62 research outputs found
The kinetic fragility of liquids as manifestation of the elastic softening
We show that the fragility , 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 (), 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
Surface -OH Profile from Reaction of a Heavy-Metal Fluoride Glass with Atmospheric Water
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