Phase transformation sequence in Al – oxide – hydroxide system occurring on a surface of crystalline aluminum substrate placed in pure water in a temperature range of 298 – 373 K (liquid) and 373 – 500 K (steam) was predicted on the basis of bulk and interface thermodynamics. Different competing oxide (amorphous Al2O3 and crystalline γ-Al2O3) and hydroxide (amorphous Al(OH)3, AlOOH and crystalline gibbsite, bayerite and boehmite) phases were taken into account. The first stage of film formation on a crystalline aluminum surface in water, as predicted by interface thermodynamics, is the development of an amorphous oxide layer Al2O3. However this initial oxide film is not stable in water and it is predicted further to transform to amorphous oxide hydroxide phase AlOOH. This phase is also not stable in water and tends to transform into the crystalline trihydroxide phase bayerite in a temperature range below approximately 350 K. Above this temperature, the amorphous oxide hydroxide AlOOH is assumed to transform directly to the crystalline boehmite. The model predictions are in good agreement with experimental observations reported in the literature.

Model predictions of phase transformation sequence in Al-oxide-hydroxide system in pure water by bulk and interface thermodynamics

2019 Fall National Meeting

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