Fabrication of graphene/ceramic composites commonly requires a high-temperature sintering step with long times as well as a vacuum or inert atmosphere,which not only results in property degradation but also significan...Fabrication of graphene/ceramic composites commonly requires a high-temperature sintering step with long times as well as a vacuum or inert atmosphere,which not only results in property degradation but also significant equipment complexity and manufacturing costs.In this work,the ambient flash sintering behavior of reduced graphene oxide/3 mol% yttria-stabilized ZrO_(2)(rGO/3 YSZ) composites utilizing rGO as both a composite component and a conductive additive is reported.When the sintering condition is carefully optimized,a dense and conductive composite can be achieved at room temperature and in the air within 20 s.The role of the rGO in the FS of the rGO/3 YSZ composites is elucidated,especially with the assistance of a separate investigation on the thermal runaway behavior of the rGO.The work suggests a promising fabrication route for rGO/ceramic composites where the vacuum and furnace are not needed,which is of interest in terms of simplifying the fabrication equipment for energy and cost savings.展开更多
The high burn-up structure(HBS)is characterized by the grain size of 100-300 nm and a porosity of up to 20%,which is formed at the rim of the nuclear fuel pellet due to 2-3 times higher local burn-up during the in-pil...The high burn-up structure(HBS)is characterized by the grain size of 100-300 nm and a porosity of up to 20%,which is formed at the rim of the nuclear fuel pellet due to 2-3 times higher local burn-up during the in-pile irradiation.HBS is considered a new potential structure for high-performance fuels.However,it is difficult to prepare HBS by conventional sintering methods.In this study,flash sintering was used to prepare HBS using CeO_(2)as a surrogate for a preliminary investigation.A new experimental configuration for rapid sintering of CeO_(2)pellets was provided,in which the green body can be rapidly preheated and pressure-assisted by the induction heating electrodes.An insulated quartz tube was used as the die for the flash sintered samples,allowing the current to flow through the sample and providing a stable condition for applying an external pressure of approximately 5.3-7.0 MPa during flash sintering process.Using an initial electric field of 141 V cm-1 and holding for 1-7 min at the maximum current density of~98 mA mm^(-2),CeO_(2)ceramics with a grain size of 114-282 nm and a relative density of 75.4-99.7%were prepared.The densification and microstructure evolution behaviors during flash sintering in this new experimental configuration have been discussed in detail.This new experimental configuration may provide a promising approach for preparing UO_(2)ceramics and their HBS.展开更多
Flash sintering has proven to be a novel and cost-efficient technique that enables the successful processing of dissimilar materials.The present work investigated how sintering under electric field input progresses in...Flash sintering has proven to be a novel and cost-efficient technique that enables the successful processing of dissimilar materials.The present work investigated how sintering under electric field input progresses in commercial anatase(A)plus rutile(B)polymorphs containing titania.Both the phase evolution and sintering dynamics were highly dependent on the strength of the field,the application of which led to(A+R)→R→flash at low fields while promoting(A+R)→flash at high fields.A temperature postponement of flash was verified at low fields,as the event was preceded by the A→R transformation,which was responsible for a detectable peak in the thermal spectra of the current.The processing temperature,applied electric field(E),and onset flash sintering temperature(T^(flash)_(furn))combine well into a phase diagram graph that summarizes the phase development that applies to this material.In addition,high-density bodies in the rutile phase were ultimately produced after flashing under a suitable current density,regardless of the field strength considered.Both the flash sintering temperature and average grain size(AGS)decreased with increasing field.In line with this,we demonstrate the existence of a direct link between the grain size and the sample sintering temperature,which is consistent with the classical grain growth model.展开更多
Understanding the onset mechanism of flash sintering is essential for advancing electric-field-assisted sintering technologies.Herein,the onset temperature of flash sintering(FS)was examined for alumina-8 mol%yttria-s...Understanding the onset mechanism of flash sintering is essential for advancing electric-field-assisted sintering technologies.Herein,the onset temperature of flash sintering(FS)was examined for alumina-8 mol%yttria-stabilized zirconia(Al_(2)O_(3)-8YSZ)composites with varying molar ratios of Al_(2)O_(3)and 8YSZ under an applied electric field of 900 V/cm.The results show a composition-dependent variation in the onset temperature,which can be divided into three different regions on the basis of the Al_(2)O_(3)content,each reflecting a different onset mechanism.In region Ⅰ(0-62.5 mol%),the flash sintering behavior is dominated by 8YSZ owing to the internal electrochemical reaction driven by the electric field.In region Ⅱ(62.5-80 mol%),flash sintering is determined by the percolation networks of 8YSZ,which offer conduction paths for current.In region Ⅲ(80-99 mol%),isolated 8YSZ particles catalyze the flash sintering of Al_(2)O_(3)through interfacial dielectric breakdown.These results highlight a composition-dependent transition in the onset mechanism of flash sintering:Composites with low Al_(2)O_(3)contents exhibit defect-dominated flash sintering associated with 8YSZ,whereas those with high Al_(2)O_(3)contents follow a thermally controlled mechanism.Thus,Al_(2)O_(3)and 8YSZ exhibit distinct onset mechanisms during flash sintering.展开更多
