Dust-Free Sol-Gel Synthesis of Neodymium Oxide Microspheres as a Surrogate for Americium-241 Fueled Radioisotope Power Systems.

New designs for radioisotope power systems (RPS) explore the use of Am-241 as a fuel source. Neodymium is a common surrogate for americium and the work here presents a citrate-modified internal gelation route was applied to synthesize neodymium oxide microspheres, as a surrogate for americium oxide microspheres with applications in these new RPS designs. Neodymium has not previously been gelled on its own using the internal gelation route as the pH of neodymium hydrolysis and precipitation is higher than that achieved in the internal gelation process. However, the inclusion of citric acid as a precursor allows for the neodymium to deprotonate and coordinate to the citrate groups rather than hydrolyze, which results in the precipitation of a 1:1 neodymium citrate gel. Subsequent heat treatment to 950 °C under adequate air flow decomposes the residual organics and citrate groups resulting in the formation of the high temperature trigonal phase of NdO. The work here details the chemistry involved in the citrate-modified internal gelation process as well as outlines methods for the optimization of microsphere fabrication. The sol-gel microspheres fabricated through this adapted synthesis method can be pelletized for use in RPS systems without the need for dust-producing steps, such as milling, thus providing the platform for the safer fabrication of RPS.