Internal oxidation of Ag–VC composites

The internal oxidation (IO) of Ag–VC composites containing 5 vol.% of carbide was examined at three oxidation temperatures (350, 400, 600 °C). Two mechanisms were observed due to the formation of double oxides with relatively low-melting points. At temperatures below the lowest eutectic point in situ, or diffusion less IO, was observed with the formation and growth of oxide layers surrounding the initial carbide. At temperatures above the eutectic point IO resulted in the formation of liquid oxide pools, which grew in size and developed into a network of oxides within the metal matrix. The kinetics confirmed the presence of two distinct mechanisms.

Research highlights
► Two mechanisms of internal oxidation in Ag–VC composite depend on the temperature of oxidation.
► The double oxide with low-melting points was observed. The rate n is in accordance to parabolic law.
► The growth of oxide layers surrounding the carbide was observed at T below the eutectic.
► The formation of liquid oxide pools was observed at temperature above the eutectic.
► The kinetic analysis indicates that oxidation at high temperature can be termed as catastrophic.