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

Abstract 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 B 2 O 3 glass. Samples were obtained by melting the B 2 O 3 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 B 2 O 3 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 B 2 O 3 glass, respectively.