共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
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
3.
Fengxia Li Li Fu Xiaojian Ma Changhui Sun LianCheng Wang Chunli Guo Yitai Qian Yitai Qian 《Journal of the American Ceramic Society》2009,92(2):517-519
Starting from Si powder, NaN3 and different additives such as N -aminothiourea, iodine, or both, Si3 N4 nanomaterials were synthesized through the nitridation of silicon powder in autoclaves at 60°–190°C. As the additive was only N -aminothiourea, β-Si3 N4 nanorods and α-Si3 N4 nanoparticles were prepared at 170°C. If the additive was only iodine, α-Si3 N4 dendrites with β-Si3 N4 nanorods were obtained at 190°C. However, when both N -aminothiourea and iodine were added to the system of Si and NaN3 , the products composed of β-Si3 N4 nanorods and α, β-Si3 N4 nanoparticles could be prepared at 60°C. 相似文献
4.
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
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.
Nanocrystalline α-Si3 N4 powders have been prepared with a yield of 93% by the reaction of Mg2 Si with NH4 Cl in the temperature range of 450° to 600°C in an autoclave. X-ray diffraction patterns of the products can be indexed as the α-Si3 N4 with the lattice constants a = 7.770 and c = 5.627 Å. X-ray photoelectron spectroscopy analysis indicates that the composition of the α-Si3 N4 samples has a Si:N ratio of 0.756. Transmission electron microscopy images show that the α-Si3 N4 crystallites prepared at 450°, 500°, and 550°C are particles of about 20, 40, and 70 nm in average, respectively. 相似文献
7.
Jun-Qi Li Fa Luo Dong-Mei Zhu Wan-Cheng Zhou 《Journal of the American Ceramic Society》2007,90(6):1950-1952
The influence of phase formation on the dielectric properties of silicon nitride (Si3 N4 ) ceramics, which were produced by pressureless sintering with additives in MgO–Al2 O3 –SiO2 system, was investigated. It seems that the difference in the dielectric properties of Si3 N4 ceramics sintered at different temperatures was mainly due to the difference of the relative content of α-Si3 N4 , β-Si3 N4 , and the intermediate product (Si2 N2 O) in the samples. Compared with α-Si3 N4 and Si2 N2 O, β-Si3 N4 is believed to be a major factor influencing the dielectric constant. The high-dielectric constant of β-Si3 N4 could be attributed to the ionic relaxation polarization. 相似文献
8.
Youren Xu Chao M. Huang Waltraud M. Kriven Avigdor Zangvil 《Journal of the American Ceramic Society》1994,77(8):2213-2216
The microstructure of a pressureless sintered (1605°C, 90 min) O'+β' SiAlON ceramic with CeO2 doping has been investigated. It is duplex in nature, consisting of very large, slablike elongated O' grains (20–30 μm long), and a continuous matrix of small rodlike β' grains (< 1.0 μm in length). Many α-Si3 N4 inclusions (0.1–0.5 μm in size) were found in the large O' grains. CeO2 -doping and its high doping level as well as the high Al2 O3 concentration were thought to be the main reasons for accelerating the reaction between the α-Si3 N4 and the Si-Al-O-N liquid to precipitate O'–SiAlON. This caused the supergrowth of O' grains. The rapid growth of O' crystals isolated the remnant α–Si3 N4 from the reacting liquid, resulting in a delay in the α→β-Si3 N4 transformation. The large O' grains and the α-Si3 N4 inclusions have a pronounced effect on the strength degradation of O'+β' ceramics. 相似文献
9.
Håkan Björklund Jonas Wasén Lena K. L. Falk 《Journal of the American Ceramic Society》1997,80(12):3061-3069
The three-dimensional grain size distribution in an experimental β-Si3 N4 material has been determined using the hexagonal prism as a model of β-Si3 N4 grain shape. Results from quantitative microscopy of polished and etched sections were compared with computer-generated two-dimensional stereological parameters of hexagonal prisms with different aspect ratios in order to determine an average grain shape (i.e., aspect ratio) in the microstructure. Section parameter distributions for the average grain shape were obtained from the computer simulations and used in a three-dimensional reconstruction of the microstructure. The results showed that this Si3 N4 ceramic had the postulated fibrous microstructure and a broad grain size distribution. 相似文献
10.
