Secondary Precipitation Research Articles

Multimodel quantification of green and blue water components and its error propagations through parameter transferability approach across input choices

A robust quantitative assessment of water security through efficient water accounting concepts like blue and green water footprints has gained a lot of attention for water resources management at river basin scale. However, such water accounting tools and models have dependencies to the choice of precipitation data used to drive the model, as the input bias propagate into simulated streamflow through interaction with different hydrological processes. This study performs a holistic investigation of sensitivity of water accounting fractions like blue water flow (BWF), green water flow (GWF), green water storage (GWS), and their dependencies on secondary precipitation datasets (SPDs) choices using a lumped conceptual rainfall-runoff model [Hydrological Simulation model (HYSIM)] and a physically based semi-distributed hydrological model [Soil and Water Assessment Tool (SWAT)] in the Damodar River basin, India. These models were driven by seven gridded precipitation datasets, including India Meteorological Department (IMD) data, Indian Monsoon Data Assimilation and Analysis (IMDAA) data, Asian Precipitation-Highly-Resolved Observational Data Integration Towards Evaluation (APHRODITE) data, Watch forcing ERA-Interim data, Climate Hazard Group Infrared Precipitation with Station data (CHIRPS), PRINCETON precipitation data and Precipitation Estimation from Remotely Sensed Information using Artificial Neural Network-Climate Data Records (PERSIANN-CDR) data. The reference IMD based multimodel results revealed that the annual average blue and green water components of the Damoder River were in the range of 558–656 mm/year, 574–728 mm/year and 34–112 mm/year for BWF, GWF, and GWS respectively during 1994–2010 period. The results obtained after applying parameter transferability approach across the input space have revealed exact quantification of choice dependent annual variations in spatial and temporal characteristics of BWF, GWF, and GWS. A further evaluation based on error propagation ratios (γCC, γrRMSE, γB) has revealed a quantification of input choice induced dampening/magnification effects on flow estimations of both the HYSIM and SWAT and these quantifications were free from the compensation effects of recalibration. The findings in this study demonstrate that the change in annual average BWF varies between −46.97% to +41.38% in comparison to benchmark IMD simulations, and the corresponding changes for GWF is between −19.63% and +17.06% and for GWS is between −29.97% to +35.5% with different choices of SPD scenarios. The systematic (γB) and random (γrRMSE) error propagation factors during monsoon season are larger for SWAT model ([0.21–0.78], [0.69–0.89] respectively) than that of HYSIM model ([0.18–0.74], [0.66–0.81], respectively) and it is varying with choice of different SPDs.

Concurrent Precipitation of Nb(C,N) and Metastable M23C6 in Alloy 347H at 700°C and 750°C: Computer Simulations and Comparison to Experiment

We present our results for the concurrent precipitation of metastable M23C6, Nb(C,N) secondary precipitates, and the Nb(C,N) primary crystals in 347H austenitic stainless steel. For precipitation modeling, we have accounted for the elastic contribution to interfacial energy, and for the Fe-spin-polarization for NbC/Fe and M23C6/Fe interfacial energy values: for NbC/Fe ~ 0.63 J/m2. For M23C6 precipitates, an error function was used to describe the interfacial energy growth with particle size. In precipitation simulations, the average size of the primary Nb(C,N) particles remained ~ 1 μm at 700°C and ~ 0.3 μm at 750°C. The M23C6 precipitates at 750°C dissolved after 120 h (our simulations) compared to 300 h (experiments). The Nb(C,N)/Fe interfacial energy was not affected by the nitrogen additions. With these modifications, reasonable agreement with the available experimental data was obtained, which allows using them in the development of the 2nd-phase particle-informed creep theory.

