The continuous-dilatometric method for the measurement of the change of dimension during the firing of the equimolecular mixture of BaCO₃ and TiO₂, the X-ray diffraction for following after the reaction and the formation of BaTiO₃, and the electron microscope for the observation of the progress of grain growth, were used for the investigation of the relation between the growth of microcrystals and some electric properties, especially the D. C. break down voltage and hysteresis curves with results as follows:
(1) BaTiO₃ was formed from about 700°C and finished at the temperature of maximum expansion (at about 1100°C), which suggest the existence of a close relation between the anomalous expansion and the formation of BaTiO₃.
(2) The microcrystals began to grow from about 1250°C, which was accompanied by the rapid increase of relative permittivity. The Curie point, however, remained unaffected by the change of firing temperature from 1200°-1400°C.
(3) The trend of rather decreasing break down voltage by the overgrowth of the microcrystals was observed.
The relation between the break down voltage and the thickness of the specimen and the holding time at the maximum firing temperature (1360°C) was found to be expressed by;
2 hrs holding V_c 2hr=9×d^0.726 (kV)
16 hrs holding V_c 16hr=6.7×d^0.788 (kV),
where V_c is the break down voltage, and d the thickness in mm.
(4) Hysteresis curves showed that space charge polarization is more liable to occur by the incomplete growth of microcrystals.

抄録全体を表示

Some uncertainties are often introduced in the measurement of electromotive force of the concentration cells of molten silicates owing to the unknown e. m. f. between the reference electrodes (R_f) and electrolyte.
The measurement may be improved if two semipermeable bridges, one (M_R) permeable to cation R, and the other (M₀) permeable to O^2-, are introduced at the liquid-liquid interfaces of two cells,
R_fI/silicate I/M_R/silicate II/R_fII…(1)
R_fI/silicate I/M₀/silicate II/R_fII…(2)
The unknown e. m. f. may be eliminated by taking the difference of e. m. f.'s of above two cells, and thus taking out the net values of potential corresponding the transfer of R_nO_m between two electrolites.
This method was applied to the concentration cell of Na₂O whose electrolyte was the molten sodium silicate of the concentration of 5 and 20 mole% with the bridge (M₀) of stabilized zirconia (Zr_0.85Ca_0.15O_1.85) which proved as having many merits. M_R may be excluded, since there is only one carrier cation Na⁺, and e. m. f. was measured at the temperatures 900°-1300°C
From the results obtained the differences of the values of chemical potential and of the entropy of mixing of both glasses. And from the change of the entropy of mixing with temperature the author concluded that the arrangement of Na₂O, or the structure of molten glass, there would be a transformation between the low temperature type and a more random arrangement at about liquidus temperature of the binary equilibrium diagram.

抄録全体を表示

The grain growth of alumina at 1600°-1960°C in various atmospheres, such as vacuum, wet or dry hydrogen, carbon monoxide, argon and air was investigated.
The accelerating effect of hydrogen was observed in the surface layer of the specimens sintered at the temperatures higher than 1700°C. Dry hydrogen proved to be the most effective, while that loaded with moisture gave a little lower values.
The grain growth of alumina sintered in CO at higher temperatures than 1900°C was investigated with a result showing that the accelerating effect was next to hydrogen.
Little difference could be observed in the grain growth of the specimens sintered in vacuum and in air.
Argon accerelated the growth a little more than vacuum, although the effect was smaller than that of CO.
The authors concluded that the mechanism could be represented by
O^2-(l)_??__??_o^2-+1/2O₂(g)+2_??_
This equation shows that the rate of diffusion of O^2- may be accelerated with the increasing number of O^2- vacancies in the crystal which is liable to be affected by the atmospheric conditions.

抄録全体を表示