Contactless surface tension measurement of molten oxides using oscillating drop method in an aerodynamic levitator

Aerodynamic levitation stands as a contactless method for thermophysical property measurement of molten oxides at high temperatures, offering the advantage of eliminating sample contamination and enabling surface tension measurement through the oscillating drop method. However, the presence of oscillation mode splitting results in an underestimation of surface tension. By improving levitation stability and optimizing the acoustic excitation method for the levitated drops, this study successfully eliminates oscillation mode splitting for the first time. The l = 2 resonance frequency is directly measured, which is used to calculate surface tension according to the Rayleigh equation. Taking Al₂O₃ as a representative of oxides, this study demonstrates the accurate surface tension measurement during the frequency scan process when oscillation mode splitting is absent. Additionally, combining damped oscillation analysis with the frequency scan reduces measurement uncertainty from 2.8 % to 1.5 %. Within the temperature range of 2336K-2923K, the surface tension of molten Al₂O₃ is determined to be γ = -(4.071 ± 2.688) × 10^{- 5} (T-2327)+(0.7465 ± 0.074) N/m. Underestimation of surface tension is prevented when the l = 2 resonance frequency is used for surface tension calculations. The frequency crossover method which is used for surface tension measurement is also found to be affected by oscillation mode splitting.