共查询到20条相似文献,搜索用时 31 毫秒
1.
Mikito Kitayama Kiyoshi Hirao Akira Tsuge Koji Watari Motohiro Toriyama Shuzo Kanzaki 《Journal of the American Ceramic Society》2000,83(8):1985-1992
Dense β-Si3 N4 with various Y2 O3 /SiO2 additive ratios were fabricated by hot pressing and subsequent annealing. The thermal conductivity of the sintered bodies increased as the Y2 O3 /SiO2 ratio increased. The oxygen contents in the β-Si3 N4 crystal lattice of these samples were determined using hot-gas extraction and electron spin resonance techniques. A good correlation between the lattice oxygen content and the thermal resistivity was observed. The relationship between the microstructure, grain-boundary phase, lattice oxygen content, and thermal conductivity of β-Si3 N4 that was sintered at various Y2 O3 /SiO2 additive ratios has been clarified. 相似文献
2.
Won-Ho Lee Hyoun-Ee Kim Seong-Jai Cho 《Journal of the American Ceramic Society》1997,80(10):2737-2740
Microstructural evolution of gas-pressure-sintered Si3 N4 with Yb2 O3 as a sintering aid was observed. Microstructures typical for in situ toughened Si3 N4 , i.e., large elongated grains randomly distributed in a fine matrix, were observed. However, the size of the elongated grains near the surface was much larger than that at the center, resulting in two distinct regions: an inner region and an outer region. The smaller the amount of Yb2 O3 added, the larger the difference in the size of the elongated grains between the outer and inner regions. The difference between microstructures was diminished when 16 wt% Yb2 O3 was added. The microstructural change with Yb2 O3 content was attributed to the evaporation of Yb-containing liquid phase from the surface. 相似文献
3.
Gang Feng Guo Jianbao Li Xiang Yang Kong Hong Lin Long Liang Mingsheng He Liu Yang Jiang Wu Bai Cui 《Journal of the American Ceramic Society》2008,91(2):611-614
The heat treatment of silicon nitride (Si3 N4 ) ceramics with additions of 8, 12, and 16 wt% Yb2 O3 was carried out at different temperatures and the evolution of grain boundary (GB) phase was investigated systematically by X-ray diffraction (XRD) as well as scanning electron and transmission electron microscopic analyses. XRD results reveal that the extent and the ease of GB crystallization increase with increasing the Yb2 O3 content, and that high heat-treatment temperatures in general favor crystallization of the quaternary compounds such as the Yb4 Si2 O7 N2 phase. These results provide an insight into the GB phase evolution in the Yb-system Si3 N4 ceramics subjected to a postsintering heat treatment. 相似文献
4.
Hyoungjoon Park Hae-Won Kim Hyoun-Ee Kim 《Journal of the American Ceramic Society》1998,81(8):2130-2134
The oxidation behaviors of monolithic Si3 N4 and nanocomposite Si3 N4 -SiC with Yb2 O3 as a sintering aid were investigated. The specimens were exposed to air at temperatures between 1200° and 1500°C for up to 200 h. Parabolic weight gains with respect to exposure time were observed for both specimens. The oxidation products formed on the surface also were similar, i.e., a mixture of crystalline Yb2 Si2 O7 and SiO2 (cristobalite). However, strength retention after oxidation was much higher for the nanocomposite Si3 N4 -SiC compared to the monolithic Si3 N4 . The SiC particles of the nanocomposite at the grain boundary were effective in suppressing the migration of Yb3+ ions from the bulk grain-boundary region to the surface during the oxidation process. As a result, depletion of yttribium ions, which led to the formation of a damaged zone beneath the oxide layer, was prevented. 相似文献
5.
