? asked in 科學及數學化學 · 1 decade ago

removal of Al protective layer

Al does not react with hot water and steam as it has a protective

aluminium oxide layer which is imprevious to both air and water.

After the removal of this layer, Al can react with steam.

How to remove the protective layer?

3 Answers

Rating
  • 1 decade ago
    Favorite Answer

    To remove the aluminium oxide layer on the surface, the aluminium article is dipped into 4 - 6 M sodium hydroxide solution. Aluminium oxide reacts with hydrochloric acid slowly, but with strong alkali solutions very rapidly.

    Al2O3(s) + 2OH-(aq) + 3H2O(l) → 2[Al(OH)4]-(aq)

    After the aluminium oxide layer is removed, the sodium hydroxide solution would then react with the aluminium to give off hydrogen gas.

    2Al(aq) + 2OH-(aq) + 6H2O(l) → 2[Al(OH)4]-(aq)

    Therefore, when a number of bubbles are observed, take out the aluminium oxide and rinse it with fresh water. Now, the aluminium article is free of aluminium oxide layer on its surface.

  • ?
    Lv 7
    1 decade ago

    Why you want to remove the protective layer ? When pure Al is formed from Al mineral , it is immediately reacted with the atmospheric oxygen to form a layer of Al2O3 , so what ever reduction to form pure Al , you need to have the reaction taken place in absent of oxygen ! Afterward you need to soak the pure Al in oil too. In fact this protective layer makes Al much useful than Ca , Na or K which are too reactive to have any practical applications.

  • 1 decade ago

    commercially Al is extracted by electrolysis of molten alumina (bauxite) dissolved in cryolite to allow lower temps

    The reaction at the cathode isAl3+ + 3 e− → Al

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