Precipitation Zone Research Articles

Experimental characterization of coupled diffusion reaction mechanisms in low permeability chalk

Reactions caused by the diffusion of reactants from different sources can alter rock diffusivity and are therefore the critical mechanisms for evaluating short and long-term behavior of low-permeability rocks used as confinement layers for underground storage, for instance. This paper presents and discusses a set of two diffusion-driven reaction experiments focusing on precipitation of two end-member types of sulfate minerals (gypsum: CaSO4.2H2O and barite: BaSO4) in low-permeability chalk. The time-resolved changes in porosity and effective diffusion coefficient (De) were evaluated along the duration of the experiments (~140 days), by analyzing the behavior of passive tracers and evaluating the amount of precipitated gypsum or barite from measuring the reactant concentration evolution in the reservoirs at both ends of the sample. Then SEM-EDS and X-ray microtomography (μCT) imaging were used to characterize the initial rock structure and the precipitated materials.Results showed that the change in porosity (from 45% to about 43%) corresponding to the volume of sulfate precipitated, are similar for gypsum and barite. Conversely, the precipitation impact on diffusion properties of the water tracers that were injected 70 days after the beginning of the precipitation step is distinctly different for the each of the studied sulfate mineral. The precipitation of barite generated a more significant impact than gypsum: Deintact = 4.15 × 10−10 m2·s−1 vs. Debarite = 1.1 × 10−10 m2·s−1 and Degypsum = 2.5 × 10−10 m2·s−1. Post-mortem imaging revealed a thin precipitated zone (~250 μm) in the center of the sample for the barite precipitation experiment, whereas isolated quasi-spherical clusters resulted from the gypsum precipitation. The μCT images at higher resolution showed that the precipitation of barite is heterogeneous at small scale, which explains the HTO diffusion curve. For gypsum, the post mortem imaging around the quasi-spherical clusters showed a significant presence of initial macropores of the connected porosity that were still unfilled. These intact chalk zones allowed HDO to diffuse through the precipitated zone lowering the impact on water tracer diffusivity. These experimental results indicate that the morphology and the distribution of barite precipitates is mainly controlled by homogeneous and heterogeneous nucleation phenomena, whereas gypsum precipitation is mainly controlled by the spatial variability of the initial porous system properties (reactive surface area, tortuosity, pore network structure).

Influence of solidification induced composition gradients on carbide precipitation in FeNiCr heat resistant steels

Secondary precipitation of Cr-rich carbides in heat resistant austenitic stainless steels has been investigated both experimentally and using finite element simulations. The microstructural evolutions in two commercial grades were characterized using electron microscopy. A special emphasis was given on the peculiar spatial distribution of M23C6 secondary carbides exhibiting precipitate free zones surrounding primary carbides, and high density precipitate zones extending with longer aging times. Solidification induced chemical composition gradients were clearly exhibited in the as-cast alloys with significant chromium depletion in the vicinity of primary M7C3 carbides. It is then proposed that these gradients play a major role in the secondary precipitation mechanism. Classical nucleation and growth theories have been adapted to account for (i) the flux of solutes with large difference in diffusion coefficients, (ii) the initial composition gradients in the matrix and, (iii) the chemical driving force for nucleation and growth of M23C6 carbides. Within this framework, the whole kinetics has been reproduced. It clearly shows that the spatial distribution of secondary carbides that play a key role in the creep resistance of these alloys is the result of a complex interaction between initial composition gradients in as-cast alloys and solute flux resulting from phase transformation during aging.

Influence of weathering-induced iron precipitation on properties of sandstone in a tropical environment

Weathering-induced iron dissolution and precipitation in rock masses lead to reduction in shear strength of discontinuities, amongst others, while precipitation leads to an increase, and precipitated iron may reduce the susceptibility to future weathering. This effect is investigated in fieldwork campaigns with detailed rock mass characterization and chemical analyses in Kota Kinabalu, Malaysia. Many cut slopes in this area consist of different zones in which iron in various forms is either dissolved or precipitated. Iron-coated and -cemented discontinuities have a marked higher shear friction, while staining has little influence on friction. Discontinuities with iron-coating and -cementing reduce the susceptibility to weathering of a rock mass as weathered material is less easily eroded and underlying material is protected from further weathering. On the other hand, dissolution zones, which are mostly found below the precipitation zones, have considerably lower rock mass quality. In engineering works the latter are invisible before excavation. Just assuming the continuation downward of the surface rock mass with precipitated iron, or, worse than this, assuming a less weathered rock mass with better characteristics, may be very erroneous. This study emphasizes that forecasting the susceptibility to weathering should include the influence of morphology, environment and climate.