A novel porous Yb4 Si2 O7 N2 material with uniform open-cell network structure was fabricated from the reaction between Si3 N4 , Yb2 O3 , and SiO2 . The formation of Yb4 Si2 O7 N2 during heating was studied using X-ray diffractometry. The porous structure was characterized using scanning electron microscopy and mercury porosimeter. It is shown that the formation of Yb4 Si2 O7 N2 phase starts at ∼1150°C and completes at 1350°C for 4 h, accompanied by the development of open-cell network structure. The necks between Yb4 Si2 O7 N2 particles become much thicker with increasing temperature because of the coarsening of Yb4 Si2 O7 N2 particles, thus leading to a uniform three-dimensional network structure. Furthermore, the pore size can be well controlled by adjusting reacting temperature and altering atmosphere. 相似文献
6.
Thermal Conductivity of Gas-Pressure-Sintered Silicon Nitride 总被引:3,自引:0,他引:3
Naoto Hirosaki Yusuke Okamoto Motohide Ando Fumio Munakata Yoshio Akimune 《Journal of the American Ceramic Society》1996,79(11):2878-2882
Si3 N4 with high thermal conductivity (120 W/(m. K)) was developed by promoting grain growth and selecting a suitable additive system in terms of composition and amount. β-Si3 N4 doped with Y2 O3 -Nd2 O3 (YN system) or Y2 O3 -A12 O3 (YA system) was sintered at 1700°-2000°C. Thermal conductivity increased with increased sintering temperature because of decreased two-grain junctions, as a result of grain growth. The effect of the additive amount on thermal conductivity with the YN system was rather small because increased additive formed multigrain junctions. On the other hand, with the YA system, thermal conductivity considerably decreased with increased additive amount because the aluminum and oxygen in the YA system dissolved into β-Si3 N4 grains to form a β-SiAlON solid solution, which acted as a point defect for phonon scattering. The key processsing parameters for high thermal conductivity of Si3 N4 were the sintering temperature and additive composition. 相似文献
7.
Evaluation of Glassy Phase in Sintered Silicon Nitride by Low-Temperature Specific Heat Measurements
Koji Watari Kozo Ishizaki Katsunori Mori 《Journal of the American Ceramic Society》1991,74(1):244-246
The specific heat of HIP sintered Si3 N4 with 3 mol% Y2 O3 and 3 mol% Al2 O3 additives was measured at different temperatures ranging from 2 to 10 K, in order to confirm the presence of a glassy phase in the sintered body. The grainboundary glassy phase in the sintered Si3 N4 was evaluated by specific heat measurements. The difference between the experimental value and the lattice specific heat calculated from the Debye theory confirmed the existence of a glassy phase in sintered Si3 N4 . 相似文献
8.
Influence of Rare-Earth Additives on Wear Properties of Hot-Pressed Silicon Nitride Ceramics under Dry Sliding Conditions 总被引:2,自引:1,他引:1
Hideki Hyuga Mark I. Jones Kiyoshi Hirao Yukihiko Yamauchi 《Journal of the American Ceramic Society》2004,87(9):1683-1686
The influence of different rare-earth sintering additives (Y, Yb, Lu) on the wear properties of Si3 N4 ceramics was investigated during sliding contact without lubricant. The kind of rare-earth additives was shown to have a significant effect on the wear behavior for contact sliding under the present testing conditions. Samples sintered with Y2 O3 as the sintering additive showed evidence of fracture type wear although this was not observed in samples sintered with Yb2 O3 and Lu2 O3 . These smaller rare earths lead to higher grain boundary bonding strength and superior high-temperature properties and resulted in higher wear resistance. These results showed that the wear properties of Si3 N4 ceramics could be tailored by judicious selection of the sintering additives. 相似文献
9.
