Strategies to Prevent Carbon Contamination of Transparent Magnesium Aluminate Spinel during Spark Plasma Sintering
TALIMIAN A. 1, POUCLY V. 2,3, KLEMENT R. 1,5, M. BETLRÁN A. 4, MACA K. 2,3, GALUSEK D. 1,5
1 Centre for Functional and Surface Functionalised Glass, Alexander Dub?ek University of Tren?ín, Študentská 2, Trencin, Slovakia; 2 Central European Institute of Technology, Brno University of Technology, Purky?ova 123, Brno, Czechia; 3 Faculty of Mechanical Engineering, Brno University of Technology, Technická 2, Brno, Czechia; 4 Departamento de Ingeniería y Ciencia de los Materiales y del Transporte, Escuela Politécnica Superior, Universidad de Sevilla, 41011, Sevilla, Spain; 5 Joint Glass Centre of the IIC SAS, TnUAD and FChPT STU, Študentská 2, Trencin, Slovakia
Carbon contamination has been considered an inevitable aspect of producing transparent ceramics using spark plasma sintering which deteriorates the optical properties. Making the carbon contamination reactions thermodynamically unfavorable is a new strategy for improving the optical properties of transparent ceramics produced by spark plasma sintering. In the present work, two approaches were adopted to decrease the sintering temperature: (i) two-stage SPS, and (ii) LiOH as a sintering aid. The samples subjected to two-stage SPS in which slow heating was applied above the “critical temperature” showed limited carbon contamination. Although slow heating suppresses carbon contamination by eliminating the porosity at lower temperatures than conventional processes, two-stage SPS is a lengthy and energy inefficient process. The addition of LiOH reduces the activation energy of sintering of magnesium aluminate spinel from 790 kJ.mol−1 to 510 kJ.mol−1 and, hence, also the sintering temperature. The incorporation of lithium ions into the spinel structure changes the defects’ chemistry which promotes mass transfer through diffusion mechanisms. This approach thus prevents carbon contamination also in samples produced using single-step SPS with high heating rates. Doping with lithium also enhances the emission intensity of transition metal doped spinel and is beneficial to its photoluminescence properties.
Acknowledgement
This paper is a part of the dissemination activities of project FunGlass. This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 739566. Financial support of this work by the grants GA?R 20-14237S, MŠMT LTT18013 (Inter-Transfer), VEGA 2/0028/21 and APVV 0019-10 is gratefully acknowledged.