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1.
Jian-Feng Yang Yoshihisa Beppu Guo-Jun Zhang Tatsuki Ohji Shuzo Kanzaki 《Journal of the American Ceramic Society》2002,85(7):1879-1881
Single-phase β'-SiAlON (Si6− z Al z O z N8− z , z = 0–4.2) ceramics with porous structure have been prepared by pressureless sintering of powder mixtures of á-Si3 N4 , AlN, and Al2 O3 of the SiAlON compositions. A solution of AlN and Al2 O3 into Si3 N4 resulted in the β'-SiAlON, and full densification was prohibited because no other sintering additives were used. Relative densities ranging from 50%–90% were adjusted with the z -value and sintering temperature. The results of X-ray diffraction, scanning electron microscopy, and transmission electron microscopy analyses indicated that single-phase β'-SiAlON free from a grain boundary glassy phase could be obtained. Both grain and pore sizes increased with increasing z -value. Low z -value resulted in a relatively high flexural strength. 相似文献
2.
Hagen Klemm Mathias Herrmann Thomas Reich Christian Schubert Lutz Frassek Gerhard Wötting Ernst Gugel Georg Nietfeld 《Journal of the American Ceramic Society》1998,81(5):1141-1148
The mechanical behavior of mixed α'/β'-SiAlON materials was studied at elevated temperatures. Two different α'/β'-SiAlON compositions along the Si3 N4 -Y2 O3 9AlN composition line in the Si3 N4 -Al2 O3 AlN-YN3AlN plane (α'-SiAlON plane) were prepared using three different raw-material mixtures. Six different materials were obtained with significantly lower values in α'-SiAlON than expected. The high-temperature properties of the materials studied were influenced strongly by the chemical composition (α' content and grain-boundary phase) of the SiAlONs. A high content of α'-SiAlON was beneficial in terms of creep behavior of the materials. The same materials, however, were characterized by a considerably degradated fracture behavior at elevated temperatures in air because of a crack-growth process enhanced by the poor oxidation resistance of these materials. It was concluded that, despite some superior features of the materials studied, a long-term application of mixed α'/β'-SiAlON materials at 1400°C in air is problematical. A combination of all properties required for such applications was not observed. For that reason, it is suggested that the real high-temperature potential of these materials in air should be limited to temperatures <1300°C. 相似文献
3.
Gian Domenico Soraru Alberto Ravagni Renzo Campostrini Florence Babonneau 《Journal of the American Ceramic Society》1991,74(9):2220-2223
A polycarbosilane has been modified with aluminum alkoxide to obtain a new preceramic compound. The pyrolysis in NH3 flow of this polyaluminocarbosilane leads to the formation of an amorphous Si-Al-O-N phase. The nitridation process has been followed by IR and 29 Si MAS-NMR spectroscopies. A fine-grained β-SiAION ceramic is obtained by firing the amorphous phase at 1500°C. The crystallization process has been studied by XRD, 29 Si MAS-NMR, and TEM techniques. 相似文献
4.
Morphology, composition, and growth defects of α'-SiAION have been studied in a fine-grained material with an overall composition Y0.33 Si10 Al2 O1 N15 prepared from α-Si3 N4 , AlN, Al2 O3 , and Y2 O3 powders. TEM analysis has shown that fully grown α'-SiAloN grains always contain an α-Si3 N4 core, implicating heterogeneous nucleation operating in the present system. The growth mode is epitaxial, despite the composition and lattice parameter difference between α-Si3 N4 and α'-SiAlON. The inversion boundary that separates two domains in the seed crystal is seen to continue in the grown α'-SiAION. Lacking a special growth habit, the growth typically proceeds from more than one site on the seed crystal, and the different growth fronts impinge on each other to give an equiaxed appearance of α'-SiAlON. Misfit dislocations on the α/α'interface are identified as [0001] type ( b = 5.62 Å) and 1/3 [1 2 10] type ( b = 7.75 Å). These nucleation and growth characteristics dictate that microstructural control of α'-SiAlON must rest on the size distribution of the starting α-Si3 N4 powder. 相似文献
5.
A. D. MORRISON R. W. STORMONT F. H. COCKS 《Journal of the American Ceramic Society》1975,58(1-2):41-43
High Na vapor pressure, peritectic decomposition, and high reactivity of the melt complicate the growth of α-alumina crystals. These difficulties were overcome by using a high-pressure (300 psig) growth chamber, Na2 O-rich melts, and Ir for all surfaces in contact with the melt. These procedures were combined with the edge-defined film-fed growth technique to produce single-crystal β alumina tubes and ribbons. 相似文献
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Thin foils of polycrystalline α-alumina were reacted with a potassium-rich vapor at ≤900°C. Potassium β-alumina formed along α-alumina grain boundaries and protruded from holes in the foils. Conventional transmission electron microscopy was used to analyze the α-alumina/β-alumina phase boundary for possible orientation relations. 相似文献
8.
