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Niobium,
like other reactive metals, owes its corrosion resistance
to a readily formed, adherent, passive oxide film. Niobium's
corrosion properties resemble those of tantalum, although
it is slightly less resistant in aggressive media such
as hot concentrated mineral acids. Table 2 gives some
typical corrosion data for niobium. Like tantalum, it
is susceptible to hydrogen embrittlement if cathodically
polarized by either galvanic coupling or by impressed
potential. In addition to being stable, the anodic niobium
oxide film has a high dielectric constant and a high
breakdown potential. These properties, coupled with
its good electric conductivity, have led to niobium's
use as a substrate for platinum-group metals in impressed-current
cathodic-protection anodes.
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