The activation effect of Pd nanoparticles on electroless nickel-phosphorous deposition

Active colloids regarding responsible for charge transfer and electron transfer are in electroless metal bath. Herein, the electrochemical analysis for the catalytic effect of Pd nanoparticles on deposition kinetic and microstructure in the electroless nickel-phosphorous bath was studied. As supported analysis by leaner sweep voltammetry (LSV), the currents for oxidation peaks corresponding to Pd nanoparticles of increasing amount are measured to be enhanced. It shows that Pd nanoparticles have excellent catalytic power for EN_pD bath. In addition, the deposition rate analyzed by mixed potential theory (MPT) was found and increased from 0.063 to 0.091 μg/cm² s. However, based on the same nanocatalyst quantity, the deposition rates which actually occurred and are in situely monitored by EQCM are measured to be faster than theoretical value given by MPT. It shows that that the cathodic currents for depositing hydrogen and phosphorous in mixed potential theory could not be neglected when the equilibrium potential reached. As an additional information supported by FE-SEM, the continuous growth of nickel crystal is found after the induction time measured by EQCM. The narrowest distribution of nanosize grain is obtained at 120 s. In addition, the deposited layer of P of higher content is found to exist in the deposited microstructure catalyzed by the Pd nanoparticles of high concentration.     

Functionalization of polyamide 6 nanofibers by electroless deposition of copper

Polyamide 6 (PA6) nanofibers were prepared via electrospinning. The electrospun PA6 nanofibers were functionalized using electroless deposition technique. Oxygen low temperature plasma treatment was applied to substitute the conventional roughening process using concentrated sulfuric acid-potassium dichromate. The deposition of copper (Cu) on the PA6 nanofibers was characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), and energy dispersive X-ray spectroscopy (EDX). The observations revealed the uniform coating of the PA6 nanofibers with thin films of Cu. It was also found that the surface conductivity of the PA6 nanofibers was significantly improved by the Cu deposition. The combination of electrospinning and electroless deposition will provide a new approach to producing the functional nanofibers for various applications.     

Electrophoretic deposition of electroless nickel coated YSZ core-shell nanoparticles on a nickel based superalloy

In this work, yttria-stabilized zirconia (YSZ) nanoparticles were covered by a thin Ni layer with approximately 10 nm thickness by electroless deposition method to reduce sintering temperature of the ceramic coating which was applied on a Ni based superalloy via electrophoretic deposition (EPD). Suspensions containing the processed Ni-YSZ core-shell nanoparticles in acetone and isopropyl alcohol solvents were stabilized by addition of 0.4 wt% iodine and 1.5 wt% polyethylenimine, respectively, to find more effective stabilization method for EPD. It was seen that the presence of the Ni layer on YSZ nanoparticles improved performance and sticking factor of EPD and uniform coatings were obtained in both suspensions. The Ni-YSZ green coating which was produced by EPD at voltage of 35 V and deposition time of 30 min in acetone with thickness of 41 μm was sintered in 1100 °C and finally a uniform NiO-YSZ coating was formed on the metallic surface.     

Density functional theory study on the oxidation mechanisms of aldehydes as reductants for electroless Cu deposition process

The oxidation mechanism of aldehydes, which are commonly used as reductants for an electroless deposition process, was studied by using Density Functional Theory (DFT) calculations. The reaction pathway of the three aldehydes, i.e., formaldehyde, acetaldehyde and glyoxylic acid, with different functional groups, were examined by calculating energy profiles of all intermediate species. It was indicated that the pathway in an isolated system proceeds via dianion-free intermediate species. Taking the solvation effect into consideration, it was indicated that the oxidation reactions of the three aldehydes preferably proceed at the solid/liquid interface. In combination with a Cu metal cluster as a model of metal surface, it was also indicated that the oxidation reactions proceed preferentially at the Cu surface. It was expected that the adsorption/desorption energy at the Cu surface of glyoxylic acid, which has an electron-accepting carboxyl group, was smaller and substituent effect lead to its high reducibility.     

