Because at pH 2.5 caused reactions Beethoven foeri click the episode melts. Make foeri away a solid side in the crystallization of aluminium oxide on the surface, there is little.
Since at pH 2.5, ferric Fenton reaction caused when melted water. Make ferric oxide solid in the crystallization of aluminum oxide on the surface is minimal.
Because pH 2.5 ferric caused by Fenton reaction of water soluble volume. The ferric oxide solid in the crystallization on the surface of aluminum oxide is minimal.