Carbon Migration Research Articles

Study on Chemical Kinetics of Carbon Migration in Superalloys in the Non-Pure Helium Environment in High Temperature Gas Cooled Reactors

The primary coolant in the high temperature gas cooled reactor (HTGR) contains impurities of low content, which will cause serious corrosion of the superalloys in the HTGR operating at the ultra-high temperature. In particular, the carbon migration between the superalloys and non-pure helium has a great influence on the material performance. This study explores the chemical kinetics principle of the carbon migration in the non-pure helium environment, from which the theoretical criteria for material decarburization and carburization are gained. Also, according to the chemical thermodynamics and kinetics principles, this study calculates the oxygen partial pressure and carbon activity in the non-pure helium environment, and indicates that a high partial pressure ratio of CH4 to H2O may lead to serious carburization of the alloys. On this basis, this study presents a widely used carbon migration model, “chromium stable phase diagram”, analyzes the chromium activity calculation method, and summarizes the recommended values. Finally, the corrosion behavior of the 10 MW HTGR (HTR-10) designed by Tsinghua University under the actual operating conditions is obtained by calculation based on the chromium stable phase diagram.

Transition of creep damage region in P91-Alloy800-SS316LN dissimilar metals weld joint

The creep behaviour of P91-Alloy800-SS316LN dissimilar metals weld joint (DMWJ) has been assessed at 823 K in the stress range of 180–260 MPa. Creep strain accumulation in the DMWJ was higher under high stress regime than the low stress regime. Transition of creep damage and fracture in the DMWJ occurred from P91 steel base metal at high stress regime to the interface region of P91 CGHAZ-IN182 weld metal at lower applied stress with significant reduction in ductility. Kernel average misorientation indicates that the localized increase in strain at the P91 CGHAZ-IN182 weld metal interface region under creep loading in comparison to that of the pre-creep condition. Enhanced heterogeneity in strain distribution, carbon migration, coarser precipitates and soft zone formation at the P91 CGHAZ-IN182 interface region have been attributed to the premature failure of DMWJ in comparison to P91 steel.

Carbon bearing aluminosilicate melt at high pressure

It is well known that volatiles such as water has significant influence on the properties of silicate melts. Carbon dioxide (CO2) is also an abundant volatile in deep Earth, however the effect of CO2 on the properties of polymerized melts, particularly the transport properties, are poorly understood. This is crucial for better understanding of the generation and migration of carbon bearing silicate magma in deep crustal and mantle settings. In this study, we explore the structure and properties of carbon bearing aluminosilicate melt up to a pressure of ~25 GPa and temperature range of 2500–4000 K using first principles molecular dynamics (FPMD) simulation. Our results show that CO2 in the aluminosilicate melts dissolves as molecular CO2 and carbonate (CO32-) at lower pressures (~0–3 GPa). However, at higher pressures (>3 GPa) relevant to most of the upper mantle, CO32- is predominant carbon species along with carbon in 4-fold coordination (CO4). Fraction of CO32- increases with decreasing temperature and increasing pressure. We find that at the reference isotherm (2500 K), the density of the aluminosilicate melt is reduced by addition of CO2 (in wt.%) with dρdXCO2 = −0.0214. Effect of water on the density of melt is more pronounced with dρdXH2O = −0.0422. Thus, the gravity-driven buoyancy of volatile rich magma will be greater than that of the magma without volatile components. The compressibility of the aluminosilicate melt is also affected by volatiles. For instance, both bulk modulus (KT0) and its pressure derivative (KT0') for volatile bearing melts are respectively lower and higher than that of dry melt. Aluminosilicate melts are highly polymerized and show an anomalous pressure dependence of melt viscosity. Pressure dependence of viscosity at low pressure regime (P < 5 GPa) is significant with dlog(η)dP=-2.06. Melt viscosity is further reduced by the addition of volatiles. Effect of volatiles on viscosity is more pronounced at low pressures and it minimizes at pressures where the melt viscosity exhibits minima. Due to the lower viscosity and larger buoyancy for both the H2O and CO2 bearing aluminosilicate melts at crustal and upper mantle depths, magma mobility (Δρη) is greater for volatile bearing melts. Thus, the residence time of such melts are expected to be shorter than volatile free melts in those settings. Like the mobility, electrical conductivity of aluminosilicate melts also increases when volatile is present in the silicate melt. We find that that as low as <1 vol.% volatile bearing aluminosilicate melt mixed with mantle matrix could be sufficient to explain the observed electrical conductivity anomalies in the upper mantle.

