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101.
Hiromi Nakano Kazuyori Urabe Hiroyuki Ikawa 《Journal of the American Ceramic Society》2003,86(4):741-43
A BaCO3 phase is found on the surfaces of hydrothermally synthesized BaTiO3 particles; it occurs as aggregates or small protuberances. A small proportion of the phase decomposes to BaO crystallites when heated by a convergent electron beam in a transmission electron microscope. The BaO and BaCO3 crystallites disappear when they are irradiated successively by the convergent electron beam. The BaO crystallites and the BaCO3 phase sublimate and/or react with BaTiO3 crystals whose surface layers are deficient in Ba2+ ions. 相似文献
102.
Hydrogel prepared by repetitive freezing and thawing of poly(vinyl alcohol) aqueous solution was chemically crosslinked with glutaraldehyde. The chemically crosslinked hydrogel hardly changed its physical appearance, and showed good elasticity and strength as original gel. However, after treating in boiling water, it swelled a little, depending on the condition of the chemical treatment. The melted gel thus obtained showed shape memorizing property, that is, it could firmly hold nearly 200% of strain, keeping its original high elasticity. The strain could be released very quickly (< 1 s) in boiling water, and the gel was suggested to be applied to a new type of gel actuator. X-ray diffraction study revealed that the melted gel does not necessarily reform the physical crosslinks in exactly the same manner as the original gel in the process of shape restoring, but the distribution of the physical crosslinks can be restored as they were. It was suggested that the chemical crosslinks which remember the distribution of the physical crosslinks plays a critical roll in the shape restoring process. 相似文献
103.
Taigo Takaishi Masahide Takahashi Jisun Jin Takashi Uchino Toshinobu Yoko Masahide Takahashi 《Journal of the American Ceramic Society》2005,88(6):1591-1596
Structure of x PbO–(100− x )SiO2 ( x =25–89) glasses has been investigated by means of the X-ray and neutron diffraction and 29 Si MAS NMR measurements. In the radial distribution functions of all the glasses, the Pb–O correlation was observed at 0.23 nm, indicating that the PbO3 trigonal pyramids units do exist in the whole glass forming composition range. Furthermore the existence of the first Pb–Pb correlation at ∼0.385 nm in the whole composition range suggests that the basic structural unit is considered to be a Pb2 O4 unit, which consists of the edge-shared PbO3 trigonal pyramids. These results strongly imply that the Pb2 O4 units participate in the glass network constructed by SiO4 tetrahedra even at low PbO content. Differing from other lead-containing glass systems, these structural characteristics of Pb ions in the PbO–SiO2 glass system are responsible for the extremely wide glass-forming region. 相似文献
104.
Yoshitsugu Kojima Takashi Ohta Mitsumasa Matsushita Minoru Takahara Toshio Kurauchi 《Polymer Engineering and Science》1992,32(10):686-689
Flat packages (FPs) were formed from epoxy molding compounds with various physical properties using a transfer molding machine. The compounds were prepared by changing kinds and amounts of additives and addition methods. The thermal shock test was carried out by the following procedures. The plastic package was soaked alternately in liquid nitrogen (?196°) and in liquid solder (200°) in the cycle of 140s. The median life to crack initiation was defined to be the cycles when half of the specimens exhibited crack initiation. According to linear fracture mechanics, the following expression was obtained relating the median life N, thermal stress σt, and strength σb; N = C/σ·(σb/σt)m. We found the linear relation between logarithm of Nσ and logarithm of σb/σt for various packages, and estimated the values of C and m as 5 × 104 MPa2 and 5.5, respectively. The value of m was the same as that obtained for a dual-in-line package. 相似文献
105.
The strength, S , of ceramic and glass fibers often can be estimated from fractographic investigation using the fracture mirror radius, r m , and the relationship S = A m /( r m )1/2 , where A m is the "mirror constant." The present work estimates the value of A m for Tyranno® Si-Ti-C-O fibers in situ in a three-dimensional woven SiC/SiC-based composite to be 2.50 ± 0.09 MPa·m1/2 . This value is within the range of 2–2.51 MPa·m1/2 previously obtained for nominally similar Nicalon® Si-C-O fibers. 相似文献
106.
Takashi Nakamura 《Lipids》1986,21(9):553-557
Prostaglandin-like substances other than 3-(2-ethyl-5-hydroxy-3-oxo)-cyclopentanyl-2-propenal (compound I), which upon reacting
with amino acids form reddish pigments, were purified, and their chemical structures were determined. Three red pigment-forming
substances (RPS) in autoxidized methyl linolenate were purified successively by gel chromatography on Sephadex LH-20, column
chromatography and thin layer chromatography on Silica Gel 60, and by high performance liquid chromatography on μ-Porasil.
