Synthesis and nanoscale characterization of (NH(4))(4)ThF(8) and ThNF.

Synthesis of (NH(4))(4)ThF(8) by a solid state reaction of ThO(2) and NH(4)HF(2) and the formation of ThNF by ammonolysis of (NH(4))(4)ThF(8) and ThF(4) under different experimental conditions were investigated. The solid state reaction of ThO(2) with NH(4)HF(2) led to the terminal product (NH(4))(4)ThF(8) through a known intermediate (NH(4))(3)ThF(7) and most likely two other unknown chemical phases as determined by X-ray powder diffraction. Conversion of (NH(4))(4)ThF(8) into ThNF occurs through a ThF(4) intermediate phase. Studies on the ammonolysis of ThF(4) revealed it converted into ThNF through a continuous formation of low-stoichiometric thorium-nitride-fluorides such as ThN(0.79)F(1.63) and ThN(0.9)F(1.3). Thermal behavior of ThNF was also examined under different atmospheres and temperatures, with evaluation of formation kinetics. The ThNF decomposed to low-stoichiometric thorium nitride fluorides (ThN(x/3)F(4-x)) under different environments up to 1100 degrees C. Significant morphological changes in the products compared to that of the precursors confirmed the reaction steps involved. Microstructural characterization of (NH(4))(4)ThF(8) and ThNF were performed by HRTEM and are presented in this work for the first time. The (NH(4))(4)ThF(8) product was shown to contain polycrystalline characteristics in the majority of its nanostructure. On the other hand, ThNF has a high order of nanostructure, which explains the high thermal stability of the compound up to 1100 degrees C and the difficulty of making ThN(x), in initial target product, from the described experimental conditions.