Flash‐sintering of magnesium aluminate spinel (MgAl₂O₄) ceramics

Abstract

The sintering behavior of commercially available MgAl2O4 spinel was investigated under DC electric field in a range of 0 and 1000 V/cm. Flash‐sintering results in densification close to theoretical density at 1410°C under the DC field of 1000 V/cm, in comparison to the higher sintering temperature of 1650°C in case of conventional sintering. It was observed that the fields less than 750 V/cm had no significant effect on the densification behavior. An abrupt increase in power dissipation was observed corresponding to the occurrence of the flash event. A significant enhancement in grain size was observed in case of flash‐sintered dense spinel samples. The gradual increase in the specimen conductivity observed in the electric field‐assisted sintering (FAST) regime led to Joule heating within the specimen. The increased specimen temperature triggered further increment of current and Joule heating, resulting in the immediate densification.

Consolidation of undoped, monoclinic zirconia polycrystals by flash sintering

“…The steep increase in the specimen current indicated the onset of the flash sintering in the ZrO 2 specimen. The hybrid behavior where the specimen sinters initially by FAST and then transitions to flash has been reported in the flash sintering of dielectric materials such as MgO doped Al 2 O 3 , Y 2 O 3 , and MgAl 2 O 4 . After the isothermal sintering for 3 hours, the linear shrinkages of more than 20% were observed in both of the materials; the relative density of the specimens was about 98% just after the isothermal sintering for 3 hours.…”

Suppression of nitridation of yttria‐doped zirconia during flash sintering

“…[2][3][4][5][6][7][8][9] Unfortunately, flash sintering does not provide excellent uniformity and flashed compacts tend to possess heterogeneous grain sizes between the cathode and anode areas. [10][11][12] For example, Yoshida and coworkers analyzed the grain size distribution of flash-sintered MgAl 2 O 4,13 showing that its heterogeneous grain size was closely related to the diffusion of Mg ions caused by the direct-current (DC) electric field. Other research has shown that grain orientation occurs during sintering under an electric field, 14 with the grain orientation tending to align along the preferred flow path of oxygen ions in undoped ZrO 2 .…”

Reactive flash sintering: MgO and α‐Al2O3 transform and sinter into single‐phase polycrystals of MgAl2O4

“…Flash sintering was first reported in 2010, where 3 mol% stabilized zirconia (3YSZ) was shown to sinter in <5 seconds at a furnace temperature of 850°C at field of 120 V/cm . Since then the method has been shown to apply to various ceramic materials, including, among others, titania (TiO 2 ), yttria (Y 2 O 3 ), Mg‐doped alumina (Al 2 O 3 ), zinc oxide (ZnO), and magnesium aluminate spinel (MgAl 2 O 4 ) …”