Thermal and Irradiation Creep Behavior of a Titanium Aluminide in Advanced Nuclear Plant Environments

Titanium aluminides are well-accepted elevated temperature materials. In conventional applications, their poor oxidation resistance limits the maximum operating temperature. Advanced reactors operate in nonoxidizing environments. This could enlarge the applicability of these materials to higher temperatures. The behavior of a cast gamma-alpha-2 TiAl was investigated under thermal and irradiation conditions. Irradiation creep was studied in beam using helium implantation. Dog-bone samples of dimensions 10×2×0.2mm3 were investigated in a temperature range of 300°C to 500°C under irradiation, and significant creep strains were detected. At temperatures above 500°C, thermal creep becomes the predominant mechanism. Thermal creep was investigated at temperatures up to 900°C without irradiation with samples of the same geometry. The results are compared with other materials considered for advanced fission applications. These are a ferritic oxide-dispersion-strengthened material (PM2000) and the nickel-base superalloy IN617. A better thermal creep behavior than IN617 was found in the entire temperature range. Up to 900°C, the expected 104 hour stress rupture properties exceeded even those of the ODS alloy. The irradiation creep performance of the titanium aluminide was comparable with the ODS steels. For IN617, no irradiation creep experiments were performed due to the expected low irradiation resistance (swelling, helium embrittlement) of nickel-base alloy

Synchrotron X-Rays for Microstructural Investigations of Advanced Reactor Materials

X-rays from synchrotron beamlines provide a powerful tool for materials analysis in circumstances where long-term materials degradation under complex loading conditions (e.g., temperature, irradiation, and stress) becomes important. This may occur for advanced gas cooled reactors. Synchrotron X-rays can help to improve lifetime assessments by providing a more in-depth understanding of microstructural damage. This article summarizes results of X-ray absorption fine spectrum analysis and X-ray magnetic circular dichroism synchrotron techniques. They were employed to evaluate various microstructural features, which are important in understanding the lifetime of materials exposed to extreme conditions. Dispersoid strengthening by yttria particles, conditions that produce nanocrystal Zircaloy, and the role of magnetism on the stability of ferritic steels were taken as example

Kinetic Control on the Depth Distribution of Superdeep Diamonds

Superdeep diamonds contain unique information from the sublithospheric regions of Earth’s interior. Recent studies suggest that reaction between subducted carbonate and iron metal in the mantle plays an important role in the production of superdeep diamonds. It is unknown if this reaction is kinetically feasible in cold slabs subducted into the deep mantle. Here we present experimental data on real‐time tracking of the magnesite‐iron reaction at high pressures and high temperatures to demonstrate the production of diamond at the surface conditions of cold slabs in the transition zone and lower mantle. Our data reveal that the diamond production rate has a positive temperature dependence and a negative pressure dependence, and along a slab geotherm it decreases by a factor of three at pressures from 14.4 to 18.4 GPa. This rate reduction provides an explanation for the rarity of superdeep diamonds from the interior of the mantle transition zone.Plain Language SummarySuperdeep diamonds originate from great depths inside Earth, carrying samples from inaccessible mantle to the surface. The reaction between carbonate and iron may be an important mechanism to form diamond through interactions between subducting slabs and surrounding mantle. Interestingly, most superdeep diamonds formed in two narrow zones, at 250–450 and 600–800 km depths within the ~2,700‐km‐deep mantle. No satisfactory hypothesis explains these preferred depths of diamond formation. We measured the rate of a diamond forming reaction between magnesite and iron. Our data show that high temperature promotes the reaction, while high pressure does the opposite. Particularly, the reaction slows down drastically at about 475(±55) km depth, which may explain the rarity of diamond formation below 450 km depth. The only exception is the second zone at 600–800 km, where carbonate accumulates and warms up due to the stagnation of subducting slabs at the top of lower mantle, providing more reactants and higher temperature for diamond formation. Our study demonstrates that the depth distribution of superdeep diamonds may be controlled by reaction rates.Key PointsReal‐time tracking of diamond production from iron‐magnesite reaction at high pressures and high temperaturesThreefold reduction in the rate of iron‐magnesite reaction from 14.4 to 18.4 GPaDepth distribution of superdeep diamonds may be explained by reaction kineticsPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/148362/1/grl58460_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/148362/2/grl58460.pd

A downshifting Eu 3+ doped glass embedded with concave pyramid microstructure to improve the efficiency of silicon solar cell

