4.7 Article

Dense strontium hexaferrite-based permanent magnet composites assisted by cold sintering process

Journal

JOURNAL OF ALLOYS AND COMPOUNDS
Volume 917, Issue -, Pages -

Publisher

ELSEVIER SCIENCE SA
DOI: 10.1016/j.jallcom.2022.165531

Keywords

Rare-earth-free permanent magnets; Hexaferrites; Cold sintering process; Composites; Magnetic properties

Funding

  1. Ministerio Espaol de Ciencia e Innovacin (MICINN) , Spain [MAT2017-86540-C4-1-R, RTI2018-095303-A-C52]
  2. European Commission [720853]
  3. MICINN through the Juan de la Cierva program [FJC2018-035532-I]
  4. Alexander von Humboldt foundation, Germany
  5. Comunidad de Madrid, Spain [2017-t2/IND5395]
  6. MICINN through the Ramon y Cajal contract [RYC-2017-23320]

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The use of rare-earth-based permanent magnets is crucial for technological development. This study introduces a cold sintering process (CSP) for sintering composite permanent magnets based on strontium ferrite (SFO). The results show that control of composition and grain size enables the production of attractive magnetic properties in the sintered magnets.
The use of rare-earth-based permanent magnets is one of the critical points for the development of the current technology. On the one hand, industry of the rare-earths is highly polluting due to the negative environmental impact of their extraction and, on the other hand, the sector is potentially dependent on China. Therefore, investigation is required both in the development of rare-earth-free permanent magnets and in sintering processes that enable their greener fabrication with attractive magnetic properties at a more competitive price. This work presents the use of a cold sintering process (CSP) followed by a post annealing at 1100 degrees C as a new way to sinter composite permanent magnets based on strontium ferrite (SFO). Composites that incorporate a percentage <= 10% of an additional magnetic phase have been prepared and the morphological, structural and magnetic properties have been evaluated after each stage of the process. CSP induces a phase transformation of SFO in the composites, which is partially recovered by the post thermal treatment improving the relative density to 92% and the magnetic response of the final magnets with a coercivity of up to 3.0 kOe. Control of the magnetic properties is possible through the composition and the grain size in the sintered magnets. These attractive results show the potential of the sintering approach as an alternative to develop modern rare-earth-free composite permanent magnets.(c) 2022 The Author(s). Published by Elsevier B.V. CC_BY_NC_ND_4.0

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