Copper deposition onto silicon by galvanic displacement: Effect of Cu complex formation in NH4F solutions

Copper was deposited onto rotating Si substrates by galvanic displacement in 6.0 M NH₄F to determine the effects of Cu complex formation on deposition rates. Deposition rates decreased with increasing rotation speed, indicating that Cu(I) intermediates, stabilized by NH₃, diffuse away from the Cu surface before they reduce to Cu(0). UV-visible spectra of contacting solutions and direct measurements of mass changes resulting from Cu deposition and Si removal confirmed this proposal. These findings contrast those reported previously for deposition from HF solutions, in which Cu(I) species are unstable and reduce rapidly to Cu(0). These data and mixed-potential theory were used to develop a reaction-transport model that accurately describes the effects of mass transfer and electrochemical reaction rates on Cu deposition dynamics and open-circuit potential (OCP) values. The effects of ascorbic acid and tartrate additives on film properties and formation rates were also examined. Cu reduction kinetics decreased significantly when ascorbic acid (0.01 M) was present. Adhesion of Cu films was improved when ascorbic acid was used, but internal stresses caused films to distort when their thicknesses exceeded 100 nm. Adding potassium sodium tartrate to solutions containing ascorbic acid decreased film stresses and led to robust films with excellent adhesion.     

CoNiP electroless deposition process for fabricating ferromagnetic nanodot arrays

An electroless deposition process for fabricating CoNiP nanodot arrays (less than 50 nm in height) with high magnetic coercivities was investigated. To fabricate such nanostructures, we improved the crystallinity of the CoNiP deposits in the initial deposition stage by applying an fcc-Cu(1 1 1) underlayer with low lattice mismatch to hcp-Co(0 0 0 2), and an autocatalytic electroless deposition process at the Cu surface was carried out by using dual reducing agents, H₂PO₂⁻ and N₂H₄. CoNiP films demonstrated high perpendicular magnetic coercivities in the initial deposition stage since the highly crystalline hcp(0 0 0 2) CoNiP layers were grown parallel to the Cu underlayers. Nanopatterned substrates were formed by UV-nanoimprint lithography. CoNiP was electroless deposited on the nanopatterned substrates. As a result, CoNiP was deposited selectively from the bottom of the nanopores with few defects in a large area. Perpendicular coercivities higher than 3000 Oe were obtained for nanodots even with heights of 50 nm. Thus, an electroless deposition process that can be used to form nanostructures with high crystallinities in the initial stage without any anomalous deposition was demonstrated.     

Hydrogenation of 3,4-epoxy-1-butene over Cu–Pd/SiO2 catalysts prepared by electroless deposition

Electroless deposition has been used to prepare Cu–Pd/SiO₂ bimetallic catalysts wherein initial Cu coverages are limited only to the pre-existing Pd surface. Cu loading on the Pd surface can be systematically varied by modification of deposition kinetic parameters. In this case deposition time was used as the kinetic variable for the preparation of a series of Cu–Pd catalysts. These materials have been characterized using atomic absorption, CO chemisorption, and FT-IR (adsorption of CO), and then evaluated for the hydrogenation of 3,4-epoxy-1-butene, a functionalized olefin having many potential reaction pathways. Catalyst performance and characterization results suggest that Cu is not distributed in a monodisperse manner on the Pd surface, indicating the existence of autocatalytic deposition of Cu on Cu sites. The FT-IR results suggest that although CO adsorption on all sites is suppressed by Cu addition, initial Cu deposition occurs more readily on certain sites. The bimetallic Cu–Pd sites that are formed exhibit unusually high activity for EpB conversion and formation of unsaturated alcohols and aldehydes. This bimetallic effect on catalyst activity and selectivity is best explained, not by the existence of either ligand or ensemble effects, but rather by the bifunctional nature of the Cu–Pd sites present on the surface of these catalysts.     

