Rate-limiting Mechanism Research Articles

A numerical study of internal transport in oxidizing liquid core–shell iron particles

In an effort to improve the understanding of the rate-limiting mechanisms in liquid iron particle combustion, this study investigates the impact of internal transport within a core–shell structure. The two-dimensional axisymmetric transient continuum model as presented in previous publication (Thijs et al., 2023) is extended, such that the boundary layer between the particle and the gas, surface processes at the particle–gas interface, as well as the internal oxide layer within the particle, considering the transport of reactive O and Fe ions, are resolved. Information from the equilibrium phase diagram, which is included as supplementary data, is used to determine oxidation rate of the particle. The study reveals that finite-rate internal transport significantly alters the temperature evolution compared to models assuming infinitely fast transport. At elevated oxygen concentrations, internal transport becomes rate-limiting, restricting the maximum particle temperature. The core–shell assumption leads to a higher local oxidation degree at the particle–gas interface than the average in the particle, reducing the overall oxygen consumption rate. The maximum particle temperature is reached when heat loss exceeds heat release. Although internal transport limits the maximum temperature, the initial heating rate remains overestimated, suggesting that the initial phase is not solely limited by external oxygen diffusion, and the L2-gas surface is not at thermodynamic equilibrium. The model does not account for the particle size effect on maximum temperature as observed in some experiments. A hypothetical explanation is that internal convection, more pronounced in larger particles, may reduce the internal transport limitation, leading to higher maximum temperatures in larger particles.Novelty and significanceThis study advances the understanding of oxidation rate-limiting mechanisms in liquid iron particle combustion by numerically investigating the impact of internal transport within a core–shell structure. By using a two-dimensional axisymmetric transient continuum model, the research reveals that finite-rate internal transport significantly affects temperature evolution of an oxidizing micron-sized iron particle, particularly at elevated oxygen concentrations where it becomes rate-limiting. The findings demonstrate that a finite-rate internal transport leads to a higher local oxidation degree at the particle–gas interface, reducing the oxygen consumption rates. The study highlights that finite-rate internal transport limits the maximum particle temperature at elevated oxygen concentrations, a trend observed in isolated iron particle combustion experiments. Furthermore, this study provides a hypothetical explanation for the experimentally observed particle size effects on the maximum particle temperature, emphasizing the role of internal convection in larger particles

Interrogating an along-strike variation in the evolution and rheology of a large continental strike-slip fault zone

Along-strike variations in lithology, temperature, fluid activity, etc. can induce rheological changes in strike-slip faults that may be recorded by different fault rocks and fabrics. This article interrogates localized formation of granite-derived mylonite in a large strike-slip fault zone in which ultramylonite is the principle granite-derived fault rock to better understand this rock record of faulting. Microtextures show that rate-limiting deformation mechanisms in mylonite were dislocation creep in quartz and diffusion creep in very-fine-grained feldspar aggregates. Microtextures also show that mylonite formation is fully compatible with continuous viscous deformation whereas coeval ultramylonite along strike formed after whole-rock cataclasis at the brittle-viscous transition. Differential stresses determined from quartz aggregates in ultramylonites are 40–150% greater than stresses in mylonites. Hence, mylonites represent a local weak sector within this otherwise relatively strong fault zone. Mylonite formation is correlated with syndeformational chemical alteration as well as quartz microstructures and mineral assemblages indicating elevated deformation temperatures. Not all mylonite samples record significant chemical alteration. Therefore, mylonite formation likely records locally elevated temperatures. These results illustrate how a local shift in deformation conditions can affect the evolution and rheology of a large strike-slip fault zone, and how fault rocks record these processes.