Using a recently developed first-principles supercell method that includes the electron and core-hole interaction, the XANES/ELNES spectra of Si- L 2,3 , Si- K , and N- K edges in α-Si3 N4 , β-Si3 N4 , spinel c -Si3 N4 , and Si2 N2 O were calculated and compared. The difference in total energies between the initial ground state and the final core-hole state provides the transition energy. The calculated spectra are found to be in good agreement with the experimental measurements on β-Si3 N4 and c -Si3 N4 . The differences in the XANES/ELNES spectra for the same element in different crystals are explained in terms of differences in local bonding. The use of orbital-decomposed local density of states to explain the measured spectra is shown to be inadequate. These results reaffirm the importance of including the core-hole effect in any XANES/ELNES spectral calculation. 相似文献
11.
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
12.
Ibram Ganesh 《International Journal of Applied Ceramic Technology》2009,6(1):89-101
In this paper, a new net-shaping process, an hydrolysis-induced aqueous gelcasting (GC) (GCHAS) has been reported for consolidation of β-Si4 Al2 O2 N6 ceramics from aqueous slurries containing 48–50 vol%α-Si3 N4 , α-Al2 O3 , AlN, and Y2 O3 powders mixture. Dense ceramics of same composition were also consolidated by aqueous GC and hydrolysis assisted solidification routes. Among three techniques used, the GCHAS process was found to be superior for fabricating defect-free thin wall β-Si4 Al2 O2 N6 crucibles and tubes. Before use, the as purchased AlN powder was passivated against hydrolysis. The sintered β-Si4 Al2 O2 N6 ceramics exhibited comparable properties with those reported for similar materials in the literature. 相似文献
13.
C. Greskovich 《Journal of the American Ceramic Society》1981,64(2):31-C-
The development of microstructure in hot-pressed Sia N4 was studiehd for a typical Si3 N4 powder with and without BeSiN2 as a densification aid. The effect of hot-pressing temperature on density, α- to β-Si3 N4 conversion and specific surface area showed that BeSiN2 appears to increase the mobility of the system by enhancing densification, α- to β-Si3 N4 transformation, and grain growth at temperatures between 1450° and 1800°. These processes appear to occur in the presence of a liquid phase. 相似文献
14.
Tetsuo Nakayasu Tetsuo Yamada Isao Tanaka Hirohiko Adachi Seishi Goto 《Journal of the American Ceramic Society》1998,81(3):565-570
First-principles molecular orbital calculations are performed by the discrete variational Xalpha method using model clusters of rare-earth-doped β-Si3 N4 and the interface between prismatic planes of β-Si3 N4 and intergranular glassy films. On the basis of the total overlap population of each cluster, the rare-earth ions are implied to be stable in the grain-boundary model, while they are not stable in the bulk model. These results are consistent with experimental observations showing significant segregation of Ln3+ ions at the grain boundary and no solubility of Ln3+ into bulk β-Si3 N4 . Grain-boundary bonding is weakened with an increase of the ionic radius of the rare-earth ions, which provides a reasonable explanation for the ionic size dependence of the crack propagation behaviors as well as the growth rate of the prismatic plane in the rare-earth-doped β-Si3 N4 during liquid-phase sintering. 相似文献
15.
L. J. GAUCKLER J. WEISS T. Y. TIEN G. PETZOW 《Journal of the American Ceramic Society》1978,61(9-10):397-398
Solid-solution formation of magnesium in β-Si3 N4 containing AlN:Al2 O3 was investigated. Samples were hot-pressed at 1700°C. Under the condition studied, very little or no magnesium entered the β-Si3 N4 lattice. 相似文献
16.
