The carburizing and oxidation of transition metals

These two processes provide examples of the moving boundary problem in diffusing systems in which a solid solution precedes the formation of a compound. The diickness of the separate phase of the product, carbide or 

When tire metal/carbide boundaiy moves away from tire free surface of the sample by an increment d, the flux balance at tlris interface reads 

The equation for the rate of oxidation of the transition metals at high temperatures, which form a solid solution of oxygen before the oxide appears at the surface has die same form as that derived for die carburizing of die metal, and 

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