The Kinetics and Mechanism of Long-Range Pore Ordering in Anodic Films on Aluminum

Abstract

Anodic aluminum oxide has unique and highly attractive properties, including self-ordering of porous structure during anodization. Although anodization regimes leading to formation of highly ordered porous structures had been found experimentally, many aspects of the self-organization mechanism remain unsolved. Here, the detailed in situ small-angle X-ray diffraction study of the self-ordering in porous alumina films is reported. Structure evolution kinetics was deduced by a quantitative analysis of diffraction patterns combined with electron microscopy. The rate of pore ordering is shown to have maximal value at the initial anodization stage and rapidly decreases inversely proportional to t 0.2 . Self-organization is shown to occur via growth of domains possessing preferential in-plane orientation and "death" of other domains, similar to Ostwald ripening governed by difference in pore growth rates for domains of different orientations. The process is accompanied by pore death and splitting making a significant impact on anodic oxides utilization in any mass-transport issues. This finding opens a novel approach for growth of highly ordered porous anodic oxide films.

Biocompatibility Of Synthesised Nano-Porous Anodic Aluminium Oxide Membranes For Use As A Cell Culture Substrate For Madin-Darby Canine Kidneys Cells: A Preliminary Study

“…Examination of the FESEM micrographs, reveal the presence of occasional non-ordered pores between the pore domains. The non-ordered pores, which have also been reported by other researchers, result from inevitable point defects, dislocations and grain boundaries in the original Al substrate [30,31]. Also present in the micrographs are a small number of minor pores merging with larger, nearby neighbouring pores to form elliptical shaped pores.…”

Factors influencing the growth behaviour of nanoporous anodic films on iron under galvanostatic anodizing

“…The present study also reveals that chemical during anodizing of aluminium in aqueous acid electrolytes, i.e., 25 V in sulphuric acid [21], 40 V in oxalic acid [22] and 195 V in phosphoric acid [23]. In the present organic electrolytes, an optimized formation voltage appears to be present for the growth the ordered porous films, which should be between 30 and 50 V. The mechanism of self-ordering of pores in porous anodic films on metals is not yet understood and is the subject of further studies, although some models, including a stress-induced flow of film materials from a pore base to a pore wall, have recently been proposed [18,[24][25][26].…”

Research Background and Motivation

“…Because of the scalloped shape of the oxide barrier layer at the pore channel bottom, each pore will leave behind a small pit on the Al substrate, and the pits pattern would directly reveal the arrangement of the pores within anodic porous alumina at the end of the first step anodization. Due to the self-organization process of pore channels during the first step anodization, the pits pattern left on the Al substrate would become a quasi-hexagonal pattern, with short-range ordering in a few µm 2 area, but long-range disordering [192]. Then, the second step anodization was conducted under the same condition as the first step.…”