Secondary Zone Research Articles

Modeling PFAS Subsurface Transport in the Presence of Groundwater Table Fluctuations: The Impact on Source‐Zone Leaching and Exploration of Model Simplifications

AbstractAir–water interfacial adsorption represents a major source of retention for many per‐ and poly‐fluoroalkyl substances (PFAS). Therefore, transient hydrological fluxes that dynamically change the amount of air–water interfaces are expected to strongly influence PFAS retention in their source zones in the vadose zone. We employ mathematical modeling to study how seasonal groundwater table (GWT) fluctuations affect PFAS source‐zone leaching. The results suggest that, by periodically collapsing air–water interfaces, seasonal GWT fluctuations can lead to strong temporal variations in groundwater concentration and significantly enhance PFAS leaching in the vadose zone. The enhanced leaching is more pronounced for longer‐chain PFAS, coarser‐textured porous media, drier climates, and greater amplitudes of fluctuations. GWT fluctuations and lateral migration above the GWT introduce a downgradient persistent secondary source zone for longer‐chain PFAS. However, the enhanced leaching and the secondary source zone are greatly reduced when subsurface heterogeneity is present. In highly heterogeneous source zones, GWT fluctuations may even lead to overall slower leaching due to lateral flow (in the GWT fluctuation zone and above the GWT) moving PFAS into local regions with greater retention capacities. Model simplification analyses suggest that the enhanced source‐zone leaching due to GWT fluctuations may be approximated using a static but shallower GWT. Additionally, while vertical 1D models underestimate source‐zone leaching due to not representing lateral migration, they can be revised to account for lateral migration and provide lower‐ and upper‐bound estimates of PFAS source‐zone leaching under GWT fluctuations. Overall, our study suggests that representing GWT fluctuations is critical for quantifying source‐zone leaching of PFAS, especially the more interfacially active longer‐chain compounds.

Unraveling the metallogenic mechanisms of uranium-rich ore bodies: Insights from Xinqiaoxi’s pitchblende geochronology and pyrite geochemistry

Granite-related uranium deposits are essential for the global uranium supply, with the uranium-rich ore bodies within these deposits being crucial to their value. However, the sources of uranium, fluid characteristics, and metallogenic mechanisms within these uranium-rich ore bodies remain unclear. In this study, we analyzed pitchblende and pyrite from the Xinqiaoxi uranium deposit to determine uranium age and clarify the mineralization of uranium-rich ore bodies. The pitchblende samples provided a U-Pb age of 58.5 ± 3 Ma (MSWD = 3.4), closely aligns with the mineralization ages in other uranium deposits within the Xiazhuang uranium ore-field. This consistency suggests a significant uranium mineralization event in South China during this period. The vein-like and concentric structure of the pitchblende, coupled with its enrichment in U, Sr, As, W, and Mo but depletion in Th, Pb, and REEs, indicates a strong association with hydrothermal activity. Moreover, its REE pattern closely resembles that of the host rock (Xiazhuang and Maofeng granites), suggesting the latter as a crucial uranium source. Pyrite and pitchblende are coeval, yet pyrite was formed slightly earlier than pitchblende. Pyrite exhibits depletion in Co and Ni but enrichment in As, along with high Co/Ni ratios ranging from 1.68 to 12.2, indicative of a medium- to low temperature hydrothermal genesis. Furthermore, the positive cerium (Ce) anomaly observed in pyrite may indicate elevated oxygen fugacity in the fluids during precipitation. The δ34S values of pyrite (−10.42 ‰ to −15.26 ‰, averaging −13.44 ‰) are consistent with those of the host rock (Xiazhuang and Maofeng granites), indicating a primary sulfur source from the host rock. Additionally, pyrite may serve as a reductant, facilitating the formation of uranium ore. Our proposed genetic model suggests that CO2-rich oxidizing fluids facilitate uranium leaching from host rocks, resulting in the formation of a uranium-enriched fluid that migrates along faults, where U6+ undergoes reduction to U4+ within secondary fracture zones, facilitated by reductants such as pyrite.

