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Ceramic matrix nanocomposites containing graphene possess superior mechanical properties. However, these nanocomposites are very difficult to be prepared using the conventional methods due to severe grain growth and simultaneous degradation of the graphene at high sintering temperatures and long dwell time. Herein, the dense ZrO2/rGO (reduced graphene oxide) nanocomposites are successfully fabricated by flash sintering of the green compacts consisting of ZrO2 nanoparticles and graphene oxide (GO) at 893–951℃ in merely 5 seconds under the alternating current (AC) electric fields of 130–150 V cm−1. The GO can be in situ thermal reduced during the flash sintering. The as‐prepared ZrO2/rGO nanocomposites exhibit excellent mechanical properties. This study presents a green and simple approach to fabricate the dense ceramic matrix nanocomposites reinforced with graphene at low temperatures in a short time. [ABSTRACT FROM AUTHOR]

Fabrication of dense KNN‐based lead‐free piezoelectric ceramics at low temperatures in short time through a cost‐effective way remains a challenge. Herein, this challenge could be addressed by using reactive flash sintering. It is demonstrated that the phase transformation of KNbO3‐NaNbO3 into (K,Na)NbO3 and densification occur simultaneously during the flash event. Most importantly, ZrO2 doping can greatly decrease the onset flash temperature, which is ascribed to the increased conductivity of sample. In addition, the current limit has a significant effect on the phase transformation and densification. The flash‐sintered KNN ceramics exhibit the good ferroelectric and piezoelectric properties. Furthermore, the ZrO2 doped and undoped KNN ceramics show a comparable coercive field Ec, which may be related to the residual point defects after the flash. Besides the Joule heating, the avalanche generation of point defects is suggested to be responsible for the ultrafast solid‐state reaction and densification rates. [ABSTRACT FROM AUTHOR]

Preparation of Gd 2 Zr 2 O 7 nanoceramics using a simple and low energy-consuming approach is significant for their wide range of applications. In this work, flash sintering (FS) and two-step flash sintering (TSFS) were first utilized to prepare Gd 2 Zr 2 O 7 nanoceramics. The effects of electric field intensity and current limit on the densification and grain growth were investigated. The grain size was decreased with the increase of electric field intensity. Meanwhile, both grain size and density were increased with the increase of current limit. The Gd 2 Zr 2 O 7 nanoceramics with an average grain size of 98 nm and a relative density of 92.8% were prepared by FS. By contrast, the Gd 2 Zr 2 O 7 nanoceramics with the higher relative densities of 96.3–97.5% and the smaller average grain sizes of 85–90 nm were prepared by TSFS. Compared to FS, TSFS can achieve suppressed grain growth and fast densification. The as-prepared Gd 2 Zr 2 O 7 nanoceramics showed excellent hardness and fracture toughness. The sample breakage caused by current localization can be avoided by controlling the current ramp after the occurrence of the flash event. [ABSTRACT FROM AUTHOR]

A simple and low-energy-consuming approach for preparing ceramic nuclear waste forms is greatly preferred for disposal of ever-increasing amounts of radioactive nuclear wastes. Herein, simulated radionuclide Ce could be rapidly incorporated into Gd 2 Zr 2 O 7 ceramic via flash sintering technique. Under an electric field of 250 V/cm, Gd 2 Zr 2−x Ce x O 7 (0.0 ≤x ≤ 1.2) waste forms with a single phase of defect-fluorite were flash sintered at relatively low temperatures of 889–997 °C in 60 s. The onset temperature of flash sintering was decreased with the enhancement of Ce content. Furthermore, the density and grain size of Gd 2 Zr 2−x Ce x O 7 waste forms were increased with the increase of the current limit. The nearly full dense Gd 2 Zr 2−x Ce x O 7 waste forms were flash sintered at a current limit of 200 mA. The normalized leaching rates of Gd, Ce, and Zr in Gd 2 Zr 0.8 Ce 1.2 O 7 after 28 d were 6.5475 × 10−5, 1.1624 × 10−7, and 1.1613 × 10−7 g·m−2·d−1, respectively, which exhibited a good chemical durability. • Gd 2 Zr 2−x Ce x O 7 waste forms are rapidly prepared by flash sintering. • Rapid solid reaction and densification occurs simultaneously in flash sintering. • Oxygen vacancies are formed in the flash sintering of Gd 2 Zr 2 O 7 and CeO 2. • Current limit has a significant effect on grain size and densification. • Gd 2 Zr 2−x Ce x O 7 waste forms exhibit good chemical durability. [ABSTRACT FROM AUTHOR]