Metal-supported solid oxide fuel cells(MS-SOFCs)have recently gained significant attention as an advanced SOFC technology,owing to their excellent mechanical robustness,ease of handling,and high manufacturability.The ...Metal-supported solid oxide fuel cells(MS-SOFCs)have recently gained significant attention as an advanced SOFC technology,owing to their excellent mechanical robustness,ease of handling,and high manufacturability.The use of metal substrates enables improved durability under thermal and redox cycling,and allows for thinner electrolyte layers,contributing to enhanced performance.However,their fabrication typically requires high-temperature sintering to ensure adequate material properties and adhesion,as most SOFC components are ceramic.These high-temperature processes can lead to undesirable effects,including metal support oxidation,chemical side reactions,and accelerated particle growth,which degrade cell performance.This study introduces an ultra-fast sintering approach for MS-SOFC fabrication by directly integrating stainless-steel metal supports with nickel-yttria-stabilized zirconia(Ni-YSZ)composite anode active layers.The application of flash light sintering-an innovative ultra-fast technique-effectively suppressed Ni catalyst particle growth,expanding the electrochemical reaction area while minimizing material diffusion between the metal support and anode layer.As a result,the fabricated cells achieved a stable open-circuit voltage(OCV)exceeding 1 V at 650℃ and a peak power density of 412 mW/cm^(2),representing an approximately 426.3% performance improvement over conventionally sintered cells.This research presents a transformative strategy for SOFC manufacturing,addressing the challenges of conventional long-duration heat treatments and demonstrating significant potential for advancing energy conversion technologies.展开更多
This is the first study to conduct the flash sintering of 3 mol%yttria-stabilized zirconia(3YSZ)ceramics at room temperature(25℃)under a strong electric field,larger than 1 kV/cm.At the standard atmospheric pressure(...This is the first study to conduct the flash sintering of 3 mol%yttria-stabilized zirconia(3YSZ)ceramics at room temperature(25℃)under a strong electric field,larger than 1 kV/cm.At the standard atmospheric pressure(101 kPa),the probability of successful sintering is approximately half of that at low atmospheric pressure,lower than 80 kPa.The success of the proposed flash sintering process was determined based on the high electric arc performance at different atmospheric pressures ranging from 20 to 100 kPa.The 3YSZ samples achieved a maximum relative density of 99.5%with a grain size of~200 nm.The results showed that as the atmospheric pressure decreases,the onset electric field of flash sintering decreases,corresponding to the empirical formula of the flashover voltage.Moreover,flash sintering was found to be triggered by the surface flashover of ceramic samples,and the electric arc on the sample surfaces floated upward before complete flash sintering at overly high pressures,resulting in the failure of flash sintering.This study reveals a new method for the facile preparation of flash-sintered ceramics at room temperature,which will promote the application of flash sintering in the ceramic industry.展开更多
Oxygen vacancy OV plays an important role in a flash sintering (FS) process. In defect engineering, the methods of creating oxygen vacancy defects include doping, heating, and etching, and all of them often have compl...Oxygen vacancy OV plays an important role in a flash sintering (FS) process. In defect engineering, the methods of creating oxygen vacancy defects include doping, heating, and etching, and all of them often have complex processes or equipment. In this study, we used dielectric barrier discharge (DBD) as a new defect engineering technology to increase oxygen vacancy concentrations of green billets with different ceramics (ZnO, TiO_(2), and 3 mol% yttria-stabilized zirconia (3YSZ)). With an alternating current (AC) power supply of 10 kHz, low-temperature plasma was generated, and a specimen could be treated in different atmospheres. The effect of the DBD treatment was influenced by atmosphere, treatment time, and voltage amplitude of the power supply. After the DBD treatment, the oxygen vacancy defect concentration in ZnO samples increased significantly, and a resistance test showed that conductivity of the samples increased by 2–3 orders of magnitude. Moreover, the onset electric field (E) of ZnO FS decreased from 5.17 to 0.86 kV/cm at room temperature (RT);while in the whole FS, the max power dissipation decreased from 563.17 to 27.94 W. The defect concentration and conductivity of the green billets for TiO_(2) and 3YSZ were also changed by the DBD, and then the FS process was modified. It is a new technology to treat the green billet of ceramics in very short time, applicable to other ceramics, and beneficial to regulate the FS process.展开更多
