Thesis of Anthony Dupont

Abstract : The objective of this thesis is to improve the understanding of the fundamental microscopic mechanisms that govern the phase transformations induced directly in the solid state by mechanical milling. In particular, three key issues have been addressed: (i) We evaluated the influence of the milling temperature on the effective amorphization rate of a crystalline material. (ii) We determined the influence of monotropic and enantiotropic characters on the mechanisms of polymorphic transformations under milling. (iii) We have shown that the polymorphic transformations under milling are not direct but involve, on the contrary, a transient amorphization mechanism. Our strategy consisted in studying these different problems through a detailed analysis of the transformation kinetics which are the direct reflection of the physical mechanisms that govern them. For this purpose, we have studied in detail the transformation kinetics of physical states of several carefully chosen compounds. These include hydrochlorothiazide, sorbitol, glycine and their mixtures. The investigations were mainly carried out by X-ray diffraction and differential scanning calorimetry (DSC). Moreover, some experimentally demonstrated transformation mechanisms could be modelled and validated by numerical simulations. In summary, all our work indicates that, in general, the transformations under milling seem to result systematically from a competition between an amorphization mechanism due to mechanical shocks and a recrystallization mechanism whose nature depends on both the milling temperature and the crystalline specificities of the material. Keywords : Milling,Amorphization,Polymorphic transformation,Kinetic of transformation,X-Ray Diffraction,DSC