Maternal investment evolves with larger body size and higher diversification rate in sharks and rays

Across vertebrates, live bearing evolved at least 150 times from ancestral egg laying into diverse forms and degrees of prepartum maternal investment.1,2 A key question is how reproductive diversity arose and whether reproductive diversification underlies species diversification.3,4,5,6,7,8,9,10,11 To test this, we evaluate the most basal jawed vertebrates: the sharks, rays, and chimaeras, which have one of the greatest ranges of reproductive and ecological diversity among vertebrates.2,12 We reconstruct the sequence of reproductive mode evolution across a phylogeny of 610 chondrichthyans.13 We reveal egg laying as ancestral, with live bearing evolving at least seven times. Matrotrophy evolved at least 15 times, with evidence of one reversal. In sharks, transitions to live bearing and matrotrophy are more prevalent in larger-bodied tropical species. Further, the evolution of live bearing is associated with a near doubling of the diversification rate, but there is only a small increase associated with the appearance of matrotrophy. Although pre-copulatory sexual selection is associated with increased rates of speciation in teleosts,3 sexual size dimorphism in chondrichthyans does not appear to be related to sexual selection,14,15 and instead we find increased rates of speciation associated with the colonization of novel habitats. This highlights a potential key difference between chondrichthyans and other fishes, specifically a slower rate of evolution of reproductive isolation following speciation, suggesting different rate-limiting mechanisms for diversification between these clades.16 The chondrichthyan diversification and radiation, particularly throughout shallow tropical shelf seas and oceanic pelagic habitats, appear to be associated with the evolution of live bearing and proliferation of a wide range of maternal investment in developing offspring.

Competition between physical search and a weak-to-strong transition rate-limits kinesin binding times.

The self-organization of cells relies on the profound complexity of protein-protein interactions. Challenges in directly observing these events have hindered progress toward understanding their diverse behaviors. One notable example is the interaction between molecular motors and cytoskeletal systems that combine to perform a variety of cellular functions. In this work, we leverage theory and experiments to identify and quantify the rate-limiting mechanism of the initial association between a cargo-bound kinesin motor and a microtubule track. Recent advances in optical tweezers provide binding times for several lengths of kinesin motors trapped at varying distances from a microtubule, empowering the investigation of competing models. We first explore a diffusion-limited model of binding. Through Brownian dynamics simulations and simulation-based inference, we find this simple diffusion model fails to explain the experimental binding times, but an extended model that accounts for the ADP state of the molecular motor agrees closely with the data, even under the scrutiny of penalizing for additional model complexity. We provide quantification of both kinetic rates and biophysical parameters underlying the proposed binding process. Our model suggests that a typical binding event is limited by ADP state rather than physical search. Lastly, we predict how these association rates can be modulated in distinct ways through variation of environmental concentrations and physical properties.

Quantifying Resistive and Diffusive Kinetic Limitations of Thiophosphate Composite Cathodes in All-Solid-State Batteries

Increasing the specific capacity and rate performance of thiophosphate composite cathodes is a major challenge in solid-state battery development. Understanding the charge transport kinetics and rate-limiting mechanisms within the cathode is key towards efficient optimization. Herein, we use quantitative analysis of chronoamperometric rate performance data to differentiate between resistive and diffusive rate limitations of NCM811—Li6PS5Cl cathodes with different morphology and composition. We substantiate our findings with separate measurements of the effective ionic conductivity and Li+ diffusion coefficients using impedance spectroscopy and GITT techniques, respectively. Increasing the active material to solid electrolyte ratio is found to increase diffusive limitations, which originate from the small contact area between the active material and solid electrolyte. The diffusive limitation is especially pronounced for single crystal NCM811 cathodes at over 84% AM. Employing fine particle catholyte significantly increases the contact area, alleviates the diffusive limitation, and increases rate performance. These results provide guidelines towards bringing the solid-state battery performance levels closer to practical targets.

