The Holes Produced by Field-Assisted Dissolution and the Pores Produced by Oxygen Bubble Mould Effect

Although field-assisted dissolution theory is widely accepted for pore formation, many unexplained problems have emerged in recent years. Here, the oxygen bubble mould effect is briefly introduced and the anodizing process of Al in different electrolytes is compared. We found that the field-assisted dissolution can only form fake holes, which were more like shallow pits and not connected to nanotubes. The real pores were formed by the oxygen bubble mould effect, and were more like channels and connected to nanotubes. Additionally, two morphology structures are discussed. Nanotube structure means the cross-sectional morphology is tubular, while the porous structure means the cross-sectional morphology channel-like. Both structures were found in the same sample, which suggests that their formation mechanism was the same; the oxygen bubble mould effect. Depending on this, the electronic current leads to the release of O-2, which exists in the nanotubes. The nanotube structure splits into porous structure because of its internal pressure. These original findings are important for correct understanding the formation mechanism of porous oxides and nanotubes.