Dissolution and evolution of interfacial oxides improving the mechanical properties of solid state bonding joints

The mechanical properties of solid state bonding joints have always been greatly deteriorated due to surface oxide scales. Here, we report a method to completely heal solid state bonding joints with recovered mechanical properties by hot compression bonding and post-holding treatment. Using scanning electron microscopy and transmission electron microscopy, we discovered that the recovery of mechanical properties of the bonding joint is attributed to the dissolution and evolution of the interfacial oxides. While holding the joint at 1200 °C, the interfacial oxides (MnCr2O4) gradually decomposed. With the decomposed oxygen ions diffusing toward the matrix, oxide particles precipitated around both sides of the interface, forming the particle precipitation zone (PPZ). As the holding time increased, the width of the PPZ increased and the oxide precipitates in the PPZ transformed from MnCrxAl2−xO4 to MnxAl3−xO4 and finally to γ-Al2O3, depending on the local oxygen activity. After holding for 24 h, the interfacial oxides completely decomposed and only a few nano-scale γ-Al2O3 oxide precipitates remained dispersed far away from the bonding interface, leading to the recovery of the mechanical properties of the bonding joints. This recovery mechanism may be of great importance to the design and manufacture of high-quality heavy bonding joints.

Interactions between Terpinen-4-ol and Nystatin on biofilm of Candida albicans and Candida tropicalis.

The aim of this study was to evaluate the antifungal activity of Terpinen-4-ol associated with nystatin, on single and mixed species biofilms formed by Candida albicans and Candida tropicalis, as well as the effect of terpinen-4-ol on adhesion in oral cells and the enzymatic activity. The minimum inhibitory concentrations and minimum fungicide concentrations of terpinen-4-ol and nystatin on Candida albicans and Candida tropicalis were determined using the microdilution broth method, along with their synergistic activity ("checkerboard" method). Single and mixed species biofilms were prepared using the static microtiter plate model and quantified by colony forming units (CFU/mL). The effect of Terpinen-4-ol in adhesion of Candida albicans and Candida tropicalis in coculture with oral keratinocytes (NOK Si) was evaluated, as well as the enzymatic activity by measuring the size of the precipitation zone, after the growth agar to phospholipase, protease and hemolysin. Terpinen-4-ol (4.53 mg mL-1) and nystatin (0.008 mg mL-1) were able to inhibit biofilms growth, and a synergistic antifungal effect was showed with the drug association, reducing the inhibitory concentration of nystatin up to 8 times in single biofilm of Candida albicans, and 2 times in mixed species biofilm. A small decrease in the adhesion of Candida tropicalis in NOK Si cells was showed after treatment with terpinen-4-ol, and nystatin had a greater effect for both species. For enzymatic activity, the drugs showed no action. The effect potentiated by the combination of terpinen-4-ol and nystatin and the reduction of adhesion provide evidence of its potential as an anti-fungal agent.

Permeability Changes Resulting from Quartz Precipitation and Dissolution around Upper Crustal Intrusions

It has long been recognized that quartz precipitation from circulating hydrothermal fluids may reduce porosity and permeability near intrusions. However, the magnitude of permeability changes and potential feedbacks between flow, heat transfer, and quartz precipitation/dissolution remain largely unquantified. Here, we present numerical simulations of fluid convection around upper crustal intrusions which explicitly incorporate the feedback between quartz solubility and rock permeability. As groundwater is heated to ~350°C, silica dissolves from the host rock, increasing porosity and permeability. Further heating to supercritical conditions leads to intensive quartz precipitation and consequent permeability reduction. The initial host rock permeability and porosity are found to be main controls on the magnitude and timescales of permeability changes. While the permeability changes induced by quartz precipitation are moderate in host rocks with a primary porosity ≥ 0.05, quartz precipitation may reduce rock permeability by more than an order of magnitude in host rocks with a primary porosity of 0.025. Zones of quartz precipitation transiently change locations as the intrusion cools, thereby limiting the clogging effect, except for host rocks with low initial porosity. This permeability reduction occurs in timescales of hundreds of years in host rocks with initial high permeability and thousands of years in host rocks with intermediate permeability.