Effect of population migration on spatial carbon emission transfers in China

Large-scale population migration entails changes in productive and consumptive activities, which has enormous implications on the spatial relocation of carbon emissions. This study uses multiple methods to empirically assess the impact of interprovincial population migration of China on its trade-induced carbon transfers from a spatial view over 2002–2012. We constructed two networks of migration and carbon transfers, and based on the analysis of their topological structure, we inferred that carbon flows and migration are complements–larger migration flows typically correlate with larger trade-related carbon flows. Furthermore, we analyzed how migration affects interprovincial carbon transfers; in addition, we explored the geographical factor by dividing Chinese provinces into five subregions. The results illustrated that trade-induced carbon emissions situation in China was shaped partly by interprovincial migration at the national level. While the contribution of migration varies markedly across subregions owing to the unbalanced regional economic development and carbon intensity, migration-focused emission control strategy should be enhanced discriminatively to better understand China's inter-provincial joint energy conservation and emission reduction policy.

Characterization and assessment of organic carbon migration and biomass formation potential of polymeric pipes using modified BioMig

To evaluate and approve the materials that can be in contact with drinking water with respect to biological contamination, organic carbon migration and biomass formation potential assays are widely employed. In previous studies, to conduct the assays, the entire material was exposed to the test water by submerging the material into glass jars. However, these are not realistic conditions since the water contact only the inner surface of the pipe in the distribution system, which may be different from the outer surface with respect to the coating layers. Furthermore, the extra components such as the glass jar containers and stainless steel holders might be the sources of organic carbon contamination. These two factors may result in imprecise conclusions. Here, we introduced a minor but essential modification to the BioMig test, which is the most current test on the migration potential and biomass formation potential. In this modified BioMig method, the outer surface and cutting edges, which are not in contact with water in practical water distribution systems, would not be exposed to the test water. Moreover, the assimilable organic carbon formation potential via chlorination in the leachates was observed and recommended as an additional test in the migration potential assay. The modified test results demonstrated that polyethylene (PE) material is the most unfavorable material, notably when used in chlorinated drinking water. This proposed test provided an alternative approach to the decision-makers with respect to evaluating the pipe material characteristics.

Eutrophication and lakes dynamic conditions control the endogenous and terrestrial POC observed by remote sensing: Modeling and application

The sources of particulate organic carbon (POC) determine its conversion, thereby playing an important role in the carbon cycle of lakes. Accurate estimation of the sources and dynamic characteristics of POC is important for understanding the migration and transformation of organic carbon. However, the synchronous observation of POC sources with large areas through remote sensing is still challenging because of the complex composition of POC and the optical conditions of inland lakes. In this study, a three-band (1/ Rrs (689)–1/ Rrs (717)) × Rrs (697)) empirical algorithm of POC sources was constructed based on remote sensing reflectance (Rrs(λ)) and the proportion of endogenous POC estimated from the field-measured stable isotope (δ13CPOC) values. The validation and calibration results of the three-band algorithm showed robust performance, with MAPE and RMSE of estimated values and measured values of 10% and 0.07, respectively. The three-band algorithm had good simulation results for the Ocean and Land Color Instrument (OLCI), Moderate Imaging Spectroradiometer (MODIS), Geostationary Ocean Color Imager (GOCI), and Medium Resolution Imaging Spectrometer (MERIS) spectra. The POC sources estimated by the three-band algorithm suggest that the endogenous POC of Taihu Lake in August showed a decreasing trend from 2006 to 2019. The variation in terrestrial POC was slow and stable for both annual and monthly variations. The analysis of POC sources with total phosphorus (TP), total nitrogen (TN), water temperature, and wind speed indicated that terrestrial POC was closely related to wind speed (r = 0.33, P < 0.001), while endogenous POC was significantly associated with TP (r = 0.6, P < 0.001), TN (r = 0.56, P < 0.001), and water temperature (r = 0.49, P < 0.001). The use of remote sensing algorithms to evaluate POC from different sources is convenient and effective; furthermore, it helps to better understand the carbon cycle in lacustrine ecosystems.