Coprecipitation mechanisms of Zn by birnessite formation and its mineralogy under neutral pH conditions

Birnessite (δ-Mn(IV)O2) is a great manganese (Mn) adsorbent for dissolved divalent metals. In this study, we investigated the coprecipitation mechanism of δ-MnO2 in the presence of Zn(II) and an oxidizing agent (sodium hypochlorite) under two neutral pH values (6.0 and 7.5). The mineralogical characteristics and Zn–Mn mixed products were compared with simple surface complexation by adsorption modeling and structural analysis. Batch coprecipitation experiments at different Zn/Mn molar ratios showed a Langmuir-type isotherm at pH 6.0, which was similar to the result of adsorption experiments at pH 6.0 and 7.5. X-ray diffraction and X-ray absorption fine structure analysis revealed triple-corner-sharing inner-sphere complexation on the vacant sites was the dominant Zn sorption mechanism on δ-MnO2 under these experimental conditions. A coprecipitation experiment at pH 6.0 produced some hetaerolite (ZnMn(III)2O4) and manganite (γ-Mn(III)OOH), but only at low Zn/Mn molar ratios (< 1). These secondary precipitates disappeared because of crystal dissolution at higher Zn/Mn molar ratios because they were thermodynamically unstable. Woodruffite (ZnMn(IV)3O7•2H2O) was produced in the coprecipitation experiment at pH 7.5 with a high Zn/Mn molar ratio of 5. This resulted in a Brunauer–Emmett–Teller (BET)-type sorption isotherm, in which formation was explained by transformation of the crystalline structure of δ-MnO2 to a tunnel structure. Our experiments demonstrate that abiotic coprecipitation reactions can induce Zn–Mn compound formation on the δ-MnO2 surface, and that the pH is an important controlling factor for the crystalline structures and thermodynamic stabilities.

Secondary Minerals Drive Extreme Lithium Isotope Fractionation During Tropical Weathering

AbstractLithium isotopes are used to trace weathering intensity, but little is known about the processes that fractionate them in highly weathered settings, where secondary minerals play a dominant role in weathering reactions. To help fill this gap in our knowledge of Li isotope systematics, we investigated Li isotope fractionation at an andesitic catchment in Puerto Rico, where the highest rates of silicate weathering on Earth have been documented. We found the lowest δ7Li values published to date for porewater (−27‰) and bulk regolith (−38‰), representing apparent fractionations relative to parent rock of −31‰ and −42‰, respectively. We also found δ7Li values that are lower in the exchangeable fraction than in the bulk regolith or porewater, the opposite than expected from secondary mineral precipitation. We interpret these large isotopic offsets and the unusual relationships between Li pools as resulting from two distinct weathering processes at different depths in the regolith. At the bedrock‐regolith transition (9.3–8.5 m depth), secondary mineral precipitation preferentially retains the lighter 6Li isotope. These minerals then dissolve further up the profile, leaching 6Li from the bulk solid, with a total variation of about +50‰ within the profile, attributable primarily to clay dissolution. Importantly, streamwater δ7Li (about +35‰) is divorced entirely from these regolith weathering processes, instead reflecting deeper weathering reactions (&gt;9.3 m). Our work thus shows that the δ7Li of waters draining highly weathered catchments may reflect bedrock mineralogy and hydrology, rather than weathering intensity in the regolith covering the catchment.

Hydrogen emissions from hydrothermal fields in Iceland and comparison with the Mid-Atlantic Ridge

Hydrogen emissions from geothermal systems are well known, for example associated with mafic and ultramafic rock formations along mid-ocean ridges (MOR). Here we report concentrations and emissions for H 2 from geothermal fields in Iceland that provides the only MOR on Earth that exposes a largely submarine rift on land and compare them with submarine vent systems along the mid-Atlantic Ridge (MAR). The concentrations of H 2 in Icelandic hydrothermal fluids are 0.022–20.5 mmol/kg comparable to H 2 concentrations in MAR hydrothermal fluids of 0.07–26.5 mmol/kg. According to geochemical modeling, the H 2 is considered to form in these settings associated with chemical reactions of primary mineral leaching, Fe +II to Fe +III oxidation and secondary mineral precipitation and reduction of water to hydrogen. The main factors influencing these reactions are rock type and source water composition. Geothermal power plants in Iceland emit in total ∼1.2 kt H 2 per year (2019–20) or on average ∼0.7 g/MWh. The H 2 is today emitted to the atmosphere but could in principle be utilized given technical aspects of such extraction are implemented. • Large quantities of H 2 are present in the fumaroles and the steam of the power plants of Iceland. • The higher values are found along the active volcanic zone. • The salinity and the type of water influence the H 2 generation from the mafic and ultra-mafic rocks. • If we consider a price of H 2 of 2€/kg, the native H 2 emitted by the existing power plants corresponds to 2.3 million €/yr.

