GLASS TRANSITION AS A FUNCTION OF COOLING RATE

On décrit une méthode permettant le calcul des relaxations de structure dans des verres refroidis très rapidement. L'obstacle majeur dans le modèle original a été l'hypothèse d'une loi d'Arrhenius pour la viscosité à l'équilibre. Ici on emploie l'équation de Macedo-Litovitz pour la viscosité à l'équilibre. On montre que la zone de transition vitreuse est déplacée vers les hautes températures et s'élargit quand on augmente la vitesse de refroidissement. Les verres à Tg élevé e.g. SiO2 ont une zone de transition vitreuse plus large que les verres de Tg plus bas mais avec une énergie d'activation similaire.The method is described for calculating structural relaxation in glasses cooled very rapidly. The major obstacle for the calculation was the assumption in the original model of Arrhenius behavior for the equilibrium viscosity. In this paper the Macedo-Litovitz' hybrid equation is used for the equilibrium viscosity. The glass transition region is shown to shift to higher temperatures and to broaden as the cooling rate increases. Glasses with higher Tg e.g. SiO2 are shown to have broader glass transition region than glasses with lower Tg but similar activation energy

Definition of the strain-stress distribution of porous glass in the retarded cooling temperature range

The estimation of the strain-stress distribution (SSD) of porous glass (foamed slag glass, FSG) is assessed by annealing temperature curves according to the given values of the thermomechanical and thermophysical properties of porous glass, which are in correlation with the properties data of the host glass and its structure. When calculating cooling processes (cooling rate) of porous glass products, the A.N. Dauvalter's formula, which takes into account only the stresses arising from the safe product cooling, but does not take into account those that remained there to the cooling start point, is usually used. The cooling rate in the interval of the annealing zone itself should be sufficiently low so that residual stresses, arising after they pass it, have small values. Since methods, that make it possible to determine the residual stresses that appear in the porous glass after passing through the initial annealing zone, are currently poorly developed, numerical simulation methods should be used to determine the porous glass SSD under the influence of thermal loads. Numerical study of the strain-stress distribution of porous glass allowing for thermal loads in the annealing temperature range was carried out in the Ansys Workbench software package