Preparation of highly dispersed PEM fuel cell catalysts using electroless deposition methods

A methodology for the electroless deposition (ED) of PtCl₆²⁻ using dimethylamine borane (DMAB) on a Rh-seeded carbon support has been developed for electrochemical and fuel cell applications. This procedure required seeding the carbon with a Rh-precursor catalyst via wet impregnation prior to the exposure of an aqueous ED bath containing PtCl₆²⁻, DMAB, and sodium citrate (complexing/stabilizing agent). Kinetic parameters that affect the extent and rate of PtCl₆²⁻ deposition include concentrations of PtCl₆²⁻, DMAB, and sodium citrate as well as pH and concentrations of Rh seed sites. A linear relationship between rate and extent of PtCl₆²⁻ deposition and DMAB and Rh concentrations was found while the citrate concentration had little effect on rate and a modest effect on extent. Lastly, extent of PtCl₆²⁻ deposition showed a maximum with respect to pH. Characterization of the Rh-seeded, carbon support by transmission electron microscopy (TEM) shows that the Rh particle diameters remain constant at 33–43 Å as the Rh weight loading increases from 0.4% to 2.2% to 4.4%. Further, after deposition of similar loadings of Pt, TEM analysis shows Pt particle diameters decrease with increasing Rh loading, since equal amounts of Pt were deposited on greater numbers of Rh seed particles. This pattern suggests a shell-core geometry, where Pt is deposited more or less uniformly around a Rh core.     

Modelisation of Ni-P electroless deposition in ammoniacal solutions

A reaction path for the electroless deposition of Ni-P layers is developed. The steady-state polarisation and impedance responses are calculated. The comparison between the experimental results and the calculation shows the adequacy of the model. The mechanism accounts for most of the experimental features observed for the steady-state and the impedance behaviours and their dependencies with pH, hypophosphite and nickel sulphate concentrations.     

Electrochemical study of electroless deposition of Fe-P alloys

Fe-P deposits were prepared by electroless deposition and the inducing effect of coupled aluminum on Fe-P deposition was studied. The partial reactions of reducer oxidation and metal ions reduction in electroless deposition Fe-P bath were investigated by electrochemical investigation. In situ mixed potentials of the process for electrolytes with different pH were measured. The plating rate of iron alloys was measured gravimetrically and calculated by the deposition current density. The results show that coupled aluminum induces the Fe-P deposition by shifting the potential negatively and decreasing the polarization resistance of anodic and cathodic reaction. The test of the mixed potential theory was performed by comparison between direct experimental values of the mixed potential and plating rate with those derived theoretically from the current-potential curves for partial reactions. Due to the hydrogen evolution, the plating rate determined by electrochemical measurement is higher than the average plating rate determined from gravimetrical measurements.     

Fabrication and characteristics of Pd nanoparticles/nanofilms on ceramics toward catalytic electrodes

We report an approach of fabricating various palladium nanostructures with tailored morphologies in nanoparticles (Ø80-300 nm), nanoporous films (Ø50-200 nm), and integrated nanotubules arrays (Ø300 nm and 5 μm long) on different ceramic materials. Microporous titanate ceramics or nanoporous alumina films were first prepared through a solid-state synthesis or an anodic oxidization of aluminum sheets. The micro- and nanoporous ceramics were then used as supporting materials in an electroless deposition to deposit Pd nanoparticles or nanofilms over the porous substrates, thus leading to various Pd nanostructures with large surface areas and high corrosion resistance for many applications. EDX and EPMA analysis disclosed that the phosphor co-deposition in 5-11 at.% P occurred in the palladium electroless deposition. XRD analysis showed that the as-deposited Pd-P alloys were polycrystalline with a preferential orientation of (1 1 1) facet. The phosphor included in the Pd-P alloy films existed as a solid solution form, rendering as a single phase Pd-P alloy with nanocrystals (∼5 nm across) of cubic palladium.     

Design and achievement of a complete bottom-up electroless copper filling for sub-micrometer trenches

The bottom-up filling of electroless copper usually depends on inhibiting the Cu deposition at the surface or accelerating the Cu deposition in the bottom of trenches to achieve a relative high deposition rate of electroless copper in the bottom of trenches. In this paper, a complete bottom-up filling of electroless copper, in which the deposition rates of the electroless copper were not only inhibited at the surface of the substrate, but also were accelerated in the bottom of the trenched, was designed and achieved in the plating bath with an addition of bis (3-sulfopropyl) disulfide (SPS) and polyethylene glycol (PEG). The cross-sectional SEM observation of trenches indicated that all trenches with different widths ranging from 100 to 290 nm were filled completely by electroless copper, and no void was found. This was attributed to three factors, the electroless Cu deposition was accelerated markedly by an addition SPS only; but it was suppressed sharply by a combination addition SPS and PEG-4000; the large molecular weight and lower diffusion coefficient of PEG-4000 resulted in concentration gradient of PEG-4000 in the trenches. The effects of PEG-4000 and SPS on the polarization behaviors of the electroless copper plating bath were investigated by the linear sweep voltammetry method and mixed potential theory.     

