Fabrication of vertically aligned Pd nanowire array in AAO template by electrodeposition using neutral electrolyte

A vertically aligned Pd nanowire array was successfully fabricated on an Au/Ti substrate using an anodic aluminum oxide (AAO) template by a direct voltage electrodeposition method at room temperature using diluted neutral electrolyte. The fabrication of Pd nanowires was controlled by analyzing the current–time transient during electrodeposition using potentiostat. The AAO template and the Pd nanowires were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) methods and X-Ray diffraction (XRD). It was observed that the Pd nanowire array was standing freely on an Au-coated Ti substrate after removing the AAO template in a relatively large area of about 5 cm2, approximately 50 nm in diameter and 2.5 μm in length with a high aspect ratio. The nucleation rate and the number of atoms in the critical nucleus were determined from the analysis of current transients. Pd nuclei density was calculated as 3.55 × 108 cm−2. Usage of diluted neutral electrolyte enables slower growing of Pd nanowires owing to increase in the electrodeposition potential and thus obtained Pd nanowires have higher crystallinity with lower dislocations. In fact, this high crystallinity of Pd nanowires provides them positive effect for sensor performances especially

A New Periodic Displacement Method Applied to Electrodeposition of Cu-Ag Alloys

ABSTRACT A new method is described for preparing multilayered alloys by periodically interrupting electrodeposition of the less noble metal to permit electroless displacement of a portion of the electrodeposited material by the more noble component. Visibly smooth, nodule-free Cu-Ag alloys of controlled composition have been prepared and shown to exhibit excellent tensile properties. The Ag displacement layers grow epitaxially on Cu(111) planes, which are preferentially aligned parallel with the cathode surface for the cyanide bath studied. In addition, periodic displacement deposition of multilayered structures potentially represents a sensitive means for studying the kinetics of such displacement reactions. Metals having significantly different reduction potentials are often difficult to electrodeposit as alloys since deposition of the more noble component is generally too fast at the more negative potentials required for deposition of the less noble component. Use of diffusion-limited deposition of the more noble metal typically results in nodule formation and poor deposit properties, and does not provide adequate control over the deposit composition under practically attainable hydrodynamic conditions. When the two metals are immiscible, the situation is expected to be exacerbated by the enhanced tendency toward agglomeration of the individual components and island formation. Consequently, controlled electrodeposition of Cu-Ag alloys, for example, has remained an elusive goal (1). Electrodeposition of multilayered structures from a single bath (2) is also difficult to attain when the deposition potentials are far apart, especially when the deposition process for the less noble component is highly reversible (3). In the present paper, we describe a special pulse plating method by which these difficulties are circumvented. Experimental The two liter cyanide bath employed in the present work contained 60 grams per liter (g/l) CuCN, 102 g/1 KCN, 15 g/1 potassium carbonate, 15 g/l KOH, 45 g/1 potassium sodium tartrate (Rochelle salt), and 34 milligrams per liter (mg/1) (0.25mM) AgCN, and was maintained at 60~ in a water-jacketed cell. All chemicals were reagent grade. Deposition was performed on a rotating (750 rpm) 304 stainless steel cylindrical mandrel (2.5 cm diameter, 7.6 cm long) sandwiched between chlorofluorocarbon plastic end pieces (4). The anode was a concentric platinized Ti mesh in the same compartment. A 2-~m thick pyrophosphate Cu basal layer was necessary to prevent intrusion of the cyanide electrolyte between the mandrel and the deposit. Copper electrodeposition was performed at a constant current (-30 mA/cm2). Unless otherwise noted, the "off time" for the displacement reaction was also held constant (18 s), the Ag content of the deposit being varied by adjusting the number of Ag layers (per unit thickness) via the Cu layer thickness. During plating, the bath Ag content was replenished at 15 min intervals by manual injection of a known volume of a stock Ag cyanide solution, and the correct final concentration was verified by atomic absorption (AA) analysis. Plated specimens were nominally 50 ~m thick and were removed from the mandrel by masking off a thin strip of the deposit (parallel to the cylinder axis) and dissolving it in an acid solution. For tensile testing, strips (13 mm wide) cut in the axial direction were clamped between dogboneshaped case hardened steel plates and ground to a dogbone configuration having a reduced section width of 6.3 mm and a gauge length of 2.8 cm. Pull testing was performed at a cross head speed of 0.1 mm/min

Preparation of silicalite-1 layers on Pt-coated carbon materials: a possible electrochemical approach towards membrane reactors

A novel kind of composites is synthesized due to the outstanding properties of carbon materials. Metallic platinum is deposited on porous carbon discs by means of Potential Step Deposition (PSD) under potentiostatic conditions. Afterwards, the Pt-coated discs were covered completely with colloidal zeolite (silicalite-1) crystals by means of the novel ElectroPhoretic Deposition (EPD) methodology. After standard hydrothermal treatment, the seed crystal coating becomes continuous, crack-free and wellintergrown, giving rise to a layer of silicalite-1 crystals of different sizes. It must be noted that Pt combined with the secondary growth methodology has a extremely important effect on the orientation of the growing zeolite crystals. These novel materials have a wide range of potential applications as membrane reactors and/or catalyst membranes after activation (i.e. template removal by calcination) of the zeolite crystals.Ministerio de Ciencia y Tecnología (PPQ-2003-03884