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We have attempted to study the formation of BaTiO 3 by hydrothermal synthesis and our experiments reveal the reaction by dissolution−precipitation as the dominant operating mechanism. Two major formation mechanisms of BaTiO 3 by hydrothermal synthesis involving either in situ transformation or dissolution−precipitation have been previously proposed. However, the exact formation mechanism is yet to be clarified unambiguously. To investigate the mechanism in detail, we used Ba(OH) 2 and three types of TiO 2 nanoparticles as precursors for the synthesis. The morphology of the BaTiO 3 obtained was cubic (with rounded edges), regardless of the morphology of the TiO 2 used, which indicated that the synthesis followed the dissolution−precipitation mechanism. In this mechanism, the surface area of TiO 2 , which affects its dissolution rate, played a critical role in determining the crystal size of the BaTiO 3 product. In this paper, we have also discussed the effects of the synthesis conditions on BaTiO 3 particle formation.

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The aim of this work was to understand the agglomeration phenomenon and to predict the agglomeration behavior of materials in the supercritical antisolvent (SAS) process. Carbon dioxide-induced melting point depression is believed to be one of the major causes of the formation of agglomerates during the SAS process. Here, we attempted to observe the CO 2 -induced melting behaviors of nine target materials and to recrystallize them in the SAS process. On the basis of the multicomponent Clapeyron equation, which describes the interaction between solute and carbon dioxide, the thermodynamic properties of 32 materials were investigated to correlate melting point depression with the agglomeration phenomenon. In this analysis, the dimensionless entropy of fusion was utilized as a simple criterion to predict agglomeration behavior. The extent of melting point depression was assumed to be inversely proportional to the entropy of fusion of the solute. This assumption enables us to predict the agglomeration behavior of recrystallized pharmaceuticals with dimensionless entropy of fusion during the SAS process. Furthermore, a correlation between the tendency of agglomeration and whether the recrystallized particles have either faceted or nonfaceted form was observed.