Glass transition, thermal expansion and relaxation in B2O3 glass measured by time-resolved X-ray diffraction

摘要

In situ heating experiments using high-energy, high-intensity synchrotron radiation, can be successfully designed to study structural evolution with temperature of glassy materials. Coherent diffraction from glassy materials forms a succession of halos or diffraction maxima in reciprocal space and the variation with temperature, of the wave-vector Q(max) or angular position of the first diffracted intensity I(Q(max)) maximum below T-g can be used to determine the iso-structural volume expansion. In the present work we have obtained synchrotron X-ray diffraction patterns in transmission during in situ heating of a B2O3 glass. Samples were obtained by melting the B2O3 glass rods which were then air-cooled or liquid nitrogen-cooled. The evolution with temperature (and time) of the position of the first diffraction maximum of the diffraction pattern accurately reflected the thermal expansion coefficient and the relaxation behavior of the B2O3 glass. Such results allowed determination by diffraction of the glass transition temperature, T-g, at 580 K, as well as information on the structural relaxation during thermal annealing. The total volume changes due to relaxation were measured to be about 1.5 vol.% and 2.5 vol.%, for the air-cooled and the liquid nitrogen-cooled B2O3 glass, respectively. (C) 2007 Elsevier B.V. All rights reserved.