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1.
Sintering Behavior of Fine Aluminum Nitride Powder Synthesized from Aluminum Polynuclear Complexes 总被引:5,自引:0,他引:5
Noboru Hashimoto Hiroyoshi Yoden Shigehito Deki 《Journal of the American Ceramic Society》1992,75(8):2098-2106
The sintering behavior of fine AIN powder synthesized from an aluminum polynuclear complex was investigated. The focus of this work was to investigate the densification behavior of the AIN powder with different particle sizes (specific surface area: 3.2–22.8 m2 /g). The AIN powder was synthesized from basic aluminum chloride and glucose mixed in a water solution. This powder was divided into two groups: one with 2 wt% Y2 O3 added as the sintering aid and the other without such an additive. The AIN powder investigated possessed favorable densification potential. The density of the AIN powder with a surface area of 16.6 m2 /g and without additives attained theoretical density at 1700°C. Adding Y2 O3 further decreased the sintering temperature required for full densification to 1600°C. It is speculated that low-temperature sintering of our fine AIN powder with Y2 O3 proceeds in two steps: in the initial stage, sintering proceeds predominantly through interdiffusion between yttrium aluminates formed on the AIN powder surface; in the second stage, the densification may occur by the interdiffusion between solid phases formed by a reaction between the yttrium aluminates and AIN. To investigate the effect of oxygen on sintering, the content of oxygen in AIN powder was varied while the particle size was kept constant. In this study, the difference in surface oxygen content scarcely affected the sintering behavior of fine AIN powder. 相似文献
2.
Peter den Exter Louis Winnubst Theo H. P. Leuwerink Anthonie J. Burggraaf 《Journal of the American Ceramic Society》1994,77(9):2376-2380
The densification behavior of ZrO2 (+ 3 mol% Y2 O3 )/85 wt% Al2 O3 powder compacts, prepared by the hydrolysis of metal chlorides, can be characterized by a transition- and an α-alumina densification stage. The sintering behavior is strongly determined by the densification of the transition alumina aggregates. Intra-aggregate porosity, resulting from calcination at 800°C, partly persists during sintering and alumina phase transformation and negatively influences further macroscopic densification. Calcination at 1200°C, however, densifies the transition alumina aggregates prior to sintering and enables densification to almost full density (96%) within 2 h at 1450°C, thus obtaining a microstructure with an alumina and a zirconia grain size of 1 μm and 0.3–0.4 μm, respectively. 相似文献
3.
The effect of rare-earth oxide additives on the densification of silicon nitride by pressureless sintering at 1600° to 1700°C and by gas pressure sintering under 10 MPa of N2 at 1800° to 2000°C was studied. When a single-component oxide, such as CeO2 , Nd2 O3 , La2 O3 , Sm2 O3 , or Y2 O3 , was used as an additive, the sintering temperature required to reach approximate theoretical density became higher as the melting temperature of the oxide increased. When a mixed oxide additive, such as Y2 O3 –Ln2 O3 (Ln=Ce, Nd, La, Sm), was used, higher densification was achieved below 2000°C because of a lower liquid formation temperature. The sinterability of silicon nitride ceramics with the addition of rare-earth oxides is discussed in relation to the additive compositions. 相似文献
4.
Yanmei Kan Peiling Wang Tao Xu Guojun Zhang Dongsheng Yan Zhijian Shen Yi-Bing Cheng 《Journal of the American Ceramic Society》2005,88(6):1631-1633
Spark plasma sintering (SPS) was used to fabricate bismuth titanate (Bi4 Ti3 O12 ) ceramics. The densification, microstructure development and dielectric properties were investigated. It was found that the densification process was greatly enhanced during SPS. The sintering temperature was 200°C lower and the microstructure was much finer than that of the pressureless sintered ceramics, and dense compacts with a high density of over 99% were obtained at a wide temperature range of 800°–1100°C. Dielectric property measurement indicated that the volatilization of Bi3+ was greatly restrained during SPS, resulting in an unprecedented low dielectric loss for pure Bi4 Ti3 O12 ceramics. 相似文献
5.
