Flash Phenomenon Research Articles

Analysis of the Flash Phenomenon in Rotor Targets with a Scatter Point Model

This paper thoroughly investigates the occurrence of the flash phenomenon in rotor targets. The flash phenomenon is discernible in rotor targets across the time and frequency domains. This phenomenon is characterized by the modulation of signal amplitude through the Singer function, resulting in periodic peaks in the time domain. The appearance of these peaks in the time domain corresponds to the presence of a corresponding frequency band in the time–frequency domain. The influence of interference between scattering points on the amplitude and phase of echo is investigated by employing the echo scattering point model and the echo analytical expression as analytical foundations. A more comprehensive examination of the mechanisms that contribute to the emergence of the flash phenomenon in the time and time–frequency domains is undertaken. Furthermore, its objective is to verify the validity of the analysis performed on the mechanism of the phenomenon. Based on theoretical investigations and simulation results, it can be concluded that the flash phenomenon observed in rotor targets is due to interference between particular scattering points. Fundamentally, it can be comprehended as a phenomenon of interference. This research achievement has specific theoretical and practical value in detecting and recognizing rotor targets.

Structural and electronic transformations in TiO2 induced by electric current

In-situ diffuse neutron scattering experiments revealed that when electric current is passed through single crystals of rutile TiO2 under conditions conducive to flash sintering, it induces the formation of parallel planes of oxygen vacancies. Specifically, a current perpendicular to the c-axis generates planes normal to the (132) reciprocal lattice vector, whereas currents aligned with the c-axis form planes normal to the (132) and to the (225) vector. The concentration of defects increases with incresing current. The structural modifications are linked to the appearance of signatures of interacting Ti3+ moments in magnetic susceptibility, signifying a structural collapse around the vacancy planes. Electrical conductivity measurements of the modified material reveal several electronic transitions between semiconducting states (via a metal-like intermediate state) with the smallest gap being 27 meV. Pristine TiO2 can be restored by heating followed by slow cooling in air. Our work suggests a novel paradigm for achieving switching of electrical conductivity related to the flash phenomenon.

Influence of particle contact on flash sintering of ZnO and 8YSZ: Microstructure and electrical conductivity

The flash phenomenon in flash sintering of ceramic materials is closely related to electrical conductivity of the material. However, our understanding of how particle-to-particle contact of ceramic powders affects this phenomenon and, consequently, the microstructure and electrical properties of flash-sintered materials remains limited. To address this, we utilized “pseudo-in-situ” impedance spectroscopy to investigate the effect of particle-to-particle contact in nanometric powders of ZnO and 8YSZ, both before and after flash sintering. The powders were prepared using two different procedures, either grinding with a binder or employing multiple milling and calcining steps. After compacting into pellets, the samples were characterized before and after flash sintering, either with current-to-voltage control or with the application of current density ramps until the flash event occurred. Pseudo-in-situ impedance was employed to demonstrate that preparing powders using multiple milling and calcining steps improved charge-carrier mobility paths, facilitated homogeneous passage of electric current, reduced thermal gradients, and consequently resulted in better microstructural homogeneity and electrical conductivity. In addition, the use of the electric-current ramp control retained microstructural homogeneity to a greater degree.

Modeling and simulation of the flash sintering: An approach to study the influence of process attributes on the flash phenomenon and microstructure

Field-assisted sintering still has gaps in explaining and modeling the flash phenomenon, as well as in enabling control over the sintering process to achieve desirable densification and microstructure control in ceramic materials.This study investigates methods for constructing computational models based on machine learning for predicting the onset temperature of the flash event (Tonset) and bulk density (BD) from a combination of various process attributes: powder composition, green sample geometry, electric field configuration, and heating. Samples of 3 mol% and 8 mol% yttria-stabilized zirconia were shaped into cylindrical geometry and were sintered using flash sintering and multi-step flash sintering processes, employing the following variations: current density; DC and AC electric field; and holding time. The experimental data were used for constructing and evaluating prediction models for Tonset and BD using k-fold cross-validation and the following algorithms: Random Forest, Support Vector Machine, Artificial Neural Network, K-Nearest Neighbors, and Multivariate Linear Regression Analysis. The model performance was assessed by comparing the measured values with the respective predicted values based on the Pearson correlation coefficient (r), mean absolute error (MAE), and root mean square error (RMSE). The models based on the Artificial Neural Network algorithm showed the best performance for predicting Tonset (r = 0.98; MAE = 11.88; RMSE = 14.88) and BD (r = 0.91; MAE = 1.86; RMSE = 2.30). The best models were used in conjunction with the Wrapper method for selecting attributes that significantly impact the sintering process, allowing the identification of 6 main attributes that impact Tonset and 9 attributes that impact BD in the flash-sintered samples.

