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Steam assisted oxide growth on aluminium alloys using oxidative chemistries: Part I Microstructural investigation

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Online Research Database In Technology
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The surface treatment of aluminium alloys under steam containing KMnO<sub>4</sub> and HNO<sub>3</sub>resulted in the formation of an oxide layer having a thickness of up to 825 nm. The use of KMnO<sub>4 </sub>and HNO<sub>3 </sub>in the steam resulted in incorporation of the respective chemical species into the oxide layer. Steam treatment with solution containing HNO<sub>3</sub> caused dissolution of Cu and Si from the intermetallic particles in the aluminium substrate. The growth rate of oxide layer was observed to be a function of MnO<sub>4</sub><sup>−</sup>and NO<sub>3</sub><sup>−</sup>ions present in the aqueous solution. The NO<sub>3</sub><sup>−</sup>ions exhibit higher affinity towards the intermetallic particles resulting in poor coverage by the steam generated oxide layer compared to the coating formed using MnO4<sup>−</sup>ions. Further, increase in the concentration of NO<sub>3</sub><sup>−</sup>ions in the solution retards precipitation of the steam generated aluminium hydroxide layer.


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