The GD-OES elemental profile of the surface treated by dipping in KMnO4 showed lower oxide layer thickness and the chemical profile exhibits uniform distribution of manganese throughout the oxide layer. The manganese concentration showed a decrease with depth towards the metal oxide interface. However in the case of steam treatment using KMnO4 solution, thickness of the produced oxide layer was high, while the manganese content in the coating
was significantly lower in the top (∼200 nm) of the surface layer as shown in Fig. 1 (e). The steam treatment of Peraluman 706TM surface with steam generated from aqueous solution of HNO3 did not indicate the incorporation of any other chemical species, neither at the surface nor in the bulk of the oxide layer (Fig. 1 (f)). The GD-OES profiling of the AA1090 and AA6060 alloys surfaces (not shown) also exhibited similar results as for Peraluman 706TM, therefore only the
summary of the results for AA1090 and AA6060 is presented.
Average thickness of the oxide layer calculated from the GDOES depth profiles on AA1090, AA6060 and Peraluman 706TM are presented in Fig. 1 (d). In general, thickness of the oxide layer was a function of the substrate type and chemistries. The highest thickness of the oxide layer resulted from steam treatment using KMnO4 on AA1090, AA6060 and Peraluman 706TM. Steam generated from the aqueous solution with low concentration of HNO3 resulted in the formation of relatively thick oxide on Peraluman 706TM and AA6060 in comparison to AA1090. The increase in the concentration of HNO3 reduced the average thickness of the oxide layer on Peraluman 706TM and AA6060. AA1090 alloy exhibited reduction
in thickness of oxide layer by the addition of HNO3 regardless of the variation in concentration of HNO3 in aqueous solution