posted on 2015-12-30, 00:00authored byVíctor Vega, Javier García, Josep M. Montero-Moreno, Blanca Hernando, Julien Bachmann, Víctor M. Prida, Kornelius Nielsch
Pores growth mechanism and their
self-ordering conditions are investigated
for nanoporous alumina membranes synthesized by hard anodization (HA)
of Al in a broad range of anodic conditions, covering oxalic acid
electrolytes with concentrations from 0.300 M down to 0.075 M and
potentiostatic anodization voltages between 120 and 225 V. The use
of linear sweep voltammetry (LSV) and scanning and transmission electron
microscopy, together with image analysis techniques allow one to characterize
the intrinsic nature of the HA regime. HA of aluminum is explained
on the basis of a phenomenological model taking into account the role
of oxalate ions and their limited diffusion through alumina nanochannels
from a bulk electrolyte. The depletion of oxalate ions at the bottom
of the pores causes an increased growth of the alumina barrier layer
at the oxide/electrolyte interface. Furthermore, an innovative method
has been developed for the determination of the HA conditions leading
to self-ordered pore growth in any given electrolyte, thus allowing
one to extend the available range of interpore distances of the highly
ordered hexagonal pore arrangement in a wide range of 240–507
nm, while keeping small pore diameters of 50–60 nm.