Journal of the Ceramic Association, Japan
Online ISSN : 1884-2127
Print ISSN : 0009-0255
ISSN-L : 0009-0255
Volume 76, Issue 876
Displaying 1-8 of 8 articles from this issue
  • Hajime SAITO, Iwao YAMAI, Nobuyuki KATO
    1968 Volume 76 Issue 876 Pages 247-253
    Published: August 01, 1968
    Released on J-STAGE: April 30, 2010
    JOURNAL FREE ACCESS
    Raw material compositions and reaction conditions were studied in detail for the synthesis of chrysotile fibers under hydrothermal-dehydration process, under which as previousley reported the fibers elongated.
    A suitable ratio of composition of the starting materials were as follows; silcic unhydride 1mol, brucite 2-2.5mol, magnesium bromide 3/4-1mol which catalyzed the formation of the fibers and promoted dehydration from the slurry, and water about 50mol which constituted 10% fill of the pressured space.
    In this case, the slurry showed pH=7.0±0.3 at room temperature, and pressure of hydrogen evolved by the dehydration reaction was the same as the water pressure after the reaction. From this fact, it was seemed that the formation and growth of fibers were occured at relatively low water pressure which condition is analogous to the formation of natural chrysotile fibers.
    Effects of other substances were examined, and it was shown from the results that magnesium bromide not only provided a suitable pH to the slurry, but also was required for the formation of intermediates in the crystallization of the fibers.
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  • Keiichi MURAKAMI, Hirobumi TANAKA, Kenro SATO, Kunio HASHIMOTO, Kazuhi ...
    1968 Volume 76 Issue 876 Pages 253-263
    Published: August 01, 1968
    Released on J-STAGE: April 30, 2010
    JOURNAL FREE ACCESS
    A large amount of phosphogypsum by-produced in wet process of phosphoric acid manufacture is being used as an available retarder of portland cement. However, some impurities in phosphogypsums, such as the water-soluble P2O5 and the water-soluble F retard the set of portland cement and hinder the early development of its mortar strength.
    In this paper, the authors have revealed the effect of impurities on the hydration of portland cement and alite and have suggested the mechanism of retarding action on the hydration of portland cement.
    The obtained results are as follows;
    (1) The water-soluble P2O5 and the water-soluble F retard the set of paste and, when they are added over some amount to cement, hinder even the early development of mortar strength. The retarding action on the hydration of portland cement is more strengthened by the co-existence of over two shorts of impurities than by a single existence of any impurities. These results well agreed with that of the preceding investigators.
    (2) The Phosphogypsums by-produced in hemihydrate-dihydrate process have a regular form, therefore, most part of the water-soluble impurities which adhered to the surface of gypsum crystals is removed by a simple washing with water after the cake of phosphogypsum was discharged from the filtration step in wet-process. Moreover, the P2O5 in phosphogypsum crystals is also a small amount.
    On the other hand, the phosphogypsums by-produced in dihydrate process have an agglomerated form and contain a large amount of impurities which can not be removed by a simple washing with water.
    (3) The heat liberation curves of hydration of portland cement containing various phosphogypsums and various artificial phosphogypsums showed that (a) the impurities in phosphogypsums mainly retard the hydration of alite phase, (b) the retarding action of water-soluble F is larger than that of the water-soluble P2O5 and (c) the dormant period of hydration of portland cement is prolonged by the action of impurities, however, the essential part of hydration of alite is scarcely affected.
    These tendencies were also confirmed by the measurement of specific surface area of hydration products of portland cement paste containing phosphogypsums and artificial phosphogypsums.
    (4) The authors suggested that the retarding action of the water-soluble impurities is caused by the formation of protective film of the difficult soluble compounds resulted from the reaction between the water-soluble impurities and the high-lime surface of cement grains. In high-lime solution of cement-water system, the water-soluble P2O5 forms the difficult soluble basic hydrates of calcium phosphate and sodium silicofluoride as the watersoluble F forms calcium fluoride, silicic acid gel and calcium silicate hydrates. These reaction products are gel-like fine particle and will temporalily coat the surface of cement grains.
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  • 1968 Volume 76 Issue 876 Pages 263
    Published: 1968
    Released on J-STAGE: April 30, 2010
    JOURNAL FREE ACCESS
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  • Michio INAGAKI, Shin-ichi HIRANO, Hajime SAITO
    1968 Volume 76 Issue 876 Pages 264-268
    Published: August 01, 1968
    Released on J-STAGE: April 30, 2010
    JOURNAL FREE ACCESS
    The pressure in a simple piston-cylinder type apparatus was calibrated by detecting volume change associated with polymorphic transformation of the specimen as the change of inductance of high frequency coil wound on the specimen. The flow of pressure transmittor of pyrophyllite during compression was also studied by means of the same method. Specimens used were KNO3 and AgI, which were known to have the transformation at a pressure of 3.6 and 3.0 kbar at room temperature, respectively. Results are summarized as follows:
    (1) The transformtion points of the specimens were measured with good accuracy and reproducibility in spite of a small volume of specimen, about 8.7% of the total volume of pressure cell. (2) Loss of pressure in the present high pressure apparatus and arrangement of pressure cell was as small as about 3%. This fact seemed to be caused from the reduction of friction between pistons and cylinder by using a Myler and asbestos composite paper and from pressure multiplication by the steel disks used. (3) At the moment pressure was reached 3 kbar, the flow of pyrophyllite was found to be completed. At 1 kbar, however, it required about 5 min. to complete the flow of pyrophyllite. The flow of pyrophyllite was greatly affected by the arrangement of pressure cell.
