共查询到20条相似文献,搜索用时 947 毫秒
1.
Hai-Bo Jin Yun Yang Yi-Xiang Chen Zhi-Ming Lin Jiang-Tao Li 《Journal of the American Ceramic Society》2006,89(3):1099-1102
Combustion synthesis (CS) of α-silicon nitride (Si3 N4 ) powders was accomplished at a nitrogen pressure lower than 3 MPa. The combination of mechanical activation and chemical stimulation was effective in enhancing the reactivity of Si powder reactants, which was responsible for the reduction of the minimum nitrogen pressure normally required for the CS of Si3 N4 . This breakthrough indicates that nitriding combustion of silicon in pressurized nitrogen could be promoted by activating the solid reactants instead of by increasing the nitrogen pressure. The phase content of α-Si3 N4 in the as-synthesized product is over 90 wt%. Scanning electronic microscopy observation showed that the combustion-synthesized Si3 N4 powders are submicron-sized particles with spherical morphologies. 相似文献
2.
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
3.
Zehn-Kun Huang Tseng-Ying Tien Tung-Sheng Yen 《Journal of the American Ceramic Society》1986,69(10):241-C
The subsolidus phase relationships in Si3 N4 –AlN–rare-earth oxide (Me2 O3 where Me=Nd, Sm, Gd, Dy, Er, and Yb) systems were studied. Solid-solution regions with the α-Si3 N4 structure were delineated along the Si3 N4 –"Me2 O3 :9AIN" joins for all of the rare-earth oxide systems studied. The solubility limits of these solid solutions increased with decreasing size of the rare-earth ions. 相似文献
4.
Jae Young Choi Chong Hee Kim Do Kyung Kim 《Journal of the American Ceramic Society》1999,82(10):2665-2671
The synthesis and structure of a monodispersed spherical Si3 N4 /SiC nanocomposite powder have been studied. The Si3 N4 /SiC nanocomposite powder was synthesized by heating under argon a spherical Si3 N4 /C powder. The spherical Si3 N4 /C powder was prepared by heating a spherical organosilica powder in a nitrogen atmosphere and was composed of a mixture of nanosized Si3 N4 and free carbon particles. During the heat treatment at 1450°C, the Si3 N4 /C powder became a Si3 N4 /SiC composite powder and finally a SiC powder after 8 h, while retaining its spherical shape. The composition of the Si3 N4 /SiC composite powder changed with the duration of the heat treatment. The results of TEM, SEM, and selected area electron diffraction showed that the Si3 N4 /SiC composite powder was composed of homogeneously distributed nanosized Si3 N4 and SiC particles. 相似文献
5.
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
6.
The phase relations in the Si3 N4 -rich portion of the Si3 N4 –AlN–Y2 O3 rystem were investigated using hot-pressed bodies. The one-phase fields of β3 and α, the twophase fields of β+α, β+M (M=melilite), and α+M, and the three-phase fields of β+α+M were observed in the Si3 N4 -rich portion. The α- and β-sialons are not two different compounds but an allotropic transformation phase of the Si–Al–O–N system, and an α solid solution expands and stabilizes with increasing Y2 O3 content. Therefore, the formulas of the two sialons should be the same. 相似文献
7.
Linus U. J. T. Ogbuji 《Journal of the American Ceramic Society》1992,75(11):2995-3000
The results of two-step oxidation experiments on chemically-vapor-deposited Si3 N4 and SiC at 1350°C show that a correlation exists between the presence of a Si2 N2 O interphase and the strong oxidation resistance of Si3 N4 . During normal oxidation, k p for SiC was 15 times higher than that for Si3 N4 , and the oxide scale on Si3 N4 was found by SEM and TEM to contain a prominent Si2 N2 O inner layer. However, when oxidized samples are annealed in Ar for 1.5 h at 1500°C and reoxidized at 1350°C as before, three things happen: the oxidation k p increases over 55-fold for Si3 N4 , and 3.5-fold for SiC; the Si3 N4 and SiC oxidize with nearly equal k p 's; and, most significant, the oxide scale on Si3 N4 is found to be lacking an inner Si2 N2 O layer. The implications of this correlation for the competing models of Si3 N4 oxidation are discussed. 相似文献
8.