Branko Matovic Georg Rixecker Fritz Aldinger 《Journal of the American Ceramic Society》2004,87(4):546-549
This paper deals with the densification and phase transformation during pressureless sintering of Si3 N4 with LiYO2 as the sintering additive. The dilatometric shrinkage data show that the first Li2 O- rich liquid forms as low as 1250°C, resulting in a significant reduction of sintering temperature. On sintering at 1500°C the bulk density increases to more than 90% of the theoretical density with only minor phase transformation from α-Si3 N4 to β-Si3 N4 taking place. At 1600°C the secondary phase has been completely converted into a glassy phase and total conversion of α-Si3 N4 to β-Si3 N4 takes place. The grain growth is anisotropic, leading to a microstructure which has potential for enhanced fracture toughness. Li2 O evaporates during sintering. Thus, the liquid phase is transient and the final material might have promising mechanical properties as well as promising high-temperature properties despite the low sintering temperature. The results show that the Li2 O−Y2 O3 system can provide very effective low-temperature sintering additives for silicon nitride. 相似文献
17.
Tzer-Shin Sheu 《Journal of the American Ceramic Society》1994,77(9):2345-2353
The in situ β-Si3 N4 /α'-SiAlON composite was studied along the Si3 N4 –Y2 O3 : 9 AlN composition line. This two phase composite was fully densified at 1780°C by hot pressing Densification curves and phase developments of the β-Si3 N4 /α'-SiAlON composite were found to vary with composition. Because of the cooperative formation of α'-Si AlON and β-Si3 N4 during its phase development, this composite had equiaxed α'-SiAlON (∼0.2 μm) and elongated β-Si3 N4 fine grains. The optimum mechanical properties of this two-phase composite were in the sample with 30–40%α', which had a flexural strength of 1100 MPa at 25°C 800 MPa at 1400°C in air, and a fracture toughness 6 Mpa·m1/2 . α'-SiAlON grains were equiaxed under a sintering condition at 1780°C or lower temperatures. Morphologies of the α°-SiAlON grains were affected by the sintering conditions. 相似文献
18.
L. J. BOWEN T. G. CARRUTHERS R. J. BROOK 《Journal of the American Ceramic Society》1978,61(7-8):335-359
The rates of densification and phase transformation undergone by α-Si3 N4 during hot-pressing in the presence of Y2 O3 , Y2 O3 −2SiO2 , and Li2 0−2Si02 as additives were studied. Although these systems behave less simply than MgO-doped Si3 N4 , the data can be interpreted during the early stages of hot-pressing as resulting from a solution-diffusion-reprecipitation mechanism, where the diffusion step is rate controlling and where the reprecipitation step invariably results in the formation of the β-Si3 N4 phase. 相似文献
19.
The subsolidus phase diagram of the quasiternary system Si3 N4 -AlN-Y2 O3 was established. In this system α-Si3 N4 forms a solid solution with 0.1Y2 O3 : 0.9 AIN. The solubility limits are represented by Y0.33 Si10.5 Al1.5 O0.5 N15.5 and Y0.67 Si9 A13 ON15 . At 1700°C an equilibrium exists between β-Si3 N4 and this solid solution. 相似文献
20.
Ellen Y. Sun Kathleen B. Alexander Paul F. Becher Shyh-Lung Hwang 《Journal of the American Ceramic Society》1996,79(10):2626-2632
Interfacial microstructures in βP-Si3 N4 ( w )-Si-Al-Y-O-N-glass systems were investigated by systematically varying the nitrogen content and the Al:Y ratio of the glass matrix. High-resolution and analytical transmission electron microscopy (HREM and AEM) studies revealed that the interfacial microstructure is a function of the glass composition. No interfacial phases were formed in glasses with low Al:Y ratios and in glasses with high Al:Y ratios and low nitrogen content, whereas epitaxial growth of an interfacial layer (100–200 μm thick) on the βP-Si3 N4 ( w ) occurred in a glass matrix with high Al:Y ratio and high nitrogen content. The interfacial layer was identified to be a β'-SiAION phase. Interfaces containing the SiAION layer exhibited high debonding energy compared to Si3 N4 ( w )–glass interfaces. HREM studies indicated that the lattice-mismatch strain in the SiAION layer was relieved by dislocation formation at the SiAION–Si3 N4 ( w ) interface. The difference in interfacial debonding energy was, hence, attributed to the local atomic structure and bonding between the glass-β-Si3 N4 and the glass–β'-SiAION phases. This observation was clear evidence of the strong influence of glass chemistry on the interfacial debonding behavior by altering the interfacial microstructure. 相似文献