Rate-limiting mechanism of all-solid-state battery unravelled by low-temperature test-analysis flow

All-solid-state batteries (ASSBs) with potentially improved energy density and safety have been recognized as the next-generation energy storage technology. However, their performances at subzero temperatures are rarely investigated, with rate-limiting process/mechanisms unidentified. Herein, the rate-limiting process/mechanisms for -40℃ ASSBs are accurately identified/analyzed by developing a standard test-analysis flow model. We reveal that the rate-limiting processes of LiCoO2 (LCO)+sulfide solid electrolyte (SE) composite cathode are the sluggish ion transport across unfavorable interfacial reaction layer and charge transfer at damaged LCO cathode surface. After inserting Li2ZrO3 (LZO) coating layer to suppress interfacial reactions, the rate-limiting process of LCO@LZO+sulfide SE composite cathode turns into the arduous ion transport across the interphase composed of the self-decomposition products of sulfide SE. Interestingly, by replacing sulfide SE with halide SE, LCO+halide SE composite cathode delivers fast charge transfer and the ion conduction through the thick SE separator becomes the rate-limiting process, thus enabling a superior capacity retention rate (41.4 %) at -40℃. Furthermore, the capacity retention of ASSB coupling LCO+halide SE composite cathode with Si anode can be boosted from 28.9 % to 38.6 % at -40℃ by employing superionic conductor with low activation energy. These successful identifications/modulations on rate-limiting process/mechanism and improvements on low-temperature performance demonstrate the significant role of this test-analysis flow in propelling the development of low-temperature ASSBs.

Assessment of QOS indicators of a network with UDP and TCP traffic under a node peak load mode

The object of research is Markov models of network nodes with UDP (User Datagram Protocol) and TCP (Transmission Control Protocol) traffic and their differences. The task solved is the lack of Markov models of network nodes describing the behavior of TCP traffic from the point of view of packet retransmissions and packet delivery guarantees. Markov models of network nodes describing traffic behavior with guaranteed packet delivery have been further advanced. Given the comparison of the models, the differences from the classic models serving TCP traffic were shown, for each packet flow, an additional dimensionally was added to the graph of states and transitions, which takes into account the retransmission of a lost packet. The comparison graph shows similar behavior of queue length and packet loss for both types of traffic. But the nature of the curves is different. With TCP traffic, packet loss can exceed 5 percent. In addition, lost packets must be retransmitted, which increases the load on the network node. More failures and packet queue lengths at a network node during peak load typically occur with TCP traffic compared to UDP traffic. At peak load, the difference in service failures can reach 20–30 percent. The main reason is that TCP uses flow control and rate-limiting mechanisms to avoid network congestion and ensure efficient data transfer between nodes. The Markov model of TCP traffic requires an additional dimensionally on the graph of states and transitions, which affects the behavior of queues and packet failures. The investigated problem was solved due to the universality and diversity of the mathematical apparatus of Markov mass service systems. The results could be used in network modeling software products for building and reengineering the topology of electronic communications networks at enterprises and organizations

An additively manufactured near-eutectic Al-Ce-Ni-Mn-Zr alloy with high creep resistance

A new additively manufactured (AM) Al-7.5Ce-4.5Ni-0.4Mn-0.7Zr (wt.%) near-eutectic alloy is reported, which shows unprecedented creep resistance up to 400 °C (a homologous temperature of 0.72). The eutectic solidification microstructure comprises ∼ 27 vol% of coarsening-resistant second phase network with an ultrafine (<100 nm) inter-phase spacing. Both Mn and Zr contribute to creep resistance of the alloy. Small amount of Mn addition promotes selection of coarsening resistant phases without compromising the alloy processability. Zr not only improves hot-tearing resistance, but further enhances the second phase coarsening resistance resulting in improved creep resistance. Neutron diffraction performed during creep deformation reveals that the underlying mechanism for creep resistance in this alloy is impedance to dislocation motion stemming from the ultrafine eutectic solidification microstructure, whereas load transfer strengthening becomes less effective as the creep temperature increases. The second phase forms a continuous network in the as-fabricated condition, which is maintained during long-term creep at 300 °C. However, this network is fragmented into fine dispersoids at higher temperatures. It is proposed that the rate-limiting deformation mechanism at 300–400 °C is (i) dislocation climb for the alloy with fragmented second phase dispersoids and (ii) Orowan looping for the alloy with a continuous second phase network. The present design of an AM-processable multicomponent eutectic alloy with high creep resistance can be applied to other metallic systems exhibiting eutectic reactions, with expected extreme creep resistance.

