CaO・TiO₂・SiO₂-Li₂O・Al₂O₃・4SiO₂-Li₂O・2SiO₂系デビトロセラムの研究

Devitrified ceramicsに関する研究

抄録

When an easily devitrifing glass including a small amount of metals such as gold, silver, or copper as nucleating agent is subjected to a stepwise heat treatment after being exposed to ultraviolet rays, X-rays, or γ-rays metal colloid separate out which act as nuclei for turning the whole mass into an assembly of minute crystallites. There are other possibilities of obtaining the same structure, i.e. by simple heat treatments making use of the characteristic property which is shown by titanium compounds etc. during the growth of crystals in glass phase. In this case such compounds act as nucleating agents.
It is the purpose of the present paper to form the “devitroceram” of the system CaO⋅TiO₂⋅SiO₂-Li₂O⋅Al₂O₃⋅4SiO₂-Li₂O⋅2SiO₂, to study the possibility of practical use, and based on the exprimental results, to investigate the influence of radiation on the process of devitrification.
For this purpose the glasses of about 20 different compositions (Fig. 1) were melted, which, after being exposed to ultraviolet rays, were subjected to differential thermal analysis, whose results were used to determine the conditions of the heat treatment.
The coefficients of thermal expansion of the devitroceram so obtained were determined, and X-ray analysis was carried out in order to know the nature of crystal phases.
Furthermore, a small number of samples were exposed to the different dosage of ultraviolet-, γ-, and X-rays, which were then given the heat treatment. They were investigated by X-ray analysis and by electronographic morphology in order to throw light on the influence of the different dosage of irradiation on the structure of devitrified mass.
The irradiation of ultraviolet rays seemed to play no important role on the result of thermal analysis, since the exothermic peak at 600°-800°C and the endothermic peak 200°-400°C above it (cf. Figs. 2, 3, 4) remained practically unchanged whether the glass was irradiated or not.
X-ray analysis of devitrified glass showed the existence of β-spodumene, calcium disilicate, lithium silicate and some other crystals (Table 2).
The coefficient of thermal expansion showed a marked fall by the heat treatment. And the nearer the composition came to Li₂O⋅Al₂O₃⋅4SiO₂ the lower was the coefficient, extending even to negative values (Fig. 8). That the expansion of devitroceram is in the same level or lower than that of low expansion glasses would come up to the expectation of the possibility of its practical use.
The results of X-ray analysis disclosed that the difference of the degree of crystallization in proportion to the difference of the dosage of irradiation was existing only in the samples quenched from the first heat treatment (cf. Figs. 9, 10-a, -b, -c, -d), while the samples received the first and second heat treatment gave no difference. The observation under electron-microscope revealed that the larger was the dosage of γ-rays the smaller became the grain size of crystallites. (cf. Fig. 11).