Jow-Lay Huang Hung-Liang Chiu Ming-Tung Lee 《Journal of the American Ceramic Society》1994,77(3):705-710
The effects of TiC addition to Si3 N4 on microstructure and the chemical aspects of Si3 N4 –TiC interphase reaction were investigated in samples hot-pressed at 1800°C in Ar and N2 . Composition of a TiC1–x Nx solid solution was predicted based on thermodynamic calculation, with titanium carbonitride taken to be an ideal solid solution. The predicted value of x = 0.7 is slightly higher than that derived from the measured lattice parameter and Vegard's law (x = 0.67). Four distinguishable areas were observed in samples hot-pressed in nitrogen atmosphere. They were identified as β-Si3 N4 , mixtures of TiC and titanium carbonitride solid solution, SiC with twins, and iron silicide. As the duration of hot-pressing increased, more titanium carbonitride was formed, while less TiC phase remained. Thermodymanic calculations indicate one source of nitrogen gas came from the decomposition of Si3 N4 . The TiC particles also became more irregular, and reactants were found inside or between TiC as the hot-pressing time was extended. Silicon carbide was not detected in samples which were hot-pressed in argon atmosphere; however, numerous pores were found around TiC. 相似文献
9.
Jae-Yuk Kim Takayoshi Iseki Toyohiko Yano 《Journal of the American Ceramic Society》1996,79(10):2744-2746
The effect of aluminum and yttrium nitrate additives on the densification of monolithic Si3 N4 and a Si3 N4 /SiC composite by pressureless sintering was compared with that of oxide additives. The surfaces of Si3 N4 particles milled with aluminum and yttrium nitrates, which were added as methanol solutions, were coated with a different layer containing Al and Y from that of Si3 N4 particles milled with oxide additives. Monolithic Si3 N4 could be sintered to 94% of theoretical density (TD) at 1500°C with nitrate additives. The sintering temperature was about 100°C lower than the case with oxide additives. After pressureless sintering at 1750°C for 2 h in N2 , the bulk density of a Si3 N4 /20 wt% SiC composite reached 95% TD with nitrate additives. 相似文献
10.
Soo Young Lee 《Journal of the American Ceramic Society》1998,81(5):1262-1268
Si3 N4 /SiC composite materials have been fabricated by reaction-sintering and postsintering steps. The green body containing Si metal and SiC particles was reaction-sintered at 1370°C in a flowing N2 /H2 gas mixture. The initial reaction product was dominated by alpha-Si3 N4 . However, as the reaction processed there was a gradual increase in the proportion of β-Si3 N4 . The reaction-bonded composite consisting of alpha-Si3 N4 , β-Si3 N4 , and SiC was heat-treated again at 2000°C for 150 min under 7-MPa N2 gas pressure. The addition of SiC enhanced the reaction-sintering process and resulted in a fine microstructure, which in turn improved fracture strength to as high as 1220 MPa. The high value in flexural strength is attributed to the formation of uniformly elongated β-Si3 N4 grains as well as small size of the grains (length = 2 μm, thickness = 0.5 μm). The reaction mechanism of the reaction sintering and the mechanical properties of the composite are discussed in terms of the development of microstructures. 相似文献
11.
TOSHIO HIRAI KOICHI NIIHARA TAKASHI GOTO 《Journal of the American Ceramic Society》1980,63(7-8):419-424
A thermo gravimetric study of the oxidation behavior of chemically vapor-deposited amorphous and crystalline Si3 N4 (CVD Si3 N4 ) was made in dry oxygen (0.1 MPa) at 1550° to 1650°C. The specimens were prepared under various deposition conditions using a mixture of SiCl4 , NH3 , and H2 gases. The crystalline CVD Si3 N4 indicated a parabolic oxidation kinetics over the whole temperature range, whereas the amorphous CVD Si3 N4 changed from a parabolic to a linear law with increased temperature. The oxidation mechanism is discussed in terms of the activation energy for the oxidation and the microstructure of the formed oxide films. 相似文献
12.