Thermal stability and diffusion characteristics of ultrathin amorphous carbon films grown on crystalline and nitrogenated silicon substrates by filtered cathodic vacuum arc deposition

Amorphous carbon (a-C) films are widely used as protective overcoats in many technology sectors, principally due to their excellent thermophysical properties and chemical inertness. The growth and thermal stability of sub-5-nm-thick a-C films synthesized by filtered cathodic vacuum arc on pure (crystalline) and nitrogenated (amorphous) silicon substrate surfaces were investigated in this study. Samples of a-C/Si and a-C/SiNx/Si stacks were thermally annealed for various durations and subsequently characterized by high-resolution transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). The TEM images confirmed the continuity and uniformity of the a-C films and the 5-nm-thick SiNx underlayer formed by silicon nitrogenation using radio-frequency sputtering. The EELS analysis of cross-sectional samples revealed the thermal stability of the a-C films and the efficacy of the SiNx underlayer to prevent carbon migration into the silicon substrate, even after prolonged heating. The obtained results provide insight into the important attributes of an underlayer in heated multilayered media for preventing elemental intermixing with the substrate, while preserving the structural stability of the a-C film at the stack surface. An important contribution of this investigation is the establishment of an experimental framework for accurately assessing the thermal stability and elemental diffusion in layered microstructures exposed to elevated temperatures.

Hydrogen production by supercritical water gasification of methylhydrazine in continuous system

Supercritical water gasification technology has ability to process unsymmetrical dimethylhydrazine (UDMH) wastewater derived from launching spacecraft, missile or satellite realizing both harmless treatment and resource utilization due to its unique property. Owning advantages such as compact structure, highly reduced reactor volume, improved heat transfer efficiency and fully mixed reactants, a spiral continuous reactor was proposed based on the characteristics of UDMH wastewater. Methylhydrazine (MMH) was used as model compound on account of UDMH’s commercial unavailability. The degradation of MMH in supercritical water is determined as an apparent first-order reaction using initial rate method. The effect of different parameters including temperature (450–550 °C), feeding flow rate (10–75 g/min), feeding concentration (5–30 %), and catalyst type on gasification were systematically investigated and subsequently the migration of carbon and nitrogen was also concerned. Results showed that addition of KOH could make the carbon gasification efficiency approach 100 % with the maximum hydrogen yield up to 21.6 mol/kg under the condition of 500 °C, 23 MPa, feeding flow rate of 30 g/min, feedstock concentration of 10 %. The proportion of organic carbon in total carbon tended to decrease with the increase of temperature. Most of nitrogen (up to 99.7 % at most) was gasified within our experimental range.

Fracture toughness behavior of dissimilar metal (SA508 Gr.3 Class 1 and SA312 Type 304LN) weld joint: With and without stress relieving treatment

AbstractDissimilar metal welds (DMW) are used to connect the low‐alloy steel (LAS) pressure vessel and austenitic stainless steel (ASS) piping in nuclear power reactors. DMWs inherently have high gradient of carbon content across fusion boundary (LAS‐ASS), leading to carbon migration from LAS to ASS. Nickel‐based alloy is the preferred buttering and welding consumable to minimize carbon migration. Stress‐relieving treatment after buttering of LAS also enhances the carbon migration, which may lead to a reduction in local fracture toughness in heat affected zone (HAZ) of LAS. Therefore, this paper aims to study the effect of stress‐relieving treatment on the fracture toughness behavior of DMW. Fracture toughnesses of different zones of DMWs have been quantified in as‐welded and stress‐relieved conditions. It has been shown that stress‐relieving leads to lowering of fracture toughness with respect to as welded condition. This is attributed to increase in the microstructural heterogeneity in HAZ (LAS) and near fusion boundary of the DMW.

