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1.
Lingling Wang Tseng-Ying Tien I-Wei Chen 《Journal of the American Ceramic Society》2003,86(9):1586-1591
Precipitation, growth, and coarsening of Si3 N4 crystals in (Si,Al,Mg,Y)(O,N) liquids at 1680°C has been studied. Contrary to the common observation in kinetics, coarsening rates of crystals in length and width are found to accelerate when the total volume of crystals remains little changed. This is attributed to the concomitant β-Si3 N4 to β'-SiAlON transformation, which introduces an additional driving force for crystal dissolution and reprecipitation. As a result of the additional driving force, which has a nonmonotonic size dependence, the normalized size distribution is expected to evolve with time, initially broadening, then shifting skewing as the transformation passes the midpoint, and finally converging to a sharp distribution as the transformation completes. These evolutions have been observed in all the compositions studied. 相似文献
2.
Rachid Belkada Toshiya Shibayanagi Masaaki Naka Masanori Kohyama 《Journal of the American Ceramic Society》2000,83(10):2449-2454
The atomic and electronic structure of the β-silicon nitride (β-Si3 N4 ) crystal have been determined using the ab initio pseudopotential method based on the density functional theory. We have obtained the stable lattice parameters and the stable positions of 14 atoms in the unit cell for the structure P 63 / m for the first time. The electronic structure and the charge distribution indicate that the Si–N bond has both ionic and covalent characters. The band structure is in good agreement with the other first-principles results and consistent with the experiments. 相似文献
3.
Rong-Jun Xie Mamoru Mitomo Gou-Dong Zhan Li-Ping Huang Xi-Ren Fu 《Journal of the American Ceramic Society》2001,84(2):471-73
A superplastic β-SiAlON was used as an interlayer to diffusionally bond a hot-pressed silicon nitride to itself. The bonding was conducted in a graphite furnace under a constant uniaxial load of 5 MPa at temperatures varying from 1500° to 1650°C for 2 h, followed by annealing at temperatures in the range of 1600° to 1750o C for 2 h. The bonds were evaluated using the four-point-bend method at both room temperature and high temperatures. The results indicate that strong, void-free joints can be produced with the superplastic β-SiAlON interlayer, with bond strengths ranging from 438 to 682 MPa, and that the Si3 N4 joints are heat resistant, being able to retain their strength up to 1000°C (635 MPa), and therefore have potential for high-temperature applications. 相似文献
4.
Dong-Duk Lee Suk-Joong L. Kang Gunter Petzow Duk N. Yoon 《Journal of the American Ceramic Society》1990,73(3):767-769
By using α-Si3 N4 and β-Si3 N4 starting powders with similar particle size and distribution, the effect of α-β (β') phase transition on densification and microstructure is investigated during the liquid-phase sintering of 82Si3 N4 ·9Al2 O3 ·9Y2 O3 (wt%) and 80Si3 N4 ·13Al2 O3 ·5AIN·5AIN·2Y2 O3 . When α-Si3 N4 powder is used, the grains become elongated, apparently hindering the densification process. Hence, the phase transition does not enhance the densification. 相似文献
5.
Hiroyuki Hayashi Kiyoshi Hirao Motohiro Toriyama Shuzo Kanzaki Kiyoshi Itatani 《Journal of the American Ceramic Society》2001,84(12):3060-3062
Si3 N4 powders with the concurrent addition of Yb2 O3 and MgSiN2 were sintered at 1900°C for 2–48 h under 0.9 MPa nitrogen pressure. Microstructure, lattice oxygen content, and thermal conductivity of the sintered specimens were evaluated and compared with Si3 N4 , Yb2 O3 , and MgO addition. MgSiN2 addition was effective for improving the thermal conductivity of Si3 N4 ceramics, and a material with high thermal conductivity over 140 W·(m·K)−1 could be obtained. For both specimens, lattice oxygen content was decreased with sintering time. However, the thermal conductivity of the MgSiN2 -doped specimen was slightly higher than the MgO-doped specimen with the same oxygen content. 相似文献
6.
The mechanical properties of Si3 N4 materials depend mainly on the microstructure, which originates during the densification process. The microscopic evidence indicates that β-Si3 N4 seeds incorporated in the starting powders play an important role in microstructural development, especially in the heterogeneous grain growth of β-Si3 N4 grains during sintering. The growth of β-grains is initiated from the β-seeds, resulting in a core/shell microstructure. The presence of Moiré fringes and dislocations is attributed to misfit strain and compositional differences between the core and the shell. Coalescence can occur at the final stage of sintering. 相似文献
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8.