Sintering of Si3 N4 powder with the addition of a Y2 O3 + Al2 O3 mixture or YAlO3 as sintering aids was investigated. Sintering was improved in the case of YAlO3 additive compared to that for the Y2 O3 + Al2 O3 mixture. An initial delay in densification was most likely caused by heterogeneity of the liquid phase formed in the case of the separate oxide additions at temperatures above 1700°C. 相似文献
6.
Improvement of Mechanical Properties and Corrosion Resistance of Porous β-SiAlON Ceramics by Low Y2 O3 Additions 总被引:2,自引:1,他引:1
Jian-Feng Yang Guo-Jun Zhang Ji-Hong She Tatsuki Ohji Shuzo Kanzaki 《Journal of the American Ceramic Society》2004,87(9):1714-1719
Addition of Y2 O3 as a sintering additive to porous β-SiAlON (Si6− z Al z O z N8− z , z = 0.5) ceramics has been investigated for improved mechanical properties. Porous SiAlON ceramics with 0.05–0.15 wt% (500–1500 wppm) Y2 O3 were fabricated by pressureless sintering at temperatures of 1700°, 1800°, and 1850°C. The densification, microstructure, and mechanical properties were compared with those of Y2 O3 -free ceramics of the same chemical composition. Although this level of Y2 O3 addition did not change the phase formation and grain size, the grain bonding appeared to be promoted, and the densification to be enhanced. There was a significant increase in the flexural strength of the SiAlON ceramics relative to the Y2 O3 -free counterpart. After exposure in 1 M hydrochloric acid solution at 70°C for 120 h, no remarkable weight loss and degradation of the mechanical properties (flexural and compression strength) was observed, which was attributed to the limited grain boundary phase, and with the minor Y2 O3 addition the supposed formation of Y-α-SiAlON. 相似文献
7.
Hot pressing kinetics of α-Si3 N4 , AIN, Al2 O3 , and Y2 O3 powder mixtures forming α'- and β'-SiAlONs have been studied. Densification proceeds in two steps, first by a small shrinkage upon ternary eutectic oxide melting (SiO2 –Al2 O3 –Y2 O3 ) at 1340°C, followed by a massive particle rearrangement and further shrinkage at higher temperature when nitride dissolution begins. With better wettability, AIN initially traps the oxide melt and delays densification. In addition, the preferential dissolution of AIN at 1450°C enriches the melt composition in AI, triggering transient precipitation of supersaturated β'-SiAlON. Full densification is readily achieved at 1550°C without complete α-Si3 N4 conversion. 相似文献
8.
New Strategies for Preparing NanoSized Silicon Nitride Ceramics 总被引:2,自引:0,他引:2
Xin Xu Toshiyuki Nishimura Naoto Hirosaki Rong-Jun Xie Yinchun Zhu Yoshinobu Yamamoto Hidehiko Tanaka 《Journal of the American Ceramic Society》2005,88(4):934-937
We report the preparation of nanosized silicon nitride (Si3 N4 ) ceramics via high-energy mechanical milling and subsequent spark plasma sintering. A starting powder mixture consisting of ultrafine β-Si3 N4 and sintering additives of 5-mol% Y2 O3 and 2-mol% Al2 O3 was prepared by high-energy mechanical milling. After milling, the powder mixture was mostly transformed into a non-equilibrium amorphous phase containing a large quantity of well-dispersed nanocrystalline β-Si3 N4 particles. This powder precursor was then consolidated by spark plasma sintering at a temperature as low as 1600°C for 5 min at a heating rate of 300°C/min. The fully densified sample consisted of homogeneous nano-Si3 N4 grains with an average diameter of about 70 nm, which led to noticeable high-temperature ductility and elevated hardness. 相似文献
9.
