共查询到20条相似文献,搜索用时 718 毫秒
1.
Jianren Zeng Yoshinari Miyamoto Osamu Yamada 《Journal of the American Ceramic Society》1991,74(9):2197-2200
Fine Si3 N4 -SiC composite powders were synthesized in various SiC compositions to 46 vol% by nitriding combustion of silicon and carbon. The powders were composed of α-Si3 N4 , β-Si3 N4 , and β-SiC. The reaction analysis suggested that the SiC formation is assisted by the high reaction heat of Si nitridation. The sintered bodies consisted of uniformly dispersed grains of β-Si3 N4 , β-SiC, and a few Si2 N2 O. 相似文献
2.
Yongsheng Liu Litong Zhang Laifei Cheng Yongdong Xu Yi Liu 《International Journal of Applied Ceramic Technology》2010,7(1):63-70
Silicon nitride particle-reinforced silicon nitride matrix composites were fabricated by chemical vapor infiltration (CVI). The particle preforms with a bimodal pore size distribution were favorable for the subsequent CVI process, which included intraagglomerate pores (0.1–4 μm) and interagglomerate pores (20–300 μm). X-ray fluorescence results showed that the main elements of the composites are Si, N, and O. The composite is composed of α-Si3 N4 , amorphous Si3 N4 , amorphous SiO2 , and a small amount of β-Si3 N4 and free silicon. The α-Si3 N4 transformed into β-Si3 N4 after heat treatment at 1600°C for 2 h. The flexural strength, dielectric constant, and dielectric loss of the Si3 N4(p) /Si3 N4 composites increased with increasing infiltration time; however, the pore ratios decreased with increasing infiltration time. The maximum value of the flexural strength was 114.07 MPa. The dielectric constant and dielectric loss of the composites were 4.47 and 4.25 × 10−3 , respectively. The present Si3 N4(p) /Si3 N4 composite is a good candidate for high-temperature radomes. 相似文献
3.
Jiang-Tao Li Lin Mei Yun Yang Zhi-Ming Lin 《Journal of the American Ceramic Society》2009,92(3):636-640
Silicon nitride (Si3 N4 ) was synthesized by a selective combustion reaction of silicon powder with nitrogen in air. The α/β-Si3 N4 ratio of the interior product could be tailored by adjusting the Si3 N4 -diluent content in the reactant mixtures. The synthetic β-Si3 N4 showed a well-crystallized rod-like morphology. Mechanical activation greatly enhanced the reactivity of silicon powder, and the slow oxidation of silicon at the sample surface promoted the combustion reaction in air. The formation mechanism of Si3 N4 was analyzed based on a proposed N2 /O2 diffusion kinetic model, and the calculated result is in good agreement with the experimental phenomenon. 相似文献
4.
Reaction and Formation of Crystalline Silicon Oxynitride in Si–O–N Systems under Solid High Pressure
Ya-Li Li Fen Zheng Yong Liang Xian-Feng Ma Suo-Jing Cui Takamasa Ishigaki 《Journal of the American Ceramic Society》2001,84(4):875-877
Oxidized amorphous Si3 N4 and SiO2 powders were pressed alone or as a mixture under high pressure (1.0–5.0 GPa) at high temperatures (800–1700°C). Formation of crystalline silicon oxynitride (Si2 ON2 ) was observed from amorphous silicon nitride (Si3 N4 ) powders containing 5.8 wt% oxygen at 1.0 GPa and 1400°C. The Si2 ON2 coexisted with β-Si3 N4 with a weight fraction of 40 wt%, suggesting that all oxygen in the powders participated in the reaction to form Si2 ON2 . Pressing a mixture of amorphous Si3 N4 of lower oxygen (1.5 wt%) and SiO2 under 1.0–5.0 GPa between 1000° and 1350°C did not give Si2 ON2 phase, but yielded a mixture of α,β-Si3 N4 , quartz, and coesite (a high-pressure form of SiO2 ). The formation of Si2 ON2 from oxidized amorphous Si3 N4 seemed to be assisted by formation of a Si–O–N melt in the system that was enhanced under the high pressure. 相似文献
5.
The abnormal grain growth of β-Si3 N4 was observed in a 70% Si3 N4 –30% barium aluminum silicate (70%-Si3 N4 –30%-BAS) self-reinforced composite that was pressureless-sintered at 1930°C; Si3 N4 starting powders with a wide particle-size distribution were used. The addition of coarse Si3 N4 powder encouraged the abnormal growth of β-Si3 N4 grains, which allowed microstructural modification through control of the content and size distribution of β-Si3 N4 nuclei. The mechanical response of different microstructures was characterized in terms of flexural strength, as well as indentation fracture resistance, at room temperature. The presence of even a small amount of abnormally grown β-Si3 N4 grains improved the fracture toughness and minimized the variability in flexural strength. 相似文献
6.