Yutaka Shinoda Michiyuki Yoshida Takashi Akatsu Fumihiro Wakai 《Journal of the American Ceramic Society》2004,87(10):1919-1926
The deformation behavior of boron- and carbon-doped β-silicon carbide (B,C-SiC) with an average grain size of 260 ± 18 nm containing 1 wt% boron was investigated by compression testing at elevated temperatures. Extensive grain growth during deformation was observed. The stress–strain curves were compensated for grain growth by assuming power-law type of dependence on grain size and strain rate. The stress exponent n was ∼1.3 and the grain size exponent p was ∼2.7 at temperatures ranging from 1593° to 1758°C. The apparent activation energy of deformation Q d was ∼760 kJ/mol, which was lower than the activation energy for lattice diffusion of silicon and carbon in SiC and higher than that for grain-boundary diffusion of carbon in SiC. These results suggest that the deformation mechanism of the fine-grained B,C-SiC is grain-boundary sliding accommodated by the grain-boundary diffusion. 相似文献
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10.
Texture,microstructures, and mechanical properties of AlN‐based ceramics with Si3N4–Y2O3 additives 下载免费PDF全文
Cong Liu Wei‐Ming Guo Shi‐Kuan Sun Ji Zou Shang‐Hua Wu Hua‐Tay Lin 《Journal of the American Ceramic Society》2017,100(8):3380-3384
Textured AlN‐based ceramics with improved mechanical properties were prepared by hot pressing using Si3N4 and Y2O3 as additives. The introduction of Si3N4–Y2O3 into AlN matrix led to the formation of secondary Y3AlSi2O7N2 and fiber‐like 2Hδ AlN‐polytypoid phases, the partial texture of all crystalline phases, and the fracture mode change from intergranular to transgranular. Consequently, Vickers hardness, fracture toughness and flexural strength of AlN‐based ceramics by the replacement of Y2O3 by Si3N4–Y2O3 increased significantly from 10.4±0.3 GPa, 2.4±0.3 MPa m½ and 333.3±10.3 MPa to 14.2±0.4 GPa, 3.4±0.1 MPa m½ and 389.5±45.5 MPa, respectively. 相似文献
11.
Yumi Fukuda Ariane Keiko Albessard Iwao Mitsuishi 《Journal of the American Ceramic Society》2019,102(7):4161-4169
The luminescence properties of yellow-emitting Ce3+-doped Sr-containing sialon phosphor Sr(Al,Si)5(O,N)7:Ce3+ were notably improved by the Ce raw material selection. By changing the Ce raw material from oxides to nitrides or chlorides, the emission wavelength shifted to above 560 nm, which is beneficial for higher color rendering index white light-emitting diodes. This result from an increase in the covalency of the host crystal being associated with a decrease in the oxygen content. When Ce chloride was used, both the absorption and internal quantum efficiency increased, resulting in an increase in the external quantum efficiency up to 65%–72%. Inductively coupled plasma mass spectrometry, X-ray diffraction, and electron spin resonance measurements showed that the reason for the absorption increase is an increase in Ce3+ content and suppression of the generation of the second phase, and the reason for the increase in the internal quantum efficiency is a decrease in the host crystal absorption via suppression of anion vacancy generation. It was found that Ce chloride not only suppresses oxygen impurities but also acts as a flux that results in improved crystallinity. 相似文献
12.
Equiaxed β–Si3N4 ceramics prepared by rapid reaction‐bonding and post‐sintering using TiO2–Y2O3–Al2O3 additives 下载免费PDF全文
Li‐Xiang Wu Wei‐Ming Guo Ling‐Yong Zeng Hua‐Tay Lin 《Journal of the American Ceramic Society》2017,100(12):5353-5357
Sintered reaction‐bonded Si3N4 ceramics with equiaxed microstructure were prepared with TiO2–Y2O3–Al2O3 additions by rapid nitridation at 1400°C for 2 hours and subsequent post‐sintering at 1850°C for 2 hours under N2 pressure of 3 MPa. It was found that α–Si3N4, β–Si3N4, Si2N2O, and TiN phases were formed by rapid nitridation of Si powders with single TiO2 additives. However, the combination of TiO2 and Y2O3–Al2O3 additives led to the formation of 100% β–Si3N4 phase from the nitridation of Si powders at such low temperature (1400°C), and the removal of Si2N2O phase. As a result, dense β–Si3N4 ceramics with equiaxed microstructure were obtained after post‐sintering at high temperature. 相似文献
13.
Mikito Kitayama Kiyoshi Hirao Koji Watari Motohiro Toriyama Shuzo Kanzaki 《Journal of the American Ceramic Society》2001,84(2):353-58
β-Si3 N4 ceramics sintered with a series of rare-earth (RE = La, Nd, Gd, Y, Yb and Sc) oxide additives were fabricated by hot pressing and subsequent annealing. Their microstructures, lattice oxygen contents, and thermal conductivities were evaluated. Mean grain size increased, while lattice oxygen content decreased, and hence, thermal conductivity increased with decreasing ionic radius of the rare-earth element. In all cases, a marked change was observed in the order of ionic radius from La to Nd to Gd, and a little change was observed below them. Rare-earth oxide additives significantly influenced the thermal conductivity of β-Si3 N4 , unlike in the case of AlN. 相似文献
14.