Modeling the impact of tissue oxygen profiles and oxygen depletion parameter uncertainties on biological response and therapeutic benefit of FLASH.

Ultra-high dose rate (FLASH) radiation has been reported to efficiently suppress tumor growth while sparing normal tissue; however, the mechanism of the differential tissue sparing effect is still not known. Oxygen has long been known to profoundly impact radiobiological responses, and radiolytic oxygen depletion has been considered to be a possible cause or contributor to the FLASH phenomenon. This work investigates the impact of tissue pO2 profiles, oxygen depletion per unit dose (g), and the oxygen concentration yielding half-maximum radiosensitization (the average of its maximum value and one) (k) in tumor and normal tissue. We developed a model that considers the dependent relationship between oxygen depletion and change of radiosensitivity by FLASH irradiation. The model assumed that FLASH irradiation depletes intracellular oxygen more rapidly than it diffuses into the cell from the extracellular environment. Cell survival was calculated based on the linear quadratic-linear model and the radiosensitivity related parameters were adjusted in 1Gy increments of the administered dose. The model reproduced published experimental data that were obtained with different cell lines and oxygen concentrations, and was used to analyze the impact of parameter uncertainties on the radiobiological responses. This study expands the oxygen depletion analysis of FLASH to normal human tissue and tumor based on clinically determined aggregate and individual patient pO2 profiles. The results show that the pO2 profile is the most essential factor that affects biological response and analyses based on the median pO2 rather than the full pO2 profile can be unreliable and misleading. Additionally, the presence of a small fraction of cells on the threshold of radiobiologic hypoxia substantially alters biological response due to FLASH oxygen depletion. We found that an increment in the k value is generally more protective of tumor than normal tissue due to a higher frequency of lower pO2 values in tumors. Variation in the g value affects the dose at which oxygen depletion impacts response, but does not alter the dose-dependent response trends, if the g value is identical in both tumor and normal tissue. The therapeutic efficacy of FLASH oxygen depletion is likely patient and tissue-dependent. For breast cancer, FLASH is beneficial in a minority of cases; however, in a subset of well oxygenated tumors, a therapeutic gain may be realized due to induced normal tissue hypoxia.

On the confluence of ultrafast high‐temperature sintering and flash sintering phenomena

AbstractUltrafast high‐temperature sintering (UHS) and flash sintering are novel methods for rapid sintering of ceramics, often completed in just a few seconds. Here, we show that both also share two additional features: an abrupt rise in electrical conductivity, which is electronic, and electroluminescence. More fundamentally, both are related to phonon physics where MD calculations have shown that proliferation of phonons at the edge of the Brillouin zone can induce Frenkel pairs without the application of electrical fields. Here, we show that, indeed, heating without the application of electric field, can also induce flash: Rapid heating processes of thin films of an oxide‐salt deposited on silk fibers, with a propane torch, are shown to induce electronic conductivity, electroluminescence, and rapid sintering of the oxide. The discussion in this article harkens back to two inventions, more than a century ago, which can now be related to flash and UHS: (i) the Nernst glow lamp circa 1900, made from zirconia, and (ii) the Welsbach mantle, constituted from ceria doped thorium oxide, in the late nineteenth century. Thus, the confluence between high heating rate and electric field induced flash phenomena links the past to the new. The emerging question is how injection of phonons that has been shown to create Frenkels can further induce high electronic conductivity and electroluminescence in oxides. Both electronic conductivity and luminescence are likely related to the generation of electron–hole pairs.

Automatic identification of septal flash phenomenon in patients with complete left bundle branch block.

