Generation of ultrasound at metal-electrolyte interfaces

Abstract

When a radio frequency potential difference is applied across a metal-electrolyte interface, ultrasound of the same frequency should be generated at the interface. This effect is expected on the basis of uncompensated volume changes in the electrolyte adjacent to the metal surface. The effect has been detected for the first time at ∼ 500 kHz and preliminary results are reported. The measurements have been made in a specially designed electroacoustic cell with gold electrodes in acid and alkaline electrolytes. The sound generated within the cell propagates into a large tank where it is detected with a ceramic hydrophone, calibrated separately against radiation pressure measurements. Pulse modulation has been used to discriminate against any electromagnetic crosstalk. The sound intensities although small (∼10−9 W/cm2) are easily detected and depend on the dc bias potential applied to the interface and the electrolyte composition. The effect is very sensitive to impurities, especially organics. This effect is a promising tool for the study of metal-electrolyte interfaces. Methods for greatly enhancing the effect will be discussed. [Research sponsored by ONR.]