Thermochemical Conditions Research Articles

Cleavable Bio-Based Epoxy Matrix for More Eco-Sustainable Thermoset Composite Components.

Cleavable bio-based epoxy resin systems are emerging, eco-friendly, and promising alternatives to the common thermoset ones, providing quite comparable thermo-mechanical properties while enabling a circular and green end-of-life scenario of the composite materials. In addition to being designed to incorporate a bio-based resin greener than the conventional fully fossil-based epoxies, these formulations involve cleaving hardeners that enable, under mild thermo-chemical conditions, the total recycling of the composite material through the recovery of the fiber and matrix as a thermoplastic. This research addressed the characterization, processability, and recyclability of a new commercial cleavable bio-resin formulation (designed by the R-Concept company) that can be used in the fabrication of fully recyclable polymer composites. The resin was first studied to investigate the influence of the different post-curing regimes (room temperature, 100 °C, and 140 °C) on its thermal stability and glass transition temperature. According to the results obtained, the non-post-cured resin displayed the highest Tg (i.e., 76.6 °C). The same post-curing treatments were also probed on the composite laminates (glass and carbon) produced via a lab-scale vacuum-assisted resin transfer molding system, evaluating flexural behavior, microstructure, and dynamic-mechanical characteristics. The post-curing at 100 °C would enhance the crosslinking of polymer chains, improving the mechanical strength of composites. With respect to the non-post-cured laminates, the flexural strength improved by 3% and 12% in carbon and glass-based composites, respectively. The post-curing at 140 °C was instead detrimental to the mechanical performance. Finally, on the laminates produced, a chemical recycling procedure was implemented, demonstrating the feasibility of recovering both thermoplastic-based resin and fibers.

Collision Energy Dependence of Particle Ratios and Freeze-out Parameters in Ultra Relativistic Nucleus Nucleus Collisions

This work investigates the thermo-chemical freeze-out condition of the multi-component hot and dense hadron resonance gas (HRG) formed in the ultra-relativistic nucleus-nucleus collisions (URNNC). The van der Waals (VDW) type model used in the present analysis incorporates the repulsive as well as attractive interactions among the hadrons. The baryons (antibaryons) are treated as incompressible objects. Using this theoretical approach the values of the model freeze-out parameters of the system are extracted over a wide range of collision energy by analyzing experimental data on like-mass antibaryon to baryon ratios. The same set of parameters is found to explain the energy dependence of several other particle ratios quite satisfactorily. We find that the horn-like structures seen in the ratios of strange particles to pions as a function of the collision energy cannot be explained by the VDW-HRG model alone without considering the strangeness imbalance effect in the system. We have compared our freeze-out line with those obtained earlier. The correlation between the p¯/p and K−/K+ ratios is also examined.

Preliminary analysis of an integrated ICE-gasifier plant for power generation from plastic waste material

Abstract The escalating global production of plastic waste is a challenge that must be rapidly addressed, but it also conceals opportunities. Currently, only a minor portion of the worldwide plastic waste is recycled, with the remainder destined for either incineration or landfill. In this context, gasification emerges as a sustainable alternative to conventional waste management methods, offering a substantial reduction in pollutant emissions. Dioxins and furans emissions, in fact, are drastically reduced when compared to incineration. Additionally, in contrast to landfill disposal, gasification allows for the recovery of chemical energy contained in plastic that would otherwise be wasted. The study of plastic gasification is gaining attention and several studies demonstrated feasibility and effectiveness, despite it is not as established as biomass gasification. The present paper aims at taking a step forward by conceptualizing an integrated gasifier-internal combustion engine power plant, operating in a closed-loop system. This layout offers potential benefits from both energetic and environmental points of view, respectively related to the recovery of engine waste gas and CO2 emission reduction. The proposed plant is based on the steam/CO2 gasification technique, which allows the complete conversion of input CO2 into syngas under certain thermochemical conditions. This feature enables the operation of engine and gasifier in a closed-loop system, directly exploiting the exhaust gas to perform plastic gasification. A thermodynamic feasibility study is performed, accounting for the efficiency of the main components, the heat fluxes and the heat absorbed by the endothermic reactions inside the gasifier. The setup of the proposed power plant shows an energy conversion efficiency up to 18% in a pure electric generation scenario and up to 56% in a cogeneration scenario.