Thermal cotreatment of municipal solid waste incineration fly ash with sewage sludge for PCDD/Fs decomposition and reformation suppression

Thermal treatment of municipal solid waste incineration fly ash (FA) is an effective method to detoxicate FA and produce secondary material with good utilization properties, but the high temperature induced migration of carbon, chlorine, and catalytic metals from FA to flue gases can result in a considerable reformation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). Herein, two typical fly ashes were thermally cotreated with sewage sludge (SS), respectively, and the decomposition and reformation of PCDD/Fs were systematically investigated. Thermal treatment effectively decomposed PCDD/Fs in all samples to a low level well meeting the reutilization criterion of 50 ng WHO-TEQ g−1. Cleavage of the oxygen bridge was identified as the primary decomposition pathway. Compared to mono-treating FA, cotreating FA with SS resulted in a better CaO-Al2O3-SiO2 ternary system for vitrification and effectively suppressed the reformation of PCDD/Fs in off-gases with inhibition efficiencies up to 96%. Based on the variation of chemical speciation of N, P, and S in SS after thermal treatment, SS appeared to be a S-N-containing inhibitor which passivated catalytic metals to suppress PCDD/Fs synthesis. The better suppression on de novo pathway than on chlorophenol-route identified by monitoring PCDD/F-fingerprints evolution further verified the suppression mechanism of passivating catalytic metals.

Cr-alloyed novel press-hardening steel with superior combination of strength and ductility

A novel press-hardening steel (PHS) with an ultra-high tensile strength of 1680 MPa and an excellent total elongation of 9.2% has been developed and produced at an industrial scale. In addition to high strength, the new PHS showed significantly improved ductility as compared to the baseline PHS grade 22MnB5 (~7.0%) mainly because of its nano-sized retained austenite (RA), which was formed as a result of dynamic carbon partitioning after the martensitic transformation during the hot forming process. Dynamic carbon partitioning from the martensite to austenite during cooling and RA stabilization was achieved by adding optimum amounts of Si and Cr to the novel PHS without alternating the industrial hot forming process. To investigate the effect of the RA on the mechanical performance of the new PHS, microstructure without RA was prepared for comparison by direct water quenching after the austenitization to suppress the carbon migration. Detailed characterization revealed that the RA was beneficial for improving both the uniform and post-uniform elongation of the novel PHS. The effects of Si and Cr on the formation of the RA were investigated with the aid of thermo-kinetic calculations. The excellent combination of strength and ductility of the novel PHS will enable a significant weight reduction when it replaces the current PHS grade 22MnB5 for a variety of vehicle body structure components.

Phosphate alters the compositional characteristics of humic acid adsorbed onto goethite

The adsorption of organic matter and phosphate on minerals is a common natural process that has an important impact on the migration and burial of carbon and phosphorus. Previous studies have focused mainly on the influence of organic matter on the adsorption of phosphate. Yet, the influence of phosphate on the adsorption of different pools of organic matter is not well understood. This study evaluates changes in different organic matter pools during their adsorption to minerals in the presence of phosphate. Firstly, the adsorption behaviors of natural organic matter (i.e., humic acid) and phosphate on goethite were evaluated separately. Secondly, humic acid and phosphate were added to goethite at different orders to elucidate the effect of phosphate on the fractionation of humic acid components adsorbed to goethite. The results showed that when phosphate and humic acid were added simultaneously, goethite was preferentially combined with phosphate. In the absence of phosphate, SUVA254 of the humic acid solution decreased and E2/E3 of the solution increased during the adsorption. Among the six EEM-PARAFAC (excitation-emission matrix fluorescence coupled with parallel factor analysis) components of the humic acid, C1, C2, and C4 (terrestrial humus-like substances) decreased significantly and exhibited strong adsorption, C3 (microbial fulvic-like substance) showed weak adsorption, whereas C5 (photodegradation products) and C6 (tyrosine-like component) did not show evident adsorption. In the presence of phosphate, phosphate inhibited, and replaced the adsorbed C1, C2, and C4, but promoted the adsorption of C5, which increased the aromaticity and the molecular weight of the humic acid solution. Our results reveal that phosphate influences the fractionation of humic acid components adsorbed onto goethite, suggesting that phosphate can alter the chemical composition of natural organic matter interacting with minerals and thus impact the burial and fractionation of natural organic matter at the mineral-water interface.

