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This work presents a straightforward strategy for achieving specific overheating during flash experiments by adjusting the initial electrical parameters. To do that, an extensive experimental analysis was performed to evaluate the temperature evolution of dense ZnO specimens during controlled‐current ramping at different furnace temperatures, which in turn modified the initial electrical resistance of the sample. A detailed electrical explanation of controlled‐current ramp flash processes is provided and, for the first time, a practical equivalence between current‐ramp and temperature‐ramp flash methodologies is established. By parameterizing the experiments in terms of an effective power density, a consistent heating pattern following the blackbody radiation trend was identified, despite the different electrical characteristics of each experiment. Finally, a “flash heating map” is introduced, which can be used to determine the starting electrical parameters necessary to achieve a specific temperature increase, whether employing current or temperature ramps. [ABSTRACT FROM AUTHOR]

In this work, high-purity alumina ceramics were prepared by using two-step reverse polarity flash sintering (PR-FS). The effects of the time distribution between the first flash and the second flash on microstructure and hardness were studied. The results show that compared to the conventional DC flash sintered alumina, the RP–FS–ed samples exhibited more uniform-microstructure, finer grains, higher relative density, and higher hardness. The underlying mechanism for such more homogeneous microstructure was related to uniform distribution of point defects under effect of reverse polarity. Two-step reverse polarity flash sintering method offers a great potential in obtaining highly densified alumina ceramics with homogeneous microstructure. [ABSTRACT FROM AUTHOR]

In so-called Field Assisted Sintering Techniques such as Spark Plasma Sintering (SPS) or Flash Sintering (FS), ceramic powder compacts are densified at high sample temperature in the presence of an electrical field. The formation of a plasma is often discussed without actual evidence for its appearance. In this work, which is the first of two parts, the mechanisms of plasma formation as well as its properties under FS conditions were investigated. Field induced breakdown of various atmospheres was conducted by a DC-field (up to 350 V/cm) at temperatures between 1000 and 1500 °C. Experiments were conducted both with and without a sample mounted between the electrodes. Alumina, boron carbide and silicon carbide in green or sintered form were used as the samples. The electrical and optical properties of the plasma were characterised, and the early stages were visualised by high-speed camera recordings. The results showed that the breakdown is caused by a flashover mechanism and the conductance of the plasma under the present conditions was of the same order as the conductivity of a boron or silicon carbide green body. Plasma formation did not lead to extensive sintering but the plasma was able to infiltrate the green body and cause transfer of matter from the interior to the surface and beyond. Based on the present results, it seems unlikely that a gas plasma is formed under the normal conditions of SPS or FS. [ABSTRACT FROM AUTHOR]

Flash sintering was officially discovered about fifteen years ago as a ground-breaking method to consolidate ceramics in very short time at furnace temperature much lower than that used for conventional sintering. Since then, it has been applied to several ceramics and composites with the common feature of being characterized by a negative temperature coefficient for resistivity while few attempts have been made on materials with metal-like electronic conduction. In the present overview the results of the investigation carried out in the last years aiming at consolidating tungsten carbide and zirconium diboride by flash sintering are reported and the conditions for inducing a thermal runaway phenomenon like in other ceramics and understand the physical mechanisms behind the flash effect are analysed. The investigation allows to point out the importance of the fundamental processing variables like the applied pressure and voltage for obtain high density material. The key role of the starting particles' surface chemistry is identified to generate specific microstructures and determine peculiar physical and mechanical properties in the flash sintered ceramic. [ABSTRACT FROM AUTHOR]

Flash healing is a technique that uses power spikes to rapidly repair microcracks on ceramic surfaces. In this study, the microstructures of flash-healed Vickers-indented microcracks near the positive/negative electrodes under a DC electric field were examined by scanning transmission electron microscopy. The microstructural morphology near the positive electrode was almost identical to that of the microcracks located between both electrodes, as previously reported. However, a decrease in the degree of healing was observed near the negative electrode. This was attributed to the insufficient recovery of dislocations generated at the indentation state, which should have occurred in the initial stage of healing. The delay in dislocation recovery prevented contact between the inner surfaces of the microcracks and is possibly related to the increase in oxygen vacancies near the negative electrode. [ABSTRACT FROM AUTHOR]

Although flash sintering (FS) is an effective method for rapidly preparing ceramics, FS of non-oxide ceramics at room temperature (RT) has not yet been achieved. In this study, we developed a feasible method for FS of SiC at room temperature (RT). A dog-bone-shape SiC sample prepared without using any sintering aid achieved a relative density of 96.5 % after sintering in a low-pressure Ar atmosphere for 60 s. Arc heating, which was constrained by the height of an alumina plate fixed above the sample, increased the conductivity of the sample, which then reached the stable stage of FS. The sintered sample exhibited a typical 6H–SiC crystal structure, which was consistent with that of the raw powder. The proposed FS method, based on constraining the arc using an alumina plate under a low-pressure inert gas atmosphere, provides a reference for developing further advanced RT FS strategies for non-oxide ceramics with low conductivities at RT. [ABSTRACT FROM AUTHOR]

Flash sintering has been used to consolidate a wide range of ceramics and ceramic composites. However, flash sintering of ceramic nanocomposite with a substantial amorphous phase is rarely studied. Meanwhile, the effects of yttrium addition on the flash sintering behaviors and microstructures of ZrO2‐based ceramic nanocomposite remain unknown. Herein, ZrO2‐SiO2 crystalline‐amorphous ceramic nanocomposites (CACNs) with different contents of amorphous phase and two types of yttrium dopants were sintered by flash sintering. Results showed that the content of amorphous phase (SiO2) had significant effects on the flash sintering behavior. The CACN with 65 mol% SiO2 was nonflash sinterable due to the high electric resistivity of SiO2, whereas, the CACN with 45 mol% SiO2 can be flash sintered to high densification within 35 seconds. The flash‐sintered CACNs consisted of ZrO2 nanocrystallites distributed in an amorphous SiO2 matrix. Flash sintering enhanced the tetragonal‐to‐monoclinic phase transformation of ZrO2. In addition, influences of yttrium dopant on CACNs were also investigated. Yttrium dopants can rapidly dissolve in ZrO2 lattices and show a tetragonal phase stabilization effect during flash sintering. Firework‐like ZrO2 microcrystallites formed by dendritic growth were observed close to the cathode region, which was attributed to athermal electric field effects and the formation and aggregation of oxygen vacancies at the cathode region. The results would provide guidance for fabricating CACNs via flash sintering. [ABSTRACT FROM AUTHOR]

