Carbon Samples Research Articles

Cenozoic stable isotope constraints on the Eurasian continental interior hydroclimate response to high CO2

The response of the terrestrial hydrologic cycle to higher atmospheric CO2 remains poorly constrained, largely due to difficulty in predicting how land surface processes may modify individual hydroclimate parameters such as precipitation (P), evapotranspiration (ET), and runoff (q). To interrogate how the terrestrial hydrologic cycle may change with warming and higher CO2, we utilize the Cenozoic geologic record of terrestrial stable oxygen isotopes (δ18O) as recorded in authigenic minerals, which reflect precipitation δ18O (δ18Op). Values of δ18Op are sensitive to changes in terrestrial hydroclimate, including to the ratio of P/ET and to precipitable water. In short, decreasing P/ET or higher precipitable water produces shallower δ18Op gradients inland, whereas increasing P/ET or lower precipitable water results in steeper δ18Op continental gradients. We compile nearly 15,000 samples of authigenic carbonate and tooth enamel across Eurasia—the largest continental landmass—that span the Cenozoic Era to reconstruct the past spatial distribution and zonal (i.e. east-to-west) gradients of δ18Op. We find that, in epochs with higher CO2, zonal δ18Op gradients increase, suggesting an increase in P/ET across Eurasia despite the expected increase in precipitable water in greenhouse climates. We compare these results to δ18Op gradients simulated by an isotope-enabled climate model (iCESM) forced with both pre-industrial (PI) and 4xPI CO2 mixing ratios. Simulated δ18Op gradients shallow as CO2 rises, in contrast to the reconstructed δ18Op gradients. This data-model mismatch suggests either that Earth system feedbacks not represented in our iCESM simulations, such as changes in Northern Hemisphere ice extent and vegetation, may have fundamentally changed Northern Hemisphere hydroclimate or that land-surface processes under high CO2 climates may be mis-represented in iCESM.

Modeling of the evolution of the porous structure during a physical activation process for the production of activated biocarbon: A novel low conversion approach

Many experimental studies have shown the feasibility of using biomass precursors to produce activated carbon, often improving the properties obtained from traditional materials. However, hardly any models focus on the development of porosity during the process. Among the so-called pore models, the random pore model (RPM) is the most popular and accurately predicts the evolution of the porous structure due to pore growth and coalescence. However, in activation processes with a low degree of conversion, in which pore formation is the dominant mechanism, the RPM does not correctly predict the evolution of the specific surface area since it does not consider the appearance and creation of new porosity. In this work, a new model is proposed that predicts the specific surface area created due to the formation of new pores. Subsequently, it is combined with the determination of the variation of the specific surface area predicted by the RPM due to the growth and coalescence of existing pores. The validation of the new pore evolution model with activated carbon samples obtained at different conversions shows that the model proposed adequately predicts the specific surface area and pore distribution evolution throughout the activation process.

Effect of carbon sequestration methods on uptake potential and characteristics of ordinary portland cement-based concrete

Cementitious concrete is considered potentially the largest avenue to utilize the captured carbon dioxide (CO2). Its capacity is significantly influenced by various parameters, including the CO2 introduction method for sequestration. This paper attempted to study the variation in carbon sequestration potential of ordinary Portland cement (OPC) based concrete and paste when the CO2 is introduced to the samples during mixing, curing and both. The carbonated samples obtained using the abovementioned methods have been compared in terms of CO2 uptake capacity, microstructural densification, porosity reduction, and strength variations. A maximum CO2 Uptake Capacity of about 25% was achieved under Standard Ambient Temperature and Pressure (SATP) conditions, with a maximum CO2 Conversion of 70.35% and 93.80% obtained at the surface for CO2 Mixing and CO2 Curing, respectively. Further, carbon-sequestered concrete (CSC) resulted in enhanced compressive strength, and reduced the size of pores in addition to making them uniform in size.

