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1.
研究了加压辅助闪烧烧结工艺参数(温度、电压、电流、压力)对钇稳氧化锆致密度、微观组织结构和成分组成的影响,该工艺在热压烧结基础上叠加闪烧效应,利用高电场强度使高温导电氧化锆瞬间发生密实化烧结.结果表明:钇稳氧化锆的闪烧临界温度为880℃,在相同的电场强度条件下,闪烧临界温度处烧结可获得最大的闪烧收缩量.氧化锆在临界烧结...  相似文献   

2.
    
The effect of direct current (DC) and alternating current (AC) on nitridation of 3 mol% Y2O3-doped ZrO2 (3YSZ) after keeping in a flash state for 1 hour was investigated. The inside of the DC-flashed compact was confirmed to exhibit blacking. Scanning transmission electron microscopy, electron energy loss spectroscopy, and X-ray diffraction analysis revealed that zirconium nitrides formed in the blackened area. In contrast, a uniformly densified compact without blackening was obtained by AC fields. No zirconium nitrides formed in the compacts exposed to AC fields even when the flash state was maintained for 1 hour. Therefore, AC fields are effective to suppress nitridation of 3YSZ during flash sintering.  相似文献   

3.
    
Microwave Pressing is a promising way to reduce microwave sintering temperatures and stabilize microwave powder materials processing. A multiphysics simulation was conducted of the regulated pressure-assisted microwave cavity. This simulation took into consideration resonance phenomena and the nonlinear temperature-dependent material parameters of zirconia. The intrinsic behaviors of microwave systems and zirconia make the regulation of the microwave pressing difficult. However, the same phenomena can be used to activate flash sintering. Flash microwave sintering uses high electric fields of the resonant microwave profile, the Negative Temperature Behavior (NTC) of zirconia resistivity, and the mechanical pressure applied to the powder via a die compaction configuration. The resulting flash microwave pressing still needs improvement in terms of the processed material structure homogeneity, but it has the capacity to become the fastest sintering treatment as it allows room temperature activation where the total process time only takes a few seconds. In addition, this 10-20 seconds processing technique has shown good potential for improving the transparency of alumina presintered specimens.  相似文献   

4.
    
Flash sintering of ceramics is characterized by rapid sintering during simultaneous application of electric field and heat. Previous studies of flash sintering have been conducted in furnace environments, where sample temperatures are approximately uniform. In this work, we use highly dynamic heating from a scanning laser to initiate flash sintering while simultaneously applying a DC electric field. Onset of flash sintering is determined by a measurable increase in current through the sample. Our results show that stage I and stage II flash sintering can be initiated by laser heating. At low-to-moderate combinations of laser energies and applied electric fields, measured current rises slightly when the laser is scanned completely across the specimen from the positive to the negative electrodes. Microstructures for these samples show that powder consolidation is minimal in this regime (stage I flash sintering), and thus the observed current is likely due to onset of neck growth between powder particles rather than densification. At higher laser energies and fields, current rises steeply and microstructures show significant consolidation (stage II flash sintering). The demonstration that flash sintering occurs when ceramic is heated by laser-scanning supports future utilization of selective laser flash sintering as an additive manufacturing process.  相似文献   

5.
    
Reactive flash sintering is a process where off-the-shelf powders of elemental oxides can be simultaneously sintered and reacted to form a multicomponent oxide in a matter of seconds at low furnace temperatures. The fact that several cation species, each residing within their own particles, can migrate over distances of several micrometers, and mix on the atomic scale to form multicomponent oxides, so quickly, is quite remarkable. The question arises as to the rate of this solid-state diffusion phenomenon. In this paper, we present measurements of this diffusion coefficient from live flash experiments. The results are obtained from millimeter scale bilayers of yttria-stabilized zirconia and lanthana where the flash initiates in the zirconia layer and then migrates into the lanthana layer, forming lanthanum zirconates. The velocities of migration of the flash-front, coupled with measurements of the length scale of the profile of zirconium and lanthanum interdiffusion, across the bilayer interface, provide an estimate of the effective diffusion coefficient. These measurements give a value for the cation diffusion to lie in the range of 2.5 × 10−10 m2 s−1 at 1380°C, with an activation energy of 200–250 kJ mol−1. In comparison, the cation diffusion coefficient in yttria-stabilized zirconia, at 1350°C, is stated to be 1.1 × 10−20 m2 s−1 with an activation energy of ∼550 kJ mol−1. A pause for reflection.  相似文献   

6.
    