We present direct evidence, for the first time, for the flash‐induced generation of crystal defects in single‐crystal cubic zirconia. The defects are characterized by multiple techniques. The crystals were flashed and then cooled down to ambient temperature in Ar atmosphere to preserve the electronic conductivity from the steady state of flash. Transmission electron microscopy revealed colonies of defects. The crystal structure, the non‐stoichiometry, and the electronic structure of oxygen ions within these colonies were characterized. They consist of oxygen‐depleted compositions. Selected area electron diffraction revealed the structure of these zirconia suboxides to be epitaxially coherent with the parent cubic structure but with a smaller lattice parameter. Electron energy loss spectroscopy spectra showed the peak near 25 mV to shift toward metallic zirconium. The electronic conductivity of the flashed cubic zirconia is attributed to this suboxide phase. The phase also gave rise to new peaks in Raman spectroscopy. A surprising finding was the presence of a distinct, ∼30 nm thick layer of the suboxide on the surface of the crystal. The surface layer showed a high degree of oxygen deficiency. It was also epitaxial, but with an even smaller lattice parameter than the defect colonies underneath the surface. Mechanical polishing of the crystal to remove this surface layer gave a broad view of the interconnected network of defects across the entire specimen; the length scale of this network was about 0.2 mm. Recent work, where an overlay of a magnetic field caused the flash to migrate from a flashing surface into a free‐standing workpiece, suggests the presence of evanescent plasma, which may have a connection to this surface layer. [ABSTRACT FROM AUTHOR]

Flash sintering has evolved into touch‐free sintering, where free‐standing workpieces can be sintered without attaching electrodes. Instead, the flash is transmitted from the surface of a reactor into the workpiece with superimposition of a magnetic field. Thus, sintering now depends on two independent parameters: the current used to sustain the flash in the reactor and the current flowing through the induction coil. We present a first report on the influence of these two parameters on the quality of the sintered workpiece. The specimens were made from whiteware, consisting of aggregates of ceramic particles interspersed with particles of a glass phase. The results are presented in a map with the reactor current and the induction current as the control variables. Three regimes are identified: insufficient sintering, good sintering, and the formation of defects. The reactor current emerges as an important variable: densification is poor if it is too low, and defects form if it is too high, with high density achieved in the intermediate regime. High induction currents are needed to achieve good sintering. Touch‐free flash sintering has also been shown to sinter and at the same time transform powders of elemental oxides into a single‐phase multicomponent ceramic. [ABSTRACT FROM AUTHOR]

The densification of yttria-stabilized zirconia (YSZ) during flash sintering is strongly dependent on the amount of residual chlorine in the sintered bodies. The residual chlorine, present as a remnant from powder synthesis, hinders densification after it is trapped and vaporized in the rapidly closing pores, limiting the final density at around 87 – 93% of theoretical. We show that this phenomenon is likely to affect all YSZ powders synthesized from chloride precursors unless the residual chlorine is reduced to ≤ 0.03 wt% before the onset of the flash sintering. This can be universally achieved by thermal purification of green bodies at a high temperature or by chemical purification in ammonium hydroxide. Furthermore, added binder in commercially available Tosoh zirconia TZ-powders (TZ-3YB, TZ-3YB-E) helps to significantly reduce chlorine content during binder burnout which in turn allows flash sintering into a high density even without green body purification. [ABSTRACT FROM AUTHOR]

Lead‐based piezo‐ceramics like lead zirconate titanate (PZT) are a mainstay for many piezoelectric applications. However, lead oxide (PbO) evaporation during sintering poses a significant environmental challenge. Flash sintering (FS) is a novel technique that can densify ceramics in seconds and at a much lower furnace temperature. The liquid‐phase FS (LPFS) of PZT (Pb (Zr0.5Ti0.5) O3, with 3 wt.% Cu2O and PbO in the molar ratio of 1:4) is investigated in this work. Further, a comparison has been made among the lead loss, dielectric, and piezoelectric properties of flash‐sintered and conventionally liquid‐phase‐sintered PZT. It has been observed that the evaporation of PbO has been brought down 3–5 times by FS. The dielectric constant of LPFS PZT is significantly higher, especially at higher frequencies with lower dielectric loss. An enhanced piezoelectric coefficient in flash‐sintered PZT has also been observed. The LPFS of PZT shows that the lead loss can be brought down significantly with the added benefit of enhanced dielectric and piezoelectric properties. XRD and Rietveld analysis show an increase in tetragonality after FS in comparison with conventional sintering. XPS and ESR studies show a difference in defect concentration after FS in comparison with conventional sintering that is likely responsible for the enhanced dielectric and piezoelectric properties. [ABSTRACT FROM AUTHOR]

Highly conducting undoped ZnO ceramics were fabricated by flash sintering using commercial pure ZnO powder as a model system. The flash-sintered samples with diameters of 15 mm and heights of 2 mm exhibited relative densities ranging from 93.6% to 97.1% and room-temperature electrical conductivities between 205 and 590 S/cm. X-ray diffraction and Raman spectra indicated a high concentration of oxygen vacancies and zinc interstitials in the flash-sintered samples, increasing the carrier concentration. Detailed microstructural analyses show that clean grain boundaries and the morphology and distribution of impurities in flash-sintered samples are favorable for improving carrier mobility. Additionally, flash sintering has the advantage of reducing conditions, which reduces acceptor defects at ZnO grain boundaries, lowers Schottky barriers, and increases carrier mobility. The results show that flash sintering can synergistically enhance the carrier concentration and mobility in ZnO ceramics, making it a promising technique for fabricating highly conducting ZnO ceramics. [ABSTRACT FROM AUTHOR]

Flash sintering has been applied to various ceramics since it was first reported. However, the flash sintering of lead zirconate titanate (PZT) at room temperature has not been accomplished. In this study, flash sintering of PZT piezoelectric ceramics at room temperature was realised for the first time. Subsequent to surface treatment in a low-pressure environment, the sample was flash-sintered at a high voltage in air. The sample became dense rapidly during sintering. The results showed that after 300 s of sintering, the flash-sintered samples had a high density (98.1%) and d 33 values (273 pC/N). The d 33 is the highest compared with flash sintering of PZT through the furnace temperature of several hundred degree Celsius. Owing to the extremely short sintering time and the absence of heating devices, this method can greatly reduce energy consumption and lead to volatilisation, providing a new method for the rapid preparation of piezoelectric ceramics. [ABSTRACT FROM AUTHOR]

