Surface Nitridation and Reduction of Iron and Nickel Under Direct H2 and H2/NH3 Flame Exposure

Abstract

In the wake of widespread decarbonization efforts due to climate change, hydrogen and ammonia have emerged as promising clean alternatives to hydrocarbon fuels. As such, H2 and NH3 have been explored in a number of industry applications ranging from manufacturing to power generation. In many such applications, the surface reactions between these fuels and common industrial materials are not well understood. In this study, the surface mechanisms of reduction and nitridation via H2 and NH3 were examined. An apparatus was designed to stagnate H2 and H2/NH3 flames on the surfaces of iron and nickel test plates mounted above a burner. Experimental investigation was supplemented by 1-D flame simulations using Cantera to develop an understanding of how temperature and radical formation led to the observed surface phenomena. X-ray photoelectron spectroscopy was used to quantify the extent to which surface processes occurred. Conditions for considerable nickel nitride formation at temperatures beyond those previously studied for this surface phenomenon were discovered. Once these conditions were established, the height of the test sample above the burner and the time of flame exposure were varied to observe the effect of changing kinetics on surface reactions. Iron was found to nitride considerably less under the same conditions. Reduction of both metals under H2 flames was minimal, though the degree of reduction of the nitrided nickel samples was much higher. The present work lays the groundwork for future study of these surface processes and their mechanisms.