Lixandru, A. (2018)
Recycling of Nd-Fe-B permanent magnets by hydrogen processes.
Technische Universität Darmstadt
Dissertation, Erstveröffentlichung
Kurzbeschreibung (Abstract)
This thesis is based on the work carried out since January 2014 as a Ph.D. student in the Functional Materials department at Technische Universität Darmstadt. In the first part of my thesis, different waste streams of electrical and electronic equipment from an industrial recycling plant were analyzed in order to localize, identify and collect rare-earth permanent magnets of Nd-Fe-B type. This particular type of magnets were mainly found in hard disk drives from laptops and desktop computers, as well as in loudspeakers from compact products such as flat screen TVs, PC screens, and laptops. The study includes a systematic survey of the chemical composition of the Nd-Fe-B magnets found in the selected waste streams, which illustrates the evolution of the Nd-Fe-B alloys over the years. The study also provides an overview over the types of magnets that are integrated in different waste electric and electronic equipment. After localizing, identifying and recovering the rare-earth permanent magnets from waste electrical and electronic equipment, these magnets were processed together with other Nd-Fe-B scrap magnets from electric motors with a hydrogen based recycling process (hydrogen decrepitation (HD) and hydrogenation disproportionation desorption and recombination (HDDR) processes). The effects of the main HDDR processing parameters: hydrogen pressure, hydrogen desorption rate and temperatures on the magnetic properties of the recycled materials have been investigated systematically and are presented in the second section of the chapter 4. The optimum hydrogen pressures required for the complete disproportionation of the various magnet compositions were determined. It was found that a hydrogen heat treatment composed of two steps (780 °C and 840 °C) and a moderate desorption rate can be used for the magnets having a higher Dy and Co content to obtain high quality anisotropic HDDR powders. In addition to this section, it was performed a study where it was investigated the effects of increasing the Dy content on the processing parameters of the HDDR process. The variation of the magnetic properties for the magnets with different Dy contents processed at different hydrogen pressure, temperature and hydrogen desorption rate are presented in this study. The obtained recycled powders by HD and by HDDR were consolidated by either sintering, spark plasma sintering or bonding with epoxy resin. For the scrap magnets with a low content of Dy and Co, a better recovery of the magnetic properties (above 90%) was achieved compared with the magnets from electric motors (high Dy and Co) where the recovery rate is ~60%. For these magnets a “refreshing” of the recycled powders with 10% Nd90Al10 and Pr75Cu6.25Co18.75 was applied. Different post sintering treatments were applied for these recycled magnets in order to equally distribute the fresh added powder. All these treatments are presented in this study.
Typ des Eintrags: | Dissertation | ||||
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Erschienen: | 2018 | ||||
Autor(en): | Lixandru, A. | ||||
Art des Eintrags: | Erstveröffentlichung | ||||
Titel: | Recycling of Nd-Fe-B permanent magnets by hydrogen processes | ||||
Sprache: | Englisch | ||||
Referenten: | Gutfleisch, Prof. Dr. O. | ||||
Publikationsjahr: | 2018 | ||||
Ort: | Darmstadt | ||||
Verlag: | Technische Universität Darmstadt | ||||
Datum der mündlichen Prüfung: | 17 Januar 2018 | ||||
URL / URN: | http://tuprints.ulb.tu-darmstadt.de/7392 | ||||
Kurzbeschreibung (Abstract): | This thesis is based on the work carried out since January 2014 as a Ph.D. student in the Functional Materials department at Technische Universität Darmstadt. In the first part of my thesis, different waste streams of electrical and electronic equipment from an industrial recycling plant were analyzed in order to localize, identify and collect rare-earth permanent magnets of Nd-Fe-B type. This particular type of magnets were mainly found in hard disk drives from laptops and desktop computers, as well as in loudspeakers from compact products such as flat screen TVs, PC screens, and laptops. The study includes a systematic survey of the chemical composition of the Nd-Fe-B magnets found in the selected waste streams, which illustrates the evolution of the Nd-Fe-B alloys over the years. The study also provides an overview over the types of magnets that are integrated in different waste electric and electronic equipment. After localizing, identifying and recovering the rare-earth permanent magnets from waste electrical and electronic equipment, these magnets were processed together with other Nd-Fe-B scrap magnets from electric motors with a hydrogen based recycling process (hydrogen decrepitation (HD) and hydrogenation disproportionation desorption and recombination (HDDR) processes). The effects of the main HDDR processing parameters: hydrogen pressure, hydrogen desorption rate and temperatures on the magnetic properties of the recycled materials have been investigated systematically and are presented in the second section of the chapter 4. The optimum hydrogen pressures required for the complete disproportionation of the various magnet compositions were determined. It was found that a hydrogen heat treatment composed of two steps (780 °C and 840 °C) and a moderate desorption rate can be used for the magnets having a higher Dy and Co content to obtain high quality anisotropic HDDR powders. In addition to this section, it was performed a study where it was investigated the effects of increasing the Dy content on the processing parameters of the HDDR process. The variation of the magnetic properties for the magnets with different Dy contents processed at different hydrogen pressure, temperature and hydrogen desorption rate are presented in this study. The obtained recycled powders by HD and by HDDR were consolidated by either sintering, spark plasma sintering or bonding with epoxy resin. For the scrap magnets with a low content of Dy and Co, a better recovery of the magnetic properties (above 90%) was achieved compared with the magnets from electric motors (high Dy and Co) where the recovery rate is ~60%. For these magnets a “refreshing” of the recycled powders with 10% Nd90Al10 and Pr75Cu6.25Co18.75 was applied. Different post sintering treatments were applied for these recycled magnets in order to equally distribute the fresh added powder. All these treatments are presented in this study. |
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URN: | urn:nbn:de:tuda-tuprints-73922 | ||||
Sachgruppe der Dewey Dezimalklassifikatin (DDC): | 600 Technik, Medizin, angewandte Wissenschaften > 620 Ingenieurwissenschaften und Maschinenbau | ||||
Fachbereich(e)/-gebiet(e): | 11 Fachbereich Material- und Geowissenschaften 11 Fachbereich Material- und Geowissenschaften > Materialwissenschaft 11 Fachbereich Material- und Geowissenschaften > Materialwissenschaft > Fachgebiet Funktionale Materialien |
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Hinterlegungsdatum: | 10 Jun 2018 19:55 | ||||
Letzte Änderung: | 10 Jun 2018 19:55 | ||||
PPN: | |||||
Referenten: | Gutfleisch, Prof. Dr. O. | ||||
Datum der mündlichen Prüfung / Verteidigung / mdl. Prüfung: | 17 Januar 2018 | ||||
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