Oxygen partial pressure critical values

When the oxygen partial pressure is raised to a critical value, the process becomes unstable An avalanche effect occurs since the rise in oxygen partial pressure decreases the pumping speed for the reactive gas. The target surface becomes fully oxidized. 

Extensive experimental observations demonstrate that on a binary A-Bd oy oxidized in an atmosphere with a low oxygen partial pressure A will not be oxidized), a continuous external 50 scale always forms on the alloy surface after a short exposure. The formation of this external oxide scale may or may not be accompanied by the formation of internal oxides in the aUoy substrate. In other words, the oxidation process starts on the alloy surface to form an external BO scale, and then it may or may not proceed into the aUoy substrate to develop internal 50 particles, depending on the alloy composition and the oxidation condition. When the content of 5 in the A B aUoy is higher than a critical value, a protective external BO scale can form and stay on the alloy surface, and the formation of internal 50particles in the alloy substrate can be completely avoided. 

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