Reactive flash sintering (RFS) in oxide systems: kinetics and thermodynamics
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Reactive flash sintering (RFS) in oxide systems: kinetics and thermodynamics Rachman Chaim1,* 1
Department of Materials Science and Engineering, Technion – Israel Institute of Technology, 32000 Haifa, Israel
Received: 23 June 2020
ABSTRACT
Accepted: 8 September 2020
The literature of the reactive flash sintering (RFS) in multi-component oxide systems nowadays consists of different types of binary phase diagrams, which were used here for analysis. Kinetic analysis of the reaction and simultaneous densification of the product phase via the liquid-film-assisted flash sintering is in agreement with a few seconds time scale of RFS. Capillarity and osmotic driving forces under the applied electric field are responsible for the ultrafast reaction and compound formation. Thermodynamic analyses of model systems with characteristic eutectic and peritectic reactions and congruent solidification show that all systems have to undergo local melting for the observed ultrafast reaction and the resultant microstructures. While the liquid film subjected to the external electric field has a transient nature, its homogenous composition is in the equilibrium state. The fragile nature of the major oxide melts imposes crystallization and growth during the cooling with partition coefficient of 1. Therefore, equilibrium phase diagrams can be used to predict the final product phases and microstructures according to the precursor powder composition and the flash conditions.
Published online: 24 September 2020
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Springer Science+Business
Media, LLC, part of Springer Nature 2020
Introduction Flash sintering (FS) is a relatively novel technique by which the application of high electric field at moderate temperatures leads to ultrafast densification of many oxides within a few seconds. Reactive flash sintering (RFS) is an adaptation of FS to simultaneous formation and densification of compounds from a mixture of their precursor oxides powders in the
green state. Although this technique was heavily applied in the recent years, it goes back to Mishra et al. who used TiO2 additives to enhance densification of alumina by plasma activated sintering [1]. The more novel attempts by reactive flash sintering were aimed toward fabrication of ceramic alloys and composites [2–10], oxide compounds [11–20], and recently high-entropy oxides [21–23] and alloys with eutectic microstructures [24]. Several investigations by different groups were conducted on flash sintering
Handling Editor: David Cann.
Address correspondence to E-mail: [email protected]
https://doi.org/10.1007/s10853-020-05320-z
J Mater Sci (2021) 56:278–289
of the Al2O3–TZP (tetragonal zirconia polycrystals) (3YSZ–ZrO2 with 3 mol% Y2O3) two-phase alloys [2–5]. All these studies reached the conclusion that pure Al2O3 is almost impossible to densify by flash sintering. However, increasing amounts of 3YSZ assisted densification of the oxide composites at lower flash temperature. M’Peko [5] reported a critical volume fraction of 30 vol% 3YSZ that needed to proceed the flash sinteri
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