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21.
Processing and Thermal Conductivity of Sintered Reaction-Bonded Silicon Nitride. I: Effect of Si Powder Characteristics 总被引:2,自引:0,他引:2
Xinwen Zhu You Zhou Kiyoshi Hirao Zoltán Lené 《Journal of the American Ceramic Society》2006,89(11):3331-3339
This paper will present sintered reaction-bonded silicon nitride (SRBSN) material with a high thermal conductivity of 121 W·(m·K)−1 , which has been successfully prepared from a coarse Si powder with lower levels of oxygen and aluminum impurities, using a mixture of Y2 O3 and MgSiN2 as sintering additives, by nitriding at 1400°C for 8 h and subsequent post-sintering at 1900°C for 12 h at a nitrogen pressure of 1 MPa N2 . This thermal conductivity value is higher than that of the materials prepared from high-purity α-Si3 N4 powder (UBE SN-E10) with the same additive composition under the same sintering conditions. In order to study the effects of Si powder characteristics on the processing, microstructure, and thermal conductivity of SRBSN, the other type of fine powder with higher native oxygen and metallic impurity (typically Al and Fe) contents was also used. The effects of Si particle size, native oxygen, and metallic impurities on the nitriding process, post-sintering process, and thermal conductivity of the resultant SRBSN materials were discussed in detail. This work demonstrates that the improvement in thermal conductivity of SRBSN could be achieved by using higher purity coarse Si powder with lower levels of oxygen and aluminum impurities. In addition, this work also shows that the nitriding temperature has no significant effect on the microstructure and thermal conductivity of SRBSN during post-sintering, although it does affect the characteristics of RBSN formed during nitridation. 相似文献
22.
Toshiaki Shimizu Mitsuo Yazawa Tsuneo Hirao Narihiko Arai 《Journal of chemical ecology》1993,19(11):2501-2512
We isolated glucosides from the royal fern,Osmunda japonica, which elicit a deterrent response in larvae ofBombyx mori. These compounds were absent in taro (Colocasia antiquorum) and castor-oil plant (Ricinus communis) leaves and did not evoke responses of sensory cells in the lateral and medial sensilla styloconica ofSpodoptera litura. This glucoside extract of the royal fern leaves stimulates receptors generally associated with deterrent. It is also possible that this compound may act as a behavioral deterrent, and from actual feeding tests, it is suggested that this compound may prevent feeding in some monophagous insects, such asBombyx mori. The deterrent glucoside possesses a noncyclic aglycon. 相似文献
23.
The effects of the various characteristics of reaction-bonded silicon nitride (RBSN), such as crystalline secondary phases, residual Si, pore size distribution, and agglomerates developed during nitridation on the post-densification behavior, were investigated in detail. A model experiment was carried out to study the effect of crystalline secondary phases in RBSN on the post-densification. The result clearly indicates that the pre-formation of crystalline secondary phases does not influence the sintering of Si3N4-powder compacts, which is further demonstrated in the post-densification of RBSN, because the formation of a liquid, including its composition and properties, is dependent on the composition of the system and sintering temperature, but independent of the presence of crystalline secondary phases. In particular, the complete melt of crystalline secondary phases is not related to their melting points and only relies on the composition of the system. The residual Si and pore size distribution in RBSN show no significant effect on the post-densification. Some large pores of 5 m in size could be eliminated by liquid filling and grain growth during post-sintering. The residual Si in RBSN could change into -Si3N4 by nitridation of liquid Si and contribute to the weight gain during the early stage of post-sintering. However, it is shown that the agglomerates in RBSN play an important role in the post-densification. The effect of agglomerates on the post-densification strongly depends on their size and amounts in RBSN. Nearly complete densification of RBSN could be reached through lowering of the nitriding temperature or adding Si3N4 powder to green bodies, which leads to the formation of more uniform microstructure during nitridation. A mechanism that explains how the agglomerates affect the post-densification of RBSN was discussed based on the theories of liquid phase sintering. 相似文献
24.
