Syntheses of Actinide Materials

The search for alternative nuclear fuels, materials suitable for nuclear waste repositories, and new superconducting materials has been underway for decades. We have explored metal flux and mixed-metal flux synthesis and supercritical hydrothermal synthesis to grow bulk crystals of compounds with potential for such applications. Metal and mixed-metal flux synthesis uses an excess of a low-melting metal or metal mixture as a solvent for crystal growth. Reactants are able to dissolve in the flux and create chemical bonds with one another as well as with the flux itself. A new arc melter has been built to premelt some of the starting materials. In this work, six new compounds have been grown from metal fluxes: two borides with Al substitution on the V sites (UV0.43Al0.57B4), and four structurally related stuffed superstructures: U8Al19Si6 (cubic), U8Al19Si6 (tetragonal), Np8Al19Si6 (tetragonal), and Pu8Al19Si6 (tetragonal). Supercritical hydrothermal reactions were carried out in a high pressure/high temperature superalloy autoclave. The supercritical water provides counterpressure on the thermally expanding sealed reaction ampules within. UO2 crystals approaching 2 mm in diameter have been grown from the supercritical reactions. These crystals have been sent to universities and national laboratories for further chemical and physical analyses.