Effect of Water and Nitrogen Coupling Regulation on the Growth, Physiology, Yield, and Quality Attributes of Isatis tinctoria L. in the Oasis Irrigation Area of the Hexi Corridor

To address the prevailing problems of high water and fertilizer input and low productivity in Isatis tinctoria L. production in the Hexi Corridor in China, the effects of different irrigation amounts and nitrogen application rates on growth characteristics, photosynthetic physiology, root yield, and quality of I. tinctoria plants were studied with the aim of obtaining the optimal irrigation level and nitrogen application rate. From 2021 to 2023, we established a two-factor split-plot experiment in the oasis irrigation area with three irrigation amounts (sufficient water, medium water, and low water are 100%, 85%, and 70% of the typical local irrigation quota) for the main zone; three nitrogen application rates (low nitrogen, 150 kg ha−1, medium nitrogen, 200 kg ha−1, and high nitrogen, 250 kg ha−1) for the secondary zone; and three irrigation amounts without nitrogen as the control to explore the response of these different water and nitrogen management patterns for I. tinctoria in terms of growth characteristics, photosynthetic physiology, root yield, and quality. The results showed the following: (1) When the irrigation amount was increased from 75% to 100% of the local typical irrigation quota and the nitrogen application rate was increased from 150 to 250 kg ha−1, while the plant’s height, leaf area index, dry matter accumulation in the stem, leaf, and root, as well as the net photosynthetic rate (Pn), the stomatal conductance (Gs), and the transpiration rate (Tr) of I. tinctoria increased gradually, and the root–shoot ratio decreased. (2) When the irrigation amount increased from 75% to 100% of the local typical irrigation quota, the yield and net proceeds of I. tinctoria increased from 43.12% to 53.43% and 55.07% to 71.61%, respectively. However, when the irrigation quota was 100% of the local typical irrigation quota, and the nitrogen application rate increased from 150 to 200 kg ha−1, the yield of I. tinctoria increased from 21.58% to 23.69%, whereas the increase in nitrogen application rate from 200 to 250 kg ha−1 resulted in a decrease in the yield of I. tinctoria from 10.66% to 18.92%. During the 3-year experiment, the maximum yield of I. tinctoria appeared when treated with sufficient water and medium nitrogen, reaching 9054.68, 8066.79, and 8806.15 kg ha−1, respectively. (3) The effect of different water and nitrogen combination treatments on the root quality of I. tinctoria was significant. Under the same irrigation level, increasing the nitrogen application rate from 150 to 250 kg ha−1 could increase the contents of indigo, indirubin, (R,S)–goitrin, total nucleoside, uridine, and adenosine in the root of I. tinctoria from 3.94% to 9.59%, 1.74% to 12.58%, 5.45% to 18.35%, 5.61% to 11.59%, 7.34% to 11.32%, and 14.98% to 54.40%, respectively, while the root quality of I. tinctoria showed a trend of first increasing and then decreasing under the same nitrogen application level. (4) AHP, the entropy weight method, and the TOPSIS method were used for a comprehensive evaluation of multiple indexes of water–nitrogen coupling planting patterns for I. tinctoria, which resulted in the optimal evaluation of the W3N2 combination. Therefore, the irrigation level was 100% of the local typical irrigation quota, the nitrogen application rate should be appropriately reduced, and controlling the nitrogen application rate at the level of 190.30–218.27 kg ha−1 can improve water–nitrogen productivity yields for I. tinctoria and root quality. The results of this study can provide a theoretical basis and technical support for a more reasonable water and fertilizer management model for the I. tinctoria production industry in the Hexi Corridor in China.

Interdiffusion mechanism between EB-PVD deposited CoCrAlY bond-coat and superalloy substrate under high-temperature oxidation service conditions in gas turbine

The interdiffusion mechanism between EB-PVD deposited CoCrAlY coating and superalloy substrate under high-temperature oxidation atmosphere in actual gas turbines was investigated both experimentally and through thermodynamics and kinetics simulation. The interdiffusion behavior differs at different regions of blade due to the different service temperatures. The elemental interdiffusion and phase transformation behavior were investigated and discussed. Needle-like topologically close-packed phase and σ-CrCoNi phase have precipitated within the secondary reaction zone due to the γ→γ’ transition and the uphill diffusion of Cr, W, and Mo. Decreasing the Co content in the MCrAlY bond-coat can inhibit the interdiffusion behavior to a certain extent.

