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1.
Enhancement of Densification and Thermal Conductivity in AlN Ceramics by Addition of Nano-Sized Particles 总被引:2,自引:0,他引:2
Jin-Yu Qiu Yuji Hotta Koji Watari † Kenshi Mitsuishi 《Journal of the American Ceramic Society》2006,89(1):377-380
The effect of addition of nano-sized particles on densification and thermal conductivity of AlN ceramics was investigated. The commercially available AlN powder (∼0.9 μm) was mixed with 1.89 mass% nano-sized AlN particles (<0.1 μm), 3.53 mass% Y2 O3 , and 2.0 mass% CaO as sintering aid. The mixture was fired at 1500° and 1600°C in a tungsten resistance furnace under flowing N2 atmosphere. The results showed that a fully densified specimen was obtained at the lower temperature of 1600°C by addition of nano-sized particles. The thermal conductivity of the resulting product was 133 W/m°C. The value is much higher than the 52 W/m°C for the sample prepared without adding the nano-sized AlN powder. This study indicates a strong potential for the use of nano-sized particles as additives in the densification of AlN ceramics. 相似文献
2.
High-Thermal-Conductivity Aluminum Nitride Ceramics: The Effect of Thermodynamic, Kinetic, and Microstructural Factors 总被引:8,自引:0,他引:8
T. Barrett Jackson Anil V. Virkar Karren L. More Ralph B. Dinwiddie Jr. Raymond A. Cutler 《Journal of the American Ceramic Society》1997,80(6):1421-1435
Improvement in the thermal conductivity of aluminum nitride (AlN) can be realized by additives that have a high thermodynamic affinity toward alumina (Al2 O3 ), as is clearly demonstrated in the aluminum nitride-yttria (AlN-Y2 O3 ) system. A wide variety of lanthanide dopants are compared at equimolar lanthanide oxide:alumina (Ln2 O3 : Al2 O3 , where Ln is a lanthanide element) ratios, with samaria (Sm2 O3 ) and lutetia (Lu2 O3 ) being the dopants that give the highest- and lowest-thermal-conductivity AlN composites, respectively. The choice of the sintering aid and the dopant level is much more important than the microstructure that evolves during sintering. A contiguous AlN phase provides rapid heat conduction paths, even at short sintering times. AlN contiguity decreases slightly as the annealing times increase in the range of 1–1000 min at 1850°C. However, a substantial increase in thermal conductivity results, because of purification of AlN grains by dissolution-reprecipitation and bulk diffusion. Removal of grain-boundary phases, with a concurrent increase in AlN contiguity, occurs at high annealing temperatures or at long times and is a natural consequence of high dihedral angles (poor wetting) in liquidphase-sintered AlN ceramics. 相似文献
3.
Koji Watari Hae J. Hwang Motohiro Toriyama Shuzo Kanzaki 《Journal of the American Ceramic Society》1996,79(7):1979-1981
The present work indicates through thermodynamic considerations that YLiO2 additive is beneficial for low-temperature sintering of AlN ceramics. Pressureless sintering of commercially available AIN powders with simultaneous additions of YLiO2 and CaO resulted in materials with high thermal conductivity (170 W·m–1 ·K–1 after sintering at 1600°C for 6 h). It is demonstrated that improvement of thermal conductivity is possible at low firing temperature by use of sintering aids. 相似文献
4.
Takeshi Yagi Kazuo Shinozaki Nobuo Ishizawa Nobuyasu Mizutani Masanori Kato Akihiko Tsuge 《Journal of the American Ceramic Society》1988,71(7):334-C
The thermal diffusivity of AlN ceramics was significantly decreased by the addition of SiO2 . The AlN ceramics with 4 wt% SiO2 could not be densified by pressureless sintering in the temperature range 1400° to 1800°C. The thermal diffusivity of these samples was very low because of their porous structure. The AlN ceramics containing 2, 4, and 8 wt% SiO2 were densified by hot-pressing and also had low thermal diffusivity. In these samples, the grains of the 27R polytype that resulted from the reaction between AlN and SiO2 were dispersed, obstructing the conduction of heat. The relation between the amount of 27R polytype and the thermal diffusivity of the AlN ceramics was determined. 相似文献
5.
