Zero-Sum Space on the Copper Surface Under Ultrasound

In the overlapped shell space between two adjacent cavitation bubbles, there theoretically exists a Zero-sum space without vibration due to the cavitation effect but still with pressure, high temperature and a high concentration of substances. Within the Zero-sum space, a stable environment for a chemical reaction is achievable under the ultrasound. In this work, some ring-shaped regions (outer diameter 48.90±3.5 μm, inner diameter 40.94±3.5 μm) on copper foil with distinctive morphology were investigated in the area covered by visible bubbles under ultrasound treatment in 1M NaOH for 3 h. The morphology and composition of these regions were found to be similar to that of sample fabricated in the same environment without ultrasound. It has confirmed the long-term existence of Zero-sum space and raised a hypothesis of Zero-sum space maintenance. This work may lead to release the ultrasonic synthesis from the limitation of ultrasonic frequency.