The reciprocity principle in mulch film deterioration and microplastic generation.

Plastic film mulching stands as a globally employed agricultural technology pivotal to agricultural progress. Nevertheless, the environmental degradation of plastic mulch films underscores their role as a major source of secondary plastic pollutants, particularly microplastics. While a growing body of research has drawn attention to the rising issue of microplastic pollution and its environmental implications stemming from the use of plastic mulch films, there remains a significant knowledge gap regarding the kinetics and rate-limiting mechanisms governing the generation of microplastics during processes driven by plastic photodegradation. Moreover, a comprehensive quantification of the connection between mulch deterioration and the behavior of microplastic release and accumulation has yet to be fully realized. In this study, a kinetic equation was formulated to characterize the degradation of plastic mulch films and the subsequent release and accumulation of microplastics under light exposure. The results demonstrate that with increasing irradiation time, the change in the release rate exhibits a bell-shaped Gaussian probability distribution, while the cumulative alteration of microplastics follows a Gaussian distribution. Remarkably, once the exposure time reaches μ + 3σ, the accumulation plateaus at 99.7%. This research establishes a theoretical framework for the prospective assessment of plastic mulch lifespan and its environmental repercussions. Moreover, the findings provide valuable insights for optimizing plastic mulch design and devising strategies to mitigate microplastic pollution.

Hybrid electromagnetic field-flow by electrode configuration for the removal of phenol from contaminated water

In this study, we introduce an electrode configuration setup to study the effect of an electromagnetic field (EMF) and electric potential (EP) on phenol removal in a continuous adsorption process. Feed water contaminated with dissolved phenol was exposed to EMF and passed through charged activated carbon electrodes prepared from Phoenix dactylifera (palm tree) biowaste. This study investigated the effects of magnetic field exposure, electric potential, feed salinity, and electrode substrate type. The results revealed that the highest adsorption uptake capacity of 47.2 mg/g was achieved using an aluminum substrate (AS) with EMF at zero salinity. The phenol adsorption kinetics followed a pseudo-second-order adsorption rate and diffusion model, indicating that intraparticle diffusion was the primary rate-limiting mechanism. The increased phenol adsorption uptake capacity brought on by the EMF may result from the improved mass transfer and mobility of the adsorbate and, consequently, the increased effectiveness of the internal diffusion of the pollutants. Finally, a regeneration efficiency of 99 % was achieved using NaOH at a salinity of 5,000 ppm.

Mass transfer in atmospheric water harvesting systems

In this work, the rate-limiting diffusion mechanisms of MOF-303, MOF-333, and a multivariate (MTV) version of these metal–organic frameworks (MOFs), where the organic linkers are present in a 50/50 ratio, are identified and quantified using concentration swing frequency response (CSFR). The data show that the single-atom precision of MOFs allows for precise tuning of the diffusion rate that is not easily achieved in traditional adsorbent materials. The Maxwell-Stefan diffusivity as a function of loading was calculated to decouple the influence of molecular mobility and equilibrium effects. To further understand the diffusion process in these MOFs, samples with different crystal sizes were synthesized and diffusion rates were measured. The results show that the controlling diffusion length scale is similar between the small and large crystal samples, as evidenced by similar diffusion rate constants. The MOFs were then incorporated into a film using a binder system and the mass transfer mechanisms were identified using CSFR. When placed in this particular binder system, the macropore diffusion behavior dominates over the MOF micropore diffusion. To illustrate how these diffusion parameters govern the adsorption rates and dynamics of water-harvesting systems, a model of the MOF-coated tube was developed. The results show that, with only milligrams of adsorbent, CSFR can quantify the diffusion rate needed to predict the adsorption times in a water-harvesting system. More broadly, the results illustrate the connectivity between atomically-precise reticular chemistry and water-harvesting system performance.

