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1.
Woo Y. Lee James R. Strife Richard D. Veltri 《Journal of the American Ceramic Society》1992,75(10):2803-2808
The crystal structure and surface morphology of Si3 N4 prepared by LPCVD were characterized as a function of processing conditions. Temperature was the most dominant variable which affected the coating microstructure. Strongly faceted crystalline Si3 N4 was deposited at temperatures above ∼ 1410°C. In the temperature range of 1300° to 1410°C, crystalline and amorphous phases were codeposited. The content of the crystalline phase rapidly decreased with decreased temperature. In this temperature range, the coating crystallinity was also influenced by kinetic factors such as deposition rate and reagent depletion. For example, Si3 N4 became more crystalline as the deposition rate was decreased by either decreasing the flow rate or increasing the NH3 /SiF4 molar ratio. At ∼ 1300°C, the coating surface appeared fully botryoidal, and the coatings were mostly amorphous. Changes in the orientation and size of Si3 N4 crystallites were parametrically documented. As the temperature was increased, the Si3 N4 grains generally became more preferentially oriented to the (102) and/or ( l 0 l ) where l = 1,2,3,., directions. The average facet size increased with coating thickness. 相似文献
2.
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
3.
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
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.
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
6.
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
7.
Thermal decomposition of silicon diimide, Si(NH)2 , in vacuum resulted in very-high-purity, fine-particle-size, amorphous Si3 N4 powders. The amorphous powder was isothermally aged at 50° to 100° intervals from 1000° to 1500°C for phase identification. Examination of ir spectra and X-ray diffraction patterns indicated a slow and gradual transition from an amorphous material to a crystalline α-phase occurring at 1200°C for >4 h and/or 1300° to 1400°C for 2 h. As the temperature was increased to ≥1450°C for 2 h, the crystalline β-phase was observed. Phase nucleation and crystallite morphology in this system were studied by electron microscopy and electron diffraction combined with TG as functions of temperature for the inorganic polymer starting materials. Powders prepared in this manner with 4 wt% Mg3 N2 added as a sintering aid were hot-pressed to high-density fine-grained bodies with uniform microstructures. The optimum hot-pressing condition was 1650°C for 1 h. Silicon concentration steadily increased as the hot-pressing temperature or time was increased. A method for chemical etching for high-density fine-grained Si3 N4 is described. Electrical measurements between room temperature and ∼500°C indicated dielectric constant and tan δ values of 8.3±0.03 and 0.65±0.05×10−2 , respectively. 相似文献
8.
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
9.
Tateoki Iizuka Hideki Kita Hideki Hyuga Takene Hirai Kazuo Osumi 《Journal of the American Ceramic Society》2004,87(3):337-341
A W2 C-nanoparticle-reinforced Si3 N4 -matrix composite was fabricated by sintering porous Si3 N4 that had been infiltrated with a tungsten solution. During the sintering procedure, nanometer-sized W2 C particles grew in situ from the reaction between the tungsten and carbon sources considered to originate mainly from residual binder. The W2 C particles resided in the grain-boundary junctions of the Si3 N4 , had an average diameter of ∼60 nm, and were polyhedral in shape. Because the residual carbon, which normally would obstruct sintering, reacted with the tungsten to form W2 C particles in the composite, the sinterability of the Si3 N4 was improved, and a W2 C–Si3 N4 composite with almost full density was obtained. The flexural strength of the W2 C–Si3 N4 composite was 1212 MPa, ∼34% higher than that of standard sintered Si3 N4 . 相似文献
10.
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
11.