Phase diagrams on the α'-SiAlON plane have been investigated for ytterbium-, yttrium-, and neodymium-containing systems at different temperatures. Phase relationships between α'-SiAlON, β'-SiAlON, AlN polytypoids, and liquid/grain-boundary phases have been determined. The stability region of the α'-SiAlON phase increases as the temperature increases and the ionic size of the rare-earth cation decreases. Meanwhile, the solubility of aluminum and oxygen in β'-SiAlON varies with the solubility of aluminum and oxygen in α'-SiAlON, which causes migration of all the phase lines on the α'-plane toward the nitrogen-rich side at lower temperatures and with larger modifying cations. These systematic variations of the phase relationships fully explain the occurrence of α'→β' reverse transformations that are sometimes observed in this system. 相似文献
9.
Heterogeneous nucleation and crystallization of lithium alumosilicate glasses with hafnia-containing nucleation agents was explored. Kinetic, thermodynamic, and structural data were considered to assess nucleation efficiency and to characterize the crystallization process. It is shown how lattice parameters and, particularly, anisotropy of the nuclei phase depend on the amount of ZrO2 –HfO2 substitution in a specific base glass. For a given crystallization treatment, the size of the derived crystallites of β-quartz structure is used as a measure of nucleation rates. A nonlinear dependence of nucleation efficiency on HfO2 content was established, with the supposedly most efficient nucleation corresponding to the lowest degree of anisotropy of the nuclei crystallites, i.e., when about 20%–30% of ZrO2 was substituted by HfO2 . Apparent activation energies and estimates of the Avrami coefficient were determined from nonisothermal crystallization experiments for selected compositions to highlight the differences between hafnia and zirconia. Hafnia can be used alone or in combination with other agents to nucleate nanocrystalline glass ceramics with a low coefficient of thermal expansion. 相似文献
10.
DONG-DUK LEE SUK-JOONG L. KANG DUK N. YOON 《Journal of the American Ceramic Society》1988,71(9):803-806
The rates of grain coarsening and α-β'transformation during the liquid-phase sintering of Si3 N4 -β'60 -YAG sialon have been measured at varying liquid fractions and z values in order to determine the rate-controlling mechanism. The average β'-grain size after sintering for 16 h at 1650°C shows no variation with the liquid-matrix fraction if the z value is fixed and a marked increase with the z value if the liquid fraction is fixed. Similarly, the amount of untransformed α-phase after sintering for 2.5 or 3.5 min at 1600°C shows no variation with the liquid-matrix fraction if the z value is fixed and a marked decrease with the z value if the liquid fraction is fixed. These results show that the grain coarsening and the α-β'transformation are controlled by the interface reaction. This conclusion is consistent with the observations in carbide-Co systems and with the theoretical predictions that the growth of faceted grains is controlled by interface reaction and that of spherical grains by diffusion. A general rule between the shape and the growth mechanism of grains in a liquid matrix is thus proposed. 相似文献
11.
The mechanism for grain growth of β-SiAlON has been investigated by annealing high-density β-SiAlON–YAG materials at 1650°C. An observed decrease in grain growth with increasing weight fraction of liquid confirms a diffusion-controlled growth mechanism in the system. The grain-growth mechanism is further characterized by the development of large elongated grains in addition to smaller grains. After prolonged heating, an equilibrium maximum grain size is developed causing a homogenization of the microstructure. 相似文献
12.
The enthalpy and entropy for the hydration of sodium β - and β '-aluminas have been determined by measuring the infrared absorbance of single-crystal samples following equilibration at elevated temperatures in water vapor pressures ranging from 3 to 70 kPa. The equilibrium water concentrations can be varied continuously and reversibly up to saturation concentrations of about 0.9H2 O-Na1.2 AI11 O17.1 for the β-phase and 0.4H2 O.Na1.67 Mg.67 Al10.33 O17 for the β'-phase. The hydration reactions are exothermic; Δ H =−56 ± 2 for sodium β '-aIumina and ΔH =−67 ± 2 kJ/mol for sodium β-alumina. The entropies of hydration are about −143 ± 6 J/(mol-K) for both sodium β - and β '-aIuminas. 相似文献
13.
M. Mitomo M. Tsutsumi H. Tanaka S. Uenosono F. Saito 《Journal of the American Ceramic Society》1990,73(8):2441-2445
The microstructures of gas-pressure-sintered materials from β-Si3 N4 powder were characterized in terms of the diameter and aspect ratio of the grains. The size distributions of diameters in materials fabricated by heating for 1 h at 1850° to 2000°C were nearly constant when they were normalized by average diameters because of normal grain growth. The rate-determining step in the densification and grain growth was expected to be the diffusion of materials through the liquid phase. The activation energy for grain growth was 372 kJ/mol. The average aspect ratio of the grains was 3 to 4, whereas that of large grains was smaller because of shape accommodation. The fracture toughness was about the same as that of material from α-Si3 N4 powder despite the smaller aspect ratio of the grains 相似文献
14.
