Boehmite formation in solutions containing rare earths

7 Boehmite formation in solutions containing rare earths 

The growth of hydrated aluminium oxides was extensively studied and reported by Vedder and Vermilea. Aluminium develops surface oxides that change with the temperature of treatment. Below 40 °C, the surface oxide is dominated by bayerite (Al(OH)3), but as the temperature increases towards the boiling point of water the amount of pseudoboehmite increases. Pseudoboehmite is an aluminium hydroxyl-oxide with varying amount of waters of hydration, with the formula AiPj uHp. 

The growth of this oxide in the presence of a range of salts has been the focus of many studies. Vedder and Vermilea reported one of the more extensive studies in this area and found that the presence of certain anions in solution such as chromate and phosphate inhibited the formation of the pseudo boehmite layer.  

The thickness of the boehmite coating varies both with the solution chemistry and the underlying alloy composition/microstructure. The cmrent model of oxide growth in an aqueous environment includes (a) formation of an amorphous oxide, 

7 Various types of porous oxides on aluminium alloy 2024-T3. 

---