Complete left bundle branch block (cLBBB) is an electrical conduction disorder associated with cardiac disease. Septal flash (SF) involves septal leftward contraction during early systole followed by a lengthening motion toward the right ventricle and affects several patients with cLBBB. It has been revealed that cLBBB patients with SF may be at risk of cardiac function reduction and poor prognosis. Therefore, accurate identification of SF may play a vital role in counseling patients about their prognosis. Generally, Septal flash is identified by echocardiography using visual "eyeballing". However, this conventional method is subjective as it depends on operator experience. In this study, we build a linear attention cascaded net (LACNet) capable of processing echocardiography to identify SF automatically. The proposed method consists of a cascaded CNN-based encoder and an LSTM-based decoder, which extract spatial and temporal features simultaneously. A spatial transformer network (STN) module is employed to avoid image inconsistency and linear attention layers are implemented to reduce data complexity. Moreover, the left ventricle (LV) area-time curve calculated from segmentation results can be considered as a new independent disease predictor as SF phenomenon leads to transient left ventricle area enlargement. Therefore, we added the left ventricle area-time curve to LACNet to enrich input data diversity. The result shows the possibility of using echocardiography to diagnose cLBBB with SF automatically.

Room temperature flash of single crystal titania: Electronic and optical properties

AbstractA single‐crystal specimen of rutile (titania) was flashed repetitively, while increasing the electric field after each cycle. As expected, the flash onset temperature continued to drop modestly at higher fields. However, when the field was increased from 400 to 450 V cm–1, the flashed onset fell dramatically down to room temperature. We have investigated the electrical and optical properties of this room temperature flashed specimen (called SZ). The specimen was electronically conducting. Optical absorption spectroscopy revealed a narrow band of new energy levels that were generated just below the conduction band. The gap between the conduction band and this flash‐induced energy level agreed with the peak in the electroluminescence spectrum. Optical second harmonic generation (SHG) is reported. The flash‐on condition significantly lowered the SHG, which rebounded when the flash was turned off. This result suggests that the structure becomes more centrosymmetric in the state of flash, which may represent a disordered state of defects. The possibility of studying flash behavior at room temperature, without a furnace (as in SZ type specimens), opens a considerable simplification for in‐situ characterization of flash behavior. For example, a possible relationship between memristor physics and the flash phenomenon can be studied.

Effect of pressure on the electrical resistance flash sintering of tungsten carbide

The application of external pressure during the Electrical Resistance Flash Sintering of tungsten carbide (WC), a “metallic ceramic” with positive temperature coefficient (PTC) for resistivity, results in a limited densification of the powder. In the present work, the effect of pressure on the ultrafast sintering of WC is analysed in detail. In particular, the application of pressure at different stages of flash sintering is studied by varying independently the processing parameters i.e., voltage, time and pressure. Microstructural characterization performed by FE-SEM and XRD identifies biphasic structures of WC and W2C, which compositions result almost unchanged for different sintering parameters. Increasing the external load from 4 up to 100 MPa leads to microporous materials, limiting the attainable final density. Pressure is demonstrated to control the flash phenomenon directly by affecting the flash duration and intensity, thus controlling the electrical energy dissipated during the power surge with respect to the overall process.

Accessing the role of Joule heating on densification during flash sintering of YSZ

Flash sintering is a novel electric field and current assisted sintering technique which densify ceramics at moderate furnace temperature and in short time (few seconds) as compared to the conventional sintering techniques. The onset of flash encompasses three unique characteristics, (i) non-linear rise in conductivity, (ii) luminescence and (iii) rapid densification. the mechanism behind the flash phenomena is not fully understood yet. The present work experimentally demonstrated that the densification in flash sintering is primarily dominated by Joule heating. Herein, we distinguished the onset of flash and the degree of densification of cubic zirconia in sintering atmospheres with different oxygen partial pressures. In this study, we demonstrate that the flash onset temperature and densification are independently influenced by the sintering atmosphere during flash sintering. Furthermore, the extent of densification is not directly influenced by the current density rather, by the power dissipated in the sample.

Design and validation of a synchrotron proton beam line for FLASH radiotherapy preclinical research experiments.

