Predicting plasma conditions necessary for synthesis of γ-Al₂O₃ nanocrystals

Nonthermal plasma (NTP) offers a unique synthesis environment capable of producing nanocrystals of high melting point materials at relatively low gas temperatures. Despite the rapidly growing material library accessible through NTP synthesis, designing processes for new materials is predominantly empirically driven. Here, we report on the synthesis of both amorphous alumina and γ-Al2O3 nanocrystals and present a simple particle heating model that is suitable for predicting the plasma power necessary for crystallization. The heating model only requires the composition, temperature, and pressure of the background gas along with the reactor geometry to calculate the temperature of particles suspended in the plasma as a function of applied power. Complete crystallization of the nanoparticle population was observed when applied power was greater than the threshold where the calculated particle temperature is equal to the crystallization temperature of amorphous alumina.