Ki-Woong Chae† Doh-Yeon Kim Koichi Niihara 《Journal of the American Ceramic Society》1995,78(1):257-259
The results obtained from the sintering of Al2 O3 –50TiC (in weight percent) composite in the temperature range from 1650° to 1800°C with addition of Y2 O3 are presented. Densification is accelerated by the formation of liquid at temperatures above 1750°C, and 99% of theoretical density can be achieved by vacuum sintering at 1800°C for 15 min. The liquid presented at the sintering temperature is crystallized to YAG (Y3 Al5 O12 ) during cooling. 相似文献
10.
Guo-Dong Zhan Joshua D. Kuntz Ren-Guan Duan Amiya K. Mukherjee 《Journal of the American Ceramic Society》2004,87(12):2297-2300
The combined effect of rapid sintering by spark-plasma-sintering (SPS) technique and mechanical milling of γ-Al2 O3 nanopowder via high-energy ball milling (HEBM) on the microstructural development and mechanical properties of nanocrystalline alumina matrix composites toughened by 20 vol% silicon carbide whiskers was investigated. SiCw /γ-Al2 O3 nanopowders processed by HEBM can be successfully consolidated to full density by SPS at a temperature as low as 1125°C and still retain a near-nanocrystalline matrix grain size (∼118 nm). However, to densify the same nanopowder mixture to full density without the benefit of HEBM procedure, the required temperature for sintering was higher than 1200°C, where one encountered excessive grain growth. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results indicated that HEBM did not lead to the transformation of γ-Al2 O3 to α-Al2 O3 of the starting powder but rather induced possible residual stress that enhances the densification at lower temperatures. The SiCw /HEBMγ-Al2 O3 nanocomposite with grain size of 118 nm has attractive mechanical properties, i.e., Vickers hardness of 26.1 GPa and fracture toughness of 6.2 MPa·m1/2 . 相似文献
11.
Xiaodong Li Ji-Guang Li Zhimeng Xiu Di Huo Xudong Sun 《Journal of the American Ceramic Society》2009,92(1):241-244
Neodymium (Nd):Y3 Al5 O12 (YAG) ceramics of excellent transparency have been fabricated by solid-reactive sintering, using nanosized γ-Al2 O3 and Y2 O3 powders as the starting materials. Reaction sequences and sintering behaviors of the powder mixture were characterized by X-ray diffractometry and dilatometry. One feature of the solid reactions involving γ-Al2 O3 is the occurrence of hexagonal YAlO3 , which is unstable and transforms to perovskite YAlO3 (YAP) upon further heating. Because of the high reactivities of the starting nanopowders, a complete conversion of the powder mixture to YAG has been achieved by heating at 1300°C for 4 h, via Y4 Al2 O9 , hexagonal YAlO3 , and YAP phases. In-line transmittances of the 1.5 at.% Nd:YAG ceramics (doped with 0.5 wt% of tetraethyl orthosilicate) at 700 nm are 81.0% and 65.7% after vacuum sintering at 1700° and 1600°C for 5 h, respectively. 相似文献
12.
Frank J. T. Lin Lutgard C. de Jonghe Mohamed N. Rahaman 《Journal of the American Ceramic Society》1997,80(11):2891-2896
The effect of an initial coarsening step (50-200 h at 800°C) on the subsequent densification and microstructural evolution of high–quality compacts of undoped and MgO–doped Al2 O3 has been investigated during fast–firing (5 min at 1750°C) and during constant–heating–rate sintering (4°C/min to 1450°C). In constant–heating–rate sintering of both the undoped and MgO–doped Al2 O3 , a refinement of the microstructure has been achieved for the compact subjected to the coarsening step. A combination of the coarsening step and MgO doping produces the most significant refinement of the microstructure. In fast–firing of the MgO–doped Al2 O3 , the coarsening step produces a measurable increase in the density and a small refinement of the grain size, when compared with similar compacts fast–fired conventionally (i.e., without the coarsening step). This result indicates that the accepted view of the deleterious role of coarsening in the sintering of real powder compacts must be reexamined. Although extensive coarsening after the onset of densification must be reduced for the achievement of high density, limited coarsening prior to densification is beneficial for subsequent sintering. 相似文献
13.
