Ferrothermal reduction of iron(III)phosphate insulating layers in soft magnetic composites

ABSTRACT

In modern AC technologies, improving the power efficiency of soft magnetic core materials is a key factor. Powder metallurgy offers a promising alternative for these applications: Soft Magnetic Composites are compacted iron-based powders, each iron particle being electrically insulated from its neighbours by a superficial layer. Accordingly, the thermal stability of the insulating layers used plays an essential role, because the stresses and defects introduced by pressing must be relieved by heat treatment. The thermal stability of FePO₄, which is a common insulating barrier, is limited. In the present study, the degrading mechanism was investigated using a mixture of high purity iron powder and FePO₄·2H₂O. The samples were characterised using a wide variety of analytical methods (DTA/TG, ATR-IR, XRD and XPS). The results show that a ferrothermal reduction takes place, the base material of SMCs – metallic Fe – acting as a reducing agent.

KEYWORDS:

• SMCs
• insulating layer
• FePO₄
• thermal degradation
• ferrothermal reduction

Acknowledgement

We acknowledge the financial support and the provision of the powder materials from Miba Sinter Austria GmbH, Vorchdorf, Austria. We would also like to thank the Fachbereich Röntgenzentrum [grant number E057-04] and the Analytical Instrumentation Center [grant number E057-05] of the TU Wien for carrying out the XRD and XPS measurements.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Notes on contributors

K. Ouda

K. Ouda studied Technical Chemistry at Technische Universität Wien (Vienna University of Technology), Vienna Austria. Hehas been investigating magnetic components since 2016. From 2017 - 2020 he was project assistant at the Powder Metallurgy Research Group, TU Wien: Institute of Chemical Technologies and Analytics. He received the PhD degree from TU Wien in September 2020.

H. Danninger

H. Danninger is full professor of Chemical Technology of Inorganic Materials at Technische Universität Wien (Vienna University of Technology), Vienna, Austria. From 2011 to 2019 he was also Dean of the Faculty of Technical Chemistry. He has been active in powder metallurgy for more than 40 years and is author/co-author of 500+ publications as well as several books and book chapters. From 2009 to 2020 he was chairman of the“Gemeinschaftsausschuss Pulvermetallurgie”, the PM association of the German-speaking countries. He holds honorary doctoral degrees of Technical University Cluj-Napoca (Romania), Universidad Carlos III de Madrid (Spain) and Universitatea din Craiova (Romania) and is Fellow of APMI and EPMA. In 2020 he was awarded the “Ivor Jenkins Medal” of IOM3.

C. Gierl-Mayer

C. Gierl-Mayer was born in Styria, Austria, in1969. He studied Technical Chemistry at TU Wien, got his Master in 1996 and his PhD in 2000 from TU Wien. After 3 years in private research institute (ofi-Austrian Research Institute of Chemistry and Technology) he re-joined the powder metallurgy group of Prof. Herbert Danninger assenior researcher. He got his habilitation in 2019 for “Thermoanalytical Investigation of Interactions between Powder Metallurgy Steels and the Atmosphere during Sintering”, and became Associate Professor in 2019. He is currently leading the research group Powder Metallurgy at TU Wien, Institute of Chemical Technologies and Analytics. His publication record is about 260 publications in journals and conference proceedings, 4 book chapters and 7 patents.

R. Hellein

R. Hellein Studied Technical Chemistry at Vienna University of Technology with PhD in the field of “Co-sintering ofcemented carbides” (Institute of Chemical Technologies and Analytics). 2016 he joined Miba Sinter Austria GmbH as R&D Engineer Materials & Processing Technology. From 2018 he has been Team leader for Material Development, R&D Sinter Group.

A. Müller

A. Müller He studied MechanicalEngineering and Economics at Vienna University of Technology with a PhD thesis in the field of RFID Technology. In 2006 he started at Miba SinterAustria GmbH as Development engineer; from 2008 he was teamleader in the area of R&D. In 2013 he became Manager R&D: AdvancedEngineering, and since 2016 he has been Head of R&D Miba Sinter Group.