Carbon encapsulation of elemental nanoparticles by spark discharge

Abstract

A study was carried out on the carbon encapsulation of a number of elements using a spark discharge generator. The study showed that elements W, V, Ti, and Si formed carbides which were encapsulated successfully by graphitic layers forming a sound core–shell structure. Copper formed a partially filled core–shell structure, attributed to its relatively low condensation temperature, where considerable shrinkage seemed to have occurred after the encapsulation. Mg could not be encapsulated in a core–shell form but rather yielded an embedded structure where Mg is condensed onto already condensed carbonaceous material. Analysis of current observations coupled with those already reported data imply a simple mechanism for encapsulation. Metals/compounds that are solid above the condensation temperature of carbon give rise to a sound core–shell structure. Elements whose condensation temperature is less than that of carbon could still produce core–shell particles but they may be partially filled. It is estimated that the process of graphitic encapsulation may be complete around 1900 K and partially filled core–shell structure might develop depending on the volume shrinkage upon cooling to room temperature. Elements/compounds whose condensation temperature is below the encapsulation temperature fail to develop core–shell structure. Instead, they form embedded composite structure.