Koji Watari Kiyoshi Hirao Motohiro Toriyama Kozo Ishizaki 《Journal of the American Ceramic Society》1999,82(3):777-779
Polycrystalline Si3 N4 samples with different grain-size distributions and a nearly constant volume content of grain-boundary phase (6.3 vol%) were fabricated by hot-pressing at 1800°C and subsequent HIP sintering at 2400°C. The HIP treatment of hot-pressed Si3 N4 resulted in the formation of a large amount of ß-Si3 N4 grains ∼10 µm in diameter and ∼50 µm long, and the elimination of smaller matrix grains. The room-temperature thermal conductivities of the HIPed Si3 N4 materials were 80 and 102 Wm−1 K−1 , respectively, in the directions parallel and perpendicular to the hot-pressing axis. These values are slightly higher than those obtained for hot-pressed samples (78 and 93 Wm−1 K−1 ). The calculated phonon mean free path of sintered Si3 N4 was ∼20 nm at room temperature, which is very small as compared to the grain size. Experimental observations and theoretical calculations showed that the thermal conductivity of Si3 N4 at room temperature is independent of grain size, but is controlled by the internal defect structure of the grains such as point defects and dislocations. 相似文献
12.
Preparation of Ultrafine Silicon Nitride, and Silicon Nitride and Silicon Carbide Mixed Powders in a Hybrid Plasma 总被引:1,自引:0,他引:1
Hyung Jik Lee Keisuke Eguchi Toyonobu Yoshida 《Journal of the American Ceramic Society》1990,73(11):3356-3362
Ultrafine Si3 N4 and Si3 N4 + SiC mixed powders were synthesized through thermal plasma chemical vapor deposition (CVD) using a hybrid plasma which was characterized by the superposition of a radio-frequency plasma and an arc jet. The reactant, SiCl4 , was injected into an arc jet and completely decomposed in a hybrid plasma, and the second reactant, CH4 and/or NH3 , was injected into the tail flame through multistage ring slits. In the case of ultrafine Si3 N4 powder synthesis, reaction effieciency increased significantly by multistage injection compared to single-stage injection. The most striking result is that amorphous Si3 N4 with a nitrogen content of about 37 wt% and a particle size of 10 to 30 nm could be prepared successfully even at the theoretical NH3 /SiCl4 molar ratio of ∼ 1.33, although the crystallinity depended on the NH3 /SiCl4 molar ratio and the injection method. For the preparation of Si3 N4 + SiC mixed powders, the N/C composition ratio and particle size could be controlled not only by regulating the flow rate of the NH3 and CH4 reactant gases and the H2 quenching gas, but also by adjusting the reaction space. The results of this study provide sufficient evidence to suggest that multistage injection is very effective for regulating the condensation process of fine particles in a plasma tail flame. 相似文献
13.
Rajat Kanti Paul Kap-Ho Lee Hai-Doo Kim Byong-Taek Lee 《Journal of the American Ceramic Society》2008,91(8):2509-2513
Using a novel microwave-assisted process, nano-Ag-coated continuous porous SiC–Si3 N4 substrate was fabricated from a solution containing AgNO3 salts and ethylene glycol. The detailed microstructure of the fabricated substrate was investigated depending on the amount of AgNO3 salts in the starting solution and the microwave irradiation time. From a solution containing 0.4 g of AgNO3 for 60 s irradiation time, the Ag nanoparticles, ∼25 nm in diameter, were homogeneously coated on the continuous porous SiC–Si3 N4 matrix as well as on the surface of the Si3 N4 whiskers. However, the Ag nanoparticles (∼15 nm) deposited from a solution containing 0.6 g of AgNO3 for 60 s irradiation time showed maximum homogeneity and narrow size distribution. The components of Si, N, and Ag were homogeneously distributed on the deposited layer. The deposited Ag nanoparticles covered with a thin (∼2 nm), amorphous layer had nanocrystallinity and adhered well to the surface of the Si3 N4 whiskers. 相似文献
14.
