83 research outputs found
Transformation of the overall strict kinetic model governing the growth of porous anodic Al2O3 films on aluminium to a form applicable to the non-stirred bath film growth
The strict and complex, overall kinetic model, governing the growth of
porous anodic Al2O3 films, was transformed to a form easily and directly
applicable to the galvanostatic anodization in a non-stirred bath at
constant bath temperature. It was shown that the transformed model
always acquires a form different from that of a stirred bath
anodization. The transformed model was applied to the experimental
results of film growth obtained at 25 degrees C, 15 mA cm(-2) and in a
wide range of H2SO4 concentration, 5-85% w/v. The application of the
transformed model provided, consistently with other experimental
observations, the existence of a critical electrolyte concentration near
5% w/v above which the normal mechanism of oxide production and film
growth is valid and below which a deficient growth of oxide is observed.
The transformed model permitted some predictions for the real pore
shapes. The experimental results and their treatment showed that the
electrolyte concentration affects parameters such as the mass and
porosity of the film, the pore base hemispherical surface area, the time
at which the pore external diameter approaches cell width, the time
interval in which the model applies and the parameters involved in the
transformed kinetic model; the manner of the effect of electrolyte
concentration on these parameters is significantly different from that
in the stirred bath. Their dependence on the electrolyte concentration
was well explained by the existence of a maximum in the rate of oxide
dissolution in an open circuit at a specific concentration, of a maximum
in the electrical conductivity at another specific concentration, and of
some resulting slight changes of the temperature inside the pores and
oxide bulk during anodization. Copyright (C) 1996 Elsevier Science Ltd
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