Correlation of long storage behavior of thorium-epoxy composites with laboratory data on the corrosion of thorium

Large thorium and Mulberry parts were adhesively bonded to polystyrene foam by means of an epoxy. Thorium surfaces were present in two forms: machined or untreated and passivated in an HNO3--HF solution. Experimental units were stored at temperatures ranging from 32 to 710C for times greater than six months in order to test the integrity of the metal to foam bond. Two types of measurements were made in the evaluation of test units. Gases were extracted from the unit, measured, and analyzed. In addition, the units were disassembled and the thorium and Mulberry surfaces were examined for separation of the adhesive from the metal surface and for oxidation of the two metals. In cases where separation had occurred between the thorium surface and the adhesive due to oxidation, oxide thickness measurements were performed. Units stored at 71.10C showed severe corrosion of the machined thorium and moderate corrosion of the passivated thorium. The Mulberry parts had a slight blue color. In both units there was separation between the thorium and the adhesive, which actually lifted a film of ThO2 from the metal. Other two units which were stored at 48.9 and 600C respectively, showed a light oxidation of the thorium both machined and passivated. Good adhesion was observed between the thorium and the adhesive. The presence of small amounts of HCl and Cl2 did not significantly contribute to the oxidation of thorium in these experiments. (U.S.)