Homogeneous Precipitation Research Articles

Gravity-driven controls on fluid and carbonate precipitation distributions in fractures

Many challenges related to carbon-dioxide (hbox {CO}_2) sequestration in subsurface rock are linked to the injection of fluids through induced or existing fracture networks and how these fluids are altered through geochemical interactions. Here, we demonstrate that fluid mixing and carbonate mineral distributions in fractures are controlled by gravity-driven chemical dynamics. Using optical imaging and numerical simulations, we show that a density contrast between two miscible fluids causes the formation of a low-density fluid runlet that increases in areal extent as the fracture inclination decreases from 90^circ (vertical fracture plane) to 30^circ. The runlet is sustained over time and the stability of the runlet is controlled by the gravity-driven formation of 3D vortices that arise in a laminar flow regime. When homogeneous precipitation was induced, calcium carbonate covered the entire surface for horizontal fractures (0^circ). However, for fracture inclinations greater than 10^circ, the runlet formation limited the areal extent of the precipitation to less than 15% of the fracture surface. These insights suggest that the ability to sequester hbox {CO}_2 through mineralization along fractures will depend on the fracture orientation relative to gravity, with horizontal fractures more likely to seal uniformly.

Defect evolution and effect on structure and electric properties of A/B site Sm doped BaTiO3 sintered in different atmospheres

BaTiO3 ceramics doped with different contents of Sm (0.5-7 mol%) are prepared by a homogeneous precipitation method and sintered in air (A-xSm) and reducing (R-xSm) atmosphere respectively. With the increase of doping amount, the phase structure of Sm-doped BaTiO3 ceramics gradually changes from tetragonal phase to cubic phase, and the cubic phase is stronger in R-xSm. In the air atmosphere, Sm ions preferentially replace Ba sites as donors at low doping concentration, which is easy to convert Ti4+ ions into Ti3+ ions, resulting high dielectric constant (>104) and semiconductor like properties. As the doping amount increases, Sm ions start to replace Ti sites as acceptors to generate oxygen vacancies, which capture the electrons generated by donor doping, thus decreasing the percentage of Ti3+ ions. As a result, the dielectric loss and permittivity are decreased, and the electrical insulation properties of A-xSm ceramics are gradually improved. However, in the reducing atmosphere, oxygen atoms in the lattice are easy to escape, resulting in many oxygen vacancies and free electrons. The increase of oxygen vacancy inhibits the substitution of Sm ion to Ti site, and the free electron leads to the increase the percentage of Ti3+ ions and R-xSm ceramics exhibit semiconductor like properties. Thermally stimulated depolarization currents (TSDC) testing verified that oxygen vacancies of A-xSm ceramics mainly capture space charges, and a small part of oxygen vacancies form defective dipoles [2SmTi′−VO..]. The complex impedance test shows that the change of resistivity of A-xSm ceramics is mainly closed to the influence of Sm doping on the grain not grain boundary of BaTiO3 ceramic.

Experimental study on the scale inhibition effect of the alternating electromagnetic field on CaCO3 fouling on the heat exchanger surface in different circulating cooling water conditions

Scaling on the heat exchanger surface resulted in large equipment cleaning, maintenance expenses and safety issues in the industrial production. To remove the heat exchanger scaling, research on the scale inhibition effect of the alternating electromagnetic field on CaCO3 fouling on the heat exchanger surface with the selected four Mg2+/Ca2+ molar ratios in circulating cooling water. Four indicators, namely, heat transfer resistance, scale inhibition rate, the growth rate of CaCO3, and conductivity were discussed extensively. The experimental results demonstrated that remarkable scale inhibition effect occurs, when the Mg2+/Ca2+ molar ratios is 0 and 1:1.2 with 46.80% and 39.28% of the scale inhibition rate, respectively. Compared with the control group, the heat transfer resistance was decreased, the adherent scale growth rate was slowed down, and the rising stage time was shortened in the experiment group. In addition, the decreased of conductivity in the experiment group indicated that the alternating electromagnetic field promoted the crystallization in the solution. XRD and SEM analysis demonstrated that the alternating electromagnetic field and Mg2+ could promote aragonite crystallization, reduce the polymerization degree, and decrease the crystal particle size of CaCO3. Affecting the crystallization process of adherent scale and promoting the homogeneous precipitation of non-adherent scale in solution is the key to the alternating electromagnetic field scale inhibition technology. This study could provide a guidance for the parameter selection in electromagnetic field scale inhibition technology of industry application.

