Small Stacks Research Articles

Effect of interface type on deformation mechanisms of γ-TiAl alloy under different temperatures and strain rates by molecular dynamics simulation

Crystalline interface plays a significant role in strengthening lamellar γ-TiAl alloys through reconciling the strength and ductility. Herein, the effects of temperature and strain rate on the tensile deformation of three lamellar γ-TiAl interface models are investigated by molecular dynamics simulations. The three interfaces, pseudo twin (PT), rotational boundary (RB), and true twin (TT), exhibit different tensile responses due to the different interface effects: TT interface only acts as a barrier of dislocation traversing to facilitate crack extension; PT interface acts as both dislocation barrier and emission source and has a stronger release of strain energy than TT interface, retarding the crack extension; RB interface can retard and resist crack extension due to the blunting and deflection of the crack tip and the best interface geometry compatibility. The defect evolution indicates that the elevated temperature suppresses dislocation propagation at low strain rate, while the high strain rate causes small lamellar stacking faults and slit-shaped holes along tensile direction at low temperature. In addition, the dual conditions of high strain rate and low temperature induce the phase transition from FCC to BCC and then BCC to HCP. These findings provide a specific insight to understand the atomistic mechanism of interface-mediated deformation.

Microscale Normal Compression Behaviors of Clay Aggregates: A Coarse-Grained Molecular Dynamics Study.

Given the limitations of micromechanical experiments and molecular dynamics simulations, the normal compression process of clay aggregates was simulated under different vertical pressures (P), numbers of particles, loading methods, and environments by a Gay-Berne potential model. On the basis of the variations of particle orientation and the distribution of stacks, the evolution of deformation and stresses was elucidated. The results showed that the effects of the pressure level and loading environment on the deformation were significant. In the range of 0.1-10 MPa, the changes in the void ratio were essentially the evolution of the distribution of stacks determined by attractive short-range van der Waals interactions. The deformation under constant pressure was larger than that under step loading. Because the interactions between clay particles were mainly controlled by mechanical force when in the range of 40-100 MPa, the void ratios under various loading conditions were consistent. It was also found that changes in three-dimensional stresses during compression were dependent on those of the distribution of stacks. In the vacuum environment, owing to the lateral movement of interlocked small stacks, the horizontal stress decreased. The lateral pressure coefficients (k) were greater in an atmospheric environment because the anisotropic particle orientation was relatively less obvious. In the range of 10-100 MPa, when the loading path became longer, k was similar in vacuum but became smaller in an atmosphere. If the initial loading pressure was increased, the number of large stacks sharply increased and the anisotropy was significant in a vacuum environment, which was less prone to lateral expansion. In contrast, more consistent particle arrangements were maintained in an atmosphere. This work will be conducive to explaining experimental observations of long-term ripening.

Few-layer graphene production through graphite exfoliation in pressurized CO2 assisted by natural surfactant

Graphene research has captivated researchers worldwide, propelling innovation across diverse industries. Through the liquid-phase exfoliation methodology of graphite powder, we have demonstrated a rapid route for obtaining few-layer and multi-layer graphene using a natural surfactant, cardanol. Aqueous phase exfoliation of graphite in the presence of cardanol as a surfactant was conducted to obtain pre-exfoliated graphite suspensions. The influence of different ultrasonication times, 10, 20, and 30 min, and contact times with the surfactant, 1 and 60 min, on the stability and concentration of dispersed exfoliated graphite was evaluated. Results indicate that ultrasonication for 20 min resulted in improved stability and reduced graphene flake sizes, making it suitable for scalable graphene production. Subsequently, the most stable dispersions of exfoliated graphite were subjected to CO2-pressurized treatment. Promising results were obtained when employing cardanol at its critical micelle concentration. The graphene exhibited good structural quality, low defect density, and small stacking, with an average size of 15 nm, where 40 % of the stacked graphene was smaller than 5 nm. The findings provide valuable recommendations for the scalable production of graphene with multilayers and a few layers (FLG/MLG), using cardanol, a friendly surfactant, and a novel method of exfoliation utilizing supercritical CO2. This technology represents an innovative approach, with potential applications in supercapacitors, solar cells, biosensors, polymer composites, and advanced materials.

Bifunctional MNPs@UIO-66-Arg core-shell-satellite nanocomposites for enrichment of phosphopeptides.

