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1.
Detailed microstructural analysis of a 10 mol% Y2 O3 fluxed hot-pressed silicon nitride reveals that, in addition to the yttrium-silicon oxynitride phase located at the multiple Si3 N4 grain junctions, there is a thin boundary phase 10 to 80 Å wide separating the silicon nitride and the oxynitride grains. Also, X-ray microanalysis from regions as small as 200 Å across demonstrates that the yttrium-silicon oxynitride, Y2 Si(Si2 O3 N4 ), phase can accommodate appreciable quantities of Ti, W, Fe, Ni, Co, Ca, Mg, Al, and Zn in solid solution. This finding, together with observations of highly prismatic Si3 N4 grains enveloped by Y2 Si(Si2 O3 N4 ), suggests that densification occurred by a liquid-phase "solution-reprecipitation" process. 相似文献
2.
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
3.
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
4.
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
5.
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
6.
Chaitanya K. Narula M. Matti Maricq Brian G. Demczyk Irving T. Salmeen Willes H. Weber 《Journal of the American Ceramic Society》1993,76(11):2727-2733
Irradiation of Ti[N(CH3 )2 ]4 by the 1.064-μm line of a pulsed Nd: YAG laser in the presence of TiO2 , Al2 O3 , or Si3 N4 particles has been found to form amorphous deposits on the oxide particles. The resulting materials can be processed into TiN/TiO2 , TiN/Al2 O3 , or TiN/Si3 N4 composites with the TiN component on the surface of the particles. The powders have been characterized by Raman spectroscopy and X-ray powder diffraction studies. The surface analysis of the composites by X-ray photoelectron spectroscopy and high-resolution electron microscopy is presented. 相似文献
7.
Hideki Hyuga Yu-ichi Yoshizawa Kiyoshi Hirao D. Amutha Rani Mark I. Jones 《International Journal of Applied Ceramic Technology》2008,5(2):111-118
The tribological behavior of Si3 N4 ceramics and Si3 N4 /carbon fiber composites sliding against stainless steel under water lubrication was investigated using a thrust-bearing-type test method with normal applied loads varying from 0 to 1000 N in 100 N increments. In the case of the monolithic Si3 N4 , the friction coefficient was found to increase up to 0.4 the first time the applied load was increased from 100 to 200 N, and sudden failure of the ceramic ring specimen occurred. In the case of the Si3 N4 /carbon fiber composite, a low friction coefficient was maintained up to the maximum normal load of 1000 N. The addition of the carbon fibers to the silicon nitride ceramics effectively restricts material transfer from the stainless steel to the Si3 N4 worn surface due to reduction of solid–solid contact through the solid lubricating effect of the carbon fibers. 相似文献
8.
Composite ceramic materials based on Si3 N4 and ZrO2 stabilized by 3 mol% Y2 O3 have been formed using aluminum isopropoxide as a precursor for the Al2 O3 sintering aid. Densification was carred out by hot-pressing at temperatures in the range 1650° to 1800°C, and the resulting micro-structures were related to mechanical properties as well as to oxidation behavior at 1200°C. Densification at the higher temperatures resulted in a fibrous morphology of the Si3 N4 matrix with consequent high room-temperature toughness and strength. Decomposition of the ZrO2 grains below the oxidized surface during oxidation introduced radial stresses in the subscalar region, and from the oxidation experiments it is suggested that the ZrO2 incorporated some N during densification. 相似文献
9.
Si3 N4 /MoSi2 and Si3 N4 /WSi2 composites were prepared by reaction-bonding processes using as starting materials powder mixtures of Si-Mo and Si-W, respectively. A presintering step in an At-base atmosphere was used before nitriding for the formation of MoSi2 and WSi2 ; the nitridation in a N2 -base atmosphere was followed after presintering with the total stepwise cycle of 1350°C × 20 h +1400°C × 20 h +1450°C × 2 h. The final phases obtained in the two different composites were Si3 N4 and MoSi2 or WSi2 ; no free elemental Si and Mo or W were detected by X-ray diffraction. 相似文献
10.
Subsolidus phase relations were established in the system Si3 N4 -SiO2 -Y2 O3 . Four ternary compounds were confirmed, with compositions of Y4 Si2 O7 N2 , Y2 Si3 O3 N4 , YSiO2 N, and Y10 (SiO4 )6 N2 . The eutectic in the triangle Si3 N4 -Y2 Si2 O7 -Y10 (SiO4 )6 N2 melts at 1500°C and that in the triangle Si2 N2 O-SiO2 -Y2 Si2 O7 at 1550°C. The eutectic temperature of the Si3 N4 -Y2 Si2 O7 join was ∼ 1520°C. 相似文献
11.
Hui-Ling Zhu Fu-Dong Han Jian-Qiang Bi Yu-Jun Bai Yong-Xin Qi Lin-Lin Pang Cheng-Guo Wang Shao-Jie Li Cheng-Wei Lu 《Journal of the American Ceramic Society》2009,92(2):535-538
Silicon nitride (Si3 N4 ) nanocrystals were synthesized at about 250°C by a simple organic–inorganic reaction between CH3 SiCl3 and NaN3 . The yield of Si3 N4 is no <70 wt% based on the amount of precursor CH3 SiCl3 used in the reaction and TGA analysis. X-ray diffraction indicates the formation of a mixture of α- and β-Si3 N4 . Particles with size from 40 to 100 nm are dominant in the products examined by transmission electron microscopy. X-ray photoelectron spectroscopy gives an atomic ratio of Si:N around 0.75:1. The formation of nanocrystalline Si3 N4 during the organic–inorganic reaction goes through an intermediate product of NaSi2 N3 , which is important for understanding the reaction mechanism. 相似文献
12.