The main purpose of this work was to generate and validate the dosimetric accuracy of proton beams of dimensions that are appropriate for in vivo small animal and in vitro ultrahigh dose rate (FLASH) radiotherapy experiments using a synchrotron-based treatment delivery system. This study was performed to enable future investigations of the relevance of a spread-out Bragg peak (SOBP) under FLASH conditions. The spill characteristics of the small field fixed horizontal beam line were modified to deliver accelerated protons in times as short as 2ms and to control the dose delivered. A Gaussian-like transverse beam profile was transformed into a square uniform one at FLASH dose rates, while avoiding low-dose regions, a crucial requirement to protect normal tissue during FLASH irradiation. Novel beam-shaping devices were designed using Monte Carlo techniques to produce up to about 6cm3 of uniform dose in SOBPs while maximizing the dose rate. These included a scattering foil, a conical flattening filter to maximize the flux of protons into the region of interest, energy filters, range compensators, and collimators. The shapes, sizes, and positions of the components were varied to provide the required field sizes and SOBPs. The designed and fabricated devices were used to produce 10-, 15-, and 20-mm diameter, circular field sizes and 10-, 15-, and 20-mm SOBP modulation widths at uniform physical dose rates of up to 375Gy/s at the center of the SOBP and a minimum dose rate of about 255Gy/s at the entrance, respectively, in cylindrical volumes. The flatness of lateral dose profiles at the center could be adjusted to within ±1.5% at the center of the SOBP. Assessment of systematic uncertainties, such as impact of misalignments and positioning uncertainties, was performed using simulations, and the results were used to provide appropriate adjustments to ensure high-accuracy FLASH beam delivery for both in vitro and in vivo preclinical experiments. It is feasible to use synchrotron-generated proton beams of sufficient dimensions for FLASH radiobiology experiments. We expect to use the system we developed to acquire in vitro and in vivo small animal FLASH radiobiology data as a function of dose, dose rate, oxygen content, and linear energy transfer to help us understand the underlying mechanisms of the FLASH phenomenon.

A Modified Lethal and Potentially Lethal Model With Explicit Oxygen Tension Dependence for FLASH RT

To modify Curtis Lethal and Potentially Lethal (LPL) model to extend it from conventional (CONV) to ultra-high dose rate (FLASH) Radiotherapy (RT) domain with explicit intracellular oxygen tension dependence.After combining radiation-induced oxygen depletion, oxygen fixation hypothesis, and the Oxygen Enhancement Ratio (OER) concept, we incorporate intracellular oxygen tension dependence into the coefficients of the ordinary differential equations describing the original Curtis LPL model. Two biochemical pre-lesion states for the LPL lesions are amended into the model to explain the oxygen post-effect on the cell radiation survival fraction (SF). We perform analytical and numerical analyses for the solutions of the average numbers of LPL lesions. Using Poisson statistics, we can use the average number of LPL lesions to predict the cell SF for FLASH RT.Our modified LPL model maintains all original LPL model characteristics at fixed intracellular oxygen tension. For variable intracellular oxygen tensions, our new model extends prediction capabilities to FLASH RT. The comparisons of the two models are summarized below: CONCLUSION: Our modified LPL model has the potential to explain the observed FLASH phenomena, i.e., FLASH RT provides better normal tissue sparing while maintaining similar tumor control compared with CONV RT. Future studies are necessary to quantitatively validate our model predictions in systematically conducted FLASH irradiation experiments.

Effect of Processing Conditions on the Flash Onset Temperature in Hydroxyapatite.

When heat and electric field are applied to the sample, sintering takes place within a short time of a few seconds by the flash phenomenon that occurs. In what condition flash does occur is a main issue for the flash sintering technique. In this study, the effect of processing conditions such as sintering atmosphere, sample size, density and grain size on the flash onset of hydroxyapatite was investigated. In a vacuum atmosphere, a flash occurred at a lower temperature by 50–100 °C than in air. The smaller the thickness of the sample, the higher the flash onset temperature due to the larger specific surface area. Flash was also observed in samples which were presintered, having a density of 86–100% and a grain size of 0.2–0.9 μm. When the density and grain size of the sample were higher and larger, the flash onset temperature was higher. It was because the diffusion and conduction path through the grain boundary and the inner surface of the pores with high defect concentration are blocked with an increase of density or grain size. When an electric field was applied during flash sintering, a color change of the sample was observed and the reason was discussed.

The Role of Flare‐Driven Ionospheric Electron Density Changes on the Doppler Flash Observed by SuperDARN HF Radars

AbstractTrans‐ionospheric high frequency (HF: 3–30 MHz) signals experience strong attenuation following a solar flare‐driven sudden ionospheric disturbance (SID). Solar flare‐driven HF absorption, referred to as short‐wave fadeout, is a well‐known impact of SIDs, but the initial Doppler frequency shift phenomena, also known as “Doppler flash” in the traveling radio wave is not well understood. This study seeks to advance our understanding of the initial impacts of solar flare‐driven SID using a physics‐based whole atmosphere model for a specific solar flare event. First, we demonstrate that the Doppler flash phenomenon observed by Super Dual Auroral Radar Network (SuperDARN) radars can be successfully reproduced using first‐principles based modeling. The output from the simulation is validated against SuperDARN line‐of‐sight Doppler velocity measurements. We then examine which region of the ionosphere, D, E, or F, makes the largest contribution to the Doppler flash. We also consider the relative contribution of change in refractive index through the ionospheric layers versus lowered reflection height. We find: (a) the model is able to reproduce radar observations with an root‐median‐squared‐error and a mean percentage error (δ) of 3.72 m/s and 0.67%, respectively; (b) the F‐region is the most significant contributor to the total Doppler flash (∼48%), 30% of which is contributed by the change in F‐region's refractive index, while the other ∼18% is due to change in ray reflection height. Our analysis shows lowering of the F‐region's ray reflection point is a secondary driver compared to the change in refractive index.