Enhanced bioethanol production from cassava waste: optimization of thermochemical pretreatment for maximum sugar recovery and characterisation of potential fractions

ABSTRACT Thermochemical pretreatment is an interesting approach for the effective separation of lignocellulosic biomass before fermentation for bioethanol production. This research focused on optimising the thermochemical pretreatment conditions of cassava waste using response surface methodology to predict the glucose yields under the optimal condition. The optimised conditions of 0.045 M of NaOH concentration at 153.59 °C for 48.03 min resulted in the maximum glucose yield of 93.87%. In addition, fermentation process can generate ethanol within a range of solid loading from 10% to 20%. The highest concentration of ethanol was 34.53 ± 0.56 g/L after 72 h, equivalent to ethanol yield of 0.46 g/g. The co-products were also characterised for further utilisation in biorefinery concept. The results of this study confirmed that the thermochemical pretreatment process using the NaOH catalyst could provide high glucose yields, which can be easily converted into bio-based fuels and further valorised of co-products to value-added chemicals.

1D modeling of plasma streamers at ammonia-air flame conditions

Abstract This work is a self-consistent 1D modeling of streamers in ammonia-oxygen-nitrogen-water mixtures. A fluid model that includes species transport, electrostatic potential, and detailed chemistry was developed and verified. This model is then used to simulate the avalanche, streamer formation and propagation phases, driven by a nanosecond voltage pulse, at different thermochemical conditions derived from a 1D laminar premixed ammonia-air flame. The applicability of the Meek’s criterion in predicting the streamer inception location was successfully confirmed. Streamer formation and propagation duration were found to vary significantly with different thermochemical conditions, due to the difference in ionization rates. The thermochemical state also affected the breakdown characteristics which was tested by maintaining the background reduced electric field constant. Detailed kinetic analyses revealed the importance of O(1D) in the production of key radicals, such as O, OH, and NH2. Furthermore, the contributions of the dissociative electronic excitation of NH3 towards the production of H and NH2 radicals have also been reported. Spatial and temporal evolution of the electron energy loss fractions for various inelastic collision processes at different thermochemical states uncovered the input plasma energy spent of fuel dissociation and the large variability in the dominant processes during the avalanche and streamer propagation phases. The methodology and analyses reported in this work are key towards developing effective strategies for controlled nanosecond-pulsed non-equilibrium plasma sources used for ammonia ignition and flame stabilization.

Cenozoic Volcanic Provinces and Shallow Asthenospheric Volumes in the Circum‐Mediterranean: Evidence From Magmatic Geochemistry, Seismic Tomography, and Integrated Geophysical‐Petrological Thermochemical Inversion

AbstractWe compile an extensive catalog comprising geochemistry and ages of Cenozoic volcanic provinces in the Mediterranean region, distinguishing between three groups according to the geochemistry of magmatic rocks: intraplate (IVP), subduction‐related (SRVP), and mixed‐origin volcanic provinces (MVP; intraplate with subduction imprint). In order to relate their spatial distribution to properties of the lithosphere‐asthenosphere system, we determine temperature‐depth profiles by integrated geophysical‐petrological inversion at representative locations, using Rayleigh and Love wave phase velocities, heat flow, rock densities, and accounting for thermochemical conditions. The results confirm the occurrence of thin lithosphere (<100 km) above warm asthenosphere (>1,300°C) in areas of low shear‐wave velocities in the shallow upper mantle. Nine shallow asthenospheric volumes (SAVs) between 70 and 300 km depths are identified, forming a partly interconnected belt across the Circum‐Mediterranean. A remarkable colocation exists between the SAVs and the intraplate and mixed‐origin volcanic provinces (IMVPs). Whereas dense networks of IMVPs have formed above the SAVs, IMVPs are absent in areas of thick mantle lithosphere. Magmatic activity in IMVPs at 60–70 Ma indicates that several SAVs existed already in the Paleogene (Central European, Adriatic, Western Mediterranean, and Moesian SAVs). The formation of SAVs is related either to asthenospheric upwelling caused by slab rollback and back‐arc extension (Aegean‐Anatolian, Moesian, Pannonian, Western Mediterranean SAVs), or to thermal upwelling (Adriatic, Central European, Middle East [MEA], North African, Rhine‐Rhone SAVs), with some of the latter coupled partly with continental rifting (Central European, MEA, North African, Rhine Rhone SAVs).