Microstructural Characterization of High-Thermal-Conductivity Aluminum Nitride Ceramic 总被引:1,自引:0,他引:1
Hiromi Nakano Koji Watari Hiroyuki Hayashi Kazuyori Urabe 《Journal of the American Ceramic Society》2002,85(12):3093-3095
An aluminum nitride (AlN) ceramic with a thermal conductivity value of 272 W·(m·K)−1 , which is as high as the experimentally measured thermal conductivity of an AlN single crystal, was successfully fabricated by firing at 1900°C with a sintering aid of 1 mol% Y2 O3 under a reducing N2 atmosphere for 100 h. Oxygen concentrations were determined to be 0.02 and 0.03 mass% in the grains and in the grain-boundary phases, respectively. Neither stacking fault in the grains nor crystalline phase in the grain-boundary regions was found by transmission electron microscopy. An amorphous phase possessing yttrium and oxygen elements was detected between the grains as thin films with a thickness of <1 nm. Because the amount of grain-boundary phase was small, the high-thermal conductivity of the ceramic was attributable to the low oxygen concentration in the AlN grains. 相似文献
6.
Young-Wook Kim Mamoru Mitomo Toshiyuki Nishimura 《Journal of the American Ceramic Society》2002,85(4):1007-1009
Using AlN and RE2 O3 (RE = Y, Yb) as sintering additives, two different SiC ceramics with high strength at 1500°C were fabricated by hot-pressing and subsequent annealing under pressure. The ceramics had a self-reinforced microstructure consisting of elongated α-SiC grains and a grain-boundary glassy phase. High-temperature strength up to 1600°C was measured and compared with that of the SiC ceramics fabricated with AlN and Er2 O3 . SiC ceramics with AlN and Y2 O3 showed the best strength (∼630 MPa) at 1500°C, while SiC ceramics with AlN and Er2 O3 the best strength (∼550 MPa) at 1600°C. 相似文献
7.
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
8.
Dense AlN ceramics with a thermal conductivity of 180W/m·K were obtained at the sintering temperature of 1750 °C using CaF2 and YF3 as additives. At temperatures below 1650 °C, the shrinkage of AlN ceramics is promoted by liquid (Ca,Y)F2 and Ca12Al14O32F2. Liquid CaYAlO4 mainly improves the densification of the sample when the sintering temperature increases to 1750 °C. The formation of liquid (Ca,Y)F2 at a relatively low temperature results in homogeneous YF3 distribution around the AlN particles, which benefits the removal of oxygen impurity in the AlN lattice, and thus a higher thermal conductivity. 相似文献
9.
Qiang Xu Wei Pan Jingdong Wang Chunlei Wan Longhao Qi Hezhuo Miao Kazutaka Mori Taiji Torigoe 《Journal of the American Ceramic Society》2006,89(1):340-342
A series of rare-earth zirconate Ln2 Zr2 O7 ceramics (Ln=Dy, Er, and Yb) with a fluorite structure (F-Ln2 Zr2 O7 ) were prepared by pressureless sintering from zirconia and rare-earth oxide powders at 1600°C for 10 h in air. The microstructure experiments were performed by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The thermal conductivity and thermal expansion of these ceramics were evaluated using a steady-state laser heat-flux technique and high-temperature dilatometry, respectively. The XRD and SEM results demonstrate that Ln2 Zr2 O7 ceramics with a single fluorite phase are synthesized and no other phases are found. The results of thermal conductivity show that their thermal conductivities (1.3–1.9 W/(m·K), 20°–800°C) are as low as those of the referenced Ln2 Zr2 O7 ceramics (Ln=La, Nd, Sm, and Gd) with pyrochlore structure (P-Ln2 Zr2 O7 ). It is concluded that rare-earth zirconate ceramics with a fluorite structure can be considered as candidate materials for future thermal barrier coatings. 相似文献
10.
Gui-hua Peng Min Liang Zhen-hua Liang Qing-yu Li Wen-lan Li Qian Liu 《Journal of the American Ceramic Society》2009,92(9):2122-2124
Silicon nitride ceramics were prepared by spark plasma sintering (SPS) at temperatures of 1450°–1600°C for 3–12 min, using α-Si3 N4 powders as raw materials and MgSiN2 as sintering additives. Almost full density of the sample was achieved after sintering at 1450°C for 6 min, while there was about 80 wt%α-Si3 N4 phase left in the sintered material. α-Si3 N4 was completely transformed to β-Si3 N4 after sintering at 1500°C for 12 min. The thermal conductivity of sintered materials increased with increasing sintering temperature or holding time. Thermal conductivity of 100 W·(m·K)−1 was achieved after sintering at 1600°C for 12 min. The results imply that SPS is an effective and fast method to fabricate β-Si3 N4 ceramics with high thermal conductivity when appropriate additives are used. 相似文献
11.