Inter-diffusion effects and tribological behaviour of electron beam evaporated Ni-YSZ nanocomposite coatings subjected to diffusion annealing with borosilicate glass for nuclear applications

Nuclear vitrification furnace made of Inconel-690 alloy fails prematurely due to alloy-borosilicate glass interaction by forming Cr rich secondary precipitates which results in the loss of corrosion resistance and incorporation of nuclear waste in the alloy-borosilicate interface. In this work, the development of a novel compositionally graded Ni-YSZ diffusion barrier coating using electron beam physical vapor deposition method was investigated to mitigate the issues related to inter-diffusion and elemental exchange across the alloy-borosilicate melt without the addition of any nuclear waste. A comparative study on the interdiffusion effects of compositionally graded Ni-YSZ nanocomposite coating with increasing Ni content from 5 to 50 wt % subjected to diffusion annealing with and without borosilicate melt at 1373 K in air was carried out. No phase transformation was observed in Ni-YSZ coating subjected to diffusion annealing at 1373 K in air as observed from XRD analysis. FESEM-EDS analysis confirms the formation of NiO and grain growth of NiO in YSZ matrix after heat treatment. Raman spectroscopic studies confirmed the outward diffusion of Ni from the adjacent Ni rich multilayer to YSZ top coat and the formation of NiO at the surface of the Ni-YSZ nanocomposite. In contrast, there was no elemental exchange across the interface between nanocomposite coating and adhered borosilicate layer as there was no traces of NiO on the surface of the glassy layer. The wear behaviour was studied on the compositionally graded Ni-YSZ nanocomposite coatings subjected to high temperature diffusion annealing with and without borosilicate glass using a linear reciprocating tribometer by analyzing different modes of wear scar and the chemical changes inside the wear track using Raman spectroscopy. The observation of higher hardness and wear resistance obtained for the diffusion annealed Ni-YSZ nanocomposite was found to be due to the formation of NiO on the surface of the coating.

Microstructure evolution of pulsed laser melting 2219 aluminum alloy: Solidification modes and inter-pulse thermal cycles

In this study, pulsed laser melting of 2219 aluminum alloy with different laser pulse periods was carried out to understand the impact of solidification modes and inter-pulse thermal cycles on soldification sturctures. The results show that the solidification transformed from single unconstrained mode to alternating constrained and unconstrained modes with the increase of pulse period. Fine dendrites with low Cu segregation were obtained under unconstrained solidification mode. While coarse dendrites with severe Cu segregation were formed under constrained solidification mode. The coarse and fine dendrites were alternately arranged under a long-period pulse. The round-shaped secondary precipitates can be obtained by adjusting the inter-pulse thermal cycles. This work not only contributes to the valuable understanding of solidification modes and inter-pulse thermal cycles of pulsed laser processing, but also provides a potential approach for site-specific control of microstructure and material properties for laser processed parts.

Assessment of the Factors Influencing Sulfur Dioxide Emissions in Shandong, China

Sulfur dioxide (SO2) is a serious air pollutant emitted from different sources in many developing regions worldwide, where the contribution of different potential influencing factors remains unclear. Using Shandong, a typical industrial province in China as an example, we studied the spatial distribution of SO2 and used geographical detectors to explore its influencing factors. Based on the daily average concentration in Shandong Province from 2014 to 2019, we explored the influence of the diurnal temperature range, secondary production, precipitation, wind speed, soot emission, sunshine duration, and urbanization rate on the SO2 concentration. The results showed that the diurnal temperature range had the largest impact on SO2, with q values of 0.69, followed by secondary production (0.51), precipitation (0.46), and wind speed (0.42). There was no significant difference in the SO2 distribution between pairs of sunshine durations, soot emissions, and urbanization rates. The meteorological factors of precipitation, wind speed, and diurnal temperature range were sensitive to seasonal changes. There were nonlinear enhancement relationships among those meteorological factors to the SO2 pollution. There were obvious geographical differences in the human activity factors of soot emissions, secondary production, and urbanization rates. The amount of SO2 emissions should be adjusted in different seasons considering the varied effect of meteorological factors.

