PHYSICAL CHEMISTRY

S. M. BREKHOVSKIKH, L. M. LANDA, N. I. CHUBKINA

CHANGE IN THE PHASE COMPOSITION OF GLASS-CERAMICS UNDER THE ACTION OF $\gamma$ RAYS

(Presented by Academician N. N. Semenov, 10 March 1964)

In studying the effect of $\gamma$ rays on glass-ceramics of the lithium aluminosilicate system, we discovered a new effect, consisting in the fact that $\gamma$ radiation is capable of exerting a direct influence on the phase composition of glass-ceramics.

A transparent glass-ceramic whose crystalline phase we identified as $\beta$-eucryptite was irradiated with $\gamma$ rays from a Co$^{60}$ source.

Fig. 1. X-ray diffraction patterns of glass-ceramic A: A — unirradiated; Б — irradiated with a dose of $10^2$ r; В — irradiated with a dose of $10^3$ r; Г — irradiated with a dose of $10^5$ r.

Irradiation doses were $10^2$, $10^3$, and $10^5$ r. X-ray diffraction patterns of the unirradiated glass-ceramic and after irradiation with different doses were obtained on a URS-50 apparatus using copper radiation (Fig. 1). Recording of a standard sample shows the constancy of the conditions for obtaining the X-ray diffraction patterns. Already at the first irradiation dose, $10^2$ r, two phenomena are noticeable in the X-ray diffraction pattern (Fig. 1, Б). First, the intensity of the $\beta$-eucryptite lines increased, which indicates an increase in its amount. The ratio of the line intensities in the X-ray diffraction pattern—

max of the unirradiated and irradiated glass-ceramics is 0.8–0.85. Second, the line corresponding to an interplanar spacing of 3.49 Å began to split, and a peak corresponding to \(d = 3.34\) Å appeared, which corresponds to the most intense line of \(\alpha\)-quartz. This maximum is expressed extremely weakly in Fig. 1, Б, and it might be overlooked; but on the X-ray diffraction pattern of the glass-ceramic irradiated with \(10^3\) r (Fig. 1, В), it is quite clearly visible, since the intensity of this maximum has increased noticeably. Upon further irradiation, the intensity of the \(\beta\)-eucryptite lines does not change.

Fig. 2. X-ray diffraction patterns of glass-ceramic B: A — unirradiated, Б — irradiated with a dose of \(10^5\) r

On the X-ray diffraction pattern of the glass-ceramic irradiated with \(10^5\) r (Fig. 1, Г), a maximum is visible corresponding to \(d = 4.25\) Å, i.e., to the second most intense line of \(\alpha\)-quartz. The same effect was also observed by us in another glass-ceramic of similar composition.

The X-ray diffraction patterns of the second glass-ceramic, unirradiated and irradiated with a dose of \(10^5\) r, are shown in Fig. 2. It is possible that the effect observed is explained as follows: \(\alpha\)-quartz is also present in the unirradiated glass-ceramic, but in an amount not detectable by X-ray phase analysis. In support of this assertion is also the “step” on diffraction pattern 2, A, corresponding to the line \(d = 3.34\) Å, which is easily overlooked.

Under the action of irradiation, the amount of the crystalline phase—the principal phase and \(\alpha\)-quartz—increases; i.e., the energy of the \(\gamma\)-rays leads to the phase transition glass \(\to\) crystal. The increase in the crystalline phase probably occurs not through the precipitation of new crystallites, but as a result of the growth of crystals already present.

In connection with the observed effect, the question arises whether the phase transition occurs as a result of local heating in the glass-ceramic upon absorption of \(\gamma\)-rays, or whether it takes place at room temperature and we are dealing here with a new mechanism of crystal formation in glass.

Received
10 III 1964