Fine particle formation by microwave irradiation: Prevention of superheat behavior by addition of alcohol

Microwave has been often used for nano-particle synthesis because rapid growth and mono-dispersed particle size are obtained. However, superheat behavior causes larger bubble and disorders temperature distribution when higher power of microwave is irradiated. Accordingly, superheat must be prevented for stable operation of nano-particle process. In previous study [1], we found that bubble formation happened during particle formation at the same time when FeCl₃ aqueous solution is heated by microwave. According to the results through in-situ particle size measurement during the irradiation, superheat behavior occurred at the condition of the higher power and lower suspension density. In this study, ethylene glycol with lower electric constant was added to promote particle nucleation and to enlarge particle number density. Moreover, the solute is not dissolved in ethylene glycol as anti-solvent although ethylene glycol is dissolved in water. The results showed that bubble size during the irradiation and particle size after the irradiation became smaller by the ethylene glycol addition. As a result, operation by higher power became possible, and higher particle number density was obtained as synergy effect of anti-solvent effect and quick thermal response by microwave. Finally, addition of alcohol became a good method for nano-particle formation process to prevent superheat behavior during higher power microwave irradiation.