    The present method is expected to be used for detecting the transformation associated with the change in dielectric constant or magnetic susceptibility.
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  • Yoshizo INOMATA, Hiroshi KOMATSU, Zenzaburo INOUE, Mamoru MITOMO
    1968 Volume 76 Issue 876 Pages 268-276
    Published: August 01, 1968
    Released on J-STAGE: April 30, 2010
    JOURNAL FREE ACCESS
    The relation between structure of SiC and growth rate was studied at 2500°C experimentally. In this experiment, the setting of the growth condition was improved by limitting the zone of recrystallization in the growth cavity and supersaturation in the cavity was changed in several steps by the use of cavity wall and thermo-insulator.
    Summerized results are as follows;
    (1) In the region of low supersaturation (growth rate for the direction of a-axis less than 90 Å/sec), crystals having c-axis elongated columnar habit were obtained. These crystals were mainly pure 6 H type and have little stacking disorder along c-axis.
    In these region, there also obtained plate like crystals. These crystals often showed the coalescence of polytypes, but have little stacking disorder. This difference for the coalescence of several polytypes and crystal habit seemed to depend on the orientation of crystals in the growth cavity.
    (2) In the region of high supersaturation (growth rate for the direction of a-axis greater than 90 Å/sec), well developed hexagonal plate like crystals were obtained. These crystals frequently showed the coalescence of polytypes and stacking disorder along c-axis.
    (3) Obtained crystals in this experiment were mainly 6 H and 15 R type and almost all crystals include 6 H structure.
    4 H and 21 R showed smaller relative amount than 6 H and 15 R. Long c-period structure were also found, but all of these showed stacking disorder along c-axis and coalescence with 6 H.
    (4) Accurate memory of stacking for the columnar crystals seemed to depend on screw dislocations which have the end on the (0001) surface that showing higher growth rate. In this experiment, some of these crystals showed a few growth spirals on their (0001) surface located on the top of these crystals.
    On the contrary, (0001) surface of plate like crystals grown in the high supersatulation region, together growth spirals, the existence of two-dimensional growth layers were frequently observed.
    (5) Corresponding to the phenomenons shown (1), (2) and (4), the value, about 1.2-1.4% was calculated for the critical supersaturation at 2500°C.
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  • Toru OGURA, Ryozo HAYAMI, Masatane KADOTA
    1968 Volume 76 Issue 876 Pages 277-284
    Published: August 01, 1968
    Released on J-STAGE: April 30, 2010
    JOURNAL FREE ACCESS
    Crystallization of the Li2O⋅(1.5-3.5) SiO2 glasses were followed by DTA, X-ray examination, optical- and electron-microscopic observations. Mechanism of the crystallization process was proposed in connection with microstructure of glasses.
    Generally, crystallization initiated at the glass surface, except Li2O⋅1.5SiO2, with zero induction period, and grew at constant rate with time at the temperatures 550°-640°C. Li2O⋅1.5SiO2 glass nucleated a number of crystals inside at any given temperature, and the determination of the thickness of crystallized layer was practically impossible.
    Crystallization of the glasses proceeded mainly in accordance with the phase diagram. For 1.5 and 1.75SiO2 glasses, crystalline phases were Li2O⋅SiO2 and Li2O⋅2SiO2, and for (2.0-3.5) SiO2 glasses, Li2O⋅2SiO2 was the only detectable crystalline phase.
    DTA suggested that exothermic peak due to crystallization appeared at higher temperature with increasing SiO2 content, but (2.5-3.5) SiO2 glasses had their peaks at exactly same temperature.
    Rate of crystallization was largest for Li2O⋅1.75SiO2 glass and decreased with increasing of SiO2 content. However, for (2.5-3.5) SiO2, rates were substantially identical: 1×10-7cm/sec at 550°C, 1×10-6cm/sec at 600°C and 3×10-6cm/sec at 630°C. Crystallization rate of Li2O⋅2SiO2 and Li2O⋅1.75SiO2 glasses were 2.5-3.0 and 3.5-4.0 times larger respectively compared with the values described above at all over the temperature range examined.
    Activation energies in the range 61-74kcal/mole were obtained.
    Electron-microscopic observations suggested that Li2O⋅(1.5-2.0)SiO2 glasses had homogeneous structure, but (2.5-3.5) SiO2 glasses heterogeneous even immediatly after the normal air quenching of melts.
    Consequently, it is conceivable that the rate of crystallization is more a consequence of microstructure in glass than of their bulk compositions as far as (2.5-3.5) SiO2 glasses concern.
    X-ray showed that Li2O⋅2SiO2 crystals nucleated at glass surface grew inward along c-axis.
    Crystallization of heterogeneous structure glasses proceeded only at the matrix part just as if it proceeded in single phase glass, i.e. independently to the existence of dispersed particles.
    Chemical composition of matrix glasses is believable to be almost exactly same for (2.5-3.5) SiO2 glasses and to be close to Li2O⋅2SiO2. Determination of crystallization rate, however, suggested that it is not identical to Li2O⋅2SiO2 but must be somehow rich in SiO2, i.e. some very limited composition between Li2O⋅2SiO2 and Li2O⋅2.5SiO2. Excess SiO2 in matrix glass is conceivable to form solid solution with Li2O⋅2SiO2.
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  • [in Japanese], [in Japanese], [in Japanese]
    1968 Volume 76 Issue 876 Pages 285-286
    Published: August 01, 1968
    Released on J-STAGE: April 30, 2010
    JOURNAL FREE ACCESS
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  • 1968 Volume 76 Issue 876 Pages A59-A65
    Published: August 01, 1968
    Released on J-STAGE: April 30, 2010
    JOURNAL FREE ACCESS
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