In this study,we reported that flash sintering(FS)could be efficiently triggered at room temperature(25℃)by manipulating the oxygen concentration within ZnO powders via a versatile defect engineering strategy,fully d...In this study,we reported that flash sintering(FS)could be efficiently triggered at room temperature(25℃)by manipulating the oxygen concentration within ZnO powders via a versatile defect engineering strategy,fully demonstrating a promising method for the repaid prototyping of ceramics.With a low concentration of oxygen defects,FS was only activated at a high onset electric field of~2.7 kV/cm,while arcs appearing on the surfaces of samples.Strikingly,the onset electric field was decreased to<0.51 kV/cm for the activation of FS initiated,which was associated with increased oxygen concentrations coupled with increased electrical conductivity.Thereby,a general room-temperature FS strategy by introducing intrinsic structural defect is suggested for a broad range of ceramics that are prone to form high concentration of point defects.展开更多
For the first time,the flash sintering(FS)of high-purity alumina at room temperature,which was previously considered unachievable due to its low electrical conductivity,was conducted herein.The electrical arc originat...For the first time,the flash sintering(FS)of high-purity alumina at room temperature,which was previously considered unachievable due to its low electrical conductivity,was conducted herein.The electrical arc originating from surface flashover was harnessed to induce FS at room temperature and low air pressure.The successful FS of high-purity alumina was realized at 60 kPa under the arc constraint,resulting in a notable relative density of the alumina sample of 98.7%.The electric–thermal coupling between the arc and high-purity alumina sample during the arc-induced FS process was analyzed via the finite element simulation method.The results revealed the thermal and electrical effects of the arc on the sample,which ultimately enhance the electrical conductivity of the alumina sample.The formation of a conductive channel on the sample surface,a result of increased electrical conductivity,was the pivotal factor in achieving FS in high-purity alumina at room temperature.The arc constraint technique can be applied to numerous materials,such as ionic conductors,semiconductors,and even insulators,under room-temperature and low-air-pressure conditions.展开更多
The introduction of oxygen vacancies into zirconia is an effective strategy for enhancing its light absorption ability and photocatalytic performance.However,the cost-efficient preparation of oxygen-deficient zirconia...The introduction of oxygen vacancies into zirconia is an effective strategy for enhancing its light absorption ability and photocatalytic performance.However,the cost-efficient preparation of oxygen-deficient zirconia(ZrO_(2−x))remains challenging,which severely limits its broad application.In this study,flash sintering treatment was used to fabricate ZrO_(2−x) bulk in very short time of 90 s.Oxygen vacancies were introduced into ZrO2 bulk through electrochemical reduction reactions.The as-prepared black ZrO_(2−x) exhibited excellent optical absorption capability,a small band gap(2.09 eV for direct and 1.67 eV for indirect),and a reduced conduction band energy,which is ascribed to the generation of oxygen vacancies and reduction of Zr cations.The as-prepared ZrO_(2−x) showed remarkable photocatalytic activity due to excellent solar light absorption and low recombination rate of electron‒hole pairs.Flash sintering treatment provides a cost-efficient approach for rapidly fabricating ZrO_(2−x) bulk materials with high concentrations of oxygen vacancies,which can also be applied to other materials.展开更多
Flash sintering(FS)is a novel technique for rapidly densifying silicon carbide(SiC)ceramics.This work achieved a rapid sintering of SiC ceramics by the utilization of ultra-high temperature flash sintering within 60 s...Flash sintering(FS)is a novel technique for rapidly densifying silicon carbide(SiC)ceramics.This work achieved a rapid sintering of SiC ceramics by the utilization of ultra-high temperature flash sintering within 60 s.Pyrolysis carbon(PyC)“bridges”were constructed between SiC particles through the carbonisation of phenolic resin,providing a large number of current channels.The incubation time of the flash sintering process was significantly reduced,and the sintering difference between the centre and the edge regions of the ceramics was minimized,with an average particle size of the centre region and edge region being 12.31 and 9.02μm,respectively.The results showed that the porosity of the SiC ceramics after the flash sintering was reduced to 14.79% with PyC“bridges”introduced,and the Vickers hardness reached 19.62 GPa.PyC“bridges”gradually evolved from amorphous eddy current carbon to oriented graphite carbon,indicating that the ultra-high temperature environment in which the sample was located during the flash sintering was successfully constructed.Ultra-high temperature flash sintering of SiC is expected to be applied to the local repair of matrix damage in SiC ceramic matrix composites.展开更多