Low-consumption ceramics processing routes are expected to replace conventional ones due to environmental concerns. In this context, flash sintering is garnering interest because it allows dense ceramics to be obtained in just a few minutes and at relatively low temperatures. This is particularly interesting for sintering alkaline-based compounds due to the easy volatilization of these elements. In this work, current-controlled flash sintering is used to obtain potassium-sodium niobate (KNN)-based piezoceramics with refined microstructure and suitable stoichiometry, leading to improved functional properties. KNN-based materials are currently outstanding lead-free piezoceramics, with their properties highly sensitive to the proper construction of the polymorphic phase boundary, as in the case of the first promising composition (K 0.44 Na 0.52 Li 0.04)(Nb 0.86 Ta 0.10 Sb 0.04)O 3. Results of this work show that sintering parameters may determine the polymorphic behavior of this system, thereby evincing flash sintering allows polymorphic phase boundary to be fine-tuned. It is demonstrated that the convergence of microstructure refinement and compositional control holds the potential for enhancing properties through a proper electric current control during flash sintering. [ABSTRACT FROM AUTHOR]

Flash sintering can prepare ceramics in extremely short time, which can significantly improve fabrication efficiency and is promising for processing nuclear waste. Herein, simulated TRPO waste (16 components containing low-melting components) was directly added into as-prepared Gd 2 Zr 2 O 7 , and a series of waste forms were successfully prepared by flash sintering at 950 °C for only 3 min. It was demonstrated that samples prepared by flash sintering showed almost no loss of simulated low-melting-point radionuclide, while samples prepared by pressureless sintering have certain losses of simulated low-melting-point radionuclide. The 42 d leaching rates of Mn, Ce, Nd, and Gd of the flash sintered samples were 8.21 × 10−5, 5.31 × 10−7, 4.04 × 10−6, and 1.04 × 10−6 g m−2 d−1, respectively, showing excellent chemical durability. This work proves that flash sintering technology can effectively suppress nuclear leaks during immobilization, along with excellent chemical durability. [ABSTRACT FROM AUTHOR]

In this paper, 3YSZ/alumina composites containing different content of alumina with different forms (powders and whiskers, respectively) were fabricated by flash sintering. The flash sintering behavior and mechanical properties of the composites were characterized and were compared with those prepared by conventional sintering. The onset temperature of the 3YSZ/alumina whiskers composites was lower than that of the 3YSZ/alumina powders composites with identical alumina content. The reason can be attributed to electrical conductivity; the conductivity of the former was lower than that of the latter. For the 3YSZ/alumina powders composites which can be densified by conventional sintering method, their relative density, Vickers hardness and fracture toughness were comparable to those prepared by flash sintering. While for the 3YSZ/alumina whiskers composites where constrained sintering existed, the flash sintering method revealed obvious advantage over the conventional sintering. A relative density of 94.5 %, hardness of 13.77 GPa and fracture toughness of 5.36 MPa m1/2 were obtained for the flash sintered 3YSZ/30 vol% alumina whisker composites. In contrast, the relative density, hardness, and fracture toughness of the conventional sintered ones were 86.4 %, 11.60 GPa and 4.82 MPa m1/2, respectively. [ABSTRACT FROM AUTHOR]

In this work, we have expanded the possibilities of the multiphase-flash sintering (MPFS) technique by investigating several configurations that involve multiple dogbone specimens (ranging from 1 to 3) and multiple phases (also ranging from 1 to 3). Unlike the traditional MPFS approach using complex 3D or cylindrical samples, this new method allows for a direct comparison with the established conventional flash sintering technique. Our experimental results with dense 8-mol% Yttria-stabilized zirconia demonstrate a significant reduction in the onset temperature as the number of phases and dogbones increases. Building on these findings, we achieved the preparation of pure bulk specimens of SrFe 12 O 19 for the first time through reactive multiphase-flash sintering. [ABSTRACT FROM AUTHOR]

A rapid, cost-effective and eco-friendly approach for fabricating SiC using Si particles derived from Si scrap is highly recommended from both economic and environmental standpoints. Herein, we demonstrate the fabrication of β-SiC effectively in argon atmosphere at 1500°C by utilizing combustion synthesis followed by flash sintering in a single-step experiment for the first time. Synthesis of β-SiC was relied on exothermic reaction between Si and C elements present in the powder compact whereas densification was accomplished eventually through flash sintering. In addition, the effects of different flash sintering conditions on the properties of β-SiC are examined with and without Y 2 O 3 sintering additive. A high relative density of 85% was realized when a current density of 60 mA/mm2 was applied for 60 min with Y 2 O 3 addition. This novel one-step fabrication approach has the potential to reduce production cost of β-SiC significantly and has both commercial and environmental advantages. [ABSTRACT FROM AUTHOR]

Flash sintering is a novel technique that involves the sintering of green bodies in few seconds at relatively very low furnace temperature as compared to what is required to sinter them conventionally. In the present work, we flash‐sintered composites of 3 mol.% yttria‐stabilized zirconia (3YSZ) and graphene oxide (GO). The main aim of this work was to see if the decomposition or oxidation of carbonaceous materials can be prevented by the high heating rates during flash sintering and if composites of 3YSZ and GO can be processed in air. 3YSZ with 5, 10, and 20 wt.% of GO were prepared and subjected to constant heating rate flash‐sintering experiments where electric field was applied across the sample right from room temperature. A DC electric field of 100 V/cm was applied and the current density was set to 100 mA/mm2. It was observed that GO decomposed from the surface of the samples; however, in the core of samples, GO was retained but was reduced to graphite. Grain size of the 3YSZ phase increased with increase in the GO content, whereas the hardness decreased. It was observed that the composites containing carbonaceous reinforcements need to be flash sintered in inert atmosphere to realize their full potential. [ABSTRACT FROM AUTHOR]

