The impact of viscosity of the electrolyte on the formation of nanoporous anodic aluminum oxide
Graphical abstract
Introduction
Self-organized anodization of aluminum provides hexagonally arranged anodic aluminum oxide (AAO). This ordered nanomaterial is well-known for its numerous applications in nanofabrication [1], [2], [3], [4], [5], [6], [7], [8], energy harvesting and storage [9], [10], [11], sensors assembly [12], [13], biomaterials development [14], [15], surface enhanced Raman spectroscopy [16], [17], [18] etc.
Typically, it is formed in accordance to the two-step self-organized procedure: after the first step of anodization, chemical etching of the grown, poorly ordered AAO is done and bare aluminum with concaves, resulting from the first step of anodization, is re-anodized at the same set of the operating conditions [19], [20]. The most commonly applied electrolytes are: sulfuric acid [21], [22], [23], oxalic acid [20], [21], [24], [25], [26] and phosphoric acid [21], [27], [28], at voltage range 15-25, 20-60 and 120-195 V, respectively. Additionally, there are numerous other electrolytes applied for AAO fabrication. For example anodizations in electrolytes like squaric [29], malic [30], [31] citric [32], malonic [31], [32], maleic [31], tartaric [31], [32], tartronic [31], glutaric [31], lactic [33], propionic [33], glycolic [33] and succinic, [31], [33] acids were successfully performed.
Electrolytes with additions of various modifiers are applied to form AAO in new conditions [34], to change the kinetics of growth [35], or to gain new properties [36]. Zaraska et al. formed AAO in phosphoric acid with addition of various alcohols to prevent anode from burning and to influence the kinetics of AAO growth [28]. In one of our previous papers, we have reported anodization in an ethylene glycol solution of sulfuric acid [37]. Nguyen et al. formed AAO in a glycerol solution of phosphoric acid at temperatures above the water boiling point [38]. Therefore, anodization even in non-aqueous electrolytes is possible.
According to the mechanism of AAO growth, changes of the viscosity occur at the anode/electrolyte interface [39]. Therefore, changing of the viscosity of the electrolyte may have an impact on the growth of AAO. Furthermore, Pashchanka and Schneider [39], taking into account viscosity and conductivity of the electrolyte, have postulated a criterion number, and ascribed to this number a major role in the AAO growth. Yet, a systematic study on the influence of electrolytes viscosity or conductivity on the growth of anodic aluminum oxide has not been reported.
There is a need for a wider range of pore distances and diameters of AAO obtained via self-ordering, due to the nanofabrication. Tailored geometric features of AAO in a much wider range, resulting also from viscosity changes of the electrolyte can expand the fields of this material applications. Moreover, viscosity is one of the important factors in the electrochemistry, influencing i.e. ionic mobility, diffusion coefficient, or current density. Thus, influence of viscosity on the formation of AAO should be studied systematically. In this paper, the task is undertaken shedding some new light on the AAO growth mechanism. The systematic study of the influence of the viscosity on the AAO formation, including its influence on the current density as well as on the formed oxide thickness and nanopores geometry is carried out.
Section snippets
Experimental
A high purity, annealed 0,25 mm thick Al foil (99,9995%, Alfa Aesar) was cut into coupons (2,5 cm x 1,0 cm), degreased in acetone and ethanol and electropolished (1:4 volume mixture of HClO4 and C2H5OH at constant current density of 500 mAcm−2 for 1 min at 10 °C, Pt grid as a cathode). Electropolishing was performed in 0,5 dm3 double-walled cell, equipped in a thermostat with circulator (Lauda 105). After electropolishing a working surface area was limited to 1,0 cm2 with the use of acid resistant
Influence of the viscosity of the electrolyte on the current density during anodization
Viscosity of the electrolyte is related to the ionic mobility (u) through the following equation (1) [43]:where z is ion's charge, e is elemental charge, η is the viscosity and a is a hydrodynamic radius of the ion including solvent particles associated with the ion. Moreover, according to the empirical Walden's principle, electrical conductivity of the electrolyte (σ) is inversely proportional to the viscosity (2) [43]:
The current density during the electrochemical processes
Conclusions
Conducted experiments allowed us to find relations between viscosity and physical values important for the anodization process. Current density and thickness of the formed oxide are linear functions of the inversed viscosity, due to the influence of the viscosity on the ionic mobility, current density and diffusion coefficient. Moreover, it was found that interpore distance is a linear function of the logarithm of the dynamic viscosity what allows to control this geometric feature not only with
Acknowledgement
The research was financially supported by the Dean Office of Faculty of Advanced Technology And Chemistry, Military University of Technology, what is cordially acknowledged.
References (52)
- et al.
