Abstract
Paraffin crystals were grown from decane
solutions using a micro-Bridgman set up for in-situ observation of the
morphology at the growth front. It is shown that for large imposed velocities,
dendrites are obtained. After dendritic growth, aging or recrystallization
processes set in rather quickly, changing the crystal shapes considerably
from the well-known dendritic shapes of melt grown dendrites. It is shown
that several factors may cause these post-growth shape transitions: surface
minimization, uptake and subsequent sweating of solvent material, and polymorphic
phase conversion. It is shown that the first two recrystallization mechanisms
are the most important for tricosane (n-C23H48) andpentacosane (n-C25H52)
dendrites. Surface minimization by increasing the thickness of the crystals
is particularly favorable. For dotriacontane (n-C32H66) dendrites, the
recrystallization behavior appears to be less dramatic. It is shown that
the uptake and sweating out of solvent material afterwards may lead to
formation of holes within the dendrites.