Various studies have been conducted on the growth of hydrated oxide films on aluminium alloys. These studies have investigated the growth mechanism, the chemical nature of the product, and the kinetics of the reaction.
The hydration of AlPO4 is a complex process that exhibits a number of phase transitions. Upon dehydration, AlPO4-H3 loses six hydrogen atoms and becomes a four-hydrogen hydrate. A new 27Al MAS NMR resonance line has been identified and assigned to the coordinations of AlO4(H2O)2.
AlPO4-H3 has the largest peak temperature and the smallest particle size of all the hydrates studied. The peak temperature of boehmite is correlated with the crystallinity of the sample and particle size. The phase transition from VFI to AET is a disruptive process that reduces the number of pore rings. This transition is reversible and is caused by a change in the topological space group of AlO4(H2O)2. The hydrated product is not locked in a crystal structure and plays an important structural role in AlPO4 hydrates.
Studies have been conducted on the growth of hydratedoxide films on aluminium alloys at temperature ranges of 40 and 50 degC. These studies have investigated the morphology and weight gain of the hydrated oxide film produced. They have also been conducted at high resolution SEM.
The hydrated oxide film studied at 50 degC was found to be thicker than those produced at 40 degC. These results suggest that the growth mechanism of hydrated oxide films is similar to that of Arnot.