(Fe, Cr)(OH)3 Coprecipitation in Solution and on Soil: Roles of Surface Functional Groups and Solution pH

The simultaneous precipitation of (Fe, Cr)(OH)3 nanoparticles in solution (homogeneous) and on soil surfaces (heterogeneous), which controls Cr transport in soil and aquatic systems, was quantified for the first time in the presence of model surfaces, i.e., bare and natural organic matter (NOM)-coated SiO2 and Al2O3. Various characterization techniques were combined to explore the surface-ion-precipitate interactions and the controlling mechanisms. (Fe, Cr)(OH)3 accumulation on negatively charged SiO2 was mainly governed by electrostatic interactions between hydrolyzed ion species or homogeneous (Fe, Cr)(OH)3 and surfaces. The elevated pH through protonation of Al2O3 surface hydroxyls resulted in higher Cr/Fe ratios in both homogeneous and heterogeneous coprecipitates. Due to ignorable NOM adsorption onto SiO2, the amounts of (Fe, Cr)(OH)3 precipitates on bare/NOM-SiO2 were similar; contrarily, attributed to favored NOM adsorption onto Al2O3 and consequently carboxyl association with metal ions or (Fe, Cr)(OH)3 nanoparticles, remarkably more heterogeneous precipitates harvested on NOM-Al2O3 than bare-Al2O3. With the same solution supersaturation, the total amounts of homogeneous and heterogeneous precipitates were similar irrespective of the substrate type. With lower pH, decreased electrostatic forces between substrates and precipitates shifted (Fe, Cr)(OH)3 distribution from heterogeneous to homogeneous phases. The quantitative knowledge of (Fe, Cr)(OH)3 distribution and the controlling mechanisms can assist in better Cr sequestration in natural and engineered settings.

Enhancing Thermoelectric and Mechanical Properties of p-Type (Bi, Sb)2Te3 through Rickardite Mineral (Cu2.9Te2) Incorporation

Bi2Te3-based alloys are widely utilized in Peltier coolers owing to their highest thermoelectric performance at near-room-temperatures. However, their peak dimensionless thermoelectric figure of merit, zT, is limited to a narrow temperature window due to minority carrier excitation emerging upon heating at around 400 K. Here, we show how this issue can be overcome by incorporating a synthetic rickardite mineral, Cu3–xTe2, in p-type (Bi, Sb)2Te3. The significant enhancement of the electronic and thermal properties could be achieved due to small Cu incorporation into the crystal structure of (Bi, Sb)2Te3 and homogeneous precipitation of Cu3–xTe2 at the grain boundaries. This leads to a high average zT value (zTave) of 1.22 between 350 and 500 K for two compositions, Bi0.5Sb1.5Te3 (BST-5) and Bi0.3Sb1.7Te3 (BST-3), with peak zT values of 1.32 at 467 K and 1.30 at 400 K, respectively. These high zT values result in a considerably high maximum device ZT of ca. 1.15 and a theoretical efficiency of up to 7% between 325 and 525 K. Additionally, room-temperature micro-hardness is substantially improved, which is desirable for constructing reliable and durable thermoelectric modules.

