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1.
Masaaki Suzuki Yves Maniette Yoshinori Nakata Takeshi Okutani 《Journal of the American Ceramic Society》1993,76(5):1195-1200
The synthesis and the structure of silicon carbide-silicon nitride (SiC─Si3 N4 ) composite ultrafine particles have been studied. SiC─Si3 N4 composite ultrafine particles were prepared by irradiating a SiH4 , C2 H4 , and NH3 gas mixture with a CO2 laser at atmospheric pressure. The composition of composite powders changed with the reactant gas flow rate. The carbon and nitrogen content of the powder could be controlled in a wide range from 0 to 30 wt%. The composite powder, which contained 25.3 wt%. carbon and 5.8 wt% nitrogen, had a (β-SiC structure. As the nitrogen con- tent increased, SiC decreased and amorphous phase, Si3 N4 , Si appeared. The results of XPS and lattice constant measurements suggested that Si, C, and N atoms were intimately mixed in the composite particles. 相似文献
2.
Guo-Jun Zhang Jian-Feng Yang Tatsuki Ohji 《Journal of the American Ceramic Society》2002,85(9):2256-2260
Thermogravimetry, differential thermal analysis, mass spectrometry, and X-ray diffractometry were used to study the reaction process of the in situ reaction between Si3 N4 , B4 C, and carbon for the synthesis of silicon carbide–boron nitride composites. Atmospheres with a low partial pressure of nitrogen (for example argon + 5%–10% nitrogen) seemed to inhibit denitrification and also maintain a high reaction rate. However, the reaction rate decreased significantly in a pure nitrogen atmosphere. The experimental mass spectrometry results also revealed that B4 C in the Si3 N4 –B4 C–C system inhibited the reaction between Si3 N4 and carbon and, even, the decomposition of Si3 N4 . The present results indicate that boron could be a composition stabilizer for ceramic materials in the Si-N-C system used at high temperature. 相似文献
3.
KOHJI NOBUGAI SHIGEKI YABE FUMIKAZU KANAMARU 《Journal of the American Ceramic Society》1984,67(7):146-C
Thin films of amorphous Si3 N4 were prepared by the rf-sputtering method, and the effects of titanium and chlorine additives on its crystallization were examined. When Ti-doped amorphous Si3 N4 was heated, TiN precipitated at >1100°C; the TiN precipitates promoted the conversion of amorphous Si3 N4 to β-Si3 N4 . Chlorine led to preferential conversion of amorphous Si3 N4 to α-Si3 N4 . 相似文献
4.
Dae-Chul Park Toyohiko Yano Takayoshi Iseki Kazuyori Urabe 《Journal of the American Ceramic Society》2000,83(12):2967-2973
A chemical adsorption method in a Si3 N4 slurry that contained a nitrate solution was studied during ball milling, with particular interest in increasing the oxide layer in the Si3 N4 powder and improving the distribution homogeneity of the sintering additives. The nitrate salts Al(NO3 )3 ·9H2 O and Y(NO3 )3 ·6H2 O were selected as sintering additives. The following characterization techniques were used: oxygen–nitrogen analysis, X-ray photoelectron spectroscopy, high-resolution electron microscopy (coupled with energy-dispersive X-ray spectroscopy), and X-ray imaging (using wavelength-dispersive X-ray spectroscopy). The thickness of the amorphous layer and the oxygen content of the Si3 N4 powder were greater for samples that were milled with nitrate additives, which were heat-treated at 600°C, than those of powders that were milled with oxide additives. The chemical composition of the oxygen-containing layer—that is, the amorphous layer that formed and/or changed on the Si3 N4 surface—was similar to Si2 N2 O in heat-treated Si3 N4 powder with nitrate additives, whereas the composition of heat-treated Si3 N4 powder with oxide additives was similar to SiO2 . Furthermore, a homogeneous distribution of the additives was achieved via the incorporation of aluminum and yttrium into the amorphous layer on the Si3 N4 surface. The metal ratio (Y:Al) of the adsorbates was somewhat higher than that of the additives. 相似文献
5.
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
6.
