ORALS

SESSION: SISAMFriPM1-R3 E: Complexity in materials	Kobe International Symposium on Science of Innovative and Sustainable Alloys and Magnets (5th Intl. Symp. on Science of Intelligent and Sustainable Advanced Materials (SISAM))
Fri Oct, 25 2019 / Room: Dr. Christian Bernard
Session Chairs: Mariana Calin; Session Monitor: TBA

15:15: [SISAMFriPM108]
Continuous 3D graphene-like networks formation from cellulose nanofibers in ceramic matrices
Andraz Kocjan¹ ; Ana Lazar² ; Eduardo Ruiz Hitzky³ ; Bernd Wicklein⁴ ; ¹Jozef Stefan Institute, Ljubljana, Slovenia; ²Jožef Stefan Institute, Ljubljana, Slovenia; ³Instituto de Ciencia de Materiales de Madrid (ICMM), Consejo Superior de Investigaciones Científicas (CSIC), Madrid, Spain; ⁴Instituto de Ciencia de Materiales de Madrid (ICMM), Consejo Superior de Investigaciones Cientificas (CSIC), Madrid, Spain;
Paper Id: 18 [Abstract]

Establishing a 3D electrically percolating network in an insulating ceramic matrix is key to numerous engineering and functional applications. Using hydrophobic carbon nanofillers like graphene or carbon nanotubes is tempting, but still results in suboptimal performance due to processing challenges including colloidal instabilities in aqueous media. Here, we demonstrate an alternative, sustainable way by a small addition of cellulose nanofibers (CNF), which render highly homogeneous aqueous ceramic dispersions due to the increased hydrophilicity character and facilitates green machining of the consolidated green bodies. During sintering the natural CNF`s [1] can be in situ transformed into graphene-like sheets connected to a 3D network enhancing both the transport and the mechanical properties of sintered Al2O3 and yttria-stabilised ZrO2 (YSZ) ceramic matrices [2] [3]. The advantage presented here is the colloidal processing in water of CNF hydrogels with ceramic powder suspensions, which guarantees uniform and homogeneous properties from the bulk scale down to the nanoscale. The network architecture of the few-layered graphene (FLG) sheets also permits the decoupling of electrical and thermal conductivities, which represents a major obstacle in attaining efficient thermoelectric materials. The microstructure of the resulting materials was characterised by electron microscopy and spectroscopy (STEM/EELS), while the electrical and dielectrical properties were analysed by impedance spectroscopy. The materials showed high electrical conductivity at only 2 % initial CNF content, while the FLG-YSZ nanocomposites exhibited mixed ionic-electronic conduction at a��1% CNF, which is interesting for electrode materials in solid-oxide fuel cells. Besides the transport properties, the incorporated CNF improve the (green) mechanical properties and also enable the use of technologically important machining methods for electro-conductive ceramics. We envisage that our results can advance the processing science and technology to provide the improved hierarchical graphene composite materials needed for advanced applications in fields like energy and telecommunications.

References:
[1] B. Wicklein, A. Kocjan, G. Salazar-Alvarez, F, Carosio, G. Camino, M. Antonietti and L. BergstrA�m, Thermally insulating and fire-retardant lightweight anisotropic foams based on nanocellulose and graphene oxide, Nature. Nanotech. 10 (2015) 277a��84.
[2] A. Kocjan, R. Schimdt, A. Lazar, J. Prado-Gonjal, J. KovaA�, M. Logar, F. j. Mompean, M. Garcia-Hernandez, E. Ruiz-Hitzky, B. Wicklein, In situ generation of 3D graphene-like networks from cellulose nanofibres in sintered ceramics, Nanoscale. 10 (2018) 10488a��97.
[3] A. Kocjan, B. Wicklein, E. Ruiz-Hitzky, Patent PCT/EP2017/078239.