Template-assisted fabrication of tin and antimony based nanowire arrays
Appl. Surf. Sci.
(2012) - et al.
Production of alumina templates suitable for electrodeposition of nanostructures using stepped techniques
Electrochim. Acta
(2009) - et al.
Synthetic control of large-area, ordered Fe nanotubes and their nanotube-core/alumina-sheath nanocables, Mat
Chem. Phys.
(2012) - et al.
One-step electrochemical synthesis and physicochemical characterization of CdSe nanotubes
Electrochim. Acta
(2013) - et al.
Electrical conductivity of carbon nanotubes grown inside a mesoporous anodic aluminum oxide membrane
Carbon
(2013) - et al.
Poly(3-hexylthiophene) Nanorods with Aligned Chain Orientation for Organic Photovoltaics
Adv. Funct. Mater
(2010) - et al.
H2 absorption at ambient conditions by anodized aluminum oxide (AAO) pattern-transferred Pd nanotubes occluded by Mg nanoparticles
Mat. Chem. Phys.
(2012) - et al.
Silver nanowire array sensor for sensitive and rapid detection of H2O2
Electrochim. Acta.
(2013) - et al.
pH sensors based on polypyrrole nanowire arrays
Electrochim Acta.
(2013) - et al.
The role of Ag particles deposited on TiO2 or Al2O3 self-organized nanoporous layers in their behavior as SERS-active and biomedical substrates
Mat. Chem. Phys.
(2013)
Surface enhanced Raman scattering substrate based on gold-coated anodic porous alumina template
Microelectron. Eng.
First step of anodization influences the final nanopore arrangement in anodized alumina
Surf. Coat. Technol.
Evaluation of pore diameter of anodic porous films formed on aluminum
Surf. Coat. Technol.
Temperature influence on well-ordered nanopore structures grown by anodization of aluminium in sulphuric acid
Electrochim Acta
Structural features of self-organized nanopore arrays formed by anodization of aluminum in oxalic acid at relatively high temperatures
Electrochim. Acta
Ultra-small nanopores obtained by self-organized anodization of aluminum in oxalic acid at low voltages
Mater. Lett.
Quantitative arrangement analysis of anodic alumina formed by short anodizations in oxalic acid
Mater. Character.
Tracer study of pore initiation in anodic alumina formed in phosphoric acid
Electrochim. Acta
The effect of n-alcohols on porous anodic alumina formed by self-organized two-step anodizing of aluminum in phosphoric acid
Surf. Coat. Technol.
Fabrication of Anodic Porous Alumina by Squaric Acid Anodizing
Electrochim. Acta
Growth behavior of anodic porous alumina formed in malic acid solution
Appl. Surf. Sci.
Self-ordering of anodic porous alumina formed in organic acid electrolytes
Electrochim. Acta.
Increased growth rate of anodic porous alumina by use of ionic liquid as electrolyte additive
Mater. Lett.
Incorporation of copper chelate ions into anodic alumina walls
Mater. Lett.
Fabrication of high quality anodic aluminum oxide (AAO) on low purity aluminum—A comparative study with the AAO produced on high purity aluminum
Electrochim. Acta
Formation behavior of nanoporous anodic aluminum oxide films in hot glycerol/phosphate electrolyte
Electrochim. Acta
Cited by (59)
Influence of oxalic additive on etidronic acid anodizing of aluminum alloy
2023, Journal of Electroanalytical ChemistryThe influence of sodium alginate in water-based electrolyte on the morphology of TiO<inf>2</inf> nanotube prepared by anodization method
2023, Materials Chemistry and PhysicsCitation Excerpt :However, the nanotube formed was disorganized and short (approximately around 1 μm even after a long anodization time) due to the massive chemical dissolution reaction. One method to improve the organization of nanotubes is controlling electrolyte viscosity by using a thickening agent so that the diffusion of ions in the electrolyte becomes slower, thus leading to the production of a more self-organized nanotube morphology [20,21]. Among many thickening agents, the most common green thickening agent studied in TNA fabrication is carboxymethyl cellulose (CMC) due to its cheap price, nontoxic, abundance, and environmentally friendly characteristics [17,22,23].
Quantum dots made with using of anodic aluminum oxide template: fabrication and application
2023, Quantum Dots: Emerging Materials for Versatile ApplicationsHydrogen production from macroalgae by simultaneous dark fermentation and microbial electrolysis cell with surface-modified stainless steel mesh cathode
2021, International Journal of Hydrogen EnergyInfluence of microstructural features on the growth of nanotubular oxide layers on β-phase Ti-24Nb-4Zr-8Sn and α + β-phase Ti-13Nb-13Zr alloys
2021, Surface and Coatings Technology