The flash-sintering behavior of Al 2 O 3 -GdAlO 3 -ZrO 2 powders with a eutectic composition was investigated. The flash-sintered bulks contained two distinct regions: a normally sintered region and a channel region. The Al 2 O 3 -GdAlO 3 -ZrO 2 eutectic microstructure observed in the channel region was caused by current localization. We suggest that the eutectic temperature is reached locally in some regions during flash sintering, thus leading to the formation of a eutectic microstructure. The produced eutectic microstructure exhibited high hardness (17.7 GPa) and relatively high fracture toughness (4.3 MPa m1/2). The results suggest that the current localization that occurs in flash sintering can be used to prepare eutectic ceramics. [ABSTRACT FROM AUTHOR]

• Gd 2 Zr 2 O 7 nanopowders are prepared by the polyacrylamide gel method. • Gd 2 Zr 2 O 7 nanopowders show the excellent sinterability. • The particle size can be controlled by the mole ratio of acrylamide/Gd. • Larger mole ratio of acrylamide/Gd leads to the better dispersion of nanoparticles. • It presents an industrially feasible method for preparing nanopowders. Well-crystallized and good-dispersed Gd 2 Zr 2 O 7 nanopowders with defect-fluorite structure are successfully prepared by the polyacrylamide gel method. The mole ratio of acrylamide/Gd and calcination temperature have the significant effects on the phase composition, particle size, and agglomeration degree of the Gd 2 Zr 2 O 7 nanopowders. The sintering behaviors of the as-prepared Gd 2 Zr 2 O 7 nanopowders are investigated at temperatures of 1200−1500 °C. The Gd 2 Zr 2 O 7 nanopowders can be sintered into dense ceramics with a high relative density of 98 % at 1500 °C for 2 h. Moreover, the defect-fluorite phase of Gd 2 Zr 2 O 7 transforms to pyrochlore phase of Gd 2 Zr 2 O 7 with the increase of sintering temperature. In addition, the two-step sintering is performed to prepare the Gd 2 Zr 2 O 7 nanoceramics using the as-prepared Gd 2 Zr 2 O 7 nanopowders as starting materials. This work presents a simple and industrially feasible approach for preparing the Gd 2 Zr 2 O 7 nanopowders with excellent sinterability. [ABSTRACT FROM AUTHOR]

Lead-free Bi 0.5 Na 0.5 TiO 3 piezoelectric ceramics were successfully prepared by reactive flash sintering of Bi 2 O 3 -NaCO 3 -TiO 2 mixed powders, where phase transformation and densification occurred simultaneously. The influence of electric field strength, current density and holding time at constant current state on the phase transformation and densification were investigated. The current density had a significant influence on the extent of phase transformation and densification. The holding time had no influence on the phase transformation, but had an important effect on crystallinity of sample. The sintered bulks exhibited the maximum polarization P m of 16.8 μC/cm2, remanent polarization P r of 9.6 μC/cm2, coercive field E c of 29 kV/cmm, maximum electric-field-induced strain of 0.053 %, and piezoelectric coefficient d 33 of 85 pC/N. The reactive flash sintering can prepare the dense and single-phase ceramics from multiphase precursor powders in one step of flash, providing a new way for rapid production of ceramic materials. [ABSTRACT FROM AUTHOR]

The flash sintering behavior of Al 2 O 3 /reduced graphene oxide (rGO) composites was investigated. rGO was used as a composite component and a conductive additive. Under the electric fields of 250–400 V cm−1, the flash event occurred at extremely low temperatures of 236–249 °C. The current density limit played a significant role in the degree of densification. A larger current density resulted in a higher density of the sample. However, current densities larger than 33.33 A cm−2 resulted in broken samples because of the localization of high current density coupled with the formation of hot spots. Flash sintering at a furnace temperature of 800 °C, electric field of 300 V cm−1 and current density limit of 33.33 A cm−2 produced nearly completely dense Al 2 O 3 /rGO composites. In addition to the current limit, the furnace temperature is also a key parameter that controls the degree of densification to achieve "safe" flash sintering. [ABSTRACT FROM AUTHOR]