Following a previous report “Studies of the Glass-formation Range of Borate Systems” (This Journal, 69, 282 (1961)), we studied the glass-formation range of silicate systems. Although silicate glasses have long been used, sufficient systematic studies of the glassformation ranges of silicate systems have not yet been made.
In this experiment, 1/80 mole (about 1g.) of materials were melted in crucibles made of pure platinum or platinum containing 20% rhodium at temperatures from 1400° to 1750°C. The oxides used besides SiO₂ were 16 kinds of the oxides of a-group elements namely Li, Na, K, Be, Mg, Ca, Sr, Ba, Al, La, Ti, Zr, Th, Nb, Ta and W.
The glass-formation ranges of binary silicate systems are shown in Table 1. These ranges differ in some points from those of borate systems. For instance, the La-silicate system has no vitrified range, while the Mg-silicate system has a wider glass-formation range than the borate. Whether a component ion enters into the glass structure as a modifier or as a network-former depends on the acidity of the glass-former and on the electronegativity of the component ion. In silicate systems, however, the actual range of glass-formation equals the difference between the glass-formation range and the immiscible range. If the latter is equal to the former or somewhat wider, the vitrified range will disappear.
The glass-formation ranges of ternary systems are shown in Fig. 1-34. The whole number of the studied systems reached about one hundred. The Experimental results show that the actual glass-formation ranges agree with the range (hatched areas in the figures) to be expected from the “Conditions of Glass-formation” (This Journaj, 67, 364 (1959)). Among these systems, the systems containing TiO₂ (cf. Figs. 12 and 13) are remarkably different from the corresponding borate systems. In the borate systems, a glass-fromation range spreads on the right side of the SiO₂-D line (cf. Fig. 10), and therefore it has been estimated that the co-ordination number of Ti⁴⁺ is 6. (In order for the Ti⁴⁺ ion to take 6-co-ordination as a network-former, the modifier of divalency must also be present, therefor, in the area on the left of the SiO₂-D line glass-formation is impossible.) However, in the silicate system the limited line of SiO₂-D is lacking. Consequently, it is concluded that the Ti⁴⁺ ion as well as the Si⁴⁺ ion takes the 4-co-ordination. The glass-formation range of the TiO₂-containing systems are shown in the hatched areas of Figs. 12 and 13, which are limited by the AD line.
The WO₃-containing silicate systems have a remarkably narrow glass-formation range compared with borate systems. The vitrified range of the B₂O₃-WO₃-alkali oxide system has two feet, but the silicate system, we suppose, lacks the left foot. Moreover, it is considered that the left foot consists of WO₃ and alkali borate in borate systems, but that this part becomes immiscible in silicate systems.
According to the devitrification of the binary system, La₂O₃ systems are classified as C-type ternary systems, and their glass-formation ranges are narrower than those of borate systems. The vitrified range of the SiO₂-Al₂O₃-La₂O₃ system (cf. Fig. 29) agrees with that of the corresponding borate system, but the limiting line, kl, of the immiscible range is lower than that of the borate and, accordingly the glass-formation range of the former is narrower than that of the latter. Other La-silicate systems are similar. Among the C-type ternary systems containing ThO₂ or Al₂O₃, which have vitrified ranges in case of the corresponding borate systems, we found the glassy state only in the SiO₂

抄録全体を表示

Microstructure of partly stabilized zirconia from Norton Company and perfectly stabilized zirconia was examined by means of polarization microscope and X-ray diffraction. A mechanism of the partial stabilization of zirconia was inferred from the results obtained with the aid of the phase diagram of the binary system CaO-ZrO₂.
Norton's partly stabilized zirconia is an aggregate of 1000-1500μ massive grains, each consisting of optically anomalous cubic zirconia showing birefringence, 5-10μ in diameter, and of monoclinic zirconia, a few or sometimes 6-10μ in diameter, all of which arranged nealy parallel to some crystallographic directions. Stabilized zirconia consists of cubic zirconia and a little amounts of monoclinic zirconia. It contains further a few glassy matrix and crystallites of a kind of gehlenite-akermanite solid solutions, i.e., melilite group minerals deposited in it.
Lime content of the Norton's sample is lower than that of the stabilized zirconia, but lime solubility in the cubic zirconia seems to be much larger in the former than in the latter. These results were discussed with the aid of phase diagram of the system CaO-ZrO₂, and it was concluded that the main process of the partial stabilization of zirconia was the exolution of tetragonal zirconia into cubic and monoclinic modifications. The exolution occurring in solid state is very difficult to reach the equilibrium, and is governed strongly by cooling condition. The faster the cooling rate, the larger the deviation from the equilibrium and the lower the solubility of lime into the cubic zirconia formed. Therefore, on the one hand the properties of the partially stabilized zirconia can be controlled with cooling conditions, on the other hand the zirconia grains seems to contain some unstable parts. If it is the case, some problems seem to exist in the use of the partially stabilized zirconia and of lime as the stabilizer of cubic zirconia.

抄録全体を表示

The stability of the forsterite porcelian in hydrogen at high temperatures, which is required in the application of the forsterite porcelain to a high frequency insulator, is governed by additives used to promote sintering. Among several additives examined kaolin has the effect to make the porcelain stable in hydrogen at high temperatures, so giving it favorable properties for Mo-Mn metallizing processed under such conditions.
In this paper 0-10% of kaolin was added to forsterite porcelains which were prepared from Fukushima siliceous stone and sea-water magnesia in the molar ratio of MgO: SiO₂=2:1.
By the addition of kaolin the temperature range for sintering was remarkably extended and the firing shrinkage was almost constant within this range. The coefficient of linear thermal expansion decreased with the increase of added kaolin, and no considerable change was found by repeated heat treatments. With the increase of kaolin content from 0 to 10%, the softening temperature under load lowered to 1160°C from 1280°C. The electric resistance at elevated temperatures lowered gradually, but was still sufficiently high for practical use. The flexural strength decreased and the modulus of elasticity lowered gradually in the temperature range from room temperature to 300°C with the increase of kaolin content. The modulus of elasticity, however, became larger with the rise of temperature in this temperature range.
Within 5% of kaolin added, the dielectric constant and dielectric loss were unvaried and these values were excellent for the high frequency insulator.
The result of X-ray diffraction gave only the pattern of the forsterite. By microscopic observation, forsterite crystal grain changed from allotriomorphic into idiomorphic and glass matrix increased with the kaolin content.
It is concluded that the addition of 2.5-5.0% of kaolin was most suitable for preparing the forsterite porcelain for this purpose.

抄録全体を表示