Zhan-Guo Liu Jia-Hu Ouyang Yu Zhou Jing Li Xiao-Liang Xia 《International Journal of Applied Ceramic Technology》2009,6(4):485-491
(Yb x Gd1− x )2 Zr2 O7 (0≤ x ≤1.0) ceramic powders synthesized with the chemical-coprecipitation and calcination method were pressureless-sintered at 1550–1700°C to develop new thermal barrier oxides with a lower thermal conductivity than yttria-stabilized zirconia ceramics. (Yb x Gd1− x )2 Zr2 O7 ceramics exhibit a defective fluorite-type structure. The linear thermal expansion coefficients of (Yb x Gd1− x )2 Zr2 O7 ceramics increase with increasing temperature from room temperature to 1400°C. The measured thermal conductivity of (Yb x Gd1− x )2 Zr2 O7 ceramics first gradually decrease with increasing temperature and then slightly increase above 800°C because of the increased radiation contribution. YbGdZr2 O7 ceramics have the lowest thermal conductivity among all the composition combinations studied. 相似文献
12.
Heon-Jin Choi June-Gunn Lee Young-Wook Kim 《Journal of the American Ceramic Society》2002,85(9):2281-2286
Silicon carbide (SiC) ceramics have been fabricated by hot-pressing and subsequent annealing under pressure with aluminum nitride (AlN) and rare-earth oxides (Y2 O3 , Er2 O3 , and Yb2 O3 ) as sintering additives. The oxidation behavior of the SiC ceramics in air was characterized and compared with that of the SiC ceramics with yttrium–aluminum–garnet (YAG) and Al2 O3 –Y2 O3 –CaO (AYC). All SiC ceramics investigated herein showed a parabolic weight gain with oxidation time at 1400°C. The SiC ceramics sintered with AlN and rare-earth oxides showed superior oxidation resistance to those with YAG and Al2 O3 –Y2 O3 –CaO. SiC ceramics with AlN and Yb2 O3 showed the best oxidation resistance of 0.4748 mg/cm2 after oxidation at 1400°C for 192 h. The minimization of aluminum in the sintering additives was postulated as the prime factor contributing to the superior oxidation resistance of the resulting ceramics. A small cationic radius of rare-earth oxides, dissolution of nitrogen to the intergranular glassy film, and formation of disilicate crystalline phase as an oxidation product could also contribute to the superior oxidation resistance. 相似文献
13.
Jun Yoshikawa Yuji Katsuda Naohito Yamada Chikashi Ihara Masaaki Masuda Hiroaki Sakai 《Journal of the American Ceramic Society》2005,88(12):3501-3506
The phase composition, microstructure, and electrical resistivity of hot-pressed AlN ceramics with 0–4.8 wt% Sm2 O3 additive were investigated. The phase composition was approximately consistent with that estimated from the Sm2 O3 –Al2 O3 phase diagram using the amount of added Sm2 O3 and oxygen content of the AlN raw material. When sintered at more than 1800°C, the AlN ceramics with 1.0–2.9 wt% Sm2 O3 additive contained an Sm-β-alumina phase wetting the grain boundaries, and their electrical resistivity considerably decreased to 1010 –1012 Ω·cm. This resistivity decrease was caused by the continuity of the Sm-β-alumina phase with a resistivity lower than that of bulk AlN. 相似文献
14.
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
15.
Fangzhi Li Bin Liu Jingyang Wang Yanchun Zhou 《Journal of the American Ceramic Society》2010,93(1):228-234
In this work, bulk Hf3 AlN ceramic was synthesized by an in situ reaction/hot pressing method using Hf and AlN as initial materials. The reaction path during the synthesis process was investigated. Hf3 AlN was found to form via the reaction of Hf and AlN above 1000°C. Furthermore, physical and mechanical properties of Hf3 AlN, such as electrical conductivity, flexural strength, and elastic moduli were also characterized. Similar to typical layered ternary ceramics Ti3 SiC2 and Ti3 AlC2 , Hf3 AlN possesses metallic conductivity and excellent damage tolerance, which is also the first one of this type that has ever been reported to crystallize in an orthorhombic structure. It is believed that a typical layered crystal structure and weak interlayer bondings contribute to the damage tolerance of Hf3 AlN. Moreover, the stiffness of Hf3 AlN can sustain a temperature as high as 1450°C, being 250°C higher than that of Ti3 AlC2 , which renders it a promising high-temperature structural material. 相似文献
16.
