Figure 5: Schematic illustration of the formation of giant cavities in hydrogenated metals during heating.
From: Effect of hydrogen on the integrity of aluminium–oxide interface at elevated temperatures
(a) At room temperature, the hydrogenated metals have gas-filled proto-cavities under the oxide layer and hydrogenated vacancies in the bulk. (b) From 20 to 100 °C, the proto-cavities coalesce to grow bigger. (c) From 100 to 150 °C, the hydrogenated vacancies tend to dissociate due to the thermal destabilization. Both interstitial hydrogen and naked vacancies are freed to diffuse outwards. As a result, the metal–oxide interface becomes further weakened, opening up a diffusion highway for surface diffusion and H2 flow under the oxide layer. The diffusion pathways of Al and H2 are marked with solid and dashed arrows, respectively. (d) At 200 °C, a giant cavity is formed where the biggest proto-cavities was found.
