Improved Electroless Plating Research Articles

A Comparison Study of Ag Composites Prepared by Spark Plasma Sintering and Hot Pressing with Silver-Coated CNTs as the Reinforcements.

In this study, carbon nanotube-reinforced silver composites (CNT/Ag) were prepared by the powder metallurgy process via spark plasma sintering (SPS) and hot pressing sintering (HP) with composite powders through an improved electroless plating method assisted by ultrasonic spray atomization. The dispersion of CNTs was effectively improved by ultrasonic spray atomization, and uniform silver layers were deposited on the surface of CNTs by electroless deposition. The property testing results showed significant improvements of the electrical conductivity, hardness, and tensile strength in the samples prepared by SPS, as compared to their HP sintered counterparts. When the volume fraction of CNTs reached 2.5%, the tensile strength reached a maximum value of 221 MPa, which was more than twice that of the pure silver samples. The structural analysis indicated different degrees of CNT agglomeration and matrix mean grain sizes in the composites prepared by SPS and HP, which are responsible for the differences in properties.

Fabrication of sliver/graphitic carbon nitride photocatalyst with enhanced visible-light photocatalytic efficiency through ultrasonic spray atomization

A composite photocatalyst, sliver/graphitic carbon nitride/pre-treated carbon fiber paper (Ag/g-C3N4/t-CFP), has been innovatively designed and successfully fabricated by loading Ag and g-C3N4 species on t-CFP using the combined methods of thermal polymerization and improved electroless plating (IEP) through ultrasonic spray atomization (USA). A micro-droplet system, USA is able to eliminate the adverse influence of concentration gradient effectively. The samples obtained were carefully characterized in terms of morphology, phase, chemical structure, and optical performance. Results suggested that compared with the conventional electroless plating (CEP), IEP strategy could ensure a better dispersibility and smaller size of Ag nanoparticles. Accordingly, the IEP-prepared Ag/g-C3N4 photocatalyst on t-CFP (ACNT-iep) exhibited a pseudo-first-order kinetics constant 12 times higher than that of the neat g-C3N4 on t-CFP for methylene blue (MB) degradation. Photoluminescence (PL) and electrochemical impedance spectra (EIS) demonstrated a more efficient separation of photogenerated carriers in ACNT-iep at the same time. The photocatalytic activity of ACNT-iep could be maintained at a high level over five cycles.

A study on the CNTs-Ag composites prepared based on spark plasma sintering and improved electroless plating assisted by ultrasonic spray atomization

Carbon nanotubes reinforced silver composites (CNTs-Ag composites) are considered as a promising candidate for high-performance contact materials with the potential properties of low contact resistance, high thermal conductivity and excellent mechanical performance. While at present the dispersion of CNTs in silver matrix and the interfacial bonding of the composites remain problems to be resolved or enhanced. In this study, silver nanoparticles coated carbon nanotubes (Ag@CNTs) were synthesized through an improved electroless plating method assisted by ultrasonic spray atomization, which inhibited excessive growth of silver particles and led to much more uniform nanometer grain-sized coating. The Ag@CNTs were solution ball-milled (SBM) with Ag powders and then were densified by spark plasma sintering (SPS). The composites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS). The results showed the CNTs dispersion in Ag matrix was improved benefitting from the homogeneous Ag nanoparticles distribution on CNTs, and correspondingly, the hardness and electrical conductivity were significantly improved. The mechanism may result from the combination of more homogeneous CNTs dispersion and tighter interface bonding in composite materials.

Improved electroless plating method through ultrasonic spray atomization for depositing silver nanoparticles on multi-walled carbon nanotubes

A novel method was developed to deposit nanosized silver particles on multi-walled carbon nanotubes (MWCNTs). The electroless plating of silver on MWCNTs accomplished in small solution drops generated by ultrasonic spray atomization, which inhibited excessive growth of silver particles and led to much more uniform nanometer grain-sized coatings. The results showed that pretreatment was essential for silver particles to deposit on the MWCNTs, and the electrolyte concentration and reaction temperature were important parameters which had a great influence on the morphology and structure of the silver coatings. Possible mechanisms of this method are also discussed in the paper.