Rong-Jun Xie Mamoru Mitomo Wonjoong Kim Young-Wook Kim 《Journal of the American Ceramic Society》2000,83(12):3147-3152
Silicon nitride–silicon oxynitride (Si3 N4 –Si2 N2 O) in situ composites have been fabricated via either the annealing or the superplastic deformation of sintered Si3 N4 that has been doped with a silica-containing additive. In this study, quantitative texture measurements, including pole figures and X-ray diffraction patterns, are used in conjunction with scanning electron microscopy and transmission electron microscopy techniques to examine the degree of preferred orientation and texture-development mechanisms in these materials. The results indicate that (i) only superplastic deformation can produce strong textures in the β-Si3 N4 matrix, as well as Si2 N2 O grains that are formed in situ ; (ii) texture development in the β-Si3 N4 matrix mainly results from grain rotation via grain-boundary sliding; and (iii) for Si2 N2 O, a very strong strain-dependent texture occurs in two stages, namely, preferred nucleation and anisotropic grain growth. 相似文献
7.
L. K. V. LOU T. E. MITCHELL A. H. HEUER 《Journal of the American Ceramic Society》1978,61(9-10):392-396
Impurity phases in commercial hot-pressed Si3 N4 were investigated using transmission electron microscopy. In addition to the dominant, β-Si3 N4 phase, small amounts of Si2 N2 O, SiC, and WC were found. Significantly, a continuous grain-boundary phase was observed in the ∼ 25 high-angle boundaries examined. This film is ∼ 10 Å thick between, β-Si3 N4 grains and ∼ 30 Å thick between Si2 N2 O and β-Si3 N4 grains. 相似文献
8.
Dong-Duk Lee Suk-Joong L. Kang Gunter Petzow Duk N. Yoon 《Journal of the American Ceramic Society》1990,73(3):767-769
By using α-Si3 N4 and β-Si3 N4 starting powders with similar particle size and distribution, the effect of α-β (β') phase transition on densification and microstructure is investigated during the liquid-phase sintering of 82Si3 N4 ·9Al2 O3 ·9Y2 O3 (wt%) and 80Si3 N4 ·13Al2 O3 ·5AIN·5AIN·2Y2 O3 . When α-Si3 N4 powder is used, the grains become elongated, apparently hindering the densification process. Hence, the phase transition does not enhance the densification. 相似文献
9.
Fabrication and Mechanical Properties of Silicon Carbide-Silicon Nitride Composites with Oxynitride Glass 总被引:1,自引:0,他引:1
Young-Wook Kim Young-Il Lee Mamoru Mitomo Heon-Jin Choi June-Gunn Lee 《Journal of the American Ceramic Society》1999,82(4):1058-1060
A microstructure that consisted of uniformly distributed, elongated β-Si3 N4 grains, equiaxed β-SiC grains, and an amorphous grain-boundary phase was developed by using β-SiC and alpha-Si3 N4 powders. By hot pressing, elongated β-Si3 N4 grains were grown via alpha right arrow β phase transformation and equiaxed β-SiC grains were formed because of inhibited grain growth. The strength and fracture toughness of SiC have been improved by adding Si3 N4 particles, because of the reduced defect size and the enhanced bridging and crack deflection by the elongated β-Si3 N4 grains. Typical flexural-strength and fracture-toughness values of SiC-35-wt%-Si3 N4 composites were 1020 MPa and 5.1 MPam1/2 , respectively. 相似文献
10.
Jun-Qi Li Fa Luo Dong-Mei Zhu Wan-Cheng Zhou 《Journal of the American Ceramic Society》2007,90(6):1950-1952
The influence of phase formation on the dielectric properties of silicon nitride (Si3 N4 ) ceramics, which were produced by pressureless sintering with additives in MgO–Al2 O3 –SiO2 system, was investigated. It seems that the difference in the dielectric properties of Si3 N4 ceramics sintered at different temperatures was mainly due to the difference of the relative content of α-Si3 N4 , β-Si3 N4 , and the intermediate product (Si2 N2 O) in the samples. Compared with α-Si3 N4 and Si2 N2 O, β-Si3 N4 is believed to be a major factor influencing the dielectric constant. The high-dielectric constant of β-Si3 N4 could be attributed to the ionic relaxation polarization. 相似文献
11.