Removal of Pyridine from Aqueous Solutions Using Lignite, Coking Coal, and Anthracite: Adsorption Kinetics

A novel coking wastewater treatment technique is proposed based on the principles of the circular economy. By utilizing coal as an adsorbent for organic pollutants in coking wastewater, the treated coal can be introduced into the coking system after the adsorption and flocculation sedimentation processes. This creates a closed-loop system with zero coking wastewater emissions. We investigated the potential of adsorption for the removal of pyridine. Batch experiments were conducted using lignite, coking coal, and anthracite as adsorbents. Both coking coal and anthracite showed favorable adsorption properties for the chosen contaminants. The experimental data were analyzed utilizing various models, including pseudo-first-order and pseudo-second-order kinetic equations, as well as intraparticle diffusion and Bangham. This study aimed to identify the rate-limiting step in the adsorption process. The results revealed that the adsorption of pyridine onto the three coal types followed pseudo-second-order kinetics. The rate-limiting mechanisms may include both boundary-layer diffusion and intraparticle diffusion. The effect of pH on coal adsorption and the activation energy of pyridine adsorption by coking coal were also examined. Adsorption offers a promising approach in advanced wastewater treatment, with coking coal emerging as a cost-effective adsorbent for addressing persistent organic pollutants during the adsorption process.

Substrate-related factors and kinetic studies of Carbohydrate-Rich food wastes on enzymatic saccharification

Food waste biorefinery is a sustainable approach to producing green chemicals, however the essential substrate-related factors hindering the efficacy of enzymatic hydrolysis have never been clarified. This study explored the key rate-limiting parameters and mechanisms of carbohydrate-rich food after different cooking and storing methods, i.e., impacts of compositions, structural diversities, and hornification. Shake-flask enzymatic kinetics determined the optimal dosages (0.5 wt% glucoamylase, 3 wt% cellulase) for food waste hydrolysis. First order kinetics and simulation results determined that reaction coefficient (K) of cooked starchy food was ∼ 3.63 h−1 (92 % amylum digestibility) within 2 h, while those for cooked cellulosic vegetables were 0.25–0.5 h−1 after 12 h of hydrolysis. Drying and frying reduced ∼ 71–89 % hydrolysis rates for rice, while hydrothermal pretreatment increased the hydrolysis rate by 82 % on vegetable wastes. This study provided insights into advanced control strategy and reduced the operational costs by optimized enzyme doses for food waste valorization.

Sorption of Pb2+, Zn2+, Cu2+ and Ni2+ Ions on Na-enriched Natural Zeolite for Wastewater Treatment Process: A Kinetic Approach

Low-cost and easily available natural zeolite is a promising adsorbent for metal ions removal in wastewater treatment. The possibility of using zeolitic tuff from Serbia in the form of Na-enriched natural zeolite (Na-Z) for the adsorption of Pb2+, Zn2+, Cu2+, and Ni2+ ions from wastewater was investigated in the presented paper. The research included Na-Z characterization and determination of adsorption kinetics in individual ion adsorption tests using non-linear pseudo-first-order (PFO), pseudo-second-order (PSO) and mixed-order (MO) kinetic models. The results indicate that the adsorption processes of metal ions on Na-Z are complex processes dominated by multiple rate-limiting mechanisms and best defined by the MO model. The mechanisms of ion diffusion and adsorption to active sites are equally represented in the Pb2+ ions adsorption process. The mechanism of ion diffusion is more pronounced in the Zn2+ ions adsorption process, while in the case of the adsorption of Cu2+ and Ni2+ ions adsorption on the active sites is the main kinetic mechanism. Within the MO model, the PFO rate (external/internal diffusion) and the PSO rate (adsorption on the active sites) were calculated and results were applied to a multicomponent wastewater sample in order to determine and explain the adsorption efficiency in wastewater treatment. The results show that the rate of adsorption of individual metal ions and the efficiency of ion removal from a multicomponent wastewater sample are influenced by several factors including the radius of the hydrated ion and the free energy of hydration. The achieved removal of metal ions by Na-Z is Pb2+ (89%) &gt; Cu2+ (72%) &gt; Zn2+ (61%) &gt; Ni2+ (58%) and defines Na-enriched natural zeolite as an effective adsorbent in wastewater treatment.