We conducted in-situ X-ray diffraction to study the crystalline phase evolution in hydroxyapatite-zirconia composites during both conventional and flash sintering processes. Additionally, we examined the thermal history and microstructure of the composite under these sintering conditions. Despite both sintering methods reaching similar average temperatures, they yielded distinct results in terms of crystalline phase composition and microstructure. In the flash sintered samples, we observed a complete transformation of hydroxyapatite into α- tricalcium phosphate and a complete tetragonal to cubic phase transition in zirconia. Conversely, the conventionally sintered samples remained practically stable. Notably, the flash sintered samples exhibited needle-like microstructures, which were absent in their conventionally sintered counterparts. This divergence suggests that the application of an electric field plays a role in generating athermal effects during the sintering of hydroxyapatite-zirconia composites. [ABSTRACT FROM AUTHOR]

We have studied the flash sintering behavior of high bandgap ceramics (halides) namely Lithium Fluoride (LiF), Magnesium Fluoride (MgF 2), and Sodium Chloride (NaCl). All three halides demonstrate flash sintering behavior albeit at elevated temperatures of ∼0.8 homologous temperature and a very high electric field. The achieved relative densities after flash sintering are 89 % for LiF, 88 % for MgF 2 , and 96 % for NaCl. Conductivity-temperature plots reveal a likely transition from ionic conduction to electronic conduction, exemplified by a substantial decrease in activation energy. Interestingly, despite their high bandgaps, the halides exhibit flash sintering and electronic conduction at the flash state. However, electronic conduction likely occurs due to electrochemical reduction. Evidence of electromigration is observed near the grain boundary triple points. This work also shows a likely correlation between band gap/electrode potential and onset electric field/homologous temperature during flash sintering for the first time. [ABSTRACT FROM AUTHOR]

We show that powder pressed specimens of nickel can be sintered to 99.96% density by injecting electrical current, without the use of a furnace. Full sintering could be accomplished in 10 to 52 s by changing the current rate from 5 to 1 A/s. In all instances, the samples sintered abruptly at a current density of ∼20 A mm−2. The grain size of the sintered samples was somewhat larger than the nickel powder particle size (∼60 μm vs. 40 μm). Tensile testing yielded a yield strength of 98 MPa, ultimate tensile stress of 323 MPa, and ductility of ∼17%. Four in‐operando measurements are reported: (i) sintering, (ii) the change in resistance with current density, (iii) the temperature, and (iv) electroluminescence. The change in resistance during flash sintering exhibited a high peak followed by a steep decline in resistance; the transient is attributed to the breakdown of particle–particle interface resistance. The same cycle repeated with the flash‐sintered, dense sample, did not show the spike, and gave reproducible results. The resistance data for these latter cycles, when viewed as a function of temperature exhibited sigmoidal behavior: initially lower, and then higher than the literature values. This unusual behavior reflects the influence of defects generated during flash. We have also measured the endothermic enthalpy, expressed by the difference between the in situ input electrical energy and the radiation, convection, and specific heat losses. Dividing by the formation energy of Frenkel pairs yields the concentration of defects, estimated to be 0.3–0.4 mol %. These concentrations are far above thermal equilibrium; it is concluded that flash of metals is a far from equilibrium phenomenon. [ABSTRACT FROM AUTHOR]

Flash sintering (FS) is a potentially rapid and low‐cost manufacturing technique for advanced ceramics. There are still many unknowns about ceramic FS, especially for highly conductive high‐temperature ceramics (HTC), which often display decreased bulk conductivity with increasing temperature. This study qualitatively characterizes the flash behavior of highly conductive HTC materials using zirconium nitride (ZrN) as an example. The effects of processing parameters (e.g., DC voltage/electrical field strength, voltage ramp rate, post‐flash holding time, mechanical pressure, sample milling, and choice of electrode materials) on ZrN flash behavior are also qualitatively studied and linked to samples microstructure and hardness. It is observed that best densification was achieved using 5 min Spex‐milled ZrN powder under 25 MPa of applied pressure and constant 8 V DC. The potential mechanism for ZrN FS and the similarity and difference from FS of conventional oxides like YSZ have been proposed based on experimental observations, and the directions for future research are also pointed out. [ABSTRACT FROM AUTHOR]

The effects of MgO doping concentration on the sintering behavior of Al 2 O 3 ceramics in flash sintering were studied. The relative density, grain size and oxygen vacancies of the flash sintered samples doped with different amounts of MgO were characterized. The results showed that the relative density and grain size increased with MgO concentration up to 0.25 wt%, and then decreased with further increasing MgO content. These were coincident with the changes in oxygen vacancies in the flash-sintered samples. Flash sintering behaviors of 0.25 wt% MgO doped Al 2 O 3 disc were different from those in conventional sintering, where the grain growth was inhibited when the MgO content is 0.25 wt%. The results can be explained by the fact that the higher oxygen vacancies in the flash sintered sample than that in the conventional sintered one, due to the applied electric field/current in flash sintering enhancing the solubility of MgO in Al 2 O 3. [ABSTRACT FROM AUTHOR]

BiFeO 3 is a promising multiferroic material for versatile device applications due to its co-existence of magnetic (i.e., antiferromagnetic) and ferroelectric ordering at room temperature. While its functional properties have been extensively investigated, the exploration of its mechanical behavior was limited mostly to the thin-film form of BiFeO 3. In this work, we conducted in situ micropillar compression experiments to investigate the deformation behavior of La-doped BiFeO 3 (La-BFO) samples processed by both conventional and flash sintering methods. The conventionally sintered La-BFO exhibited limited deformability at room temperature and 450 °C. In contrast, the deformability of the flash-sintered La-BFO specimens was substantially improved by nearly 100% at both testing temperatures. Detailed post-mortem studies suggest that preexisting dislocations and wide anti-phase boundaries introduced during flash sintering can toughen flash-sintered La-BFO by easing dislocation migration and ferroelastic domain switching. This study provides a fresh perspective to design an advanced multifunctional system with improved mechanical properties. • Flash sintering introduced high population of pre-existing dislocations and anti-phase boundaries into La-BFO. • The flash sintered La-BFO deformed at room temperature exhibited an over 100% deformability enhancement. • At 450 °C, the flash-sintered La-BFO outperformed the conventionally sintered counterpart by showing plastic deformability. [ABSTRACT FROM AUTHOR]