Remco van Weeren Edgar A. Leone Sean Curran Lisa C. Klein Stephen C. Danforth 《Journal of the American Ceramic Society》1994,77(10):2699-2702
Amorphous silicon oxynitride powder was synthesized by nitridation of high-purity silica in ammonia at 1120°C. The resulting material was X-ray amorphous, and its chemical characteristics were determined by X-ray photoelectron spectroscopy (XPS) and 29 Si nuclear magnetic resonance (NMR). The XPS analysis showed a shift to lower binding energies for the Si2 p peak with increasing nitrogen content. Upon initial nitridation, the full width at half maximum (FWHM) of the Si2 p peak increased, but decreased again at higher nitrogen contents, thus showing the formation of a silicon oxynitride phase with a single or small range of composition. The 29 Si NMR analysis showed the formation of (amorphous) Si3 N4 (Si–N4 ) and possibly two oxynitride phases (Si–N3 O, Si–N2 O2 ). It is concluded that while XPS, FT-IR, and nitrogen analysis may show the formation of an homogeneous, amorphous silicon oxynitride (Si2 N2 O) phase, the formation of phase–pure, amorphous Si2 N2 O is extremely difficult via this route. 相似文献
7.
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
8.
Densification and Mechanical Properties of Titanium Diboride with Silicon Nitride as a Sintering Aid 总被引:3,自引:0,他引:3
June-Ho Park Young-Hag Koh Hyoun-Ee Kim † Cheol Seong Hwang Eul Son Kang 《Journal of the American Ceramic Society》1999,82(11):3037-3042
Titanium diboride (TiB2 ) was hot-pressed at a temperature of 1800°C, and silicon nitride (Si3 N4 ) was added as a sintering aid. The amount of Si3 N4 that was added had a significant influence on the sinterability and mechanical properties of the TiB2 . When a small amount (2.5 wt%) of Si3 N4 was added, the Si3 N4 reacted with titania (TiO2 ) that was present on the surface of the TiB2 powder to form titanium nitride (TiN), boron nitride (BN), and amorphous silica (SiO2 ). The elimination of TiO2 suppressed the grain growth effectively, which led to an improvement in the densification of TiB2 . The formation of SiO2 also was deemed beneficial for densification. The mechanical properties-especially, the flexural strength-were enhanced remarkably through these improvements in the sinterability and microstructure. On the other hand, when a large amount (greaterthan equal to5 wt%) of Si3 N4 was added, the mechanical properties were not improved much, presumably because of the extensive formation of a glassy Si-Ti-O-N phase at the grain boundaries. 相似文献
9.
Hui Gu Rowland M. Cannon Hans J. Seifert Michael J. Hoffmann Isao Tanaka 《Journal of the American Ceramic Society》2002,85(1):25-32
The nitrogen solubility in the SiO2 -rich liquid in the metastable binary SiO2 -Si3 N4 system has been determined by analytical TEM to be 1%–4% of N/(O + N) at 1973–2223 K. Analysis of the near edge structure of the electron energy loss peak indicates that nitrogen is incorporated into the silicate network rather than being present as molecular N2 . A regular solution model with a positive enthalpy of mixing for the liquid was used to match the data for the metastable solubility of N in the presence of crystalline Si3 N4 and to adjust the computed phase diagram. The solubility of Si3 N4 in fused SiO2 is far less than reported in liquid silicates also containing Al, Mg, and/or Y. Apparently, these cations act as modifiers that break anion bridges in the silicate network and, thereby, allow further incorporation of Si3 N4 without prohibitive amounts of network cross-linking. Finally, indications emerged regarding the diffuse nature of the Si3 N4 -SiO2 interface that leads to amorphous regions of higher N content. 相似文献
10.
Hui Gu 《Journal of the American Ceramic Society》2002,85(1):33-37
Contrary to the widely accepted observation that grain-boundary amorphous films for a given Si3 N4 composition have common (equilibrium) widths and compositions, a significant variation for both parameters from film to film was observed in an undoped high-purity Si3 N4 prepared using a hot isostatic pressing method. This material previously has been reported to have an equilibrium film width of 0.6 nm, as measured using a high-resolution electron microscopy (HREM) method; this value is significantly different from that which is typical for other high-purity Si3 N4 ceramics (1.0 nm). A total of four boundaries were analyzed, using spatially resolved electron energy-loss spectroscopy methods, which can give the chemical width and composition for the film. Widths of these grain-boundary films were substantially different from each other; only the thinnest matches the previous HREM observations. The nitrogen content in the film decreased concurrently as the film thickened. This material had many cavities and complicated configurations at triple pockets, because of the very low total-SiO2 content (0.55 vol%). They created locally different equilibrium conditions for grain-boundary films, in comparison with other fully densified Si3 N4 , causing such strong variation in both film structure and chemistry. This observation reveals the importance of triple pockets in equilibrium film structures, providing new insight in evaluating the absorption and wetting models. The thinnest film may correspond to the amorphous structure that is required to bind two randomly oriented Si3 N4 grains under greater local stress. 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.