W. OSTERTAG G. R. FISCHER J. P. WILLIAMS 《Journal of the American Ceramic Society》1968,51(11):651-654
Synthetic β-Spodumene and several β-Spodumene-silica solid solutions were prepared, and their thermal expansion behavior was studied using high-temperature X-ray diffraction techniques. Data indicate that all β-Spodumenes are characterized by a pronounced anisotropy of thermal expansion much the same as that of the silica polymorph keatite. Anisotropy increases slightly and the volume expansion decreases as the compositions become richer in SiO2 . Specimens with more than 80.8 wt% SiO2 at 130O°C and 1 atm contain P-cristobalite along with β-Spodumene. The lattice parameters of β-Spodumene compositions throughout the solid solution range were determined. The structural aspects of the anisotropy of thermal expansion are discussed. 相似文献
15.
Hidehiko Tanaka Naoto Hirosaki Toshiyuki Nishimura Dong-Woo Shin Sam-Shik Park 《Journal of the American Ceramic Society》2003,86(12):2222-2224
α(6 H )- and β(3 C )-SiC powders were sintered with the addition of AlB2 and carbon. α-SiC powder could be densified to ∼98% of the theoretical density over a wide range of temperatures from 1900° to 2150°C and with the additives of 0.67–2.7 mass% of AlB2 and 2.0 mass% of carbon. Sintering of the β-SiC powder required a temperature of >2000°C for densification with these additives. Grains in the α-SiC specimens grew gradually from spherical-shaped to plate-shaped grains at 2000°C; the 6 H polytype transformed mainly to 4 H . On the other hand, grains in the β-SiC largely grew at >2000°C; the 3 C polytype transformed to 4 H , 6 H , and 15 R . The stacking faults introduced in grains were denser in β-SiC than in α-SiC. The rapid grain growth in the β-SiC specimen was attributed to polytype transformation from the unstable 3 C polytype at the sintering temperature. 相似文献
16.
Chao Dong Guifu Zou Erkai Liu Baojuan Xi Tao Huang Yitai Qian 《Journal of the American Ceramic Society》2007,90(2):653-656
Novel kelp-like crystalline β-SiC nanobelts have been synthesized through direct pyrolysis of methyltrichlorosilane at 600°C in an autoclave. The products are characterized by X-ray powder diffraction, field emission scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, electron diffraction, and Raman spectroscopy. On the basis of morphology and structural characterization, an apical growth mechanism is proposed to clarify the formation of as-prepared nanobelts. Also, at 420 nm, a broad peak is observed in the visible photoluminescence emission. 相似文献
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18.
Remco de Jong Ronald A. Mccauley Paul Tambuyser 《Journal of the American Ceramic Society》1987,70(11):338-C
Whiskers of twinned SiC in the cubic form were produced by the vapor-liquid-solid process as a byproduct of the corrosion of silicon nitride. These whiskers were characterized and their properties related to their use in reinforced materials. 相似文献
19.
Jianhua Yang Helfried Näfe Fritz Aldinger Dongsheng Yan 《Journal of the American Ceramic Society》2005,88(10):2897-2901
The activities of Na2 O and K2 O dissolved in mixed-alkali Na–K–(β+β")-Al2 O3 (NKBA) have been determined by using yttria stabilized zirconia (YSZ) as a solid electrolyte in the following galvanic cells: The approach enables to verify in situ the establishment and maintenance of the β/β"-equilibrium, and to characterize it as a function of the phase composition of NKBA. The results can be expressed as follows: 相似文献
20.
Sumin Zhu Hong-An Xi Qin Li Ruoding Wang 《Journal of the American Ceramic Society》2005,88(9):2619-2621
Polycarbosilane (PCS) was used as a precursor to prepare porous silicon carbide (SiC) ceramics with in situ growth of β-SiC nanowires. The pore size of the as-prepared porous ceramics was 1.37 μm in average, and had a narrow distribution. The nanowires with diameters ranging from ∼10 to 50 nm existed in the channels of the porous body. Their morphology, microstructure, and composition were characterized by field emission scanning electron microscopy, transmission electron microscopy, and energy-dispersive X-ray spectroscopy, which confirmed that the nanowires had a single-crystal β-SiC structure with the 〈111〉 growth direction. A vapor–liquid–solid process was discussed as a possible growth mechanism of the β-SiC nanowires. 相似文献