 1T. The hysteresis curve results show that the coercivity of Co-MWCNTs is 1285.2 Oe, which is about four times that of cobalt powder itself.

The Ni-P/TiN coating was used as bipolar plate by electroless plating on Ti. Surface morphology and phase structure of the coatings were characterized by SEM and XRD, respectively. Corrosion resistance of Ni-P and Ni-P/TiN coating was measured in the simulated solution of Proton exchange membrane fuel cells (PEMFCs). The interfacial contact resistance (ICR) was conducted by applied different forces. SEM images indicated that the particles of core–shell structure were formed on the surface of coating on Ti substrate. The core–shell structure was composed of TiN core and Ni-P electroless plating shell. Compared with Ni-P coatings, the Ni-P/TiN coating showed better corrosion resistance behaviors and low ICR (below 10m$\mathrm{\Omega }$ cm${}^{-2}$ under pressure of 200 N/cm${}^2)$. TiN particles and distribution of core–shell were in favor of the formation of coating and compact surface morphology. The good conductivity was attributed to the compact surface morphology of coating. The Ni-P/TiN coating showed excellent interfacial conductivity and good corrosion resistance at applied high potential in simulated solution of PEMFCs.

In this work, electroless copper plating on the surface of CaCO₃ powders modified with hydrophobic and hydrophilic coating was developed in that order. It was found that the surface structure of modified CaCO₃ powders could absorb Sn${}^{2+}$ and then reduce Ag${}^{+}$. The Ag atoms were used as catalysts for the electroless face-centered copper crystallites plating on the CaCO₃ surface. The compact and uniform copper particles were plated on the CaCO₃ surface. The plated coating has a two-layer structure. The size of copper particles in the first layer was around 20nm, the one in surface layer was around 100nm. The lowest volume resistivity of conductive coating was $6.2\times 10^{-2}\mathrm{\Omega }\cdot \mathrm{\text{cm}}$.

Electroless plating can be used to prepare metal particle/CaCO₃ composite powder, but the use of noble metal as catalytic site would increase the cost. In this work, we adopt the combined 3-amino-propyltriethoxysilane (KH550) modification and NiCl₂ activation to coat CaCO₃ powder by a uniform layer of Ni particles/polymer brush which acts as non-noble metal catalyst, then, a low-cost electroless plating to prepare Cu particle/CaCO₃ composite powder was developed. Results showed hydrolyzed KH550 coated on the CaCO₃ surface in the form of polymer brush. The active group on the polymer brush surface could chemisorb Ni${}^{2+}$ and then Ni particles/polymer brush was attached on its surface. The Ni particle/polymer brush structure acted as catalytic site and could catalyze electroless copper plating on its surface. The $M_{\mathrm{\text{plated particle}}}∕M_{(\mathrm{\text{plated particle}}+{\mathrm{\text{CaCO}}}_3)}$ is 1%, its average diameter is about 100nm. This means that the dependable technology has great potential application in preparing metal inorganic powder at a low cost.

Electroless nickel plating is an important process in the fabrication of metal microstructures on silicon substrates. Adhesion of the metal film to the substrate is a key parameter. We report a study of the adhesion of electroless nickel plating on polished silicon for different surface treatments (prior to plating), substrate areas and plating durations. Three different surface treatments considered are: mild etching, palladium activation and nickel activation. Adhesion strength in excess 9.8 × 10⁷N / m² has been obtained. Adhesion requirements for using nickel plating for masking the silicon substrate during anisotropic etching is also discussed.

The synthesis of bimetallic nanostructures using galvanic replacement displays a versatile route toward efficient catalysts for fuel cell reactions. We show that electrolessly plated Ag nanotubes (NTs) are a unique template for the synthesis of double-walled Ag–Pt NTs. After replacement reaction, different dealloying protocols are applied to adjust the residual Ag content. The structures were thoroughly characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy, providing evidence of a hollow tube structure composed of Ag–Pt alloy. Experiments under harsh conditions reveal, that a significant amount of Ag remain in the NTs, which strongly affects the methanol oxidation performance. With optimized Ag–Pt ratio, the specific activity of Pt/C catalysts can be outperformed. From the obtained results, we emphasize that each effort using galvanic replacement should be accompanied by detailed compositional analysis.