Search

Hot spots produced by long-wavelength infrared (LWIR) radiation in an energetic material, crystalline RDX (1,3,5-trinitroperhydro-1,3,5-triazine), were studied by thermal-imaging microscopy. The LWIR source was a CO2 laser operating in the 28-30THz range. Hot spot generation was studied using relatively low intensity (~100W cm-2), long-duration (450 ms) LWIR pulses. The hot spots could be produced repeatedly in individual RDX crystals, to investigate the fundamental mechanisms of hot spot generation by LWIR, since the peak hot-spot temperatures were kept to ~30K above ambient. Hot spots were generated preferentially beneath RDX crystal planes making oblique angles with the LWIR beam. Surprisingly, hot spots were more prominent when the LWIR wavelength was tuned to be weakly absorbed (absorption depth ~30 μm) than when the LWIR wavelength was strongly absorbed (absorption depth ~5 μm). This unexpected effect was explained using a model that accounts for LWIR refraction and RDX thermal conduction. The weakly absorbed LWIR is slightly focused underneath the oblique crystal planes, and it penetrates the RDX crystals more deeply, increasing the likelihood of irradiating RDX defect inclusions that are able to strongly absorb or internally focus the LWIR beam. [ABSTRACT FROM AUTHOR]

We report transmission electron tomography of nanoporous gold fabricated by chemically dealloying Au35Ag65 films. A number of algorithms were employed to quantitatively characterize the complex three-dimensional nanoporous structure. It was found that gold ligaments and nanopore channels are topologically and morphologically equivalent, i.e., they are inverses of each other in three-dimensional space. Statistical analysis reveals that this bicontinuous nanostructured material is actually quasiperiodic and has, on average, a near zero surface curvature. These quantitative measurements will help in understanding the structural stability of nanoporous gold and in modeling its physical and chemical performances. [ABSTRACT FROM AUTHOR]