Room-temperature flash sintering(FS)for ceramics is a highly efficient and energy-saving new ceramic sintering technique.Addressing the current challenges in room-temperature flash sintering research,such as small pro...Room-temperature flash sintering(FS)for ceramics is a highly efficient and energy-saving new ceramic sintering technique.Addressing the current challenges in room-temperature flash sintering research,such as small product sizes,shape limitations,and high power requirements,limits their real application in the FS industry.In particular,for dog bone shape and small size,which are usually smaller than 10 mm,no records of sizes larger than 20 mm have been reported.In this study,a novel flash sintering device based on a composite layered carbon electrode structure was developed to conduct large-diameter sample flash sintering at room temperature(RT)in an air atmosphere under a direct current(DC)voltage below 10o V.Specifically,room-temperatureflash sintering was achievedfor Zn0 ceramic disks with diameters of 40.0 mm and thicknesses of 1.80 mm,achieving a maximum relative density of 96.02%.Furthermore,room-temperature flash sintering was achieved for ZnO varistor ceramic disks with a diameter of 40.0 mm and a thickness of 1.93 mm,reaching a maximum relative density of 99.27%,a maximum voltage gradient of 330.5 V·mm^(-1),and the highest nonlinearity coefficient(a)of 23.0.Room-temperature flash sintering was also achieved for 3 mol%yttrium-doped zirconia(3YSZ)ceramic disks,achieving a maximum relative density of 98.48%.The proposed flash sintering device and corresponding process demonstrate broad applicability for the ceramics industry.展开更多
The effect of the applied electric field on the conductive behavior of zirconia ceramics is studied by measuring its initial current-voltage curve at various temperatures. The results show that when the field strength...The effect of the applied electric field on the conductive behavior of zirconia ceramics is studied by measuring its initial current-voltage curve at various temperatures. The results show that when the field strength is higher than the threshold for flash-sintering, the curves exhibit a nonlinear behavior by having an additional current on top of the linear current according to Ohm＇s law. Analyzing its transport behavior reveals that the additional current density is due to the extra oxygen vacancies induced by the electric field. The formation rate of the extra vacancies and associated current was related to the field strength.展开更多
The dense ZnO-Bi_(2)O_(3)-MnO_(2)(ZBMS)varistors for x=0,1,2,3 wt% were fabricated by flash sintering method under the low temperature of 850℃ within 2 min.The sample temperature was estimated by a black body radiati...The dense ZnO-Bi_(2)O_(3)-MnO_(2)(ZBMS)varistors for x=0,1,2,3 wt% were fabricated by flash sintering method under the low temperature of 850℃ within 2 min.The sample temperature was estimated by a black body radiation model in the flash sintering process.The crystalline phase assemblage,density,microstructure,and electrical characteristics of the flash-sintered ZBMS varistors with different SiO_(2)-doped content were investigated.According to the XRD analysis,many secondary phases were detected due to the SiO_(2) doping.Meanwhile,the average grain size decrease with increasing SiO_(2)-doped content.The improved nonlinear characteristics were obtained in SiO_(2)-doped samples,which can be attributed to the ion migration and oxygen absorption induced by the doped SiO_(2).The flash-sintered ZBMS varistor ceramics for x=2 wt% exhibited excellent comprehensive electrical properties,with the nonlinear coefficient of 24.5,the threshold voltage and leakage current of 385 V·mm^(-1 )and 11.8μA,respectively.展开更多
基金supported by Shanghai Pujiang Program[No.18PJ1406500]the National Natural Science Foundation of China[No.51902197]the Start-up Foundation for the Youth Scholars of Shanghai Jiao Tong University[No.18×100040024]。
文摘Fabrication of graphene/ceramic composites commonly requires a high-temperature sintering step with long times as well as a vacuum or inert atmosphere,which not only results in property degradation but also significant equipment complexity and manufacturing costs.In this work,the ambient flash sintering behavior of reduced graphene oxide/3 mol% yttria-stabilized ZrO_(2)(rGO/3 YSZ) composites utilizing rGO as both a composite component and a conductive additive is reported.When the sintering condition is carefully optimized,a dense and conductive composite can be achieved at room temperature and in the air within 20 s.The role of the rGO in the FS of the rGO/3 YSZ composites is elucidated,especially with the assistance of a separate investigation on the thermal runaway behavior of the rGO.The work suggests a promising fabrication route for rGO/ceramic composites where the vacuum and furnace are not needed,which is of interest in terms of simplifying the fabrication equipment for energy and cost savings.
