Nanostructure evolution during chemical processing of gels: A high-resolution electron microscope study. 1. Rare earth oxide and hydroxycarbonate colloids

The steps in the evolution of colloidal gels during drying, aging, and crystallization into ceramic oxides are followed by high-resolution electron microscopy. Two systems are discussed in this paper. Colloidal ceric hydroxide gels in two morphologies were studied. In one, spherical gel particles with only short-range order were observed to dehydrate to polycrystalline CeO2 with large grain size. In the other a polycrystalline precipitate of CeO2 was observed to increase its order without altering its grain size. Colloidal terbium hydroxycarbonate is also observed to have short-range order even in the earliest stages. In contrast to the cerium oxide these disordered materials are observed to crystallize and decompose in dynamic stages (even revealing reversibilities) through the intermediate dioxymonocarbonate to the oxide as carbon dioxide and water are removed. Observations are made by real-time video recording and time-lapse photography.