Journal of the Ceramic Association, Japan
Online ISSN : 1884-2127
Print ISSN : 0009-0255
ISSN-L : 0009-0255
Volume 88, Issue 1024
Displaying 1-7 of 7 articles from this issue
  • Sukezo KAWAMURA, Riichi KUROKAWA
    1980 Volume 88 Issue 1024 Pages 703-712
    Published: December 01, 1980
    Released on J-STAGE: April 30, 2010
    JOURNAL FREE ACCESS
    In order to study a densification mechanism in kaolin-limestone mixtures, the phase and microstructural changes, and melt formation, which are related with the body densification during firing process, were in detail examined. The result obtained are as follows.
    Densification of the kaolin-limestone mixtures during firing process occurs at 900°-950°C and above 1250°C separately. At 900°-950°C, active CaO reacts rapidly with metakaolin to form gehlenite, which always appears prior to anorthite and wollastonite, that results in the rapid shrinkage. At the intermediate temperatures, the reaction of calcia and metakaolin proceeds to attain equilibrium in the solid state and build up the three solid phases without sintering or vitrification. Above 1250°C, the onset of vitrification occurs depending upon the melt formation by eutectic reaction of the three solid phases, it follows that the mixtures containing 25-40wt% CaO results in the reduction of vitrification-range due to the excess amount of initial eutectic melt. Consequently, the experimental results for the vitrification process and the relation between calcia content and the vitrification temperature agreed well with the estimation from the pseud-binary system CaO-Al2O3⋅2SiO2 constructed from the CaO-Al2O3-SiO2 phase equilibrium diagram.
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  • Masayuki NOGAMI, Yoshiro MORIYA, Junji HAYAKAWA, Toru KOMIYAMA
    1980 Volume 88 Issue 1024 Pages 712-718
    Published: December 01, 1980
    Released on J-STAGE: April 30, 2010
    JOURNAL FREE ACCESS
    Fabrication of hollow glass microspheres for laser fusion targets was tried using the gel powders prepared from metal alkoxides. The gel was prepared by hydrolysis of the solution containing Si(OC2H5)4, B(OCH3)3 and NaOCH3 with HCl solution. It was dried, crushed and sieved to obtain the powders fanging from 44 to 63μm. Such powders were dropped into the vertical type electric furnace which was held at appropriate temperatures.
    When the gel powder was rapidly heated, the surface of it transformed to the glass to form the shell in which gases contained in the gel powder were encapsulated. During passing through the furnace, the shell expanded to be a hollow glass microsphere.
    The expansion rate of the hollow glass microsphere was calculated on the hypothesis that the expansion of microsphere was governed by the pressure of gases encapsulated and the viscous relaxation of the glassy shell. It was estimated that the time required for the microsphere to expand to the final size was about 0.1s at 1300°C and the gases effective for expansion were those contained within a third of radius of the gel powder.
    When the highest temperature of furnace was held at 1300°-1500°C, the hollow glass microspheres ranging from 80 to 100μm in diameter with the wall thickness of 1.0μm were obtained. Their sphericity and the wall thickness uniformity were satisfactory for the laser fusion target requirements.
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  • Toshihiko NISHIDA, Yasunari HOTTA, Tomozo NISHIKAWA
    1980 Volume 88 Issue 1024 Pages 718-724
    Published: December 01, 1980
    Released on J-STAGE: April 30, 2010
    JOURNAL FREE ACCESS
    Deformation and fracture behavior of polycrystalline aluminum nitride in three-point bending creep was studied under constant rate of loading. Two kinds of polycrystalline aluminum nitride were fabricated by hot-pressing of aluminum nitride powder under the conditions of 2000°C, 200kg/cm2, 30 minutes (Sample-A), and 180 minutes (Sample-B). Relative density and grain size of these polycrystalline materials were 95-96% and 2-2.5μm for Sample-A, and 99% and 8-10μm for Sample-B, respectively. Under the loading rate of 12.7kg/cm2⋅min, the brittle-ductile transition temperatures were about 1400°C for Sample-A and about 1600°C for Sample-B. The cause of the fracture in the brittle region was discussed from the view point of fracture mechanics, and the effect of the surface flaw size of the specimans on fracture strength was also discussed. On the other hand, the gain boundary separation in the deformation process at the ductile region for Sample-A was observed, while the diffusional deformation must have been operative at the same time. The yield value of Sample-A decreased with increasing temnperature. For Sample-B, the yield value did not change up to temperature of 1800°C, and also the grain boundary separation in the ductile deformation process was not observed even at 2000°C. From above observations, it is concluded that high density is not sufficient condition to obtain the excellent high temperature structurual material of polycrystalline aluminum nitride and the polycrystal must have enough heat treatment to attain the strong grain boundary strength.
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  • Minoru IMAOKA, Suguru SUZUKI, Hiroyasu SAKAMURA
    1980 Volume 88 Issue 1024 Pages 725-733
    Published: December 01, 1980
    Released on J-STAGE: April 30, 2010
    JOURNAL FREE ACCESS
    Creep was measured for glasses in the system of As-Se by a torsional method under a constant torque in the glass transition range. Compliance, J(t), of retarded elasticity can be normally described as
    J(t)=∑iJi(1-e-ti) (1)
    where t is time and τ is retardation time. When i was even 1, a correlation coefficient obtained for each run was higher than 0.95 and thus it was considered that calculated curves (at i=1) fitted well with the measured ones.