Optimization of electroless Ni-Zn-P deposition process: experimental study and mathematical modeling

A mathematical model based on mixed potential theory was developed which was used to optimize a non-anomalous Ni-Zn-P electroless deposition process developed by us at USC. The model was developed by assuming an adsorption step in addition to the electrochemical steps. The concentrations of the Zn and Ni complex were estimated by solving the material balances in addition to the electroneutrality condition and the equilibrium relations. The composition of the coating was estimated from the partial current densities of all charge transfer reactions, which occur at the electrode-electrolyte interface. The model results showed that the adsorption plays a significant role in the alloy deposition process. From the model results, it was seen that the addition of Zn ions to the bath inhibits the deposition rate by changing the surface coverage of the adsorbed electroactive species on the electrode surface. The model indicated that an increase of pH of the bath increases the alloy deposition rate.     

Study on surface modification of AB5-type alloy electrode with polyaniline by electroless deposition

A new polyaniline (PANI)-coated technique was adopted for a AB₅-type alloy (La_0.64Ce_0.25Pr_0.03Nd_0.08Ni_4.19Mn_0.31Co_0.42Al_0.23) in order to improve its electrochemical and kinetic properties. FE-SEM observation and FT-IR analysis results revealed that the PANI electroless deposited to the surface of alloy particles. Through the PANI-coating the initial discharge capacity increased from 299 to 331 mAh/g and the high rate discharge ability (HRD) increased from 8.5 to 45.0% at discharge current density of 1440 mA/g. For kinetic properties, linear polarization, EIS, anodic polarization and cyclic voltammetry measurements suggested that charge-transfer resistance decreased and the hydrogen absorption rate of the alloys increased after PANI-coating.     

Significance of sensitization process in electroless deposition of Ni on nanosized Al2O3 powders

The electroless deposition of Ni on nanosized α-Al₂O₃ powders of about 150 nm diameter has been studied by employing SnCl₂ sensitization and PdCl₂ activation approach. The bath for electroless deposition was prepared by using NiCl₂·6H₂O, C₆H₅NaO₇·H₂O, NH₄Cl and NaH₂PO₂·H₂O, and the deposition was carried out at a bath temperature of 70 °C with a pH value of 8.5. The morphology, microstructure and phase structure of Ni-coated α-Al₂O₃ nanopowders were characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffractometry (XRD), respectively. It is found that, the sensitization process followed by repetitive resining greatly affects the morphology of Ni deposited in the form of nanoparticles onto the ultrafine alumina particles, different from the conventional continuous electroless film/coating deposited on coarser particles. The resining of the SnCl₂ sensitized ultrafine α-Al₂O₃ particles prior to PdCl₂ activation process leads to varied amount of deposited Ni particles with diameters of 50–80 nm on the Al₂O₃. It is revealed that, subsequent reduction process (activation) from Pd²⁺ to Pd is linked to the original sites of Sn²⁺ by simultaneous oxidation process from Sn²⁺ to Sn⁴⁺ on the previously sensitized α-Al₂O₃ nanopowders. Consequently, the form of deposited Ni correlated closely to the surface distribution of reduced Pd which may be continuous or discrete determined predominantly by the density of adsorbed Sn²⁺ on the powders during sensitization process. It demonstrates a possibility of depositing different distribution structures of metals on nanosized α-Al₂O₃ powders through controlling SnCl₂ sensitization process.     