The grain refinement mechanisms of various phases in shot-peened Nickel-Aluminum bronze (NAB) alloy

In this study, coarse-grained Nickel-Aluminum bronze (NAB) alloy is subjected to shot-peening (SP) treatment, and the grain refinement mechanisms of various phases in shot-peened NAB alloy are investigated separately. The results show that severe deformation layers are produced on the surface. Meanwhile, refined grains with the average size below 100 nm are induced through SP treatment indicated by the results of X-ray diffraction (XRD) patterns. Various phases in NAB alloy including α, β' and three intermetallic phases (κii, κiii and κiv) display different grain refinement mechanisms. The grain refinement in the α phase involves dislocation segmentation in the precipitation-free zone and the twinning intersection in the precipitation zone. The formation of nanotwins by emitting partial dislocations at the grain boundary is found to be responsible for the grain refinement in the β' phase. As for the κ phases, the strip-shaped κiii phases are fragmented after severe deformation, and the κiv and κii phases exhibit the twinning and dislocation deformation modes, respectively. Also, the microhardness is significantly enhanced after SP treatment, which is mainly attributed to the work hardening effect and grain refinement.

Climatic Response of Conifer Radial Growth in Forest-Steppes of South Siberia: Comparison of Three Approaches

We compared three approaches to study climatic signals of Pinus sylvestris and Larix sibirica treering width chronologies from the forest-steppe zone of South Siberia, where both temperature and precipitation limit the conifer tree growth: 1—paired correlation of chronologies with monthly climatic variables; 2— paired and partial correlations with monthly and seasonal series of primary and secondary climatic factors, calculated in the Seascorr program; 3—paired correlation with a 15-day moving average series of climatic variables. The comparison showed that simple paired correlation with monthly series as the simplest approach could be used for a wide range of dendroclimatic studies, both as a main procedure and for preliminary analysis. The Seascorr analysis is the most suitable for assessing climate-growth relationship in extreme growth conditions and for reconstructions of extremes, e.g. droughts, and of their impact periods. The application of the 15-day moving average series is limited by availability of daily climatic data, but it describes the seasonal window of climatic response with high precision. Altogether, the combination of three approaches allowed to explore the spatial-temporal pattern of the conifers radial growth climatic response in South Siberia.

Hydrogeochemical Modeling of the Shallow Thermal Water Evolution in Yangbajing Geothermal Field, Tibet

The exploitation of thermal water and the mix of cold water changed the properties of geofluid in shallow reservoir, which altered the concentration of the chemical constitutes and continuously built new water-rock reaction. This paper deduced reservoir pressure and temperature variation tendency from 2004 to 2013, analyzed the change of some components in the shallow reservoir water, and finally obtained the evolution of the shallow geothermal water with hydrogeochemical model. The results show the reservoir pressure decreased significantly compared with the slight decline of reservoir temperature, and much cold groundwater infiltrated into the shallow reservoir, which affected the solubility of SiO2 and led to precipitation, the increased CO2 in shallow reservoir promoted the dissolution of aluminosilicate. Calcite and kaolinite precipitation zone has extended to the north in the field, which influenced the porosity of the reservoir rock.

Trend Analysis of Relationship between Primary Productivity, Precipitation and Temperature in Inner Mongolia

This study mainly examined the relationships among primary productivity, precipitation and temperature by identifying trends of change embedded in time-series data. The paper also explores spatial variations of the relationship over four types of vegetation and across two precipitation zones in Inner Mongolia, China. Traditional analysis of vegetation response to climate change uses minimum, maximum, average or cumulative measurements; focuses on a whole region instead of fine-scale regional or ecological variations; or adopts generic analysis techniques. We innovatively integrate Empirical Mode Decomposition (EMD) and Redundancy Analysis (RDA) to overcome the weakness of traditional approaches. The EMD filtered trend surfaces reveal clear patterns of Enhanced Vegetation Index (EVI), precipitation, and temperature changes in both time and space. The filtered data decrease noises and cyclic fluctuations in the original data and are more suitable for examining linear relationship than the original data. RDA is further applied to reveal partial effect of precipitation and temperature, and their joint effect on primary productivity. The main findings are as follows: (1) We need to examine relationships between the trends of change of the variables of interest when investigating long-term relationships among them. (2) Long-term trend of change of precipitation or temperature can become a critical factor influencing primary productivity depending on local environments. (3) Synchronization (joint effect) of precipitation and temperature in growing season is critically important to primary productivity in the study area. (4) Partial and joint effects of precipitation and temperature on primary productivity vary over different precipitation zones and different types of vegetation. The method developed in this paper is applicable to ecosystem research in other regions.

