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Rapid oxidation takes place both in the laboratory and in industrial conditions when alloy 925 is contaminated by oxide powder, and the oxidation rate is much higher than normal. Herein, the rapid oxidation behavior and mechanism of alloy 925 were investigated by a series of comparison tests at 1160 °C. It is found that the oxide powder produced during the oxidation process is mainly composed of NiCr2O4 spinel, accompanied by NiO and NiMoO4. The oxide powder plays a triggering role in the rapid oxidation of alloy 925, as NiO has a strong affinity with O. A composition adjustment experiment of alloy 925 shows that rapid oxidation is the synergetic effect of Mo and Cu in the alloy. Mo and Cu easily combine to form low melting point eutectics. The formation and volatilization of MoO3 oxide can destroy the completeness of the protective oxide layer. The MoO3 flux can dissolve protective Cr2O3 and prevent the repair of the oxide layer and also promote the formation of nonprotective and easy-spall NiCr2O4 spinel. The synergetic effect of Cu and Mo in accelerating oxidation should be considered in any nickel-based alloy with a high content of Cu and Mo. [ABSTRACT FROM AUTHOR]