Effect of Temperature and Vapor-phase Encapsulation on Particle Growth and Morphology

The effect of in situ vapor phase salt-encapsulation on particle size and morphology was systematically investigated in a sodium co-flow/furnace reactor. The temperature of the furnace was varied, and the primary particle size and degree of agglomeration of the resulting silicon and germanium particles were determined from transmission electron micrograph images of particles sampled in situ. Particle size increased with increasing temperature, a trend expected from our understanding of particle formation in a high-temperature process in the absence of an encapsulant. Germanium, which coalesces faster than silicon, formed larger particles than silicon at the same temperatures, also in agreement with observations of particle growth in more traditional aerosol processes. At the highest temperatures, unagglomerated particles were formed, while at low temperatures, agglomerated particles were formed, with agglomerate shape following the shape of the salt coating.