Palladium thickness

For a composite membrane that is relatively free of pinholes, there is apparently a limiting palladium thickness that depends primarily on support quaUty and somewhat on deposition method. For example, unmodified PSS requires at least 10 pm of palladium to bridge a majority of the pores [149, 227]. Invariably, a few macrodefects remain that preclude the attainment of perfect hydrogen permselectivity. On porous asymmetric a-alumina supports with 100-200 nm pore size on the surface, approximately 7 pm appears to be the limiting thickness that is proba-... 

The potential of membrane reactors has been widely verified and documented for a large number of reactions. However, all the studies made are stUl confined to the laboratory scale, and their implementation in industrial systems has yet to occur. Research into new membrane materials and improvement in the properties of currently available membranes (permselectivity, resistance to poisoning, stability, reduction of palladium thickness, etc.) are always in progress. The development of procedures to deposit the catalyst within the membrane structure without changing its initial permeability and selectivity is an example of the ongoing research for the preparation of catalytic membranes. 

Membrane in the MR Catalyst Palladium thickness (urn) H2O/ C2H5OH T(°C) p (bar) Conversion (%) H2 recoverycox-free (%) H2 yieldcox-free (%) Reference... 

Moreover, since also the mismatch of palladium and alumina thermal expansion coefficients is reduced, high temperature delamination and defects formation in the membrane are also reduced. It is also possible to control the palladium thickness (to about 5 pm) by increasing the hydrogen flux and so minimizing the cost of the composite membrane. 

Electronic Applications. The PGMs have a number of important and diverse appHcations in the electronics industry (30). The most widely used are palladium and mthenium. Palladium or palladium—silver thick-film pastes are used in multilayer ceramic capacitors and conductor inks for hybrid integrated circuits (qv). In multilayer ceramic capacitors, the termination electrodes are silver or a silver-rich Pd—Ag alloy. The internal electrodes use a palladium-rich Pd—Ag alloy. Palladium salts are increasingly used to plate edge connectors and lead frames of semiconductors (qv), as a cost-effective alternative to gold. In 1994, 45% of total mthenium demand was for use in mthenium oxide resistor pastes (see Electrical connectors). 

Electroless reactions must be autocatalytic. Some metals are autocatalytic, such as iron, in electroless nickel. The initial deposition site on other surfaces serves as a catalyst, usually palladium on noncatalytic metals or a palladium—tin mixture on dielectrics, which is a good hydrogenation catalyst (20,21). The catalyst is quickly covered by a monolayer of electroless metal film which as a fresh, continuously renewed clean metal surface continues to function as a dehydrogenation catalyst. Silver is a borderline material, being so weakly catalytic that only very thin films form unless the surface is repeatedly cataly2ed newly developed baths are truly autocatalytic (22). In contrast, electroless copper is relatively easy to maintain in an active state commercial film thicknesses vary from <0.25 to 35 p.m or more. 

Palladium and gold Palladium electrodeposition is of special interest for catalysis and for nanotechnology. It has been reported [49] that it can be deposited from basic chloroaluminate liquids, while in the acidic regime the low solubility of PdCl2 and passivation phenomena complicate the deposition. In our experience, however, thick Pd layers are difficult to obtain from basic chloroaluminates. With different melt compositions and special electrochemical techniques at temperatures up to 100 °C we succeeded in depositing mirror-bright and thick nanocrystalline palladium coatings [10]. 

Platinum work-hardens at approximately the same rate as palladium or copper, a 25% cold reduction in thickness raising the hardness from about 40 HV in the fully annealed state to 75 HV. Cast platinum is usually slightly harder than the same grade of metal in the wrought and annealed state. 

Bursting discs may be fabricated of gold, silver, platinum or palladium. The recommended maximum temperatures for continuous use are 80 C for gold, 150 C for silver, 300 C for palladium and 450 C for platinum. Figure 6.6 gives bursting pressure/disc thickness data for these metals and for aluminium and nickel. 

The largest uses of platinum group metals in electronics are ruthenium for resistors and palladium for multilayer capacitors, both applied by thick film techniques . Most anodes for brine electrolysis are coated with mixed ruthenium and titanium oxide by thermal decomposition . Chemical vapour deposition of ruthenium was patented for use on cutting tools . 

This has been used, for instance, to follow the formation of palladium silicide in a silicon wafer for thicknesses up to 6nm [Vanleerdam et al., 1990]. More recently, investigation of the tails in LEIS has been used as a tool for high resolution nondestructive in-depth composition analysis of ultrathin layers [Brongersma et al., 2003] and shallow interfaces [Janssen et al., 2004]. 

The type of intermediate shown in structure (B) has also been supported by Muller and Gault (119) who showed that in the reaction of 1,1-dimethylcyclopropane with deuterium over a series of thick evaporated metal film catalysts, it was only on platinum that 1,1,3-da-neopen-tane (and 1,1,3,3-d4-neopentane) were dominant products. On palladium, iron, rhodium, nickel, and cobalt the major product was 1,3-d2-neopentane. 

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