Surfactant Assisted Self-assembly and Synthesis of Highly Uniform Spherical CL-20 Microparticles

ABSTRACTMorphological control of energetic materials (EM) is highly desired because ill-defined morphology arising from variations in processing method and supplier make it impossible to reproducibly engineer their physicochemical properties. As the most powerful, non nuclear energetic material to date, 2,4,6,8,10,12-hexanitro -2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) has been the subject of significant interest for improved applications in military grade explosives. Here we report a new method for recrystallization of CL-20 from irregular bulk EMs using a surfactant assisted self-assembly process to produce uniform spherical micron-sized particles. Detailed electron microscopy studies indicate that surfactant plays a critical role in controlling CL-20 morphology. Combined X-ray diffraction and Raman spectroscopy results reveal that the resultant spherical CL-20 particles exhibit an orthorhombic β-phase crystal structure. This material is expected to display enhanced functional reproducibility due to its monodisperse nature as well as decreased shock sensitivity due to their sub-micron particle size.

The Influence of Alumina Addition on the Microstructures of YSZ

It is well known that the martensitic transformation of YSZ from the metastable tetragonal phase (T-phase) to the monoclinic phase (M-Phase) is accelerated in hot water (especially at 473K). Trace quantities of alumina are known to aid densification, and is also exceptionally resistant to low-temperature degradation (LTD). The current contribution describes a detailed electron microscopy investigation to determine the location of trace quantities of Al2O3 in a YSZ.

Amorphous Ta-N as a Diffusion Barrier for Cu Metallization

ABSTRACTAmorphous Ta-N thin films (14 and 62 nm thick) are deposited on Si substrates by reactive magnetron sputtering followed by Cu film deposition. The interlayer reaction and failure mechanism of the annealed metallization stacks are investigated by resistance measurements, xray diffraction (XRD) and detailed electron microscopy analysis accompanied with electron energy-loss spectroscopy (EELS). Amorphous Ta-N crystallizes at 600°C by a polymorphous transformation to Ta2N. The crystallized Ta2N barrier prevents Cu-Si interaction and intermixing up to 700-800°C, depending on the barrier thickness. Copper appears to be the main diffusing species and reacts with Si at the Ta-N/Si interface to form η˝-Cu3Si. Local Cu-Si reaction enhances the formation of TaSi2 precipitates. Silicon also diffuses, though at a much slower rate, to the surface and reacts with Cu. Local oxidation of Cu3Si occurs upon exposure to air, accompanied by SiO2 formation.

The hydration of Portland cement

Electron microscopy and conduction calorimetry have been employed to study the hydration of Portland cement. In situ studies of wet cement pastes in an environmental cell in the high voltage microscope confirm that the reaction involves two stages: ( a ) the rapid initial formation of gelatinous hydrate coatings around the cement grains and, ( b ) after a dormant period, the growth from these coatings of fine fibrillar calciumsilicate-hydrate (C-S-H) gel material into a reticulate network between the cement grains. Detailed electron microscopy indicates that the individual fibres are not solid but consist of fine hollow tubes. Attention is drawn to the striking visual analogy between the sequence of hydration of cement and the tubular growth forms that are obtained in ‘silicate gardens’. The latter are known to depend on the development of osmotic pressure as a driving force and, in spite of obvious differences in the scale and rate of growth, the basic parallels are close enough to suggest that a similar osmotic mechanism probably applies to the hydration of cement. On this basis, a model is proposed which explains the two-stage nature of the hydration process and provides a viable mechanism for the transport of the silicate material during growth of the secondary, fibrillar C-S-H product.