CHANGES IN ELASTICITY AND VISCOSITY OF A SIYALON GLASS DURING STRUCTURAL RELAXATION IN THE TRANSFORMATION RANGE

Ultrasonic echography and a three-point bending creep test have been u sed to study the change in Young's modulus, E, and viscosity, eta, dur ing the structural relaxation of a SiYAlON glass at 870 degrees C, i.e ., 40 degrees C below the glass transition temperature. The increase i n viscosity has been discussed and modelled in the frame of the fictiv e temperature theory and a relatively good fitting has been obtained b etween calculation and experimental results. In addition to the evolut ion of E and eta, Raman scattering measurement are presented, which br ings to light a microstructural change during the relaxation process.