Argon nucleation in a cryogenic nucleation pulse chamber

Area of Science:

• Physical Chemistry
• Thermodynamics
• Materials Science

Background:

• Homogeneous nucleation is a fundamental process in phase transitions.
• Previous studies lacked systematic nucleation onset data for argon.
• Classical nucleation theory (CNT) often overestimates nucleation rates.

Purpose of the Study:

• To present the first systematic nucleation onset data for argon.
• To compare experimental data with predictions from various nucleation theories.
• To determine the size of the critical nucleus for argon droplet formation.

Main Methods:

• Utilized a newly designed cryogenic nucleation pulse chamber.
• Measured nucleation onset data across a temperature range of 42-58 K and vapor pressures of 0.3-10 kPa.
• Employed optical detection and Gibbs-Thomson equation for analysis.

Main Results:

• Experimental nucleation rates differ from CNT by 16-26 orders of magnitude.
• Self-consistent theory (Girshick and Chiu) showed improved temperature dependence but still large discrepancies (11-17 orders of magnitude).
• Thermodynamically consistent theory (Kashchiev) agreed well with temperature dependence, predicting rates 5-7 orders of magnitude below experimental values.

Conclusions:

• Classical and self-consistent nucleation theories significantly overestimate argon nucleation rates.
• The thermodynamically consistent theory provides a better, though still quantitatively different, prediction.
• The critical nucleus for argon contains approximately 40-80 atoms.