Systematic Study of Graphite Encapsulated Nickel Nanocrystal Synthesis with Formation Mechanism Implications

Abstract

By systematically varying the carbon content, chamber pressure, arc current, 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 designed experiments revealed that the properties of the arc translate into changes in the encapsulated product. Specifically, a larger, hotter arc results in more encapsulation in the final sample. These findings, along with evidence of graphite layers which have formed on precrystallized particles, indicate that the graphite layers may form by two sequential formation steps. The first step is the simple phase segregation of carbon from a cooling liquid particle, resulting in surface graphite. The second step is the growth of carbon on a crystallized nickel particle, regardless of the temperature at which this occurs. The proposed formation mechanism has significant implications for both a scientific understanding of the encapsulation phenomena, and possible commercial applications.