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1.
Effect of Excess PbO on the Densification of PLZT Ceramics 总被引:1,自引:0,他引:1
Byung-Moo Song Doh-Yeon Kim Shin-ichi Shirasaki Hiroshi Yamamura 《Journal of the American Ceramic Society》1989,72(5):833-836
The densification behavior and electrical properties of PLZT ceramics as a function of excess PbO in the starting powder have been investigated. The hot-pressed PLZT ceramics, prepared from powders containing 0% to 4% excess PbO, were transparent, and their electrical properties were similar in general. PLZT with PbO deficiency up to 1.4 mol% from stoichiometry can be regarded as a single phase-PLZT. 相似文献
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Sintering of PZT Ceramics: I, Atmosphere Control 总被引:1,自引:0,他引:1
Methods of PbO atmosphere control during the sintering of PZT ceramics are briefly reviewed. The problem of atmosphere control of PZT compositions containing a PbO excess (PbO/(Zr,Ti)O2 >1) is discussed. Weight-loss experiments were performed to compare with behavior predicted by reference to the PbO-rich part of the ternary PbO-ZrO2 -TiO2 phase diagram. The results indicated that the PbO activity of a PZT composition is a function of the excess PbO content, contrary to earlier reports. Experimental procedures were established in order to control the PbO content within satisfactory limits. The effects of various packing powders on the PbO content of sintered PZT compacts were evaluated. 相似文献
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Aravind Mohanram Gary L. Messing David J. Green 《Journal of the American Ceramic Society》2005,88(10):2681-2689
In this paper, we present sintering and uniaxial viscosity data of three commercial low-temperature co-sintered ceramic systems, i.e., DuPont 951Tape (DU), Heraeus CT2000 (CT), and Ferro A6M (FE), measured by cyclic loading dilatometry. The viscosity initially decreases with temperature, changes little during the intermediate stage, and increases towards the end of densification. The viscosity increases sharply beyond the onset of crystallization. At slower heating rates, the viscosity increases at lower temperature, because of densification and crystallization. The isothermal viscosity data range from 0.1 to 100 GPa·s between 73% and 95% density. Ceramic particle-filled glasses show a higher isothermal viscosity compared with pure glass system, i.e., FE. From master viscosity curves based on isothermal data, the activation energies for viscous flow were ∼375±30 and 450±10 kJ/mol for DU and FE, respectively. These energies are comparable to values obtained from the master sintering curve approach. 相似文献
4.
The initial sintering kinetics of alumina have been studied by measuring the isothermal shrinkage of compacts of several alumina powders in air. The shrinkage of these compacts can best be described by a grain-boundary vacancy diffusion model for the temperature range 1200° to 1600°C. The behavior of the compacts is consistent with the model after an initial shrinkage has occurred. The magnitude of this initial shrinkage is constant for identical specimens and is independent of the sintering temperature. 相似文献
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Jun Wang Jian Zhang Kaijie Ning Dewei Luo Hao Yang Danlei Yin Dingyuan Tang Ling Bing Kong 《Journal of the American Ceramic Society》2016,99(5):1671-1675
Highly transparent 0.5 at.% Tm:Y2O3 ceramics were prepared by using solid‐state reaction combined with vacuum sintering method, with ZrO2 and Al2O3 as sintering aids. Doping amount of ZrO2 was fixed at 1 at.%, while the effect of Al2O3 on densification, microstructure evolution, and transmittance of the Y2O3 ceramics was carefully studied. It was found that the addition of Al2O3 was very effective in improving densification of Y2O3, due to the formation of an Al‐rich eutectic phase Y4Al2O9 (YAM) during the sintering process. As the content of Al2O3 was increased from 0 to 81.8 wt ppm, porosity of the ceramics was decreased and transmittance was increased. However, when the content of Al2O3 was increased to 137 wt ppm, a secondary phase began to segregate at grain junctions. Further increase in the amount of Al2O3 led to an increase in both amount and size of the secondary phase. At the optimized content of Al2O3 with 81.8 wt ppm, the Tm:Y2O3 ceramics sintered at 1860°C for 13 h exhibited an in‐line transmittance of 83.0% at 2000 nm and 76.5% at 600 nm. It is expected that this finding can be readily applied to other transparent ceramics. 相似文献
7.