A framework for territorial spatial ecological restoration zoning integrating “Carbon neutrality” and “Human-geology-ecology”: Theory and application

Global climate change worsens the imbalance among human environment, geological environment and ecological environment (human-geology-ecology), leading to increasingly prominent ecosystem damage. Constructing a scientifically effective territorial spatial ecological restoration zoning (TSERZ) framework will promote the coordination between nature and human. However, the fundamental role of geological environment in TSERZ has been overlooked, and there is lack of theoretical frameworks and empirical research on TSERZ oriented towards carbon neutrality goal. Therefore, we have proposed a new TSERZ framework by integrating “carbon neutrality” and “human-geology-ecology”, which employs models such as CECM, LCA, IUEMS and ESP to divide primary zones, secondary zones and key areas, and also provides restoration directions for various zones. Taking the typical alpine-gorge region of Yulong County as an example, we conduct empirical research to verify the validity of the TSERZ framework. The findings indicate that, firstly, besides human and ecological factors, geological factors like lithology are indispensable factors for TSERZ, and understanding the dynamic balance relationship of human-geology-ecology is the prerequisite and basis for TSERZ. Secondly, the proposed TSERZ framework emphasizes the fundamental role of carbon source/sink and lithology in TSERZ, constructing the three-level zones division method oriented towards carbon neutrality goal with the research line of “natural background conditions—dominant ecological functions—ecological stress problems”. Thirdly, the framework has been successfully applied to TSERZ in Yulong County, dividing it into 8 primary zones, 17 secondary zones, and 7 types key areas. Given its complex geological conditions, fragile ecological environment and increasingly human interference, Yulong County urgently needs to focus on restoring ecological problems such as rocky desertification and geological disasters to improve carbon sink capacity. This study innovatively constructs a cascading path for TSERZ from theoretical cognition to practical application, which can provide a reference for solving the TSERZ problem in geologically complex regions, especially in alpine-gorge regions.

Study on Extraordinarily High-Speed Cutting Mechanics and Its Application to Dry Cutting of Aluminum Alloys with Non-Coated Carbide Tools

The friction/adhesion between the tool and chip is generally large in metal cutting, and it causes many problems such as high cutting energy/rough surface finish. To suppress this, cutting fluid and tool coating are used in practice, but they are high in energy/cost and environmentally unfriendly. Therefore, this paper investigates the extraordinarily high-speed cutting (EHS cutting) mechanics of mainly soft and highly heat-conductive materials and proposes their application to solve the friction/adhesion problem in an environmentally friendly manner. In order to clarify the EHS cutting mechanics, a simple analytical model is constructed and experiments are conducted with measurement of the cutting temperature and forces. As a result, the following points are clarified/found: (1) heat softening at the secondary plastic deformation zone rather than the primary plastic deformation zone, (2) friction coefficient drop to 0.170 in EHS cutting, and (3) gradually increasing trend of cutting temperature in EHS cutting. Finally, EHS cutting is applied to dry cutting of aluminum alloys with a non-coated carbide tool and compared to conventional wet cutting with a DLC-coated carbide tool, and it is shown that a coating/coolant can be omitted in this region to achieve environmentally friendly cutting.

Experimental study of rotating direction for dual-axial swirlers on the flow field and combustion characteristics of aero-engine combustor

The flow field structure for aero-engine combustor is one of the most important factors for combustion performance. To investigate how the rotating direction of dual-axial swirlers affects the flow field and combustion characteristics, particle image velocimetry (PIV) experiments were conducted in the primary combustion and intermediate zones. Additionally, planar laser induced fluorescence (PLIF) was used to map the distribution of kerosene and OH in the primary combustion zone. The results show that the swirling jets in co-swirl exhibit greater jet momentum, resulting in a longer primary recirculation zone and a larger deflection angle of the primary jets. This ultimately leads to a higher recirculation rate compared to counter-swirl. The primary jets define the boundary of the flow field structure. The rotating direction primarily affects the flow field structure upstream of the primary jets, exerts a relatively weaker influence on the intermediate zone, which is mainly affected by the deflection direction of the primary jets, and essentially has no impact on the dilution jets. Co-swirl has a relatively stable flow field than counter-swirl, whereas the flow field in counter-swirl is more chaotic, featuring a greater number of vortex cores in the primary recirculation zone. The coupling between the primary and swirling jets affects the mass transfer direction in the intermediate zone, which is reflected in the fact that the mass transfer is from top-left to bottom-right in co-swirl, while it is in the opposite direction in counter-swirl. OH is predominantly found in the swirling shear layers, the primary and secondary combustion zones, whereas kerosene is mainly concentrated in the shear layers of swirling jets. The kerosene distribution in co-swirl shows a larger and more concentrated expansion angle compared to counter-swirl. In contrast, the OH distribution downstream of counter-swirl is broader, with more intense combustion due to enhanced kerosene decomposition and fuel-air mixing. The smaller primary recirculation zone in counter-swirl forces the primary combustion zone to extend downstream, leading to a more intense reaction in the secondary recirculation zone.

