Platinum core composition

This platinum-gold cluster, of core composition triangulo-PtA Xi, is a white product, which is soluble in THF, CH Clj, and CHCI3. The compound is best characterized by its P NMR spectrum [in CH2CI2 distilled from P40,o, external reference H3PO4 and external D2O lock, 335.7 (t with i Pt satellites, PEtj, 4Hz, = 2197 Hz), 42.0 (t with > Pt... 

Enormous developments in the area of soluble noble metal clusters protected with monolayers are discussed. Mass spectrometry has been the principal tool with which cluster growth has been examined. The composition and chemistry of clusters have been examined extensively by mass spectrometry. Besides gold, silver, platinum, copper and iron clusters have been examined. Clusters have also been examined by tandem mass spectrometry and the importance of ligands in understanding closed shell electronic structure is understood from such studies. Protein protected noble metal clusters belong to a new group in this family of materials. Naked metal clusters bearing the same core composition as that of monolayer protected clusters is another class in this area, which have been discovered by laser desorption ionization from protein templates. 

Toshima [162, 164, 165] has studied a series of PVP protected colloidal bimetallic PtPd catalysts in olefin hydrogenation catalysis. The highest activity for the hydrogenation of 1,3-cyclooctadiene to cyclooctene was observed at a Pd Pt radio of 4 1. On the basis of EXAFS analysis [165] it was concluded that the distribution of the two metals in the particles is nonuniform, and that at the most active composition the colloid particles had a platinum core coated with palladium. A less active 1 1 Pd/Pt catalyst, with the same particle size, apparently had a more uniform distribution of metals, with both platinum and p ladium atoms at the surface. 

Platinum is a very expensive metal and therefore unsuitable for such mass-produced glass-to-metal seals as are found in radio valves and electric lamps. No other pure metal has a suitable coefficient of expansion or a suitable electrical resistance for sealing to lead or soda glasses. A composite wire has been developed as a substitute for platinum. It consists of a core of nickel-iron alloy (43% nickel) covered with a thin sheath of electrically deposited copper. The composite wire is drawn out to about 0.5 mm diameter, the copper sheath is then about 0.03 mm thick. This composite wire has a comparatively high electrical resistance and a short length, just sufficient for the seal, is butt welded to a nickel wire on the vacuum side of the seal and to a copper wire on the other side. 

This scenario calls for a deep characterization of Pt based materials in terms of how many alloyed phases and segregated phases are present in the mixture as well as their composition. The more accurately the bulk of the Pt based materials is characterized the more precise the characteristics of surface are because the bulk and surface should not be so dissimilar, above the micrometric dimension, in terms of phases and composition. However, the same should not be strictly expected for nanoscale dimensions. Platinum nanoparticle based materials may not form a true alloy but a surface composition much dissimilar from the core given the equalized quantity of both the bulk and surface free energy. To complicate the picture even more, the electrochemical results often depend on the technique used to evaluate the activity of the catalysts. 

The term electrode is widely used in electrochemistry. However, it designates objects that can significantly vary depending on the situation. For the purposes of this document, in examples chosen to illustrate simple electrochemical systems, the term will most often refer to the metal which constitutes one of the terminals in the system in question. For instance, a platinum electrode or a copper rotating disc electrode will be mentioned. When the system includes more than three materials, then the term electrode usually refers to the whole set of successive materials inserted between the metallic ending and the electrolyte material which makes up the core of the system. For instance, the term modified electrode will be used to refer to a metal whose surface has been covered with a film of conducting material or the term positive electrode in a battery will be used to refer to the composite material which is in contact with the electrolyte. In a third context, the term electrode will be used for an electrochemical half-cell this is the case with the electrode or reference electrode. In the final version of its meaning, the term electrode even stands for two half-cells combined to form the device, e.g., in the case of commercial systems for pH measurements by means of a combined electrode... 

Trimmel et al. prepared a series of amphiphilic block copolymers with different lengths of apolar and polar segments, and studied the micellization of these block copolymers in alcohol. The size of the micelles, as well as those of the core and shell could be nicely tuned [147]. In a follow-up paper, they studied the self-assembly of the block copolymers in the solid state and demonstrated how the composition polymers translates into different solid-state structures [148]. The approach was used to seU-assemble platinum dyes on the nanoscale [149]. Although the syntheses of most block copolymers have been successfully accomplished, some restrictions have also been reported [89]. Particularly, monomers with the ability to strongly interact with the initiator have been shown to cause problems, which could be circumvented by polymerizing them as the second monomer [150, 23]. 

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