A study of the Co-coated Ni cathode prepared by electroless deposition for MCFCs

In this study, we made a novel alternative cathode material of molten carbonate fuel cell (MCFC) using electroless deposition of Co on the surface of the Ni powder. Using this manufacturing method, we expect that economical and large-scale cathode can be made easily. The cathode prepared by this method formed LiCo_1−yNi_yO₂ phase in molten (Li_0.62K_0.38)₂CO₃ at 650 °C under CO₂:O₂=66.7:33.3% atmosphere, its solubility is 40% lower than that of NiO cathode. In the unit cell test, the performance of the cell composed of Co-coated Ni cathode was same as that of the cell composed of NiO cathode. Thus the cathode made by Co-coated Ni powder used as an alternative cathode can maintain the advantages of NiO cathode and lengthen the lifetime of MCFC.     

Nickel layer deposition on SiC nanoparticles by simple electroless plating and its dielectric behaviors

Surface modification of the silicon carbide nanoparticles (SiC_P) by electroless nickel plating was performed. The XRD, TEM and XPS results showed that a nanoscale agglomerative nickel layer was coated on the SiC_P. Dielectric permittivities of the original SiC_P and nickel-coated SiC_P were measured respectively in the GHz frequency range from 8 to 12 GHz. The real part and dielectric loss tangent of the nickel-coated SiC_P were significantly enhanced. The origin of the enhancement was discussed in theory, and also explained by discussing practical influence factors.     

Morphology controlled 1D Pt nanostructures synthesized by galvanic displacement of Cu nanowires in chloroplatinic acid

One-dimensional platinum (Pt) nanostructures with different shape, size, and morphology were synthesized by galvanic displacement of sacrificial Cu nanowires in chloroplatinic acid baths. By increasing the concentration of H₂PtCl₆, the morphology of Pt nanostructures greatly altered from Pt nanoparticles decorated Cu nanowires, Pt coated Cu core-shell nanowires, dense Pt nanotubes to porous Pt nanotubes. At low concentration of H₂PtCl₆ (<1 mM), the Pt content monotonically increased with an increase in [H₂PtCl₆] (upto approx. 80 at.%). The Pt content became independent of [H₂PtCl₆] at higher concentration. The average external diameter and wall thickness of Pt nanotubes decreased with increasing [H₂PtCl₆] suggesting that the dissolution of copper is strongly dependent on [Cl⁻], which led to changes in the morphology of Pt nanostructures.     

Design of core-shell structured YSZ@Cu cermet powders with thermal conductivity anisotropy by electroless deposition

Core-shell structured cermet powders with thermal conductivity anisotropy have been brought into focus because they have a great potential application as the horizontal thermal diffusion layer material in multilayer thermal protective coating (TPC). In this contribution, core-shell structured YSZ@Cu cermet powders were fabricated by electroless deposition (ED) of Cu on yttria-stabilised zirconia (YSZ) powder. The surface of YSZ powder was uniformly coated with a thin Cu shell of approximately 2 μm. Through X-ray photoelectron spectra (XPS) analysis, it was found that trace CuO and Cu₂O oxides formed on the surface of Cu shell. Results of thermal spraying adaptability analysis show the flowability of core-shell structured YSZ@Cu cermet powder improved to 56.8 s/50 g, which conforms better to the basic requirements of thermal spraying material. By differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) tests, the YSZ@Cu powder had good thermal stability. In particular, between 25 and 500 °C, the anisotropy thermal conductivity rose higher than 1.8 and it remained stable at approximately 1.6 with temperature as high as 900 °C. All these features promise it a high-performance thermal conductivity anisotropy material.     

柠檬酸对Ni-P合金化学镀沉积速度和镀层性能的影响

研究了柠檬酸浓度对乙酸盐缓冲体系Ni-P合金化学镀沉积速度、镀层含磷量及其耐蚀性与结构的影响，并对镀层在镀态下和经热处理后的耐蚀性与结构进行了比较。结果表明，随柠檬酸浓度的增加，沉积速度先增加后l牵低，而镀层中磷含量则先降低后增加；镀态时高磷合金为非晶态结构且具有较好的耐蚀性，中磷合金则为非晶 微晶结构，耐蚀性较低，而所有镀层经350℃热处理1h后，结构都转变为晶态，且耐蚀性明显提高。