Abstract(#br)The average photoelectric conversion efficiency (PCE) of a bare mono crystalline silicon solar cell is 14.71 (±0.03)% under AM1.5. It decreases to 14.20 (±0.005)% when covering an un-doped flat glass on the solar cell, and it goes down to 14.10 (±0.005)% by using a 5 wt% Eu 3+ doped glass. The absorptions of the Eu 3+ doped CPM glass one-to-one match the excitation spectrum at 362, 381, 393, 400, 413 and 464 nm, which are related to the transitions of 7 F 0 →( 5 D 4 , 5 G 2 , 5 L 6 , 5 D 3 ), 7 F 1 → 5 D 3 , and 7 F 0 → 5 D 2 , respectively. In addition, a concave pyramid microstructure (CPM) is embedded in the glass surface to increase light transmittance. The average PCE increases to 14.61 (±0.07)% when a 5 wt% Eu 3+ doped CPM glass covers on the silicon solar cell. Comparing to the un-doped flat glass, a net increase of the PCE is 0.41%, where the 0.16% increment of PCE is from the lighting trapping of the CPM structure, and the downshifting of near ultraviolet (NUV) light by Eu 3+ ion donates the other 0.25% increment. It confirms that the as-prepared Eu 3+ doped CPM glass has a good downshifting and antireflection function

Elastic fractal higher-order topological states

In this work, elastic fractal higher-order topological states are investigated. Bott index is adopted to characterize the topological property of elastic fractal structures. The topological corner and edge states of elastic waves in fractal structures are realized theoretically and experimentally. Different from traditional two-dimension (2D) high-order topological insulators based on periodic structures, the high-order topological states based on elastic fractal structures in this work intuitively reflect the fractal dimension in physics, supporting not only abundant topological outer corner states, but also rich inner corner states. The richness of corner states is much higher than that of topological insulators based on periodic structures. The strong robustness of the topological corner states in the fractal structure are verified by introducing disorders and defects. The topological phenomenon of in elastic fractal structures revealed in this work enriches the topological physics of elastic systems and breaks the limitation of that relies on periodic elastic structures. The results have important application prospects in energy harvesting, information transmissions, elastic energy acquisitions and high-sensitivity detections

Near ultraviolet excited white light emitting diode (WLED) based on the blue LiCaPO 4 :Eu 2+ phosphor

Abstract(#br)One near ultraviolet (NUV) chip coated with tricolor phosphors to fabricate the white light emitting diode (WLED) has been attractive widely. In this paper, the blue emitting LiCaPO 4 :Eu 2+ , together with the red CaSiAlN 3 : Eu 2+ and the green (Sr, Ba)SiO 4 : Eu 2+ phosphor, is selected as the tricolor components for the NUV excited WLED preparation. The as-prepared WLED exhibits good luminescent performances with the color rendering index (Ra) of 88.6, the correlation color temperature of 3351 K, the lumen efficiency of 77.05 lm/W, and the color coordinates located at (0.4399, 0.4389). It is worth mentioning that the blue-light of the warm WLED succeeds to keep away from the hazard zone centered at 450 nm. Furthermore, a full spectrum warm WLED with the color rendering index (CRI) of 95.8 is fabricated by adding the fourth component as the Sr 5 (PO 4 ) 3 Cl:Eu 2+ phosphor. The prepared full spectrum WLED achieves the performance index of museum lighting

Compound microsatellites in complete Escherichia coli genomes

AbstractCompound microsatellites consisting of two or more repeats in close proximity have been found in eukaryotic genomes. So far such compound microsatellites have not been investigated in any prokaryotic genomes. We have therefore examined compound microsatellites in 22 complete genomes of Escherichia coli, which is one of the ideal model organisms to analyze the nature and evolution of prokaryotic compound microsatellites. Our results indicated that about 1.75–2.85% of all microsatellites could be accounted as compound microsatellites with very low complexity, and most compound microsatellites were composed of very different motifs. Compound microsatellites were significantly overrepresented in all surveyed genomes. These results were dramatically different from those in eukaryotes. We discussed the possible reasons for the observed divergence

Synthesis, Elasticity, and Spin State of an Intermediate MgSiO3‐FeAlO3 Bridgmanite: Implications for Iron in Earth’s Lower Mantle