A facile and mild method based on self-assembled lysozyme (LYZ) to fabricate bifunctional MNPs@UIO-66-Arg core-shell-satellite nanocomposites (CSSNCs) is reported for the high-efficiency enrichment of phosphopeptides. Under physiological conditions, LYZ rapidly self-assembled into a robust coating on Fe3O4@SiO2 magnetic nanoparticles (MNPs) with abundant surface functional groups, which effectively mediate heterogeneous nucleation and growth of UIO-66 nanocrystals. Well-defined MNPs@UIO-66 CSSNCs with stacked pores, showing high specific surface area (333.65 m2 g- 1) and low mass transfer resistance, were successfully fabricated by fine-tuning of the reaction conditions including reaction time and acetic acid content. Furthermore, the UIO-66 shells were further modified with arginine to obtain bifunctional MNPs@UIO-66-Arg CSSNCs. Thanks to the unique morphology and synergistic effect of Zr-O clusters and guanidine groups, the bifunctional MNPs@UIO-66-Arg CSSNCs exhibited outstanding enrichment performance for phosphopeptides, delivering a low limit of detection (0.1 fmol), high selectivity (β-casein/BSA, mass ratio 1:2000), and good capture capacity (120 mg g- 1). The mechanism for phosphopeptides capture may attribute to the hydrogen bonds, electrostatic interactions, and Zr-O-P bonds between phosphate groups in peptides and guanidyl/Zr-O clusters on bifunctional MNPs@UIO-66-Arg CSSNCs. In addition, the small stacking pores on the core-shell-satellite architecture may selectively capture phosphopeptides with low molecular weight, eliminating interference of other large molecular proteins in complex biological samples.

A proof-of-concept Bitter-like HTS electromagnet fabricated from a silver-infiltrated (RE)BCO ceramic bulk

A novel concept for a compact high-field magnet coil is introduced. This is based on stacking slit annular discs cut from bulk rare-earth barium cuprate ((RE)BCO) ceramic in a Bitter-like architecture. Finite-element modelling shows that a small 20 turn stack (with a total coil volume of < 20 cm3) is capable of generating a central bore magnetic field of > 2 T at 77 K and > 20 T at 30 K. Unlike resistive Bitter magnets, the high-temperature superconducting (HTS) Bitter stack exhibits significant non-linear field behaviour during current ramping, caused by current filling proceeding from the inner radius outwards in each HTS layer. Practical proof-of-concept for this architecture was then demonstrated through fabricating an uninsulated four-turn prototype coil stack and operating this at 77 K. A maximum central field of 0.382 T was measured at 1.2 kA, with an accompanying 6.1 W of internal heat dissipation within the coil. Strong magnetic hysteresis behaviour was observed within the prototype coil, with ≈30% of the maximum central field still remaining trapped 45 min after the current had been removed. The coil was thermally stable during a 15 min hold at 1 kA, and survived thermal cycling to room temperature without noticeable deterioration in performance. A final test-to-destruction of the coil showed that the limiting weak point in the stack was growth-sector boundaries present in the original (RE)BCO bulk.

Landslide velocity mapping using ALOS-2 PALSAR-2 ScanSAR data

This work discusses landslide velocity mapping in the Swiss Alps using ALOS-2 PALSAR-2 ScanSAR differential interferometry and interferometric time series analyses based on small data stacks of about 10 images over eight years. A wide area coverage is possible due to the 350km swath width of the ScanSAR data. In our processing sequence we resampled the sub-swath SLCs to a common spatial grid. The co-registered sub-swath SLCs were mosaiced into large co-registered mosaic SLCs. We then applied normal procedures also used for stripmap mode data to generate differential interferograms and conduct a Persistent Scatterer Interferometry (PSI) processing. The results obtained over the Swiss Alps provide a good spatial coverage, with line-of-sight displacement velocities also extracted for some landslides in forested areas. The future applicability of the technique is very promising with upcoming L-band SAR missions (NISAR, ROSE-L and PALSAR-3) that provide data of even better suitability – higher spatial resolution, shorter revisit time intervals, and free and open data access.

