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1.
Shock Synthesis of Cubic Silicon Nitride 总被引:2,自引:0,他引:2
Toshimori Sekine 《Journal of the American Ceramic Society》2002,85(1):113-116
The phase transitions of α-Si3 N4 and β-Si3 N4 have been investigated by shock compression through the recovery technique and Hugoniot measurements. α- and β-Si3 N4 are transformed into a cubic spinel structure ( c -Si3 N4 ). The yield of c -Si3 N4 increases with increasing shock pressure and reaches 100% at 63 GPa. The shock-synthesized c -Si3 N4 powders are nanocrystals and display a high-temperature metastability up to about 1620 K. c -Si3 N4 is one of the hard materials based on the measured equation of state. c -Si3 N4 powders have been characterized by electron microscopy and 29 Si magic angle spinning NMR spectroscopy. The purification and separation method has been developed to obtain pure c -Si3 N4 powders. 相似文献
2.
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
3.
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
4.
Ultrafine powder of α-Si3 N4 several tens of nanometers in size was successfully consolidated using a shock-compaction technique under 40 GPa. The bulk density of the most dense portion attained 99% of the theoretical value, and the Vick-ers microhardness was 2300 kg/mm. Consolidation was achieved through both densificarion by plastic deformation of constituent grains and interparticle bonding by surface melting. A transition process to β-Si3 N4 was observed by transmission electron microscopy: Surface melting of the individual grains propagated into the center as temperature increased, and a large mass formed. A precursor of β–Si3N4 then emerged from the mass and finally grew into a β-Si3 N4 crystal. 相似文献
5.
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
6.
Chun-Keung Loong James W. Richardson Jr. Sugura Sukuzi Masakuni Ozawa 《Journal of the American Ceramic Society》1996,79(12):3250-3256
The crystal structure and phonon densities of states (DOS) of β-SiAlON ceramics, Si6 _ z Al z O z N8-z (0 < z < 4), prepared by a novel slipcast method, are studied by neutron-scattering techniques. The samples with z < 4 form a single-phase solid solution of Si-Al-O-N isostructural to β-Si3 N4 (space group P 6 3 /m). A consistent preferential occupation of the 2c sites by oxygen atoms and the 6 h sites by nitrogen atoms exists within this structure. The phonon DOS of β'-SiAlON displays phonon bands at ∼50 and 115 meV. These features are considerably broader than the corresponding ones in β-Si3 N4 powder. 相似文献
7.
J. Qian C. Pantea J. Zhang L. L. Daemen Y. Zhao M. Tang T. Uchida Y. Wang 《Journal of the American Ceramic Society》2005,88(4):903-906
Through the analysis of peak broadening of energy-dispersive diffraction lines from a powdered sample, the yield strength of α-Si3 N4 was investigated at a pressure of 9 GPa and temperatures up to 1234°C. During compression at room temperature, the lattice strain deduced from peak broadening increased linearly with pressure up to 9.2 GPa, with no clear indication of strain saturation. While heating at 9 GPa, diffraction peaks narrowed and significant stress relaxation was observed at temperatures above 400°C, indicating the onset of yielding. The yield strength of α-Si3 N4 decreases rapidly with increasing temperature: from 8.7 GPa at 400°C to 4.0 GPa at 1234°C. The low temperature for the onset of yielding and decrease of yield strength upon further heating bring up concern regarding the performance of α-Si3 N4 as an engineering material. Finally, the grain size variation is also outlined together with the dependence of differential strain on pressure and on temperature. This provides crucial information for clarifying the "fine structure" of the evolution of the differential strain. 相似文献
8.
Takafumi Kusunose Tohru Sekino Yong Ho Choa Koichi Niihara 《Journal of the American Ceramic Society》2002,85(11):2678-2688
A chemical process for fabrication of Si3 N4 /BN nanocomposite was devised to improve the mechanical properties. Si3 N4 /BN nanocomposites containing 0 to 30 vol% hexagonal BN ( h -BN) were successfully fabricated by hot-pressing α-Si3 N4 powders, on which turbostratic BN ( t -BN) with a disordered layer structure was partly coated. The t -BN coating on α-Si3 N4 particles was prepared by reducing and heating α-Si3 N4 particles covered with a mixture of boric acid and urea. TEM observations of this nanocomposite revealed that the nanosized hexagonal BN ( h -BN) particles were homogeneously dispersed within Si3 N4 grains as well as at grain boundaries. As expected from the rules of composites, Young's modulus of both micro- and nanocomposites decreased with an increase in h -BN content, while the fracture strength of the nanocomposites prepared in this work was significantly improved, compared with the conventional microcomposites. 相似文献
9.
Zdenk Pánek 《Journal of the American Ceramic Society》1995,78(4):1087-1088
Experimental thermochemical data (temperature, pressure) corresponding to the equilibrium conditions between finegrained β-SiC and β-Si3 N4 for carbon activity a (C) = 1 are presented. Based on these data, the temperature dependence of ΔG°f (β-Si3 N4 ) has been expressed for standard states Si( s ), C( s ), and p(N2 ) = 0.1 MPa by the equation ΔA°f (β-Si3 N4 ) = (-995.9 + 0.4547 T/K) kJ mol for T/K ε〈1650; 1968〉. 相似文献
10.