Hierarchical microstructure based crystal plasticity-continuum damage mechanics approach: Model development and validation of rolling contact fatigue behavior

A microstructure-based integrated crystal plasticity (CP) and continuum damage mechanics (CDM) model is proposed for simulating rolling contact fatigue (RCF). The damage process through the formation of the dark etching region (DER) under RCF is implemented, i.e., a DER-CPCDM approach. A hierarchical microstructure of lath martensite is virtually generated by the Voronoi tessellation technique and the theoretical Kurdjumov-Sachs orientation relationship between the prior austenite grains and substructures of lath martensite. Moreover, the micro-plasticity calculated from the polycrystal finite element is coupled with dislocation-assisted carbon migration theory, which enables accurate predictions of the deformation inhomogeneity and the DER/damage distribution at the subsurface. The RCF lifespan of AISI 52100 bearing steel can be predicted within reasonable accuracy, in terms of Weibull probability analysis, when the jump-in-cycles approach is implemented in the DER-CPCDM model. The predicted representative lifespan of the Weibull plot is within an error of 13% when compared with reported experimental data. Process factors, including contact pressure, rotational speed, temperature, carbon concentration, and grain size, are analyzed in a numerical sensitivity study, which can be utilized for potential optimization of the RCF process for improving the performance of materials and parts.

Semi-empirical model for predicting LAB and HAB formation in bearing steels

The formation of white etching bands (WEBs), including both low- (LAB) and high- (HAB) angle bands, in the subsurface of steel bearings due to rolling contact fatigue (RCF) has been investigated over decades to understand their characteristics and predict their formation during operation. A few studies recently have modelled the development of LABs theoretically based on thickening of lenticular carbides adjacent to the band controlled by dislocation-assisted carbon migration. To date, no study has been reported to predict the formation of HABs. Based on the percentage of white etched region formed in the subsurface of the bearings, this study presents a semi-empirical model that predicts the formation of both LABs and HABs in steel bearings for different contact pressures. The LAB semi-empirical model is compared with a theoretical model from literature and experimental data. According to this, the new model more realistically predicts the initiation of LABs than the carbide thickening model. This is achieved by involving the formation of ferrite (cellular and elongated) shown as white areas under optical images. Literature data have been used to evaluate the LAB and HAB models. The growth pattern obtained in this study provides strong evidence of a diffusion-based mechanism leading to WEB formation.

Shaping mechanism of ultrafine metastable austenite in HSLA steels through a cumulative process of hot rolling, partitioning and tempering

We have uniquely combined hot rolling, partitioning and tempering to formulate a new pathway for tailoring shape, size and stability of ultrafine metastable austenite (γ) in a low-alloy steel and understand the associated mechanism. The formation of 1-D ultrafine γ in partitioned-tempered steels was governed by 1-D micro-segregation of Mn/Ni in partitioned steels because nucleation of 1-D ultrafine was promoted in 1-D micro-segregation region of Mn/Ni during the initial stage of tempering. Migration of carbon from adjacent martensite to γ in micro-segregation region restricted nucleation of 2-D/3-D ultrafine γ. Tuning of alloying design and partitioning process effectively reduced 1-D micro-segregation of Mn/Ni, restrained the nucleation of 1-D ultrafine γ, and promoted the formation of 2-D/3-D ultrafine γ grains between martensite. Thus, low level of 1-D micro-segregation of Mn/Ni in partitioned steels contributed to the refinement of γ. But high degree of micro-segregation of Mn/Ni at the phase boundary of γ in partitioned and tempered steels significantly improved its stability, which was induced by austenitization (between martensite and austenite) and ferritic transformation (between annealed martensite and austenite). The micro-segregation of Mn/Ni design approach presented here for low alloy steels can be extended to other multiphase microstructure alloys.

Intercropping and N application enhance soil dissolved organic carbon concentration with complicated chemical composition