Wei-Ying Sun Tseng-Ying Tien Tung-Sheng Yen 《Journal of the American Ceramic Society》1991,74(10):2547-2550
The solubility limit of α'-SiAION solid solutions on the Si3 N4 ─YN:3AIN composition join in the system Si3 N4 ─YN─AIN has been determined at 1800°C. The end members of these solid solutions are Y0.43 Si10.7 Al1.3 N16 and Y0.8 Si9.6 Al2.4 N16 . Unit-cell dimensions of the α'-SiAION solid solutions in the system Si,Al,Y/N,O can be expressed as follows: a o (Å) = 7.752 + 0.045 m + 0.009 n , c o (Å) = 5.620 + 0.048 m + 0.009 n , where the α'-SiAION solid solution has the formula Y x Si12-( m+n ) Al m+n N16- n O n . The single-phase boundary of the solid solution α'-SiAION on the composition triangle Si3 N4 ─YN:3AIN─AIN:Al2 O3 is delineated. The present paper also reports the phase relationships involving α'-SiAION. 相似文献
15.
Eric Laarz ers Meurk Joseph A. Yanez Lennart Bergström 《Journal of the American Ceramic Society》2001,84(8):1675-1682
Direct measurements of forces between silicon nitride surfaces in the presence of poly(acrylic acid) (PAA) are presented. The force-distance curves were obtained at pH > pHiep with an atomic force microscopy (AFM) colloidal-probe technique using a novel spherical silicon nitride probe attached to the AFM cantilever. We found that PAA adsorbs onto the negatively charged silicon nitride surface, which results in an increased repulsive surface potential. The steric contribution to the interparticle repulsion is small and the layer conformation remains flat even at high surface potentials or high ionic strength. The general features of the stabilization of ceramic powders with PAA are discussed; we suggest that PAA adsorbs onto silicon nitride by sequential adsorption of neighboring segments ("zipping"), which results in a flat conformation. In contrast, the long-range steric force found in the ZrO2 /PAA system at pH > pHiep arises because the stretched equilibrium bulk conformation of the highly charged polymer is preserved via the formation of strong, irreversible surface-segment bonds on adsorption. 相似文献
16.
The formation of superconducting phases in the Bi(Pb)─Sr─Ca─Cu─O system has been systematically investigated using DTA/TG, XRD, SEM/EDAX, TEM, EPMA, ICP-AES, fourprobe dc resistance, and ac susceptibility. Starting compositions, firing temperature, and the duration of heat treatment, together with the atmosphere, were found to be critical in determining the preferred formation of the 2223 phase. This paper reports the effect of the initial chemical composition, emphasizing the importance of compositional control in the synthesis of the single 2223 phase. It has been shown that, with a correct starting composition and predetermined synthesis conditions, single 2223 phase can be obtained without intergrowth by the 2212 and other impurity crystalline phases. The optimum starting composition for the preferred growth of the 2223 phase was identified as being Bi1.7 Pb0.3+ y Sr2 Ca2 Cu3 O x ( y = 0.1), with excess Pb added in order to compensate for its loss at high temperatures. The effect of Pb doping and excess Cu on the phase formation in the Bi oxide based superconducting system is discussed. 相似文献
17.
Sealing Glass‐Ceramics with Near Linear Thermal Strain,Part I: Process Development and Phase Identification 下载免费PDF全文
Steve Dai Mark A. Rodriguez James J. M. Griego 《Journal of the American Ceramic Society》2016,99(11):3719-3725
A widely adopted approach to form matched seals in metals having high coefficient of thermal expansion (CTE), e.g. stainless steel, is the use of high CTE glass‐ceramics. With the nucleation and growth of Cristobalite as the main high‐expansion crystalline phase, the CTE of recrystallizable lithium silicate Li2O–SiO2–Al2O3–K2O–B2O3–P2O5–ZnO glass‐ceramic can approach 18 ppm/°C, matching closely to the 18 ppm/°C–20 ppm/°C CTE of 304L stainless steel. However, a large volume change induced by the α‐β inversion between the low‐ and high‐ Cristobalite, a 1st order displacive phase transition, results in a nonlinear step‐like change in the thermal strain of glass‐ceramics. The sudden change in the thermal strain causes a substantial transient mismatch between the glass‐ceramic and stainless steel. In this study, we developed new thermal profiles based on the SiO2 phase diagram to crystallize both Quartz and Cristobalite as high expansion crystalline phases in the glass‐ceramics. A key step in the thermal profile is the rapid cooling of glass‐ceramic from the peak sealing temperature to suppress crystallization of Cristobalite. The rapid cooling of the glass‐ceramic to an initial lower hold temperature is conducive to Quartz crystallization. After Quartz formation, a subsequent crystallization of Cristobalite is performed at a higher hold temperature. Quantitative X‐ray diffraction analysis of a series of quenched glass‐ceramic samples clearly revealed the sequence of crystallization in the new thermal profile. The coexistence of two significantly reduced volume changes, one at ~220°C from Cristobalite inversion and the other at ~470°C from Quartz inversion, greatly improves the linearity of the thermal strains of the glass‐ceramics, and is expected to improve the thermal strain match between glass‐ceramics and stainless steel over the sealing cycle. 相似文献
18.