Double flame dynamics in hotspot ignition

Hotspot ignition is a key problem in fundamental flame initiation, combustion control and prevention of abnormal combustion phenomena. Depending on the characteristics of the hotspot and the thermochemical condition of the reactive mixture, subsequent reaction front initiated from a hotspot can vary substantially. The current paper focus on the dynamics and chemistry for one of the most complicated scenarios - hotspot induced double flames, which include a cool and a hot flame segment. This work adopts a recently developed compressible reacting flow simulation code COGNAC to investigate the initiation and propagation of double flame dynamics from hotspot ignition in a one-dimensional spherical coordinate. The results have shown that under atmospheric pressure, double flame initiation is not feasible for sufficiently small hotspot. Under elevated pressures, double flame can be initiated within a much wider hotspot window, exhibiting complex flame dynamics, such as variations in cool and hot flame bifurcation behaviors and their initiation locations. Analysis on thermochemical structure and dynamics of double flame has shown that the interaction of cool and hot flames in a double flame structure is inherently intermutual, in that the leading cool flame enhances trailing hot flame speed through reform of the unburnt mixture, while the trailing hot flame initiation affects the leading cool flame via thermal expansion effects.

Impact of Thermochemical Treatments on Electrical Conductivity of Donor-Doped Strontium Titanate Sr(Ln)TiO3 Ceramics.

The remarkable stability, suitable thermomechanical characteristics, and acceptable electrical properties of donor-doped strontium titanates make them attractive materials for fuel electrodes, interconnects, and supports of solid oxide fuel and electrolysis cells (SOFC/SOEC). The present study addresses the impact of processing and thermochemical treatment conditions on the electrical conductivity of SrTiO3-derived ceramics with moderate acceptor-type substitution in a strontium sublattice. A-site-deficient Sr0.85La0.10TiO3-δ and cation-stoichiometric Sr0.85Pr0.15TiO3+δ ceramics with varying microstructures and levels of reduction have been prepared and characterized by XRD, SEM, TGA, and electrical conductivity measurements under reducing conditions. The analysis of the collected data suggested that the reduction process of dense donor-doped SrTiO3 ceramics is limited by sluggish oxygen diffusion in the crystal lattice even at temperatures as high as 1300 °C. A higher degree of reduction and higher electrical conductivity can be obtained for porous structures under similar thermochemical treatment conditions. Metallic-like conductivity in dense reduced Sr0.85La0.10TiO3-δ corresponds to the state quenched from the processing temperature and is proportional to the concentration of Ti3+ in the lattice. Due to poor oxygen diffusivity in the bulk, dense Sr0.85La0.10TiO3-δ ceramics remain redox inactive and maintain a high level of conductivity under reducing conditions at temperatures below 1000 °C. While the behavior and properties of dense reduced Sr0.85Pr0.15TiO3+δ ceramics with a large grain size (10-40 µm) were found to be similar, decreasing grain size down to 1-3 µm results in an increasing role of resistive grain boundaries which, regardless of the degree of reduction, determine the semiconducting behavior and lower total electrical conductivity of fine-grained Sr0.85Pr0.15TiO3+δ ceramics. Oxidized porous Sr0.85Pr0.15TiO3+δ ceramics exhibit faster kinetics of reduction compared to the Sr0.85La0.10TiO3-δ counterpart at temperatures below 1000 °C, whereas equilibration kinetics of porous Sr0.85La0.10TiO3-δ structures can be facilitated by reductive pre-treatments at elevated temperatures.

