firstly, in oil rigs they use aluminium to protect the rig as a form of sacrifical protection but however aluminium react with oxygen does it not,then does the aluminium oxide is now a protective layer for the oil rig? as the oxide protects the aluminium and in return it prevents aluminium from "doing its job."
secondly, why should the electrode of the anode be the same as the cation of the electrolyte if the concentration were to remain the same.what if it were to use silver(lower than copper in the reactivity series) as the anode would the silver for Ag ion in the electrolyte?
secondly, why should the electrode of the anode be the same as the cation of the electrolyte if the concentration were to remain the same.what if it were to use silver(lower than copper in the reactivity series) as the anode would the silver for Ag ion in the electrolyte?
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I am not expert, but have had long experience with steel structures in the sea. As you are protecting steel, the anode is zinc, cadmium, aluminium etc, because these are more anodic than steel. The composition of the steel and oxides etc change the situation. The reactions that occur are not straight forward, so the actual choice of anode is a judgement call, taking into account the situation, calling on experience, galvanic testing in the same conditions etc. There is no clear cut black and white answer, and oxides can have an effect on the position that a given material has in a galvanic series even. For example the water temperature, oxygen levels, carbonates, fouling, water action are significant. Note for example that steel is different to iron if you are looking at a galvanic series. The aluminium oxide certainly has a tendency to isolate the anode, but trade this against the toxicity of cadmium, and zinc also has oxide issues. It comes down to some anode is better than no anode, even with oxides. I haven't had much experience with aluminium anodes, but have used steel as an anode with stainless steel because the cell is not so galvanically active as with zinc or aluminium, so less plating of the stainless steel.
Generally active protection (applying a current to the electrodes) is more predictable, but it doesn't work well with solar panels on their own, as the process stops at night.
Generally active protection (applying a current to the electrodes) is more predictable, but it doesn't work well with solar panels on their own, as the process stops at night.