Flash sintering of alumina is more difficult than of yttria-stabilized zirconia (YSZ). Whereas (MgO doped) alumina requires fields greater than 1 kVcm–1 and temperatures often significantly higher than 1000°C, YSZ can be flashed sintered at ∼100 Vcm–1 at temperatures below 800°C. Mixed powders of such bi-phasic ceramics, on the other hand, can be flashed under conditions below those for alumina. This effect is usually subscribed to the influence of YSZ on the overall electrical conductivity of the composite. However, such rationalization leaves open the mechanism by which YSZ catalyzes the flash event in alumina. Here, we present results for the onset of flash in a layered structure of YSZ and alumina where both constituents extend from one electrode to the other. We find that the flash initiates, at first, exclusively in the YSZ layer, under conditions identical to those in usual voltage-to-current experiments in single phase YSZ, and then, after a brief incubation period, spreads transversely through the thickness of the alumina layer at a speed of ∼3.3 mm s–1, while the power supply is held at constant current. This observation opens a new question as to how flash once initiated in an “easy” phase can migrate normal to itself into a second ceramic, which is nominally more-difficult-to flash. (In the present experiments, the alumina layer sintered to full density with all the shrinkage being accommodated in the thickness direction, consistent with an earlier study that articulated that flash obviates constrained sintering.) It is noteworthy that the catalytic effect depends not only on the volume fraction of YSZ, but also on the architecture of the green state (for example a two-phase powder mixture vs. layered structure), which may affect the initiation of the flash in YSZ but, likely, not its migration behavior into the second phase.  相似文献   

7.
It is difficult to obtain pure ZrO2 sintered compacts with a bulk style at room temperature because a large volumetric expansion from tetragonal to monoclinic phase (t/m) transformation occurs at around 1000°C, which is lower than the sintering temperature. In contrast, pure monoclinic ZrO2 can be consolidated without shattering using flash‐sintering at 1350°C for 5 minutes under an applied DC electric field of 175 V/cm. High‐resolution transmission electron microscopy and electron energy loss spectroscopy have revealed that amorphous films are formed along grain boundaries after flash‐sintering at 1350°C for 5 minutes. Monoclinic ZrO2 flash‐sintered compact including the amorphous films are able to survive without shattering through the t/m transformation, as the amorphous films partially absorb the large volumetric expansion arising from the t/m transformation. The formation of the amorphous films results from the severe reducing condition due to the applied DC electric fields during flash‐sintering.  相似文献   

8.
    
In this study, flash joining experiments were conducted using an AC field on 3 mol% Y2O3-stabilized tetragonal ZrO2 polycrystal (Y-TZP) bodies. Furthermore, the necessary conditions to obtain an almost complete self-joining of Y-TZP bodies were clarified. The specimens were successfully joined by applying an AC field at 60 mA mm−2 for 80 s at a furnace temperature of 1000°C, thus resulting in a successfully joined specimen with 92% of the flexural strength of the as-sintered Y-TZP body. Almost complete self-joining of Y-TZP was achieved at current densities above 30 mA mm−2, and input energy densities of >24 J mm−3. Both the input energy density and electric current were critical factors for producing the reliable joining of ceramics.  相似文献   

9.
    