Preparation of Pd-TS-1 Composite Membrane for Hydrogen Separation

Palladium composite membranes have been prepared by improved electroless plating on macroporous α-Al2O3 tubes. TS-1 zeolite layer was introduced in the palladium composite membrane to modify macroporous α-Al2O3 tubes and prevent the diffusion between Pd and alumina. The detailed microstructure and morphology of the Pd-TS-1 composite membrane were examined by SEM and XRD. Moreover, gas permeation performance was tested at the temperature range of 623~773K. Results showed that the H2 permeance and H2/N2 ideal selectivity for Pd-TS-1 composite membrane could be up to 3.7×10-7 mol·m-2·s-1·Pa-1 and 310 at 773K, respectively.

Role of La in PS/Ni Composite Microspheres Prepared by Electroless Plating

Core-shell composite microspheres have been extensively used. However, uniform coating of a metal on a polymer substrate by electroless plating is still a key challenge. In this report, to improve surface roughness, subsidiary fracture of the plated layer and high density, La was added into electroless nickel plating (ENP) bath to prepare PS/Ni composite microspheres. Morphology, structures and electrical property of PS/Ni composites were characterized. The results revealed that a dense, stable and uniform Ni-P-La nanoshell formed on the surface of PS microspheres. With the increase of La content from 0 to 50 mg/L, the average shell thickness of the composites reduced from 240 nm to 95 nm, and the density of the composites decreased gradually from 4.068 g/cm3 to 1.515 g/cm3 which overcame the sedimentation problem in the preparation of anisotropic conductive film. Based on a series of experiment results, the deposition mechanism in the presence of La was discussed. In the acid ENP bath, La plays a role of an “additive” and takes part in the co-deposition reaction. The improved electroless plating approach provides an extensive and facile route to prepare core-shell composite microspheres with the ideal surface morphology, microstructure and electrical property.

Synthesis of high conductivity Polyaniline/Ag/graphite nanosheet composites via ultrasonic technique

A new process for the synthesis of high conductivity polyaniline/Ag/graphite nanosheet (PANI/Ag/NanoG) composites was developed. Graphite nanosheet was prepared by treating the expanded graphite in aqueous alcohol solution using sonication, and a uniform silver film about 470 nm thick was obtained on graphite nanosheet surface via an improved electroless plating method. Then PANI/Ag/NanoG composites were fabricated via in situ polymerization of aniline monomer in the presence of silver coated graphite nanosheet through using ultrasonic technique. The sliver particles and composites were evidenced by scanning and transmission electron microscopy examinations, the results showed that the silver coated graphite nanosheet particles played an important role in forming conducting bridge in polyaniline matrix. According to the electrically test, the conductivity of the PANI/Ag/NanoG composites was dramatically increased compared with pure PANI. From the thermogravimetric analysis, the PANI/Ag/NanoG composites exhibited a beneficial effect on the thermal stability of pure PANI.

Fabrication of super-hydrophobic nano-sized copper films by electroless plating

Super-hydrophobic nano-sized copper films were fabricated on smooth glass substrates by an improved electroless plating technology. The copper film deposited for 1 min showed extremely high hydrophobicity with a water contact angle of 138.0 o and super-hydrophobicity with a water contact angle of 152.4 o when it was modified with 1-octadecanethiol (CH3–(CH2)17–SH). Such super-hydrophobicity is attributed to the combined roles of the surface hierarchical structure consisting of the micro-sized island-shaped agglomerates that are composed of the nano-sized copper nodules and the low surface energy formed through the chemical modification.

Electroless deposition of silver particles on graphite nanosheets

A uniform silver film about 50 nm thick was obtained on a graphite nanosheet (GN) surface via an improved electroless plating method. 3-aminepropyltrimethoxysilane (APTMS) was used as an encapsulator, limiting growth and aggregate formation. Furthermore, APTMS also acted as a coupling agent favoring deposition of silver particles on the GNs. The silver-coated GNs exhibited excellent conductivity up to 106 S m−1, equivalent to silver powder.

Synthesis of polyacrylonitrile/Ag core–shell nanowire by an improved electroless plating method

A simple synthetic route for fabricating continuous Ag shell on electrospun polyacrylonitrile (PAN) nanofibers has been presented via an improved electroless plating method. To avoid the complex steps (wet surface activation, pre-treatment) of the electroless plating methods reported before, UV photoreduction is used to fabricate dense Ag nanoparticles on the outer surfaces of PAN nanofibers. These Ag nanoparticles act as seeds in the following metal electroless plating step for the growth of continuous Ag shell. Additionally, our method can be easily applied to synthesize other metallic shell on the outer surfaces of PAN nanofibers with Ag nanoparticles as seeds.

