(408d) Experimental Characterization and Modeling of Steel Nitridation By Ammonia Combustion Products

Mitsubishi Heavy Industries (MHI) has declared its commitment to achieving carbon neutrality by 2040 under the initiative "MISSION NET ZERO" emphasizing the importance of decarbonizing existing infrastructure. One of the key aspects of this effort is reducing CO₂ emissions through the use of ammonia fuel, which does not emit CO₂ during combustion. We are advancing the development of technology that enables the use of ammonia as fuel in combustion systems.

However, the nitriding phenomenon of structural materials during ammonia combustion presents a challenge. Simulations utilizing the Reaction Mechanism Generator (RMG) conducted at Northeastern University suggest that the nitriding phenomenon associated with ammonia combustion is primarily driven by adsorption reactions on the material surface.

In this study, several metallic materials were reacted in environments of ammonia, oxygen, or water vapor at temperatures ranging from 400°C to 900°C at the laboratory scale. The results analyzed by EDX or other methods revealed that under conditions of high ammonia concentration, a nitriding layer was observed beneath the surface oxide layer, indicating that the nitriding layer is replaced by the thermodynamically stable oxide layer. Furthermore, under experimental conditions where the adsorption rate of ammonia was greater than that of oxygen, as suggested by surface reaction analysis using the RMG, the presence of the nitriding layer was confirmed.