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.  相似文献   

10.
ABSTRACT

The graphene/ZrO2 composites were fabricated by impregnating graphene dispersion into the ZrO2 ceramic matrix and sintered by microwave, and the microstructure and mechanical properties were investigated. The results showed that the graphene was well dispersed in the ceramic matrix and refined the grain size. The fracture toughness reached 8.62?MPa?m1/2, confirmed by single-edge notched beam, which was 42% higher than that of the pure ZrO2. Also, the toughening mechanisms were investigated by micro-hardness testing and showed that a combination of crack deflection, micro-crack and crack bridging increased the fracture toughness.  相似文献   

11.
    
Implementing pressure-assisted flash sintering of ZnO powder without pretreatment by a new experimental configuration is presented. Rapid and energy-concentrated heating of electrode-sample-electrode area by induction heating allows preheating and flash sintering of loose-pack powder in the die with pressure assistance. Using an insulated die enables the current to flow through the sample during flash sintering. ZnO ceramics with a relative density of 95.1% can be achieved in less than 3 min. The whole process includes 104 s of preheating by a low-power induction heating device and 30 s of flash sintering assisted by a pressure of 26 MPa using the pulsed direct current (DC). The process characteristics of pressure-assisted flash sintering using the pulsed DC are discussed. The effect of pressure on densification and grain size is analyzed in detail, and some potential mechanisms are provided.  相似文献   

12.
ZTA陶瓷微波烧结研究   总被引：10，自引：1，他引：10  
采用２．４５ＧＨＺ，５ＫＷ功率源的多模腔微波烧结装置对１５％（按质量计，下同）ＺｒＯ２（２．５％ｍｏｌ）Ｙ２Ｏ３＋８５％Ａｌ２Ｏ３的ＺＴＡ陶瓷的微波加热烧结特性，显微结构和力学性能作了较系统的研究，并与常规烧结进行比较，通过合理的保温结构设计和良好的爱人本负载阻抗匹配实现了微波快速绕结。实验发现：在多模腔中ＺＴＡ陶瓷坯体经微波加热约３０ｍｉｎ至１５４０℃保温２０ｍｉｎ（共约５０ｍｉｎ），其密度可达  相似文献   

13.
    
Flash sintering (FS) is an important technique in the field of ceramic sintering. Nevertheless, conventional FS is less attractive for practical applications because of the complex shapes and small sizes of the specimens. In this study, using the novel electric field-assisted hot pressing (FAHP) technique, we successfully achieved FS during the net-shape hot pressing (HP) process for the first time. It was found that the 3 mol% yttria-stabilized zirconia (3YSZ) can be flash sintered at 909°C using a fairly low DC field of 33 V/cm under 30 MPa pressure. The grain sizes of the FAHP-sintered samples were 20% smaller than that of the HP-sintered sample. When the current density limit is ≥240 mA/mm2, 3YSZ can be fully densified during the flash events. Careful analysis of the sintering curves suggests that although the carrier type or concentration is changed during flash events, it cannot explain the ultrafast densification. Additionally, we devised a qualitative method to analyze the densification mechanism. The results indicated that the ultrafast densification observed during flash events resulted from the synergistic effects of the rapid heating rate and peak sample temperature. Finally, the atomic force microscopy confirmed the lower grain boundary energy for the FAHP-sintered samples, which accounts for the smaller grain sizes than the HP-sintered sample. We believe that the FAHP technique could create new possibilities for theoretical and applied research on field-assisted sintering techniques.  相似文献   

14.
    
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.  相似文献   

15.
    
Electric field-assisted sintering (FAST) is a rapidly growing scientific and engineering domain. In the present paper, we describe the process of flash sintering (FS) in a configuration of classical spark plasma sintering (SPS) (graphite punch and boron nitride (BN) die), also called flash spark plasma sintering (FSPS). The densification process of Gd0.1Ce0.9O2-x powder is studied in detail with a focus on the transition from FAST to FS. We discuss the electrical, geometrical, and thermal evolution of the process and the characteristics of the final compacts. Low electrical fields are sufficient for the onset of FS. Ceria is a material difficult to sinter by FAST techniques due to its known mechanochemical transformations. We observed the disintegration of pellets after experiments with well-pronounced flash event.  相似文献   

16.
    