SESSION: SISAMSatPM1-R3 H: Characterisation	Kobe International Symposium on Science of Innovative and Sustainable Alloys and Magnets (5th Intl. Symp. on Science of Intelligent and Sustainable Advanced Materials (SISAM))
Sat Oct, 26 2019 / Room: Dr. Christian Bernard
Session Chairs: A. Lindsay Greer; Session Monitor: TBA

14:25: [SISAMSatPM106] Invited
Consolidation and Characterization of Ferrite-Based Hybrid Magnets: Towards Rare-Earth-Free Magnets for Energy Storage
Petra Jenus¹ ; Andraz Kocjan² ; Claudio Sangregorio³ ; Michele Petrecca⁴ ; César De Julian Fernandez⁵ ; Blaž Belec⁵ ; Spomenka Kobe⁶ ; ¹Jožef Stefan Institute, Ljubljana, Slovenia; ²Jozef Stefan Institute, Ljubljana, Slovenia; ³ICCOM-CNR, Sesto Fiorentino, Italy; ⁴Dept. of Chemistry, University of Florence and ICCOM - CNR and INSTM, Sesto Fiorentino, Italy; ⁵IMEM-CNR, Parma, Italy; ⁶Josef Stefan Institute, Ljubljana, Slovenia;
Paper Id: 97 [Abstract]

In the last years, much effort has again been devoted to the research of ferrite-based permanent magnets due to the so-called rare-earth crisis.[1],[2] In particular, a quest to enhance ferrites' BHmax, is still underway.[3] Large BHmax values are found in magnets combining substantial magnetisation at remanence (Mr) with high coercivity. Both parameters are influenced by materials properties, such as crystalline and shape anisotropy and particle' size.<br />Here, the influence of composition, particle size, sintering conditions, and exposure to the external magnetic field before compaction on microstructure and consequently, magnetic properties of strontium ferrite (SFO)-based hybrid composites will be presented. <br />Powders' mixtures consisted of commercial SFO powder consisting of micron-sized, isotropic particles, or hydrothermally (HT) synthesised SFO with hexagonally-shaped platelets with a diameter of 1 micron and thickness up to 90 nm, and a soft magnetic phase in various ratios. Powders were sintered with spark plasma sintering (SPS) furnace. Starting powders and hybrid magnets were examined by means of phase composition (XRD) and microstructure (TEM, SEM). Their magnetic properties were evaluated with vibrating sample magnetometer (VSM), permeameter and by single-point-detection (SPD) measurements. <br />Depending on the concentration and composition of the soft phase, the MR of the composite can be altered. Application of the external magnetic field before the consolidation induces the anisotropy in commercial, and HT synthesised SFO, leading to the increase in the Mr of hybrid magnets [4]. Moreover, sintering with SPS promotes the alignment of HT synthesised SFO particles in the direction of the applied pressure, which is also the direction of SFOs' easy axis. Thus the enhancement in MR is perceived leading to the Mr/Ms higher than 0.8. Besides, after SPS, almost no grain growth was observed, which is beneficial for exploiting advantages of nanosized-induced phenomena also in bulk sintered samples. <br />This work received financial support from the European Commission through the project AMPHIBIAN (H2020-NMBP-2016-720853).

References:
[1] J. M. D. Coey, Permanent magnets: Plugging the gap, Scr. Mater., vol. 67, no. 6, pp. 524-529, 2012.\n[2] M. Stingaciu, M. Topole, P. McGuiness, and M. Christensen, Magnetic properties of ball-milled SrFe12O19 particles consolidated by Spark-Plasma Sintering, Sci. Rep., vol. 5, p. 14112, 2015.\n[3] R. Skomski and J. M. D. Coey, Magnetic anisotropy: How much is enough for a permanent magnet? Scr. Mater., vol. 112, pp. 3-8, 2016.\n[4] P. Jenuš et al., Ferrite-Based Exchange-Coupled Hard-Soft Magnets Fabricated by Spark Plasma Sintering, J. Am. Ceram. Soc., vol. 8, no. 37805, p. n/a-n/a, 2016