Jian-Feng Yang Tatsuki Ohji Koichi Niihara 《Journal of the American Ceramic Society》2000,83(8):2094-2096
The present study investigates the influence of the content of Y2 O3 –Al2 O3 sintering additive on the sintering behavior and microstructure of Si3 N4 ceramics. The Y2 O3 :Al2 O3 ratio was fixed at 5:2, and sintering was conducted at temperatures of 1300°–1900°C. Increased sintering-additive content enhanced densification via particle rearrangement; however, phase transformation and grain growth were unaffected by additive content. After phase transformation was almost complete, a substantial decrease in density was identified, which resulted from the impingement of rodlike β-Si3 N4 grain growth. Phase transformation and grain growth were concluded to occur through a solution–reprecipitation mechanism that was controlled by the interfacial reaction. 相似文献
14.
Morphology and Sinterability of Thermally Treated Carbothermally Synthesized Silicon Nitride Powders
Alan W. Weimer Daniel F. Carroll David W. Susnitzky Donald R. Beaman 《Journal of the American Ceramic Society》1999,82(6):1635-1638
Carbothermally produced alpha-Si3 N4 powder is thermally treated (1400°-1500°C for 4-12 h) in nitrogen-gas to determine the impact of thermal treatment on powder composition, particle size, morphology, and sinterability. Thermal treatment reduces residual carbon and oxygen content and reduces internal porosity (lower surface area), which results in a rounding of the particles. The lower oxygen content of the heat-treated, carbothermally produced alpha-Si3 N4 powder allows Y2 O3 -Al2 O3 -SiO2 sintering formulation to be adjusted so that an improvement in the early stage of densification can be achieved. 相似文献
15.
Koji Matsui Nobukatsu Ohmichi Michiharu Ohgai Naoya Enomoto Junichi Hojo 《Journal of the American Ceramic Society》2005,88(12):3346-3352
The sinterabilities of fine zirconia powders including 5 mass% Y2 O3 were investigated, with emphasis on the effect of Al2 O3 at the initial sintering stage. The shrinkage of powder compact was measured under constant rates of heating (CRH). The powder compact including a small amount of Al2 O3 increased the densification rate with elevating temperature. The activation energies at the initial stage of sintering were determined by analyzing the densification curves. The activation energy of powder compact including Al2 O3 was lower than that of a powder compact without Al2 O3 . The diffusion mechanisms at the initial sintering stage were determined using the new analytical equation applied for CRH techniques. This analysis exhibited that Al2 O3 included in a powder compact changed the diffusion mechanism from grain boundary to volume diffusions (VD). Therefore, it is concluded that the effect of Al2 O3 enhanced the densification rate because of decrease in the activation energy of VD at the initial sintering stage. 相似文献
16.
Koji Matsui Takanori Yamakawa Masato Uehara Naoya Enomoto Junichi Hojo 《Journal of the American Ceramic Society》2008,91(6):1888-1897
The isothermal shrinkage behavior of 2.9 mol% Y2 O3 -doped ZrO2 powders with 0–1 mass% Al2 O3 was investigated to clarify the effect of Al2 O3 concentration on the initial sintering stage. The shrinkage of the powder compact was measured at constant temperatures in the range of 950°–1050°C. The Al2 O3 addition increased the densification rate with increasing temperature. The values of apparent activation energy ( nQ ) and apparent frequency-factor term (β0 n ), where n is the order depending on the diffusion mechanism, were estimated at the initial sintering stage by applying a sintering-rate equation to the isothermal shrinkage data. The diffusion mechanism changed from grain-boundary diffusion (GBD) to volume diffusion (VD) by Al2 O3 addition and both nQ and β0 n increased with increasing Al2 O3 concentration. The kinetic analysis of the sintering mechanism suggested that the increase of densification rate by Al2 O3 addition largely depends on the increase of β0 n , that is, the increases of n with GBD→VD change and β0 with an increase in Al2 O3 content, although the nQ also increases with Al2 O3 addition. This enhanced sintering mechanism is reasonably interpreted by the segregated dissolution of Al2 O3 at ZrO2 grain boundaries. 相似文献
17.
