Open AccessFormation of Bright White Plasma Electrolytic Oxidation Films with a Uniform Maze-Like Structure by Anodizing Aluminum in Ammonium Tetraborate Solutions
Author(s) -
Tatsuya Kikuchi,
M. Sato,
Mana Iwai,
Daiki Nakajima,
Junji Nunomura,
Yoshiyuki Oya,
Shungo Natsui
Publication year - 2022
Publication title -
journal of the electrochemical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.258
H-Index - 271
eISSN - 1945-7111
pISSN - 0013-4651
DOI - 10.1149/1945-7111/ac62bc
Subject(s) - anodizing , materials science , plasma electrolytic oxidation , wetting , amorphous solid , contact angle , layer (electronics) , chemical engineering , aluminium , ammonium fluoride , electrolyte , lightness , barrier layer , composite material , optics , crystallography , chemistry , electrode , physics , engineering
Bright white plasma electrolytic oxidation (PEO) films with uniform maze-like structures were obtained by anodizing Al in an ammonium tetraborate solution. High-purity Al plates were galvanostatically anodized in 0.3–2.4 M ammonium tetraborate solutions at 303–343 K and 10–100 Am −2 . A PEO film consisting of an outer porous layer consisting of amorphous alumina and crystalline alumina with α -and γ -phases and an inner amorphous barrier alumina layer was obtained on the Al surface. An extremely uneven PEO film with various pore sizes and many cracks was formed in a 0.3 M ammonium tetraborate solution, whereas a relatively uniform porous PEO film with similar pore sizes was obtained in 0.9–2.4 M solutions. This difference in the PEO film morphology was due to the plasma generation behavior while anodizing. The lightness of the PEO film increased with increasing anodizing time and PEO film thickness; thus, a bright white PEO film measuring 87.5 in lightness (L*) was formed on the Al surface. The water wettability of the PEO film exhibited weak hydrophilicity. Moreover, a superhydrophobic PEO film with a contact angle of 154° was easily fabricated by self-assembled monolayer modification. Similar bright white PEO coatings were successfully fabricated on various industrial alloys.