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Gas-phase triggered phase evolution in pressure-less sintered LiF doped Mg-Al spinel.

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Title: Gas-phase triggered phase evolution in pressure-less sintered LiF doped Mg-Al spinel.
Authors: Müller, Mathis M.1 (AUTHOR) mathis_m_mueller@yahoo.de, Stricker, Kerstin1 (AUTHOR), Kleebe, Hans-Joachim1 (AUTHOR)
Source: Journal of the European Ceramic Society. Aug2021, Vol. 41 Issue 10, p5400-5404. 5p.
Subjects: Spinel, Gas phase reactions, Atmospheric pressure, Electron microscopy, X-ray microscopy
Abstract: • LiF is one of the most promising sintering aid to fully densify spinel ceramics. However, the phase evolution is not completely understood. • A number of interactions were postulated, including a wetting de-wetting mechanism and the formation of transient phases like LiAlO2 or MgF2. • The formation of LiAlO2 was shown for the first time by means of electron microscopy in combination with x-ray diffraction methods. • Moreover, the formation of a second generation of Mg-Al spinel was shown to be the result of a recombination of solid LiAlO2 and a gas phase. • Shown results will influence further efforts in this system since a gaseous phase hinders full densification and thus full transparency. Within the studies of the LiF-MgAl 2 O 4 system, a dissolution - reprecipitation process is postulated at high pressure synthesis, involving LiAlO 2 and MgF 2 as transient phases. Heating experiments at atmospheric pressure, combined with a dedicated sample geometry enabled the identification of LiAlO 2 and MgO via XRD and, for the first time, with electron microscopic examinations. Moreover, it is shown that a second generation of spinel precipitates as the result of a gas-phase reaction. The involvement of a gaseous phase is seen as the major reason, why it seems impossible to produce transparent spinel in a pressure-less sintering regime. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
Description
Abstract:• LiF is one of the most promising sintering aid to fully densify spinel ceramics. However, the phase evolution is not completely understood. • A number of interactions were postulated, including a wetting de-wetting mechanism and the formation of transient phases like LiAlO2 or MgF2. • The formation of LiAlO2 was shown for the first time by means of electron microscopy in combination with x-ray diffraction methods. • Moreover, the formation of a second generation of Mg-Al spinel was shown to be the result of a recombination of solid LiAlO2 and a gas phase. • Shown results will influence further efforts in this system since a gaseous phase hinders full densification and thus full transparency. Within the studies of the LiF-MgAl 2 O 4 system, a dissolution - reprecipitation process is postulated at high pressure synthesis, involving LiAlO 2 and MgF 2 as transient phases. Heating experiments at atmospheric pressure, combined with a dedicated sample geometry enabled the identification of LiAlO 2 and MgO via XRD and, for the first time, with electron microscopic examinations. Moreover, it is shown that a second generation of spinel precipitates as the result of a gas-phase reaction. The involvement of a gaseous phase is seen as the major reason, why it seems impossible to produce transparent spinel in a pressure-less sintering regime. [ABSTRACT FROM AUTHOR]
ISSN:09552219
DOI:10.1016/j.jeurceramsoc.2021.03.059