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Besides radiation resistance, thermal recovery of radiation damage provides another critical criterion to evaluate the host phase for immobilizing high-level waste (HLW) produced by nuclear plants. Despite the increasing investigations, a comprehensive atomic-scale understanding remains elusive on thermal annealing of radiation damage in ceramics. Here, using in situ heating high-resolution transmission electron microscopy, we investigate the thermal annealing of radiation damage in natural metamict titanite (CaTiSiO 5) caused by a high alpha decay dose from the incorporated U and Th during the geologic time. The recovery of the fully amorphous titanite precursor starts at 456 ℃ from the appearances of monoclinic nanoparticles 2–5 nanometers wide, and more nanoparticles form as the temperature gradually increases. At 1000 ℃, the amorphous phase recovers through epitaxial growth with titanite nanoparticles as templates. This study provides information for a unit-cell-scale understanding of the thermal stability of radiation damage in titanite-based ceramics, having significance for immobilizing HLW. • Thermal recovery of totally amorphous titanite was investigated by in situ heating HRTEM. • The recovery of amorphous titanite starts from the appearance of nanoparticles. • The epitaxial growth with a titanite nanoparticle being the template was observed in real time. [ABSTRACT FROM AUTHOR]

We report on the first observation of fine structure of latent tracks in rutile TiO 2 , which changes from cylinder to dumbbell-shape and then to sandglass-shape as a function of the ion path length. Moreover, the cone length of the track was found to be dependent on electronic energy loss. The results indicate that outflow of the thermal spike-induced molten phase produces the hillocks on surface and the void-rich zone near surface after epitaxial recrystallization due to material deficit, while at a deep depth, the lack of efficient outflow and recrystallization result in the absence of tracks. We propose that the various morphologies of tracks in rutile TiO 2 are a consequence of the molten phase outflow and recrystallization during rapid cooling down. [ABSTRACT FROM AUTHOR]

Here we identified atomic-scale defects in ion irradiated 4H-SiC, by integrated differential phase contrast technique equipped on aberration-corrected transmission electron microscopy and Raman scattering spectrometer. In 21 MeV Ni+ ions irradiated 4H-SiC, in which electronic energy loss is dominant almost at the whole penetration depth, Si- and C-related vacancies and interstitials are successfully imaged. In 900 keV Si+ ions irradiated 4H-SiC, however, the electronic energy loss plays the key role near the surface, and the nuclear and electronic energy loss are comparable at the depth of the peak damaged zone. As a result, 900 keV Si+ ions produce more point defects, atomic-scale in-plane and out-of-plane lattice distortions, and plenty of dislocations at the depth of damage peak. Meantime, these imaged point defects may provide direct detailed information for the vibration modes of defects in the Raman spectrum of the damaged 4H-SiC. This study illustrates the compelling intrinsic nature of point defects induced by energetic ions, providing important fundamental information for nuclear and electronic applications. • Atomic-scale defects in 4H-SiC induced by electronic and nuclear energy loss are imaged. • Electronic energy loss introduces Si, C-related vacancies and interstitials. • Nuclear energy loss induces in-plane and out-of-plane elastic strains. • Dislocations form in nuclear energy loss damaged 4H-SiC. • Atomic-scale defects provide alternative interpretations for defective Raman bands. [ABSTRACT FROM AUTHOR]

Although modifying high-pressure behavior through the particle-size of a material is well recognized, a clear mechanism, underlying the start and subsequent growth of a high-pressure phase, remains elusive. Here, we investigate the effects of particle-size on the formation of reidite (ZrSiO 4 , I 4 1 / a), a high-pressure phase of zircon (ZrSiO 4 , I 4 1 / amd), by comparing zircon nanoparticles with bulk. This is done by high pressure Raman scattering and synchrotron X-ray diffraction experiments on zircons pressurized in diamond anvil cells and subsequent transmission electron microscopy analysis of quenched samples. As compared to bulk, the larger surface energy of nanoparticles is the cause of a higher critical pressure required to start the transition to reidite. However, after passing the critical pressures, the similar growth trends between nanoparticles and bulk indicate that the reidite growth is dependent on the core, rather than the surface. These results are important to identify craters caused by meteorite impacts using reidite as a high-pressure indicator, as nanoparticles are formed in naturally-occurring, highly radiation-damaged zircon. • Zircon nanoparticles are more difficult to transfer to reidite than zircon bulk. • Nanoparticles with larger surface require a higher pressure to start the transition. • Nanoparticles and bulk show a similar growth trend above the starting pressure. • The core rather than the surface controls the growth of reidite. • HRTEM images evidence the coexistence of zircon and reidite. [ABSTRACT FROM AUTHOR]

In this paper, the mechanism of flame intensification during the suppression of transformer oil pool fire is investigated for foam and water sprays. The results show that the extinguishment time is proportional to the discharge height and inversely proportional to the discharge pressure because greater height or lower pressure reduces the amount of suppression agent reaching the fuel bed thus extending extinguishment time. The increase of heat release rate following activation is inversely proportional to the discharge height and directly proportional to the discharge pressure; again, affected by the amount of suppression agent. When the nozzle is above the flame, the foam spray is affected by the entrapped air within, resulting in greater flame intensification, which is 3.5 times compared to water spray. For radiation, when the nozzle is above the flame, the heat flux increase is inversely proportional to the discharge pressure, which differs from the relationship for heat release rate increase. This difference is due to the shielding effect of the blanketing spray. For predict the heat release rate increase, an empirical model is developed, and an air mixing coefficient, τ, is introduced for foam spray to account for a 20%–35% increase in the heat release rate. [ABSTRACT FROM AUTHOR]