    The micro-viscosity, ηG, of retarded elasticity (Fig. 1) can be obtained by using τ and J (compliance at the final stage in each run, ≅1/G2). The plots of log ηG agaist 1/T gave essentially a straight line for each sample as shown in Fig. 6. Thus the apparent activation energy for the process of deformation due to retarded elasticity was calculated by the following equation, ΔEηG=R⋅d(logηG)/d(1/T), where R is the gas constant. The activation energy was approximately one-half of that for viscous flow as shown in Fig. 7 and was lower than the bonding energy of As-Se.
    Final compliance, J, showed a maximum at η≅1014 poise in every composition of As-Se glasses. The following equation expressed as a function of viscosity is proposed,
    J=(1-k2ηG/η)(f1[k1/η]+f2[nk1/η]) (10)
    where k1, k2, n, f1 and f2 are parameters for fitting. When [k1/η] and [nk1/η] exceed 1, they were always replaced by 1. This equation means that J is mainly dominated by the term, (1-k2ηG/η), in lower viscosity range (η<1014 poise), while in higher viscosity range (η>1014 poise) it is controlled by the term, [k1/η] or [nk1/η]. The term (1-k2ηG/η) formulates the competition between ηG and η, and the terms [k1/η] and [nk1/η] can be attributed to the interactions of layers in glass structure. The calculated curves based on Eq. (10) agreed well with the measured values as shown in Fig. 8 (a), (b) and (c).
    Coefficient f1 was found to decrease with increasing Se content and f2 increased conversely with Se content (Fig. 10). Though k2 should theoretically be equal to 1, it decreased with As content. In addition, it was found that f2 and k2, when they were plotted against the Se atom fraction, changed appreciably their slopes at Se≅80 atom% (around As2Se8) as shown in Figs. 9 and 10. It was therefore presumed that f1 would depend on the ring structure of network and f2 and k2 would depend on the chain structure.
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  • Studies on the Crystallization of ZnO-Al2O3-SiO2 Glasses, No. 4
    Syoji YOKOISHI, Hajime SAITO
    1980 Volume 88 Issue 1024 Pages 733-740
    Published: December 01, 1980
    Released on J-STAGE: April 30, 2010
    JOURNAL FREE ACCESS
    The precipitating region of β-quartz solid solutions from ZnO-Al2O3-SiO2(ZnO/Al2O3>1) glasses, the types of substitution which may occur in their structures and its thermal decomposition products are investigated. Results obtained are as follows.
    (1) As for ten glasses of different compositions studied, the glass compositional region in which oniy β-quartz solid solutions are precipitated is 3.45≥ZnO/Al2O3≥1 (molar ratio), SiO2>46mol% and ZnO<38mol%. However, SiO2 rich region where metastable phase separation occurs on quenching melts is excluded from the above compositioual region because single crystalline phase, β-quartz solid solution, is not obtained.
    (2) While it is generally considered that 1/2 ZnO(VI)+Al(IV) can replace one Si(IV) of β-quartz structure with the molar ratio ZnO/Al2O3=1, it is presumed that at ZnO/Al2O3>1, there exist excess ZnO that can not enter the structure together with Al(IV) and part of them substitutes for the Si site owing to 4-fold coordination preference of Zn2+, the rest entering the holes of β-quartz structure, 6-fold coordination site, in order to maintain electrical neutrality.
    (3) Change of lattice parameters of β-quartz solid solutions on their compositions (ZnO/Al2O3>1) can be well explained when their compositions are represented in the SiO2-Zn (VI)⋅Zn(IV)O2-Zn(VI)1/2⋅Al(IV)O2 pseudo-ternary system.
    (4) β-quartz solid solution with ZnO/Al2O3>1 decomposes to β-quartz solid solution with ZnO/Al2O3=1 and β-Zn2SiO4 solid solution on heating to 950°C, while β-quartz solid solution with ZnO/Al2O3=1 decomposes to gahnite and SiO2 rich β-quartz solid soiution at above 1000°C.
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  • Koichi KITAZAWA, Akira KISHI, Kazuo FUEKI
    1980 Volume 88 Issue 1024 Pages 741-746
    Published: December 01, 1980
    Released on J-STAGE: April 30, 2010
    JOURNAL FREE ACCESS
    The viscosities of soda-lime, lead, and borosilicate glasses as determined by the sinusoidal profile decay (SPD) method decreased with increase in the atmospheric water vapor pressure during measurement. Since the bulk viscosities were not affected by the presence of the atmospheric water, the change was discussed in terms of the water penetration into the surface layer of thickness about several to several tens of micrometers under the experimental conditions and the subsequent change in the surface layer viscocity. A linear relationship was observed between the reciprocal viscosity 1/η and square root of the water vapor pressure √PH2O.
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  • Takayasu IKEGAMI, Shin-ichi MATSUDA, Yusuke MORIYOSHI, Hiroshige SUZUK ...
    1980 Volume 88 Issue 1024 Pages 746-753
    Published: December 01, 1980
    Released on J-STAGE: April 30, 2010
    JOURNAL FREE ACCESS
    Rate equations were statistically derived for grain growth with simultaneous densification (RdR=6γIΩD[1-1.4(1-ρ)]k12k2dt/kTW) and for particle growth by surface drffusion (R4-R04=KSt). They were successfully applied to grain growth of the sinterable BeO purchased from NGK Insulators Ltd., (CF-BeO) and to particle growth of a nonsinterable one derived from a hydroxide, respectively. Difference in the growth behaviors of grains and particles was explained from the viewpoint of their geometrical configurations.
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