Preparation of Cu coating on graphite electrode foil and its suppressive effect on PC decomposition

Cu-coated graphite electrode foil was prepared by an improved electroless plating method. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis were used to study the surface morphology and composition of Cu-coated graphite electrode foil. Tests of discharge and charge and cyclic voltammograms suggest that the decomposition of propylene carbonate and exfoliation of graphite are greatly suppressed, and lithium ions can reversibly intercalate into and de-intercalate from the Cu-coated graphite electrode. Results from electrochemical impedance spectroscopy show that the Cu-coated graphite electrode has lower charge-transfer resistance and higher diffusion coefficient of lithium ions in comparison with the original graphite.

AN INVESTIGATION OF SMOOTH NANOSIZED COPPER FILMS ON GLASS SUBSTRATE BY IMPROVED ELECTROLESS PLATING

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.

H 2/N 2 gaseous mixture separation in dense Pd/α-Al 2O 3 hollow fiber membranes: Experimental and simulation studies

Thin Pd/α-Al 2O 3 hollow fiber (HF) membranes were prepared by an improved electroless plating technique. Pure gas permeation experiments showed that the membranes were defect free and had high hydrogen permeance. Feeding an equimolar mixture of H 2/N 2, the total diffusion flow rate of hydrogen through the composite membranes was measured in dependence of the total feed flow rate at the inlet of the shell/retentate chamber, of the temperature and of the total trans-membrane pressure difference. Furthermore, a mathematical model was derived to describe the hydrogen diffusion in pure and mixture gas experiments. The pure gas experiments were used to determine the membrane parameters. Applying the adapted model parameters, the fluxes of hydrogen occurring in the mixture gas experiments were simulated. The comparison between experimental and calculated data showed a very good agreement in a broad parameter range.

Thin Defect-Free Pd Membrane Deposited on Asymmetric Porous Stainless Steel Substrate

Commercially available asymmetric porous stainless steel (APSS) tube filters with a smooth top layer were employed as substrates for preparing thin Pd-based composite membranes. The simple electroless plating and electroplating methods cannot successfully prepare defect-free thin (less than 6 μm) Pd-based membranes on the APSS substrates. Using the improved electroless plating technique based on a multidimensional plating mechanism, it is easy to prepare thin defect-free (less than 6 μm) Pd/APSS composite membranes. The heat treatment of the APSS substrates has an important effect on membrane performance. The as-prepared 3-μm Pd/APSS composite membrane under optimum conditions has a hydrogen flux as high as 0.409 mol/(m2 s) at 773 K with a pressure difference of 100 kPa while keeping the complete hydrogen selectivity versus helium. The stability of the hydrogen flux and the hydrogen selectivity were also proven by operating times as long as 200 h and gas-exchanging cycles as many as 40.

Thin and dense Pd/CeO 2/MPSS composite membrane for hydrogen separation and steam reforming of methane

A dense Pd/CeO 2/MPSS composite membrane having a thin Pd layer of 13 μm deposited on a macro porous stainless steel (MPSS) tube was prepared using an improved electroless plating method with the commercial activating and plating solutions. The hydrogen permeation behavior of the as-prepared composite membrane under the H 2/H 2 gradient indicated that the hydrogen permeation process may be mainly controlled by the bulk diffusion through the Pd layer. The hydrogen permeability was almost equal to the theoretical value of the pure Pd membrane. In addition, the hydrogen permeation flux as high as 0.275 mol/(m 2 s) was obtained at 823 K under the pressure difference of 200 kPa. However, the operating conditions such as hydrogen feed flux, sweep gas flux, hydrogen pressure, and temperature had a great effect on the permeation flux and resistance when it was operated under the H 2/H 2 + N 2 (sweep gas) gradient. After permeation tests, the catalytic membrane reactor for steam reforming of methane was constructed, appearing a high methane conversion of 97% at 773 K. The membrane stability was proven by steady hydrogen permeation flux, complete hydrogen selectivity versus helium, and unchanged membrane surface morphology after long-term operation.

