Catalysis of Organic..

Yamauchi 163shown in Fig. 12. It was less than 20% for the conventional precursors such asprecipitated or solution treated ones, where the Ag 2 Al phase was stable and thesolubility of Ag in theα-Al phase is negligibly small.Similar result was obtained for skeletal Si 15) . The solubility of Si in the α-Al solidsolution is negligibly small so that the two phases α-Al and relatively coarse Siexisted in the conventionally prepared Al-Si alloy. By hydrochloric acid leaching,only the coarse stable Si remains after leaching, so that it is difficult to form fine Siparticles by leaching. In this case, the rapid solidification increases the solubility toabout 12 at%. The specific surface area of skeletal Si formed from RWA was in therange of 65-75m 2 /g and the mean particles size was about 30-50nm by directobservation of the skeletal Si.Bulk material formation from leached particles by SPS processOne of the excellent characteristics ofRaney catalyst is a porous skeletalstructure composed of ultra fine particles.From the macroscopic view, the size ofthe precursor particles is not changedafter leaching and they can be treatedlike conventional particles in powdermetallurgy. To extend the applicationfield as catalysts in fixed bed orelectrodes, bodies with large regulargeometric size and shape are oftendesired. In the conventional powdermetallurgical consolidation process,compaction has occurred duringconsolidation and it leads to decrease ofthe specific surface area. Recently, thespark plasma sintering process (SPS) as Figure 13. Schematic illustration of SPSshown in Fig.13 has been developed for equipmentthe consolidation of ordinary nonskeletalparticles. This process can be operated at relatively low temperature inFigure 14. Example of disk consolidatedby SPS (Ni-Ag , 15mm x 2mm, specificSA = 28m 2 /g )Figure 15. Variation of specificsurface area with SPS temperature forNi-Ag