Alida Bellosi Frédéric Monteverde Diletta Sciti 《International Journal of Applied Ceramic Technology》2006,3(1):32-40
This work investigated suitability and efficacy of the sintering technique known as spark plasma sintering to produce ultra-high-temperature-based Hf and Zr borides. Ceramic–matrix composites in the systems HfB2 –SiC, ZrB2 –MoSi2 , and ZrB2 –ZrC–SiC were processed by spark plasma sintering and hot pressing. The effects of processing were evaluated comparing the materials microstructure and properties. Compared with hot-pressing technique, spark plasma sintering offers the great advantage to fabricate successfully in short time (i.e., cuts in costs) poorly sinterable powder compositions without the help of any sintering activators. 相似文献
8.
Densification and Sintering Kinetics in Sintered Silicon Nitride 总被引:1,自引:0,他引:1
The sintering sequence of Y2 O3 -Al2 O3 -doped Si3 N4 was investigated with respect to the relationship between densification, α→β transformation, and microstructural development. Quenching studies were performed to reveal these interactions during a complete sintering cycle. Isothermal studies were conducted to examine the sintering kinetics and compared to Kingery's liquid-phase sintering model. The bulk density increased to ≥90% of theoretical density with only minor transformation taking place. Major transformation occurred in a late sintering stage and was accompanied by the development of elongated grains. The kinetic order of the densification process, taking into account an appropriate correction, was larger than any of the rate exponents predicted by the Kingery model, indicating that other single or mixed mechanisms were active. 相似文献
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Elliott B. Slamovich Frederick F. Lange 《Journal of the American Ceramic Society》1993,76(6):1584-1590
A kinetic analysis of densification is presented for the case of isolated, identical pores separated by dense, polyerystal-line material where the grain size is a variable (smaller to larger, relative to the pore size). The analysis includes the influence of both grain growth and mass transport rates on the driving potential for mass transport to the pore. For the expected condition where the rate of grain growth is much greater than the rate of pore shrinkage, it is shown that the driving potential is relatively independent of pore surface curvature, and approaches (2γs / R po ) sin (ψe /2) during grain growth, where γs is the surface energy per unit area of the material, ψe is the dihedral angle, and R po is the initial pore radius. Using this driving potential, an expression is derived for the current densification rate. The proposed mechanism for mass transport is radial diffusion through a spherical polycrystalline unit cell containing a spherical pore, where diffusion is restricted to grain boundaries that intersect the pore. The expression includes the average separation distance between pores and the grain boundary area intersecting each pore. This expression is in qualitative agreement for data reported in Part I for a Zr(3Y)O2 material where the grain size is always smaller than the pore size, and a Zr(8Y)O2 material where the grain size is larger than the pore size. 相似文献
10.
以β-Si3N4粉末为原料,以YAG(钇铝石榴石)为烧结助剂,通过气氛压力烧结(GPS)制备出致密的β-氮化硅陶瓷材料,形成大小均匀的柱状颗粒和小球状颗粒复合显微结构,研究了烧结助剂质量分数、烧结温度以及保温时间对β-氮化硅陶瓷致密化程度及力学性能的影响. 相似文献
11.
Olivier Sudre Gang Bao Bo Fan Fred F. Lange Anthony G. Evans 《Journal of the American Ceramic Society》1992,75(3):525-531
Experimental studies conducted in conjunction with a numerical analysis of strain-rate gradients have established the origin of the damage process that occurs upon the densification of powders containing nonsintering inclusions and reinforcements. The underlying phenomenon is the development of localized compressive strains in the porous matrix, both around high-aspect ratio reinforcements and between closely spaced reinforcements. These regions of compression densify first and then support grain growth. This process produces nondeformable networks that constrain the shrinkage of the adjacent, porous matrix. The constraint causes desintering and cracklike void formation in the lowdensity regions. The variables shown to be of importance are the volume fraction and aspect ratio of the reinforcements. The process is shown to be sensitive to the green density, such that a high initial density reduces initial damage and lowers the differential in densification. 相似文献
12.