Jaehan Park Woohyun Jung Young Jin Kim 《Journal of the American Ceramic Society》2017,100(5):2136-2143
Sr2‐xBaxSi(O,N)4:Eu2+ (SBxSON:Eu2+) oxynitridosilicate phosphors were prepared via incorporation of N3?, Eu2+, and Ba2+ ions into Sr2SiO4 (SSO) lattices. X‐ray diffraction patterns of the prepared powders revealed that SBxSON:Eu2+ was a solid‐solution form of SSO. An increase in x values caused a phase transition and an expansion of the unit cell. The photoluminescence excitation (PLE) spectra of SBxSON:Eu2+ were broad, covering the ultraviolet range to the visible range. Corresponding PL emission spectra strongly depended on the excitation wavelengths and consisted of two emission bands, one in the green‐blue region (A‐band) and the other in the red region (B‐band), which were assigned to Eu(I) and Eu(II), respectively. The B‐band resulted from a dramatic red‐shift of the green emission band assigned to Eu(II) of SSO:Eu2+, revealing that the nitridation process preferentially affected the Eu(II) sites. This behavior was explained by crystal field splitting, the fluorescence decay time, and thermal quenching. The Ba2+ substitution caused evolution of the PL spectra, and its effects on the spectra were discussed under consideration of ionic size and covalence. 相似文献
19.
Yingjie Zhang Tao Wei Zhaoming Zhang Linggen Kong Pranesh Dayal Daniel J. Gregg 《Journal of the American Ceramic Society》2019,102(12):7699-7709
Uranium brannerite phases with terbium(III) or dysprosium(III) ions have been investigated. The precursors with molar ratio of 0.5:0.5:2 (Ln: U: Ti with Ln = Tb or Dy) were prepared and calcined at 750°C in argon. Sintering the pelletized samples in argon at 1200°C led to the formation of pyrochlore phases with TiO2 rutile and U-rich oxides while sintering in air led to the formation of brannerite phases with the nominal composition close to Ln0.5U0.5Ti2O6 together with trace amounts of TiO2 rutile and LnUO4. Incorporating an excess of TiO2 (20 wt%) and sintering at higher temperature (1300°C) resulted in no obvious change to the phase equilibrium. As designed, pentavalent uranium has been proven to be dominant in these brannerite phases with diffuse reflectance spectroscopy. The relationships between the cell parameters and the ionic radii of the A-site cations have been explored and rationalized from the structure point of view for a range of titanate brannerite phases (ATi2O6). In addition, the crystallization of Ln0.5U0.5Ti2O6 brannerite in glass has been achieved via heat treatment at 1200°C and confirmed with X-ray diffraction, scanning electron microscopy-energy dispersive spectroscopy and transmission electron microscopy–selected area electron diffraction. 相似文献
20.
Yanzheng Wu Weiqiang Li Yifan Zheng Yiqin Xu Dawei Wen Maxim S. Molokeev Zaifa Pan 《Journal of the American Ceramic Society》2023,106(5):2985-2996
During pursuing high color rendering index for full-color-emitting phosphor, low quantum efficiency (QE) is usually accompanying. We intend to elevate the luminescence efficiency when realizing a solar-like spectra distribution, by constructing apatite structure oxynitride, inheriting high covalence and rigidity from oxynitride, and suitable multiple cation sites from oxyapatite compounds. Full-color-emitting apatite structure oxynitride phosphor (Mg,Y)5Si3(O,N)13:Ce3+,Mn2+ has been prepared, and the crystal sites’ occupancies of activators in this host were favorable for white emission. (Mg,Y)5Si3(O,N)13:Ce3+,Mn2+ phosphor shows whole visible light with emission wavelength ranging from 370 to 750 nm, matching the spectra of sunlight quite well. The fabricated white light-emitting diode lamp demonstrated the distinctive overall performance of QE and chromaticity properties (Ra and R9). Furthermore, correlated color temperature is tunable from cool nature to warm white. The obtained lamp possesses the feature of less blue light hazard and high saturation of red degree, compared with the commercial YAG-based lamp. 相似文献