Investigation on mechanical, electrical and morphological of high-density polyethylene (HDPE) reinforced with different particle size and composition of graphene nanoplatelets (GNP)

Graphene nanoplatelets (GNP) are just one of the attractive graphene-based nanomaterials that are rapidly emerging and have sparked the interest of many industries. These small stacks of platelet-shaped graphene sheets have a unique size and morphology that quickly disperse into other materials such as polymers, resulting in higher-value composite materials with improved thermal, conductivity, and mechanical capabilities. A detailed analysis of reinforced High-Density Polyethylene (HDPE) using different sizes (2, 15, 25 µm) and compositions (8, 10, 15 wt.%) of Graphene Nanoplatelets (GNP) has been conducted. The microstructure of the HDPE/GNP nanocomposites was extensively examined during the melt blending and injection moulding processes. Based on the results, the nanocomposites with different sizes of GNP exhibited dissimilar behaviour with different compositions. Furthermore, scanning electron microscope (SEM) results indicated a homogeneous dispersion for GNP in melt mixing. Moreover, thermogravimetric (TG) data demonstrate that increasing filler showed a slight increase in the material's thermal stability. The use of GNP improved mechanical properties, as evidenced by the increases in Young's modulus of yield strength from around 100 MPa to over 400 MPa. This study provides a practical reference for the industrial preparation of polymer-based graphene nanocomposites.

Performance of a Small PEMFC Stack Operated with CO/H2 Mixtures

Hydrogen produced by reforming processes may include sulfur (S),carbon monoxide (CO) and other impurities.. Presence of ppm level impurities in hydrogen may adsorp onto Pt catalyst and lower performance and lifetime. There are efforts to overcome cost and performance issues by reducing Pt amount and utilizing new catalyst and support materials, more tolerant to CO. Ru catalyst are often added to oxidize CO before poisoning Pt. Ti0.7Mo0.3O2 was investigated as an alternative support material for anode catalyst. It has been shown that the stoichiometric ratio between Ti and Mo have significant impact on the CO tolerance. Ti0.8Mo0.2O2 was synthesized and used as anode electrode in PEM fuel cell testing. In this paper, titanium/molybdenum alloy on carbon (Ti0.8Mo0.2O2-C) is evaluated as catalyst support to prevent performance decay by CO poisoning. 3-cell stack was developed and tested for performance and degradation issues. Cell hardware with 15 cm2 active area was used for fuel cell measurements. Cathode was loaded with 0.6 mgPt/cm2 (20 wt.% Pt/C) and anode with 0.5 mgPt/cm2 (40 wt.% Pt/Ti0.8Mo0.2O2-C) onto Sigracet 29BC GDL by painting. Bipolar plates for single cell and stack were designed using Solid Works. End plates, anode bipolar plate and cathode bipolar plate with cooling channels on the other surfaces were designed and produced from graphite composite in-house. Seals from silicon was also designed and produced in-house. MEA had active area of 15 cm2. Figure 1 shows stack formation with all components put together in order. Stack was conditioned under 100% humidified hydrogen. There was no effect of stack orientation on performance. Performance for 2-cell stack was better going from atmospheric pressure to 2 bar. When polarization was 0.6V, pressurized operation provided improvement in current density going from 1300 mA/cm2 (no pressure) to 2000 mA/cm2 (15 psig). When this 2-cell stack was subjected to different concentrations of CO, polarization values of Figure 2 was obtained. Increasing concentration of CO caused decrease in current densities. Utilizing a DC/DC converter, stack has provided power to charge a cell phone. More details will be shared for 2, 3 cell stack operation under CO conditions. Figure 1

Electrodialysis of Lithium Sulfate Solutions from Hydrometallurgical Recycling of Spent Lithium-Ion Batteries

