RESUMO
Sequential ultra-small-angle and small-angle and X-ray scattering (USAXS and SAXS) measurements of hierarchical microstructure of a common energetic material, the high explosive 2,4,6-Triamino-1,3,5-trinitrobenzene (TATB), were performed to follow the microstructure evolution upon applied pressure. The pellets were prepared by two different routes-die pressed from a nanoparticle form and a nano-network form of TATB powder. The derived structural parameters, such as void size, porosity, and the interface area, reflected the response of TATB under compaction. Three populations of voids were observed in the probed q range from 0.007 to 7 nm-1. The inter-granular voids with size larger than 50 nm were sensitive to low pressures and had a smooth interface with the TATB matrix. The inter-granular voids with size of ~10 nm exhibited a less volume-filling ratio at high pressures (>15 kN) as indicated by a decrease of the volume fractal exponent. The response of these structural parameters to external pressures implied that the main densification mechanisms under die compaction were the flow, fracture, and plastic deformation of the TATB granules. Compared to the nanoparticle TATB, the applied pressure strongly influenced the nano-network TATB due to its more uniform structure. The findings and research methods of this work provide insights into the structural evolution of TATB during densification.
RESUMO
The interactions between natural colloidal organic matter and actinides in solutions are complex and not fully understood. In this work, a crew-cut polystyrene-b-poly(acry1ic acid) (PS-b-PAA) micelle is proposed as a model particle for humic acid (HA) colloid with the aim to better understand the sequestration, aggregation, and mobility of HA colloids in the presence of uranyl ions. The effects of uranyl ions on the structure of PS29k-b-PAA5k micelles in aqueous solution were mainly investigated by synchrotron small-angle X-ray scattering. A core-shell model, accounting for the thickness and contrast changes of the PAA corona induced by the adsorption of uranyl, was employed to analyze the scattering data. A combination of transmission electron microscopy, dynamic light scattering, and zetametry showed a strong affinity of uranyl ions to PAA segments in water at pH 4-5 that resulted in the shrinkage and improved contrast of the PAA corona, as well as colloidal destabilization at a high uranyl concentration.