A reactive transport modeling perspective on the dynamics of interface-coupled dissolution-precipitation

In interface coupled dissolution-precipitation systems, the dynamics of the mineral-fluid interface depends on two intertwining processes: the dissolution of the primary mineral that is needed for subsequent precipitation and the passivation of the dissolution reaction as a result of secondary mineral precipitation. The resulting thickness and texture of the precipitating coating layer will affect the progression of geochemical reactions, flow and transport processes at the macroscopic scale. Understanding the interplay between macroscopic flow regimes and microscopic reaction mechanisms (e.g., nucleation and crystal growth pathways) in controlling the dynamics of the mineral-fluid interface has important implications for predicting natural weathering processes, scaling in the subsurface energy production systems, etc. In this study, we use a micro-continuum pore-scale reactive transport model to investigate the feedback loop between reaction rate and solute transport with explicit consideration of the surface passivation and the diffusion process through the coating layer, as well as the impacts of saturation-dependent nucleation rate on the textures of precipitates that will largely dictate the diffusion properties of the coating layer. Our model results highlight that the drastically different coating behaviors at the macroscopic scale and their dependence on solution supersaturation observed in previous column experiments are primarily controlled by the interplay between mineral reaction rates, advective flow, and diffusion through the dynamically forming coating layer. The diffusion properties of the coating layer also play a secondary but non-negligible role in shaping the evolution of the co-dissolution and precipitation system. The probabilistic nucleation model building on the framework of classical nucleation theory highlights the complex dependence of precipitates’ texture on solution chemistry and substrate properties, which can affect the diffusion process within the precipitates. The modeling observations also underscore the necessity of further investigations to better characterize the properties of the coating layer and to improve modeling descriptions of the nucleation processes.

Promene padavina u pobrđu gornjeg sliva reke Nišave (1961-2020)

The study represents a report on the monthly, seasonal and annual amounts of precipitation, extremely dry and extremely rainy periods. The paper analyzes two 30-year periods from 1961-1990. and from 1991-2020. Data from the four meteorological stations in the upper part of the Nišava basin (Babušnica, Bela Palanka, Pirot and Dimitrovgrad) have ben used, three of which are in the Nišava basin and one of which (Babušnica) is in the immediate vicinity of the basin. The main goal of the paper is to provide an overview of the change in the precipitation in Pirot district at the end of the 21st century. The district is mainly an agricultural area and rainfall is very important for its development. The continental type of pluviometric regime is represented in the district of Pirot. The analysis of annual precipitation shows that the area of Pirot records a decrease in the annual sum of the precipitation with the increase in Dimitrovgrad, while Bela Palanka and Babušnca have no significant changes. In the first period that was considered by the conducted analysis (1961-1990), the secondary maximum precipitations occur on the average during the month of November and for the period of 1991-2020, the secondary maximum precipitation is a month earlier, in October, except for the station in Bela Palanka.

Effect of the nanostructuring by high-pressure torsion process on the secondary phase precipitation in UNS S32750 Superduplex stainless steel

In this work, the precipitation and the morphology of secondary phases after severe plastic deformation (SPD) processing followed by an isothermal treatment was investigated. High-pressure torsion (HPT) was the SPD process carried out on superduplex 2507 (UNS S32750) stainless steel material under P = 6 GPa at room temperature. At this high strain levels (ε up to 170) samples have shown grain size decrease and strained microstructure with high dislocation density and nanostructure features. After a short isothermal treatment at 830 °C, the sigma phase and chromium nitrides were revealed as the main secondary phases identified by scanning and transmission electron microscopy and element analysis by energy dispersive spectroscopy. Scanning precession electron diffraction and automated crystal orientation mapping have been carried out in order to confirm the precipitation of the secondary phases. In fact, the results provide evidence that the precipitation of chromium nitrides seems to be the preferred nucleation site for sigma phase at higher deformation strain, in addition to the intergranular precipitation of sigma. Both the sigma phases nucleated integranularly and besides chromium nitrides are randomly orientated.

