Influx of nitrogen-rich material from the outer Solar System indicated by iron nitride in Ryugu samples

Large amounts of nitrogen compounds, such as ammonium salts, may be stored in icy bodies and comets, but the transport of these nitrogen-bearing solids into the near-Earth region is not well understood. Here, we report the discovery of iron nitride on magnetite grains from the surface of the near-Earth C-type carbonaceous asteroid Ryugu, suggesting inorganic nitrogen fixation. Micrometeoroid impacts and solar wind irradiation may have caused the selective loss of volatile species from major iron-bearing minerals to form the metallic iron. Iron nitride is a product of nitridation of the iron metal by impacts of micrometeoroids that have higher nitrogen contents than the CI chondrites. The impactors are probably primitive materials with origins in the nitrogen-rich reservoirs in the outer Solar System. Our observation implies that the amount of nitrogen available for planetary formation and prebiotic reactions in the inner Solar System is greater than previously recognized

Four‐dimensional‐STEM analysis of the phyllosilicate‐rich matrix of Ryugu samples

Ryugu asteroid grains brought back to the Earth by the Hayabusa2 space mission are pristine samples containing hydrated minerals and organic compounds. Here, we investigate the mineralogy of their phyllosilicate-rich matrix with four-dimensional scanning transmission electron microscopy (4D-STEM). We have identified and mapped the mineral phases at the nanometer scale (serpentine, smectite, pyrrhotite), observed the presence of Ni-bearing pyrrhotite, and identified the serpentine polymorph as lizardite, in agreement with the reported aqueous alteration history of Ryugu. Furthermore, we have mapped the d-spacings of smectite and observed a broad distribution of values, ranging from 1 to 2 nm, with an average d-spacing of 1.24 nm, indicating significant heterogeneity within the sample. Such d-spacing variability could be the result of either the presence of organic matter trapped in the interlayers or the influence of various geochemical conditions at the submicrometer scale, suggestive of a range of organic compounds and/or changes in smectite crystal chemistry

A dehydrated space-weathered skin cloaking the hydrated interior of Ryugu

Without a protective atmosphere, space-exposed surfaces of airless Solar System bodies gradually experience an alteration in composition, structure and optical properties through a collective process called space weathering. The return of samples from near-Earth asteroid (162173) Ryugu by Hayabusa2 provides the first opportunity for laboratory study of space-weathering signatures on the most abundant type of inner solar system body: a C-type asteroid, composed of materials largely unchanged since the formation of the Solar System. Weathered Ryugu grains show areas of surface amorphization and partial melting of phyllosilicates, in which reduction from Fe3+ to Fe2+ and dehydration developed. Space weathering probably contributed to dehydration by dehydroxylation of Ryugu surface phyllosilicates that had already lost interlayer water molecules and to weakening of the 2.7 µm hydroxyl (–OH) band in reflectance spectra. For C-type asteroids in general, this indicates that a weak 2.7 µm band can signify space-weathering-induced surface dehydration, rather than bulk volatile loss

Radiation Damage Behavior in Multiphase Ceramics (YSZ, Al2O3 and MgAl2O4) and the Effect of Heterointerfaces

Current technology ceramics for radiation environments rely on their intrinsic properties for damage tolerance, but the they can be further improved by designing the microstructure for use in applications for space, nuclear fission/fusion and nuclear waste environments. Interfaces are known to be sinks for point defects, which enhance radiation damage tolerance, and more disordered interfaces work better than clean interfaces. Heterointerfaces, or interfaces between dissimilar phases, are expected to have more disorder than grain boundaries in a single-phase system. In this study, radiation damage behavior of a multiphase ceramic material with heterointerfaces and submicron grains was systematically investigated and compared to single phase polycrystalline materials with grain boundaries. The multiphase composite survived a high fluence while single phase materials fractured. X-ray diffraction and transmission electron microscopy analysis showed more efficient point defect annihilation in the multiphase system than in the single-phase system. This work shows that high radiation damage tolerance can be achieved without complicated careful grain boundary modification or ultra nano grain fabrication, which is difficult to scale up and unreliable at elevated temperatures

Radiation Damage Behavior in Multiphase Ceramics (YSZ, Al2O3 and MgAl2O4) and the Effect of Heterointerfaces

Current technology ceramics for radiation environments rely on their intrinsic properties for damage tolerance, but the they can be further improved by designing the microstructure for use in applications for space, nuclear fission/fusion and nuclear waste environments. Interfaces are known to be sinks for point defects, which enhance radiation damage tolerance, and more disordered interfaces work better than clean interfaces. Heterointerfaces, or interfaces between dissimilar phases, are expected to have more disorder than grain boundaries in a single-phase system. In this study, radiation damage behavior of a multiphase ceramic material with heterointerfaces and submicron grains was systematically investigated and compared to single phase polycrystalline materials with grain boundaries. The multiphase composite survived a high fluence while single phase materials fractured. X-ray diffraction and transmission electron microscopy analysis showed more efficient point defect annihilation in the multiphase system than in the single-phase system. This work shows that high radiation damage tolerance can be achieved without complicated careful grain boundary modification or ultra nano grain fabrication, which is difficult to scale up and unreliable at elevated temperatures

Process time variation and critical growth onset analysis for nanofoam formation in sucrose-based hydrothermal carbonization

Brooks C, Lee J, Frese N, Ohtaki K, Wortmann M, Sattler K. Process time variation and critical growth onset analysis for nanofoam formation in sucrose-based hydrothermal carbonization. Journal of Materials Science . 2021;56(27):15004–15011.The paper presents a systematic study of the formation of carbon nanofoam from sucrose by hydrothermal carbonization. It is shown that for the process temperature of 150 degrees C, carbonization is not a gradual process but rather occurs suddenly at a specific threshold time of 4.5 h. pH value and electrical conductivity (EC) of the sucrose solution were monitored during carbonization. In the first 4.5 h prior to carbonization, the sucrose solution shows a sharp drop from pH 7.8 to pH 2 and sharp increase of EC. From this point on the values of pH and EC remain approximately constant. After the 4.5 h threshold, we examined the evolution of mass yield, density and morphology of the resulting carbon nanofoam. The yield first shows a steep increase around 4.5 h and then a further gradual increase up to 38% at 54.6 h. The mass density just after the 4.5 h threshold is 0.28 g/cm(3) and decreases with process time to reach a constant value of 0.14 g/cm(3), between 20 and 54.6 h. This shows that desired conditions, such as low density and high yield, are obtained with sufficient process time below 5 h. Due to the release of intermediates of the conversion reaction into the sucrose solution, both pH and EC were found to be excellent indicators for the progression of hydrothermal carbonization