A Si3 N4 /TiC composite was previously demonstrated to exhibit improved wear resistance compared to a monolithic Si3 N4 because of the formation of a lubricious oxide film containing Ti and Si at 900°C. Further improvements of the composite have been made in this study through additions of SiC whiskers and improved processing. Four materials—Si3 N4 , Si3 N4 /TiC, Si3 N4 /SiCwh , and Si3 N4 /TiC/SiCwh — were processed to further optimize the wear resistance of Si3 N4 through improvements in strength, hardness, fracture toughness, and the coefficient of friction. Oscillatory pin on flat wear tests showed a decrease in the coefficient of friction from ∼0.7 (Si3 N4 ) to ∼0.4 with the addition of TiC at temperatures reaching 900°C. Wear track profiles illustrated the absence of appreciable wear on the TiC-containing composites at temperatures above 700°C. Microscopic (SEM) and chemical (AES) characterization of the wear tracks is also included to deduce respective wear and lubricating mechanisms. 相似文献
15.
Riham M. Morcos Alexandra Navrotsky Tamas Varga Dongjoon Ahn Atanu Saha Fabrizia Poli Klaus Müller Rishi Raj 《Journal of the American Ceramic Society》2008,91(7):2391-2393
This communication reports new results on the enthalpy of formation of pseudo-amorphous ceramic compounds constituted from silicon, carbon, oxygen, and nitrogen (SiCNO), made from the polymer route. Again, like the SiCO materials, although with one exception, the enthalpy of formation from crystalline components (SiO2 cristobalite, β-Si3 N4 , SiC, and excess C) is negative. Some of the alloyed oxygen–nitrogen compositions yield enthalpies that are much more negative (∼100 kJ/g·atom) in comparison with compositions that contain mainly oxygen or nitrogen (∼20 kJ/g·atom). The exception, having a N/O ratio near 2, has a positive value for the enthalpy. This may reflect the presence of nanoclusters of stoichiometric Si2 N2 O instead of the pseudo-amorphous nanodomain structure seen for the other samples. 相似文献
16.
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
17.
Scott C. Thompson Anjali Pandit Nitin P. Padture Subra Suresh 《Journal of the American Ceramic Society》2002,85(8):2059-2064
The processing of stepwise graded Si3 N4 /SiC ceramics by pressureless co-sintering is described. Here, SiC (high elastic modulus, high thermal expansion coefficient) forms the substrate and Si3 N4 (low elastic modulus, low thermal expansion coefficient) forms the top contact surface, with a stepwise gradient in composition existing between the two over a depth of ∼1.7 mm. The resulting Si3 N4 contact surface is fine-grained and dense, and it contains only 2 vol% yttrium aluminum garnet (YAG) additive. This graded ceramic shows resistance to cone-crack formation under Hertzian indentation, which is attributed to a combined effect of the elastic-modulus gradient and the compressive thermal-expansion-mismatch residual stress present at the contact surface. The presence of the residual stress is corroborated and quantified using Vickers indentation tests. The graded ceramic also possesses wear properties that are significantly improved compared with dense, monolithic Si3 N4 containing 2 vol% YAG additive. The improved wear resistance is attributed solely to the large compressive stress present at the contact surface. A modification of the simple wear model by Lawn and co-workers is used to rationalize the wear results. Results from this work clearly show that the introduction of surface compressive residual stresses can significantly improve the wear resistance of polycrystalline ceramics, which may have important implications for the design of contact-damage-resistant ceramics. 相似文献
18.
Molecular Dynamics Study of Atomic Structure and Diffusion Behavior in Amorphous Silicon Nitride Containing Boron 总被引:1,自引:0,他引:1
We have performed molecular dynamics simulations of amorphous Si3 N4 containing boron (Si-B-N). We have examined short-range atomic arrangements and self-diffusion constants of amorphous Si-B-N systems with various boron contents. Our simulations show that boron atoms are threefold coordinated by nitrogen atoms and that nitrogen atoms are bonded to both silicon and boron atoms in the amorphous network of Si-B-N. Also, the self-diffusion constant of nitrogen in Si-B-N is much decreased compared with that in amorphous Si3 N4 . This suggests that boron is important in decreasing the mobility of atoms in amorphous Si-B-N, which may explain the improved thermal stability of amorphous Si-B-N relative to amorphous Si3 N4 observed experimentally. 相似文献
19.
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
20.
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