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Volume 25, Issue 5
Displaying 1-6 of 6 articles from this issue
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Kiyoshi Okazaki1978 Volume 25 Issue 5 Pages 147-153
Published: July 25, 1978
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSLanthanum modified lead zirconate titanate (PLZT) ceramics are useful for electrooptic devices. However, as far as the defect structure of PLZT, there are still some arguments. In this study, the single phase widths of the completely pore-free transparent PLZT x/65/35 ceramics have been studied as a function of La concentration x. The PbO loss data corresponding to the upper and lower limits of the single phase from the starting composition were measured by the thermogravimetric method in controlling atmospheres. Also, the density approach corresponding to the single phase region has been tried for the almost completely porefree specimens prepared by Two-Stage Processing. The defect structures are discussed so as to fit in both the single phase regions. Some electrical properties are measured for specimens with various PbO deficiency within the single phase region.View full abstractDownload PDF (518K) -
Kuniaki Ushijima, Takeo Otsuka1978 Volume 25 Issue 5 Pages 154-158
Published: July 25, 1978
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSUsing WO3 and WO2 as the starting material, the change of the particle size on the H2-reduction process was taken by a measurement of specific surface area, and the effect of particle size of the starting material on the particle size of the produced W was investigated. From the result, it was found that, in the case of the smaller particle size of W than that of WO3 is obtained, the particle size is not depend on that of WO3, especially, on the reduction process of WO2 to W, the particle size of W obtained is not affected by that of WO2, but a similar particle size of W is obtained.View full abstractDownload PDF (1736K) -
Tetsuo Kato, Katsusi Kusaka1978 Volume 25 Issue 5 Pages 159-163
Published: July 25, 1978
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSAn investigation was made on the pressing and sintering behavior of water-atomized 15/25% Cr-Ni stainless steel powders bearing 0.34% or less of nitrogen.
The results were summarized as follows:
(1) Nitrogen was successfully added into powders up to near the nitrogen-solubility in the molten state at pulverizing temperature, on account of rapid solidification by quench-atomization.
(2) Compressibility was found to be higher in nitrogen-rich lower Cr powders, only in the case that athermal martensite was less formed under the favorable influence of nitrogen as an austenite stabilizer, with less affecting sintering behavior.
(3) Compressibility was appreciably improved by heat-decomposing (in the range 600-700°C) metastable phases quenched from high temperatures, especially for 15/17% Cr powders with the normal amount of nitrogen.
(4) Excess nitrogen-added powders were outgassed in the early stage of vacuum-sintering at temperatures higher than 1000°C.
As a result, it was found that fairly good mechanical properties of sintered materials can be obtained irrespective of the original amount of nitrogen.View full abstractDownload PDF (1676K) -
Yoshiko Suwa, Yoshiki Sugimoto, Shigeharu Naka1978 Volume 25 Issue 5 Pages 164-167
Published: July 25, 1978
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSThe stability of several compounds in the system BaO-TiO2 coprecipitated from the alkoxides were investigated. The samples in which the mole ratios of BaO to TiO2 were 2/1, 1/1, 1/2, 1/3, 1/4, 2/9, 1/5 and 1/9 were prepared by the simultaneous hydrolysis of barium isopropoxide and titanium isopropoxide. On the as-prepared specimens, only 1/1 specimen crystallized as a single phase of cubic BaTiO3, 2/1 was composed of cubic BaTiO3 and Ba(OH)2·H2O, and all others in the TiO2-rich region were of amorphous forms. It is suggested that Ba2+ in the 1/1 solution reacts as a strong Lewis acid and directly combines with Ti(OiPr)62-, and a double alkoxide, Ba[Ti(OiPr)6] is formed in isopropanol solution. In the TiO2-rich region, the polymerization takes place on the formation of Ti-O-Ti bridge following the hydrolysis of Ti(OiPr)4, resulting in the precipitation of amorphous phase.
By heating at 800°C of 1/2 and 1/5 specimens, the single phases of BaTi2O5 and BaTi5O11 were formed respectively. Thus far the single phases of these compounds have not been obtained. Since BaTi2O5 and BaTi5O11 begin to decompose above 1200°C, they are considered to be a low temperature form or a metastable form.View full abstractDownload PDF (262K) -
Osamu Yamaguchi, Hirohisa Nakano, Kenzo Matsumoto, Kiyoshi Shimizu1978 Volume 25 Issue 5 Pages 168-173
Published: July 25, 1978
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSA mixture with the mole ratio of Mg2+/Si4+=3 : 2 was prepared by the simultaneous hydrolysis of magnesium and silicon alkoxides. The phases and thermal properties of the mixture were studied by means of differential thermal analysis, thermogravimetric analysis and X-ray diffraction. The results obtained are summarized as follows:
1) 2 MgO-SiO2 and MgO·SiO2 were formed at 770°C and 865°C, respectively.
2) For the three modifications of MgO·SiO2, it is presumed that orthoenstatite and clinoenstatite are the low temperature phases, on the other hand, protoenstatite is the high temperature phase.
3) It was considered that the formation of 2 MgO·SiO2 and MgO-SiO2 was followed by the mechanism described by Ball and Taylor for surpentine (3 MgO·2 SiO2·2 H2O).
4) The rate of formation of 2 MgO-SiO2 was determined. Reaction isotherms were best described by the first-order plots. The nucleation process maybe the rate-determing step. The values of the activation energies are about 82 kcal/mol and 27 kcal/mol for initial and final stages, respectively.View full abstractDownload PDF (1628K) -
Makoto Kinoshita, Chuzo Toyota, Ryohei Terai1978 Volume 25 Issue 5 Pages 174-178
Published: July 25, 1978
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSIn order to enhance the thermal conductivity of the glass containing high-level radioactive waste oxides, copper-glass composite compacts were fabricated as a model, The compacts were prepared by pressure sintering of the mixtures of electrolytic copper and Pyrex glass powders at 200 kg/cm2 in graphite dies. Thermal conductivity of the compact was measured by a laserflash method.
The compacts of the copper powder showed the relative densities over 0.95 by sintering at the tem-peratures higher than 500°C, but the density was observed to decrease slightly as the increase of temperature by the release of the adsorbed gas to form the entrapped pores. The compacts of the glass powder were fully densified at the temperatures higher than the yield point of the glass, 625°C. The composite compacts could be successfully prepared at 650°C or above. Linear relationships were observed between the density or the thermal expansion coefficient of the compact and the volume fraction of copper. The thermal conductivity increased as the copper content increased. It was found that the conductivity followed the socalled logarithmic rule, one of the mixture rules of thermal conductivity, up to the copper content of about 20 vol%. Over this content, the conductivity increased remarkably apart from the rule as copper formed a continuous phase in the compact.View full abstractDownload PDF (1599K)
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