共查询到20条相似文献,搜索用时 31 毫秒
1.
Michel W. Barsoum Leonid Farber Igor Levin Adam Procopio Tamer El-Raghy Alex Berner 《Journal of the American Ceramic Society》1999,82(9):2545-2547
The structure and chemistry of what initially was proposed to be Ti3 Al2 N2 are incorrect. Using high-resolution transmission electron microscopy, together with chemical analysis, the stoichiometry of this compound is concluded to be Ti4 AlN3-delta (where delta = 0.1). The structure is layered, wherein every four layers of almost-close-packed Ti atoms are separated by a layer of Al atoms. The N atoms occupy ∼97.5% of the octahedral sites between the Ti atoms. The unit cell is comprised of eight layers of Ti atoms and two layers of Al atoms; the unit cell is hexagonal with P 63 / mmc symmetry (lattice parameters of a = 0.3 nm and c = 2.33 nm). This compound is machinable and closely related to other layered, ternary, machinable, hexagonal nitrides and carbides, namely M2 AX and M3 AX2 (where M is an early transition metal, A is an A-group element, and X is carbon and/or nitrogen). 相似文献
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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
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Juergen Heinrich Eberhard Backer Manfred Böhmer 《Journal of the American Ceramic Society》1988,71(1):28-C-
Hot isostatically pressed silicon nitride was produced by densifying Si3 N4 powder compacts and reaction-bonded Si3 N4 (RBSN) parts with yttria as a sintering additive. The microstructure was analyzed using scanning electron microscopy, X-ray diffraction, and density measurements. The influence of the microstructure on fracture strength, creep, and oxidation behavior was investigated. It is assumed that the higher amount of oxygen in the Si3 N4 starting powder compared with the RBSN starting material leads to an increased amount of liquid phase during densification. This results in grain growth and in a larger amount of grain boundary phase in the hot isostatically pressed material. Compared with the hot isostatically pressed RBSN samples therefore, strength decreases whereas the creep rate and the weight gain during oxidation increase. 相似文献
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Fumiyasu Oba Kazuyoshi Tatsumi Isao Tanaka Hirohiko Adachi 《Journal of the American Ceramic Society》2002,85(1):97-100
First-principles calculations have been conducted to investigate impurities in cubic Si3 N4 and Ge3 N4 . Impurity species suitable for n - and p -type doping are suggested, in terms of the formation and ionization energies. The suggested species are P and O as n -type dopants and Al as a p -type dopant for c -Si3 N4 , and Sb and O as n -type dopants and Al as a p -type dopant for c -Ge3 N4 . The dependence of the formation energies on the chemical potentials indicates that a proper choice of growth conditions is mandatory for suppressing the incorporation of these impurities into anti and interstitial sites, where the impurities can be charged to compensate carriers. 相似文献
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Solid-liquid equilibria in the system Si,Al,Y/N,0 were determined for the compatibility triangle bounded by the β-SiAlON solid-solution line and the compound Y3 Al5 O12 . X-ray diffraction was used to determine the crystalline phases present in the equilibrated, rapidly cooled specimens. The liquid phase was quantified with volume fraction measurements performed on scanning electron micrographs. The solid-liquid tie lines at 1650° and 1750°C were established from lattice parameters of the β-SiAlON phase and from the amount of liquid phase in equilibrium with the crystalline solid. The liquid phase was crystallized to verify the location of the starting composition. 相似文献
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D. Amutha Rani Y. Yoshizawa M. I. Jones H. Hyuga K. Hirao Y. Yamauchi 《Journal of the American Ceramic Society》2005,88(6):1655-1658
We report here the study on tribological behavior of α-Sialon in aqueous medium. The results derived from a wide range of test conditions are briefly discussed. A reduction in friction coefficient from 0.7 to 0.03 and a decrease in wear rate by two orders of magnitude were achieved under low load (9.8 N) and high speed (>0.54 m/s) conditions. The tribological behavior of α-Sialon/Si3 N4 ceramics was then compared with Si3 N4 /Si3 N4 tribopairs. 相似文献
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RobertM. Williams Andre Ezis John C. Caverly G.Y. Onoda 《Journal of the American Ceramic Society》1984,67(4):c64-c66
The properties of Si3 N4 compositions produced by nitriding slip-cast Si bodies containing up to 16% Si3 N4 grog were determined. The introduction of grog consistently lowered the densities, the room- and high-temperature strengths, and the resistance to oxidation. The open structure of the grog-containing mixes favored low-temperature gas-phase reactions leading to α-Si3 N4 formation. In higher-density compositions containing predominantly Si, gas-liquid-solid reactions at higher temperatures produced a relatively greater content of the β phase. 相似文献
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The densification behavior of Si3 N4 containing MgO was studied in detail. It was concluded that MgO forms a liquid phase (most likely a magnesium silicate). This liquid wets and allows atomic transfer of Si3 N4 . Evidence of a second-phase material between the Si3 N4 grains was obtained through etching studies. Transformation of α- to β-Si3 N4 during hot-pressing is not necessary for densification. 相似文献
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Reaction mechanisms occurring in the systems ZrO2-Si3 N4 and TiO2-Si3 N4 have been compared. The thermodynamics of several overall reaction mechanisms have been analyzed, including the effects of the gas phase composition to determine the most energetically favorable course of each reaction . 相似文献
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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
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IRVIN C. HUSEBY† HANS L. LUKAS GÜNTER PETZOW 《Journal of the American Ceramic Society》1975,58(9-10):377-380
The 1780°C isothermal section of the reciprocal quasiternary system Si3 N4 -SiO2 -BeO-Be3 N2 was investigated by the X-ray analysis of hot-pressed samples. The equilibrium relations shown involve previously known compounds and 8 newly found compounds: Be6 Si3 N8 , Be11 Si5 N14 , Be5 Si2 N6 , Be9 Si3 N10 , Be8 SiO4 N4 , Be6 O3 N2 , Be8 O5 N2 , and Be9 O6 N2 . Large solid solubility occurs in β-Si3 N4 , BeSiN2 , Be9 Si3 N10 , Be4 SiN4 , and β-Be3 N2 . Solid solubility in β-Si3 N4 extends toward Be2 SiO4 and decreases with increasing temperature from 19 mol% at 1770°C to 11.5 mol% Be2 SiO4 at 1880°C. A 4-phase isotherm, liquid +β-Si3 N4 ( ss )Si2 ON2 + BeO, exists at 1770°C. 相似文献
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Martin Krämer 《Journal of the American Ceramic Society》1993,76(6):1627-1629
α-Si3 N4 core structures within β-Si3 N4 grains have been studied by transmission electron microscopy. The grains were dispersed in an oxynitride glass which was previously melted at 1600°C. The cores were topotactically related to the as-grown β-Si3 N4 crystallites and are related to epitactical nucleation during heat treatment as the most probable mechanism. 相似文献
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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
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Koichiro Fukuda Satoshi Mori Shinobu Hashimoto 《Journal of the American Ceramic Society》2005,88(12):3528-3530
The crystal structure of Zr2 Al3 C4 was refined by the Rietveld method from conventional X-ray powder diffraction data. The structure was hexagonal (space group P 63 mc , Z =2) with a =0.334680(6) nm, c =2.22394(3) nm, and V =0.215731(6) nm3 , being isomorphous with that of U2 Al3 C4 . The final reliability indices were R wp =8.57%, R p =6.06%, and S =1.32. The crystal showed an intergrowth structure with NaCl-type ZrC slabs separated by Al4 C3 -type Al3 C2 layers. 相似文献