Palladium electroless deposition

Palladium electroless deposition was used for coating of Nafion 117 for the application as a membrane in direct methanol fuel cell.59 After the activation of the polymer membrane (Nafion 117) with Pd(II) complexes, reduction was carried out with sodium boro-hydride, NaBH4. Further, autocatalytic deposition of palladium was performed using a commercially available solution. Compared to bare Nafion, the Nafion/Pd composites considerably reduced methanol crossover. This resulted in enhanced cell performance, which was attributed to the existence of the Pd layer at the surface of polymer. 

Electroless plating — An autocatalytic process of metal deposition on a substrate by reduction of metal ions from solution without using an external source of electrons. It is promoted by specific reductants, namely formaldehyde, sodium hypophosphide, sodium boro-hydride, dialkylamine borane, and hydrazine. Electroless deposition has been used to produce different metal (e.g., nickel, cobalt, copper, gold, platinum, palladium, silver) and alloy coatings. It can be applied to any type of substrate including non-conductors. Some substrates are intrinsic catalytic for the electroless deposition other can be catalyzed usually by sensibilization followed by Pd nucleation also, in some non-catalytic metallic substrates the electroless process can be induced by an initial application of an appropriate potential pulse. In practical terms, the evaluation of the catalytic activity of a substrate for the electroless deposition of a given metal is... 

Many electroless deposition processes are very useful for the fabrication of various devices in the electronics industry. Significant importance for the electronics applications have metals such as silver, gold, nickel, copper, cobalt, palladium, and related alloys. All of these mentioned metals can quite simply and successfully be deposited via electroless deposition. 

Electroless deposition can successfully be used in the production of various composite materials useful for the electronics applications. The examples include silver-coated copper or nickel particles, used in screen printing,43 gold-coated nickel powders, silver and/or palladium-coated polymers or glass powders used in ball grid array, etc. 

Palladium membranes have been prepared by electroless deposition on porous stainless steel substrates.60 The performance of these membranes as hydrogen diffusion electrodes was evaluated using a three-electrode cell in alkaline solution. The technical feasibility of these membranes as gas diffusion electrodes has been proven however, the activity of hydrogen oxidation was high at the beginning and significantly decreased with time. This behavior was attributed to the slow entry of hydrogen at the H2/Pd interface. 

The formation of elemental gold layer at the surface of conductive polymers has been reported in the literature 92,93 Synthesis of nanostructures and self-assembled palladium nanowires from Pd(II) complexed solutions using hydrazine as a reducing agent were reported by Shi et al.94,95 The process was carried out for 120s at 60°C. Electroless deposition of nanowires of other metals is also possible and quite realistic. However, no particular engineering applications are yet known. 

P. C. Hidber et al.. Microcontact printing of palladium colloids Micron-scale patterning by electroless deposition of copper, Langmuir, 12, 1375, 1996. 

H. Kind et al.. Patterned electroless deposition of copper by microcontact printing palladium(II) complexes on titanium-covered surfaces, Langmuir, 16, 6367, 2000. 

The group of Nishimura at Tsukuba has employed a wide variety of deposition techniques in their membrane work [59-68]. In their early studies, palladium was electroplated onto both sides of the substrates [61]. Electroless deposition using PdCl2 with SnCl2 sensitizers was also used [59, 60]. The authors recommend abrasion using 0.05 pm (50 nm) diameter alumina particles to remove thick native layers of contaminants after alloy fabrication and rolling of foils [60]. It should be noted that workers skilled in the art avoid abrasives such as diamond paste or silicon carbide (SiC) to nunimize possible formation of refractory carbides or silicides with the reactive substrates. 

Palladium acts as a nucleating agent for the electroless deposition of copper. By treating the surface with palladium [II] chloride in hydrochloric add a monolayer or so of palladium is deposited on the TiW surface. The palladium chloride solution also contains 1% of hydrofluoric acid which attacks the silica, undercutting the TiW islands (Fig. 5(b)). Electroless copper is now deposited, nucleating on the palladium-covered TiW and growing from it. Finally copper is eleetrodeposited and is thus mechanically anchored to the silicon surface (Figs. 5(c) and (d)). 

As shown in Fig. 1, palladium is mainly consumed as an autocatalyst now[l, 2]. Palladium is also an important nohle metal element widely applied in the development of electrocatalytic materials [46, 48, 72]. ft is widely used as a promoter for electroless deposition of metals on various substrates. Palladium is also known for its extraordinary ability to absorb a large amount of hydrogen. The growth of palladium thin layers on various substrates in UHV has been investigated in detail [3-8]. Electrodeposition of palladium is widely used, and a number of commercially available electroplating baths of palladium for different purposes have been developed [56-58, 61, 72]. However, the rapid increase in the... 

This heat energy is necessary to force palladium atoms to migrate in the polymer matrix. This process yields small catalytic-sized Clusters. Heat activates the coating by causing the palladium atoms to form catalytic-sized clusters. Electroless deposition can now take place. 

Additional evidence of oxygen being involved as pait of the metal polymer link was obtained by examining the thiclmess of the metal oxide layer on the outer surface of the metal and at the metal/polymer interface prior to and subsequent to the heat-tieatment step. Analysis of the backside of the intetphase region was accomplished via dissolution of the polymer substrate The data in Table VI show that the oxide thicknesses were nominally equal at the air and polymer sides of the structure. The oxide thicknesses were independent of metal deposition technique although the presence of the palladium catalyst employed for electroless deposition complicated the analyses. X-ray photoelectron spectroscopy identified the oxide species as cuprous oxide 10,17. Excellent adhesion was obtained once the oxide thickness exceeded 3 nm at the metal/polyetherimide interfacial zone. 

Before electroless plating plastic parts, the surfaces have to be treated to ensure good adhesion. The etching process usually involves the use of a chromic acid solution to provide a microscopically roughened surface to the plastic part. The catalytic process is sometimes referred to as seeding. Here very small particles of an inactive noble metal catalyst, normally palladium, are deposited into the micro-cracks created during the etching process. The palladium will act as active catalyst sites for chemical reduction of the electroless... 

A double tube type of MR, in which a 20-mm-thick palladium layer is formed by means of electroless deposition on a porous alumina tube 11 mm in diameter and... 

Other surface finishes include reflowed tin-lead, electrolytic nickel/electrolytic gold, antitarnish and reflux, electroless palladium, electroless gold, direct immersion gold, and solid solder deposit. 

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