Numerical study of NOx emission reduction by MILD and air staged synergistic combustion in a new type of coke oven flue

In order to address the issue of high emissions in the coke industry, we require innovative solutions. This article designs a coke oven flue with an array type secondary air nozzle, achieving the synergistic occurrence of MILD combustion and air staged combustion, which can significantly reduce nitrogen oxide emissions. However, further research is needed on the optimal control methods for synergistic combustion effects. First, Analyzed the mixing state of air and fuel under different air mass flow ratios. Next, by taking into account the oxygen distribution law, analyze the temperature distribution in both the primary and secondary combustion zones. Finally, analyze the distribution of NOx concentration. Study the impact of temperature differences caused by air mass flow ratio in synergistic effects on NOx emissions. The results indicate that by adjusting the air flow ratio, the air vortex intensity in the collaborative combustion process can be enhanced. This method can reduces flame temperature, achieving the objective of reducing NOx concentration. In the new type of coke oven flue, when the air mass flow ratio is 0.4, the combustion state in the primary and secondary combustion zones is optimal, and the NOx emission concentration is 312.88 mg/m3, representing a reduction of 38 %.

Ecological space management and control zoning of Giant Panda National Park from the perspective of ecosystem services and land use

Since China proposed building a national park system in 2017, the establishment of a planning system for nature reserves, with national parks as the main body, is being actively promoted around the country. Among them, scientific ecological space management and control zoning (ESMCZ) is an important link in maintaining the ecological stability of national parks. How to zone national parks and how to improve the precision of zoning has become a new task for national parks. Therefore, this study takes the Giant Panda National Park as the study area, takes ecosystem services and land use/cover change as the research perspective, integrates the InVEST model, PLUS model and bayes belief network (BBN) model, and builds a set of ecological space management and control zoning (ESMCZ) spatial zoning framework based on raster scale, dividing the study area into strictly protected zone, ecological buffer zone, ecological control zone and controlled development zone. The results showed that: (1) The study area showed an increasing trend in water conservation, soil conservation and carbon storage from 2005 to 2020, and the habitat quality index was generally high. The spatial heterogeneity of ecosystem services in the study area was significant, and the effect of a single factor on ecosystem services was most pronounced. (2) Large variation in area for different land uses under natural development scenarios and ecological protection scenarios. In both scenarios, the area of cultivated land, the area of grassland and the area of unused land decrease relative to 2020, and the area of forested land, the area of water and the area of constructed land increase relative to 2020. (3) The Giant Panda National Park is divided into strictly protected zone, ecological buffer zone, ecological control zone and control development zone, of which the strictly protected zone have the largest area and the best ecosystem background condition, and the control development zone have the smallest area and the worst ecosystem background condition. (4) The ecological space management and control zoning (ESMCZ) framework provides a more refined method for the secondary zoning of nature reserves such as the Giant Panda National Park, which is valuable for the implementation of zoning and categorization management for ecological conservation in the Giant Panda National Park.

Vertical Crustal Deformation Due To Viscoelastic Earthquake Cycles at Subduction Zones: Implications for Nankai and Cascadia

AbstractDespite significant progress in studying subduction earthquake cycles, the vertical deformation is still not well understood. Here, we use a generic viscoelastic earthquake‐cycle model that has recently been validated by horizontal observations to explore the dynamics of vertical earthquake‐cycle deformation. Conditioned on two dimensionless parameters (i.e., the ratio of earthquake recurrence interval T to mantle Maxwell relaxation time tM (T/tM) and the ratio of downdip seismogenic depth D to elastic upper‐plate thickness Hc (D/Hc)), the modeled viscoelastic deformation exhibits significant spatiotemporal deviations from the simple time‐independent elastic solution. Caution thus should be exercised in interpreting fault kinematics with vertical observations if ignoring Earth's viscoelasticity. By systematically exploring these two parameters, we further investigate three metrics that characterize the predicted vertical deformation: the coastal pivot line (CPL), the uplift zone (UZ) landward above the downdip seismogenic extent, and the secondary subsidence zone (SSZ) in the back‐arc region. We find that these metrics can all be time‐dependent, subject to D/Hc and T/tM. The CPL location and the UZ width are mainly controlled by D/Hc and T/tM, respectively. The presence of the SSZ is prevalent during the interseismic phase due to viscous mantle flow driven by ongoing plate convergence. Contemporary vertical deformation in Nankai and Cascadia is largely consistent with the model predictions and features differences mainly related to contrasting D/Hc values in the two margins. These findings suggest that vertical crustal deformation bears fruitful information about subduction‐zone dynamics and is potentially useful for inversions of key subduction‐zone parameters, deserving properly designed monitoring.