Frenkel pairs cause elastic softening in zirconia: theory and experiments

Recent results from molecular dynamics simulations have shown that significant concentrations of Frenkel pairs can be introduced by the proliferation of phonons lying at the edge of the Brillouin zone and when above the Debye temperature. Following the work of Granato (2014 Eur. Phys. J. B 87 18) we extend those calculations to the influence of Frenkels on the elastic modulus. Significant softening is predicted which is confirmed by in situ measurements of the elastic modulus during flash. Frenkel pairs have been proposed to play a central role in the flash phenomena.

Evaluation of machine learning based models to predict the bulk density in the flash sintering process

Flash Sintering (FS) has still unexplained issues of the flash phenomenon that do not allow the construction of dynamic models to predict the ceramic microstructure. This work investigates computational models based on supervised machine learning techniques for modelling the FS process to predict the bulk density (BD) using the holding time (TH) and electric current density (J). Samples of 3YSZ (zirconia stabilised with 3 mol% of yttria) were prepared and shaped in cylindrical geometry (6 mm in diameter and 4 mm in height). The FS parameters were adjusted at a heating rate of 20 °C/min, maximum current density of 100 mA/mm² and an electric field in alternating current mode of 90 V/cm (1 kHz). FS processes were performed for different J values set to 80, 100 and 200 mA/mm² and different TH values set to 60 s, 120 s and 180 s. After preliminary regression analysis, four learning methods were applied to generate the models: Artificial Neural Network, K-Nearest Neighbours, Random Forest, and Support Vector Machine. The results show moderate correlations (>0.5) between the values measured and predicted by the different models in the prediction of BD through TH. The Support Vector Machine based method allowed the best BD prediction models to be built, with r equal to 0.62, MAE equal to 0.95 and RMSE equal to 1.37. These results indicate the potential of applying the methods and allow the definition of new hypotheses to improve the models.

Deciphering Time-Dependent DNA Damage Complexity, Repair, and Oxygen Tension: A Mechanistic Model for FLASH-Dose-Rate Radiation Therapy

Irradiation with ultra-high dose-rates (FLASH) has reemerged as a promising radiotherapy approach to effectively lower potential damage burden on normal tissue without sacrificing tumor control; however, the large number of recent FLASH studies are conducted under vastly different experimental conditions and circumstances i.e. investigated biological endpoint, radiation quality and environmental oxygen level, with unverified biological mechanisms of action and unexplored interplay effect of the main dependencies. To facilitate radiobiological investigation of FLASH phenomena and assessment of clinical applicability, we present an extension of the mechanistic radiobiological model "XXX" († MODELX). The dynamic (time-dependent) extension of MODELX is developed here incorporating fundamental temporal mechanisms necessary for dose-rate effect prediction, i.e. DNA damage repair kinetics (DDRK), oxygen depletion and re-oxygenation during irradiation. Model performance in various experimental conditions is validated based on a large panel of in-vitro and in-vivo data from the literature. Impact of dose, dose-rate, oxygen tension, tissue-type, beam quality and DDRK is analyzed. MODELX adequately reproduces dose-, dose-rate and oxygen tension-dependent influence on cell killing. For the studied systems, results indicate that the extent of cell/tissue sparing effect, if present at all, strongly depends on DDRK and beam quality used for reference conventional irradiation. A validated mechanistic framework for predicting clinically relevant end-points comparing conventional and FLASH high-dose-rate effect has been successfully established, relying on time-dependent processing of radiation-induced damage classes taking into account variable oxygen tension. Highlighted by MODELX itself, the multi-dimensional nature of this relative sparing effect using high dose-rate radiation compared to conventional means underlines the importance of robust quantification of biophysical characteristics and consistent/well-documented experimental conditions both in-vitro and in-vivo prior to clinical translation. To further elucidate underlying mechanisms and appraise clinical viability, MODELX can provide reliable prediction for biophysical investigations of radiotherapy using ultra-high dose-rate.