An expanding mechanical role for the tiny mammalian endolymphatic duct: 2. An explanation for the beaching of whales–failure of osmotic pressure counterbalancing mechanism in the cochlea causing acute vertigo attack

Endolymphatic Hydrops (EH) describes a swelling of the endolymphatic duct (ED). It is a key correlate of human Ménière’s disease featuring incapacitating giddy attacks. Direct measurements by micropuncture to be presented support the hypothesis that swelling occurs because water flows through aquaporins into the ED under an osmotic gradient to stabilize basilar membrane position against deep dive pressures. Patients having vestibular attacks often display nystagmus if not also perilymphatic fistulae or dehiscences. As shown by Ketten et al. (2004), stranded whales also exhibit nystagmus and also intracochlear bleeding. Here, EH is modelled as a normal rate-limited osmotic mechanism which likely evolved to cope with synoptic variation. It has been extensively adapted by beaked whales to allow diving to feed on squid at great depths—where they still need to hear. Their more-robust EDs normally cope with very slow equalization against megapascal pressures. An unexpected undersea pressure transient may trigger perilymph-endolymph membrane rupture and consequent vertigo attack, well documented in humans. Due to acoustic spread, whole pods may be variously affected. Humans need to remain stationary while waiting hours for their attack to subside. Marine mammals with limited oxygen stores may panic and surface too quickly, accounting for life-threatening decompression sickness.

Diffusion of halogens (F, Cl, Br, I) in silicic melt

Chemical diffusion of the halogens F, Cl, Br, and I in silica-rich natural melts was experimentally investigated by the diffusion couple technique. Experiments were conducted under anhydrous conditions at atmospheric pressure and hydrous conditions (∼1.5 wt% H2O) at 160 MPa, over a temperature range of 750–1000 °C and 1000–1200 °C, respectively. Quenched trachytic melt samples were analyzed using an electron microprobe (EPMA) and secondary ion mass spectrometry (SIMS).All halogens exhibit Arrhenian behaviour during diffusion in the investigated melt compositions with F always diffusing fastest. The other halogens show progressively slower diffusion (F > Cl > Br > I) correlated to their ionic radii. In anhydrous melt a diffusivity range of 3–4 orders of magnitude is covered among the halogens with DF(1000 °C) ∼5 × 10−13 m2s−1 and DI(1000 °C) ∼1 × 10−16 m2s−1. The diffusivities of all halogens increase in hydrous melt with the largest increase being observed for the slowest-diffusing halogens, e.g., resulting in an increase of up to 2 orders of magnitude for iodine at 1000 °C compared to the anhydrous case. This behavior yields a narrower overall diffusive range of only 1–2 orders of magnitude among all halogens. Activation energies (EA) of diffusion consistently range from ∼200 to 390 kJ mol−1 in anhydrous melts. In hydrous melt EA generally decreases, with the highest decrease determined for F (∼131 kJ mol−1) and only slight changes for the other halogens (∼201–222 kJ mol−1).Our diffusivity data of the anhydrous series exhibit a pronounced correlation of diffusivity with the ionic radii, however, this correlation is attenuated in hydrous melt. While in anhydrous melt, halogen diffusion is closely related to ionic porosity, in hydrous experiments, the process of ionic detachment becomes more important as a rate-limiting diffusion mechanism, e.g., comparable to the case of diffusion of divalent/trivalent cations.The results of this study provide the first consistent diffusion dataset including all halogens under naturally relevant magmatic conditions and highlight the pronounced compositional effect of both, major element and dissolved H2O on halogen diffusion. The derived diffusion parameters may be readily used for modelling of diffusive fractionation in silicic melts or determining the timescales of natural silicic volcanic processes based on halogen concentration measurements. Furthermore, these data emphasize the potential of diffusive fractionation among the halogens, which may be applied as a monitoring tool for volcanic unrest on actively degassing volcanoes.