Stability of immobilization remediation of several amendments on cadmium contaminated soils as affected by simulated soil acidification

Chemical immobilization is a practical approach to remediate heavy metal contamination in agricultural soils. However, the potential remobilization risks of immobilized metals are a major environmental concern, especially in acid rain zones. In the present study, changes in the immobilization efficiency of several amendments as affected by simulated soil acidification were investigated to evaluate the immobilization remediation stability of several amendments on two cadmium (Cd) contaminated soils. Amendments (hydrated lime, hydroxyapatite and biochar) effectively immobilized Cd, except for organic fertilizer, and their immobilizations were strongly decreased by the simulated soil acidification. The ratio of changes in CaCl2-extractable Cd: pH (△CaCl2-Cd/△pH) can represent the Cd remobilization risk of different amended soils. Hydroxyapatite and biochar had a stronger durable immobilizing effect than did hydrated lime, particularly in soil with a lower pH buffering capacity, which was further confirmed by the Cd concentration and accumulation in lettuce. These results can be attributed to that hydroxyapatite and biochar transformed greater proportions of exchangeable Cd to other more stable fractions than lime. After 48 weeks of incubation, in soil with a lower pH buffering capacity, the immobilization efficiencies of lime, hydroxyapatite, biochar and organic fertilizer in the deionized water group (pH 6.5) were 71.7%, 52.7%, 38.6% and 23.9%, respectively, and changed to 19.1%, 33.6%, 26.5% and 5.0%, respectively, in the simulated acid rain group (pH 2.5). The present study provides a simple method to preliminarily estimate the immobilization efficiency of amendments and predict their stability in acid rain regions before large-scale field application. In addition, hydrated lime is recommended to be combined with other acid-stable amendments (such as hydroxyapatite or biochar) to remediate heavy metal-contaminated agricultural soils in acid precipitation zones.

Cholesterol Assimilation of Saccharomyces cerevisiae B-18 isolated from gastrointestinal tract of Javanese duck

This study had a purpose of obtaining potential indigenous yeasts for assimilating cholesterol and assessed the in vitro activity of Bile Salt Hydrolase (BSH) using Chloramphenicol Yeast Glucose (CYG) media supplemented CaCl2 and Taurodeoxycholic Acid (TDCA). Yeasts were collected from the gastrointestinal tract of Indonesian native chicken (Gallus javanicus), Javanese duck (Anas javanicus), and Muscovy duck (Anas moschata). The BSH assay was performed to determine secretion of BSH from yeast strain to conjugate bile salts into cholic acid-free by measuring precipitation zone in a specific medium. The quantitative measurement to assimilate cholesterol in yeast using CYG broth contained soluble cholesterol (500 ppm) and incubated at 30°C for 72 hours. Microplate reader used to analyze cholesterol content in the supernatant. Data were analyzed using Analysis of Variance (ANOVA) with one way completely randomized. Precipitation zone found among isolates did not significantly different (P>0.05). Isolate B-18 from Javanese duck performed the highest percentage of assimilating cholesterol with the value of 51.83% and identified as S. cerevisiae. This isolate was closely related to S. cerevisiae mt 21s (accession number X00149.1)based on phylogenetic tree analysis. It could be concluded that S. cerevisiae B-18was potential for assimilating cholesterol in vitro.

Evaluation of some in vitro probiotic properties of Lactobacillus fermentum Strains.