IR spectra of the RPS showed the absorption of an ester group (νC=O 1730 cm−1 in CHCl3) and of a longer branched chain (νC-H 2800–3100 cm−1), in addition to the absorption bands observed in compound I. Electron impact mass spectra of the trimethylsilyl ethers obtained
after reduction with NaBH4 and NaBD4 were analyzed in detail and compared with those of compound I. The structures of the RPS were identified as stereoisomeric
methyl 8-[2-(2-formylvinyl)-3-hydroxy-5-oxo-cyclopentanyl]-octanoates derived from methyl 12-hydroperoxy-linolenate.
Presented at the general meeting of the Japanese Society of Scientific Fisheries, held at Tohoku University, Sendai, Japan,
October 1984. 相似文献
107.
Dimethylsiloxane-tetramethyl-p-silphenylenesiloxane-dimethylsiloxane (DMS-TMPS-DMS) triblock copolymer was synthesized by employing living anionic polymerization of hexamethylcyclotrisiloxane (D3). Two synthetic methods were carried out for the polymerization. One of those methods was the anionic polymerization of D3 initiated at the silanolate anion which was prepared from the terminal hydroxyl group of silanol-terminated TMPS prepolymer by reaction with n-butyllithium (method 1). The other was the coupling reaction of vinyl-terminated TMPS prepolymer with hydrosilyl-terminated DMS prepolymer obtained from the anionic polymerization of D3 by using diphenylmethylsilanolate anion as initiator (method 2). In method 1, DMS contents of the copolymers ranged from 25.8 to 72.5 wt% and the values agreed with the ratio of D3 to TMPS prepolymer. The weight-average molecular weights ranged from 1.36×104 to 19.4×104 and were close to the predicted values calculated from the of the TMPS prepolymer and the amount of D3 added. In the case of method 2, weight-average molecular weights ranged from 19.5×104 to 24.2×104. The high molecular weight copolymer could thus be obtained by method 2. Intrinsic viscosity values of the triblock copolymers agreed with calculated values obtained by considering the copolymer as a binary mixture of these homopolymers. Differential scanning calorimetry and thermogravimetry were carried out on the triblock copolymers. The equilibrium melting temperatures of each of the copolymers were very close to that of poly-TMPS (160°C). The glass transition temperature and heat of fusion were decreased as the DMS content was increased. The thermogravimetric curves for the copolymers indicated that the thermal stability of the triblock copolymer was intermediate between the DMS and TMPS homopolymers. 相似文献
108.
Efficient usage of highly dispersed Pt on carbon nanotubes for electrode catalysts of polymer electrolyte fuel cells 总被引:2,自引:0,他引:2
T. Matsumoto T. Komatsu H. Nakano K. Arai Y. Nagashima E. Yoo T. Yamazaki M. Kijima H. Shimizu Y. Takasawa J. Nakamura 《Catalysis Today》2004,90(3-4):277-281
A Pt-deposited carbon nanotube (CNT) shows higher performance than a commercial Pt-deposited carbon black (CB) with reducing 60% Pt load per electrode area in polymer electrolyte fuel cells (PEFCs) below 500 mA/cm2. K2PtCl4 and H2PtCl6·6(H2O) are used for the Pt deposition onto multi-walled CNTs (MWCNTs), which are produced by the catalytic decomposition of hydrocarbons. The electric power densities produced using the Pt/CNT electrodes are greater than that of the Pt/CB by a factor of two to four on the basis of the Pt load per power. CNTs are thus found to be a good support of Pt particles for PEFC electrodes. TEM images show 2–4-nm Pt nanoparticles dispersed on the CNT surfaces. These high performances are considered to be due to the efficient formation of the triple-phase boundaries of gas–electrode–electrolyte. The mechanisms of Pt deposition are discussed for these Pt-deposited CNTs. 相似文献
109.
110.
As previously reported, high surface area microporous carbons with long-range order can be synthesized by using zeolite Y as a template. In this work, an attempt is made to synthesize porous carbon using several other types of zeolites (zeolite β, ZSM-5, mordenite and zeolite L). Special attention is paid to whether the structural regularity of each zeolite can be transferred to the carbon structure as well as with the case of zeolite Y. The carbon filling method was then examined to see which gives the highest regularity to the carbon structure. It has been found that the optimum carbon filling method for zeolite Y is not an optimum one for the other zeolites and the degree of the regularity of long-range ordering in the carbons strongly depends on zeolite type. The order of the regularity in the resultant carbons is zeolite β>>zeolite L>mordenite>ZSM-5. The effect of zeolite type on the regularity is discussed in relation to the size and the shape of the zeolite channels. 相似文献