INCORR Pt/Ti anode will work equally well if it is replaced by a platinium anode. But it is so expensive that we have to substitute the metal with the cheaper titanium and coat it with a thin layer of platinium of a few micron thickness. When Pt/Ti is used as an anode and when it is loaded, a very strongly adhered titanium oxide layer will form on the titanium section. This oxide layer is not conductive, hence, all the current will be discharged from the platinium section. Since platinium has very minimum wear rate, the Pt/Ti anode therefore wear at a very slow rate of 8 mg/Amp-yr.
When an excessive voltage (e.g. > 12 volts) is applied across the titanium anode, the titanium oxide layer will breakdown and the titanium will corrode very fast and cause premature anode failure. The following table shows the corrosion rates of platinium and platinised titanium in various environment:
|Conditions||Corrosion rate (mg/Amp-yr)|
|Pure Pt in seawater 54 to 540 mA/cm²||6 to 7|
|Pure Pt in seawater 500 mA/cm²||13.14|
|Pure Pt in seawater 130 mA/cm²||8.76|
|Pt/Ti in seawater 32 to 320 mA/cm² (0oC to 15oC DC 100 Hz ripple and above)||8.76 average|
|As above with high frequency chopped supply||13.8|
|Pt/Ti in highly acid conditions caused by deposits etc.||up to 100 x normal rate|
|Indicated by replacement sales in UK of Pt/Ti||8.76 to 17.52|
Platinised Titanium anodes can be used in fresh and seawater but care should be taken not to apply excessive voltage.
It may also be applied in soil but the backfill material has to be specially selected and the system to be carefully designed to prevent failure.
|Click on thumbnails for photographs.|