Inspired by the Seeking Knowledge Strategy for Analects of Confucius to Screen Highly Electrochemically Active Porous Carbon: The Critical Source of Electroactive Sites

In this work, the forestry wastes are converted into a series of porous carbons using H3PO4 activation. These porous carbons feature a large specific surface area (1045.20 m2 g−1) and porosity that combines micro‐, meso‐, and macropores in various amounts depending on the fuel properties recorded for precursors used. Importantly, the C content recorded for forestry waste is one of the crucial factors in defining the specific surface area of the derived porous carbons. In addition, the total capacitance of the pine‐sawdust‐based porous carbon (PS‐C) sample is the highest, such as 220.55 F g−1 upon 5 mV s−1. Notably, the electrical double‐layer capacitance recorded for the samples remains essentially constant with increasing scan rates, such as ≈91.50 F g−1 for the olive‐shell‐based porous carbon, ≈123.70 F g−1 for PS‐C, and ≈105.66 F g−1 for the pine‐needle‐based porous carbon. Encouragingly, the pore‐associated sp3 site holds significant roles in the electrochemical application of the porous carbons. More importantly, the O/C value recorded for the precursor can be employed as a universal predictor of electrochemically active sites produced in porous carbons. In the findings, crucial insights are exhibited into the optimized fabrication of porous carbon with target electrochemically active sites for other applications such as catalysis.

Petrographical and petrophysical characterization of pre-salt Aptian carbonate reservoirs from the Santos Basin, Brazil

Reservoir quality in carbonates is influenced by various factors such as the depositional environment, burial history and diagenesis processes. Understanding these geological heterogeneities is essential for successful petroleum exploration. This study characterizes Brazilian pre-salt reservoirs and aims to understand how their heterogeneity impacts reservoir quality. We analysed carbonate samples from the Barra Velha Formation (Santos Basin) through an integration of petrographical and core plug descriptions, petrographical facies characterization, porosity and permeability measurements, and image analysis to identify the principal controls on porosity and permeability, pore-size distribution, and groups with similar petrophysical properties using the hydraulic flow unit (HFU) concept. Five facies groups were recognized: Spherulitestone (F1); Shrubstone (F2); Intraclastic Grainstone (F3); Intraclastic Packstone, Spherulitestone with mud and Shrubstone with mud (F4); and Shrub–Spherulite Intercalations and Bioclastic Grainstone (F5). The analysis of porosity and permeability showed that their variations are associated with pore type and cementation rate. Greater contributions of inter-aggregate, interparticle and vugular porosity, combined with a reduced amount of cement, results in higher porosity and permeability but an increase in cement tends to reduce the porosity and permeability. Among the facies groups, F2 and F3 exhibited the best porosities and permeabilities, followed by F1, F4 and F5. From image analysis, small pores (1.5 × 10 −5 –0.01 mm 2 ) are the most common in all rocks. However, these small pores contributed significantly to total porosity only in F4 and some samples of F3. For F2 and F3, the large pores (from 0.01 mm 2 to a maximum of 19.62 mm 2 ) are the main contributors, while F5 has a homogeneous contribution. Finally, the data were grouped into five HFUs: HFU1 and HFU2 represent the zones with the best reservoir quality, primarily composed of F2 and F3.

Determination of Trace Elemental Composition of CaCO3: Application to Mass Limited Abiogenic and Biogenic Carbonates

AbstractAn improved method for accurate and precise determination of metal to calcium ratio in mass limited calcium carbonate samples has been developed. We used an Agilent®5800 ICP‐OES for major element (Na/Mg/Sr to Ca) and an Agilent®8900 ICP‐QQQ‐MS for minor and trace element (Li/B/Na/Mg/Al/Mn/Fe/Zn/Sr/Cd/Ba/U to Ca) ratio determination. We report a long‐term precision of ≤1% (1σ) by repeat analysis, spread over ≥6 analytical sessions, of multiple external standards that spanned a large range of concentration. We quasi‐quantitatively eliminated potential matrix effect from high [Ca] by concentration matching samples and standards (∆[Ca] ≤ ±5%) during both ICP‐OES and ICP‐QQQ‐MS sessions. The ICP‐OES analyses were done on 200 μl of sample at 60 ppm [Ca], consuming ∼30 μg of CaCO3 per analysis. Whereas trace element analyses by ICP‐QQQ‐MS required ∼150 μl of sample at 20 ppm [Ca], consuming ∼7.5 µg of CaCO3 per analysis. Thus, the present method allows for high precision determination of TE/Ca in <40 μg of CaCO3. We present a comprehensive approach for optimization of ICP‐OES sensitivity and stability to select elemental (Ca/Na/Mg/Sr) wavelengths with minimal interferences, high sensitivity and linearity. For choice of Ca lines, we focused on the minimization of self‐matrix effect. For the ICP‐MS method, we improved reproducibility and precision by lowering [Ca] of analyte and preconditioning of cones. Furthermore, the present method allows for precise B/Ca determination sans the use of HF matrix. In summary, we present an easily adoptable method based on readily available instrumentation for determining element‐to‐calcium ratios that is suitable for analyzing mass‐limited carbonate samples.

