Abstract
Nitriding of nanocrystalline iron and reduction of nanocrystalline iron nitride with gaseous mixtures of hydrogen with ammonia were studied at 375 °C and atmospheric pressure using the chemical potential programmed reaction (CPPR) method coupled with in situ XRD. In this paper, a series of phase transitions occurring during the processes is shown, and a detailed analysis of the phase composition and the structure of the material is given. The influence of a variable nitriding potential on the lattice parameters of α-Fe, γ′-Fe4N, and ε-Fe3-2N phases is shown. The α phase interplanar space changes irrelevantly in the one phase area but decreases linearly with average increases in crystallite size when α→γ′ transformation occurs. The nanocrystallite size distributions (nCSDs) were determined, with nCSD of the α phase for nitriding and nCSD of the ε phase for reduction. The reduction of the ε phase can occur directly to α or indirectly with an intermediate step of γ′ formation as a result of ε→γ′→α transformations. The determining factor in the reducing process method is the volume of ε phase nanocrystallites. Those with V < 90,000 nm3 undergo direct transformation ε→αFe(N), and V > 90,000 nm3 transforms to αFe(N) indirectly. It was determined at what value of nitriding potential which fraction of the ε phase nanocrystallites starts to reduce
Highlights
Published: 31 January 2021The main application of nanocrystalline iron doped with hardly reducible metal oxides is its usage as the most common ammonia synthesis catalyst
We presented the chemical method chemical potential programmed reaction (CPPR) for determining the critical nitriding potential at which the nanocrystallite fraction undergoes aa crystal crystal transition, transition, which which is based on on one one analytical analytical fraction of of concrete concrete size size undergoes is based method, namely in situ method, namely in situ XRD measurements
The phenomenon of ammonia decomposition was omitted in the calculations due to the low temperature of the process, and the small amount of solid state substrate in comparison with the quantity of ammonia in the reaction chamber. This is the first work where the results of in situ XRD measurements coupled with the CPPR method are the basic method
Summary
The main application of nanocrystalline iron doped with hardly reducible metal oxides (ncFe) is its usage as the most common ammonia synthesis catalyst. This catalyst served as a basic model system for research, leading to understanding of the mechanisms of ammonia synthesis and decomposition [1,2,3,4,5,6,7]. There is a view that these nanocrystalline iron nitrides formed in industrial reaction conditions are the real catalyst in the ammonia synthesis reaction by the creation of highly disordered crystal structures [15].
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
