Li_2O-MgO-Al_2O_3-SiO_2系ガラス結晶化物の強度に及ぼす加熱処理条件の影響

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In the previous paper (J. Ceram. Assoc. Japan, 68 [10] 223 (1960)) the authors reported that some glasses of low lithium content (4%) in the system Li2O-MgO-Al2O3-SiO2 could be converted, by the heat treatment, into a polycrystalline material without showing any appreciable deformation even if no special nucleating agent, such as platinum, was added. The present paper contains the results of experiments designed to determine the optimum conditions of heat treatment of the glass of this type for producing a polycrystalline material of high mechanical strength.(1) Chemical composition of the glass studied The glasses of the composition, MgO x, Al2O3 y, SiO2 z, Li2O 4, where x+y+z=100 by weight, were melted and formed into a specimen of the size 2.5×5×50mm. They were heated from room temperature to 1200°C with the rate of 5°C/min. and then held there for two hours. Among the polycrystalline materials, the one produced from a glass of the composition of Li2O 4, MgO 15, Al2O323, SiO262 showed the highest modulus of rupture (1, 550kg/cm2).(2) Process of cristallization of the glass during heat treatment Thermal differential and X-ray analysis made with the glass specimen of above composition showed that, during its heat treatment, β-eucryptite was first precipitated at about 850°C and then β-spodumene at about 1000°C (Fig. 9). Microscopic examination showed that β-spodumene, after its precipitation, decreased its grain size by fission, by still unknown reason, with increasing temperature (Fig. 10, b, c, d). Above 1000°C the marked increase in specific density of the specimen with increasing temperature was also observed (Fig. 12).(3) Effects of heat treatments on strength The conditions of heat treatment such as the heating rate and the maximum holding temperature were varied and their effects on the modulus of rupture of the resultant polycrystalline materials were determined. The slow heating with the rate at least below 5°C/min. in the temperature interval of 800 to 900°C, in which β-eucryptite was first precipitated in the specimen, was found to be necessary increasing the strength (Fig. 6). The specimen which missed this heat treatment had poor strength (Fig. 5). The strength was also found to increase with increasing the maximum holding temperature (Fig. 7). This change was attributed to the decrease in grain size of β-spodumene and also to the compacting of microstructure.
社団法人日本セラミックス協会の論文
1961-02-01

Li_2O-MgO-Al_2O_3-SiO_2系ガラス結晶化物の強度に及ぼす加熱処理条件の影響

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