基金The work was financially supported by the National Natural Science Foundation of China(Nos.51874023,U1860206)the Fundamental Research Funds for the Central Universities(No.FRF-TP-20-02B)the Recruitment Program of Global Experts.
文摘The high burn-up structure(HBS)is characterized by the grain size of 100-300 nm and a porosity of up to 20%,which is formed at the rim of the nuclear fuel pellet due to 2-3 times higher local burn-up during the in-pile irradiation.HBS is considered a new potential structure for high-performance fuels.However,it is difficult to prepare HBS by conventional sintering methods.In this study,flash sintering was used to prepare HBS using CeO_(2)as a surrogate for a preliminary investigation.A new experimental configuration for rapid sintering of CeO_(2)pellets was provided,in which the green body can be rapidly preheated and pressure-assisted by the induction heating electrodes.An insulated quartz tube was used as the die for the flash sintered samples,allowing the current to flow through the sample and providing a stable condition for applying an external pressure of approximately 5.3-7.0 MPa during flash sintering process.Using an initial electric field of 141 V cm-1 and holding for 1-7 min at the maximum current density of~98 mA mm^(-2),CeO_(2)ceramics with a grain size of 114-282 nm and a relative density of 75.4-99.7%were prepared.The densification and microstructure evolution behaviors during flash sintering in this new experimental configuration have been discussed in detail.This new experimental configuration may provide a promising approach for preparing UO_(2)ceramics and their HBS.
基金supported by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior-Brazil(CAPES),under Finance Code 001the Conselho Nacional de Desenvolvimento Científico e Tecnológico-Brazil(CNPq),under grant Nos.309410/2017-7 and 308474/2021-0the Fundação de AmparoàPesquisa do Estado de São Paulo-Brazil(FAPESP),under grants Nos.12/06448-0 and 07/54974-5.R.N.R.
文摘Flash sintering has proven to be a novel and cost-efficient technique that enables the successful processing of dissimilar materials.The present work investigated how sintering under electric field input progresses in commercial anatase(A)plus rutile(B)polymorphs containing titania.Both the phase evolution and sintering dynamics were highly dependent on the strength of the field,the application of which led to(A+R)→R→flash at low fields while promoting(A+R)→flash at high fields.A temperature postponement of flash was verified at low fields,as the event was preceded by the A→R transformation,which was responsible for a detectable peak in the thermal spectra of the current.The processing temperature,applied electric field(E),and onset flash sintering temperature(T^(flash)_(furn))combine well into a phase diagram graph that summarizes the phase development that applies to this material.In addition,high-density bodies in the rutile phase were ultimately produced after flashing under a suitable current density,regardless of the field strength considered.Both the flash sintering temperature and average grain size(AGS)decreased with increasing field.In line with this,we demonstrate the existence of a direct link between the grain size and the sample sintering temperature,which is consistent with the classical grain growth model.
基金financially supported by the National Natural Science Foundation of China(No.52272074)the Department of Science and Technology of Sichuan Province(No.2021JDJQ0019)+1 种基金the State Key Laboratory of Solidification Processing,Northwestern Polytechnical University(No.SKLSP202104)the Fundamental Research Funds for the Central Universities(Nos.2682025ZTPY011 and 2682024GF011).
文摘Understanding the onset mechanism of flash sintering is essential for advancing electric-field-assisted sintering technologies.Herein,the onset temperature of flash sintering(FS)was examined for alumina-8 mol%yttria-stabilized zirconia(Al_(2)O_(3)-8YSZ)composites with varying molar ratios of Al_(2)O_(3)and 8YSZ under an applied electric field of 900 V/cm.The results show a composition-dependent variation in the onset temperature,which can be divided into three different regions on the basis of the Al_(2)O_(3)content,each reflecting a different onset mechanism.In region Ⅰ(0-62.5 mol%),the flash sintering behavior is dominated by 8YSZ owing to the internal electrochemical reaction driven by the electric field.In region Ⅱ(62.5-80 mol%),flash sintering is determined by the percolation networks of 8YSZ,which offer conduction paths for current.In region Ⅲ(80-99 mol%),isolated 8YSZ particles catalyze the flash sintering of Al_(2)O_(3)through interfacial dielectric breakdown.These results highlight a composition-dependent transition in the onset mechanism of flash sintering:Composites with low Al_(2)O_(3)contents exhibit defect-dominated flash sintering associated with 8YSZ,whereas those with high Al_(2)O_(3)contents follow a thermally controlled mechanism.Thus,Al_(2)O_(3)and 8YSZ exhibit distinct onset mechanisms during flash sintering.