Glasses in the Ge-S, Ge-As-Se, and Ge-As-Se-Te systems, doped with Si3 N4 , were melted after sealing under reduced pressure, and their crystallization behavior was examined using differential thermal analysis/differential scanning calorimetry and X-ray diffractometry. The effect of Si3 N4 doping on the suppression of the crystallization of chalcogenide glasses was confirmed for all three systems and is attributed to the increased crosslinking upon substitution of the chalcogens by nitrogen atoms, presumably forming structural units that are similar to Ge3 N4 . 相似文献
13.
Xiaoqing Pan 《Journal of the American Ceramic Society》1996,79(11):2975-2979
The structure of interfaces formed by a Si3 N4 grain and the silica-rich intergranular amorphous phase was investigated by quantitative high-resolution transmission electron microscopy (QHRTEM). It was found that the contrast and periodicity of the HRTEM image of β-Si3 N4 strongly depend on the specimen thickness and objective lens focus value. The different thinning rate between Si3 N4 and the glass phase during ion-milling results in gradients of the specimen thickness at the interfaces. The interface roughness can also lead to a thickness variation of Si3 N4 near the interface parallel to the electron beam. As a result, the HRTEM micrographs, taken from the thin specimen regions near the interfaces at a certain defocus value, show the occurrence of an artifact of an ordered structure seemingly different from Si3 N4 . The present investigations, however, showed that no ordered phase actually different from that of Si3 N4 at the interfacial region in Si3 N4 could be identified so far. The interfacial structure is likely direct Si3 N4 /glass bonding, rather than an ordered transition phase between the Si3 N4 and the glass phase. 相似文献
14.
Relationship between the Average Coordination Number and Properties of Chalconitride Glasses 总被引:2,自引:0,他引:2
Chalconitride glasses obtained by doping Ge-As-Se and Ge-S chalcogenide glass systems with Si3 N4 (0.35 and 0.50 wt%) have been studied; these glasses have been doped with Si3 N4 to improve their thermal and mechanical prop-erties. The glasses have been melted under vacuum in sealed silica ampoules, quenched in air, and subsequently annealed. Measured properties include the transition temperature ( T g ), microhardness ( H v ), and thermal expansion coefficient (α). The effect of Si3 N4 doping is system depen-dent. The concept of average coordination number () is used to explain this dependence. For the glasses in the chal-cogen-rich region, a greater increase in thermal and mechanical properties with Si3 N4 doping is assigned to the fact that both the introduction of silicon and the substitution of nitrogen for chalcogens enhance the degree of crosslinking within the substructures. However, for the glasses in the chalcogen-deficient region, extra silicon atoms that are in-troduced with Si3 N4 doping are not helpful in further crosslinking the network, because of the deficiency in the bridging chalcogens. A slight increase in T g with increasing , in the case of chalcogen deficiency, might result from the "wrong-bond effect," which provides some additional crosslinking in connections of the networked island sub-structural units. 相似文献
15.
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
16.
Stability of Silicon Carbonitride Phases 总被引:1,自引:0,他引:1
Andrzej Badzian 《Journal of the American Ceramic Society》2002,85(1):16-20
Important hard phases are included in the quaternary compositional system Si-N-C-B. This paper reviews ternary amorphous and crystalline phases in the system Si-N-C and deliberates on the issue of stability of the binary C3 N4 , a hypothetical phase harder than diamond, and instability of nitrides in general. There is a tendency for nitrogen atoms to agglomerate and be released as nitrogen molecules. Stabilization of CN radicals can be achieved through ternary phases: carbonitrides metal-C-N. Ternary Si-N-C phases have been synthesized by pyrolysis of polyorganosilazanes, physical vapor deposition, and chemical vapor deposition. The crystalline α-Si3 N4 :C phase can incorporate about 6 at.% C and yields enhancement of hardness and wear resistance. Other crystalline phases contain more carbon, for example, Si2 CN4 . 相似文献
17.
