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Organisationseinheit der BAM
The primary crystallite size of titania powder relates to its properties in a number of applications. Transmission electron microscopy was used in this interlaboratory comparison (ILC) to measure primary crystallite size and shape distributions for a commercial aggregated titania powder. Data of four size descriptors and two shape descriptors were evaluated across nine laboratories. Data repeatability and reproducibility was evaluated by analysis of variance. One-third of the laboratory pairs had similar size descriptor data, but 83% of the pairs had similar aspect ratio data. Scale descriptor distributions were generally unimodal and were well-described by lognormal reference models. Shape descriptor distributions were multi-modal but data visualization plots demonstrated that the Weibull distribution was preferred to the normal distribution. For the equivalent circular diameter size descriptor, measurement uncertainties of the lognormal distribution scale and width parameters were 9.5% and 22%, respectively. For the aspect ratio shape descriptor, the measurement uncertainties of the Weibull distribution scale and width parameters were 7.0% and 26%, respectively. Both measurement uncertainty estimates and data visualizations should be used to analyze size and shape distributions of particles on the nanoscale.
Optimizing the properties of next-generation high-temperature and corrosion-resistant alloys is rooted in balancing structure-property relationships and phase chemistry. Here, we implement a complementary approach based on transmission electron microscopy (TEM) and atom probe tomography (APT) to ascertain aspects of hierarchical phase separation behavior, by understanding the microstructural evolution and the three-dimensional (3D) nanochemistry of a single crystal Fe79.5Si15.5V5.0 (at%) alloy. A maze-like hierarchical microstructure forms, in which a complex network of metastable disordered α plates (A2 phase) emerges within ordered α1 precipitates (D03 phase). The supersaturation in α1 (D03) precipitates with Fe and V drives the formation of α (A2) plates. The morphology of α (A2) plates is discussed concerning crystal structure, lattice misfit, and elastic strain. Phase compositions and a ternary phase diagram aid the thermodynamic assessment of the hierarchical phase separation mechanism via the Gibbs energy of mixing. A perspective on the stabilization of hierarchical microstructures beyond Fe79.5Si15.5V5.0 is elaborated by comparing hierarchical alloys. We find that the ratio of elastic anisotropy (Zener ratio) serves as a predictor of the hierarchical particles’ morphology. We suggest that the strengthening effect of hierarchical microstructures can be harnessed by improving the temporal and thermal stability of hierarchical particles. This can be achieved through phase-targeted alloying aiming at the hierarchical particles phase by considering the constituents partitioning behavior. Beyond Fe79.5Si15.5V5.0, our results demonstrate a potential pathway for improving the properties of high-temperature structural materials.
Long Term Temperature and Humidity Evolution Forecast in Near Field of Nuclear Waste Container
(2018)
The paper aims to simulate the corrosion environment of nuclear waste containers at different geological disposal periods to obtain temperature and humidity information at the interface between the container and the surrounding environment. The simulated data and calculation results of long term temperature evolution at the surface of nuclear waste (HLW) containers from some typical nuclear countries about the safety disposition were reviewed. Combining different burial patterns, this paper speculated the long term temperature evolution rule for China. According to the study about saturation variation of buffer/backfill material at home and abroad, the humidity evolution of bentonite at the surface of HLW containers was specu- lated. The study showed that the temperature of the container surface increased rapidly at the beginning, and gradually decreased after the climax. For safety reasons, the maximum temperature was designed below 100°C. The saturation of bentonite was af- fected by the mutual influences of the heat released by nuclear waste decay and the infiltration of groundwater. It was dominated by the released heat in the early stage, and later was influenced greatly by the infiltration of groundwater. It is generally believed that the water content at the surface of the container will increase obviously in about 3 years, and will be saturated in about 10 years. The prediction of long-term temperature and humidity evolution will lay a foundation for study of corrosion evolution of nuclear waste containers in China.
Surface environment changes of nuclear waste container, mainly including oxygen contents, buffer pore water components and pH under the conditions of “borehole” type and “In-floor” type with bentonite buffer/backfill and concrete buffer were summarized. This summarization provides a basic corrosion environment reference for the corrosion evolution re- search of high-level radioactive waste disposal repository in our country.