Chemistry:Valve metals

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In electrochemistry, a valve metal is a metal which passes current in only one direction. Usually, in an electrolytic cell, it can function generally as a cathode, but not generally as an anode because a (highly resistive) oxide of the metal forms under anodic conditions.[1] Valve metals include commonly aluminium, titanium, tantalum, and niobium. Other metals may also be considered as valve metals, such as tungsten, chromium, zirconium, hafnium, zinc, vanadium, bismuth or antimony.[2]

References

  1. "Electrochemistry Dictionary". http://knowledge.electrochem.org/ed/dict.htm. 
  2. "Method of anodizing valve metal derived anode bodies and electrolyte therefore" US patent 7248462