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Formation, stability, and presence of magnesium nitride in magnesium recycling processes

Christoph Bauer, Aberra Mogessie and Ulrike Galovsky

Abstract

In this study an attempt has been made to identify analytical methods for detecting magnesium nitride, and document in which part of the magnesium recycling process this phase is concentrated. The samples were taken from a continuous fluxfree recycling session, where an AZ91D magnesium alloy was remelted and purified by blowing nitrogen through the melt. Exothermic reactions took place when magnesium nitride reacted to ammonia and Brucite and also when aluminium nitride reacted to ammonia and Gibbsite in a moisture-bearing environment. Because of this, it was essential to avoid any contact with moisture during the whole sampling and preparation process. The samples were exclusively handled in an argon atmosphere. Due to their crystallinity and Raman activity the nitrides were detected with X-ray diffraction and Raman spectroscopy, respectively. With the scanning electron microscope it was difficult to analyze small concentrations of nitrides since large, stable crystals were absent and the carbon coating absorbs the nitrogen Kα line.

The Mg-alloy was found to be free of impurities. Although nitrides were expected to be concentrated in the slag because of their greater density, they were found adhering at the nitrogen bubbles and accumulating in the dross. Large amounts of oxides were concentrated in the slag.


1 Correspondence address: Mag. Christoph Bauer, Institute of Earth Sciences, Department of Mineralogy and Petrology, Karl-Franzens University of Graz, Universitätsplatz 2/II, A-8010 Graz, Tel.: +433163808717, Fax: +433163809865. E-mail:

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Received: 2004-09-16
Accepted: 2005-08-21
Published Online: 2013-03-01
Published in Print: 2006-02-01

© 2006, Carl Hanser Verlag, München