Li2O-ZnO-Al2O3-SiO2系ガラスの結晶化の研究
1961 年 69 巻 784 号 p. 109-118
詳細
1961 年 69 巻 784 号 p. 109-118
Studies were carried out for the purpose of finding out the range of compositions in the system Li2O-ZnO-Al2O3-SiO2, in which the change by rehearing to polycrystalline bodies occurs without acccompanying the defects as flaw and crease, and of measuring properties of the devitrified glasses.
The results obtained are as follows:
1) Changing the Li2O content as 4, 6, 8, 12 and 16 against ZnO+Al2O3+SiO2=100 the range, in which the batches may be melted at 1300-1400°C to clear glasses and produce perfect polycrystalline specimens by reheating, was determined.
2) Occasionally, above specimens supported by two knife edges deformed by their own weight during the reheating. When Li2O content was as low as 4, 6, 8 the amount of ZnO has proved to be most influential in the deformation, and it was confirmed that such trend was becomming smaller with the increasing amount of ZnO.
3) The differential thermal and X-ray analyses have disclosed that from the specimens of low Li2O (4, 6, 8) the primary crystals were ZnO-compounds such as 2ZnO⋅SiO2, while from those of high Li2O the primary crystalline phase was composed of lithium compounds such as Li2O⋅2SiO2.
When the repeating was carried out at higher temperatures, i.e., 50-100°C below the deformation temperature of polycrystalline specimens, the crystals were composed of willemite, β-eucryptite, β-spodumene, cristobalite, quartz, and lithium mono- and di-silicates, having the size of 1-2μ measured under microscope.
4) The bending strength of polycrystalline specimens changed in a high degree by composition (Fig. 4., Table 5). Although there seemed to exist no simple relation between the composition and the bending strength, the values of those of low alkali (Li2O=4, 6, 8) and Al2O3=0 gave the exceptionally low values, which probably due to the existence of minute hair cracks came from the abnormal volume change at around 250°C of cristobalite formed in large amount in the specimens during the repeating.
5) The amount of Al2O3 produced a large effect on the thermal expansion of the specimens in the composition range given above. There was a trend that the expansion coefficient became smaller with the increase of Al2O3 content (Fig. 5 and Table 6). Especially, high Al2O3 glasses containing small amount of Li2O (=4 and 6) gave the products having exceedingly low expansion coefficient (5.4×10-7). The specimens of Al2O3=0 have larger expansion coefficient. This may be interpreted by the formation of cristobalite having large expansion coefficent instead of β-eucriptite which lowers the expansion of devitrified products.