Dissimilar linear friction welding of selective laser melted Inconel 718 to forged Ni-based superalloy AD730™: Evolution of strengthening phases

The continuous growth in the manufacture of aerospace components such as blisks has led to an increase in the application of different hybrid materials fabricating methods, and thus the requirements for joining and strengthening of dissimilar welds. According to this goal, selective laser melted (SLM) Inconel 718 was joined with forged AD730™ Nickel-based superalloy through linear friction welding (LFW) in this study. Microstructure variation, specifically with respect to secondary phases precipitation was investigated. The microhardness and strengthening mechanisms of the weldment were also studied. The precipitation (volume fraction and size of particles) at different regions of both sides of the weld line was characterized. Close to the weld line, the dissolution of γ'/γ" and Laves phases and grain refinement occurred which reveals the effects of both compression strain and high temperature on recrystallization and high degree of elemental diffusion in the weld zone (WZ). It is shown that the size, volume fraction, and shape of secondary phases increased and changed (from spherical to long-striped for Laves particles) as we went from the WZ toward the base metal. However, the measured microhardness indicated that the strength of AD730™ alloy depends significantly on the grain size, while strength in SLM Inconel 718 was dominated by shape (or size) and the presence of secondary phases (γ'/γ" and Laves).

Effect of Cerium and Aluminium on the phase stability and properties of polycrystalline Cu-Al-Be shape memory alloys

This study presents the outcomes of an investigation of the effect of wt% of cerium and Aluminium on the phases, crystal structure, microstructure, morphology, phase transformation temperatures, shape recovery ratio and mechanical properties of the polycrystalline Cu-Al-Be shape memory alloys (SMAs). SMAs exhibit martensite phase at room temperature up to 0.49 wt% of Be and ≥ 0.52 wt% of Be transforms to austenite phase. An increase in cerium by 0, 0.05, 0.1, 0.15 and 0.2 wt% decreases the grain size by 0, 70.87%, 82.73%, 83.8% and 94.6%, respectively. An increase in cerium increases the transformation temperatures owing to the Al-rich secondary precipitates, and the shape recovery ratio reduces. Alloying cerium of 0.1 wt% exhibits a maximum tensile strength of 474 ± 23 MPa with the ductility of 24.11 ± 1.42%. • Alloying cerium of 0.2 wt.% refines the grains to 25 μm from 463.45 μm. • Addition of beryllium >0.49 wt.% transforms martensite to metastable austenite. • Increase in Ce increases the transformation temperatures and deterioration in recovery.

Multi-Pass Friction Stir Lap Welding of AA 6061-T6: Implication of Tool Pin Overlapping on Microstructure and Mechanical Properties of Joints

The present study focuses on the influence of a 5-pass overlapped friction stir lap welding of AA6061-T6 on the mitigation of defects and its simultaneous effect on microstructure and mechanical properties. Tool pin overlapping percentage of 0%, 25%, 50% and 75% was employed, from which it was observed that defects significantly reduced at higher overlapping. Fine equiaxed grains were observed across all the nugget zones in both top, and bottom regions were developed due to simultaneous overlapped passes; the grain size of which varied from 8.5 µm to 3.5 µm. The grains became finer, which increased of overlapping percentage. The microhardness of the processed zone was significantly reduced during overlapping that varied from a range of 43 HV0.1 to 49 HV0.1 as compared to base metal which was interpreted due to changes in grain size and secondary precipitate distribution during overlapping. A maximum ultimate tensile strength of 230 MPa was achieved at 50% overlapping, whereas minimum ultimate tensile strength of 160 MPa was achieved at 0% overlapping. Fractography of fracture surface showed a ductile failure at 50% that showed a number of dimples of varying shapes and sizes.