Further Improvement in Mechanical Properties of Highly Anisotropic Silicon Nitride Ceramics 总被引:1,自引:0,他引:1
Hisayuki Imamura Kiyoshi Hirao Manuel E. Brito Motohiro Toriyama Shuzo Kanzaki 《Journal of the American Ceramic Society》2000,83(3):495-500
Si3 N4 ceramics were fabricated by tape casting of a raw-powder slurry seeded with three types of rodlike β-Si3 N4 particles. The effects of seed size on the microstructure and mechanical properties of the sintered specimens were investigated. All the seeded and tape-cast silicon nitrides presented an anisotropic microstructure, where the elongated grains grown from seeds were preferentially oriented parallel to the casting direction. The orientation degree of these grains, f 0 , was affected by seed size, and small-seed addition led to the highest f 0 value. This material exhibited high bending strength (∼1.4 GPa) and high fracture toughness (∼12 MPa. m1/2 ) in the direction normal to the grain alignment, which were attributed to the highly anisotropic and fine microstructure. 相似文献
11.
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
12.
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
13.
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
14.
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
15.
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
16.
Naoto Hirosaki Yoshinobu Yamamoto Toshiyuki Nishimura Mamoru Mitomo Junichi Takahashi Hisanori Yamane Masahiko Shimada 《Journal of the American Ceramic Society》2002,85(11):2861-2863
Phase relationships in the Si3 N4 –SiO2 –Lu2 O3 system were investigated at 1850°C in 1 MPa N2 . Only J-phase, Lu4 Si2 O7 N2 (monoclinic, space group P 21 / c , a = 0.74235(8) nm, b = 1.02649(10) nm, c = 1.06595(12) nm, and β= 109.793(6)°) exists as a lutetium silicon oxynitride phase in the Si3 N4 –SiO2 –Lu2 O3 system. The Si3 N4 /Lu2 O3 ratio is 1, corresponding to the M-phase composition, resulted in a mixture of Lu–J-phase, β-Si3 N4 , and a new phase of Lu3 Si5 ON9 , having orthorhombic symmetry, space group Pbcm (No. 57), with a = 0.49361(5) nm, b = 1.60622(16) nm, and c = 1.05143(11) nm. The new phase is best represented in the new Si3 N4 –LuN–Lu2 O3 system. The phase diagram suggests that Lu4 Si2 O7 N2 is an excellent grain-boundary phase of silicon nitride ceramics for high-temperature applications. 相似文献
17.
Mamoru Mitomo Yoh-ichiro Sato Nobuo Ayuzawa Isamu Yashima 《Journal of the American Ceramic Society》1991,74(4):856-858
Plasma etching of β-Si3 N4 , α-sialon/β-Si3 N4 and α-sialon ceramics were performed with hydrogen glow plasma at 600°C for 10 h. The preferential etching of β-Si3 N4 grains was observed. The etching rate of α-sialon grains and of the grain-boundary glassy phase was distinctly lower than that of β-Si3 N4 grains. The size, shape, and distribution of β-Si3 N4 grains in the α-sialon/β-Si3 N4 composite ceramics were revealed by the present method. 相似文献
18.
Tensile Strength of Silicon Nitride Whiskers Synthesized by Reacting Amorphous Silicon Nitride and Titanium Dioxide 总被引:2,自引:0,他引:2
The tensile strength of α-Si3 N4 whiskers synthesized by reacting amorphous Si3 N4 and TiO2 at 1490°C under a N2 pressure of 700 torr was measured using a microbalance, and the diameter dependence of the strength was investigated. The Si3 N4 whiskers had diameters of 0.04 and 0.8 μm and dominant [1011] and [1010] growth directions. Chemical analysis showed that they contained Ti and O impurities. The tensile strength of six Si3 N4 whiskers increased from 17 to 59 GPa with decreasing whisker diameter. 相似文献
19.
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
20.
K. HIRAGA M. HIRABAYASHI S. HAYASHI T. HIRAI 《Journal of the American Ceramic Society》1983,66(8):539-542
Microstructures of Si3 N4 -TiN composites prepared by chemical vapor deposition (CVD) were investigated by the multibeam imaging technique using a 1 MV electron microscope. High-resolution images showed a number of fibrous TIN crystallites dispersed in the matrix of CVD β-Si3 N4 . Crystallographic orientation relations between β-Si3 N4 and TiN were determined directly from the observed images in the subcell scale. The fibrous axis of TiN is parallel to the (110) direction of the NaCl structure and lies along the c axis of the hexagonal β-Si3 N4 crystal. Domain boundaries, planar faults, nonplanar faults, and dislocations were found in the CVD β-Si3 N4 matrix near the TiN crystallites. The origin of the structure defects is briefly discussed in connection with the formation of TiN crystallites in the matrix. 相似文献