Investigating the microwave properties of carbon materials from microwave-driven methane pyrolysis

Rising carbon dioxide emissions due to fossil fuel combustion has led to the urgent need to investigate and adopt different energy solutions that can mitigate this problem. Hydrogen has surfaced as a promising alternative in the pursuit for CO2-neutral energy systems. Microwave pyrolysis of methane has recently emerged as an innovative method to accomplish this goal. To enhance our understanding of this technique and its scalability, it is essential to explore the microwave characteristics of the carbon used and generated during this process. This work investigates the microwave properties of two carbon samples (seed carbon; SC and product carbon; PC) from microwave-driven pyrolysis of methane. The cavity perturbation technique was employed from room temperature to 1250 °C for frequencies of 397, 912, 1429, 1948 and 2467 MHz. Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) analysis were also performed to elucidate the permittivity results. It was found that SC initially showed a decline in permittivity values up to 200 °C which is attributed to the release of moisture from the sample. These results were correlated to TGA/DSC which showed 5 % mass loss from 100 to 155 °C. The permittivity gradually reached a peak after which it started to fall due to high conductivity. In the case of the PC, the permittivities exhibited undulations but the values remained consistent. Since this form of carbon is formed at elevated temperature, no loss in moisture was seen in TGA/DSC. These findings indicate that the microwaves can penetrate and heat both the samples uniformly across their entire volume, resulting in efficient heating. SC demonstrated higher permittivity magnitudes compared to PC, suggesting its better responsiveness to microwave fields. Nonetheless, the possibility of thermal runaway in SC renders it less favorable for applications involving microwave-driven pyrolysis. XRD analysis showed that the samples SC and PC demonstrated amorphous carbon structures, with PC showing indications of graphitization to some extent. Both SC and PC have the potential to serve as microwave heat carriers in the methane pyrolysis process. This suggests that utilizing the carbon produced can enable a self-sufficient process, eliminating the necessity for costly catalysts.

Enhanced electrochemical behavior of C@CdS Core-Shell heterostructures

The current work presents hydrothermally synthesized carbon@cadmium sulfide core–shell nanostructures with varying carbon nanosphere concentrations. The series is prepared to investigate the shell thickness depending on the concentration of precursors and consequently impacting the optical and electrochemical properties of the core–shell structures. XRD analysis reveals enhanced crystallinity with reduced carbon. SEM & TEM confirm uniform spherical core–shell structures, with optimal uniformity at lower carbon levels. UV–vis spectroscopy demonstrates visible range absorption and reduced band gap with decreased carbon. Electrochemical analysis exhibits diffusion-controlled behavior and Warburg impedance, making the low-carbon sample most suitable for solar cells. Core-shell structures outperform pure carbon samples in absorbance and impedance spectroscopy, showcasing potential for solar cell applications.

Study of the efficiency of machine learning algorithms based on data of various rocks

Background: Absolute permeability plays an important role in studying the fluids flow in porous media during the development of oil and gas reservoirs, the injection of CO2 into reservoirs for storage, the monitoring of pollutants migration in underground aquifers, and the modeling of catalytic systems. Therefore, an accurate and fast evaluation of its values is an important task.
 Aim: The purpose of this article is to study the applicability of machine learning methods for predicting the absolute permeability of carbonate samples, as well as ways to improve the prediction of permeability.
 Materials and methods: The input data is 408 small volumes extracted from four cylindrical carbonate samples composed almost entirely of calcite. Input data includes total and connected porosity, specific surface area, radii of all and only connected pores, coordination number, throat radius and length, tortuosity, and absolute permeability. Permeability prediction is carried out using regression machine learning methods such as random forest, extremely random trees and extended gradient boosting. Parameters (data) of small volumes were determined using pore-scale modeling of water flow in their pore space applying a specialized Avizo software.
 Results: Data of small volumes extracted from fractured and non-fractured samples were analyzed, and the results showed that there are good relationships between many parameters of small volumes. For example, the connected and total porosity have a second-order polynomial relationship with a high correlation coefficient. Using the above-mentioned regression machine learning methods, absolute permeability values were predicted when input data divided into training and testing data in a ratio of 80/20 and 70/30.
 Conclusion: Using the logarithm of permeability instead of permeability itself and considering fractured and non-fractured samples separately, can increase the accuracy of absolute permeability prediction using the above-mentioned machine learning methods up to 90%. The extremely random trees method is the most accurate among the three machine learning methods considered for our task.