Metallized reactive materials – a road to clean and sustainable pyrotechnics

Since the introduction of nitroglycerine as a blasting explosive by Nobel in 1867, enormous progress has been made in improving the performance and reducing the sensitivity of energetic materials. The introduction of nitrogen rich (N>60 %) oxidizers such as 5,5′-hydrazinebistetrazole (HBT) was one very important step in increasing the detonation performance and thermal stability of high explosives. Concurrently, the introduction of metal fuels which can react at high temperatures attracted significant interest, improving combustion performance while also reducing the sensitivity of propellants and pyrotechnics. This is largely because metals such as aluminum, magnesium, titanium, zirconium and boron have very high volumetric (30–140 kJ cm−3) and gravimetric energy densities (10–50 kJ g−1) compared with other chemical fuels. These fuels are also chemically stable solids, which simplifies storage and transport. Furthermore, they can be ignited and burned with oxidizers (air, metal nitrate, metal oxides) or water, to produce large amounts of heat, or hydrogen and heat. The study of metal fuel combustion dates back to the 1960s, and is driven by the potential applications of these fuels as additives in propellants, explosives and pyrotechnics to increase energy density and burn rates. Since then, significant research efforts have been devoted to thermites and nanothermites using different metal/metal oxide combinations and custom nanostructured architectures. Unlike explosives, these materials undergo a rapid deflagration driven by a carbon free oxidation-reduction reaction, which forms stable reaction products (metal oxides or hydroxides) that can be recycled with zero-carbon reduction processes. Moreover, these products have stronger mechanical strength and heat resistance than explosives. They are versatile: different combustion effects can be obtained by manipulating the reactive system (metal and oxide powders) and their microscopic and mesoscopic morphology. They can be printed, which enables unique geometries and control over their energetic behavior – such as ignitability and mechanical characteristics – which is not easily possible with explosives manufactured by slurry loading, melt-casting, cast-curing or powder-pressing. Finally, thermites and nanothermites can burn in high vacuum, underwater and in other harsh environments. For this reason, from the year 2000 onwards, metallized reactive materials and related processes have attracted considerable attention from industry as extremely useful energetic substances and technologies for: i) initiation, ii) clean propulsion and power generation (thermal batteries), iii) self-destructing microchips and infrastructure protection, iv) energy sources or supplies for outer space use, v) long ceramic-lined pipes welding in geothermal power plants, and vi) agent deactivation. Many other applications will likely be addressed in the future. Yet, the effective deployment of such promising energetic materials into these various applications faces a major hurdle. The “Edisonian” approach based on trial-and-error processes used in most research laboratories is not suited to these complex energetic systems, in which not only the chemistry but also the microscopic (particle scale) and mesoscopic properties (systems of hundreds of particles, binder) influence macroscopic energetic performance. A requirement-driven design approach relying on both mechanistic and statistical models should be preferred for a cost-effective customization of the best metal/oxide configurations to each function, considering all application requirements such as cost, technological compatibility and other constraints. To achieve these ambitious objectives research is needed on several fronts, specifically: i) developing mechanistic models for metal combustion in various oxidizing environments; ii) quantifying the key condensed and gas phase mechanisms that govern metal oxidation at elevated temperatures, particularly above the critical point where oxide solubility could change significantly and improve reaction rates and yields; iii) enhanced understanding of the physics of turbulent and “discrete” flames. These requirements necessitate the use of advanced diagnostics (laser-based optical diagnostics, time-resolved mass spectrometry) and state-of-the-art experimental methods to enable determination of reaction rates, energies, and rate-limiting mechanisms of these complex reactive systems. Collaboration with data science researchers is also urgently needed to develop not only surrogates for physical models but also inverse models which will enable the discovery of new metal fuel/oxidizer configurations that cannot be imagined by the user because of the quantity of variables impacting metal fuel combustion, e. g., shape and size of the grain of each powder, compaction, stoichiometry, environment, etc. In conclusion, the fusion of physics simulation and machine learning approaches will enable us to fully realize the benefits of metallized reactive materials, and may consequently lead to a paradigm shift in pyrotechnics.

