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

Patermarakis, G; Papandreadis, N

dc.contributor.author	Patermarakis, G	en
dc.contributor.author	Papandreadis, N	en
dc.date.accessioned	2014-03-01T01:09:23Z
dc.date.available	2014-03-01T01:09:23Z
dc.date.issued	1993	en
dc.identifier.issn	0013-4686	en
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/10939
dc.subject	aluminium	en
dc.subject	anodizing	en
dc.subject	hydration mechanism.	en
dc.subject	oxide	en
dc.subject	porous	en
dc.subject.classification	Electrochemistry	en
dc.subject.other	Aluminum corrosion	en
dc.subject.other	Anodic oxidation	en
dc.subject.other	Corrosion resistance	en
dc.subject.other	Films	en
dc.subject.other	Hydration	en
dc.subject.other	Porous materials	en
dc.subject.other	Alumina films hydration	en
dc.subject.other	Anodic alumina films	en
dc.subject.other	Hydrothermal treatment effects	en
dc.subject.other	Pore closure	en
dc.subject.other	Porous alumina films	en
dc.subject.other	Alumina	en
dc.title	Effect of the structure of porous anodic Al2O3 films on the mechanism of their hydration and pore closure during hydrothermal treatment	en
heal.type	journalArticle	en
heal.identifier.primary	10.1016/0013-4686(93)80078-E	en
heal.identifier.secondary	http://dx.doi.org/10.1016/0013-4686(93)80078-E	en
heal.language	English	en
heal.publicationDate	1993	en
heal.abstract	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
heal.publisher	PERGAMON-ELSEVIER SCIENCE LTD	en
heal.journalName	Electrochimica Acta	en
dc.identifier.doi	10.1016/0013-4686(93)80078-E	en
dc.identifier.isi	ISI:A1993LJ41800015	en
dc.identifier.volume	38	en
dc.identifier.issue	10	en
dc.identifier.spage	1413	en
dc.identifier.epage	1420	en