(Ca, Ta) co-doped TiO 2 ceramics were successfully prepared using flash sintering technology, and the effects of oxygen vacancies on the rapid densification and giant dielectric properties were studied. The results suggest that the maximum volume fraction of oxygen vacancies in flash-sintered samples is approximately 10%. Oxygen vacancies decrease the barrier energy level of atomic diffusion and provide convenient diffusion channels, resulting in rapid densification of the sample within 24 min at 1100 °C. All flash-sintered samples exhibit high relative density, exceeding 95%. Oxygen vacancies promote the electron-pinning defect dipole effect at low temperatures. As the temperature increases, carriers such as oxygen vacancies move to the grain boundary, forming an internal barrier layer capacitance effect. The optical dielectric constant reaches 7.25 × 104, and the dielectric loss drops to 0.09. Oxygen vacancy play an important role in both flash sintering technology and the giant dielectric properties of co-doped TiO 2 ceramics. [ABSTRACT FROM AUTHOR]

This review discusses the groundbreaking advancements in electric current-assisted sintering techniques, specifically Flash Sintering (FS) and Ultrafast High-Temperature Sintering (UHS), for their application in Solid Oxide Fuel Cells (SOFCs). These innovative sintering methods have demonstrated remarkable potential in enhancing the efficiency and quality of SOFC manufacturing by significantly lowering sintering temperatures and durations, thereby mitigating energy consumption and cost. By providing a detailed overview of the mechanisms, process parameters, and material characteristics associated with FS and UHS, this paper sheds light on their pivotal role in the fabrication of SOFC components such as electrolytes, electrodes, multilayered materials, and interconnect coatings. The advantages, challenges, and prospective opportunities of these sintering technologies in propelling SOFC advancements are thoroughly assessed, underlining their transformative impact on the future of clean and efficient energy production technologies. [ABSTRACT FROM AUTHOR]

A flash sintering method at room temperature based on combined power supplies is proposed in this paper. Flash sintering is performed in two steps. First, a high voltage is used to break down the sample and then disconnect the power supply. Second, a low-voltage power supply is used to provide a large current to densify the sample. The method does not require changing the properties of the material or the sintering atmosphere. In addition to reducing the capacity of the required power supply, there is no need for external auxiliary equipment. Different types of high-voltage breakdown are also studied. The temperature and grain size corresponding to different currents of low-voltage flash sintering are studied. The results show that the sintered ZnO ceramics reach 98.5% relative density. A possible mechanism of flash sintering using combined power supplies is analysed. [ABSTRACT FROM AUTHOR]

ZrO2-SnO2 nanocomposite was produced in nanofiber (NF) form in three different ratios by volume (%v/v) by electro-spinning technique. Microstructure and morphological characterization of NFs reveal the ternary system of ZrO2-SnO2-ZrSnO4. Also, when the composition ratio of NFs was changed, both the band gap and the electrical (flash) sintering (ES or FS) event affected the temperature and sinter time variation. FS experiments were used at 3.77mA/mm² current cutoff under thermal (844-878°C) and electric field (420V/mm). Highly dense nanocomposites were obtained in less than 80 seconds with a maximum power absorption of 1.58W/mm³. Thanks to the low sintering temperature and time, the nanostructured surface morphology of the nanocomposites was obtained. In addition to the FS process, ZrO2-SnO2-ZrSnO4 CNFs were sintered for 1 hour at 1200°C using the conventional sintering (GS) method. This study investigated the effects of the difference in sintering techniques on the sintering temperature and time, as well as on properties such as density and hardness. As the amount of Sn (%v/v) in the composition increases, the density increases, but the hardness value decreases. It has been proven that in ZrO2-SnO2-ZrSnO4 CNFs, denser and harder compositions are obtained with FS treatment compared to GS. When all these results are evaluated, it is believed that the synthesized nanocomposites can be used as a valid candidate in the health system such as dental implants due to their antimicrobial effect and non-toxicity in the model organism. [ABSTRACT FROM AUTHOR]

In this study, the effects of different sintering methodology on grain formation, density, and hardness of blended leach residue (B‐LR) pellets is investigated. For the first time, the flash sintering (FS) method, an environmentally friendly process, is used to make multiphase ceramic composites using B‐LR under 100 V/mm at 675∘$^\circ $C. The outcomes of this study revealed that the FS process is faster and more energy‐efficient than the conventional sintering (CS) methods performed at 800°C for 4 h. The formation of abnormal grain growth is prevented by FS in B‐LR material composition after it is exposed to a max power absorption 61.4 mW/mm3 and whole FS is completed less than 100 s. Besides, FS method does not lead to any melting on grain boundaries due to excessive joule heating, compared with the CS sample. It is noted that FS also provides better density and hardness values for this material system along with compositional integrity in this multiphase system. The significant outcome of this study is reducing lead volatility and emission by decrement on the sintering temperature. Ultimately, this study has planned the practicality of reusage and recycle of this material with green, safe, and eco‐friendly methods. [ABSTRACT FROM AUTHOR]

This study estimated the amount of oxygen deficiency in SrTiO 3 polycrystals that were flash sintered under direct current (DC) and alternating current (AC) electric fields, mainly by using the fine structural change of the Ti L 23 -edges collected by electron energy-loss spectroscopy. The DC electric field corresponded to formation of the maximum amount of oxygen deficiency at approximately δ = 0.07 as SrTiO 3−δ , which corresponds to a lattice expansion of roughly 0.1% as a lattice constant of SrTiO 3. Furthermore, the oxygen deficiency was distributed unevenly. The formation of dislocation networks in DC-flash-sintered SrTiO 3 polycrystals might be related to the lattice strain field caused by this nonuniform oxygen deficiency. In contrast, an AC electric field did not correspond to the oxygen deficiency of SrTiO 3 , which is similar to the results in thermally sintered SrTiO 3 polycrystals. [ABSTRACT FROM AUTHOR]

