Recrystallization phenomena of solution grown paraffin dendrites

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) and pentacosane (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.