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Causes of resistivity increase in iridium oxide coated titanium anodes

I am looking for the causes of resistivity increase in iridium oxide coated titanium anodes in tin plating baths.

Oktay Elkoca
ERDEMIR - Kdz. Eregli, Turkey

The causes of resistivity increase in iridium oxide coated titanium anodes is because of a week dissolution of titanium in sulfuric acid - (I suppose) that your Sn bath is based upon sulfuric or sulfonic acid. It is well known, that titanium is not stable in reducing acid such as H2SO4. The corrosion speed of Ti in H2SO4 is about 1 mm/year. When the Ir-oxide starts to scale the titanium anodes will be covered with oxides (anodes) because of the anodic oxidation (anodizing). In practice the voltage will raise and the current will decrease and at the end the anodes will totally passivate.

Per Moller
- Denmark

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