A kinetic model for determining morphology transitions and growth kinetics of titania nanotubes during anodization of titanium in ethylene glycol based electrolytes


Seckin E., Urgen M.

SURFACE & COATINGS TECHNOLOGY, vol.409, 2021 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 409
  • Publication Date: 2021
  • Doi Number: 10.1016/j.surfcoat.2021.126840
  • Title of Journal : SURFACE & COATINGS TECHNOLOGY

Abstract

During porous anodization of titanium different surface morphologies can be observed. However, the influence of this morphological variance on nanotube growth has not been defined with a consistent model. In this study, we aim to develop a kinetic model-approach that combines the growth process with the final morphologies of the different nanotubular titania structures that are formed during anodization in ethylene glycol based electrolytes. Accordingly, we divide the nanotube growth process into three sequential stages. Morphological transitions and growth kinetics during anodization are investigated individually for all stages. In the first stage, nanotubes grow under gradually dissolving initial barrier oxide. Nanopore/nanotube transition occurs at the second stage after the complete dissolution of the initial barrier oxide. Nanograss formation starts and progresses at the third stage of the anodization. Growth of nanotubes under the gradually dissolving top barrier layer (Stage 1) obeyed the field-assisted growth model with a growth rate equivalent to 0.7 mu m C-1 cm(2). However, the completion of the chemical dissolution of top barrier layer totally changes the growth rate leading to a shortening of the nanotubes (Stage 3). After experimental determination of the chemical shortening rate of the nanotubes (CSR) at this stage, a kinetic model has been produced to determine the top barrier layer dissolution time (BDT). The experimental determination of the temperature dependency of BDT allowed us to calculate the activation energy of the process and determination of BDT values for different processing temperatures by extrapolation. Extrapolated BDT values for different temperatures showed well consistency with the experimental results and validate that open tube-top nanotubes can be obtained at calculated anodization durations.