The kinetic fragility of liquids as manifestation of the elastic softening

We show that the fragility $m$, the steepness of the viscosity and relaxation time close to the vitrification, increases with the degree of elastic softening, i.e. the decrease of the elastic modulus with increasing temperature, in universal way. This provides a novel connection between the thermodynamics, via the modulus, and the kinetics. The finding is evidenced by numerical simulations and comparison with the experimental data of glassformers with widely different fragilities ($33 \le m \le 115$), leading to a fragility-independent elastic master curve extending over eighteen decades in viscosity and relaxation time. The master curve is accounted for by a cavity model pointing out the roles of both the available free volume and the cage softness. A major implication of our findings is that ultraslow relaxations, hardly characterised experimentally, become predictable by linear elasticity. As an example, the viscosity of supercooled silica is derived over about fifteen decades with no adjustable parameters.Comment: 7 pages, 6 figures; Added new results, improved the theoretical sectio

MECHANISMS OF INITIAL SINTERING OF A FINE ALUMINA POWDER

Nous avons étudié par microscopie électronique et diffraction des rayons X le mécanisme du frittage de l'alumine. La transformation de l'alumine gamma en alumine alpha influence la vitesse de frittage. Cette transformation semble entraîner la déformation plastique de l'alumine. L'énergie d'activation que l'on mesure pour le frittage de la poudre d'alumine alpha est comparable à celle de la diffusion d'oxygène dans les joints de grains.The mechanism of initial sintering of alumina was explored by electron microscopy and X-ray diffraction. The transformation of gamma to alpha alumina influenced sintering behavior. This transformation appears to involve plastic deformation in the alumina. Sintering of fine alpha alumina powder directly occurs with an activation energy close to that of grain boundary diffusion of oxygen