Silicon Nitride Joining 总被引:1,自引:0,他引:1
M. L. MECARTNEY R. SINCLAIR R. E. LOEHMAN 《Journal of the American Ceramic Society》1985,68(9):472-478
Hot-pressed Si3 N4 was joined using an Mgo-A12 O3 -SiO2 glass composition chosen to approximate the oxide portion of the grain-boundary phase in the ceramic. After it has been heated at 1550° to 1650°, the interface of the joined ceramic is an interlocking mixture of Si2 N2 O, β-Si3 N4 , and a residual oxy-nitride glass. The kinetics of reactions between Si3 N4 and the molten joining composition were studied by X-ray diffraction analysis of the phases present in Si3 N4 powder-glass mixtures quenched after varied heat treatments. Analytical transmission electron microscopy of the composition and micro-structure of the reaction zone in joined specimens, together with the X-ray diffraction results, suggests that the driving force for joining is the lowering of the Si3 N4 interfacial energy when it is wet by the molten silicate, augmented by the negative Gibbs energy for the reaction SiO2 ( l ) + Si3 N4 = 2Si2 N2 O. 相似文献
12.
The rate of dissolution of β-Si3 N4 into an Mg-Si-O-N glass was measured by working with a composition in the ternary system Si3 N4 -SiO2 -MgO such that Si2 N2 O rather than β-Si3 N4 was the equilibrium phase. Dissolution was driven by the chemical reaction Si3 N4 (c)+SiO2 ( l )→Si2 N2 O(c). Analysis of the kinetic data, in view of the morphology of the dissolving phase (Si3 N4 ) and the precipitating phase (Si2 N2 O), led to the conclusion that the dissolution rate was controlled by reaction at the crystal/glass interface of the Si3 N4 , crystals. The process appears to have a fairly constant activation energy, equal to 621 ±40 kJ-mol−1 , at T=1573 to 1723 K. This large activation energy is believed to reflect the sum of two quantities: the heat of solution of β-Si3 N4 hi the glass and the activation enthalpy for jumps of the slower-moving species across the crystal/glass interface. The data reported should be useful for interpreting creep and densification experiments with MgO-fluxed Si3 N4 . 相似文献
13.
Effect of Sintering Additives on Microstructure and Mechanical Properties of Porous Silicon Nitride Ceramics 总被引:2,自引:0,他引:2
Jun Yang Jian-Feng Yang Shao-Yun Shan Ji-Qiang Gao Tatsuki Ohji 《Journal of the American Ceramic Society》2006,89(12):3843-3845
Porous silicon nitride (Si3 N4 ) ceramics with about 50% porosity were fabricated by pressureless sintering of α-Si3 N4 powder with 5 wt% sintering additive. Four types of sintering aids were chosen to study their effect on the microstructure and mechanical properties of porous Si3 N4 ceramics. XRD analysis proved the complete formation of a single β-Si3 N4 phase. Microstructural evolution and mechanical properties were dependent mostly on the type of sintering additive. SEM analysis revealed the resultant porous Si3 N4 ceramics as having high aspect ratio, a rod-like microstructure, and a uniform pore structure. The sintered sample with Lu2 O3 sintering additive, having a porosity of about 50%, showed a high flexural strength of 188 MPa, a high fracture toughness of 3.1 MPa·m1/2 , due to fine β-Si3 N4 grains, and some large elongated grains. 相似文献
14.
Maria Antonia Sainz Pilar Miranzo Maria Isabel Osendi 《Journal of the American Ceramic Society》2002,85(4):941-946
Dense hot-pressed β-Si3 N4 blocks were joined using both SiO2 and SiO2 -Y2 O3 powder slurries as bonding interlayers. The assembled specimens (Si3 N4 /interlayer/Si3 N4 ) were heated in a flowing N2 atmosphere in the temperature range of 1500°–1650°C. The joining interlayer was clearly distinguished from the Si3 N4 bulk. The microstructure and the reaction products found in the bonding interlayer were very different in both compositions. Reactions occurring between the Si3 N4 and the ceramic joining compositions have been explained based on existing diagrams of the YN–Si3 N4 -Y2 O3 -SiO2 system. 相似文献
15.
Silicon nitride (Si3 N4 ) ceramics, prepared with Y2 O3 and Al2 O3 sintering additives, have been densified in air at temperatures of up to 1750°C using a conventional MoSi2 element furnace. At the highest sintering temperatures, densities in excess of 98% of theoretical have been achieved for materials prepared with a combined sintering addition of 12 wt% Y2 O3 and 3 wt% Al2 O3 . Densification is accompanied by a small weight gain (typically <1–2 wt%), because of limited passive oxidation of the sample. Complete α- to β-Si3 N4 transformation can be achieved at temperatures above 1650°C, although a low volume fraction of Si2 N2 O is also observed to form below 1750°C. Partial crystallization of the residual grain-boundary glassy phase was also apparent, with β-Y2 Si2 O7 being noted in the majority of samples. The microstructures of the sintered materials exhibited typical β-Si3 N4 elongated grain morphologies, indicating potential for low-cost processing of in situ toughened Si3 N4 -based ceramics. 相似文献
16.
