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1.
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
2.
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
3.
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
4.
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
5.
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
6.
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
7.
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
8.
Subsolidus phase relations were established in the system Si3 N4 -SiO2 -Y2 O3 . Four ternary compounds were confirmed, with compositions of Y4 Si2 O7 N2 , Y2 Si3 O3 N4 , YSiO2 N, and Y10 (SiO4 )6 N2 . The eutectic in the triangle Si3 N4 -Y2 Si2 O7 -Y10 (SiO4 )6 N2 melts at 1500°C and that in the triangle Si2 N2 O-SiO2 -Y2 Si2 O7 at 1550°C. The eutectic temperature of the Si3 N4 -Y2 Si2 O7 join was ∼ 1520°C. 相似文献
9.
Composite ceramic materials based on Si3 N4 and ZrO2 stabilized by 3 mol% Y2 O3 have been formed using aluminum isopropoxide as a precursor for the Al2 O3 sintering aid. Densification was carred out by hot-pressing at temperatures in the range 1650° to 1800°C, and the resulting micro-structures were related to mechanical properties as well as to oxidation behavior at 1200°C. Densification at the higher temperatures resulted in a fibrous morphology of the Si3 N4 matrix with consequent high room-temperature toughness and strength. Decomposition of the ZrO2 grains below the oxidized surface during oxidation introduced radial stresses in the subscalar region, and from the oxidation experiments it is suggested that the ZrO2 incorporated some N during densification. 相似文献
10.
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
11.
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
12.
Detailed microstructural analysis of a 10 mol% Y2 O3 fluxed hot-pressed silicon nitride reveals that, in addition to the yttrium-silicon oxynitride phase located at the multiple Si3 N4 grain junctions, there is a thin boundary phase 10 to 80 Å wide separating the silicon nitride and the oxynitride grains. Also, X-ray microanalysis from regions as small as 200 Å across demonstrates that the yttrium-silicon oxynitride, Y2 Si(Si2 O3 N4 ), phase can accommodate appreciable quantities of Ti, W, Fe, Ni, Co, Ca, Mg, Al, and Zn in solid solution. This finding, together with observations of highly prismatic Si3 N4 grains enveloped by Y2 Si(Si2 O3 N4 ), suggests that densification occurred by a liquid-phase "solution-reprecipitation" process. 相似文献
13.
Subsolidus Phase Relationships in Part of the System Si,Al,Y/N,O: The System Si3 N4 ─AIN─YN─Al2 O3 ─Y2 O3
Wei-Ying Sun Tseng-Ying Tien Tung-Sheng Yen 《Journal of the American Ceramic Society》1991,74(11):2753-2758
The subsolidus phase relationships in the system Si,Al,Y/N,O were determined. Thirty-nine compatibility tetrahedra were established in the region Si3 N4 ─AIN─Al2 O3 ─Y2 O3 . The subsolidus phase relationships in the region Si3 N4 ─AIN─YN─Y2 O3 have also been studied. Only one compound, 2YN:Si3 N4 , was confirmed in the binary system Si3 N4 ─YN. The solubility limits of the α'─SiAION on the Si3 N4 ─YN:3AIN join were determined to range from m = 1.3 to m = 2.4 in the formula Y m /3 Si12- m Al m N16 . No quinary compound was found. Seven compatibility tetrahedra were established in the region Si3 N4 ─AIN─YN─Y2 O3 . 相似文献
14.
The densification behavior of Si3 N4 containing MgO was studied in detail. It was concluded that MgO forms a liquid phase (most likely a magnesium silicate). This liquid wets and allows atomic transfer of Si3 N4 . Evidence of a second-phase material between the Si3 N4 grains was obtained through etching studies. Transformation of α- to β-Si3 N4 during hot-pressing is not necessary for densification. 相似文献
15.
The phase relations in the Si3 N4 -rich portion of the Si3 N4 –AlN–Y2 O3 rystem were investigated using hot-pressed bodies. The one-phase fields of β3 and α, the twophase fields of β+α, β+M (M=melilite), and α+M, and the three-phase fields of β+α+M were observed in the Si3 N4 -rich portion. The α- and β-sialons are not two different compounds but an allotropic transformation phase of the Si–Al–O–N system, and an α solid solution expands and stabilizes with increasing Y2 O3 content. Therefore, the formulas of the two sialons should be the same. 相似文献
16.
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
17.
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
18.
The effects of fabrication variables on the high-temperature strength of hot-pressed Si3 N4 containing 5 wt% Y2 O3 were studied. Materials containing a crystalline grain-boundary phase, formed as a consequence of a high-temperature presintering heat treatment and identified as Si3 N4 ·Y2 O3 , had high-temperature strengths significantly superior to those observed for materials containing a glass phase. 相似文献
19.
F. F. LANGE S. C. SINGHAL R. C. KUZNICKI 《Journal of the American Ceramic Society》1977,60(5-6):249-252
Composite powders were hot-pressed to determine the phase relations in the Si3 N4 -SiO2 -Y2 O3 pseudoternary system. Four quaternary compounds, Si3 Y2 O3 N4 , YSiO2 N, Y10 Si7 O23 N4 , and Y4 Si2 O7 N2 , were identified. Studies of polyphase and single-phase materials in this system showed that these 4 compounds are unstable under oxidizing conditions. Materials within the Si3 N4 -Si2 N2 O-Y2 Si2 O7 compatibility triangle precluded the unstable compounds, and are extremely resistant to oxidation. 相似文献
20.
The melting behaviors of selected compositions in the Si3 N4 -AlN-Y2 O3 system were determined under 1 MPa of nitrogen. The phase diagrams of the ternary and their binary systems are presented. The lowest melting composition of the ternary system contains 15 mol % Si3 N4 , 25 mol % AIN, and 60 mol % Y2 O3 and has a melting temperature of 1650°C. The binary eutectic compositions and temperatures are 15 mol % Si3 N4 and 85 mol % Y2 O3 at 1720°C, and 20 mol % AIN and 80 mol% Y2 O3 at 1730°C. 相似文献