Determine the Electrode Configuration and Sensitivity of the Enclosure Dimensions When Performing Arc Flash Analysis

Arc flash hazard prediction methods have become more sophisticated because the knowledge about arc flash phenomenon has advanced since the publication of IEEE Std. 1584-2002. The IEEE Std. 1584-2018 has added parameters for more accurate arc flash incident energy (IE), arcing current, and protection boundary estimation. The parameters in the updated estimation models include electrode configuration, open circuit voltage, bolted fault current, arc duration, gap width, working distance, and enclosure dimension. The sensitivity and effect changes of other parameters have been discussed in the previous literatures. This article explains the fundamental theory on the selection of electrode configurations and performs sensitivity analysis of the enclosure dimension that have been introduced in the IEEE Std. 1584-2018. According to the newly published model for IE estimation, the IE between vertical conductors inside a metal box (VCB) and horizontal conductors inside a metal box (HCB) can differ by a factor of two with other parameter constants. Using HCB as the worst-case scenario to determine the personal protection requirements may not be the best practice in all circumstances. This article provides guidance for electrode configuration selection and a sensitivity analysis for determining a reasonable engineering margin when actual dimension is not available.

Umbral chromospheric fine structure and umbral flashes modelled as one: The corrugated umbra

Context.The chromosphere of the umbra of sunspots features an assortment of dynamic fine structures that are poorly understood and often studied separately. Small-scale umbral brightenings (SSUBs), umbral microjets, spikes or short dynamic fibrils (SDFs), and umbral dark fibrils are found in any observation of the chromosphere with sufficient spatial resolution performed at the correct umbral flash stage and passband. Understanding these features means understanding the dynamics of the umbral chromosphere.Aims.We aim to fully understand the dynamics of umbral chromosphere through analysis of the relationships between distinct observed fine features and to produce complete models that explain both spectral profiles and the temporal evolution of the features. We seek to relate such understanding to umbral flashes.Methods.We studied the spatial and spectral co-evolution of SDFs, SSUBs, and umbral flashes in Ca II8542 Å spectral profiles. We produced models that generate the spectral profiles for all classes of features using non-local thermodynamic equilibrium radiative transfer with a recent version of the NICOLE inversion code.Results.We find that both bright SSUBs and dark SDF structures are described with a continuous feature in the parameter space that is distinct from the surroundings even in pixel-by-pixel inversions. We find a phase difference between such features and umbral flashes in both inverted line-of-sight velocities and timing of the brightenings. For umbral flashes themselves we resolve, for the first time in inversion-based semi-empirical modelling, the pre-flash downflows, post-flash upflows, and the counter-flows present during the umbral flash phase. We further present a simple time-dependent cartoon model that explains the dynamics and spectral profiles of both fine structure, dark and bright, and umbral flashes in umbral chromospheres.Conclusions.The similarity of the profiles between the brightenings and umbral flashes, the pattern of velocities obtained from the inversions, and the phase relationships between the structures all lead us to put forward that all dynamic umbral chromospheric structures observed to this date are a locally delayed or locally early portion of the oscillatory flow pattern that generates flashes, secondary to the steepening large-scale acoustic waves at its source. Essentially, SSUBs are part of the same shock or merely compression front responsible for the spatially larger umbral flash phenomenon, but out of phase with the broader oscillation.

Effects of powder dispersion on reactive flash sintering of 8 mol% yttria-stabilized zirconia and MgAl2O4 composites

A three-phase system consisting of alumina (Al2O3), magnesia (MgO) and 8 mol% yttria‐stabilized zirconia (8YSZ) was reactive flash sintered to produce MgAl2O4-8YSZ composites. We show that a critical volume fraction of the ionic conductor 8YSZ is required to promote the flash phenomenon, indicating a typical percolation behavior. The easy path for conduction could be reached with a smaller critical volume fraction when using agglomerated powders for producing the green bodies. Furthermore, microstructure and X-ray diffraction analyses demonstrate that both sintering and phase transformation largely depend on the mixing level of the precursors. Although the presence of agglomerates resulted in a decrease of the flash onset temperature, poor sintering and incomplete phase transformation were verified. This behavior is attributed to inhomogeneous heat distribution within those samples during the flash state, which could be explained by the electrical current percolation.