This study aimed to check the in vitro probiotic properties of eleven Lactobacillus fermentum strains previously isolated from fermented dairy products and infant faeces. These cultures were tested for their tolerance to different pH such as 2.0, 2.5, 3.0, 3.5 and 6.5, bile salt hydrolysis and cell surface hydrophobicity. All the strains were persistent at pH 3.5 for 3h whereas only faecal origin isolates such as L. fermentum BIF-19, BIF-20, BIF-18 and MTCC 8711 had shown considerable growth at pH 2.5. The strains NCDC-400, MTCC 8711, BIF-18, BIF-19 and BIF-20 showed slight to intense precipitation zone of bile salt hydrolase activity by agar plate assay. The strain L. fermentum BIF-19 exhibited best preliminary probiotic properties was selected for the adhesion to Caco-2 cell lines, which shows similar adhesion to that observed for standard probiotic Lactobacillus rhamnosus GG.

RegCM4 model sensitivity to horizontal resolution and domain size in simulating the Indian summer monsoon

The sensitivity to model resolution and domain size of the regional climate model RegCM4 is examined in simulating a deficit (1987), excess (1988), and normal (1989) Indian summer monsoon (ISM) rainfall. The initial and boundary conditions are prescribed by the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim reanalysis at 1.5° × 1.5° (EIN15). The model simulated precipitation is compared with India Meteorological Department (IMD) gridded precipitation data (0.25° × 0.25°) and other parameters are compared with EIN15. In the present study, eight different horizontal resolutions such as 60, 55, 50, 45, 40, 36, 27 and 18 km are used whereas four different domain sizes (D01, D02, D03, and D04; largest to smallest) centered at the Indian landmass are considered to investigate the model performance.Results illustrate that the RegCM4 has the capability to depict the important semi-permanent features of the ISM, however, skills vary with the resolutions and domain sizes. Experiments with different resolutions reveal that the lower (850 hPa) and upper (200 hPa) tropospheric circulations are stronger over the Arabian Sea and Bay of Bengal in the 36 and 40 km grid-spacing simulations and closer to EIN15, however, it is weaker in the high-resolution simulations at 27 and 18 km grid-spacing. The biases in vertically integrated moisture transport (VIMT) are positive in the model simulations with resolutions from 36 to 60 km, but, it is negative with 27 and 18 km grid resolution. The simulated precipitation intensity increases as one moves from coarse to higher resolution till grid spacing 36 km. The model efficiency reduces to simulate higher precipitation intensity over the maximum precipitation zones of India during summer monsoon season when grid spacing 27 km and 18 km are used. The overall performance is better with the use of 36–40 km grid spacing than other resolutions in simulating ISM and associated rainfall. The sensitivity of domain sizes is examined by confining the model resolution at 40 km. The model simulated meteorological parameters, as well as derived parameters (such as pattern and intensity of precipitation, geopotential height, relative humidity, air temperature, wind, and CAPE), are represented better in D02 than other domains. The present study proposes a Comprehensive Rating Matrices (CRM) to evaluate the model performance considering all experiments (horizontal resolution and domain size) and different homogeneous regions, including errors obtained using different statistical methods. The CRM and statistical based skill score (SS) suggest that the performance of RegCM4 is the best at 40 km horizontal resolution followed by 36 km and 45 km grid-spacing and the D02 domain is suitable for ISM simulation.

Study on the Interfacial Reactions between an Fe–Mn–Si Alloy and Complex Oxides Containing FeO during Isothermal Heating

To precisely control the characteristics of complex oxides by heat treatment, the effect of FeO on the interfacial reactions that occur between an Fe–Mn–Si alloy and CaO–SiO2–Al2O3–MgO–MnO–FeO oxide was studied and clarified. Eight types of diffusion couples with different compositions of oxides were produced using a confocal scanning laser microscope (CSLM). The morphologies of the alloy–oxide interfaces and the changes in their chemical compositions with isothermal heating at 1273 and 1473 K for 10 h were investigated. A modified dynamic calculation model was established and verified to achieve better understanding on the interfacial reaction mechanism between the Fe–Mn–Si alloy and the multicomponent oxide with different FeO content during isothermal heating. The results showed that during isothermal heating at 1273 and 1473 K, “solid–solid” and “solid–liquid” alloy–oxide reactions occurred in the A-1-x and A-2-x diffusion couples, respectively. The interfacial alloy–oxide reactions were enhanced by increasing the initial FeO content in the oxide and the heating temperature. The particle precipitation zone (PPZ), Mn-depleted zone (MDZ) and Si-depleted zone (SDZ) widths in the A-1-x and A-2-x diffusion couples after heating also showed a positive correlation with the increase in the initial FeO content in the oxide, as well as the size and number of MnO·SiO2 inclusions. The diffused oxygen from the oxide reacting with elemental Mn and Si in the alloy plays a dominant role in the A-1-x diffusion couple during heating, whereas for A-2-x, the dominant reaction is between elemental Si in the alloy and MnO in the oxide.