Quantitative measurement of sodium emissions during oxy-fuel combustion of a beech wood biomass particle using laser-induced breakdown spectroscopy

Oxy-fuel biomass combustion in a circulating fluidized bed is a clean and sustainable biomass utilization technology. Woody forest biomass is considered a promising source of renewable energy because of its widespread availability across the globe. However, effective biomass utilization in thermal power plants is largely limited by severe ash deposition and corrosion of heat transfer surfaces due to alkali metal and chlorine emissions during biomass combustion. In this study, laser-induced breakdown spectroscopy (LIBS) was applied to detect in-situ gas phase sodium (Na) emission during single particle combustion of widely available forest biomass, namely, beech wood. The operating conditions simulate the thermo-chemical conditions relevant to a fluidized bed combustor system, where the operating temperature varies between 1073K–1273K. This work aims to investigate the effect of O2 concentration, CO2 (oxyfuel environment), and particle size on the emission of sodium during the combustion of a single beech wood particle. The unresolved sodium doublet was used as the LIBS signal to quantify sodium emission concentration.Oxygen concentration is the most critical parameter affecting Na emissions, and an increase in O2 concentration led to higher Na emissions. It is observed that there is a significant reduction in the emission of Na in an O2/CO2 environment as compared to an O2/N2 environment. It is hypothesized that this drop in Na emissions in O2/CO2 environment could be due to lower particle temperatures caused by the lower diffusivity of O2 in CO2 as well as the endothermic gasification reaction in high CO2 environments. In addition, it is reported that the dissociation of sodium carboxylates and carbonates in the biomass matrix to release gaseous Na due to thermal decomposition is retarded at higher CO2 concentrations which could explain the drop in Na emissions. The effect of biomass particle size is pronounced mainly at lower concentration of O2 where, larger particles keep Na trapped in its matrix, however, at higher O2 concentrations (30%), the effect of particle size on Na emission is negligible.

Alkali hydrolysis of wool fibres using microwave irradiation as a recycling approach for handling wool-waste

The aim of the present work is to investigate the influence of microwave irradiation on alkali hydrolysis, under various thermochemical conditions, of wool fibres. This perspective seems to be a promising alternative for the valorization of wool waste. The reaction yield is calculated in every case in order to determine the optimum hydrolysis conditions. The solid residue, as well as the filtrate, are subjected to instrumental chemical analysis in order to identify and isolate useful products. The optimal conditions for the hydrolysis of wool resulted to be the use of 5% w/v NaOH, microwave treatment for 10 min in absence of phase-transfer catalyst. In addition, the analysis in the Pyrolysis-Gas Chromatography/Mass Spectrometry (Py-GC/MS) allowed the identification of certain small molecules like N2, H2S, NH3, C6H5OH, C4H9NO and larger ones like amino acids, such as alanine, cystine, proline, valine and leucine. Additionally, the content of wool hydrolysate was specified upon identifying several substituted products of tyrosine, proline and alanine amino acids. Liquid Chromatography–Orbitrap High-Resolution Mass Spectrometry (LC–Orbitrap HRMS) was also employed to identify the components present in the wool hydrolysate, detecting mainly various dipeptides as well as leucylproline and cysteic acid. In this light, the amino acids produced by wool alkali hydrolysis degradation could valorise the wool waste once inserted in industrial chemistry, as a prominent alternative for “greener” adhesives of two components, outlining by these means the feasibility of a practically sustainable circular economy.

Time domain NMR evaluation of thermal and thermochemical aging of nitrile rubber on crosslinking and mechanical properties

This study investigates the impact of aging on nitrile rubber (NBR) compositions under thermal and thermochemical aging conditions. The effects of aging were assessed using the 1H Double Quantum Time Domain NMR (DQ-NMR) technique, providing molecular-scale insights into average cross-link density, spatial heterogeneity, and network inelastic defects. The aging's influence on the macroscopic mechanical properties of NBR, including hardness, elongation, and stress at break, known to be closely related to cross-linking, was examined. It was observed that temperature-induced aging affected NBR differently based on the acrylonitrile content and solvent absorption capacity. 1H Double Quantum Time Domain NMR provided evidence of increasing heterogeneous cross-linking, which created a denser network structure. The changes in mechanical properties during aging were consistent with the NMR analyses, providing valuable insights for understanding, customizing, and predicting the service life of a specific O-Ring based NBR formulation.

