A. Buri

Surface and bulk crystallization in non-isothermal devitrification of glasses

Abstract The surface and bulk crystallization of Li 2 O · 2 SiO 2 glass has been studied by differential thermal analysis and the influence of the specific surface area of the sample and the nucleation heat treatment on the crystallization kinetics is pointed out. The kinetic parameters were also evaluated from the DTA curves and related to the crystallization mechanism. The results agree well with the isothermal data reported in the literature.

Evaluation of glass stability from non-isothermal kinetic data

Abstract Non-isothermal devitrification of 1.1Li 2 O·1.9SiO 2 glass has been studied and is compared with that of Li 2 O·2SiO 2 glass reported in the literature. In both cases the devitrification mechanism appears to be controlled by the crystal-glass interface reaction. The maximum nucleation rate temperature is, also, the same. With respect to the Li 2 O·2SiO 2 glass, the crystal growth activation energy, E c , is slightly greater and the DTA devitrification peaks are shifted towards lower temperatures. If T p is the devitrification peak temperature on a DTA curve recorded under conveniently selected experimental conditions, a dimensionless parameter, E c / RT p , can be defined which can be used to compare the devitrification tendency of different glass compositions. The glass studied has a greater value of E c / RT p with respect to the parent glass and in the light of the present work thus shows a lower thermal stability.

Nucleation and crystal growth in Na2O · 2 CaO · 3 SiO2 glass: a DTA study

Abstract The non-isothermal devitrification of Na 2 O · 2 CaO · 3 SiO 2 glass has been studied by differential thermal analysis in order to evaluate, from DTA curves, the temperature of maximum nucleation rate, T m , and the activation energy values, E c , for crystal growth. The temperature, T m =580°C, is very close to the glass transition temperature, T g =570°C, and the value of E c =78 Kcal mole −1 for the surface crystal growth is nearly the same as the value E c =89 kcal mole −1 for the bulk crystal growth; both are consistent with the activation energy for viscous flow. It is also pointed out that the nucleation rate—temperature curve and the crystallization rate—temperature curve are partially overlapped.

Structure and devitrification behaviour of sodium, lithium and barium borophosphate glasses

Thermal properties and devitrification behaviour of sodium, lithium and barium borophosphate glasses have been studied by differential thermal analysis. The results are in good agreement with the hypothesis that BO 4 groups form when a network modifier oxide (Na 2 O or Li 2 O or BaO) is added to B 2 O 3 . The excess of negative charge is compensated by metallic cations or positively charged PO 4 groups. Activation energy for crystal growth and devitrification mechanism under non isotermal condition in sodium, lithium and barium metaphosphate glasses were also evaluated.

Kinetics of crystal growth in Na2O · 2 SiO2 glass. A DTA study

Abstract The non-isothermal devitrification of Na 2 O·2 SiO 2 glass is investigated by differential thermal analysis (DTA). The kinetic parameters for the viscous flow of the glass and the temperature of maximum crystallization rate are evaluated from DTA curves. The limits of the Arrhenius-type relationship between the rate constant of crystal growth and the absolute temperature are also discussed.

Glass transition temperature and devitrification behaviour of glasses in the Li2SiO3Na2SiO3 composition range

Abstract A series of glasses in the lithium metasilicate-sodium metasilicate composition range was studied by differential thermal analysis and X-ray diffraction. The effect of replacing LiO2 by Na2O on the glass transition temperature and devitrification behaviour has been determined. The crystallizing phases have been identified and related to the devitrification mechanism. Kinetic parameters for nucleation and crystal growth were estimated from DTA curves.

Nucleation in glass-forming systems. A DTA study.

Abstract A simple method recently proposed (ref. 1) for evaluating the temperature of maximum nucleation rate is applied to several different glass-forming systems. The results well agree with those obtained by means of traditional methods.

The non-isothermal devitrification of Na2O · 2 SiO2 gel-glass

Abstract The non-isothermal devitrification of Na 2 O · 2 SiO 2 glass prepared by gel-glass transformation is investigated by differential thermal analysis. The glass transition temperature, T g , and the activation energy, E , for the crystal growth are evaluated from DTA and DDTA curves. The results are compared with those obtained for Na 2 O · 2 SiO 2 prepared by fusion of oxides. The influence of the specific surface area of the samples on devitrification kinetics is also discussed.

Nucleation and crystal growth in a 0.9Li2O · O.1BaO · 2SiO2 glass: a DTA study

Abstract The devitrification behaviour of a 0.9Li 2 O· 0.1BaO· 2SiO 2 glass has been studied by differential thermal analysis in order to evaluate the effect of substitution of a small amount of BaO for Li 2 O on the nucleation and the growth kinetics of lithium disilicate crystals. The value of the activation energy for crystal growth is very close to that for crystal growth in a lithium disilicate glass. A method for evaluating the effect of heat treatments in the nucleation temperature range on bulk crystallization kinetics is also proposed. The results suggest that the bulk nucleation rate of lithium disilicate crystals is lowered remarkably by the presence of BaO.

A new parameter to evaluate nucleation in glasses from DTA curves

Abstract Non-isothermal kinetic data relative to five silicate glasses are compared. The analysis of data suggests the use of a new parameter to obtain a rough estimate of the ability of different glass compositions to form nuclei and to select glass compositions which can, easily, give fine-grained glass ceramics.