Catalysis of Organic..

Yamauchi 157transformation is schematically illustrated by an arrow at a constant temperature asimposed in Fig.3. A conventional phase transformation may be achieved by changein temperature at constant composition, but in this leaching process, it is achieved bychange in the compositionat constant temperature.The majority ofmetallurgists may notaccept the above evidence.They usually suppose thatthe mobility of atoms atleaching temperature is toolow to rearrange for thephase transformation.However, transformationhas clearly occurred exceptin a few cases. One of themotivations for our researchstudies on Raney catalystsis to clarify what happens duringthe leaching process.Figure 3. Principle of phase transformationFrom a general phase transformation theory, the crystallographic structure and thespecific surface area may depend on kinetics and thermodynamics. Therefore, if wecan control these factors, new Raney catalysts can be developed.We have developed a process to make metastable materials by rapid solidification(7) and have applied it to various alloy systems (8). There were few reports on such ametastable processing to make precursors for Raney catalyst. The metastableprocesses maybe extend the probability of precursor design by decreasing the limitof additive amount to precursor.In this paper, a few examples of Raney catalysts produced by metastable processesand their catalytic properties are discussed. Then, some examples of multi alloysystems, their microstructures and general properties will be shown. Finally, we willdiscuss the possibility of forming large particle materials with high specific surfacearea.Results and DiscussionRapid Solidification and Mechanical Alloying for Preparing Super-saturatedPrecursorsAs mentioned above, the formation of skeletal structure is a sort of phasetransformation by rearrangement of retained atoms. Therefore, it was important forthe skeletal structure formation to control the kinetics of rearrangement. In the past