Area-selective metallization

By the laser treatment, the surface of PTFE films could be made hydrophilic and the surface energy increased in comparison with that of a native PTFE film. As the results, we intended to extend the hydrophilic modification technique into metallization on the PTFE film by using a chemical (electroless) plating technique. If the activators for the plating will deposit only on the hydrophilic region, area-selective metallization will be performed on the surface of PTTE films modified upon the laser-irradiation through a mask by a projection method. 

Both of the surface area techniques described in this article are well established. However, the determination of total surface area by physical adsorption using the BET equation is a very general method of wide applicability. The use of selective chemisorption to determine the surf e area of metals is much newer, and has only... 

Since the catalyst is so important to the cracking operation, its activity, selectivity, and other important properties should be measured. A variety of fixed or fluidized bed tests have been used, in which standard feedstocks are cracked over plant catalysts and the results compared with those for standard samples. Activity is expressed as conversion, yield of gasoline, or as relative activity. Selectivity is expressed in terms of carbon producing factor (CPF) and gas producing factor (GPF). These may be related to catalyst addition rates, surface area, and metals contamination from feedstocks. 

The aim of this overview is first to present the general principles of electrocatalysis by metal complexes, followed by a series of selected examples published over the last 20 years illustrating the major electrochemical reactions catalyzed by metal complexes and their potential applications in synthetic and biomimetic processes, and also in the development of sensory devices. The area of metal complex catalysts in electrochemical reactions was reviewed in 1990.1... 

On non-zeolitic particles in the absence of a vanadium passivator, vanadium (when present at the 0.4 wt% level) makes a greater contribution to contaminant coke and hydrogen yields than nickel at constant surface area and metals loading. Incorporation of a vanadium passivator into the catalyst matrix can greatly alter the selectivity effects of vanadium, and can essentially negate its effect on non-zeolitic particles as in the case of magnesium. 

The development within the area of asymmetric 1,3-dipolar cycloadditions since the first edition of this series is too extensive to be completely covered in this chapter and we have therefore chosen selected examples to illustrate the different aspects of the subject. The examples have been chosen on the basis of general importance and also to complement recent monographs in the area. Special attention will be given to recent developments within the area of metal-catalyzed reactions. Intramolecular 1,3-dipolar cycloadditions are only briefly described. 

Figure 5.32 Variation of percent reduction in area (%RA, top graph) and yield strength (bottom graph) with temperature for selected metals. From K. M. Ralls, T. H. Courtney, and J. Wulff, Introduction to Materials Science and Engineering. Copyright 1976 by John Wiley Sons, Inc. This material is used by permission John Wiley Sons, Inc.

Alternative techniques do exist, however, for obtaining information regarding the distribution and number of catalytic components dispersed within or on the support. Selective gas adsorption, referred to as chemisorption, can be used to measure the accessible catalytic component on the surface indirectly by noting the amount of gas adsorbed per unit weight of catalyst. The stoichiometry of the chemisorption process must be known in order to estimate the available catalytic surface area. One assumes that the catalytic surface area is proportional to the number of active sites and thus reaction rate. This technique has found use predominantly for supported metals. A gas that will selectively adsorb only onto the metal and not the support is used under predetermined conditions. Hydrogen and carbon monoxide are most commonly used as selective adsorbates for many supported metals. There are reports in the literature of instances in which gases such as NO and O2 have been used to measure catalytic areas of metal oxides however, due to difficulty in interpretation they are of limited use. 

Access to compounds of the calixresorcinarene class [63] can be achieved by an acid-catalyzed reaction between resorcinol and various aldehydes. The ease of synthesis of many calixarenes and calixresorcinarenes. along with the ready availability of the starting materials, renders them of great potential for studying both academically and industrially motivated problems. These span many areas [58] from adhesives to the selective metal ion response of calixarene monolayers [64]. 

An obvious solution to the surface area limitation is to distribute the selected metal over a high surface area support. However, as metal is consumed in the process, a conventional metal support system would require frequent replacement. A more attractive proposition is offered by the availability of permeable monolithic carbon fiber composites, which were discussed earlier in this chapter. The ability to make these composites electrically conducting allows metals to be... 

Deposition initiates only on exposed (non-overmolded) "first shot" catalyzed resin areas. Second shot (non-plateable) material is "non receptive" to electroless plating. The resulting selective metallization is shown in Figure 7. 

A variety of methods for the determination of total metals and metal species/fractions have been described. While the most common method of sample decomposition of environmental samples is probably acid digestion, other approaches, most notably the use of fusion, have some specialist application areas, e.g. geological samples. The area of metal speciation is an ever expanding one, with new approaches being developed and evolving on a regular basis. The major limitation to this area of activity is the development of robust and reliable approaches to analysis. Some selected examples have been provided to assist the reader to evaluate some of the procedures that have already been developed. However, after reading this chapter you will have quickly realized that the methods are limited to only a few metal species. 

The yield of citronellol is given in Figure 5 over catalysts with different metal loading. The hydrogenation rate of citrai and the selectivity to citronellol increased with increasing support surface area and metal dispersion (Table 4), characteristic for a structure insensitive reaction. The highest initial hydrogenation rate and 92% selectivity to citronellol (at maximum yield) was achieved over the... 

Dissolved and particulate metals in rivers and estuaries are derived from natural weathering process in the catchment area, and reflect the geological composition of the watershed (see Table 1 for the crustal abundance of selected metals) and the local climatic conditions. Natural concentrations of metals can be augmented in catchment areas that are mineralized, and there may be a significant anthropogenic perturbation downstream because of mineral extraction... 

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