The generation of nano sandwich sheets in ring area around cavitation erosion pit on the surface of carbon steel

The ring area around cavitation erosion pit on carbon steel (ASTM A283) was studied using ultrasonic cavitation. We discovered that both the structure and chemical composition of ring area varied with the component of water. The ring area was composed of flocculent γ-FeOOH structures and nano sandwich α/β-FeOOH sheets when experiment was performed in deionized water and tap water, respectively. The formation of flocculent γ-FeOOH structures and sandwich α/β-FeOOH sheets was due to corrosion which occurs in the ring area on carbon steel. The ring area played the role as well as inclusion in carbon steel during corrosion. γ-FeOOH was the typical corrosion product in deionized water. SO42− and Cl− in the tap water probably contributed to the formation of α-FeOOH and β-FeOOH, respectively. The different growth features of α-FeOOH and β-FeOOH ultimately generated the sandwich structure. Since ultrasonic cavitation simultaneously produced large amount of such ring areas on the surface of carbon steel, obtaining nano structured iron oxide by cavitation erosion-corrosion provided a new convenient method to obtain nano structured metal oxide.