Fe‐Al‐bearing bridgmanite may be the dominant host for ferric iron in Earth’s lower mantle. Here we report the synthesis of (Mg0.5Fe3+0.5)(Al0.5Si0.5)O3 bridgmanite (FA50) with the highest Fe3+‐Al3+ coupled substitution known to date. X‐ray diffraction measurements showed that at ambient conditions, the FA50 adopted the LiNbO3 structure. Upon compression at room temperature to 18 GPa, it transformed back into the bridgmanite structure, which remained stable up to 102 GPa and 2,600 K. Fitting Birch‐Murnaghan equation of state of FA50 bridgmanite yields V0 = 172.1(4) Å3, K0 = 229(4) GPa with K0′ = 4(fixed). The calculated bulk sound velocity of the FA50 bridgmanite is ~7.7% lower than MgSiO3 bridgmanite, mainly because the presence of ferric iron increases the unit‐cell mass by 15.5%. This difference likely represents the upper limit of sound velocity anomaly introduced by Fe3+‐Al3+ substitution. X‐ray emission and synchrotron Mössbauer spectroscopy measurements showed that after laser annealing, ~6% of Fe3+ cations exchanged with Al3+ and underwent the high‐ to low‐spin transition at 59 GPa. The low‐spin proportion of Fe3+ increased gradually with pressure and reached 17–31% at 80 GPa. Since the cation exchange and spin transition in this Fe3+‐Al3+‐enriched bridgmanite do not cause resolvable unit‐cell volume reduction, and the increase of low‐spin Fe3+ fraction with pressure occurs gradually, the spin transition would not produce a distinct seismic signature in the lower mantle. However, it may influence iron partitioning and isotopic fractionation, thus introducing chemical heterogeneity in the lower mantle.Plain Language SummaryFe‐Al‐bearing bridgmanite may be the dominant mineral in the lower mantle, which occupies more than half of Earth’s volume. A subject of much debate is whether spin transition of Fe in bridgmanite produces an observable influence on the physics and chemistry of the lower mantle. In this study, we synthesized a new (Mg0.5Fe3+0.5)(Al0.5Si0.5)O3 bridgmanite with the highest Fe3+‐Al3+ coupled substitution known to date. We studied its structure, elasticity, and spin state by multiple experimental and theoretical methods. The high Fe content allowed us to better resolve a pressure‐induced spin transition of Fe3+ caused by Fe‐Al cation exchange at high temperature. Our results suggest that the spin transition is enabled by cation exchange but has a minor effect on the seismic velocity, although it may introduce chemical heterogeneity in the lower mantle. Our study helps resolve existing discrepancies on the nature of spin transition of Fe‐Al bridgmanite and its influence on the physics and chemistry of the lower mantle.Key PointsBridgmanite may contain 50% trivalent cations through Fe3+‐Al3+ coupled substitutionThe bulk sound velocity of (Mg0.5Fe3+0.5)(Al0.5Si0.5)O3 bridgmanite is 7.7% lower than MgSiO3Through Fe‐Al cation exchange, Fe3+ in (Mg0.5Fe3+0.5)(Al0.5Si0.5)O3 bridgmanite undergoes gradual spin transition at lower mantle conditionsPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/156245/3/jgrb54280-sup-0001-2020JB019964-SI.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156245/2/jgrb54280.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156245/1/jgrb54280_am.pd

Hidden carbon in Earth’s inner core revealed by shear softening in dense Fe₇C₃

Earth’s inner core is known to consist of crystalline iron alloyed with a small amount of nickel and lighter elements, but the shear wave (S wave) travels through the inner core at about half the speed expected for most iron-rich alloys under relevant pressures. The anomalously low S-wave velocity (v_S) has been attributed to the presence of liquid, hence questioning the solidity of the inner core. Here we report new experimental data up to core pressures on iron carbide Fe_7C_3, a candidate component of the inner core, showing that its sound velocities dropped significantly near the end of a pressure-induced spin-pairing transition, which took place gradually between 10 GPa and 53 GPa. Following the transition, the sound velocities increased with density at an exceptionally low rate. Extrapolating the data to the inner core pressure and accounting for the temperature effect, we found that low-spin Fe_7C_3 can reproduce the observed v_S of the inner core, thus eliminating the need to invoke partial melting or a postulated large temperature effect. The model of a carbon-rich inner core may be consistent with existing constraints on the Earth's carbon budget and would imply that as much as two thirds of the planet's carbon is hidden in its center sphere

Research on decision-making of water diversion supply chain considering both social welfare and water quality utility

When water diversion projects become important part of the water network around the world, the effective operation and management of the projects play important roles in giving full play to the optimal allocation of water resources. For the operation and management of water transfer, the decision-making of water supply chain under the scenario of economic benefit, producer surplus, and water quality utility should be considered simultaneously. According to the idea of supply chain, this paper regards water transfer operation management as a water supply chain composed of water transfer companies, water supply companies, and consumers. From the perspective of social welfare and water quality utility, a comprehensive optimization and coordination decision model for water transfer is proposed. Taking the South-to-North Water Diversion Project as the research object, the cost-sharing contract is designed, and the Stackelberg game method is used to optimize the decision-making and coordination of the water supply chain. The results show that when the concern coefficient and the cost-sharing ratio are evaluated within a given feasible value region, the profits of both the water transfer company and the water supply company can be improved. The feasible value interval of the concern coefficient decreases with the increase in the cost-bearing proportion. When the concern coefficient increases, the profit of the water transfer company decreases, while profit of the water supply company, water quality, consumer surplus, water quality utility, and utility of the water transfer company increase gradually. The results provide valuable references for water transfer decision-making