基金supported by the National Research Foundation of Korea(NRF)grant funded by the Korea government(MSIT)(RS-2024-00395914)the Korea Institute of Energy Technology Evaluation and Planning(KETEP)granted financial resource from the Ministry of Trade,Industry&Energy,Republic of Korea(20213030030040 and 20212020800090).
文摘Metal-supported solid oxide fuel cells(MS-SOFCs)have recently gained significant attention as an advanced SOFC technology,owing to their excellent mechanical robustness,ease of handling,and high manufacturability.The use of metal substrates enables improved durability under thermal and redox cycling,and allows for thinner electrolyte layers,contributing to enhanced performance.However,their fabrication typically requires high-temperature sintering to ensure adequate material properties and adhesion,as most SOFC components are ceramic.These high-temperature processes can lead to undesirable effects,including metal support oxidation,chemical side reactions,and accelerated particle growth,which degrade cell performance.This study introduces an ultra-fast sintering approach for MS-SOFC fabrication by directly integrating stainless-steel metal supports with nickel-yttria-stabilized zirconia(Ni-YSZ)composite anode active layers.The application of flash light sintering-an innovative ultra-fast technique-effectively suppressed Ni catalyst particle growth,expanding the electrochemical reaction area while minimizing material diffusion between the metal support and anode layer.As a result,the fabricated cells achieved a stable open-circuit voltage(OCV)exceeding 1 V at 650℃ and a peak power density of 412 mW/cm^(2),representing an approximately 426.3% performance improvement over conventionally sintered cells.This research presents a transformative strategy for SOFC manufacturing,addressing the challenges of conventional long-duration heat treatments and demonstrating significant potential for advancing energy conversion technologies.
基金This work was supported by the National Natural Science Foundation of China(No.52077118)the Guangdong Basic and Applied Basic Research Foundation(No.2021A1515011778)the State Key Laboratory of New Ceramics and Fine Processing Tsinghua University(No.KFZD201903).
文摘This is the first study to conduct the flash sintering of 3 mol%yttria-stabilized zirconia(3YSZ)ceramics at room temperature(25℃)under a strong electric field,larger than 1 kV/cm.At the standard atmospheric pressure(101 kPa),the probability of successful sintering is approximately half of that at low atmospheric pressure,lower than 80 kPa.The success of the proposed flash sintering process was determined based on the high electric arc performance at different atmospheric pressures ranging from 20 to 100 kPa.The 3YSZ samples achieved a maximum relative density of 99.5%with a grain size of~200 nm.The results showed that as the atmospheric pressure decreases,the onset electric field of flash sintering decreases,corresponding to the empirical formula of the flashover voltage.Moreover,flash sintering was found to be triggered by the surface flashover of ceramic samples,and the electric arc on the sample surfaces floated upward before complete flash sintering at overly high pressures,resulting in the failure of flash sintering.This study reveals a new method for the facile preparation of flash-sintered ceramics at room temperature,which will promote the application of flash sintering in the ceramic industry.
基金supported by the National Natural Science Foundation of China(No.52077118)the Guangdong Basic and Applied Basic Research Foundation(No.2021A1515011778)State Key Laboratory of Power System Operation and Control,Tsinghua University(No.SKLD22KM01).
文摘Oxygen vacancy OV plays an important role in a flash sintering (FS) process. In defect engineering, the methods of creating oxygen vacancy defects include doping, heating, and etching, and all of them often have complex processes or equipment. In this study, we used dielectric barrier discharge (DBD) as a new defect engineering technology to increase oxygen vacancy concentrations of green billets with different ceramics (ZnO, TiO_(2), and 3 mol% yttria-stabilized zirconia (3YSZ)). With an alternating current (AC) power supply of 10 kHz, low-temperature plasma was generated, and a specimen could be treated in different atmospheres. The effect of the DBD treatment was influenced by atmosphere, treatment time, and voltage amplitude of the power supply. After the DBD treatment, the oxygen vacancy defect concentration in ZnO samples increased significantly, and a resistance test showed that conductivity of the samples increased by 2–3 orders of magnitude. Moreover, the onset electric field (E) of ZnO FS decreased from 5.17 to 0.86 kV/cm at room temperature (RT);while in the whole FS, the max power dissipation decreased from 563.17 to 27.94 W. The defect concentration and conductivity of the green billets for TiO_(2) and 3YSZ were also changed by the DBD, and then the FS process was modified. It is a new technology to treat the green billet of ceramics in very short time, applicable to other ceramics, and beneficial to regulate the FS process.
