Jade Raimbault1,Maxime Durelle2,David Carriere1,Corinne Chevallard1,Frederic Gobeaux1,Mark Levenstein1,Fabienne Testard1,Florent Mallogi1,Ovidiu Ersen3,Dris Ihiawakrim3
CEA de Saclay1,University of Leeds2,Institut de Physique et Chimie des Matériaux de Strasbourg3
Jade Raimbault1,Maxime Durelle2,David Carriere1,Corinne Chevallard1,Frederic Gobeaux1,Mark Levenstein1,Fabienne Testard1,Florent Mallogi1,Ovidiu Ersen3,Dris Ihiawakrim3
CEA de Saclay1,University of Leeds2,Institut de Physique et Chimie des Matériaux de Strasbourg3
Crystallization from solution can occur through a “nonclassical” route where amorphous or liquid transient species are formed prior to final crystals<sup>[1]</sup>. These intermediates, often ignored in theoretical modeling, can however have a significant impact on crystallization mechanisms and therefore on nucleation rates. Most industrial processes still rely on single step Classical Nucleation Theory (CNT) and then overlook cases where these routes are followed.<br/><br/>Cerium oxalate, a well-known surrogate for plutonium oxalate in nuclear waste recycling, shows evidence of a transient amorphous structure prior to crystallization<sup>[2]</sup>. However, we revealed that not one, but two non-crystalline transient species are involved: amorphous nanoparticles and dense liquid droplets. Formed in less than a minute, they may also coexist depending on the chemical conditions<sup>[3]</sup>. It challenges not only their characterization but also their theoretical description, making the validation of a nucleation model even more delicate.<br/><br/>We used in situ X-ray scattering at synchrotron and liquid cell TEM to characterize cerium oxalate precipitation down to the millisecond reaction times and the nanometer scale. In addition to their identification, we confirmed the amorphous and liquid nature of these intermediates. Their impact on experimental nucleation rates was also assessed and revealed a drastic increase when liquid droplets are formed, far from the values expected by a single step model. Finally, we determined the different phase transition mechanisms involved depending on the nature of the transient structure, which gives us a hint on compatible nucleation theories.<br/><br/><b>References :</b><br/>[1] Yoreo, J. J. D. <i>et al.</i> Crystallization by particle attachment in synthetic, biogenic, and geologic environments. <i>Science</i> 349, aaa6760 (2015)<br/>[2] Rodriguez-Ruiz, I. et <i>al. </i>Ultra-fast precipitation of transient amorphous cerium oxalate in concentrated nitric acid media. <i>CrystEngComm</i>, 20, 3302-3307 (2018)<br/>[3] Durelle, M. <i>et al.</i> Coexistence of Transient Liquid Droplets and Amorphous Solid Particles in Nonclassical Crystallization of Cerium Oxalate. <i>J. Phys. Chem. Lett.</i> 13, 8502–8508 (2022)