Sintering Kinetics of Porous Ceramics from Natural Diatomite 总被引:7,自引:0,他引:7
Xuebin Zhang Xingqin Liu Guangyao Meng 《Journal of the American Ceramic Society》2005,88(7):1826-1830
The sintering kinetics of the porous ceramics from natural diatomite is investigated by means of stepwise isothermal dilatometry (SID) accompanied with XRD, scanning electron microscope (SEM), and porosity measurement. We find that the isothermal shrinkage data from SID could be well analyzed to get kinetic parameters according to the empirical rate equation developed by Makipirtti–Meng , where Y is the fractional volume shrinkage during sintering process and n a dimensionless exponent. The apparent activation energy Δ E values obtained for 850°–1000°C and 1050°–1150°C are 911.8 and 610.5 kJ/mol, respectively. Correspondingly, the exponent n values for the two temperature ranges are also much different and can be served to reveal the morphology changing during the sintering process, which is well consistent with the SEM observation. 相似文献
13.
将比表面积分别为30 m2/g和1 m2/g的纳米(50 nln)和微米(2 μm)金红石TiO2陶瓷坯体在高温热膨胀仪中自室温至1200℃进行恒速无压烧结,升温速率为1℃/min,3℃/min和5℃/min,热膨胀仪自动记录烧结收缩.为阐明比表面对无压烧结初期致密化行为的影响,研究了氧化钛陶瓷的烧结收缩行为.同时,利用Arrhenius曲线研究了纳米和微米氧化钛陶瓷的烧结激活能.结果表明:随烧结温度的增加,比表面积的增加加速了致密化速率;纳米和微米氧化钛的烧结激活能分别为115±10 kJ/mol和302±15 kJ/mol;对于纳米氧化钛,当烧结体的瞬时相对密度为70~80%时,出现最大致密化速率,而对于微米氧化钛陶瓷,最大致密化速率出现在相对密度为75~85%. 相似文献
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Mohamed N. Rahaman Lutgard C. De Jonghe May-Ying Chu 《Journal of the American Ceramic Society》1991,74(3):514-519
The effect of green density on both the densification rate and the creep rate was measured simultaneously during sintering by loading dilatometry. The experiments were performed on zinc oxide powder compacts with five different green densities covering a range of 0.39 to 0.73 of theoretical. The samples were heated at a constant rate of 4°C/min up to 1100°C in air. The densification rate at any temperature increases significantly with decreasing green density. The data for the densification rate and creep rate as a function of density show two quite distinct regimes of behavior; the rates were strongly dependent on density below 0.80, while above this value they were weakly dependent on density. The ratio of the densification rate to the creep rate was almost independent of temperature but increased almost linearly with increasing green density. The representation of the data in terms of models for sintering and creep is discussed. 相似文献
17.
Normal sintering of Li-doped and Li/Ta-codoped potassium sodium niobate (KNbO3 –NaNbO3 , KNN)-based ceramics was investigated to clarify the optimal sintering condition for densification, microstructure, and electrical properties. It was found that density increased greatly within a narrow temperature range but tended to decrease when the sintering temperature slightly exceeded the optimal one, accompanied by the appearance of abnormal grain growth, which was considered to be due to the intensified volatilization of alkali metal oxides. Piezoelectric and dielectric properties also showed a similar relationship between the density and sintering temperature, but the highest piezoelectric strain coefficients were obtained at the temperatures lower than that for the highest density, because both densification and composition affect the electrical properties. The highest d 33 value of 206 pC/N was obtained for the Li- and Ta-codoped KNN ceramics prepared at 1090°C. 相似文献
18.
The effect of matrix grain growth kinetics on the densification behavior of a particulate composite has been investigated. Large alumina inclusions were added to two types of zirconia matrices having different grain growth kinetics, i.e., Zr(8Y)O2 and Zr(3Y)O2 . Despite the evolution of different grain sizes, both matrices reached an end-point relative density of 0.92 and 0.94, respectively, even though they contained 0.25 volume fraction of inclusions (based on total solid volume). However, the morphology and spatial distribution of the residual pores were distinct. The Zr(8Y)O2 matrix, which developed very large grains, had a dual microstructure with porous regions surrounded by a connective, denser region, as previously reported for an alumina matrix containing zirconia inclusions. Conversely, the Zr(3Y)O2 matrix was fully dense and uniform, but the composite contained large cracklike voids at inclusion/matrix interfaces. The large opening displacement of these cracklike voids locally relaxed the constraint to matrix shrinkage imposed by the inclusion network. 相似文献
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