Homogeneous nucleation of nitrogen

Area of Science:

• Physical Chemistry
• Thermodynamics
• Fluid Dynamics

Background:

• Homogeneous nucleation is a fundamental process in phase transitions.
• Understanding nucleation is crucial for various applications, including atmospheric science and materials processing.
• Previous studies have explored nucleation of different substances, but nitrogen nucleation requires further investigation.

Purpose of the Study:

• To experimentally investigate the homogeneous nucleation of nitrogen in a cryogenic expansion chamber.
• To determine the onset conditions and nucleation rates of nitrogen.
• To compare experimental findings with predictions from classical nucleation theory (CNT) and the Reguera-Reiss theory.

Main Methods:

• Adiabatic expansion of nitrogen-helium gas mixtures in a cryogenic chamber.
• Detection of nucleation onset using constant angle light scattering.
• Measurement of nitrogen vapor pressures and temperatures during expansion.
• Estimation of critical nucleus size using the Gibbs-Thomson equation.
• Comparison of experimental nucleation rates with theoretical models.

Main Results:

• Nucleation onset was observed at specific nitrogen vapor pressures (1.3-14.2 kPa) and temperatures (42-54 K).
• An analytical fit function accurately describes experimental onset pressures within +/-15% error.
• Estimated critical nucleus sizes range from approximately 50 to 70 molecules.
• Experimental nucleation rates are significantly lower (9-19 orders of magnitude) than CNT predictions.
• The Reguera-Reiss theory shows better agreement with temperature dependence and reduces deviation to 7-13 orders of magnitude.

Conclusions:

• Classical nucleation theory significantly underestimates nitrogen nucleation rates.
• The Reguera-Reiss theory provides a better approximation but still shows deviations.
• An empirical correction function for CNT effectively describes the experimental results.
• The derived correction parameters show remarkable similarity to those for argon and water, suggesting universality.