Glass - Back to the Future!



Presenting Author:
Alisson Mendes Rodrigues
<alisson_mendes@ymail.com>

article posted 04 April 2016


Alisson Mendes Rodrigues
Graduate in Chemistry – Brazil - 2008
Master in Engineer of Materials – Brazil – 2010
Doctor In Science and Engineer Materials – Brazil – 2014
Pos doc in University of Rostock – Germany – 2016






Isothermal and non-isothermal activation energy for crystal growth in a silicate glass

Alisson Mendes Rodrigues*, Daniel Roberto Cassar, Oscar Peitl and Edgar Dutra Zanotto.
CeRTEV – Center for Glass Research Technology and Education in Vitreous Materials (www.certev.ufscar.br)


In this work we tested whether the activation energy for crystal growth (EK) obtained by non-isothermal experiments is comparable to the lengthier but more trustable value (EC) obtained by isothermal experiments. The stoichiometric lead metasilicate (PbO.SiO2) glass was used. The non-isothermal activation energy was obtained from differential scanning calorimetry (DSC) experiments carried out using a relatively wide range of heating rates (5-150 ºC/min). From these experiments and using the Kissinger equation the resulting activation energy was EK = 273 ± 13 kJ.mol-1. On the other hand, a value of activation energy of EC = 265 ± 5 kJ.mol-1 resulted from the use of our own isothermal crystal growth rate data and also data measured by other authors. These values of activation energies so obtained are statistically equal, but some conditions must be met for reliable results: crystallization should occur from a constant number of nuclei; unidirectional crystal growth must take place; the growth mechanism should not change in the temperature range of measurements; and the used temperatures must be below the “decoupling” or “breakdown” temperature.


Fig. 1. Samples of lead metasilicate glass (PbO.SiO2) obtained by pouring the melt into a graphite mould. The samples were annealed at 350 °C (Tg = 406 ºC) for 3 hours.


Fig. 1. Kissinger plot for PbO.SiO2 glass obtained from the values of heating rates and crystallization peak temperatures.


Fig. 2. Ln(U) versus 1/T plot for temperature range 505oC–Td. The activation energy from slope is 267 ± 5 kJ.mol-1.