Analysis of the beneficial effects of prior soybean cultivation to the field on corn yield and soil nitrogen content.

Corn-soybean rotation is a cropping pattern to optimize crop structure and improve resource use efficiency, and nitrogen (N) fertilizer application is an indispensable tool to increase corn yields. However, the effects of N fertilizer application levels on corn yield and soil N storage under corn-soybean rotation have not been systematically studied. The experimental located in the central part of the Songnen Plain, a split-zone experimental design was used with two planting patterns of continuous corn (CC) and corn-soybean rotations (RC) in the main zone and three N application rates of 0, 180, and 360 kg hm-2 of urea in the secondary zone. The research has shown that RC treatments can enhance plant growth and increase corn yield by 4.76% to 79.92% compared to CC treatments. The amount of N fertilizer applied has a negative correlation with yield increase range, and N application above 180 kg hm-2 has a significantly lower effect on corn yield increase. Therefore, a reduction in N fertilizer application may be appropriate. RC increased soil N storage by improving soil N-transforming enzyme activity, improving soil N content and the proportion of soil organic N fractions. Additionally, it can improve plant N use efficiency by 1.4%-5.6%. Soybeans grown in corn-soybean rotations systems have the potential to replace more than 180 kg hm-2 of urea application. Corn-soybean rotation with low N inputs is an efficient and sustainable agricultural strategy.

Numerical simulation on reservoir stimulation assisted depressurization development of hydrate bearing layers based on embedded discrete fractures

As the global demand for energy escalates, the increasing severity of environmental pollution underscores the urgent need for efficient development of hydrates—a promising, clean energy source with vast reserves. It is imperative to carry out reservoir stimulation on low-permeability hydrate reservoirs to enhance fluidity. In order to simulate the geometric morphology of complex fractures, based on the bifurcation fracture morphology in existing laboratory experiments, combined with embedded discrete fracture model and tree fractal theory, the multiphase and multi-component seepage mechanism, thermal conduction, thermal convection, and hydrate phase change in hydrate-bearing layers were comprehensively considered. Based on the TOUGH code, a TOUGH-EDFM module is developed to realize numerical simulation of three-dimensional four-phase four-component hydrate reservoir stimulation assisted depressurization development. We clarify the production capacity change characteristics, main methane dissociation zones, and gas-water migration trends after reservoir stimulation. The results indicate that in the multi-level branching fracture area, the increase in hydrate production in the primary fracture area of the reservoir is greater than that in the secondary fracture branching area. When the fractal scale factor is 0.56, the increase in production in the secondary branch fracture zone is 48% of that in the primary fracture zone. The cumulative gas production after the reservoir stimulation of Class III hydrate reservoirs can surpass that of the basic depressurization scheme by a remarkable 2.21 times, and the overall hydrate dissociation proportion has increased by 60%, indicating the ability of the reservoir to effectively utilize the energy within hydrate reservoirs, thereby significantly improving its depressurization development potential.

Metasomatic Interaction of Ultramafic Mantle Xenoliths with their Felsic HP–UHT Granulite Host (Moldanubian Domain, Bohemian Massif in Lower Austria)

Abstract The St. Leonhard granulite massif in Lower Austria, dominantly formed by kyanite-bearing felsic granulite, encloses countless up to 5 cm sized mantle xenoliths of garnet clinopyroxenite and peridotite. The mineralogical, textural and chemical consequences of a mutual metasomatic interaction at the contact between these xenoliths and the host orthopyroxene-bearing felsic granulite are described. Movement of Mg, Al and, especially, Ca from the garnet clinopyroxenite to the granulite and migration of K and Na in the opposite direction, caused the breakdown of clinopyroxene and formation of orthopyroxene–plagioclase symplectite coronae at the expense of the garnet clinopyroxenite xenoliths. Around the peridotite xenoliths, monomineralic orthopyroxene coronae have developed due to the supply of Si from the host granulite. The P–T conditions of this interaction were established to 900°C to 1000°C and 1.0 to 1.2 GPa by thermodynamic modelling. The duration of coronae growth was constrained to 13 to 532 ka based on modelling of Fe–Mg interdiffusion underlying secondary compositional zoning of garnet from the garnet clinopyroxenite xenolith extending to the coronae. The most significant change in the host granulite was caused by the supply of Ca from the garnet clinopyroxenite xenolith, which led to the breakdown of the Al2SiO5 phase—probably kyanite—and stabilization of orthopyroxene. K-feldspar-poor haloes surrounding mantle xenoliths formed due to the depletion of K in the granulite adjacent to the garnet clinopyroxenite. The observed origin of felsic–intermediate orthopyroxene-bearing granulite by transformation of felsic kyanite-bearing granulite through the metasomatic interaction with mantle xenoliths implies that the deep crustal chemical exchange between mantle- and crust-derived lithologies may have an important consequences on composition, thermal structure and geodynamic evolution of orogenic lower crust especially in hot collisional orogens, such as the European Variscides.

