When a substance can exist in more than one crystalline state it is said
to exhibit polymorphism. Two polymorphs have the same chemical composition
but different physical and chemical properties (solubility,
compressibility, melting point…) and then are considered as two different
materials. Thus it is crucial to fully characterize all the polymorphs of
a compound to avoid any transformation during manufacturing or storage.
This work deals with the study of the polymorphism of L-Glutamic acid
(LGlu) which can crystallize in two known monotropic polymorphs: the
stable form β with needle like shape and the metastable form α
with prismatic shape. Two experimental devices were used. Cooling
crystallizations in water were performed in both a stirred double jacketed
vessel of 2 L and a non-agitated thermostated cell of 4 mL. The
crystallization was monitored in situ by a video probe in stirred
conditions and by a microscope in stagnant conditions. Effect of
temperature and supersaturation on the polymorphism of LGlu was
investigated in stirred and stagnant conditions. Then the results were
compared.