Microstructure and sliding wear behavior of FeCoNiCr0.8Al0.2 high-entropy alloy for different durations

In this study, FeCoNiCr0.8Al0.2 high-entropy alloy was fabricated by vacuum arc melting, followed by aging treatment for different durations. And the phase structure, microstructure, mechanical properties, and tribological behavior of the alloys were systematically studied. The results show that all the HEAs in this work have good structural stability and they consist of the FCC matrix phase and γ' precipitated phase with L12 structure, in which the FCC matrix is rich in Fe, Co, and Cr, while the γ' precipitates rich in Ni and Al. The changes of the precipitates of the alloys with the aging time are divided into two stages. In the first stage (the aging time is 6 h, 12 h, and 24 h), the volume fraction of the precipitates of HEAs increases initially, but when the durations beyond 12 h, the size of it gradually increases but the volume fraction of the precipitates decrease. After the durations beyond 48 h, the alloy will undergo secondary precipitation effect again but the volume fraction of the reprecipitated phases is lower, and the precipitates gradually coarsen with the increase of durations. All the HEAs occurred abrasive wear and oxidative wear during the wear process. In addition, delamination wear and spalling wear occurred on the 6hHEA and the 168hHEA, respectively. The 12hHEA has the best wear properties due to the highest volume fraction and the uniform distribution of the precipitates. Our study indicates that the alloys can have good wear properties inducing a certain volume fraction of L12 precipitated phase by proper heat treatment, and it can provide theoretical reference for the development and design of the alloys with good wear resistance.

Pore changes of slickwater-containing shale under supercritical CO2 treatment

Application of liquid CO2-slickwater hybrid fracturing technology can significantly improve the energy-enhancing efficiency and fracturing fluid flowback efficiency of shale reservoirs. However, supercritical CO2 (ScCO2) fluid and slickwater are inevitably retained in reservoirs after fracturing, resulting in limited understanding of the changes of shale pore structure, further impacting the evaluation of the gas adsorption and transportation behaviors as well as CO2 sequestration capacity in shale reservoirs. Therefore, the influences of the ScCO2-slickwater coupling effect on shale pore structure was analyzed by using X-ray diffraction, low-pressure nitrogen gas adsorption (N2GA), mercury intrusion porosimetry (MIP), field emission-scanning electron microscopy (FE-SEM), and fractal analysis. After ScCO2-slickwater treatment, the calcite and albite contents decreased, while the quartz and clay minerals contents increased in shale. The increase in number of micropores and mesopores and the reduction in number of macropores were observed by a combination of N2GA and MIP, which led to the total specific surface area (TSSA) and total pore volume (TPV) of the shale enlarged, while the average pore size reduced. Meanwhile, the fractal dimensions calculated by N2GA (D1, D2) and MIP (D3) were raised, indicating that pore surface roughness and structural complexity were strengthened. D1, D2 and D3 can roughly reflect fractal characteristic of micropores (<3.5 nm), mesopores (3.5–50 nm) and macropores (>50 nm), respectively. Thus, D1 and D2/D3 can be used to evaluate the gas adsorption and flow behaviors of shale, respectively. By analyzing the control experimental results of ScCO2-water and He-slickwater treatment and the FE-SEM images, shale pore changes after ScCO2-slickwater treatment can be explained by CO2 extraction and dissolution, secondary mineral precipitation and polyacrylamide adsorption. After treatment, the increase of micropores and mesopores as well as TSSA and TPV makes the gas-adsorption capacity of shale improved, showing that the coupling effect of ScCO2-slickwater can not only improve shale gas productivity, but also benefit geological storage of CO2.