The influence of heat treatment process on the dynamic recrystallization evolution mechanism of Inconel 718 during high-speed machining

This study aims to investigate the cutting mechanisms of Inconel 718 alloy under different heat treatment processes and the grain refinement patterns of the transformed layer. By establishing a constitutive model suitable for cutting and importing it into DEFORM-3D for heat treatment processing and single-factor cutting experiment simulation, the effects of heat treatment processes and cutting parameters on cutting force, cutting temperature, and surface grain refinement were studied. The results indicate that the increase in cutting force is maximum, approximately 12 %, after the aging temperature is raised from 668 °C to 718 °C. The cutting force generated after aging heat treatment shows a negative correlation with cutting speed, whereas the cutting force after solution heat treatment rises significantly between 1400 and 1600 mm/s. The maximum cutting temperature occurs in workpieces after solution heat treatment, about 112 % of that of workpieces treated at 718 °C aging heat treatment. At the onset of cutting, the size relationship of the original grain volume is as follows: untreated < solution heat treatment < aging heat treatment; the number of nucleation points for dynamic recrystallization at grain boundaries is as follows: aging heat treatment < solution heat treatment < untreated. The most significant increase in the number of dynamic recrystallizations is observed after aging heat treatment at 621 °C, with the relationship of the number of recrystallizations in different cutting deformation zones being: secondary deformation zone < primary deformation zone < tertiary deformation zone. With the increase in cutting depth, the grain size of the workpiece after solution heat treatment first increases then decreases during the cutting process; the grain size of the workpiece after aging heat treatment first decreases then increases. The grain size of the workpiece during the cutting process after heat treatment is negatively correlated with cutting speed. Specifically, when the cutting speed is 600 mm/s, the grain size after solution heat treatment is the largest, about 1.1 times that of the 718 °C aging heat-treated workpiece.

Effects of secondary air on the emission characteristics of ammonia–hydrogen co-firing flames with LES-FGM method

Ammonia, being a carbon-free fuel, is garnering increasing attention in the combustion community. However, its application is still impeded by its limited stability range and significantly NOx emissions. This study delves into the impact of primary and overall equivalence ratios (ϕpri and ϕovr) on emissions production in ammonia–hydrogen co-firing flames, utilizing a two-stage swirling model gas turbine combustor. The emissions concentration is measured using Fourier Transform Infrared Spectroscopy (FTIR). The physical and chemical processes influencing emissions production are comprehensively analyzed through a combination of Large Eddy Simulation (LES) and Flamelet-Generated Manifold (FGM) method. The reliability of the simulation is validated by the experimental data, showing a good capability in predicting the combustion. Results indicate that the two-stage combustion strategy exhibits significantly controlling effects on NOx and unburned NH3 emission. The NO emission exhibits a non-monotonic variation with ϕpri, reaching its lowest value at ϕpri≈ 1.2. Further analysis shows that ϕpri plays a crucial role in determining the temperature and OH concentration in the primary combustion zone, thereby influencing NOx production in this area. When the primary zone is operated at lean condition, the reduction on NO in secondary zone is primarily attributed to dilution effect by the secondary air. In contrast, when ϕpri> 1, the concentrations of the main emissions in secondary zone are dominated by chemical effects. In this scenario, unburned NH3 and H2 from the primary zone are consumed, resulting in a substantial production of NO in the secondary combustion zone. Additionally, with an increase in ϕpri, the secondary NO production also increases. The ϕovr exhibits two considerable effects. On one hand, an increase in ϕovr results in a higher local equivalence ratio in the secondary zone, thereby promoting local NOx production. Simultaneously, the elevated flame temperature enhances the consumption of N2O. On the other hand, the rise in ϕovr results in a reduction in vortex scale and residence time in the secondary combustion zone, leading to a decrease in local NO production.