Recycling lithium-ion battery materials is a crucial step to achieving a circular economy. A hydrometallurgical recycling process of spent lithium-ion battery materials involves leaching by acids and precipitation by bases. A large amount of Li2SO4 leachate solution is generated at the end of the recycling process. Such Li2SO4 solution can be separated by electrodialysis (ED) to form H2SO4 and LiOH solutions, which are reused for leaching and precipitation, respectively, making the recycling a closed-loop process. In this study, an ‘electrodialysis stack constructed with bipolar membranes’ (EDBM) is built with repetitive unit cells consisting of a bipolar membrane, anion exchange membrane (AEM), and cation exchange membrane (CEM), see Fig. 1(a). The effective area for each membrane is 121.8 cm2 (70mm×174mm). The gap between these membranes is 0.8mm, with a mesh inserted to allow flow mixing. All experiments were operated at constant current mode. The feed, acid, and base solutions were recirculated through their tanks at initial concentrations of 1.1, 0.1, and 0.1 mol/L. The ion concentrations of the solutions were measured with Inductively coupled plasma mass spectrometry periodically. The weight and the pH value of the solution tanks were also recorded.The trend of concentration variations of the present stack with up to 6 cell pairs is found to be consistent with that observed with a three-compartment configuration in our previous study [1]. The concentration of H2SO4 increases with time linearly, whereas that of LiOH levels off due to a significant electro-osmosis that drags water through the CEM into the concentrate channel. The present setup differs from the three-compartment design in the bipolar membrane, which splits water to produce H+ and OH- at the internal interface, eliminating the formation of bubbly flows in the unit cell. It is found that the voltage loss across the bipolar membrane ca. 1V accounts for a major part of the unit cell of about 1.27V.The effects of current density, number of cell pairs, and flow rates on the overall stack performance are investigated. Increasing the stack current density accelerates the separation process at the cost of higher voltage losses. It is found that increasing the number of cell pairs can improve the overall production efficiency and reduce energy consumption per cell pair. For instance, at 800 A/m2, the specific energy consumption for LiOH production is reduced to 3.40 kWh/kg with five cell pairs versus 5.83 kWh/kg with two cell pairs. It is also found that increasing the solution flow rate can result into the increase of LiOH solution concentration, ion recovery rate, and current efficiency (Fig. 1b), although the impact of flow rate is low.A small EDBM stack is constructed and tested for Li2SO4 separation in the present study. This work demonstrates that EDBM can be a simple and energy-saving alternative to the current chemical precipitation method to produce LiOH from Li2SO4. The present study provides new insights into optimal operation and design for Li2SO4 EDBM. The findings are helpful in determining how the stack can be scaled up for practical application. Furthermore, a 2D multiphysics model is currently under development to elucidate the coupled transport processes within the unit cell. The model will be validated with experimental data of the present setup. Figure 1

Flameback identification and air intrusion prevention in small flow hydrogen flare stack emissions

In some hydrogen production, storage and applications, the flare stack is used as an indispensable protection system for the emission and ignition of surplus hydrogen. However, there is a risk of flameback when emissions at small flow rate. Thus, a series of studies were carried out to explore the flameback identification and air intrusion prevention in small flow emissions. In this study, a flare stack with a molecular sealing, which was 12 m in height and 100 mm in diameter, was selected as the physical object. And a 3D numerical model was established. (1) The small flow hydrogen flare stack emissions were performed when the nitrogen purge was completed, and in this study the purge was finished in 80 s (2) The flameback case of the numerical model in this paper was used along with the US Bureau of Mines experimental to verify the accuracy of the flameback limit flow theoretical model. Furthermore, the lower limit of the theoretical curve was extended from 100 mm to 1 mm by theoretical calculation. (3) In order to comprehensively consider the combined influence of turbulence and buoyancy at the flare stack outlet, we proposed a new dimensionless parameter Fd to represent the flow state by the Reynolds and Richardson numbers. Based on this, a general flameback identification criterion was proposed. (4) When the nitrogen/hydrogen ratio was within the range of 40–56 vol%, nitrogen auxiliary pressurization effectively inhibited air intrusion and the expansion of the flammable range.

Performance of a Small PEMFC Stack Operated with CO/H2 Mixtures

CO tolerance of Ti0.8Mo0.2O2–C supported 40 wt.% Pt electrocatalysts was measured at 0.5 mg/cm2 loading with a 2-cell PEM fuel cell stack. Long-term operation under CO and switching gas composition between hydrogen and CO shows recovery of performance after poisoning. Anode catalyst loading of 0.5 mgPt/cm2 was enough to give reasonable performance under 100 ppm CO. There was no effect of stack orientation on short-term performance.

Experimental study of homogeneity improvement and degradation mitigation in PEMFCs using improved reaction area utilization

The durability and degradation issues of Polymer Electrolyte Membrane Fuel Cells (PEMFCs) utilized in high-humidity environments and small stack sizes are investigated in this study. To address the lack of uniformity in operation and the resulting degradation, a method for improving the uniformity of current density distribution and reducing degradation in PEMFCs is proposed. This is achieved by periodically controlling the flow direction using a reverse-flow configuration. The proposed method resulted in a delay of degradation by approximately 7% based on the end of degradation experiment. Furthermore, the uniformity of current density distribution and voltage differences between cells in the stack were improved. The proposed method exhibits potential for enhancing the durability and performance of PEMFCs in high-humidity environments and small stack sizes, thereby mitigating carbon or Pt degradation, particularly in applications such as micro mobilities.

