Effect of the structure of porous anodic Al2O3 films on the mechanism of their hydration and pore closure during hydrothermal treatment

 
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Effect of the structure of porous anodic Al2O3 films on the mechanism of their hydration and pore closure during hydrothermal treatment (EN)

Patermarakis, G (EN)
Papandreadis, N (EN)

N/A (EN)

Porous anodic Al2O3 films (prepared galvanostatically in a vigorously stirred bath with 15% w/v H2SO4 at bath temperatures of 20, 25 and 30-degrees-C, current densities of 5, 15 and 35 mA cm-2 and various anodization times with thicknesses generally varying between 1.5 mum and the maximum limiting values achieved) were hydrated on prolonged treatment in H2O at 100-degrees-C for 4.5 h. The amount of H2O retained and its ratio to the pore void volume of the dry films were determined. The results showed that pore mouth plugs completely blocking pore necks are indeed formed, significantly retarding the hydration process taking place behind them. For the average pore, the plug is formed up to a pore length which is usually shorter than, or close to the half of the maximum limiting pore length achieved. The formation of pore mouth plugs appeared to be the consequence of the spinning top shape of pores as well as of other structural features such as the size distribution of microcrystallites around the pore walls. Moreover, it appeared that the strong retardation of the hydration process behind the plugs cannot be ascribed exclusively to plug formation per se but rather to some other phenomena occurring in the space just behind plugs; the most probable appears to be the existence or the formation of a gas phase, as long as the hydration of the pore wall oxide is in advance, occupying a part of the unfilled pore volume. For pores longer than the above, ''open plugs'' around pore mouths are formed; the factors responsible for the retardation of the hydration process around pore walls are eliminated and the mechanism of pore closure becomes similar to that of conical pores. (EN)

journalArticle

Pore closure (EN)
Porous alumina films (EN)
Films (EN)
Hydration (EN)
Porous materials (EN)
anodizing (EN)
Alumina films hydration (EN)
porous (EN)
hydration mechanism. (EN)
Anodic alumina films (EN)
Hydrothermal treatment effects (EN)
Aluminum corrosion (EN)
Corrosion resistance (EN)
Anodic oxidation (EN)
oxide (EN)
aluminium (EN)
Alumina (EN)

Εθνικό Μετσόβιο Πολυτεχνείο (EL)
National Technical University of Athens (EN)

Electrochimica Acta (EN)

1993


PERGAMON-ELSEVIER SCIENCE LTD (EN)



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