ISIJ International
Online ISSN : 1347-5460
Print ISSN : 0915-1559
ISSN-L : 0915-1559
Regular Article
Reduction and Nitriding Behavior of Hematite with Ammonia
Naoto YasudaYuuki MochizukiNaoto TsubouchiTomohiro Akiyama
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2015 Volume 55 Issue 4 Pages 736-741

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Abstract

This paper describes the reduction and nitriding behavior of hematite with ammonia in the context of ironmaking. The effects of temperature and ammonia concentration on the products were investigated. In the temperature range from 793 to 863 K, hematite was directly reduced to magnetite by ammonia (1/2Fe2O3 + 1/9NH3 → 1/3Fe3O4 + 1/6H2O + 1/18N2). The ammonia started to decompose at 873 K, triggered by the generation of α-Fe. Magnetite was reduced mainly to iron by hydrogen generated from the decomposition of ammonia (1/3Fe3O4 + 4/3H2 → Fe + 4/3H2O). According to in-situ X-ray diffraction (XRD) measurements, α-Fe was immediately nitrided to an ε-Fe3-xN (0 ≤ x ≤ 1) phase, and the N/Fe atomic ratio decreased gradually with increasing temperatures. The rate of hematite reduction increased with the ammonia concentration for 5% to 20% NH3, but plateaus for NH3 concentrations greater than 20%. This was attributed to the mechanism of ammonia decomposition; the amount of hydrogen generated also plateaus at ammonia concentrations above 20%. The reduction rate was therefore limited by the rate at which hydrogen was generated during ammonia decomposition. The N content of the product was affected not only by the temperature but also by the nitriding potential (KN = PNH3/PH23/2). The nitriding potential increased with increasing ammonia concentrations and decreasing temperatures. The addition of nitrogen gas to the reactive gas inhibited ammonia decomposition and increased the nitrogen potential and N content of the product.

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© 2015 by The Iron and Steel Institute of Japan
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