In-Situ Electrolyzer Monitoring Using Electrochemical Impedance Spectroscopy (EIS)

The development of technologies that improve the efficiency and reliability of green hydrogen production and distribution systems is key to lowering the cost and spurring widespread adoption of hydrogen. Electrolyzer reliability is affected by factors such as degradation of catalytic materials and development of anomalies in the membrane electrode assembly, which can in turn lead to hazardous mixing of Hydrogen and Oxygen. Most methods to lower the manufacturing cost further negatively affect the reliability. The effect of such degradation can be alleviated with improved cell monitoring technology [i]—for instance, the ability to predict failures in advance enables predictive maintenance to improve system utilization and minimize impact to the amount of hydrogen produced.Electrochemical Impedance Spectroscopy (EIS) is a widely used tool in lab settings to understand the properties of electrochemical cells. However, due to a combination of cost and technological barriers, scaling EIS technology to in-situ, in-operando monitoring of megawatt scale electrolyzer stacks has proven challenging. In this talk, Analog Devices presents Andromeda (Fig. 1) – a system that can monitor small electrolyzer stacks (up to 4 cells, 100cm2 at current densities up to 3A/cm2) in-situ. In a lab environment, Andromeda enables the use of EIS during long degradation studies with arbitrary power supplies without interrupting the study. We will show that, with appropriate modifications to the hardware, the architecture of the Andromeda system can be scaled to monitor Megawatt-scale electrolyzer stacks.We will additionally show data gathered on small cells that indicates that EIS can be a good indicator of failure mechanisms in an electrolytic cell [ii, iii], which further indicates that in-situ monitoring using EIS can be a powerful tool to monitor electrolyzer state-of-health. As an example, Figure 2 shows that corresponding I/V curves show no discernible difference between a baseline cell and cells with pinholes, indicating that small pinholes, which can be safety hazards, can be challenging to detect during operation. Examination of EIS data (Figure 3a), on the other hand, reveals a widening and depression of the semicircle in the curve from the cell with the pinhole. Detectability has also been demonstrated for defects such as catalyst degradation, membrane poisoning, and drifts in mass transport properties within the cell, proving that an in-situ monitoring system, when combined with modeling and AI, has the potential to give asset owners visibility into their operations that will improve utilization, decrease cost and enable safer production of hydrogen at scale.Future work on the integration of semiconductor technology into hydrogen equipment has focused on bypassing failing cells in the stack [iv] (Figure 4) and designing power systems that enable electrolyzers to exploit existing economies of scale.

Small-sample stacking model for qualitative analysis of aluminum alloys based on femtosecond laser-induced breakdown spectroscopy.

Material characterization using laser-induced breakdown spectroscopy (LIBS) often relies on extensive data for effective analysis. However, data acquisition can be challenging, and the high dimensionality of raw spectral data combined with a large-scale sample dataset can strain computational resources. In this study, we propose a small sample size stacking model based on femtosecond LIBS to achieve accurate qualitative analysis of aluminum alloys. The proposed three-layer stacking algorithm performs data reconstruction and feature extraction to enhance the analysis. In the first layer, random forest spectral feature selection and specific spectral line spreading are employed to reconstruct the data. The second layer utilizes three heterogeneous classifiers to extract features from the reconstructed spectra in different feature spaces, generating second-level reconstructed data. Finally, the third layer utilizes the reconstructed dataset for qualitative prediction. Results indicate that the Stacking algorithm outperforms traditional methods such as k-nearest neighbors (KNN), support vector machine (SVM), and random forest (RF), including those combined with principal component analysis (PCA). The Stacking algorithm achieves an impressive 100% recognition rate in classification, with Accuracy, precision, recall, and F1 scores reaching 1.0. Moreover, as the number of samples decreases, the gap between the recognition accuracy of the Stacking algorithm and traditional approaches widens. For instance, using only 15 spectra for training, the Stacking algorithm achieves a recognition accuracy of 96.47%, significantly surpassing the improved RF's accuracy of 71.76%. Notably, the model demonstrates strong robustness compared to traditional modeling approaches, and the qualitative prediction error remains consistently below 5%. These findings underscore the model's enhanced generalization ability and higher prediction accuracy in small sample machine learning. This research contributes significantly to improving the applicability of the LIBS technique for fast detection and analysis of small samples. It provides valuable insights into the development of effective methodologies for material characterization, paving the way for advancements in the field.

