| 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: 18/SISAM/Regular (Oral) SCHEDULED: 15:15/Fri. 25 Oct. 2019/Dr. Christian Bernard 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. |