Ellen Y. Sun Paul F. Becher Kevin P. Plucknett Chun-Hway Hsueh Kathleen B. Alexander Shirley B. Waters Kiyoshi Hirao Manuel E. Brito 《Journal of the American Ceramic Society》1998,81(11):2831-2840
Significant improvements in the fracture resistance of self-reinforced silicon nitride ceramics have been obtained by tailoring the chemistry of the intergranular amorphous phase. First, the overall microstructure of the material was controlled by incorporation of a fixed amount of elongated ß-Si3 N4 seeds into the starting powder to regulate the size and fraction of the large reinforcing grains. With controlled microstructures, the interfacial debond strength between the reinforcement and the intergranular glass was optimized by varying the yttria-to-alumina ratio in the sintering additives. It was found that the steady-state fracture toughness value of these silicon nitrides increased with the Y:Al ratio of the oxide additives. The increased toughness was accompanied by a steeply rising R -curve and extensive interfacial debonding between the elongated ß-Si3 N4 grains and the intergranular glassy phase. Microstructural analyses indicate that the different fracture behavior is related to the Al (and O) content in the ß´-SiAlON growth layer formed on the elongated ß-Si3 N4 grains during densification. The results imply that the interfacial bond strength is a function of the extent of Al and Si bonding with N and O in the adjoining phases with an abrupt structural/chemical interface achieved by reducing the Al concentration in both the intergranular phase and the ß´-SiAlON growth layer. Analytical modeling revealed that the residual thermal expansion mismatch stress is not a dominant influence on the interfacial fracture behavior when a distinct ß´-SiAlON growth layer forms. It is concluded that the fracture resistance of self-reinforced silicon nitrides can be improved by optimizing the sintering additives employed. 相似文献
25.
Misao Koide Jinta Ukawa Waichiro Tagaki Seizo Tamagaki 《Journal of the American Oil Chemists' Society》1997,74(1):49-54
Two different types of methyl esters of β-glycyrrhizinate (GK2) have been prepared to delineate the mechanism of the catalytic
action of each carboxyl group of GK2 in the hydrolysis of nonionic fatty acid surfactants. In the acidic pH region of less
than 4, the hydrolysis is catalyzed by the carboxyl groups of the sugar moiety, while in the close-to-neutral acidic region,
the carboxyl group at the hydrophobic triterpenoid end becomes important in catalysis. 相似文献
26.
The flux growth of emerald crystals by slow cooling in the PbO · V2O5 flux is reported. The crystals exhibited the typical emerald-green colour, were up to 1.8 mm in size and transparent. Their
form was a regular hexagonal rod bounded by the well-developed {0001} and {10ˉ10} faces. The solubility of emerald in PbO
· V2O5 was also investigated; about 9.0 g emerald was dissolved in 100 g PbO · V2O5 at 1200 °C. The solubility decreased gradually with decreasing temperature. Taking the solubility data into account, the
presence of undissolved particles in the solution was found to be a necessary condition for the growth of large emerald crystals.
Unsaturated solution at a soak temperature produced good and relatively small emerald crystals in a subsequent cooling experiment.
Advantages of the PbO · V2O5 flux are also mentioned. Emerald crystals showing various kinds of imperfections, and even good crystals, were also present. 相似文献
27.
28.
Yukitoshi Takeshita Takuya Kamisho Seizo Sakata Takashi Sawada Yoshikazu Watanuki Ryuichi Nishio Toshinobu Ueda 《Journal of Coatings Technology and Research》2013,10(4):503-514
To improve alkaline resistance, a newly mixed powder coating film using thermoplastic polyethylene terephthalate (PET) was investigated. Two kinds of polyvinyl butyral (PVB) and two kinds of polyamide (PA) were chosen as the secondary polymer. The melting temperatures (T ms) of these materials were lower than that of primary PET polymer so the mixed powder coating was able to form a dual phase film through a fluidized bed coating process. Microscope and Fourier transform infrared spectroscopy (FTIR) observations revealed that the dual phase structure was indeed successfully formed and there was a secondary layer over the entire surface area of the film. This mixed powder coating film significantly enhanced the alkaline resistance to an environment filled with NaOH solution at 40°C in which a secondary material would be effective in protecting the film. With regard to both alkaline resistance and film formability, PET/PVB was superior to the PET/PA mixture. 相似文献
29.
30.
I Hirao S Yoshinari S Yokoyama Y Endo AD Ellington 《Canadian Metallurgical Quarterly》1997,(37):283-284
Ribosome-inactivating proteins, such as ricin, pepocin and gypsophilin, catalyze the hydrolysis of a single N-glycosidic bond at a specific position in rRNAs. Aptamers targeting pepocin were selected from a random sequence RNA pool that spanned 30 positions. After 8 rounds, the anti-pepocin aptamers were sequenced and a conserved hairpin motif was identified. Interestingly, the selected motif is quite different from the toxin-binding domains of rRNAs. 相似文献