Experimental study of carbonate samples dissolution using X-ray microcomputer-based tomography

Background: The study of the interaction of hydrochloric acid with carbonate materialsis important in the oil and gas industry. Carbonate rocks are common rock types, and half of all petroleum reserves worldwide are found in carbonate deposits. Understanding the mechanisms and characteristics of dissolution of carbonate rocks is of great practical importance in the production of hydrocarbons and the injection of carbon dioxide into formations.
 Aim: The purpose of this article is to study the dissolution processes of carbonate samples in laboratory conditions using X-ray microcomputer-based tomography.
 Materials and methods: The study used 5 cylindrical carbonate samples, which were tested during the injection of hydrochloric acid solutions. Additional experimental and digital data from 8 samples are also used. The three-dimensional pore space of the samples was obtained using specialized software based on tomographic images.
 Results: The results obtained demonstrate the significance of the use of X-ray computed tomography for a deeper understanding of dissolution processes in geological and engineering studies. The study highlighted the complexity of the rock dissolution process, which depends on many factors. The created three-dimensional models of the samples allowed us to visualize wormholes, including branched and dominant wormholes. 3D imaging provided valuable information about changes in the pore structure of the samples before and after acid exposure.
 Conclusion: The results of this study highlight the importance of considering physical and structural properties when analyzing dissolution processes in carbonate samples. These data can have practical applications in the oil and gas industry, contributing to a more accurate understanding and optimization of the processes of interaction of acid solutions with carbonate samples.

A Proposed Methodology for Determining the Economically Optimal Number of Sample Points for Carbon Stock Estimation in the Canadian Prairies

Soil organic carbon (SOC) sequestration assessment requires accurate and effective tools for measuring baseline SOC stocks. An emerging technique for estimating baseline SOC stocks is predictive soil mapping (PSM). A key challenge for PSM is determining sampling density requirements, specifically, determining the economically optimal number of samples for predictive soil mapping for SOC stocks. In an attempt to answer this question, data were used from 3861 soil organic carbon samples collected as part of routine agronomic soil testing from a 4702 ha farming operation in Saskatchewan, Canada. A predictive soil map was built using all the soil data to calculate the total carbon stock for the entire study area. The dataset was then subset using conditioned Latin hypercube sampling (cLHS), both conventional and stratified by slope position, to determine the total carbon stocks with the following sampling densities (points per ha): 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, and 0.8. A nonlinear error function was then fit to the data, and the optimal number of samples was determined based on the number of samples that minimized soil data costs and the value of the soil carbon stock prediction error. The stratified cLHS required fewer samples to achieve the same level of accuracy compared to conventional cLHS, and the optimal number of samples was more sensitive to carbon price than sampling costs. Overall, the optimal sampling density ranged from 0.025 to 0.075 samples per hectare.

Accurate measurement of K/Ca in low-[K] carbonate samples using laser-ablation sector-field inductively coupled plasma mass spectrometry.

Potassium (K) is a major component of several silicate minerals and seawater, and, therefore, constraining past changes in the potassium cycle is a promising way of tracing large-scale geological processes on Earth. However, [K] measurement using inductively coupled plasma mass spectrometry (ICP-MS) is challenging due to an ArH+ interference, which may be of a similar magnitude to the K+ ion beam in samples with <0.1% m/m [K]. In this work, we investigated the effect of the ArH+ interference on K/Ca data quality by comparing results from laser-ablation (LA)-ICP-MS measured in medium and high mass resolution modes and validating our LA results via solution ICP-optical emission spectroscopy (OES) and solution ICP-MS measurements. To do so, we used a wide range of geological reference materials, with a particular focus on marine carbonates, which are potential archives of past changes in the K cycle but are typically characterised by [K] < 200 μg/g. In addition, we examine the degree to which trace-element data quality is driven by downhole fractionation during LA-ICP-MS measurements. Our results show that medium mass resolution (MR) mode is sufficiently capable of minimising the effect of the ArH+ interference on K+ . However, the rate of downhole fractionation for Na and K varies between different samples as a result of their differing bulk composition, resulting in matrix-specific inaccuracy. We show how this can be accounted for via downhole fractionation corrections, resulting in an accuracy of better than 1% and a long-term reproducibility (intermediate precision) of <6% (relative standard deviation) in JCp-1NP using LA-ICP-MS in MR mode. Our [K] measurement protocol is demonstrably precise and accurate and applicable to a wide range of materials. The measurement of K/Ca in relatively low-[K] marine carbonates is presented here as a key example of a new application opened up by these advances.

