Predicting Plasma Conditions Necessary for Synthesis of γ-Al₂O₃ Nanocrystals

Nonthermal plasma constitutes a unique synthesis environment which has proven capable of producing nanocrystals of several high melting point materials at relatively low gas temperatures over the last decade. Despite these efforts, the design of processes targeting new materials is almost entirely empirically driven. Here we present a simple particle heating model suitable for predicting plasma power necessary to crystallize Al₂O₃ nanoparticles. The model is used to calculate the temperature of particles suspended in the plasma as a function of applied power using only composition, pressure, background gas temperature and reactor geometry as inputs. Crystallization of the Al₂O₃ nanoparticle population was observed by X-ray diffraction and ²⁷Al solid-state NMR when the predicted nanoparticle temperature was equal to the crystallization temperature of amorphous alumina.