Jianren Zeng Yoshinari Miyamoto Osamu Yamada 《Journal of the American Ceramic Society》1990,73(12):3700-3702
Fine sialon powders (Si6-z Alz Oz N8-z , Z = 0.3, 0.6) were prepared by nitriding combustion. Silicon powders was reacted with AlN and Si3 N4 under 10 MPa of nitrogen gas. The reaction temperature reached above 2000°C and single-phase sialon powders were synthesized within minutes. The obtained powders were fully densified without additives by hot isostatic pressing. The sintered body had a flexural strength of 600 MPa by 4-point bending. 相似文献
13.
Full-density Si3 N4 -SiO2 -Ce2 O3 compositions were prepared by sintering with 2.5 MPa nitrogen pressure at temperatures of 1900° and 2090°C. Room-temperature flexural strengths near 700 MPa for sintered material compared favorably with the strength of hot-pressed material. At 1370°C, where flexural strengths as high as 363 MPa were obtained, it was observed that the coarsest structure was the strongest and the finest structure was the weakest. One of the compositions tested, Si3 N4 -8.7 wt% SiO2 -8.3 wt%-Ce2 O3 , was found to have excellent 200-h oxidation resistance at 700°, 1000°, and 1370°C, without incidence of 700° to 1000°C phase instability and cracking. 相似文献
14.
Advanced sintering techniques for consolidation of Si3 N4 powders in the presence of an oxygen-rich liquid phase(s) require high temperatures and usually high nitrogen pressures. A stability diagram is constructed for Si3 N4 as a function of the partial pressures of nitrogen (PN2 ) and silicon (PSi ). High PN2 (20 to 100 atm) increases the stability of Si3 N4 and the oxygen-rich liquid phase by reducing the PSi and PSi0 , respectively. The region of high sinterability is outlined for submicrometer Si3 N4 powders containing 7 wt% BeSiN2 and 7 wt% SiO2 as densification aids . 相似文献
15.
Eirik Hagen Tor Grande Mari-Ann Einarsrud 《Journal of the American Ceramic Society》2004,87(7):1200-1204
Microporous two-phase AlN–SiC composites were prepared using Al4 C3 and either Si (N2 atmosphere) or Si3 N4 (Ar atmosphere) as precursors. The reaction mechanisms of the two synthesis routes and the effect of processing conditions on reaction rate and the material microstructures were demonstrated. The exothermic reaction between Si and Al4 C3 under N2 atmosphere was shown to be a simple processing route for the preparation of porous two-phase AlN–SiC materials. The homogeneous two-phase AlN–SiC composites had a grain size in the range of 1–5 μm, and the porosity varied in the range of 36%–45%. The bending strength was 50–60 MPa, in accordance with the high porosity. 相似文献
16.
Byung-Jin Choi Young-Hag Koh Hyoun-Ee Kim 《Journal of the American Ceramic Society》1998,81(10):2725-2728
The effects of microstructure and residual stress on the mechanical properties of Si3 N4 -based three-layer composite materials were investigated. The microstructure of each layer was controlled by the addition of two differently sized silicon carbides: fine SiC nanoparticles (∼200 nm) or relatively large SiC platelets (∼20 µm). When the SiC nanoparticles were added, the average grain size of Si3 N4 was reduced because of the inhibition of grain growth by the particles. On the other hand, when the SiC platelets were added, the microstructure of Si3 N4 was not much changed because of the large size of the platelets. Three-layer composites were fabricated by placing the Si3 N4 /SiC-nanoparticle layers on the surface of the Si3 N4 /SiC-platelet layer. The residual stress was controlled by varying the amount of SiC added. The mechanical properties of three-layer composites with various combinations of microstructure and residual stress level were investigated. 相似文献
17.