Progression of creep deformation from grain boundaries to grain interior in Al-Cu-Mn-Zr alloys

Creep mechanisms are studied in θ′-Al2Cu-strengthened Al-Cu-Mn-Zr alloys at 300 and 350°C for (i) ACMZ, a base alloy without further alloying elements and (ii) RR350, a commercial alloy with additions of Ni and Co forming distinct grain-boundary precipitates. At high stresses, creep is dominated by dislocations bypassing θ′ precipitates within grains via the Orowan mechanism, as evidenced by (ⅰ) very high stress exponent (n∼20-25) and (ⅱ) α-Al and θ′ lattice strains (measured via in-situ neutron diffraction) evolving during creep in a manner consistent with load transfer from the plastically-deforming α-Al matrix to elastically-deforming θ′ precipitates. At intermediate stresses, both alloys exhibit a n∼3 regime, where α-Al and θ′ lattice strains scale near-linearly with applied stress while remaining largely unaffected by strain accumulation, indicating that Orowan looping or dislocation pile-up around θ′ is now inactive within the grains. Rather, dislocation motion occurs solely in θ′-precipitate-free zones (θ′-PFZ) where high dislocation densities are observed via TEM after creep deformation. Plastic flow at θ′-PFZ and/or localized pipe diffusion are expected to enable grain-boundary sliding (GBS), which is proposed as the rate-limiting mechanism in the n∼3 regime. Ni/Co-rich precipitates at RR350 grain-boundaries, with negligible θ′-PFZ around them, share load (as determined via neutron diffraction) with the α-Al matrix more effectively than θ-Al2Cu precipitates at ACMZ grain-boundaries, with wide surrounding θ′-PFZ. Thus, high creep resistance in the n∼3 GBS regime of RR350 is enabled by coarsening-resistant grain-boundary precipitates, forming without concomitant development of weak θ′-PFZ, which effectively share load with the grains.

Are Three-Dimensional Batteries Beneficial? Analyzing Historical Data to Elucidate Performance Advantages

Conventional lithium-ion batteries (LIBs) are composed of planar stacks of anodes, cathodes, and separators, all immersed in electrolyte and sandwiched between current collectors. However, planar LIBs have a performance trade-off where increasing electrode thickness leads to higher capacity but lower rate capability. Three-dimensional (3D) batteries circumvent this issue with 3D electrode architecture. Herein, we systematically analyze 3D LIBs from experimental publications over the past 20 years. Using a previously developed empirical model, we obtain parameters to quantify the rate capability and rate-limiting mechanisms of 3D LIBs. Compared to conventional LIBs, 3D LIBs exhibit better rate capability─confirming their expected performance benefit. To provide further insight, we investigate the impact of liquid-phase and solid-phase diffusion mechanisms on this performance benefit. Lastly, we discuss the design landscape of 3D LIBs across multiple electrode designs and material sets and highlight our perspective on the applicability of 3D LIBs at different application scales.

Influence of Pore Size on Hydrocarbon Transport in Isostructural Metal-Organic Framework Crystallites.

Hydrocarbon separations using porous materials such as metal-organic frameworks (MOFs) have been proposed to reduce the energy demands associated with current distillation-based methods. Despite the potential of these materials to distinguish hydrocarbons through thermodynamic or kinetic mechanisms, experimental data quantifying hydrocarbon transport in MOFs is lacking. Such mass transfer measurements are vital to elucidate structure-property relationships and design future high-performing separation materials. In this work, we aim to isolate the influence of pore size on hydrocarbon diffusion by studying a pair of isoreticular MOFs, Co2Cl2BBTA and Co2Cl2BTDD. We use a volumetric method to extract mass transport coefficients for six hydrocarbon probe molecules of varying size and chemical functionality. From these nonequilibrium mass transport measurements, we determine the rate-limiting diffusion mechanism and identify trends in hydrocarbon surface permeabilities in the MOFs based on pore size, hydrocarbon chain length, and temperature.