Generally, a high temperature (>1100°C) is required to sinter Lead Zirconate Titanate (PZT) ceramics. Such a high sintering temperature results in significant lead oxide evaporation which is a major environmental problem due to its toxicity. In this work, we have performed flash sintering of Lead zirconate Titanate (Pb (Zr 0.5 Ti 0.5) O 3)) using a novel setup and compared the phase and microstructural evolution, dielectric, piezoelectric properties and lead loss with conventionally sintered Lead zirconate Titanate (PZT). The lead oxide evaporation has been reduced by 5–10 times compared to conventionally sintered PZT. Results also show that the flash-sintered samples' dielectric constant is about ∼ six times higher than the conventionally sintered samples with similar dielectric loss. Ferroelectric and piezoelectric properties of flash sintered PZT on the other hand are lower than conventionally sintered PZT. The mechanisms behind the anomalous properties are discussed using structural and microstructural observations. [ABSTRACT FROM AUTHOR]

In this paper, Bi 2 O 3 doped BaTiO 3 -0.01MgO-0.01Nb 2 O 5 ceramics are designed to increase dielectric constant, reduce dielectric loss and improve temperature dielectric stability through inducing defects, and are prepared by flash sintering method to inhibit the volatilization of Bi element and ensure the element ratio. The microstructure, polarization mechanisms, dielectric properties and conduction mechanism of the ceramics are studied. The doping of Bi 2 O 3 can enhance the relaxation behavior and dielectric properties. The defects evolution in BaTiO 3 -0.01MgO-0.01Nb 2 O-0.01Bi 2 O 3 ceramics are studied. The results show that the BaTiO 3 ceramics doped with different amounts of Bi 2 O 3 can form defect dipoles { [ Bi Ba ∙ ‐ Mg Ti ″ ‐ Bi Ba ∙ ] ×, [ Nb Ti ∙ ‐ V Ba ″ ‐ Nb Ti ∙ ] ×, [ Mg Ti ″ ‐ V O ∙ ∙ ] ×} and oxygen vacancy, which enhance the short-range transition within the grain and inhibit the movement of free electrons at the grain boundary. The ceramics have excellent room temperature properties, high dielectric constant (ε r = 2894) and low dielectric loss (tan δ < 0.03). The ceramics have superior temperature stability and satisfying the EIA X8R (Δ ε r / ε 25 ≤ ±15 %, over the temperature range from −55 °C to 150 °C). It is found that flash sintering can effectively guarantee the stoichiometric concentration of bismuth element and obtain good properties of ceramics. This study demonstrates the potential of Bi 2 O 3 doped BaTiO 3 -based ceramics synthetized by flash sintering as high-performance electronic device materials. [ABSTRACT FROM AUTHOR]

This study demonstrated the reactive flash sintering (RFS) for two powder mixtures: TiN-ZrN (both conducting) and AlN-TiN (TiN conducting but AlN insulating), targeting ternary metal nitrides (TMN) of Ti 0.5 Zr 0.5 N and Ti 0.5 Al 0.5 N, respectively. A constant volage and pressure (e.g., 8 V DC, ∼15 MPa) at room temperature triggered the flash (current density up to 27 A/mm2) without pre-heating, and the entire RFS process finished in a few minutes. For TiZrN, the flash was instantaneous whereas for TiAlN, there was a long incubation before the flash followed by a quick and dramatic flash. Both conventional ex situ XRD and in situ synchrotron study had been carried out. They showed a uniform Ti 0.57 Zr 0.43 N solution formed in RFS and persisted upon cooling, while (Ti, Al) N solid solution formed at high temperature was not stable and likely went through a very quick phase separation in the cooling process. The final products from RFS had been characterized using SEM/EDS for microstructure. Both TiZrN and TiAlN were dense. Distribution of Ti, Zr, and N was uniform for TiZrN; for TiAlN, Ti and N distribution was uniform, while association of Al with oxygen was observed. TGA-DSC revealed the onset oxidation temperature for TiZrN was comparable to TiN and ZrN, while it was higher by ∼200 °C for TiAlN, likely due to the formation of Al 2 O 3. In terms of mechanical properties such as hardness or fracture toughness, forming a single-phase solid solution (like TiZrN) does not offer obvious benefits. while large grain size from RFS seemed to be unfavorable. Future optimization of RFS condition and in-depth study by both experiments and simulation are needed to fully understand the composition-processing-structure-property relationships for such TMN from the reactive flash sintering process. [ABSTRACT FROM AUTHOR]

This study investigated the combination of Direct Ink Writing (DIW) and Flash Sintering of zirconia stabilized with 3 mol. % Y 2 O 3 (3Y-TZP). The samples were printed in two stacking configurations, and flash sintering was performed without current ramp control (FS) and using current ramp (CRFS) for comparison purposes. In both conditions, an electric field of 80 V cm−1 and a current density of 150 mA mm−2 were applied. The physical, microstructural, and mechanical properties of the printed samples were evaluated. The stacking configuration influenced both the grain size gradients and mechanical properties. Furthermore, controlling the current density ramp resulted in a slight homogenization of the grains' size across different regions of the sample (core, edge, and flat surfaces). The presence of zirconia polymorphs, such as ZrO 2 -t and ZrO 2 -c , as well as a distorted form of the tetragonal phase (ZrO 2 -t'), was observed in the samples. These phases were affected by both the printing strategy and the current ramp control during the flash sintering step. In addition, the samples demonstrated typical values of Vickers hardness for 3Y-TZP (ranging from 10.5 to 11.8 GPa) and fracture toughness (ranging from 3.6 to 4.7 MPa m1/2), with a minor current density ramp control influence. Therefore, both FS and CRFS techniques represent viable pathways for producing dense 3D printed ceramic materials. [Display omitted] • Additive Manufacturing and Flash Sintering were combined to produce 3Y-TZP components. • The strategy of stacking the filaments during the 3D printing influenced the mechanical properties. • Current ramp control enhanced the uniformity of grain structure in 3Y-TZP. [ABSTRACT FROM AUTHOR]

Flash sinter‐crystallization (FSC) is a new technique for concurrently crystallizing and sintering glasses, derived from flash sintering. In this study, we explore, for the first time, the use of FSC as a processing method for producing Li1.3Al0.3Ti1.7(PO4)3 (LATP) glass ceramics. Using FSC, LATP with NaSICON structure is produced at a furnace temperature as low as 460°C and a processing time of 5 min. The FSC‐processed samples with different current density limits were compared with those conventionally sinter‐crystallized (CSC) at 950°C for 1 h. We show that FSC can significantly improve the densification of LATP glass ceramics due to the volumetric high heating rate. Furthermore, the LATP samples processed by FSC exhibit superior total ionic conductivity than those processed by CSC, also surpassing the reported results for LATP with similar levels of densification. Therefore, our results suggest that FSC is a promising method for processing glass ceramics, particularly for materials with high crystallization kinetics like LATP, opening up new possibilities for the production of solid electrolytes. [ABSTRACT FROM AUTHOR]