The Effect of pH on Stability of an Isolation Barrier Made of Dolomite Post-Floatation Waste

Dolomite post-floatation waste has been proposed as an alternative material for the construction of separation barriers. The aim of this study was to determine the effect of the pH of leaching solutions on the stability of such barriers. The present research included the determination of selected physical and chemical properties of waste, i.e., density, grain composition, and filtration coefficient. Column tests of leaching by solutions of different pH values modeling varying environmental conditions were performed. Selected ions were determined in the eluates. Grain analyses were carried out for the column material after leaching to determine the changes in grain composition of dolomite due to washing with leaching solutions. The determined value of the filtration coefficient is 6.52 × 10−9 m∙s−1, which confirms the impermeability of the waste. The material is fine-grained, with a grain diameter of d ≤ 200 µm. During leaching, a decrease in the content of the analyzed ions and the diameter of grains and their movement down the barrier, resulting in its sealing, was observed. The central part of all columns showed more grains with a diameter of 7 μm, which is probably due to secondary precipitation of CaSO4. Irrespective of the initial pH of the leaching solution, the reaction of all eluates obtained was slightly alkaline (pH 7.52–8.20). Dolomite post-floatation waste has properties that ensure the tightness and durability of the separation barrier, which, combined with its ability to alkalize solutions and the sealing process, ensures its effectiveness.

Response of ferrite, bainite, martensite, and retained austenite to a fire cycle in a fire-resistant steel

Understanding the kinetics of microstructural degradation during the event of a fire is of major relevance to future optimization of fire-resistant steels (FRS). In this work, we use in situ synchrotron X-ray diffraction to assess the rapid thermally-assisted degradation of different starting microstructures, such as (i) ferrite + pearlite; (ii) bainite + retained austenite, and (iii) martensite + retained austenite, during the simulation of a fire cycle in a Fe-0.13C-0.11Cr-0.38Mo-0.04V FRS. Our results show that retained austenite is the most unstable phase, especially when generated by faster cooling rates, decomposing at temperatures as low as 180 °C during fire simulations. Bainite and martensite are both unstable and undergo recovery and carbon desaturation via secondary precipitation of cementite. However, bainite is comparatively more stable than martensite since its decomposition starts at 400 °C, while for martensite it occurs at 320 °C. We also present a methodology to deconvolute the effect of temperature on the increased background and signal intensities of the X-ray spectra, allowing the direct observation of the kinetics of secondary cementite precipitation. • Different starting microstructures were submitted to a simulated fire cycle. • The kinetics of microstructural decomposition was studied using synchrotron X-ray diffraction. • Bainite, martensite and retained austenite underwent carbon desaturation during heating. • The kinetics of secondary precipitation of cementite was revealed for each microstructure .

Degradation behaviour of selective laser melted CoCrMo alloys in H2O2-containing chloride solutions

H2O2 usually develops after implanting an implant of biomedical material in human body. Our study showed that H2O2 has dual effects on degradation behaviour of biomedical material depending on its concentration. As for a SLMed CoCrMo alloy, a critical concentration of H2O2 exists, below which the corrosion potential shifts positively as the concentration increases, facilitating the passive film formation; and above which, the film becomes less protective due to the change in composition of the film. The corrosion resistance of XOZ plane of the alloy is better than that of XOY plane due to less grain boundaries and secondary precipitates.

Lithium isotopic composition of soil pore water: Responses to evapotranspiration

Abstract Lithium isotopes show great potential to trace Earth surface processes due to the large mass discrimination between 6Li and 7Li associated with clay uptake. However, factors controlling the Li isotopic composition (δ7Li) of river water, especially those with a water-bedrock δ7Li difference higher than that of the equilibrium fractionation associated with clay formation (ΔW-C), have not yet been fully resolved. Traditional interpretation involves the Rayleigh distillation, but it unrealistically separates the stage of clay formation from that of silicate dissolution using fractionation factors that are much lower than laboratories can constrain. We propose an in situ mechanism that simulates high δ7Li by evapotranspiration. A model with coupled mineral dissolution and clay precipitation shows that evaporative enrichment of pore-water Li progressively increases the incorporation of Li into clays with light δ7Li, resulting in higher δ7Li values in the residual water than ΔW-C. We also provide evidence from the Chinese Loess Plateau, where an evaporative effect readily explains the observed δ7Li. The influence of evapotranspiration on riverine δ7Li implies that changes in aridity may partly explain the variations of seawater δ7Li. The same principle may also apply to other stable isotopic systems whereby incorporation into secondary precipitates controls the isotopic fractionation.