共查询到20条相似文献,搜索用时 46 毫秒
1.
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
2.
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
3.
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
4.
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
5.
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
6.
Gui-hua Peng Min Liang Zhen-hua Liang Qing-yu Li Wen-lan Li Qian Liu 《Journal of the American Ceramic Society》2009,92(9):2122-2124
Silicon nitride ceramics were prepared by spark plasma sintering (SPS) at temperatures of 1450°–1600°C for 3–12 min, using α-Si3 N4 powders as raw materials and MgSiN2 as sintering additives. Almost full density of the sample was achieved after sintering at 1450°C for 6 min, while there was about 80 wt%α-Si3 N4 phase left in the sintered material. α-Si3 N4 was completely transformed to β-Si3 N4 after sintering at 1500°C for 12 min. The thermal conductivity of sintered materials increased with increasing sintering temperature or holding time. Thermal conductivity of 100 W·(m·K)−1 was achieved after sintering at 1600°C for 12 min. The results imply that SPS is an effective and fast method to fabricate β-Si3 N4 ceramics with high thermal conductivity when appropriate additives are used. 相似文献
7.
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
8.
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
9.
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
10.
β-Si3 N4 ceramics sintered with Yb2 O3 and ZrO2 were fabricated by gas-pressure sintering at 1950°C for 16 h changing the ratio of "fine" and "coarse" high-purity β-Si3 N4 raw powders, and their microstructures were quantitatively evaluated. It was found that the amount of large grains (greater than a few tens of micrometers) could be drastically reduced by mixing a small amount of "coarse" powder with a "fine" one, while maintaining high thermal conductivity (>140 W·(m·K)−1 ). Thus, this work demonstrates that it is possible for β-Si3 N4 ceramics to achieve high thermal conductivity and high strength simultaneously by optimizing the particle size distribution of raw powder. 相似文献
11.
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
12.
Xuguang Tong Jianbao Li Xiaozhan Yang Hong Lin Gangfeng Guo Mingsheng He 《Journal of the American Ceramic Society》2006,89(5):1730-1732
In this work, self-reinforced silicon nitrides with β-Si3 N4 seeds doped with Re2 O3 (Re=Yb, Lu) were investigated. Firstly, the two kinds of seeds were obtained by heating α-Si3 N4 powder with Yb2 O3 or Lu2 O3 , respectively. Then the self-reinforced silicon nitride ceramics were prepared by HP-sintering of α-Si3 N4 powder, Re2 O3 as additive, and the as-prepared seeds. Oxidation test was carried out at 1400°C in air for 100 h with thermogravimetry analysis (TGA) measurement. Mechanical properties, scanning electronic microscopy microstructures, and X-ray diffraction patterns were measured before and after oxidation. The results indicated that the introduction of the seeds doped with Re2 O3 (Re=Yb, Lu) could obviously increase the toughness and keep the room temperature and high-temperature strength of the ceramics at high values. After oxidation, the crystalline phase in grain boundary changed and the mechanical properties decreased. TGA showed a parabolic weight gain and the oxidation mechanism was discussed. 相似文献
13.
Soo Young Lee 《Journal of the American Ceramic Society》1998,81(5):1262-1268
Si3 N4 /SiC composite materials have been fabricated by reaction-sintering and postsintering steps. The green body containing Si metal and SiC particles was reaction-sintered at 1370°C in a flowing N2 /H2 gas mixture. The initial reaction product was dominated by alpha-Si3 N4 . However, as the reaction processed there was a gradual increase in the proportion of β-Si3 N4 . The reaction-bonded composite consisting of alpha-Si3 N4 , β-Si3 N4 , and SiC was heat-treated again at 2000°C for 150 min under 7-MPa N2 gas pressure. The addition of SiC enhanced the reaction-sintering process and resulted in a fine microstructure, which in turn improved fracture strength to as high as 1220 MPa. The high value in flexural strength is attributed to the formation of uniformly elongated β-Si3 N4 grains as well as small size of the grains (length = 2 μm, thickness = 0.5 μm). The reaction mechanism of the reaction sintering and the mechanical properties of the composite are discussed in terms of the development of microstructures. 相似文献
14.
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
15.
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
16.
The kinetics of anisotropic β-Si3 N4 grain growth in silicon nitride ceramics were studied. Specimens were sintered at temperatures ranging from 1600° to 1900°C under 10 atm of nitrogen pressure for various lengths of time. The results demonstrate that the grain growth behavior of β-Si3 N4 grains follows the empirical growth law Dn – D0 n = kt , with the exponents equaling 3 and 5 for length [001] and width [210] directions, respectively. Activation energies for grain growth were 686 kJ/mol for length and 772 kJ/mol for width. These differences in growth rate constants and exponents for length and width directions are responsible for the anisotropy of β-Si3 N4 growth during isothermal grain growth. The resultant aspect ratio of these elongated grains increases with sintering temperature and time. 相似文献
17.
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
18.
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
19.
Gui-hua Peng Guo-jian Jiang Wen-lan Li Bao-lin Zhang Li-dong Chen 《Journal of the American Ceramic Society》2006,89(12):3824-3826
α/β-Si3 N4 composites with various α/β phase ratios were prepared by hot pressing at 1600°–1650°C with MgSiN2 as sintering additives. An excellent combination of mechanical properties (Vickers indentation hardness of 23.1 GPa, fracture strength of about 1000MPa, and toughness of 6.3 MPa·m1/2 ) could be obtained. Compared with conventional Si3 N4 -based ceramics, this new material has obvious advantages. It is as hard as typical in-situ-reinforced α-Sialon, but much stronger than the latter (700 MPa). It has comparable fracture strength and toughness, but is much harder than β-Si3 N4 ceramics (16 GPa). The microstructures and mechanical properties can be tailored by choosing the additive and controlling the heating schedule. 相似文献
20.
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