Light-emission data were collected before, during, and after the occurrence of the flash event in pressureless electric-field-assisted (flash) sintering experiments on ZrO2: 8 mol% Y2O3 (8YSZ) and CeO2: 20 mol% Sm2O3 (20SDC) ceramic green pellets to analyze the luminescent emission from the samples. The experiments were performed at 800 °C with an applied electric field of 100 V·cm−1 at 1 kHz, limiting the electric current to 1 A. Luminescence data were obtained in the 200–1200 nm (ultraviolet–visible–near-infrared) range. The deconvolution of the optical spectra allowed for the identification of emission bands in the visible range due exclusively to the samples. The wavelength maxima of the emission bands in 8YSZ were found to be different from those in 20SDC. It is suggested that these bands might originate from the interaction of the electric current, resulting from the application of the electric field, with the depleted species located at the space-charge region at the grain boundaries of these ceramics. The main results represent a contribution to help to clarify the mechanisms responsible for the fast densification with inhibition of grain growth in electroceramics. [ABSTRACT FROM AUTHOR]

Light-emission data were collected before, during, and after the occurrence of the flash event in pressureless electric-field-assisted (flash) sintering experiments on ZrO2: 8 mol% Y2O3 (8YSZ) and CeO2: 20 mol% Sm2O3 (20SDC) ceramic green pellets to analyze the luminescent emission from the samples. The experiments were performed at 800 °C with an applied electric field of 100 V·cm−1 at 1 kHz, limiting the electric current to 1 A. Luminescence data were obtained in the 200–1200 nm (ultraviolet–visible–near-infrared) range. The deconvolution of the optical spectra allowed for the identification of emission bands in the visible range due exclusively to the samples. The wavelength maxima of the emission bands in 8YSZ were found to be different from those in 20SDC. It is suggested that these bands might originate from the interaction of the electric current, resulting from the application of the electric field, with the depleted species located at the space-charge region at the grain boundaries of these ceramics. The main results represent a contribution to help to clarify the mechanisms responsible for the fast densification with inhibition of grain growth in electroceramics.

Preparation of high-entropy ceramics (HECs) requires long duration at high temperatures, which limits their wide application. In this study, high-entropy (La 0.2 Ce 0.2 Nd 0.2 Sm 0.2 Eu 0.2) 2 Zr 2 O 7 ceramics was prepared at low temperatures of 762–885 °C in very short time of 60 s using the flash sintering. The effects of electric field strength and current limit on the densification and grain growth, as well as the phase transformation were systematically investigated. Both density and grain size were increased with the increase of the electric field strength and current limit. The phase transformation from defective fluorite to pyrochlore occurred at large current limit. The flash-sintered bulks exhibited good mechanical properties. This study demonstrates that flash sintering is an effective method for rapid preparation of HECs at low temperatures. Moreover, the microstructure of HECs can be controlled by adjusting the electric field strength and current limit. [ABSTRACT FROM AUTHOR]

Sintering of tungsten nominally requires several hours at ultrahigh temperatures. We show this refractory metal can be sintered quickly by direct injection of current into dog bone shaped specimens. The current rate was varied from 10 A s−1 (fast) to 0.1 A s−1 (slow), leading to sintering in 2–200 s, respectively. Sintering occurred at the same current density, regardless of the current rate. In all instances, the samples sintered when they reached 1000°C. The phenomenological behavior of flash sintering of metals is described by three stages: an incubation time followed by electroluminescence, and finally by abrupt sintering to full density. It is conjectured that rapid sintering is instigated by the formation of Frenkel pairs (vacancies and interstitials), as well as electrons and holes. The point defects accelerate mass transport, whereas electrons and holes recombine to form photons. Calorimetric measurements show an endothermic reaction attributed to the creation of defects. Estimates suggest an unusually large concentration of Frenkel pairs. PS: Flash sintering is different than electro‐discharge‐sintering where a capacitor is discharged in a few milliseconds to sinter a metal. Here, instead of dumping large amount of energy at once, a power supply is programed to control the rate of current injection. [ABSTRACT FROM AUTHOR]

Two‐step reactive flash sintering (TSRFS) was employed to achieve fast densification of high entropy pyrochlore (La0.2Nd0.2Sm0.2Eu0.2Gd0.2)2Zr2O7 with suppressed grain growth and improved microstructural homogeneity. Theoretical density of ∼98.15% with a grain size of ∼684 nm was achieved by TSRFS, representing only half the grain size compared with conventional one‐step reactive flash sintering (RFS), while the total holding time of TSRFS was only 1.5 times that of RFS. Although longer duration in step 1 benefited faster densification, it was demonstrated that the shorter time in step 1 not only resulted in smaller grain size in TSRFS samples with identical densities but also helps mitigate the grain size heterogeneity between sample cores and surfaces. Therefore, the art of efficiently using TSRFS lies in the reasonable manipulation of the time and power in step 1 and 2, achieving a balance between densification, grain growth, and microstructural homogeneity. [ABSTRACT FROM AUTHOR]

It is widely acknowledged that electrochemical reduction occurs during DC flash sintering (FS) of YSZ. In situ experiments have shown the emergence of new phases during FS that disappear again when the current is switched off. In addition, it has recently been reported that YSZ flash sintered in the absence of oxygen has a high electrical conductivity at room temperature. In this investigation electrical loading of YSZ was conducted in Ar and N 2 and maintained as the furnace cooled down such that on removing the current, the sample was rapidly quenched, avoiding reoxidation or other diffusion-limited phase transformations. XRD showed that the tetragonality of the ZrO 2-δ phase was diminished and the volume of the unit cell increased, the effect of the electrochemical reduction being similar to an increase in Y 2 O 3 content. In addition, rocksalt structure Zr(O,N) with a lattice constant of 0.4580 nm was formed at the surface and retained at room temperature. This phase had a metallic lustre and electrical conductivity approaching those of metals. The results enable several recent results in the literature to be reconciled and the implications for flash sintering are briefly discussed. [ABSTRACT FROM AUTHOR]

