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The recent jump in tantalum pricing for the CPI has many end users asking about replacement materials. This has caused us to reassess the corrosion resistance of niobium in media where Ta is used extensively. Initially the effort has been aimed at hydrochloric acid media. In general, niobium is similar to both Ta and Ti since it is more resistant to oxidizing media. But as with Ta and Ti, Nb can absorb hydrogen from the corrosion process and become embrittled, even at relatively low temperatures. It is particularly susceptible to hydrogen pickup in alkaline solutions. Table 1 compares Nb's corrosion resistance to Zr, Ta, and Ti in various media.

Other aspects of niobium that apply to its use in corrosive applications include:

• Resistant to most organic and mineral acids below 100°C
• Good in nitric acid to 250°C
• Good in chrome plating baths
• Inert to aqua regia at 55°C ¥ Low levels of fluoride ion improves resistance in phosphoric acid
• Resistant in alkalis, but can absorb hydrogen and become embrittled
• Inert to 10% Ferric Chloride at ambient temperature
• Oxidizes in air above 200°C
• Nitrides above 350°C
• Resists water vapor to 300°C
• Resists chlorine gas to 200°C
• Resists carbon monoxide and dioxide, and hydrogen gas to 250°C

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INDEX  •  CORROSION RESISTANCE PROPERTIES  •  FABRICATION   
NIOBIUM PRODUCTS   •  SPECIFICATIONS of NIOBIUM   
NIOBIUM ELECTRONICS APPLICATIONS