Microphysical Characteristics of Squall-Line Stratiform Precipitation and Transition Zones Simulated Using an Ice Particle Property-Evolving Model

Abstract A quasi-idealized 3D squall-line case is simulated using a novel bulk microphysics scheme called the Ice-Spheroids Habit Model with Aspect-ratio Evolution (ISHMAEL). In ISHMAEL, the evolution of ice particle properties (e.g., mass, shape, maximum diameter, density, and fall speed) are predicted during vapor growth, sublimation, riming, and melting, allowing ice properties to evolve from various microphysical processes without needing separate unrimed and rimed ice categories. ISHMAEL produces both a transition zone and an enhanced stratiform precipitation region, and ice particle properties are analyzed to determine the characteristics of ice that lead to the development of these squall-line features. Rimed particles advected rearward from the convective region produce the enhanced stratiform precipitation region. The transition zone results from hydrometeor sorting; the evolution of ice particle properties in the convective region leads to fall speeds that favor ice advecting rearward of the transition zone before reaching the melting level, causing a local minimum in precipitation rate and reflectivity there. Sensitivity studies show that the fall speed of ice particles largely determines the location of the enhanced stratiform precipitation region and whether or not a transition zone forms. The representation of microphysical processes, such as rime splintering and aggregation, and ice size distribution shape can impact the mean ice particle fall speeds enough to significantly impact the location of the enhanced stratiform precipitation region and the existence of the transition zone.

Spatiotemporal distribution and fluctuation of radiocesium in Tokyo Bay in the five years following the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident.

A monitoring survey was conducted from August 2011 to July 2016 of the spatiotemporal distribution in the 400 km2 area of the northern part of Tokyo Bay and in rivers flowing into it of radiocesium released from the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. The average inventory in the river mouth (10 km2) was 131 kBq⋅m-2 and 0.73 kBq⋅m-2 in the central bay (330 km2) as the decay corrected value on March 16, 2011. Most of the radiocesium that flowed into Tokyo Bay originated in the northeastern section of the Tokyo metropolitan area, where the highest precipitation zone of 137Cs in soil was almost the same level as that in Fukushima City, then flowed into and was deposited in the Old-Edogawa River estuary, deep in Tokyo Bay. The highest precipitation of radiocesium measured in the high contaminated zone was 460 kBq⋅m-2. The inventory in sediment off the estuary of Old-Edogawa was 20.1 kBq⋅m-2 in August 2011 immediately after the accident, but it increased to 104 kBq⋅m-2 in July 2016. However, the radiocesium diffused minimally in sediments in the central area of Tokyo Bay in the five years following the FDNPP accident. The flux of radiocesium off the estuary decreased slightly immediately after the accident and conformed almost exactly to the values predicted based on its radioactive decay. Contrarily, the inventory of radiocesium in the sediment has increased. It was estimated that of the 8.33 TBq precipitated from the atmosphere in the catchment regions of the rivers Edogawa and Old-Edogawa, 1.31 TBq migrated through rivers and was deposited in the sediments of the Old-Edogawa estuary by July 2016. Currently, 0.25 TBq⋅yr-1 of radiocesium continues to flow into the deep parts of Tokyo Bay.

Calcium isotope fractionation in sedimentary pore fluids from ODP Leg 175: Resolving carbonate recrystallization