Microstructure and Properties of Self-Reinforced Silicon Nitride 总被引:3,自引:0,他引:3
Problems associated with manufacturing Si3 N4 /SiC-whisker composites have been overcome by developing selfreinforced Si3 N4 with elongated β-Si3 N4 grains formed in situ from oxynitride glass. This Si3 N4 –Y2 O3 –MgO–SiO2 –CaO-based material has a flexure strength >1000 MPa and fracture toughness >8 MPa·m½ . The optimum combination of mechanical properties has been obtained with Y2 O3 :MgO ratios ranging from 3:1 to 1:2, CaO contents ranging from 0.1 to 0.5 wt%, and Si3 N4 contents between 90 and 96 wt%. 相似文献
17.
Silicon Carbide Whisker Stability During Processing of Silicon Nitride Matrix Composites 总被引:1,自引:0,他引:1
Steven A. Bradley Keith R. Karasek Michael R. Martin Harry C. Yeh James L. Schienle 《Journal of the American Ceramic Society》1989,72(4):628-636
The effects of two different sources of SiC whiskers on the chemistry and microstructure of the SiC-whisker—Si3 N4 composites were evaluated using scanning transmission electron microscopy. Analyses were performed after presintering in N2 and after encapsulated hot isostatic pressing. Significant differences in the porosity, α- to β-Si3 N4 conversion, and whisker degradation were observed after presintering. It was also noted that whiskers containing surface iron impurities were converted to Si3 N4 during processing. Whiskers from the source having low surface iron exhibited little reaction. After hot isostatic pressing, some oxidation of the cleaner whiskers was observed. 相似文献
18.
Jianren Zeng Isao Tanaka Yoshinari Miyamoto Osamu Yamada† Koichi Niihara 《Journal of the American Ceramic Society》1992,75(1):148-152
The influence of SiO2 addition on the densification and microstructural development of high-purity Si3 N4 during hot isostatic pressing (HIP) was studied. During HIP, densification was promoted, but the phase transformation from α -Si3 N4 to β -Si3 N4 was impeded by SiO2 . Analysis using a simple model shows that the enhanced densification was mainly due to the viscous flow of SiO2 . The microstructure changed remarkably at between 10 and 20 wt% SiO2 additions. Analysis of the phase transformation kinetics suggests that the diffusion of Si3 N4 through SiO2 glass is the ratecontrolling step for the transformation. 相似文献
19.
Thermal Conductivity of Gas-Pressure-Sintered Silicon Nitride 总被引:3,自引:0,他引:3
Naoto Hirosaki Yusuke Okamoto Motohide Ando Fumio Munakata Yoshio Akimune 《Journal of the American Ceramic Society》1996,79(11):2878-2882
Si3 N4 with high thermal conductivity (120 W/(m. K)) was developed by promoting grain growth and selecting a suitable additive system in terms of composition and amount. β-Si3 N4 doped with Y2 O3 -Nd2 O3 (YN system) or Y2 O3 -A12 O3 (YA system) was sintered at 1700°-2000°C. Thermal conductivity increased with increased sintering temperature because of decreased two-grain junctions, as a result of grain growth. The effect of the additive amount on thermal conductivity with the YN system was rather small because increased additive formed multigrain junctions. On the other hand, with the YA system, thermal conductivity considerably decreased with increased additive amount because the aluminum and oxygen in the YA system dissolved into β-Si3 N4 grains to form a β-SiAlON solid solution, which acted as a point defect for phonon scattering. The key processsing parameters for high thermal conductivity of Si3 N4 were the sintering temperature and additive composition. 相似文献
20.
Sang-Hoon Rhee Jae Do Lee Doh-Yeon Kim 《Journal of the American Ceramic Society》2001,84(12):3040-3042
When a small amount of β-Si3 N4 seed particles is added during the preparation of Si3 N4 ceramics, a bimodal microstructure is obtained by sintering at 1760°C. When the specimen is further heat-treated at 1900°C to enhance the bimodal characteristic, the growth of large β grains is limited. The addition of a controlled amount of β seeds of uniform and large size is suggested to obtain the intended bimodal microstructure of Si3 N4 ceramics. 相似文献