Processing and Thermal Conductivity of Sintered Reaction-Bonded Silicon Nitride: (II) Effects of Magnesium Compound and Yttria Additives 总被引:1,自引:0,他引:1
Xinwen Zhu You Zhou Kiyoshi Hirao Zoltán Lené 《Journal of the American Ceramic Society》2007,90(6):1684-1692
The effects of the magnesium compound and yttria additives on the processing, microstructure, and thermal conductivity of sintered reaction-bonded silicon (Si) nitride (SRBSN) were investigated using two additive compositions of Y2 O3 –MgO and Y2 O3 –MgSiN2 , and a high-purity coarse Si powder as the starting powder. The replacement of MgO by MgSiN2 leads to the different characteristics in RBSN after complete nitridation at 1400°C for 8 h, such as a higher β-Si3 N4 content but finer β-Si3 N4 grains with a rod-like shape, different crystalline secondary phases, lower nitrided density, and coarser porous structure. The densification, α→β phase transformation, crystalline secondary phase, and microstructure during the post-sintering were investigated in detail. For both cases, the similar microstructure observed suggests that the β-Si3 N4 nuclei in RBSN may play a dominant role in the microstructural evolution of SRBSN rather than the intergranular glassy chemistry during post-sintering. It is found that the SRBSN materials exhibit an increase in the thermal conductivity from ∼110 to ∼133 (Wm·K)−1 for both cases with the increased time from 6 to 24 h at 1900°C, but there is almost no difference in the thermal conductivity between them, which can be explained by the similar microstructure. The present investigation reveals that as second additives, the MgO is as effective as the MgSiN2 for enhancing the thermal conductivity of SRBSN. 相似文献
10.
The oxygen content of silicon nitride with 1 mol% Y2 O3 —Nd2 O3 additive was measured after firing to determine the compositional change during gas-pressure sintering. Oxygen content decreases from 2.5 to 0.94 wt% during firing for 4 h at 1900°C and 10-MPa pressure in N2 . This decrease in oxygen results from the release of SiO gas generated by a thermaldecomposition reaction between Si3 N4 and SiO2 . The resultant sintered silicon nitride material contains less than 1 wt% oxygen. 相似文献
11.
Reaction Synthesis of Magnesium Silicon Nitride Powder 总被引:2,自引:0,他引:2
Zoltán Lené Kiyoshi Hirao Yukihiko Yamauchi Shuzo Kanzaki 《Journal of the American Ceramic Society》2003,86(7):1088-1093
The synthesis of magnesium silicon nitride (MgSiN2 ) by direct nitridation of a Si/Mg2 Si/Mg/Si3 N4 powder mixture is described. A nucleation period at 550°C and stepwise heat-treatment schedule up to 1350°C was adopted for the synthesis of MgSiN2 powder, based on TG-DTA measurements. The influence of the ratio of constituents on the final phase composition also has been studied. The content of magnesium and silicon in the starting powder should fulfill the conditions Mg2 Si/Mg ≥ 3 and Si3 N4 /Sitot ≥ 0.5 to obtain single-phase MgSiN2 . The silicon particle size of <0.5 μm is preferable to decrease the time of nitridation. The oxygen content of as-synthesized powders is in the range 0.9–1.2 wt%. However, the oxygen content of MgSiN2 powder decreases further by the addition of 2 wt% CaF2 or 0.75 wt% carbon and reaching the lowest value of 0.45 wt% oxygen after carbothermal reduction in an alumina-tube furnace. 相似文献
12.
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
13.
This study shows that the amount ofAl2 O3 needed to form high density Si3 N4 -15Y2 -O3 samples can be reduced by using high surface area Si3 N4 powder and high N2 overpressure (high sintering temperatures) during the sintering process. The reduction in AI2 O3 content results in improved oxidation resistance of the sintered samples. 相似文献
14.