Sintering kinetics of the system Si3 N4-Y2O3 -Al2 O3 were determined from measurements of the linear shrinkage of pressed disks sintered isothermally at 1500° to 1700°C. Amorphous and crystalline Si3 N4 were studied with additions of 4 to 17 wt% Y2 O3 and 4 wt% A12 O3 . Sintering occurs by a liquid-phase mechanism in which the kinetics exhibit the three stages predicted by Kingery's model. However, the rates during the second stage of the process are higher for all compositions than predicted by the model. X-ray data show the presence of several transient phases which, with sufficient heating, disappear leaving mixtures of β ' -Si3 N4 and glass or β '-Si3 N4 , α '-Si3 N4 , and glass. The compositions and amounts of the residual glassy phases are estimated. 相似文献
13.
Subsolidus Phase Relationships in Part of the System Si,Al,Y/N,O: The System Si3 N4 ─AIN─YN─Al2 O3 ─Y2 O3
Wei-Ying Sun Tseng-Ying Tien Tung-Sheng Yen 《Journal of the American Ceramic Society》1991,74(11):2753-2758
The subsolidus phase relationships in the system Si,Al,Y/N,O were determined. Thirty-nine compatibility tetrahedra were established in the region Si3 N4 ─AIN─Al2 O3 ─Y2 O3 . The subsolidus phase relationships in the region Si3 N4 ─AIN─YN─Y2 O3 have also been studied. Only one compound, 2YN:Si3 N4 , was confirmed in the binary system Si3 N4 ─YN. The solubility limits of the α'─SiAION on the Si3 N4 ─YN:3AIN join were determined to range from m = 1.3 to m = 2.4 in the formula Y m /3 Si12- m Al m N16 . No quinary compound was found. Seven compatibility tetrahedra were established in the region Si3 N4 ─AIN─YN─Y2 O3 . 相似文献
14.
F. F. LANGE 《Journal of the American Ceramic Society》1978,61(1-2):53-56
Phase relation studies of Si3 N1 , SiO2 , and MgO have established three important subsolidus tie lines, viz. Si3 N4 -MgO, Si3 N4 -Mg2 SiO4 , and Si2 N2 O-Mg2 SiO4 for nonoxidizing fabrication conditions. Strength measurements at 1400°C show that optimum strengths are obtained for compositions approaching the Si3 N4 -MgO and Si3 N4 -Si2 N2 O tie lines and that inferior strengths are obtained for compositions approaching the Si3 N4 -Mg2 SiO4 tie line. Oxidation measurements at 1375°C show that the oxidation kinetics depend on the content of MgO and Mg2 SiO4 phases. Optimum oxidation resistance is observed for compositions approaching the Si3 N4 -Si2 N2 O tie line. Strength and oxidation results are discussed with regard to phase equilibrium considerations. 相似文献
15.
Yoon-Suk Oh Woo-Seok Cho Chang-Sam Kim Dae Soon Lim Deock-Soo Cheong 《Journal of the American Ceramic Society》1999,82(4):1076-1078
We have synthesized Si3 N4 /SiC nanocomposites using a commercial polymer. Formation behavior of SiC nanoparticles has been studied using X-ray photoelectron spectroscopy (XPS). Based on the XPS results, we concluded that SiC nanoparticles were formed by a chemical reaction of Si provided from Si3 N4 with free carbon obtained by pyrolysis of a polymer around 1300°C. The presence of CN x compounds in samples processed in an Ar atmosphere supported our explanation. 相似文献
16.
Zhaohui Wang Egil Skybakmoen Tor Grande 《Journal of the American Ceramic Society》2009,92(6):1296-1302
A thorough analysis of a silicon nitride (Si3 N4 )-bonded SiC sidelining material from a Hall-Heroult electrolysis cell is reported. Phase composition before and after chemical degradation of the material is obtained by quantitative analysis using Rietveld refinement of X-ray diffraction data and chemical analysis. The main degradation products as a result of the oxidation of Si3 N4 binder phase are Si2 ON2 in the upper part and Na2 SiO3 in the lower part of the sidelining. The microstructure of α-Si3 N4 (needle) and β-Si3 N4 (shell) as well as the degradation products Si2 ON2 (fiber) and Na2 SiO3 (flake) were revealed by electron microprobe analysis. Chemical reactions and degradation mechanisms are proposed based on the presented findings. The degradation in the lower part is more severe than that in the upper part because Na diffusion from the cathode enhances the oxidation of Si3 N4 . The degradation changes the physical properties of Si3 N4 -bonded SiC such as density and porosity. 相似文献
17.
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
18.
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
19.
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
20.
Shuichi Kawano Junichi Takahashi Shiro Shimada 《Journal of the American Ceramic Society》2003,86(4):701-705
TiN-coated Si3 N4 particles were prepared by depositing TiO2 on the Si3 N4 surfaces from Ti(O- i -C3 H7 )4 solution, the TiO2 being formed by controlled hydrolysis, then subsequently nitrided with NH3 gas. A homogeneous TiO2 coating was achieved by heating a Si3 N4 suspension containing 1.0 vol% H2 O with the precursor at 40°C. Nitridation successfully produced Si3 N4 particles coated with 10–20 nm TiN particles. Spark plasma sintering of these TiN/Si3 N4 particles at 1600°C yielded composite ceramics with a relative density of 96% at 25 vol% TiN and an electrical resistivity of 10−3 Ω·cm in compositions of 17.5 and 25 vol% TiN/Si3 N4 , making these ceramics suitable for electric discharge machining. 相似文献