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采用共沉淀－球磨法制得纳米级氧化锆粉料，用ＳＥＭ对其烧结性作了研究，ＳＥＭ结果表明不同的烧结制度导致烧结体的显微组织有很大的差异，９００℃～１３００℃是烧结的重要阶段，这期间晶粒由大→小→大的变化，而气孔则由大→小，１３００℃时烧结体的气孔形状，数量和位置分布与烧结终期极为相似；在１３００℃以上晶粒进一步长大，气孔作自身调整直至烧结结束。 相似文献
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An oscillatory pressure sintering of zirconia powder: Densification trajectories and mechanical properties 
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下载免费PDF全文 Yao Han Shuang Li Tianbin Zhu Weiwei Wu Di An Feng Hu Zunlan Hu Jian Liu Jingkun Xu Zhipeng Xie 《Journal of the American Ceramic Society》2018,101(5):1824-1829
The densification trajectories and mechanical properties of zirconia ceramics obtained by oscillatory pressure sintering (OPS) process were investigated, during the sintering process an oscillatory pressure was applied at three stages. Current results indicated that at intermediate stage the oscillatory pressure revealed a favorable improvement of mechanical properties compared with conventional hot pressing (HP) and pressureless sintering (PS) procedures, while the enhancement was not obvious at initial stage. When the oscillatory pressure was applied at final stage, the OPS specimens exhibited the highest bending strength and hardness of 1455 ± 99MPa and 16.6 ± 0.31GPa compared with the PS and HP specimens. Considering the high elastic modulus and Moiré patterns observed in the OPS specimen, the oscillatory pressure applied at intermediate and final stages was detected to facilitate the sliding of grain boundary, plastic deformation of monolithic grains, the removal of pores and the strengthening of atomic bonds. 相似文献
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由不同成型方法,单面或双面加压,制备了氧化锆层状复合陶瓷,研究了制备方法和工艺参数,如：加压压力、时间,对生坯密度的影响.探讨了生坯密度与烧结收缩之间的相关性.研究结果表明：选取成型压力在250 MPa左右,双向加压方式,可以获得沿x,y,z轴方向收缩较一致的层状陶瓷制品.引入评价不同方向的烧结收缩变化参数k（=a/b,a和b分别为沿x,y和z方向的烧结收缩率）,kxy,kz,当kxy=kz=1时,表示烧结过程基本完成,坯体中颗粒已达到致密化状态;当kxy-1/kz^2=0或接近于0时,表示沿x,y轴和z轴方向的烧结收缩基本无差别,是一种最佳的层状陶瓷烧结状态. 相似文献
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《Ceramics International》2020,46(6):7523-7530
Partially stabilized zirconia (PSZ) occupies an important application portion in ceramics materials and refractories materials. In this work, calcium oxide-partially stabilized zirconia (CaO-PSZ) ceramics were prepared from fused zirconia by microwave sintering, with its microstructure and stability properties characterized by XRD and SEM. Results indicated that the heating rate, cooling rate, quenching temperature and isothermal treatment time rendered different influence on the stability properties, which was mainly ascribed to the reversible martensitic transformation of zirconia ceramics. Additionally, a mixed-phase composed by cubic phase ZrO2 (c-ZrO2) and monoclinic phase ZrO2 (m-ZrO2) appeared after fused zirconia treated by microwave sintering at 1450 °C for 2 h, indicating the formation of CaO-PSZ ceramics, which the finding was consistent with the SEM and EDAX analysis. Meanwhile, CaO stabilizer precipitated behavior at the crystal boundary, with the formation of acicular grains and fine particles, further rendering a toughening effect to CaO-PSZ ceramics. This work can provide important theoretical and practical significance for applications of microwave sintering to prepare CaO-PSZ ceramics material, even extending further applications in functional materials and structural materials. 相似文献
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Yao Han Shuang Li Tianbin Zhu Zhipeng Xie 《Journal of the American Ceramic Society》2017,100(7):2774-2780
A novel oscillatory pressure sintering (OPS) process is reported to prepare high‐quality ceramics. The oscillatory pressure was applied at three stages (initial, intermediate, and final) during sintering process of zirconia ceramics for the first time. The microstructure of the samples prepared by OPS develops in a more homogeneous manner, leading to a higher final density, a smaller average grain size, and a narrower distribution of grain sizes compared with the samples prepared by conventional pressureless sintering (PS) and hot‐pressing (HP) processes. Remarkably, the OPS samples was obtained at relatively lower heating temperature and less soaking time for 1300°C and 0.5 hours than the samples prepared by other two techniques at 1450°C and 1 hour. The current results suggest that OPS is an effective technique for preparing high‐quality zirconia ceramics with low heating temperature and short sintering time, thus, it obviously reduces cost. 相似文献
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《Ceramics International》2019,45(10):13269-13274
In this work, the NBT ceramics are successfully flash sintered at a direct current 30 mA/mm2 for 30 s under different initial electric field. Subsequently, the actual temperature of samples is estimated by blackbody radiation theory under different conditions. The calculation results show that the sample temperature is close to the densification temperature of NBT ceramics used in conventional method. The rapid densification mechanism is discussed by wetting of local contact particles due to the asymmetrical Joule heating. In particular, we analyzed the particle transport mode during flash sintering in terms of particle diffusion. It is believed that the transform in the particles transport mode from solid diffusion to flow mass transfer accelerated the particles diffusion rate, which ensure the particle rearrangement and achieve the local shrinkage of particles in a short period of time. 相似文献