Norimasa Uchida MITSUE KOIZUMI MASAHIKO SHIMADA 《Journal of the American Ceramic Society》1985,68(2):38-C-
High-density Si3 N4 ceramics with nitride additives such as TiN, AlN, ZrN, VN, NbN, YN, TUN, Mg3 N2 , and HfN were fabricated by isostatic hot-pressing. The temperature dependence of Vickers microhardness, fracture toughness, and thermal conductivity were measured; these properties, as well as microstructure, were strongly influenced by the additive used. 相似文献
17.
Mamoun Medraj Robert Hammond William T. Thompson Robin A. L. Drew 《Journal of the American Ceramic Society》2003,86(4):717-26
The importance of aluminum nitride (AlN) stems from its application in microelectronics as a substrate material due to high thermal conductivity, high electrical resistance, mechanical strength and hardness, thermal durability, and chemical stability. Yttria (Y2 O3 ) is the best additive for AlN sintering. AlN densifies by a liquid-phase mechanism, where the surface oxide, Al2 O3 , reacts with Y2 O3 to form an Y-Al-O-N liquid that promotes particle rearrangement and densification. Construction of the phase relations in this multicomponent system is essential for optimizing the properties of AlN. The ternary phase diagram of the AlN–Al2 O3 –Y2 O3 was developed by Gibbs energy minimization using interpolation procedures based on modeling the binary subsystems. This paper aims at testing the resultant understanding experimentally at selected compositions using in situ high-temperature neutron diffractometry. These experimental results agree with the thermodynamic calculations of AlN–Al2 O3 –Y2 O3 . The ternary phase diagram has been constructed for the first time in this work. High-temperature neutron diffractometry has permitted real time measurement of the reactions involved in this ternary system, especially to determine the temperature range for each reaction, which would have been difficult to establish by other means. 相似文献
18.
Masahiko Tajika Hideaki Matsubara William Rafaniello 《Journal of the American Ceramic Society》1999,82(6):1573-1575
Thermal diffusivity of AlN-based ceramics was studied as a function of second-phase amount and heat-treatment time. The Y2 O3 ·Al2 O3 contents varied over the range of 13-31 vol%. The thermal diffusivity decreased as the amount of second phase increased. After sintering at 1850°C, the AlN ceramics consisted of rounded, largely isolated grains. Heat treatment of these samples for 5-50 h at 1800°C resulted in microstructures that consisted of largely contiguous AlN grains. There was a substantial increase in the thermal diffusivity after the heat-treatment step, and the incremental improvement was essentially constant for the three compositions that have been studied. The amount of second phase was unchanged during heat treatment; therefore, the increase in thermal diffusivity is assumed to be a direct result of the enhanced contiguity of AlN grains. 相似文献
19.
Andreas Bausewein Birgitta Hacker Maximilian Fleischer Hans Meixner 《Journal of the American Ceramic Society》1997,80(2):317-323
The gas sensitivity of Ga2 O3 thin-film n -type conductors was investigated at temperatures of 500–1000°C. Palladium dispersions whose particle sizes are dependent on the preceding annealing processes were deposited by a wet-chemical technique onto Ga2 O3 thin-film ceramics. The palladium clusters and their temperature-dependent growth were detected using scanning electron microscopy micrographs and X-ray photoemission spectroscopy measurements. The effect of the palladium dispersions on the gas-sensitive behavior of the Ga2 O3 ceramics was investigated in various O2 /H2 mixtures in the N2 carrier gas at 700°C. The conductivity of the ceramics treated in this way was dependent on the O2 partial pressure, as well as on the H2 partial pressure of the surrounding gas atmosphere. The ceramic conductivity can be described as a function of the O2 :H2 ratio, in accordance with the relation σ( p O2 / p H2 /)−1/3 . 相似文献
20.
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