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Synthesis, morphology, thermal stability and magnetic properties of α″-Fe16N2 nanoparticles obtained by hydrogen reduction of γ-Fe2O3 and subsequent nitrogenation

Dirba, I. and Schwöbel, C. A. and Diop, L. V. B. and Duerrschnabel, M. and Molina-Luna, L. and Hofmann, K. and Komissinskiy, P. and Kleebe, H.-J. and Gutfleisch, O. (2017):
Synthesis, morphology, thermal stability and magnetic properties of α″-Fe16N2 nanoparticles obtained by hydrogen reduction of γ-Fe2O3 and subsequent nitrogenation.
In: Acta Materialia, Elsevier Science Publishing, pp. 214-222, 123, ISSN 13596454,
[Online-Edition: http://dx.doi.org/10.1016/j.actamat.2016.10.061],
[Article]

Abstract

Typical synthesis of α″-Fe16N2 nanoparticles involves reduction of iron oxides by hydrogen at elevated temperatures which is disadvantageous due to the particle coalescence. Here we report on a process for reduction of iron oxides at elevated pressures and show that by increasing hydrogen pressure from atmospheric to 53 MPa, it is possible to reduce the reaction temperature from 663 K down to 483 K, resulting in phase-pure α-Fe nanoparticles without noticeable particle growth. By subsequent nitrogenation in an ammonia flow, fine, 99% phase-pure α″-Fe16N2 nanoparticles could be synthesized. The reduction temperature and the respective particle size has a significant influence on the nitrogenation step. α″-Fe16N2 nanoparticles exhibit semi-hard magnetic properties with Ms(0) = 215 Am2 kg−1, μ0Hc = 0.22 T, TC = 634 K and exchange stiffness Ac = 6.84 pJ m−1, Aa,b = 7.53 pJ m−1. Synthesis conditions, microstructure, chemical composition and thermal stability of the nanoparticles are systematically studied and correlated with the observed magnetic properties.

Item Type: Article
Erschienen: 2017
Creators: Dirba, I. and Schwöbel, C. A. and Diop, L. V. B. and Duerrschnabel, M. and Molina-Luna, L. and Hofmann, K. and Komissinskiy, P. and Kleebe, H.-J. and Gutfleisch, O.
Title: Synthesis, morphology, thermal stability and magnetic properties of α″-Fe16N2 nanoparticles obtained by hydrogen reduction of γ-Fe2O3 and subsequent nitrogenation
Language: English
Abstract:

Typical synthesis of α″-Fe16N2 nanoparticles involves reduction of iron oxides by hydrogen at elevated temperatures which is disadvantageous due to the particle coalescence. Here we report on a process for reduction of iron oxides at elevated pressures and show that by increasing hydrogen pressure from atmospheric to 53 MPa, it is possible to reduce the reaction temperature from 663 K down to 483 K, resulting in phase-pure α-Fe nanoparticles without noticeable particle growth. By subsequent nitrogenation in an ammonia flow, fine, 99% phase-pure α″-Fe16N2 nanoparticles could be synthesized. The reduction temperature and the respective particle size has a significant influence on the nitrogenation step. α″-Fe16N2 nanoparticles exhibit semi-hard magnetic properties with Ms(0) = 215 Am2 kg−1, μ0Hc = 0.22 T, TC = 634 K and exchange stiffness Ac = 6.84 pJ m−1, Aa,b = 7.53 pJ m−1. Synthesis conditions, microstructure, chemical composition and thermal stability of the nanoparticles are systematically studied and correlated with the observed magnetic properties.

Journal or Publication Title: Acta Materialia
Volume: 123
Publisher: Elsevier Science Publishing
Uncontrolled Keywords: Reduction, Nanoparticles, Permanent magnets, Fe16N2, Magnetic properties
Divisions: 11 Department of Materials and Earth Sciences
11 Department of Materials and Earth Sciences > Earth Science
11 Department of Materials and Earth Sciences > Earth Science > Geo-Material-Science
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences > Material Science > Advanced Electron Microscopy (aem)
11 Department of Materials and Earth Sciences > Material Science > Advanced Thin Film Technology
11 Department of Materials and Earth Sciences > Material Science > Functional Materials
Date Deposited: 11 Nov 2016 09:18
Official URL: http://dx.doi.org/10.1016/j.actamat.2016.10.061
Identification Number: doi:10.1016/j.actamat.2016.10.061
Funders: I. D. thanks the BMBF for financial support within the project 03X3582., The authors thank the LOEWE project RESPONSE funded by the Ministry of Higher Education, Research and the Arts (HMWK) of the Hessen state., The transmission electron microscope used in this work was partially funded by the German Research Foundation (DFG/INST163/2951).
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