The Dissolution of Aluminum in Sodium Hydroxide Solutions

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The effect of immersion time, temperature, concentration, and an applied external current on the dissolution of commercially pure aluminum in sodium hydroxide solutions is described. A technique resulting in reproducible dissolution rates is given. The instantaneous rate of dissolution increases at a decreasing rate with immersion‐time and is directly proportional to the weight‐loss and inversely proportional to the immersion‐time. The effect of temperature on the rate of dissolution is given by the Arrhenius equation. It is shown that the changing rate and electrode potential are determined by the precipitate which forms local cathodes on the surface of the metal during dissolution. The electrode potential varies as the rate of dissolution, a measure of the local cell current, varies.When aluminum is made cathodic in sodium hydroxide solutions, the rate of dissolution is decreased only slightly. Making aluminum anodic in sodium hydroxide solutions gradually eliminates hydrogen evolution at the anode as the current density is increased until it is stopped entirely (local cell action is suppressed), and the weight‐loss is electrochemically equivalent to the external current. This decrease in local cell action (normal dissolution) is directly proportional to the anodic current density and is reproducible.It is found that the various phenomena accompanying the dissolution of aluminum in sodium hydroxide solutions, as described in this paper, may be explained in terms of electrochemical theory.