The structural role of different cations in inorg. glasses is compared by measuring the glass transition temps. and relating them to field strength and coordination. The hypotheses confirmed by thermal expansion measurements and by identifying the crystg. phases. The results on Na2iO-M2O3-SiO2 (M=Ga, In, Sc, Y, La) glasses show that Sc+3, Y+3, La+3, and In+3 are linked to oxygens by non-directional bonds, with high ionicity degrees and coordination and, compared to Na+, raise the degree of cross-linking and the O d. Conversely, Ga+3 is tetrahedrally linked by more covalent bonds. The temp. of max. nucleation rate and the kinetic parameters for crystal growth in glasses are estd. by DTA measurements. On the basis of the Johnson-Mehl-Avrami equation, -In (1-α)=(kt)n, the activation energy and a parameter related to the mechanism of the process are evaluated. A simple method, based on the shift of the DTA crystn.-peak, is described to evaluate the influence of temp. and time of heat-treatments on bulk nucleation.

Thermal evolution of inoganic glasses: glass transition temperature, phase separation, nucleation and crystal growth / A., Buri; A., Marotta; Saiello, Silvana; Branda, Francesco; D., Caferra. - In: GAZZETTA CHIMICA ITALIANA. - ISSN 0016-5603. - ELETTRONICO. - 112:(1982), pp. 65-70.

Thermal evolution of inoganic glasses: glass transition temperature, phase separation, nucleation and crystal growth

SAIELLO, SILVANA;BRANDA, FRANCESCO;
1982

Abstract

The structural role of different cations in inorg. glasses is compared by measuring the glass transition temps. and relating them to field strength and coordination. The hypotheses confirmed by thermal expansion measurements and by identifying the crystg. phases. The results on Na2iO-M2O3-SiO2 (M=Ga, In, Sc, Y, La) glasses show that Sc+3, Y+3, La+3, and In+3 are linked to oxygens by non-directional bonds, with high ionicity degrees and coordination and, compared to Na+, raise the degree of cross-linking and the O d. Conversely, Ga+3 is tetrahedrally linked by more covalent bonds. The temp. of max. nucleation rate and the kinetic parameters for crystal growth in glasses are estd. by DTA measurements. On the basis of the Johnson-Mehl-Avrami equation, -In (1-α)=(kt)n, the activation energy and a parameter related to the mechanism of the process are evaluated. A simple method, based on the shift of the DTA crystn.-peak, is described to evaluate the influence of temp. and time of heat-treatments on bulk nucleation.
1982
Thermal evolution of inoganic glasses: glass transition temperature, phase separation, nucleation and crystal growth / A., Buri; A., Marotta; Saiello, Silvana; Branda, Francesco; D., Caferra. - In: GAZZETTA CHIMICA ITALIANA. - ISSN 0016-5603. - ELETTRONICO. - 112:(1982), pp. 65-70.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11588/490441
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