Nithyanantham Thangamani Ashutosh S. Gandhi Vikram Jayaram Atul H. Chokshi 《Journal of the American Ceramic Society》2005,88(10):2696-2701
This study examined pressure consolidation of amorphous Al2 O3 –15 mol% Y2 O3 powders prepared by co-precipitation and spray pyrolysis. The two amorphous powders had similar true densities and crystallization sequences. Uniaxial hot pressing was carried out at 450°–600°C with a moderate pressure of 750 MPa. The co-precipitated powder could be hot pressed to a maximum relative density of 98% and remained amorphous. Pressure adversely affected the densification of the spray-pyrolyzed powder by favoring an early crystallization of γ-Al2 O3 phase at 580°C. Plastic deformation of the amorphous phase is believed to be responsible for the large densification of the amorphous powders. 相似文献
18.
Spark Plasma Sintering of Alumina 总被引:7,自引:1,他引:7
Zhijian Shen Mats Johnsson Zhe Zhao Mats Nygren 《Journal of the American Ceramic Society》2002,85(8):1921-1927
A systematic study of various spark plasma sintering (SPS) parameters, namely temperature, holding time, heating rate, pressure, and pulse sequence, was conducted to investigate their effect on the densification, grain-growth kinetics, hardness, and fracture toughness of a commercially available submicrometer-sized Al2 O3 powder. The obtained experimental data clearly show that the SPS process enhances both densification and grain growth. Thus, Al2 O3 could be fully densified at a much lower temperature (1150°C), within a much shorter time (minutes), than in more conventional sintering processes. It is suggested that the densification is enhanced in the initial part of the sintering cycle by a local spark-discharge process in the vicinity of contacting particles, and that both grain-boundary diffusion and grain-boundary migration are enhanced by the electrical field originating from the pulsed direct current used for heating the sample. Both the diffusion and the migration that promote the grain growth were found to be strongly dependent on temperature, implying that it is possible to retain the original fine-grained structure in fully densified bodies by avoiding a too high sintering temperature. Hardness values in the range 21–22 GPa and fracture toughness values of 3.5 ± 0.5 MPa·m1/2 were found for the compacts containing submicrometer-sized Al2 O3 grains. 相似文献
19.
Conventional ramp-and-hold sintering with a wide range of heating rates was conducted on submicrometer and nanocrystalline ZrO2 –3 mol% Y2 O3 powder compacts. Although rapid heating rates have been reported to produce high density/fine grain size products for many submicrometer and smaller starting powders, the application of this technique to ZrO2 –3 mol% Y2 O3 produced mixed results. In the case of submicrometer ZrO2 –3 mol% Y2 O3 , neither densification nor grain growth was affected by the heating rate used. In the case of nanocrystalline ZrO2 –3 mol% Y2 O3 , fast heating rates severely retarded densiflcation and had a minimal effect on grain growth. The large adverse effect of fast heating rates on the densification of the nanocrystalline powder was traced to a thermal gradient/differential densification effect. Microstructural evidence suggests that the rate of densification greatly exceeded the rate of heat transfer in this material; consequently, the sample interior was not able to densify before being geometrically constrained by a fully dense shell which formed at the sample exterior. This finding implies that rapid rate sintering will meet severe practical constraints in the manufacture of bulk nanocrystalline ZrO2 –3 mol% Y2 O3 specimens. 相似文献
20.
MgO addition to 3 mol% Y2 O3 –ZrO2 resulted in enhanced densification at 1350°C by a liquid-phase sintering mechanism. This liquid phase resulted from reaction of MgO with trace impurities of CaO and SiO2 in the starting powder. The bimodal grain structure thus obtained was characterized by large cubic ZrO2 grains with tetragonal ZrO2 precipitates, which were surrounded by either small tetragonal grains or monoclinic grains, depending on the heat-treatment schedule. 相似文献