Reactive flash sintering of SrFe12O19 ceramic permanent magnets

Contents lists available at ScienceDirect JournalofAlloysandCompounds journal homepage: www.elsevier.com/locate/jalcom ResearchArticle ReactiveflashsinteringofSrFe 12 O 19 ceramicpermanentmagnets A.F.Manchón-Gordón a, ⁎ ,P.E.Sánchez-Jiménez a,b ,J.S.Blázquez c ,A.Perejón a,b , L.A.Pérez-Maqueda a, ⁎ a Instituto de Ciencia de Materiales de Sevilla, ICMSE CSIC-Universidad de Sevilla, C. Américo Vespucio 49, Sevilla 41092, Spain b Departamento de Química Inorgánica, Facultad de Química, Universidad de Sevilla, Sevilla 41012, Spain c Dpto. Física de la Materia Condensada, ICMSE-CSIC, Universidad de Sevilla, P.O. Box 1065, 41080 Sevilla, Spain article info Article history: Received19February2022 Receivedinrevisedform20June2022 Accepted4July2022 Availableonline5July2022 Keywords: Reactiveflashsintering Strontiumferrite Permanent magnets Mössbauerspectroscopy Magnetic properties abstract Reactive flash-sintering technique has been used in order to obtain strontium ferrite magnets from a mixtureofSrCO 3 andFe 2 O 3 commercialpowders.ThistechniqueallowspreparingsinteredSrFe 12 O 19 ata furnacetemperatureofjust973Kduringjust2minbyapplyingamodestfieldof40Vcm -1 ,insteadofthe conventionalsinteringprocessemployedinferritemagnetmanufacturingthatdemandshightemperature andlongdwelltimes.Analysisofstructuralandmagneticpropertieswereperformedasafunctionoftime in which the flash event was held. Mössbauer spectra show the existence of five different kinds of local environments,confirmingtheformationofstrontiumhexaferrite.Theresultingsamplesexhibitcomparable magnetic properties to the state-of-the-art ferrite magnets. In particular, produced samples reach a coer- civityof0.4Tandaspecificsaturationmagnetizationof70Am 2 kg -1 . ©2022TheAuthor(s).PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBY-NC-ND license(http://creativecommons.org/licenses/by-nc-nd/4.0/). 1. Introduction Magneticmaterialsand,particularly,permanentmagnetsplaya keyroleinmanyapplicationsincludingmotors,recordingmediaor high frequency devices, such as millimeter wave absorbers and ro- tators [1–3].Onthequesttofindalternativestotherare-earthbased permanent magnets, hexaferrites are one of the most important alternatives families, reaching an annual production of one million tons [4–7]. Among them, one of the most studied compounds is strontiumhexaferrite,SrFe 12 O 19 ,duetothecompetitiveadvantages it offers including availability, price and environmental friendliness during both mining and production [6]. This hexaferrite, with magnetoplumbitestructure,exhibitssuperiorchemicalstability [8], outstandingmagnetocrystallineanisotropyandrelativelyhighCurie temperature [9]. ThepreparationtechniqueusedtoproduceSrFe 12 O 19 playsakey role in determining the magnetic properties and structure of the finalproduct.Theconventionalandearliestmethodtopreparethis compoundisbycalcinationandsubsequentsinteringofamixtureof oxides and carbonates in a furnace at 1573 K [10]. However, this method consumes extensive energy and time, and produces large particles,whichdecreasethehardmagneticbehaviorofthesample [6]. For that reason, different chemical synthesis approaches have been considered to prepare nanostructured ferrites, such as sol-gel [11] and hydrothermal [12] followed by calcination at high temperatures or precipitation in molten salt at temperatures up to 1473 K [13].Thesemethodsusuallyrequiretheuseofsolventsand relatively long or complex preparation procedures. Moreover, me- chanochemical synthesis has been also proposed for preparing this compound with high coercivity and magnetic saturation [14]. However, it requires of high milling times ( > 5+ h) [14–16] that promote iron contamination from the milling media limiting the energy-saving and cost-reducing. In this sense, flash sintering, a relativelynoveltechniquebywhichtheapplicationofelectricfield at moderate temperatures leads to the fast densification of most oxides within a few seconds [17], has attracted the interest of the scientificcommunity.ThemainadvantagesofFSwheniscompared toconventionaltechniquesarethesignificantlyreducedprocessing timesandtemperatures,whichallowsforsubstantialenergysaving [18] and, at the same time, results in reduced grain size and vola- tilizationlosses [19].Moreover,ithasbeenrecentlyshownthatitis possible to simultaneously induce the reaction and densification of compounds from a mixture of their precursors oxides powders in green state [20]. This new methodology has been denominated reaction (or reactive) flash sintering (RFS) and has been used to pre- paredifferentmaterials.ThemorenovelattemptsbyRFShavebeen aimed towards preparation of a wide range of ceramic composites [21–23], oxide compounds [18,24] and recently, even high-entropy oxides [25–27]. https://doi.org/10.1016/j.jallcom.2022.166203 0925-8388/©2022TheAuthor(s).PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBY-NC-NDlicense(http://creativecommons.org/licenses/by-nc-nd/4.0/). ]] ]] ]]]]]] ⁎ Correspondingauthors. E-mail addresses: [email protected] (A.F.Manchón-Gordón), [email protected] (A. Perejón), [email protected] (L.A. Pérez-Maqueda). JournalofAlloysandCompounds922(2022)166203

Reactive flash sintering of SrFe12O19 ceramic permanent magnets

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reactive flash sintering

strontium ferrite

permanent magnets

mã ssbauer spectroscopy

magnetic properties