Investigation on the interdiffusion mechanism between single-crystal superalloy and FeCrNiAl-based medium entropy alloys

High and medium entropy alloys (HEAs, MEAs) have emerged as promising candidates for bond-coat materials in the thermal barrier coating systems due to their exceptional oxidation resistance. However, understanding the interdiffusion behavior between these alloys and single-crystal superalloys (SXs) substrates requires further investigation. In this study, diffusion couples were created between SXs and two types of MEAs, namely FeCrNiAl and FeCrNi0.4Al0.4, and the interdiffusion behavior was simulated using the commercial DICTRA code. The results reveal significant interdiffusion at 1100 °C in the couples, attributed to the substantial elemental differences between SXs and MEAs. This led to the formation of the interdiffusion zone (IDZ) and the secondary reaction zone (SRZ). Within the SRZ, phase transformation of SXs occurred, resulting in the precipitation of topologically close-packed (TCP) phases. Three types of TCP phases (σ, μ, and P) were observed. Along the {11¯02} plane of the μ phase, twins and stacking faults have formed. The glide of P phase contributed to the bending of bar-like precipitates. Notably, the amorphization of the σ phase was observed for the first time, suggesting an intermediate state during the phase transformation. Despite elemental differences between the two MEAs, the growth mechanism of IDZ and SRZ, as well as the precipitation of TCP phases, exhibited similarities. This underscores the importance of Cr and Ni diffusion alongside Al diffusion. The pronounced interdiffusion behavior raises concerns about the suitability of 3-d transition metal MEAs as bond-coat materials due to the lack of slow diffusion effect.

Tracing the Origin and Magmatic Evolution of the Rejuvenated Volcanism in Santa Clara Island, Juan Fernández Ridge, SE Pacific

Oceanic intraplate volcanoes sometimes experience late-stage eruptive activity known as rejuvenated volcanism, and contrasting interpretations for its petrogenesis depend on the compositional characteristics. In the Juan Fernández Ridge (JFR), a volcanic chain approximately 800 km in length emplaced on the Nazca Plate, some subaerial occurrences of rejuvenated volcanism have been recognized on the Robinson Crusoe and Santa Clara Islands, both part of the same deeply eroded shield volcano complex. This study aims to understand the origin and magmatic evolution of rejuvenated volcanism on Santa Clara Island, emplaced after ~2.15 Ma of quiescence above the shield sequence, mainly via the analysis of unpublished geochemical and isotopic data. Field reconnaissance identified two nearly coeval rejuvenated sequences on Santa Clara Island: Bahía W (BW) and Morro Spartan (MS), both formed by basanitic and picro-basaltic lava flows with brecciated levels and local intercalations of sedimentary and pyroclastic deposits. In comparison to the chemical signature of the preceding shield-building stage (comprised mainly of basalts and picrites), the two rejuvenated sequences exhibit a notable enrichment in incompatible elements, but the Sr, Nd, and Pb isotopes are very similar to the FOZO mantle endmember, with an apparent additional contribution of HIMU and EM1 components. The geochemistry of lavas revealed the involvement of various processes, including contamination by ultramafic xenoliths, high-pressure fractional crystallization of olivine and clinopyroxene, and potential partial assimilation of oceanic lithospheric components. While the oceanic lithosphere has been considered as a potential source, the isotopic data from Santa Clara lies outside of the mixing curve between depleted mantle (DM, here represented by the North Chile Rise and the East Pacific Rise) and the previous shield stage, suggesting that a lithospheric mantle is not the primary source for the rejuvenated stage volcanism. Therefore, we favor an origin of the rejuvenated volcanism from the mantle plume forming the JFR, supported by similarities in isotopic signatures with the shield stage and high values of 208Pb/204Pb (only comparable to San Félix—San Ambrosio in the vicinity of JFR), implying the presence of a regional source with radiogenic 208Pb/204Pb isotope ratios. In addition, isotopic variations are subparallel to the mixing line between HIMU and EM1 components, whose participation in different proportions might explain the observed trends. In conclusion, we propose that the source of the rejuvenated volcanism on Santa Clara Island is a heterogeneous mantle plume, the same one that fed the shield stage. The rejuvenated volcanism is derived from a secondary melting zone away from the main axis of the plume.

