Interstitial Impurities Alloys and Hydrides

There are many metal alloys that contain interstitial atoms embedded in the metal structure. Traditionally, the interstitial alloys most studied are those of the transition metals with carbon and nitrogen, as the addition of these atoms to the crystal structure increases the hardness of the metal considerably. Steel remains the most important traditional interstitial alloy from a world perspective. It consists of carbon atoms distributed at random in interstitial sites within the face-centered cubic structure of iron to form the phase austenite, which exists over the composition range from pure iron to approximately 7 at % carbon. 

More recently, hydrogen storage has become important, and interstitial alloys formed by incorporation of hydrogen into metals are of considerable interest. Niobium is typical of these. This metal is able to incorporate interstitial hydrogen up to a limiting composition of approximately NbH0.i- 

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