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
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
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
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
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 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 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.