Effects of Stack Structure and Heat Loss on the Stability and Efficiency of Steam-Methanol Reforming Microreactors for Hydrogen Production

The linear scale-out approximation ignores the influence of exterior heat loss and thus cannot address extinction issues. The present study is focused primarily upon the roles of stack structure and heat loss in the stability and efficiency of microreactors for hydrogen production by steam-methanol reforming. Computer simulations are performed to model the complex physicochemical processes in a variety of different heat loss situations. The effects of channel number, wall thermal conductivity, and surface-area-to-volume ratio are investigated to assess the importance of stack structure and heat loss in microreactor design. The results indicate that the total heat loss becomes increasingly significant for designing reactors with small stacks of channels. About half of heat released is lost if a global-type extinction occurs. The critical heat loss coefficient depends heavily upon the number of channels. The design with a large stack of channels more closely beneficially improves heat utilization and reduces heat loss. There is a significant linear relationship between energy efficiency and heat loss coefficient. Significant heat loss may cause extinction in edge channels while still permitting very high conversion in center channels. The wall thermal conductivity is of vital importance to ensure stability operation. Higher wall thermal conductivity provides stability benefits, but walls with very low thermal conductivity can be employed to reduce heat loss by sacrificing the thermal coupling capability.

Highly Efficient Quasi 2D Blue Perovskite Electroluminescence Leveraging a Dual Ligand Composition

AbstractPerovskite light‐emitting diodes (PeLEDs) are advancing because of their superior external quantum efficiencies (EQEs) and color purity. Still, additional work is needed for blue PeLEDs to achieve the same benchmarks as the other visible colors. This study demonstrates an extremely efficient blue PeLED with a 488 nm peak emission, a maximum luminance of 8600 cd m−2, and a maximum EQE of 12.2% by incorporating the double‐sided ethane‐1,2‐diammonium bromide (EDBr2) ligand salt along with the long‐chain ligand methylphenylammonium chloride (MeCl). The EDBr2 successfully improves the interaction between 2D perovskite layers by reducing the weak van der Waals interaction and creating a Dion–Jacobson (DJ) structure. Whereas the pristine sample (without EDBr2) is inhibited by small stacking number (n) 2D phases with nonradiative recombination regions that diminish the PeLED performance, adding EDBr2 successfully enables better energy transfer from small n phases to larger n phases. As evidenced by photoluminescence (PL), scanning electron microscopy (SEM), and atomic force microscopy (AFM) characterization, EDBr2 improves the morphology by reduction of pinholes and passivation of defects, subsequently improving the efficiencies and operational lifetimes of quasi‐2D blue PeLEDs.

Effects of γ-Irradiation, Cation Size, and Salt Concentration on the Aggregation of Boehmite Nanoplatelets

Effects of radiation on the aggregation of nanoplatelets of aluminum oxyhydroxide (boehmite) in slurries of M1+ cation nitrates have been observed using tumbler small- and ultra-small-angle neutron scattering. Nitrate solutions of H, Li, Na, K, and Rb at concentrations of 10–5, 10–3, 10–1, 2, and 4 molal were compared to the results for pure H2O. Primary aggregates consisting of small stacks of boehmite platelets that form immediately after the boehmite is placed in water are smaller for irradiated boehmite than the pristine material. The primary aggregates for irradiated boehmite also appear to have a rougher surface than those observed for unirradiated materials. Both results are possibly due to breaking of the surface OH species and neutralization of the surface. At low salt concentrations, the pH of the irradiated boehmite slurries is lower than that of the corresponding pristine material, indicating that irradiated boehmite adsorbs fewer protons or more hydroxide onto its surface than the pristine boehmite. Increasing the salt concentration decreases the pH to near neutral at 7 due to screening of the electric double layer at the solid/liquid interface. Irradiation does not seem to affect the size of secondary aggregates formed from the aggregation of primary aggregates or the overall size of the primary aggregates.