Morphology of Thin-Film Nafion on Carbon as an Analogue of Fuel Cell Catalyst Layers.

Species transport in thin-film Nafion heavily influences proton-exchange membrane (PEMFC) performance, particularly in low-platinum-loaded cells. Literature suggests that phase-segregated nanostructures in hydrated Nafion thin films can reduce species mobility and increase transport losses in cathode catalyst layers. However, these structures have primarily been observed at silicon-Nafion interfaces rather than at more relevant material (e.g., Pt and carbon black) interfaces. In this work, we use neutron reflectometry and X-ray photoelectron spectroscopy to investigate carbon-supported Nafion thin films. Measurements were taken in humidified environments for Nafion thin films (≈30-80 nm) on four different carbon substrates. Results show a variety of interfacial morphologies in carbon-supported Nafion. Differences in carbon samples' roughness, surface chemistry, and hydrophilicity suggest that thin-film Nafion phase segregation is impacted by multiple substrate characteristics. For instance, hydrophilic substrates with smooth surfaces correlate with a high likelihood of lamellar phase segregation parallel to the substrate. When present, the lamellar structures are less pronounced than those observed at silicon oxide interfaces. Local oscillations in water volume fraction for the lamellae were less severe, and the lamellae were thinner and were not observed when the water was removed, all in contrast to Nafion-silicon interfaces. For hydrophobic and rough samples, phase segregation was more isotropic rather than lamellar. Results suggest that Nafion in PEMFC catalyst layers is less influenced by the interface compared with thin films on silicon. Despite this, our results demonstrate that neutron reflectometry measurements of silicon-Nafion interfaces are valuable for PEMFC performance predictions, as water uptake in the majority Nafion layers (i.e., the uniformly hydrated region beyond the lamellar region) trends similarly with thickness, regardless of support material.

Experimental Study of Seismic Wave Attenuation in Carbonate Rocks

Summary Seismic wave attenuation has a great potential for studying saturated and fractured media, due to its high sensitivity to the physical properties of geological media. However, accurately estimating this parameter can be challenging due to its sensitivity to signal noise, particularly in heterogeneous media such as carbonate rocks. This explains the paucity of attenuation studies carried out in carbonate rocks compared with sandstones, and the ambiguity around its mechanisms and its relationship with petrophysical properties. To investigate further, we conducted an experimental study of ultrasonic waveform signals (0.5–3 MHz) reordered under dry and fully saturation conditions in 13 samples covering a wide range of petrophysical values and subjected them to differential pressure reaching reservoir pressure. The resulting increase in attenuation magnitudes and their variation with pressure due to brine saturation were more pronounced than in velocity magnitudes, confirming the higher sensitivity of attenuation to fluid content. However, understanding the relationship between attenuation and petrophysical properties required a careful examination of the results and more elucidation about attenuation mechanisms. We suggested that multiple attenuation mechanisms coexist, including scattering, cracks slipping, solid frictional relative motion, and global and squirt flow. This explains the frequency dependence of attenuation, with higher magnitudes at sonic frequencies, where the squirt flow mechanism may be dominant. In contrast to sandstone, the magnitude of compressional to shear attenuation ratio (QP−1/QS−1) was found to be greater than unity in both dry and brine fully saturated carbonate samples at ultrasonic frequencies. This result may be due to the complex porosity structure of carbonate rocks, which makes it not appropriate to the sandstone rock physics models.