Soil dissolved organic carbon (DOC) plays a critical role in migration and transformation of soil organic carbon. For revealing effects of intercropping and N application on dynamics of DOC concentration and chemical structure, a multi-year located field experiment with cropping patterns (maize monocropping and maize-potato intercropping) subjected to four N levels (0 kg ha−1, 125 kg ha−1, 250 kg ha−1, 375 kg ha−1) was conducted. The results showed that N application raised DOC concentration while DOC accumulation, had a quadratic relationship with N application rate during the entire growth period of maize. At the same N level, intercropping increased the concentration and accumulation of DOC compared with monocropping. Meanwhile N application promoted the contents of amines and aromatic compounds and average molecular weight of DOC molecules, which reached the highest value at rate of 125 kg N ha-1. Compared with monocropping at the same N level, there was a tendency to increase the content of amines and aromatic compounds and the average molecular weight of DOC in intercropping, thus improving the degree of humification and aromatization of soil DOC. Soil temperature, water content and NH4+-N were the main factors mediating DOC concentration, while DOC concentration and soil temperature significantly affected the chemical structure of DOC. The structural equation model showed intercropping and N application elevated soil DOC concentration by increasing soil temperature, litter and root biomass, and the improvement of DOC concentration and soil temperature further enhanced the average molecular weight of DOC, resulting in accumulation of DOC.

Supplementing the model of the global biogeochemical carbon cycle

The article considers possible anthropogenic carbon sources and migration ways that were not previously included in the global biogeochemical cycle. Complementing the carbon cycle model is important for clarifying the scenarios awaiting the Earth.

Insights on the deep carbon cycle from the electrical conductivity of carbon-bearing aqueous fluids

The dehydration and decarbonation in the subducting slab are intricately related and the knowledge of the physical properties of the resulting C–H–O fluid is crucial to interpret the petrological, geochemical, and geophysical processes associated with subduction zones. In this study, we investigate the C–H–O fluid released during the progressive devolatilization of carbonate-bearing serpentine-polymorph chrysotile, with in situ electrical conductivity measurements at high pressures and temperatures. The C–H–O fluid produced by carbonated chrysotile exhibits high electrical conductivity compared to carbon-free aqueous fluids and can be an excellent indicator of the migration of carbon in subduction zones. The crystallization of diamond and graphite indicates that the oxidized C–H–O fluids are responsible for the recycling of carbon in the wedge mantle. The carbonate and chrysotile bearing assemblages stabilize dolomite during the devolatilization process. This unique dolomite forming mechanism in chrysotile in subduction slabs may facilitate the transport of carbon into the deep mantle.

Assessment of organic carbon migration and biofilm formation potential on polymeric tubes in contact with water

Biofilm formation has been frequently identified as a pathway of nosocomial infection in polymeric tubes used for patients of all ages. Biofilm formation on tube surfaces can lead to hygienic failure and cause diarrhea, stomach pain, inflammation, and digestive system disease. This study investigated the influence of polymeric tube materials in contact with water on the biomass formation potential and migration potential of microbially available carbon from plasticizers using a BioMig test. The thermoplastic elastomer tube, which is reusable, leached a relatively low amount of assimilable organic carbon to water. In contrast, the assimilable organic carbon migration potential of polyurethane was the most significant, 6-fold greater than that of the thermoplastic elastomer. Moreover, the same materials (e.g., silicone) produced via different manufacturing processes showed significant differences in migration behaviors. The potential biomass formation observed in polyurethane was approximately 7 × 109 cells cm−2 for both Aeromonas hydrophila and Escherichia coli strains. This study highlights the importance of choosing the correct material characteristics of polymeric tubes in contact with water to protect them from bacterial contamination. Therefore, manufacturers can use the BioMig test to evaluate and produce more hygienic and biostable tubes.

Dissimilar Metal Welds used in AUSC Power Plant, Fabrication and Structural Integrity Issues

ABSTRACTIn the current era, the Advanced Ultra Super-Critical (AUSC) plants have been used to substantially increased efficiency with environmental protection. AUSC components boiler header, re-heater and super-heater tube etc. are fabricated by using advanced materials to join by the welding process. Any failure of the power plant can lead to grave consequences, not only of substantial financial losses but additionally immensely treasured and irreparable human life loss. In this review, the dissimilar metal welds (DMWs) have many issues such as metallurgical issue, cracking, carbon migration, welding electrode selection, creep properties, suitable welding process and structure integrity issues which enhanced the failure of weldments. The results of our review showed that DMWs of AUSC power plant are joined by activated flux Tungsten Inert Gas (A-TIG) and Pulse A-TIG process to increase the productivity and cut the significant fraction of cost. However, A-TIG process with Post Weld Heat Treatment (PWHT) improved the mechanical properties and high-temperature creep resistance properties of DMWs. This state of the art is encouraged the researchers about the enormous future scope.