A novel method for the preparation of thin dense Pd membrane on macroporous stainless steel tube filter

Thin Pd membranes were in situ deposited on macroporous stainless steel (MPSS) tubes using an improved electroless plating method consisting of material filling in the substrate pores, Pd plating on the filled substrate, and recovery and activation of the substrate pores. The Pd/MPSS composite membranes resulted from the filling materials of both aluminum hydroxide gel and Pd/aluminum hydroxide gel have been studied in detail and compared with each other. The hydrogen permeation mechanism through both membranes may be controlled by surface reactions, while the hydrogen permeation flux and activation energy for the membrane resulted from Pd/aluminum hydroxide gel are higher than these for the membrane resulted from aluminum hydroxide gel. In the case of the former membrane, which is almost pinhole free, the hydrogen permeation flux is as high as 0.302 mol/(m 2 s) with a pressure difference of 100 kPa at 773 K. Good membrane stability is also proven by the unchanged membrane surface morphology, the steady hydrogen permeance, and the complete hydrogen selectivity. The deposition mechanism of the membrane has been proposed and interpreted in detail.

Synthesis of Bimetallic Nanoshells by an Improved Electroless Plating Method

In the Letter, we demonstrate an improved electroless plating method for the synthesis of bimetallic shell particles. The procedure involves a combination of surface reaction, seeding growth, and removal of supporting cores. We modified ammonical AgNO3 in ethanol with a controlled amount of HCHO in the seeding process and a uniform and relatively dense coverage of silver nanoparticle seeds on colloid cores was achieved. Following the second kind of metal plating, we extended this method to prepare continuous bimetallic core-shell and hollow particles with a submicrometer diameter. The morphologies of the bimetallic Cu/Ag and Pt/Ag particles were studied with transmission electron microscopy and scanning electron microscopy, and their crystallinity and chemical composition were confirmed by X-ray diffraction. The prepared materials may be of applied value in areas such as catalysis, optics, and plasmonics.

Preparation and characterization of Pd–Ag/ceramic composite membrane and application to enhancement of catalytic dehydrogenation of isobutane

Pd–Ag/ceramic composite membrane, prepared by the improved electroless plating, was characterized. It exhibited higher hydrogen permeating flux (0.759 mol s−1 m−2 at 773 K, ΔP=1.936 atm) and the separation factor of hydrogen to nitrogen or argon was close to infinite. Effects of various operating parameters on the catalytic dehydrogenation of isobutane in the membrane reactor, such as reaction temperature and pressure, space velocity of feed gas, flow rate of purge gas, and molar ratio of nitrogen to isobutane in feed gas, on the conversion of isobutane were investigated. The conversion of isobutane (50.5% at 723 K) in the membrane reactor exceeded the equilibrium conversion (18.8%) and that (15.5%) in the fixed-bed reactor. Maintaining a certain partial pressure of hydrogen in the reaction side of the membrane reactor is favorable to reduce the deactivation rate of catalyst and membrane by carbon deposition.

Amorphous Ni–B alloy/ceramic composite membrane prepared by an improved electroless plating technique

A new amorphous Ni–B alloy/ceramic composite membrane was prepared by an improved electroless plating technique. The composite membrane exhibited not only high permeability, but also high permselectivity for hydrogen separation.

Preparation of a Palladium Composite Membrane by an Improved Electroless Plating Technique

An ultrathin palladium membrane was prepared by an improved electroless plating technique on the surface of a porous titania ceramic substrate. A simple yet new and valuable activation technique named photocatalytic deposition (PCD) has been presented. The thickness of the resulting palladium membrane was about 0.3−0.4 μm. Hydrogen permeation through the composite membrane was proportional to the hydrogen partial pressure difference. The hydrogen permeability and H2:N2 selectivity through the palladium composite membrane are 6.3 × 10-6 mol m-2 s-1 Pa-1 and 1140 at 773 K, respectively. The activation energy for hydrogen permeation is 21.27 kJ/mol at the temperature range of 673−773 K. Long-term hydrogen permeation operation at 673 K indicated that the flux through the resulting membrane under hydrogen/nitrogen gradients requires 80 h to reach a steady state. The steady-state hydrogen flux showed no observable changes during the thermal cycles between 673 and 773 K.