Estimation of pore structure and permeability in tight carbonate reservoir based on machine learning (ML) algorithm using SEM images of Jaisalmer sub-basin, India

Analyzing the pore structure in carbonate reservoirs plays a crucial role in predicting fluid flow characteristics within these formations. The goal of the study was to use machine learning techniques for pore structure analysis and estimation of permeability in carbonate reservoirs. We implemented these algorithms by examining 2D scanning electron microscope (SEM) images of carbonate samples from the Jaisalmer sub-basin captured at various magnifications. In the initial stage of the analysis, various binarization algorithms were applied to determine carbonate sample porosity. Among these algorithms, the MaxEntropy algorithm gave a porosity value closely aligned with those obtained through petrography analysis. We employed the watershed algorithm to find the pore network parameters of carbonate samples at various magnifications. We observed that changes in magnification affected pore network parameters, resulting in a reduction in pore size distribution, throat radius, and grain size. Subsequently, we employed the numerical lattice Boltzmann method (LBM) to estimate the permeability of carbonate samples and compared to values derived from well logs. We employed machine learning (ML) algorithms, specifically Artificial Neural Network (ANN) and Support Vector Machine (SVM), to predict the permeability of carbonate samples. The input features for these models were the pore network parameters, while the LBM permeability values served as the output. We examine the prediction performance of these methods against the measured LBM permeability by conducting the error analysis and the coefficient of determination (R2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${R}^{2}$$\\end{document}) calculation. Our findings revealed that the ANN models outperformed the SVM models. Specifically, the ANN model displayed an impressive R2 value of 0.892, along with root mean square error (RMSE), mean squared error (MSE) and, mean absolute error (MAE) values of 1.927, 3.716 and 1.580, respectively. In contrast, the SVM model yielded an R2 value of 0.849, with RMSE, MSE and, MAE values of 2.324, 5.401 and, 2.166 respectively, when assessed on testing data of measured permeability. This study found that ANN is more dependable, robust, and precise than SVM in forecasting carbonate sample permeability.

Preparation and characterization of cellulose-based activated carbon by cesium chloride chemical method

Carbon adsorbent material with a specific surface area as high as 436 m2/g was prepared by chemical activation method using cellulose as raw material and cesium chloride as activator, and its structure was characterized. Its adsorption performance on methylene blue solution was investigated, and the adsorption thermodynamics of crystalline violet dye at different temperatures was studied. The results showed that the surface of the prepared activated carbon material was smooth with abundant pores. The methylene blue adsorption value was as high as 176 mg/g, and it could adsorb methylene blue solution quickly and efficiently. It had good adsorption effect on crystal violet solution, the saturated adsorption amount reaches 281 mg/g at 40 °C, and the removal reached 92%, which indicated a self-heating adsorption reaction. Thus, CsCl could be used as an activator of wood raw material for the preparation of activated carbon samples.

Diagenesis of carbonate density-flow deposits controlled by differential uplift of platform segments: examples from the Cretaceous of the Gargano Promontory, Italy

ABSTRACT Thin-section investigation (polarized-light, cathodoluminescence, and ultraviolet microscopy) combined with isotopic (δ18O, δ13C,87Sr/86Sr) analyses of bulk carbonate samples form the basis for evaluating the diagenetic alteration of Albian–Cenomanian and Maastrichtian density-flow deposits off two segments of the Apulia Carbonate Platform in the Gargano Promontory, Italy. We propose that differential platform uplift south and north of the Mattinata Fault controlled the diagenesis of density-flow deposits during Albian–Cenomanian times. In both cases, the: i) abundant blocky cement and vuggy pores in clasts, and ii) remnant blocky cement on allochems in the corresponding matrix samples with interparticle pores, indicate disintegration of at least partially cemented deposits before failure and reworking into density flows. The abundant rudist fragments suggest that they were sourced from the margin and upper slope. However, the δ13C compositions of the density-flow deposits south and north of the Mattinata Fault are different, and geochemical modeling based on presumed marine and terrestrial δ13C compositions indicates: A) The marine δ13C values of deposits south of the Mattinata Fault suggest that the margin- and upper-slope deposits were subjected to predominantly marine-burial diagenesis before failure. Albian–Cenomanian Sr-isotope ages support the marine-burial diagenetic scenario where strontium was redistributed locally during calcitization of aragonitic allochems and during precipitation of calcite cements. However, post-uplift precipitation of vadose cement in pores formed during marine-burial diagenesis has lowered the δ13C and increased the 87Sr/86Sr ratio in many of the samples. B) Twenty-five km north of the Mattinata Fault, the negative δ13C values suggest that oxidation of terrestrial plants supplied 12C-enriched CO2 to the pore-water carbon pool during subaerial exposures, thus lowering the δ13C compositions of the margin- and upper-slope deposits from values obtained during marine-burial diagenesis. This diagenetic model requires that residual aragonitic and high-Mg calcitic allochems were available in the deposits during penetration of meteoric water. However, the Albian–Cenomanian Sr-isotope ages and the geochemical modeling support a predominantly marine-burial scenario, with intraformational redistribution of strontium during meteoric diagenesis. A similar diagenetic model is envisaged for the Maastrichtian density-flow deposits south of the Mattinata Fault, but the less negative δ13C and geochemical modeling suggest less influence of meteoric diagenesis before reworking. The majority of separate- and touching-vug pores likely also formed during marine burial before failure and reworking of the margin- and upper-slope deposits. The large range in porosity (4–31%) of density-flow deposits with predominantly interparticle pores are inferred to reflect varying degrees of compaction caused by variable overburden thickness as well as sedimentary processes. The results of the present study indicate that the geochemical imprint of meteoric diagenesis can be expected to vary in density-flows deposited along coeval segments of carbonate platforms in tectonically active regions.

