Electrode for electrolytic processes
An electrode on valve metal substrate suitable for the evolution of oxygen in electrolytic processes is provided with a coating having a catalytic layer containing platinum group metals and one or more protective layers based on tin oxide modified with a doping element selected from bismuth, antimony or tantalum and with a small amount of ruthenium. The electrode is useful in processes of non-ferrous metal electrowinning.
1. Electrode suitable for oxygen evolution in electrolytic processes comprising a valve metal substrate provided with a coating, said coating comprising a catalytic layer and at least one protective layer external to said catalytic layer, said protective layer consisting of a mixture of oxides having a weight composition referred to the metals containing 89-97% of tin, 2-10% of at least one doping element selected from the group consisting of bismuth, antimony and tantalum and 1-9% of ruthenium.
2. The electrode according to claim 1 wherein said at least one protective layer consists of a mixture of oxides having a weight composition referred to the metals containing 89-97% of tin, 2-10% of bismuth and 1-9% of ruthenium.
3. The electrode according to claim 1 , wherein said at least one protective layer has a thickness of 1 to 5 μm.
4. The electrode according to claim 1 , wherein said a catalytic layer is contact with said protective layer, said catalytic layer comprising a mixture of oxides having a weight composition referred to the metals containing 40-46% of platinum group metals, 7-13% of at least one element selected from the group consisting of bismuth, antimony, niobium and tantalum and 47-53% of tin, said catalytic layer having a thickness of 2.5 to 5 μm.
5. The electrode according to claim 4 , wherein said catalytic layer comprises a mixture of oxides having a weight composition referred to the metals containing 40-46% of iridium, 7-13% of bismuth and 47-53% of tin, said catalytic layer having a thickness of 2.5 to 5 μm.
6. The electrode according to claim 4 , wherein said catalytic layer consists of a mixture of oxides having a weight composition referred to the metals containing 47-53% of tin, 7-13% of bismuth, 40-46% as the sum of ruthenium and iridium, said catalytic layer having a thickness of 2.5 to 5 μm.
7. The electrode according to claim 6 wherein the weight ratio referred to the metals of iridium to ruthenium in said sum of iridium and ruthenium ranges between 60:40 and 40:60.
8. The electrode according to claim 4 comprising at least two of said protective layers, said catalytic layer being interposed between said at least two protective layers.
9. Process of cathodic electrodeposition of metals from an aqueous solution comprising the anodic evolution of oxygen on the surface of an electrode according to claim 1 .