Soybean hulls activated carbon for metronidazole adsorption: Thermochemical conditions optimization for tailored and enhanced meso/microporosity

In this work, the use of soybean hulls as a residual biomass precursor for highly porous carbon materials through thermochemical treatments was assessed, aim to modify the surface chemistry and obtain enhanced chemistry and textural properties for the metronidazole (MTN) drug adsorption. Initially, the biomass was subjected to different chemical treatments followed by pyrolysis under fixed conditions. The modified carbon materials were evaluated in terms of residual surface charge, surface chemistry, and adsorption capacity. After determining the most appropriate chemical treatment, the optimized thermochemical conditions were investigated. Remarkable textural properties (Stotal= 1355.7 m2 g−1) of the activated carbon derived from dilute acid-alkali combined treatment (AC-CT) were achieved under the following conditions: T = 925 °C; t = 145 min and C= 0.3 mol L−1, which led to an increase in the adsorption capacity up to q= 51.25 mg g−1 (50% higher than the biochar). This increase in MTN adsorption performance is possibly related to the increase in the micropore area (SMICRO= 800.7 m2 g−1) and volume values, in addition to a tailored and narrow pore size distribution with an adequate size ratio to the MTN molecule (ØP/ØMTN= 2.3 – 2.6). Based on the results, it was identified that this tuned pore size distribution and the presence of surface oxygen groups provided adequate affinity to the MTN molecule due to H–bonds, π–interactions, and pore-filling effect retention mechanisms.

Accelerating the prediction of inorganic surfaces with machine learning interatomic potentials.

The surface properties of solid-state materials often dictate their functionality, especially for applications where nanoscale effects become important. The relevant surface(s) and their properties are determined, in large part, by the material's synthesis or operating conditions. These conditions dictate thermodynamic driving forces and kinetic rates responsible for yielding the observed surface structure and morphology. Computational surface science methods have long been applied to connect thermochemical conditions to surface phase stability, particularly in the heterogeneous catalysis and thin film growth communities. This review provides a brief introduction to first-principles approaches to compute surface phase diagrams before introducing emerging data-driven approaches. The remainder of the review focuses on the application of machine learning, predominantly in the form of learned interatomic potentials, to study complex surfaces. As machine learning algorithms and large datasets on which to train them become more commonplace in materials science, computational methods are poised to become even more predictive and powerful for modeling the complexities of inorganic surfaces at the nanoscale.

Ca2Fe2O5-Based WGS Catalysts to Enhance the H2 Yield of Producer Gases

Ca2Fe2O5-based catalysts were synthesized from siderite and calcite precursors, which were processed in the form of pelletized samples and tested as water gas shift catalysts. Catalytic tests were performed in a tubular reactor, at temperatures in the range 400–500 °C and with different H2O:CO ratios, diluted with N2; this demonstrates the positive impact of Ca2Fe2O5 on conversion of CO and H2 yield, relative to corresponding tests without catalyst. The catalytic performance was also remarkably boosted in a microwave-heated reactor, relative to conventional electric heating. Post-mortem analysis of spent catalysts showed significant XRD reflections of spinel phases (Fe3O4 and CaFe2O4), and SiO2 from the siderite precursor. Traces of calcium carbonate were also identified, and FTIR analysis revealed relevant bands ascribed to calcium carbonate and adsorbed CO2. Thermodynamic modelling was performed to assess the redox tolerance of Ca2Fe2O5-based catalysts in conditions expected for gasification of biomass and thermochemical conditions at somewhat lower temperatures (≤500 °C), as a guideline for suitable conditions for water gas shift. This modelling, combined with the results of catalytic tests and post-mortem analysis of spent catalysts, indicated that the O2 and CO2 storage ability of Ca2Fe2O5 contributes to its catalytic activity, suggesting prospects to enhance the H2 content of producer gases by water gas shift.