Si3 N4 test bars containing additions of BN, B4 C, and C, were hot isostatically pressed in Ta cladding at 1900° and 2050°C to 98.9% to 99.5% theoretical density. Room-temperature strength data on specimens containing 2 wt% BN and 0.5 wt% C were comparable to data obtained for Si3 N4 sintered with Y2 O3 , Y2 O3 and Al2 O3 , or ZrO2 . The 1370°C strengths were less than those obtained for additions of Y2 O3 or ZrO2 but greater than those obtained from a combination of Y2 O3 and Al2 O3 . Scanning electron microscope fractography indicated that, as with other types of Si3 N4 , roomtemperature strength was controlled by processing flaws. The decrease in strength at 1370°C was typical of Si3 N4 having an amorphous grainboundary phase. The primary advantage of non-oxide additions appears to be in facilitating specimen removal from the Ta cladding. 相似文献
15.
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
16.
The optimization of concentrated Si3 N4 powder aqueous slurry properties to achieve high packing density slipcast compacts and subsequent high sintered densities was investigated. The influence of pH, sintering aid powder (6% Y2 O3 , 4% Al2 O3 ), NH4 PA dispersant, and Si3 N4 oxidative thermal treatment was determined for 32 vol% Si3 N4 slurries. The results were then utilized to optimize the dispersion properties of 43 vol% solids Si3 N4 -sintering aid slurries. Calcination of the Si3 N4 powder was observed to result in significantly greater adsorption of NH4 PA dispersant and effectively reduced the viscosity of the 32 vol% slurries. Lower viscosities of the optimized dispersion 43 vol% Si3 N4 -sintering aid slurries resulted in higher slipcast packing density compacts with smaller pore sizes and pore volumes, and corresponding higher sintered densities. 相似文献
17.
The existence of compounds between Si3 N4 -CeO2 and Si3 N4 -Ce2 O3 was investigated for firing temperatures of 1600° to 1700°C. The two new monoclinic compounds found were Ce2 O3 ·2Si3 N4 with lattice parameters a = 16.288, b = 4.848, and c =7.853 Å and β=91.54° and Ce4 Si2 O7 N2 with lattice parameters a = 10.360, b = 10.865, and c =3.974 Å and β=90.33°. Cerium orthosilicate (Ce 4.67 (SiO4 )3 O) is present during firing as a glassy intermediate phase which promotes sintering and densification and then reacts with silicon nitride to form cerium silicon oxynitrde (CeSiO2 N). 相似文献
18.
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
19.
Gayle S. Painter Paul F. Becher Ellen Y. Sun 《Journal of the American Ceramic Society》2002,85(1):65-67
In Si3 N4 ceramics sintered with Al2 O3 , the interfacial strength between the intergranular glass and the reinforcing grains has been observed to increase with increases in the aluminum and oxygen content of the epitaxial β-Si6- z Al z O z N8– z layer that forms on the Si3 N4 grains. This has been attributed to the formation of a network of strong bonds (cross bonds) that span the glass-crystalline interface. This proposed mechanism is considered further in light of first-principles atomic cluster calculations of the relative stabilities of bridge and threefold-bonded atomic fragments chosen to represent compositional changes at the glass/Si3 N4 grain interface. Calculated binding energies indicate Al-N binding is favorable at the Si3 N4 grain surface, where aluminum occupancy can promote the growth of SiAlON, further enhancing the cross-bonding mechanism of interfacial strengthening. 相似文献
20.
Junichi Tatami Tomofumi Katashima Katsutoshi Komeya Takeshi Meguro Toru Wakihara 《Journal of the American Ceramic Society》2005,88(10):2889-2893
Carbon nanotube (CNT)-dispersed Si3 N4 ceramics with electrical conductivity were developed based on the lower temperature densification technique, in which the key point is the addition of both TiO2 and AlN as well as Y2 O3 and Al2 O3 as sintering aids. This new ceramic with a small amount of CNTs exhibits very high electrical conductivity in addition to high strength and toughness. Since Si3 N4 ceramics with Y2 O3 –Al2 O3 –TiO2 –AlN were originally used as a wear material, electrically conductive Si3 N4 ceramics are expected to be applied for high-performance static-electricity-free bearings for aerospace and other high-performance components. 相似文献