基金This work was supported by the National Natural Science Foundation of China(No.52077118)the Guangdong Basic and Applied Basic Research Foundation(No.2021A1515011778)the State Key Laboratory of New Ceramics and Fine Processing Tsinghua University(No.KFZD201903).
文摘In this study,we reported that flash sintering(FS)could be efficiently triggered at room temperature(25℃)by manipulating the oxygen concentration within ZnO powders via a versatile defect engineering strategy,fully demonstrating a promising method for the repaid prototyping of ceramics.With a low concentration of oxygen defects,FS was only activated at a high onset electric field of~2.7 kV/cm,while arcs appearing on the surfaces of samples.Strikingly,the onset electric field was decreased to<0.51 kV/cm for the activation of FS initiated,which was associated with increased oxygen concentrations coupled with increased electrical conductivity.Thereby,a general room-temperature FS strategy by introducing intrinsic structural defect is suggested for a broad range of ceramics that are prone to form high concentration of point defects.
基金This work was supported by the National Natural Science Foundation of China(52077118)Guangdong Basic and Applied Basic Research Foundation(2021A1515011778)Key Laboratory of Engineering Dielectrics and Its Application(Harbin University of Science and Technology),Ministry of Education(KFM202204).
文摘For the first time,the flash sintering(FS)of high-purity alumina at room temperature,which was previously considered unachievable due to its low electrical conductivity,was conducted herein.The electrical arc originating from surface flashover was harnessed to induce FS at room temperature and low air pressure.The successful FS of high-purity alumina was realized at 60 kPa under the arc constraint,resulting in a notable relative density of the alumina sample of 98.7%.The electric–thermal coupling between the arc and high-purity alumina sample during the arc-induced FS process was analyzed via the finite element simulation method.The results revealed the thermal and electrical effects of the arc on the sample,which ultimately enhance the electrical conductivity of the alumina sample.The formation of a conductive channel on the sample surface,a result of increased electrical conductivity,was the pivotal factor in achieving FS in high-purity alumina at room temperature.The arc constraint technique can be applied to numerous materials,such as ionic conductors,semiconductors,and even insulators,under room-temperature and low-air-pressure conditions.
基金financially supported by the National Natural Science Foundation of China(Nos.52472064 and 12305298)the Open Project of State Key Laboratory of Environmentally-friendly Energy Materials(No.23kfhg06)+1 种基金the Sichuan Science and Technology Program(No.2022JDTD0017)the Natural Science Foundation of Jiangsu Province(No.BK20230864).
文摘The introduction of oxygen vacancies into zirconia is an effective strategy for enhancing its light absorption ability and photocatalytic performance.However,the cost-efficient preparation of oxygen-deficient zirconia(ZrO_(2−x))remains challenging,which severely limits its broad application.In this study,flash sintering treatment was used to fabricate ZrO_(2−x) bulk in very short time of 90 s.Oxygen vacancies were introduced into ZrO2 bulk through electrochemical reduction reactions.The as-prepared black ZrO_(2−x) exhibited excellent optical absorption capability,a small band gap(2.09 eV for direct and 1.67 eV for indirect),and a reduced conduction band energy,which is ascribed to the generation of oxygen vacancies and reduction of Zr cations.The as-prepared ZrO_(2−x) showed remarkable photocatalytic activity due to excellent solar light absorption and low recombination rate of electron‒hole pairs.Flash sintering treatment provides a cost-efficient approach for rapidly fabricating ZrO_(2−x) bulk materials with high concentrations of oxygen vacancies,which can also be applied to other materials.
基金supported by the National Natural Science Foundation of China(No.92160202)the National Natural Science Foundation of China(No.52375188)+1 种基金the National Key R&D Program of China(No.2021YFB3703100)the Ningbo Key Technology Research and Development(No.2023T007).