Atomic origin of CO2-promoted oxidation dynamics of chromia-forming alloys

The development of atomic imperfections within oxide films from high-temperature oxidation of heat-resistant alloys significantly limits the self-protectiveness of the surface oxide, contributing to the failure of energy generating system components such as turbines, engines, and heat exchanges. Directly probing the dynamics of such atomic defects is challenging because of the extreme thermochemical conditions of high-temperature oxidation. Using environmental transmission electron microscopy observations, here we directly capture atomic-scale dynamics of vacancies in growing Cr2O3 film during high-temperature oxidation of NiCr alloy in CO2. Coordinated with theory modeling, we delineate the atomistic mechanisms associated with the effect of interstitial carbon derived from CO2 on promoting the formation, migration and clustering of atomic vacancies to result in the enhanced alloy oxidation. The identified oxidation mechanism can find broader applicability in utilizing the atmosphere to tune the formation and evolution of atomic-scale defects, thereby affecting the mass transport properties of the growing oxide film.

Dynamics of magma mixing and magma mobilisation beneath Mauna Loa—insights from the 1950 AD Southwest Rift Zone eruption

Eruptions from Mauna Loa’s Southwest Rift Zone (SWRZ) pose a significant threat to nearby communities due to high eruption rates and steep slopes resulting in little time for evacuation. Despite the large body of research done on Mauna Loa, knowledge of the timing and duration of magma residence and transfer through its internal plumbing system is still poorly constrained. This study presents a first quantitative look at thermochemical conditions and timescales of potentially deep storage and disaggregation of magmatic mush during the run-up to the voluminous 1950 AD SWRZ eruption. Details of heterogeneous compositions and textures of the macrocryst and glomerocryst cargo in 1950 AD lavas suggest magma mixing and crystal recycling along the entire plumbing system. Furthermore, the crystal cargo contains evidence for the direct interaction between primitive, deeply stored magma and pockets of more evolved magma stored at shallow to intermediate depths. An enigmatic attribute of 1950 near-vent lava is the near-ubiquitous presence of subhedral, unreacted Mg-rich orthopyroxene phenocrysts (Mg#>80). Phase relations of Mauna Loa olivine-tholeiite indicate that orthopyroxene joins olivine as a primary phase at pressures higher than 0.6 GPa. Coexisting Mg-rich olivine and orthopyroxene and the occurrence of harzburgitic (olivine-orthopyroxene) glomerocrysts provide evidence for cognate crystallisation at near-Moho (~ 18 km) depths (Thornber and Trusdell 2008). Petrogenetically diverse populations of glomerocrysts and macrocrysts alongside evidence of multilevel magma storage indicate a network of ephemeral and possibly interconnected magma pockets from near-Moho depths to the upper/mid-crust. Fe-Mg diffusion chronometry applied to 1950 AD olivine populations implies rapid mobilisation and transport of large volumes of magma (376×106 m3) from near-Moho storage to the surface within less than 8 months, with little residence time (~ 2 weeks) in the shallow (3–5 km) plumbing system.

Numerical study on three-stage ignition of dimethyl ether by hot air under engine-relevant conditions

Non-premixed combustion often occurs in practical engines, and it is affected by the coupling effects of chemical kinetics and transport. This study aims to elucidate the individual effect of chemical kinetics, molecular diffusion, and convective transport on non-premixed combustion. To this end, three types of reactive systems are investigated by numerical simulations considering detailed chemistry and transport: (1) thermochemical system: 0D homogeneous autoignition, (2) thermochemical-diffusive system: 1D non-premixed ignition in a static diffusion layer, (3) thermochemical-diffusive-convective system: 1D non-premixed ignition in a counterflow and 2D lifted flame in a coflow. The simulations are carried out for diluted dimethyl ether and hot air under engine-relevant conditions with a pressure of 40 atm and hot air temperatures of 700∼1500 K. First, homogeneous ignition process of DME/air premixture is investigated. It is found that, apart from the low- and high-temperature chemistry which are essential in the typical two-stage ignition, the intermediate-temperature chemistry can also play an important role, especially for slow reaction process in fuel rich regions. Then, the effects of thermochemical conditions and molecular diffusion are assessed for non-premixed ignition process in the 1D diffusion layer. The results show that, the reaction front always initiates from local autoignition in most reactive regions; then it propagates either in sequential auto-ignition mode or in diffusion-driven mode as a deflagration wave. With various thermochemical conditions, the chemical kinetics behave differently and produce complex multibrachial (tetrabrachial, pentabrachial and hexbrachial) structures during the reaction front propagation. Decreasing the diffusion layer thickness generally delays the reaction front initiation but enhances its transition into a diffusion-driven flame. Finally, it is shown that 1D diffusion layer simulations can qualitatively reproduce the complex multibrachial structures in 1D counterflow and 2D coflow at certain conditions. A regime diagram is proposed to separate the effects of chemical kinetics, molecular diffusion, and convective transport.