On the Highly Ordered Graphene Structure of Non-Graphitic Carbons (NGCs)—A Wide-Angle Neutron Scattering (WANS) Study

Non-graphitic carbons (NGCs), such as glass-like carbons, pitch cokes, and activated carbon consist of small graphene layer building stacks arranged in a turbostratic order. Both structure features, including the single graphene sheets as well as the stacks, possess structural disorder, which can be determined using wide-angle X-ray or neutron scattering (WAXS/WANS). Even if WANS data of NGCs have already been extensively reported and evaluated in different studies, there are still open questions with regard to their validation with WAXS, which is usually used for routine characterization. In particular, using WAXS for the damping of the atomic form factor and the limited measured range prevent the analysis of higher-ordered reflections, which are crucial for determining the stack/layer size (La, Lc) and disorder (σ1, σ3) based on the reflection widths. Therefore, in this study, powder WANS was performed on three types of carbon materials (glass-like carbon made out of a phenol-formaldehyde resin (PF-R), a mesophase pitch (MP), and a low softening-point pitch (LSPP)) using a beamline at ILL in Grenoble, providing a small wavelength and thus generating WANS data covering a large range of scattering vectors (0.052 Å−1 &lt; s &lt; 3.76 Å−1). Merging these WANS data with WANS data from previous studies, possessing high resolution in the small s range, on the same materials allowed us to determine both the interlayer and the interlayer structure as accurately as possible. As a main conclusion, we found that the structural disorder of the graphene layers themselves was significantly smaller than previously assumed.

Ultrastrong and ductile (CoCrNi)94Ti3Al3 medium-entropy alloys via introducing multi-scale heterogeneous structures

• A three-level heterogeneous structure was introduced in CoCrNi alloy. • (CoCrNi) 94 Ti 3 Al 3 delivers ultimate tensile strength of 1.6 GPa and strain of 13.1%. • Heterogeneous matrix, γ’ precipitate and defects led to high strength and ductility. The coarsening-grained single-phase face-centered cubic (fcc) medium-entropy alloys (MEAs) normally exhibit insufficient strength for some engineering applications. Here, superior mechanical properties with ultimate tensile strength of 1.6 GPa and fracture strain of 13.1% at ambient temperature have been achieved in a (CoCrNi) 94 Ti 3 Al 3 MEA by carefully architecting the multi-scale heterogeneous structures. Electron microscopy characterization indicates that the superior mechanical properties mainly originated from the favorable heterogeneous fcc matrix (1–40 µm) and coherent spherical γ' precipitate (10–100 nm), together with a high number density of crystalline defects (2–10 nm), including dislocations, small stacking faults, Lomer–Cottrell locks, and ultrafine deformation twins.

Resolving minute temporal seismic velocity changes induced by earthquake damage: the more stations, the merrier?

SUMMARYGround shaking induced by earthquakes often introduces transient changes in seismic velocity monitored with ambient noise. These changes are usually attributed to relaxation behaviour following the coseismic damage in the subsurface and are of relevance for post-seismic hazard mitigation. However, the velocity evolution associated with this phenomenon can occur at very small timescales and amplitudes that are not resolved with seismic interferometry and are therefore challenging to link to laboratory experiments. A way to improve the temporal resolution of the velocity time-series is to test whether the estimation of the relative seismic velocity changes dv/v obeys the ergodic hypothesis in which the joint use of colocated stations would lead to better resolved measurements. In this study, we present results from a dense seismic array that was deployed for 2 weeks at the remarkable Patache site in Chile. Thanks to high temporal averaging capabilities, we are able to resolve seismic velocity changes in the 3–6 Hz frequency band at a 10-min resolution around the occurrence of a moderate earthquake (PGV ∼1 cm s–1). We report a velocity drop of ∼0.4 per cent in the first 10 min after ground shaking. Half of this initial drop was recovered within the 2 following days. The shape of the recovery follows a log-linear shape over the whole observed recovery phase, analogous to slow dynamics experiments. When normalized by the total amount of processed data, we show that the ergodic hypothesis almost perfectly holds in our network: the dv/v signal-to-noise ratio (SNR) obtained when averaging a few observation with large stacking durations for the correlation functions is almost equal to the SNR when using a large number of observations with small stacking durations. To understand if the ergodicity is linked to a particular site property, we use the array capabilities to identify the surf at the shoreline as the source of the noise and to derive a 1-D shear velocity profile with the focal spot imaging technique and a transdimensional Bayesian inversion framework. The inversion shows that hard rocks lie close to the surface indicating that this material hosts the observed shallow velocity changes. We discuss our high-resolution measurements and attribute them to a stable noise source excited by the shore, the ergodicity property and an ideal subsurface structure. Finally, we discuss the effect of moderate earthquakes on subsurface damage and the potential relaxation processes in hard rocks.