FABRICATION OF SPINEL COATING ON HP40 ALLOY AND ITS INHIBITION EFFECT ON CATALYTIC COKING DURING THERMAL CRACKING OF LIGHT NAPHTHA

Abstract A novel two-step process of Cr-Mn pack cementation and thermal oxidation was applied to fabricate a MnCr2O4 spinel coating on HP 40 alloy. The Cr-Mn diffusion layer formed after the Cr-Mn pack cementation process is lacking in Fe and Ni. A dense and uniform coating formed on the alloy following thermal oxidation. The coating is mainly composed of MnCr2O4 spinel phase, while the outer surface of the coating is completely MnCr2O4 spinel. The coating exhibits a favorable thickness of about 7 µm according to SEM and EDS maps of its cross-section. The MnCr2O4 spinel coating significantly affects the coking mechanism and coke property according to coking experiments. Raman spectroscopy shows that the coated sample inhibits catalytic coke formation as more disordered carbon and amorphous carbon layers are present. Moreover, the coating is stable in coking and decoking environments.