文摘Flash sintering(FS)is a novel technique for rapidly densifying silicon carbide(SiC)ceramics.This work achieved a rapid sintering of SiC ceramics by the utilization of ultra-high temperature flash sintering within 60 s.Pyrolysis carbon(PyC)“bridges”were constructed between SiC particles through the carbonisation of phenolic resin,providing a large number of current channels.The incubation time of the flash sintering process was significantly reduced,and the sintering difference between the centre and the edge regions of the ceramics was minimized,with an average particle size of the centre region and edge region being 12.31 and 9.02μm,respectively.The results showed that the porosity of the SiC ceramics after the flash sintering was reduced to 14.79% with PyC“bridges”introduced,and the Vickers hardness reached 19.62 GPa.PyC“bridges”gradually evolved from amorphous eddy current carbon to oriented graphite carbon,indicating that the ultra-high temperature environment in which the sample was located during the flash sintering was successfully constructed.Ultra-high temperature flash sintering of SiC is expected to be applied to the local repair of matrix damage in SiC ceramic matrix composites.
基金supported by the National Natural Science Foundation of China(No.52077118)the Open Fund of the State Key Laboratory of High-Efficiency and High-Quality Conversion for Electric Power(No.2024KF006)+2 种基金the Guangdong Basic and Applied Basic Research Foundation(No.2024A1515012597)the State Grid Jiangxi Electric Power Company Science and Technology Project(No.52182025000H)the Jiangxi Key Research and Development Program(No.20243BBG71028).
文摘Room-temperature flash sintering(FS)for ceramics is a highly efficient and energy-saving new ceramic sintering technique.Addressing the current challenges in room-temperature flash sintering research,such as small product sizes,shape limitations,and high power requirements,limits their real application in the FS industry.In particular,for dog bone shape and small size,which are usually smaller than 10 mm,no records of sizes larger than 20 mm have been reported.In this study,a novel flash sintering device based on a composite layered carbon electrode structure was developed to conduct large-diameter sample flash sintering at room temperature(RT)in an air atmosphere under a direct current(DC)voltage below 10o V.Specifically,room-temperatureflash sintering was achievedfor Zn0 ceramic disks with diameters of 40.0 mm and thicknesses of 1.80 mm,achieving a maximum relative density of 96.02%.Furthermore,room-temperature flash sintering was achieved for ZnO varistor ceramic disks with a diameter of 40.0 mm and a thickness of 1.93 mm,reaching a maximum relative density of 99.27%,a maximum voltage gradient of 330.5 V·mm^(-1),and the highest nonlinearity coefficient(a)of 23.0.Room-temperature flash sintering was also achieved for 3 mol%yttrium-doped zirconia(3YSZ)ceramic disks,achieving a maximum relative density of 98.48%.The proposed flash sintering device and corresponding process demonstrate broad applicability for the ceramics industry.
基金financially supported by National Natural Science Foundation of China(Grant Nos.51372202,51402237,51532003,51602264)State Key Laboratory of Traction Power(Grand No.2015TPL Z01)
文摘The effect of the applied electric field on the conductive behavior of zirconia ceramics is studied by measuring its initial current-voltage curve at various temperatures. The results show that when the field strength is higher than the threshold for flash-sintering, the curves exhibit a nonlinear behavior by having an additional current on top of the linear current according to Ohm＇s law. Analyzing its transport behavior reveals that the additional current density is due to the extra oxygen vacancies induced by the electric field. The formation rate of the extra vacancies and associated current was related to the field strength.
基金financially supported by National Natural Science Foundation of China(Grant Nos.51802003 and 51572113)State Key Laboratory of New Ceramic and Fine Processing Tsinghua University(No.KF201808)the Project National United Engineering Laboratory for Advanced Bearing Tribology(No.201912).
文摘The dense ZnO-Bi_(2)O_(3)-MnO_(2)(ZBMS)varistors for x=0,1,2,3 wt% were fabricated by flash sintering method under the low temperature of 850℃ within 2 min.The sample temperature was estimated by a black body radiation model in the flash sintering process.The crystalline phase assemblage,density,microstructure,and electrical characteristics of the flash-sintered ZBMS varistors with different SiO_(2)-doped content were investigated.According to the XRD analysis,many secondary phases were detected due to the SiO_(2) doping.Meanwhile,the average grain size decrease with increasing SiO_(2)-doped content.The improved nonlinear characteristics were obtained in SiO_(2)-doped samples,which can be attributed to the ion migration and oxygen absorption induced by the doped SiO_(2).The flash-sintered ZBMS varistor ceramics for x=2 wt% exhibited excellent comprehensive electrical properties,with the nonlinear coefficient of 24.5,the threshold voltage and leakage current of 385 V·mm^(-1 )and 11.8μA,respectively.
