SYSTEMATIC STUDY OF GRAPHITE ENCAPSULATED NICKEL NANOCRYSTAL SYNTHESIS WITH FORMATION MECHANISM IMPLICATIONS

By systematically varying the carbon content, chamber pressure, are cu rrent, and blowing gas velocity in a tungsten-arc encapsulation setup, the effects of each of these variables on the encapsulation of nickel in graphite layers were observed. The data from these optimally desig ned experiments revealed that the properties of the arc translate into changes in the encapsulated product. Specifically, a larger, hotter a re results in more encapsulation in the final sample. These findings, along with evidence of graphite layers which have formed on precrystal lized particles, indicate that the graphite layers may form by two seq uential formation steps. The first step is the simple phase segregatio n of carbon from a cooling liquid particle, resulting in surface graph ite. The second step is the growth of carbon on a crystallized nickel particle, regardless of the temperature at which this occurs. The prop osed formation mechanism has significant implications for both a scien tific understanding of the encapsulation phenomena, and possible comme rcial applications.