Peculiar Porous Aluminum Oxide Films Produced via Electrochemical Anodizing in Malonic Acid Solution with Arsenazo-I Additive.

Alexander Poznyak,Andrei Pligovka,Gerhard Knörnschild,Małgorzata Norek,Anatoly Karoza

doi:10.3390/ma14175118

Abstract

The influence of arsenazo-I additive on electrochemical anodizing of pure aluminum foil in malonic acid was studied. Aluminum dissolution increased with increasing arsenazo-I concentration. The addition of arsenazo-I also led to an increase in the volume expansion factor up to 2.3 due to the incorporation of organic compounds and an increased number of hydroxyl groups in the porous aluminum oxide film. At a current density of 15 mA·cm−2 and an arsenazo-I concentration 3.5 g·L−1, the carbon content in the anodic alumina of 49 at. % was achieved. An increase in the current density and concentration of arsenazo-I caused the formation of an arsenic-containing compound with the formula Na1,5Al2(OH)4,5(AsO4)3·7H2O in the porous aluminum oxide film phase. These film modifications cause a higher number of defects and, thus, increase the ionic conductivity, leading to a reduced electric field in galvanostatic anodizing tests. A self-adjusting growth mechanism, which leads to a higher degree of self-ordering in the arsenazo-free electrolyte, is not operative under the same conditions when arsenazo-I is added. Instead, a dielectric breakdown mechanism was observed, which caused the disordered porous aluminum oxide film structure.

Highlights

The current area of nanotechnology, which is rapidly developing at present, is the creation of functional materials using porous and tubular anodic oxides of aluminum and other valve metals [1,2,3,4,5,6,7,8,9,10,11]
The rest of the sample surfaces were electrically isolated by previous anodizing in 1% citric acid (Sigma-Aldrich, Darmstadt, Germany) with a maximum voltage of 290 V, which was held until the current density fell below 5% of its initial value
Galvanostatic aluminum anodizing at 0.6 M malonic acid (MA)

Summary

Introduction

The current area of nanotechnology, which is rapidly developing at present, is the creation of functional materials using porous and tubular anodic oxides of aluminum and other valve metals [1,2,3,4,5,6,7,8,9,10,11]. Different kinds of metal dissolution during anodic oxidation of aluminum and other valve metals lead to the formation of oxide films with different morphologies: barrier layers, quasi-regular porous layers, high degree self-ordering porous layers as well as tubular and nanocomposite structures [6,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34]. Due to the oxide chemical properties of most refractory metals (titanium, hafnium, niobium, tantalum, tungsten, vanadium, and zirconium) [37], the dissolving power of the electrolyte can be controlled by introducing small additions of fluoride ions that form stable complex compounds with the ions of the listed metals [38]. Enhanced dissolution was used as an explanation given for TiO2 nano-tube formation in fluoride–glycerol electrolytes, in this case, the dissolution of a fluoride-rich layer, which separates the nano-tubes [39]

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Results

Conclusion