Effect of PtAl coating on the HCF property of a coated third-generation single crystal superalloy with sheet specimens at 900 ℃

High-cycle fatigue (HCF) is one of the primary failure modes for turbine blades in aero-engines. Therefore, comprehending the effect of coating on the HCF property of single crystal (SX) superalloys is vital for the safe service of turbine blades. In order to mimic the degradation of the fatigue property for the turbine blades during service, this study investigated the effect of PtAl coating on the HCF property of a third-generation Ni-based SX superalloy using sheet specimens at 900 ℃ and different maximum stresses (σmax). The results indicated that both coating and σmax affected the fatigue properties and crack initiation process of SX superalloy. A transition in fatigue crack initiation site from the internal micropores to the surface cracks for both uncoated and coated alloys has been observed as the σmax decreased. However, the coating significantly increased the σmax required for the transition of the crack initiation site. Meanwhile, the HCF property of the SX superalloy was reduced with the deposition of PtAl coating at lower σmax, and the debit in HCF life was more pronounced with decreasing the σmax. The coating facilitated the rapid nucleation of surface cracks and promoted the transition of the fatigue crack initiation site under higher σmax. On the other hand, since the HCF life is controlled by the crack growth rate, grain boundaries in the interdiffusion zone (IDZ) and secondary reaction zone (SRZ) accelerated the growth of the surface crack under lower σmax, resulting in a shorter crack initiation stage and lower fatigue life compared to the uncoated alloy. This study will be helpful in accurately predicting the HCF life of the coated Ni-based SX superalloys.

Pore Structures and Evolution Model of Reservoirs in Different Secondary Structural Zones in the Eocene Shahejie Formation, Chezhen Sag, Bohai Bay Basin.

Although abundant unconventional oil resources have been discovered in conglomerate and sandstone reservoirs in rift basins, the mechanism of differential pore evolution in conglomerates and sandstone reservoirs within different secondary structural zones of rift basins is not yet clear. The pore structures of conglomerate and sandstone reservoirs in the distinct secondary structural zones in the Chezhen Sag were quantified in three dimensions using high-resolution microcomputed tomography (micro-CT). Thin section and scanning electron microscopy observations were used to investigate the differential evolution mechanisms of conglomerate and sandstone reservoirs. Micro-CT analysis of the pore structures of conglomerate and sandstone reservoirs revealed that sandstone reservoirs are superior to conglomerate reservoirs with regard to the pore number and pore connectivity and that sandstone reservoirs are more heterogeneous than conglomerate reservoirs. Triangles dominate the pore and pore throat geometries of sandstone and conglomerate reservoirs, while the sandstone reservoir pores are more regular than conglomerate reservoir pores. The depositional environment, mineral composition, and diagenetic intensity jointly control the quality of the reservoirs. Because of the lengthy transportation distance of their parent rocks, the compositional maturity and sorting behavior of sandstone reservoirs in depression and gentle slope zones are better than those of conglomerate reservoirs in steep slope zones, and thus sandstone reservoirs have a higher initial porosity than conglomerate reservoirs. The rapid compaction experienced by the conglomerate reservoirs in steep slope zones in their early stages creates a closed diagenetic environment, making it difficult to effectively improve reservoir porosity through dissolution. However, the widely developed microfractures in the reservoirs provide channels for fluid migration, promote the development of dissolution pores, and form a tight reservoir dominated by secondary pores. With weak compaction and an open diagenetic environment, the primary pores in sandstone reservoirs in the gentle slope zone are preserved in large quantities. Meanwhile, dissolution expands the secondary pores of the reservoir, resulting in a high-quality reservoir having both primary and secondary pores. In addition, an approach based on primary, secondary, and total porosity was proposed in the study to efficiently evaluate reservoir quality and identify reservoir evolution mechanisms.

Analysis of cutting tool geometry induced machining response, surface integrity and anisotropy relation of additively manufactured 316L stainless steel

Although the machining responses of additively manufactured (AM) materials generally differ from wrought materials due to their microstructural properties, there is no study examining the effects of varying cutting tool rake angles in the machining of AM 316L stainless steel material. The aim of this paper is to evaluate the effects of machining using varying cutting tool rake angles and cutting speeds on the cutting response in terms of cutting force, tool wear, chip morphology and surface integrity characteristics such as microstructure, micro-hardness and x-ray diffraction (XRD) analysis of powder bed fusion – laser beam (PBF-LB) 316L. The effect of the tool rake angle on the anisotropic structure of the material was revealed by examining the machining-induced affected layer from both the built and scan planes and by comparing it with the wrought material. The findings showed that PBF-LB 316L behaves more abrasively than the wrought, creating higher cutting force and tool wear due to the differences in the friction coefficient and thermal conductivity of the materials. Although the machining-induced affected layer is not the same in the built and scan planes of the PBF-LB material due to anisotropy, it is considerably higher compared to the wrought material, especially at negative rake angles. While the hardness of PBF-LB material is higher at a low cutting speed and negative rake angle, the hardening capacity of wrought material is higher at high cutting speed and negative rake angle. PBF-LB chips have repeated adiabatic shear bands and the secondary deformation zone is more evident in wrought chips.