For the first time, isothermal pressureless flash sintering of 1.5 mol% yttria-stabilized zirconia (1.5YSZ) polycrystals designed for high toughness was performed in a 1-kHz alternating current field (120 V·cm−1). The parameters governing tetragonal phase stability and densification needed to maximize the toughness of 1.5YSZ were investigated by varying the applied current density limit and holding time. A sample with relative density exceeding 98% and indentation toughness of about 13 MPa·m0.5 was sintered at 1100°C by applying 40 mA·mm−2 to the green body for 2 min, where the average steady-state temperature during flash reached 1330°C. Unlike flash sintering of conventional oxide ceramics, the applied current density and densification were not positively correlated despite pore closure. While Joule heating intensified when applying higher current densities, sample densification was hindered as the accelerated grain growth resulted in intergranular cracks which were generated by spontaneous tetragonal-to-monoclinic martensitic phase transformation during cooling. [Display omitted] • First study on flash sintering of high-toughness 1.5 mol% yttria-stabilized zirconia. • Sample with relative density > 98% and toughness of about 13 MPa·m0.5 was produced in 2 min. • Applying higher current density promoted grain growth and hindered densification. • Tetragonal phase stability degraded with increasing grain size. • Cracks formed around monoclinic grains deteriorated sample density and toughness. [ABSTRACT FROM AUTHOR]

Additive manufacturing is typically an open-loop process. Consequently, it results in poor material matching at the junctions in multimaterial printing, affecting the performance of functional components. This study investigated the surface accumulation characteristics of parts in three-dimensional (3D) inkjet printing. Moreover, an intelligent additive manufacturing system for array nozzles was developed to improve the material accumulation accuracy and printing efficiency. First, a height prediction model was established to predict the printing height information, and a P-type closed-loop iterative learning control compensation algorithm with initial value correction was formulated based on the layer thickness experimental data. This algorithm reduced the root-mean-squared error (RMSE) of the sample's surface by 69.3%. Second, a set of random offset nozzle compensation algorithms was developed and combined with the laser vision scanning method to obtain the nozzle clogging information and compensate for sample defects by adjusting the parameters of the random algorithm. Finally, a microstrip antenna was fabricated. The surface roughness of the sample in this study was lower than that of the open-loop printed sample, resulting in a good antenna radio frequency (RF) layer connection. In addition, the S11 parameters were closer to the simulation results. These results validate the significance of this research in electronic printing. [ABSTRACT FROM AUTHOR]

Due to environmental concerns, extensive research has been carried out to develop high-performance lead-free piezoceramics capable of replacing commercial lead-based materials. The lead-free (Ba 0.7 Ca 0.3)TiO 3 −Ba(Zr 0.2 Ti 0.8)O 3 system has emerged as a candidate for room temperature transducer applications because a high piezoelectric charge coefficient is achieved in this system for compositions at the morphotropic phase boundary. However, conventional ceramic processing of these eco-friendly piezoceramics demands high energy consumption because long-lasting, high-temperature heat treatments are needed, which often lead to microstructural degradation that compromises the material reliability. Field-assisted flash sintering has started to be explored since the application of an adequate electric field was shown to significantly reduce the sintering time and temperature, thereby controlling grain growth. In this work, Ba 0.85 Ca 0.15 Zr 0.1 Ti 0.9 O 3 ceramics are obtained by current-controlled flash sintering of mechanosynthesized nanopowders. Exhaustive control of the sintering parameters allows tailoring of the microstructure, which allows dense fine-grained flash-sintered ceramics exhibiting a high electric field-induced strain response to be obtained. [ABSTRACT FROM AUTHOR]

The effects of the current density and holding time on the densification and microstructure of flash-sintered (FS-ed) magnesium aluminate (MgAl 2 O 4) ceramic discs were investigated. The results showed that the MgAl 2 O 4 discs exhibited typical flash characteristics at a furnace temperature of 1350 °C and required a critical electric field of 6500 V/cm. Compared with pressureless sintering, the densification and grain growth were distinctly accelerated in the case of flash sintering. The relative density and grain size of the FS-ed samples increased with increasing current density and holding time; the relative density attained a value of 99.66% when the current density was increased to 50 mA/mm2 and the holding time was 150 s. Additionally, the grain sizes on the positive side were found to be larger than those on the negative side, and the microstructure gradients increased with an increasing holding time. [ABSTRACT FROM AUTHOR]

Flash sintering (FS) is an ultrafast sintering method with low energy consumption and facile operation even at room temperature. Research has shown that the FS of 3 mol.% yttria-stabilised zirconia (3YSZ) at room temperature is induced by the appearance of an electric arc at both ends of the sample. In this study, we experimentally observed the arc-induced FS of 3YSZ, simulated the arc generation process based on magnetohydrodynamic equations, and analysed the arc-induced FS mechanism from the perspectives of heat conduction and current distribution. The simulation results showed the surface-flashover-induced microsecond-level generation of the arc. The results also demonstrated that the electrical conductivity of the sample varied with the temperature distribution due to the thermal conductivity of the sample, which resulted in the occurrence of arcs and arc-induced FS. Therefore, increasing the thermal and electrical conductivities of a sample can improve the experimental success rate of FS at room temperature. • Arc-induced flash sintering of 3YSZ at room temperature analysed. • Arc generation simulated using magnetohydrodynamic equations. • Arc formation within microseconds due to surface flashover. • Competitive relation between the current densities of arc and sample. [ABSTRACT FROM AUTHOR]

Systematic explorations of complex insulator–conductor composites may help in better comprehending the nature of flash sintering. In this study, flash sintering of alumina–8 mol% yttria stabilized zirconia (Al2O3–8YSZ) binary system with different mixing molar ratios was investigated. The results indicate that Al2O3 content significantly affects the flash-sintering behavior of Al2O3–8YSZ ceramics. The onset temperature of flash sintering increased with the increase in the Al2O3 content under 900 V cm−1. For the Al2O3 content above 20 mol%, Al2O3–8YSZ multiphase ceramics with eutectic morphology could be obtained at 800 °C-700 V⋅cm−1-120 s. Eutectic structures with different morphologies were obtained by adjusting the content of Al2O3. Formation of the eutectic structures is related to the Joule heating and defects introduced by the electric field. Flash sintering is a promising and novel sintering technology for the rapid fabrication of high-performance oxide eutectic ceramics.