Unconventional Pathways to Carbide Phase Synthesis via Thermal Decomposition of UI4(1,4-dioxane)2

Laser-Induced Thermal Decomposition of Uranium Coordination Compounds with Non-oxidic Ligands to Produce Nitride and Carbide Materials

The production of ceramics from uranium coordination compounds can be achieved through thermal processing if an excess amount of the desired atoms (i.e., C or N), or reactive gaseous products (e.g., methane or nitrogen oxide) is made available to the reactive uranium metal core via decomposition/fragmentation of the surrounding ligand groups. Here, computational thermodynamic approaches were utilized to identify the temperatures necessary to produce uranium metal from some starting compounds─UI4(TMEDA)2, UCl4(TMEDA)2, UCl3(pyridine)x, and UI3(pyridine)4. Experimentally, precursors were irradiated by a laser under various gaseous environments (argon, nitrogen, and methane) creating extreme reaction conditions (i.e., fast heating, high temperature profile >2000 °C, and rapid cooling). Despite the fast dynamics associated with laser irradiation, the central uranium atom reacted with the thermal decomposition products of the ligands yielding uranium ceramics. Residual gas analysis identified vaporized products from the laser irradiation, and the final ceramic products were characterized by powder X-ray diffraction. The composition of the uranium precursor as well as the gaseous environment had a direct impact on the production of the final phases.

Route to Stabilization of Nanotechnetium in an Amorphous Carbon Matrix: Preparative Methods, XAFS Evidence, and Electrochemical Studies

Technetium-carbon nanophases are obtained by thermal decomposition of pertechnetates with large organic cations under an argon atmosphere. Parallel carbonization of organic cations (hexamethyleneiminium and triphenylguanidinium), which occurs during the thermal decomposition of their pertechnetates, leads to the formation of X-ray amorphous solid products. An X-ray absorption fine structure study revealed that they have a crystal structure containing technetium-carbon bonds with a length of 1.76 Å. After subsequent annealing treatment at 1073-1673 K, the synthesized technetium-carbon phase has a cubic lattice with an a of 4.01 ± 0.03 Å. The products of thermal decomposition of the same perrhenates are also X-ray amorphous; however, unlike that of pertechnetates, the distance between rhenium and carbon atoms in them is significantly greater (2.14 Å). After subsequent annealing, they have a hexagonal lattice. The electrochemical properties of technetium-carbon nanophases prepared by thermal decomposition of pertechnetates with large organic cations are different from the properties of those prepared with metallic technetium. The oxidation of technetium carbide to its oxides at the electrode surface observed in the first anodic scan of cyclic voltammograms can be used for the deposition of noble metal nanoclusters under open-circuit conditions to prepare composite catalysts for the hydrogen evolution reaction. Nanotechnetium in the amorphous carbon matrix can also be a prospective material for reactor transmutation of technetium to stable isotopically pure ruthenium-100.