We report on the discharge of the capacitance formed at the electrodes in flash experiments with yttria stabilized zirconia. The experiments were carried out by disconnecting the current, and, instead, short circuiting the electrodes through a resistor. The time dependent voltage across the resistor was measured; the ratio yielded the discharge current. The current decayed exponentially with time, as expected in an RC circuit, which allowed the measurement of the capacitance. Experiments were carried out in two ways. In one case the specimens were flashed within a glove box filled with Ar (< 1 ppm O2): these yielded electronic conductors. In the other case the specimens were flashed in ambient air: while electronically conducting in-flash these specimens recover their prior insulating behavior as soon as the current is turned off. The stored charge was two orders of magnitude greater in the Ar experiments. Rather unexpectedly, the sign of the voltage expressed at the electrodes was opposite in experiments carried out in air and in Ar. The capacitance measured in the discharge experiments is attributed to the formation of space charge adjacent to the electrodes. In the case of Ar experiments, the capacitance is very large, approaching 1 F; in this case the space charge is expected to be constituted from ions. In the air experiments the specimen becomes insulating, trapping the electrons as a space charge. Hall effect measurements of the carrier density and X-ray photoelectron spectroscopy characterization of electronically conducting single crystal specimen of cubic zirconia are reported.  相似文献   

17.
    
This work presents an extension of the touch-free flash sintering technique. In the proposed technique, chemical reaction and sintering occur in a single step, without the use of electrodes, in the presence of electric and magnetic fields. We show that a dense, single-phase strontium hexaferrite magnet can be produced from a mixture of commercial carbonate and oxide powders in a single step in a little more than a minute. This new technique implies significant reduction in energy and time consumption (primarily because of ultrafast processing) relative to conventional sintering.  相似文献   

18.
王浩  薛群虎  樊拓 《硅酸盐通报》2017,36(12):4151-4156
分别以化学法和电熔法制备的氧化锆及二者混合共磨粉为原料,通过造粒、成型、干燥、烧成制得样品,对烧成样品物理性能和微观结构进行分析,研究原料活性对烧结性能的影响.研究结果表明:在加入同样稳定剂的条件下,电熔氧化锆活性较差,烧结后气孔率较高,化学氧化锆烧结后收缩大,开裂严重,两者都无法满足作为制备氧化锆质定径水口基质原料要求,当二者的混合比例为1:1时,试样的烧结温度合适,气孔率、烧成收缩、耐压强度等各项理化指标较好,满足用作制备氧化锆质定径水口基质要求.  相似文献   

19.
Direct and hybrid microwave sintering of 3Y‐ZrO2 are comparatively studied at frequency of 2.45 GHz. Using the continuum theory of sintering, a fully coupled electromagnetic‐thermal‐mechanical (EMTM) finite element simulation is carried out to predict powder samples deformation during their microwave processing. Direct and hybrid heating configurations are computationally tested using advanced heat transfer simulation tools including the surface to surface thermal radiation boundary conditions and a numeric proportional‐integral‐derivative regulation (PID). The developed modeling framework shows a good agreement of the calculation results with the known experimental data on the microwave sintering of 3Y‐ZrO2 in terms of the densification kinetics. It is shown that the direct heating configuration renders highly hot spot effects resulting in nonhomogenous densification causing processed specimen's final shape distortions. Compared with the direct heating, the hybrid heating configuration provides a reduction of the thermal inhomogeneity along with a densification homogenization. As a result of the hybrid heating, the total densification of the specimen is attained without specimen distortions. It is also shown that the reduction of the sample size has a stabilization effect on the temperature and relative density spatial distributions.  相似文献   

20.
通过改进混合加热模式,实现了ZTA陶瓷微波烧结。材料的类型及配比直接影响微波烧结的升温速率;输入功率的提高有助于提高烧结速率;辅助加热体的老化现象降低微波烧结速率;微波烧结过程中应避免出现热剧变现象。  相似文献   

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