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In this paper, the usefulness of a mathematical model based on equations describing the diffusional phenomena which are variable with time, is developed and discussed in relation to serve as a model for experimental data of drying of Thompson seedless grapes. This model represents more closely the drying curves tested, than the classic diffusion model normally utilized to analize drying processes 相似文献
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Landen Cross Rishi Raj Syed I.A. Jalali 《Journal of the American Ceramic Society》2022,105(6):3746-3752
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
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《Journal of the European Ceramic Society》2022,42(15):7187-7195
This work describes the development of transparent high-strength Yttria-Stabilized Zirconia (YSZ) ceramics with ultra-fine grain size utilizing conventional pressure-less densification. Starting with nanoparticles with diameter < 10 nm, it was possible to achieve full densification (>99.5% of theoretical density) at a sintering temperature of 1100–1200 °C. The average grain size of the resulting dense ceramics was 75 nm in 3 mol. % YSZ and 85 nm in 8 mol. % YSZ, showing in-line light transmission of 38% and 51% at a wavelength of 800 nm and average biaxial strength (piston on three balls test on samples of diameter 12 mm and thickness 1 mm) of 1980 MPa and 680 MPa, respectively. The nano-grained structure, absence of color centers, and miniaturization of residual pores enable the excellent light transmission. The high biaxial strength is attributed to the refined microstructure, but also to the martensitic tetragonal-to-monoclinic phase transformation that remains active even in nano-sized zirconia grains. 相似文献
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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
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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
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We report the preparation of a category of ultrastrong tough zirconia ceramics by engineering defects using an oscillatory pressure during pressure assisted sintering. The introduced oscillatory pressure enhances the dynamic grain rearrangement, plastic deformation, mass transportation, and pore removal, leading to the formation of pore-free ceramics characterized by the rich coherent grain boundaries among individual mesocrystalline grains with intragranular quasi-interfaces. As a proof of concept, the pressure required by oscillatory pressure sintering (OPS) for preparing fully dense 3Y-TZP ceramics is significantly reduced, which is just ∼1/5 of that required by hot isostatic pressing. The OPS-prepared 3Y-TZP ceramics reached a record-breaking high bending strength and fracture toughness, being up to 1.8 GPa and 16 MPa·m1/2, respectively. This success illustrates a universal principle of engineering defects for making breakthrough in exploring other ultrastrong tough ceramics. 相似文献
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Yingchun Shan Xialu Wei Xiannian Sun Elisa Torresani Eugene A. Olevsky Jiujun Xu 《Journal of the American Ceramic Society》2019,102(2):662-673
High heating rates ranging from 50 to 250°C/min are selected to rapidly sinter transparent aluminum oxynitride (AlON) ceramics by spark plasma sintering (SPS) at 1600°C under 60 MPa using a bimodal AlON powder synthesized by the carbothermal reduction and nitridation method. With 1 minute holding time before cooling, all the specimens show high density and high transparence. The maximum transmittance is up to 74.5%-80.6%, where the maximum transmittance is positively correlated with the heating rate. Further analysis reveals that faster heating rates enable the decrease in the amount of the AlON phase decomposed into the α-Al2O3 and AlN phases during heating. These α-Al2O3 and AlN phases have to be converted back to AlON at the final stage of sintering, which indicates that a decrease in the amount of the α-Al2O3 and AlN phases via the boosted heating leads to the higher transmittance of the AlON ceramics. The high heating rates and short holding duration of the SPS utilized in this study result in the fine grain size of the obtained ceramics (1-6 μm) compared to that of the AlON ceramics fabricated by the conventional sintering method. This effect of high heating rates is confirmed by the coupled densification-grain growth modeling. In turn, the obtained AlON specimens exhibit a Vickers hardness of 15.87-16.62 GPa. 相似文献
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Fully coupled electromagnetic‐thermal‐mechanical comparative simulation of direct vs hybrid microwave sintering of 3Y‐ZrO2 下载免费PDF全文
下载免费PDF全文 Charles Manière Tony Zahrah Eugene A. Olevsky 《Journal of the American Ceramic Society》2017,100(6):2439-2450
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
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