Enhanced removal of Pb2+, Cd2+ and Zn2+ ions on porous carbon from aqueous solutions by capacitive deionization: Performance study and underlying mechanism

In this paper, nitrogen-doped porous carbon materials were successfully prepared using sucrose and activated carbon as raw materials and NH4Cl as nitrogen dopant by foaming and pyrolysis. The nitrogen-doped porous carbon (NPC-1) sample has a large specific surface area (798.425 m2/g) and good electrochemical properties. Capacitive deionization (CDI) tests showed that the removal rate was over 87% and 85% in the mixture of three ions (Pb2+, Cd2+ and Zn2+), when the initial concentration of ternary mixed solution was 10 mg/L and 20 mg/L and the voltage was 1.2 V. Density-functional-transfer theory (DFT) calculations revealed that materials containing pyridine-N and pyrrolic-N have better adsorption properties for Pb2+, Cd2+ and Zn2+ than materials containing graphite-N and materials without doped nitrogen. Meanwhile, the adsorption energy of pyridine-N and pyrrolic-N models for Pb atom are larger than those of pyridine-N and pyrrolic-N models for Cd and Zn atoms. This indicated that the NPC-1 electrode has better electrosorption capacity for Pb2+, which was consistent with the experimental results. After twenty cycles experiments, the NPC-1 electrode maintained a high removal rate for Pb2+ (95%), Cd2+ (82%), and Zn2+ (87%). This showed that the electrode material has a good recycling regeneration ability.

Mode-I analysis of glass fiber-reinforced polymer laminates toughened by interleaved polyamide 66 nanofibers and chopped carbon using acoustic emission

The fracture toughness of epoxy resins is weak, so enhancing its properties is essential. In this research it was found that interleaving chopped carbon fibers and polyamide 66 nano mats between fiberglass reinforced plastic laminates with 110 µm thickness, increased fracture toughness in Mode I by 35 and 112%, respectively. Acoustic emission technique showed that damage mechanisms begin at further displacements of load point in modified samples. A hierarchical clustering model was used to classify various failure types. It was observed that matrix cracking, fiber breakage, and matrix cracking were the major damage mechanisms for Reference, chopped carbon, and nanomodified samples, respectively. The cumulative energy released by nanomodified samples was 83% lower than that of Reference and chopped carbon samples. A scanning electron microscope was used to validate different types of damage mechanisms.

Stress and frequency dependence of wave velocities in saturated rocks based on acoustoelasticity with squirt-flow dissipation

SUMMARY We perform seismic and ultrasonic measurements in carbonate and shaley sandstone samples as a function of differential pressure. The velocities show a strong frequency and pressure dependence. The dispersion disappears with increasing pressure and the squirt flow in turn inhibits the pressure dependence. To model these effects, we combine the Gurevich's squirt-flow model with the Mori–Tanaka scheme and the David Zimmerman model, and extend it with third-order elastic constants, to obtain a frequency-dependent acoustoelasticity model. Comparisons between measurements from this study and literature and modelling results show that the P-wave velocity increases non-linearly first and then nearly linearly, dominated by crack closure and acoustoelasticity, respectively. The pressure dependence of wave velocities is reduced by liquid substitution and further by the squirt-flow mechanism. The effects of fluid properties and crack closure on P-wave velocity decrease with differential pressure. The results will feed a new model and help better understanding the wave propagation in pre-stressed rocks at different scales.