We present calcium isotope data from pore fluids and solids from Ocean Drilling Program Leg 175: Sites 1081 and 1086 (off the coast of West Africa). These sites are similar with respect to geographic location, sediment age (from modern to 8 Myr), and water depth (800 m), but Site 1081 is carbonate-poor, whereas Site 1086 is carbonate-rich. Therefore, these sites are suited for the exploration of the influence of sediment type on carbonate dissolution, precipitation, and recrystallization. We use two numerical modelling approaches to explore the rates of carbonate dissolution and precipitation in the sediment column. The first is the standard diffusion-reaction approach, using the strontium concentration within the pore fluid to ascertain a dissolution rate for the carbonate, which is then applied to a second model of calcium isotopes within the pore fluid to calculate precipitation rates. Given the high sedimentation rates we also apply an advection-reaction model (Huber et al., 2017) which results in the same depth distribution of carbonate precipitation but significantly higher overall rates, which is discussed. Calcium isotope ratios in pore fluid calcium increase in zones where our model predicts carbonate precipitation, and approach isotopic equilibrium with the solid in zones where our model predicts equivalent rates of dissolution and precipitation, similar to previous findings. Contrary to previous findings in marine sediments, our model requires a calcium isotope fractionation on carbonate precipitation to fit the data, as there is an offset between the δ44Ca of the fluid and the solid. Using the zones of carbonate precipitation determined from the models and previously published carbon isotope profiles of the dissolved inorganic carbon from these sites, we suggest that the δ13C of the authigenic carbonate is uniformly lower than biogenic carbonate but by a wider range than was previously suggested.

Uneven Precipitation Behavior during the Solutionizing Course of Al‐Cu‐Mn Alloys and Their Contribution to High Temperature Strength

The dispersoid precipitation behavior during the solutionizing and aging of Al‐xwt.%Cu‐1.0 wt.% Mn alloys (x = 2.0, 4.5, and 7.5) and contribution to mechanical properties were investigated using tensile testing and microstructural characterization. A shell‐core structure of primary α‐Al dendrites is found in Al‐Cu‐Mn alloys, in which the Cu content in the shell is higher than that in the core. The area of shell zone (Cu‐rich) increases with an increase in Cu content in the alloy. Large amounts of fine dispersoid Al‐Cu‐Mn particles precipitate in solution. An alloy with low Cu content results in only the TMn (Al20Cu2Mn3) particles being precipitated. However, in an alloy with high Cu content, AlCu3Mn2 particles are first found to precipitate beside TMn. However, this precipitation behavior is uneven. The precipitation zones in the solution microstructure are consistent with the Cu‐rich regions in the as‐cast microstructure. A number of fine particles (dozens nanometer in size) are first found to precipitate on the rod‐like TMn particles during the aging phase. The redissolution and granulation of the eutectic CuAl2 phase during the solutionizing process result in the formation of particle‐free bands between the precipitation zones. The tension test at 300°C demonstrates that the increase in high temperature strength is due to the dispersoid precipitation during solutionizing, and the precipitation behavior in the aging phase has little or no effect, however, largely improves the tensile strength at room temperature. High temperature strength is significantly increased with an increase in Cu content, which correlates to an increase in number and decrease in size of TMn and AlCu3Mn2 particles.

Multiphase flow modeling of asphaltene precipitation and deposition

Asphaltene precipitation in reservoirs during production and Enhanced Oil Recovery (EOR) can cause serious problems that lead to reduction of reservoir fluid production. In order to study asphaltene tendency to precipitate and change in flow rate as a function of distance from wellbore, an equation of state (Peng-Robinson) based model namely Nghiem et al.’s model has been employed in this study. The heaviest components of crude oil are separated into two parts: The first portion is considered as non-precipitating component (C31A+) and the second one is considered as precipitating component (C31B+) and the precipitated asphaltene is considered as pure solid. For determination of the acentric factor and critical properties, Lee-Kesler and Twu correlations are employed, respectively. In this study, a multiphase flow (oil, gas and asphaltene) model for an asphaltenic crude oil for which asphaltene is considered as solid particles (precipitated, flocculated and deposited particles), has been developed. Furthermore, effect of asphaltene precipitation on porosity and permeability reduction has been studied. Results of this study indicate that asphaltene tendency to precipitate increases and permeability of porous medium decreases by increasing oil flow rate in under-saturated oil reservoirs and dropping reservoir pressure under bubble point pressure. On the other hand, asphaltene tendency to precipitate decreases with pressure reduction to a level lower than bubble point pressure where asphaltene starts to dissolve back into oil phase. Moreover, it is observed that precipitation zone around the wellbore develops with time as pressure declines to bubble point pressure (production rate increases up). Also, there is an equilibrium area near wellbore region at which reservoir fluid properties such as UAOP (Upper Asphaltene Onset Pressure) and LAOP (Lower Asphaltene Onset Pressure) are constant and independent of the distance from wellbore.