Porous Alumina Films Fabricated by Reduced Temperature Sulfuric Acid Anodizing: Morphology, Composition and Volumetric Growth.

Alexander Poznyak,Marco Salerno,Andrei Pligovka,Tsimafei Laryn

doi:10.3390/ma14040767

Abstract

The volumetric growth, composition, and morphology of porous alumina films fabricated by reduced temperature 280 K galvanostatic anodizing of aluminum foil in 0.4, 1.0, and 2.0 M aqueous sulfuric acid with 0.5–10 mA·cm−2 current densities were investigated. It appeared that an increase in the solution concentration from 0.4 to 2 M has no significant effect on the anodizing rate, but leads to an increase in the porous alumina film growth. The volumetric growth coefficient increases from 1.26 to 1.67 with increasing current density from 0.5 to 10 mA·cm−2 and decreases with increasing solution concentration from 0.4 to 2.0 M. In addition, in the anodized samples, metallic aluminum phases are identified, and a tendency towards a decrease in the aluminum content with an increase in solution concentration is observed. Anodizing at 0.5 mA·cm−2 in 2.0 M sulfuric acid leads to formation of a non-typical nanostructured porous alumina film, consisting of ordered hemispheres containing radially diverging pores.

Highlights

Electrochemical anodizing in various aqueous acid solutions results in porous alumina films (PAFs) having a quasi-regular nanoscale cellular structure of pores, which occurs naturally as a result of self-organization [1,2]
The paper investigated the dependence of volumetric growth factor, anodizing current efficiency, and amount of residual un-oxidized metal during porous alumina films fabrication by low temperature galvanostatic anodizing of aluminum foil (99.99%) with an initial thickness of 10.5 μm, in aqueous sulfuric acid solutions with 0.4, 1.0, and 2.0 M concentration, in the current density range of 0.5–10 mA·cm−2
As a result of the work, the following points emerged: 1. Reduced temperature 280 K electrochemical anodizing of aluminum at extremely low current density and high sulfuric acid (SA) concentration leads to the formation of a nontypical nanostructured porous alumina film consisting of hemispheres with radially diverging pores

Summary

Introduction

Electrochemical anodizing in various aqueous acid solutions results in porous alumina films (PAFs) having a quasi-regular nanoscale cellular structure of pores, which occurs naturally as a result of self-organization [1,2]. Reliable knowledge about the parameters of the PAF cellular structure, thickness, and properties is required to create various types of materials and devices In this regard, over the years Dr Viktor Surganov and coworkers have undertaken systematic comprehensive investigation of the PAF formation, dissolution, and growth in solutions of oxalic [54,55], orthophosphoric [56,57], malonic [44,46], and sulfosalicylic [45] acids, under comparable conditions. In ref. [41], 1050 A aluminum alloy (99.5% purity) was used, whereas in ref. [35], aluminum foil of 99.9% purity as well and aluminum films deposited on silicon wafers (without detailed characterization) were used as initial samples

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