Inna G. Talmy James A. Zaykoski Mark M. Opeka 《Journal of the American Ceramic Society》2008,91(7):2250-2257
The effect of Si3 N4 , Ta5 Si3 , and TaSi2 additions on the oxidation behavior of ZrB2 was characterized at 1200°–1500°C and compared with both ZrB2 and ZrB2 /SiC. Significantly improved oxidation resistance of all Si-containing compositions relative to ZrB2 was a result of the formation of a protective layer of borosilicate glass during exposure to the oxidizing environment. Oxidation resistance of the Si3 N4 -modified ceramics increased with increasing Si3 N4 content and was further improved by the addition of Cr and Ta diborides. Chromium and tantalum oxides induced phase separation in the borosilicate glass, which lead to an increase in liquidus temperature and viscosity and to a decrease in oxygen diffusivity and of boria evaporation from the glass. All tantalum silicide-containing compositions demonstrated phase separation in the borosilicate glass and higher oxidation resistance than pure ZrB2 , with the effect increasing with temperature. The most oxidation-resistant ceramics contained 15 vol% Ta5 Si3 , 30 vol% TaSi2 , 35 vol% Si3 N4 , or 20 vol% Si3 N4 with 10 mol% CrB2 . These materials exceeded the oxidation resistance of the ZrB2 /SiC ceramics below 1300°–1400°C. However, the ZrB2 /SiC ceramics showed slightly superior oxidation resistance at 1500°C. 相似文献
18.
Fei Chen Qiang Shen Faqiang Yan Lianmeng Zhang 《Journal of the American Ceramic Society》2007,90(8):2379-2383
A new method for preparing high bending strength porous silicon nitride (Si3 N4 ) ceramics with controlled porosity has been developed by using pressureless sintering techniques and phosphoric acid (H3 PO4 ) as the pore-forming agent. The fabrication process is described in detail and the sintering mechanism of porous ceramics is analyzed by the X-ray diffraction method and thermal analysis. The microstructure and mechanical properties of the porous Si3 N4 ceramics are investigated, as a function of the content of H3 PO4 . The resultant high porous Si3 N4 ceramics sintered at 1000°–1200°C show a fine porous structure and a relative high bending strength. The porous structure is caused mainly by the volatilization of the H3 PO4 and by the continous reaction of SiP2 O7 binder, which could bond on to the Si3 N4 grains. Porous Si3 N4 ceramics with a porosity of 42%–63%, the bending strength of 50–120 MPa are obtained. 相似文献
19.
Takayuki Narushima Takashi Goto Yoshio Yokoyama Jun Hagiwara Yasutaka Iguchi Toshio Hirai 《Journal of the American Ceramic Society》1994,77(9):2369-2375
The oxidation behavior of chemically vapor-deposited silicon nitride in N2 –O2 and Ar–O2 atmospheres was studied using a thermogravimetric technique at temperatures 1823 to 1923 K. Active oxidation was observed at low oxygen partial pressures. The active oxidation rates increased with increasing oxygen partial pressure ( P O2 ) up to a certain P O2 , and then passive oxidation occurred. The transition oxygen partial pressures from active to passive oxidation were determined. The rate-controlling step for the active oxidation could be oxygen diffusion through a gaseous boundary layer near the Si3 N4 surface. Decomposition of Si3 N4 does not seem to be associated with the mass loss behavior. The Wagner model was employed to explain the oxidation behavior. 相似文献
20.
Chaitanya K. Narula Brian G. Demczyk Paul Czubarow Dietmar Seyferth 《Journal of the American Ceramic Society》1995,78(5):1247-1251
[(Trimethylsilyl)amino]titanium trichloride, (CH3 )3 -SiNHTiClj, was isolated as a red-orange crystalline solid in 58% yield from the reaction of TiCl4 with [(CH3 )3 Si]2 NH in 1:1 molar ratio in dichloromethane at —78°C. Pyrolysis of (CH3 )3 SiNHTiCl3 at 600°C furnished titanium nitride. This precursor is suitable for the preparation of composites and was employed to prepare Si3 N4 -TiN and Ti-TiN powders by adding Si3 N4 particles or titanium powders to a solution of (CH3 ), SiNHTiCl3 in dichloromethane, drying and pyrolyzing the resulting solid. This precursor also has been used as a binder to prepare Si3 N4 -TiN and Ti-TiN bodies. High-resolution transmission electron microscopic studies of the Si3 N4 -TiN composite showed that titanium nitride is concentrated on the surface of the Si3 N4 particles. 相似文献