Application of a two-progress variable model for carbon monoxide emissions from turbulent premixed and partially premixed enclosed flames

A large eddy simulation study is undertaken with the objective of improving carbon monoxide (CO) estimations compared to measurements of enclosed turbulent flames in laboratory scale burners. The sub-grid combustion is modelled using a presumed joint probability density function approach with tabulated chemistry based on unstrained flamelets. The thermochemical conditions are mapped using the mixture fraction and reaction progress variable. A second progress variable is used to represent the post-flame oxidation of CO. The CO mass fraction is transported, and the CO production and consumption rates are stored in separate look-up tables using each progress variable. The two-progress variable model is assessed using enclosed flames that are stabilised behind a bluff body and in a gas turbine model combustor with swirling flows. The performance of the two-progress variable model is assessed by using standard practice approaches to compute the CO mass fraction with a single progress variable, which include obtaining the CO mass fraction from a look-up table or from its transport equation. Transporting the CO mass fraction with a single progress variable gives significant overestimations in the burnt regions of the bluff body stabilised flame. The two-progress variable model gives significant improvements in the burnt regions, since the disparate time scales of CO production and consumption are captured by this model. The look-up approach also significantly overestimates the CO mass fraction in the flame stabilisation region in both configurations, where convection and diffusion processes are dominant. Therefore, the CO mass fraction needs to be transported with two progress variables to capture the intricate convection-diffusion-reaction balance in the flame stabilisation region and within the flame brush. Furthermore, the two-progress variable model gives improvements in the post-flame oxidation regions towards the chamber exit in the gas turbine model combustor, whereas the look-up approach gives significant overestimates.

Continental Thermal Blanketing Explains the Compositional Dichotomy of the Diffuse Basaltic Province Across Central‐Eastern Asia

AbstractA diffuse magmatic province covering central‐eastern Asia continent displays a compositional transition at 120–100 Ma and probably reflects melting initiation in isotopically enriched lithospheric mantle, followed by melting of the asthenosphere. However, the cause for the transition across such a vast landmass remains poorly constrained. Here, analyses of newly found Chaoge basalts (∼95 Ma, central Asia) and compiled data from across the basaltic province are combined to reveal the factors controlling the basalt dichotomy. The Chaoge basalts are considered to originate from a hot pyroxenite‐bearing asthenosphere with potential temperatures of ∼1,450°C, overlapping the source thermochemical conditions for most post‐transition basaltic rocks. The asthenosphere in 120–100 Ma is suggested to be hotter and to have controlled the compositional transition in the studied basaltic province. We suggest that asthenospheric warming resulted from prolonged continental thermal blanketing and can account for other diffuse igneous provinces with similar compositional variations and tectonic histories.

Investigating the Dynamics of Pt/CeO2 Catalysts at the Powder Agglomerate Scale by Combining In Situ Hyperspectral Raman Imaging and SEM‐EDX Analysis

AbstractThe dynamics of Pt/CeO2 catalysts is a hot topic since its knowledge can be used to (re)generate more active sites for redox reactions, even at low temperature (<500 °C). While numerous works focus on the atomic scale, the spatial extent of Pt surface diffusion is poorly known. In this work, it is evaluated at the powder agglomerate scale using an original methodology combining SEM‐EDX analysis and in situ optical/microRaman hyperspectral imaging performed on a Pt/CeO2+CeO2 mechanical mixture. No intergranular diffusion of platinum during redox cycles at 500 °C is revealed by these techniques, in particular by the Raman images of Ce3+ and peroxo species, which are highly sensitive to the presence of Pt atoms. It strongly suggests that Pt surface diffusion takes place only at the nanometer scale and could be limited by atom trapping on Pt/CeO2 agglomerates. Our method for investigating diffusion processes at the micrometer scale may be extended to other thermochemical conditions and other materials.