Tantalum galvanic effect

Anodic oxide formation Lakhiani and Shreir have studied the anodic oxidation of niobium in various electrolytes, and have observed that temperature and current density have a marked effect on the anodising characteristics. The plateau on the voltage/time curve has been shown by electron microscopy to correspond with the crystallisation of the oxide and rupture of the previously formed oxide. It would appear that this is a further example of field recrystallisation —a phenomenon which has been observed previously during anodisation of tantalum" . No significant data on the galvanic behaviour of niobium are available however, its behaviour can be expected to be similar to tantalum. 

The second observation is that with the addition of benzotri-azole (BTA) to a nitric acid slurry the polish rates of both titanium and tantalum appear to be unaffected by the presence of copper ions. The BTA appears to suppress the galvanic interaction between the metals. One possible explanation is that the BTA surrounds the copper ions in solution and prevents interaction with the barrier metal. In the BTA slurry, the high selectivity makes the barrier metal an effective polish stop. BTA slurries are discussed in more detail in Chapter 7. 

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