Study of Phase Transformation Processes Occurring in the Nanocrystalline Iron/Ammonia/Hydrogen System by the Magnetic Permeability Measurement Method

Abstract

Phase transformations over a nanocrystalline iron catalyst in the nitriding process were carried out at 350 °C and under atmospheric pressure. The process was conducted under conditions of changing nitriding potential both during the nitriding and reduction of iron nitrides. These processes were monitored by measuring the magnetic permeability and changes of mass and reaction gas composition. Four stages of nitriding were observed and ascribed to the following general schematic reactions:The measurements of magnetic permeability revealed that the magnetic properties of the investigated samples strongly depended on the nitriding degree and can be described with linear equations of two variables. For γ′-Fe 4 N, the value of magnetic permeability was 1.280 times larger than for the iron catalyst, while for ε-Fe x N, it was more than 3 times smaller. However, in the case of the smallest nanocrystallites both in the process of iron nitriding and reduction of iron nitrides, the magnetic permeability did not change with the nitriding degree. It was also claimed that the composition of iron nitrides, concentrations of nitrogen in iron nitrides, and the magnetic permeability depend on the direction of the reaction (nitriding or reduction). A hysteresis phenomenon was observed.

Mechanical and Magnetic Investigations of Balls Made of AISI 1010 and AISI 1085 Steels after Nitriding and Annealing

“…The composition of the obtained iron nitrides depends on t nitriding temperature and the nitrogen potential [19,20]. Arabczyk et al [21] annealed nanocrystalline iron catalyst in an NH3/H2 atmosphere at 350 °C with a varying nitrog potential value during both nitriding and iron nitride reduction. During the process, t authors recorded a change in the magnetic permeability of the created nitride phase Tests showed that the magnetic permeability of γ′-Fe4N was 1.280 times higher than th of an iron catalyst, while that of ε-FexN was more than 3 times lower.…”

“…The composition of the obtained iron nitrides depends on the temperature and the nitrogen potential [19,20]. Arabczyk et al [21] annealed a stalline iron catalyst in an NH3/H2 atmosphere at 350 °C with a varying nitrogen l value during both nitriding and iron nitride reduction. During the process, the recorded a change in the magnetic permeability of the created nitride phases.…”

Phase Transformations of Iron Nitrides during Annealing in Nitrogen and Hydrogen Atmosphere

“…The first such research was conducted by Lehrer, who nitrated iron powder in a stream of a flowing mixture of ammonia and hydrogen [11]. Moszy ńska et al and Arabczyk et al demonstrated that during nitriding, phase transformations in the iron nitride layer can be induced by changing the value of the nitrogen potential [12,13].…”