Cha-Yang Chu Jitendra P. Singh Jules L. Routbort 《Journal of the American Ceramic Society》1993,76(5):1349-1353
The high-temperature flexural strength of hot-pressed silicon nitride (Si3 N4 ) and Si3 N4 -whisker-reinforced Si3 N4 -matrix composites has been measured at a crosshead speed of 1.27 mm/min and temperatures up to 1400°C in a nitrogen atmosphere. Load–displacement curves for whisker-reinforced composites showed nonelastic fracture behavior at 1400°C. In contrast, such behavior was not observed for monolithic Si3 N4 . Microstructures of both materials have been examined by scanning and transmission electron microscopy. The results indicate that grain-boundary sliding could be responsible for strength degradation in both monolithic Si3 N4 and its whisker composites. The origin of the nonelastic failure behavior of Si3 N4 -whisker composite at 1400°C was not positively identified but several possibilities are discussed. 相似文献
18.
Silicon Nitride Based Ceramic Nanocomposites 总被引:7,自引:0,他引:7
Xiaoqing Pan Joachim Mayer Manfred Rühle Koichi Niihara 《Journal of the American Ceramic Society》1996,79(3):585-590
Nanocomposites (Si3 N4 /SiC) were studied by combined high-resolution transmission electron microscopy and electron energy-loss spectroscopic imaging (ESI) techniques. In ESI micrographs three types of crystalline grains were distinguished: Si3 N4 matrix grains (0.5 μΩ), nanosized SiC particles (<100 nm) embedded in the Si3 N4 , and large SiC particles (100–200 nm) at grain boundary regions (intergranular particles). Amorphous films were found both at Si3 N4 grain boundaries and at phase boundaries between Si3 N4 and SiC. The Si3 N4 grain boundary film thickness varied from 1 to 2. 5 nm. Two kinds of embedded SiC particles were observed: type A has a special orientation with respect to the matrix, and type B possesses a random orientation with respect to the matrix. The surfaces of type B particles are completely covered by an amorphous phase. The existence of the amorphous film between the matrix and the particles of type A depends on the lattice mismatch across the interface. The mechanisms of nucleation and growth of Ω-Si3 N4 grains are discussed on the basis of these experimental results. 相似文献
19.
Surface Modification of Silicon Nitride Powder with Aluminum 总被引:2,自引:0,他引:2
K. R. Han C. S. Lim M. J. Hong S. K. Choi S. H. Kwon 《Journal of the American Ceramic Society》1996,79(2):574-576
Surface modification of Si3 N4 with alumina was tried. It was achieved by simply mixing Si3 N4 powder with an alumina sol up to ∼2 wt% as alumina in an aqueous medium, dried, and followed by calcination at 400°C for 1 h. A TEM micrograph showed a coating layer of ∼15 nm thickness. The isoelectric point of the modified Si3 N4 powder with porous alumina was at pH 7.8, which is different from 5.8 and 8.6 for Si3 N4 and amorphous alumina, respectively. 相似文献
20.
Grain-Boundary Microstructure and Chemistry of a Hot Isostatically Pressed High-Purity Silicon Nitride 总被引:1,自引:0,他引:1
Xiaoqing Pan Hui Gu Remco van Weeren Stephen C. Danforth Rowland M. Cannon Manfred Rühle 《Journal of the American Ceramic Society》1996,79(9):2313-2320
Two high-purity Si3 N4 materials were fabricated by hot isostatic pressing without the presence of sintering additives, using an amorphous laser-derived Si3 N4 powder with different oxygen contents. High-resolution transmission electron microscopy and electron energy-loss spectroscopy (EELS) analysis of the Si3 N4 materials showed the presence of an amorphous SiO2 grain-boundary phase in the three-grain junctions. Spatially resolved EELS analysis indicated the presence of a chemistry similar to silicon oxynitride at the two-grain junctions, which may be due to partial dissolution of nitrogen in the grain-boundary film. The chemical composition of the grain-boundary film was SiNx Oy , (x ∼ 0.53 and y ∼ 1.23), and the triple pocket corresponded to the amorphous SiO2 containing ∼2 wt% nitrogen. The equilibrium grain-boundary-film thickness was measured and found to be smaller for the material with the lower oxygen content. This difference in thickness has been explained by the presence of the relatively larger calcium concentration in the material with the lower amount of SiO2 grain-boundary phase, because the concentration of foreign ions has been shown to affect the grain-boundary thickness. 相似文献