Characterization of Solid-Solution and Aging Process in Mg-5 wt.%Sn Alloy

Firstly, the properties and the microstructure evolution of the solid-solution process of Mg-5 wt.%Sn were studied. From the motion analysis of resistivity and microhardness during solution treatment, the reasonable solution technology of Mg-5 wt.%Sn should be 12–16 h at 480 °C. After solution treatment at 480 °C for 16 h, the precipitating behavior in supersaturated solid solution. Mg-5 wt.%Sn alloy was investigated. In the aging process, it was observed that there were precipitated phases in the both grain and grain boundaries, and continuous inhomogeneous precipitation occurred along the grain boundaries, and continuous homogeneous precipitation happened in the grain. Transmission Electron Microscope (TEM) analysis indicated the plate- and lath-shaped precipitates within the grains and only the plate-shaped precipitates along the grain boundary. High-Resolution Electron Microscopy (HRTEM) studies have shown that metastable precipitates may occur during aging, coherently or semi-coherent with the matrix. Energy Dispersive Analysis by X-ray (EDAX) analysis showed that the Mg/Sn ratio was not actually constant, and the Sn content of the metastable phase was lower than that of the Mg2Sn equilibrium phase. X-ray diffraction (XRD) studies confirm the existence of this metastable phase, which is supposed to be GP zone and metastable Mg3Sn phase.

Preparation and characterization of titania supported on layered double hydroxide precipitated on glass fiber cloth

Support of titania nanoparticles on platy particles of a layered double hydroxide (LDH) on glass fiber cloth (GFC) is demonstrated. MgAl-LDH was deposited onto the GFC surface via homogenous precipitation using urea hydrolysis in the presence of GFC. X-ray diffraction (XRD) patterns, field-emission scanning electron microscopy (FE-SEM) images, and elemental analyses revealed that MgAl-LDH platy particles were deposited and vertically aligned on the GFC surfaces, forming MgAl-LDH-coated GFC. The resultant specimen was soaked in a water dispersion of P25 standard, a well-known titania photocatalyst, for 5 min at room temperature and then extensively washed with an excess of water. The presence of P25 nanoparticles on the MgAl-LDH platy particles on GFC surfaces was evidenced by FE-SEM imaging, elemental analyses, and MB decomposition experiments in which an MB solution showed a greater decrease in concentration under 365 nm irradiation in the presence of the supported P25 than in the presence of MgAl-LDH-coated GFC and GFC subjected to the P25 deposition procedure without MgAl-LDH deposition. In addition, FE-SEM images and elemental analysis of the supported P25 specimen showed only small differences before and after the MB experiment. Therefore, the results mentioned above show the facile support of P25 on MgAl-LDH supported on a GFC surface.

Citrate-Assisted One-Pot Hydrothermal Preparation of Carbonated Hydroxyapatite Microspheres

Carbonated hydroxyapatite (CHA) microspheres have aroused wide concern in biofields because of their excellent biological and surface properties. However, the facile preparation of CHA microspheres from organic compounds, especially the microstructural transformation during synthesis, has been rarely reported. In this work, CHA microspheres with an average diameter of 2.528 μm and a BET surface area of 51.0658 m2/g were synthesized via a one-pot hydrothermal method at 180 °C for 10 h by using calcium chloride, diammonium hydrogen phosphate, urea, and trisodium citrate (TSC) with a molar ratio of TSC to Ca of 1:2. The effects of hydrothermal treatment temperature and molar ratio of TSC to Ca on the morphology of the products were investigated. As a chelating agent, TSC is crucial to the formation of CHA microspheres during the hydrothermal homogeneous precipitation process. A possible mechanism of the microstructural transformation from bundle to dumbbell, dumbbell ball, and finally, microspheres regulated by TSC and urea was proposed. The CHA microspheres can be used as effective drug carriers for biomedical applications.

How does the explicit treatment of convection alter the precipitation–soil hydrology interaction in the mid-Holocene African humid period?

Abstract. Global climate models with coarse horizontal resolution are largely unable to reproduce the monsoonal precipitation pattern over North Africa during the mid-Holocene. Here we present the first regional, storm-resolving simulations with an idealized but reasonable mid-Holocene vegetation cover. In these simulations, the West African monsoon expands farther north by about 4–5∘, and the precipitation gradient between the Guinea coast and the Sahara decreases compared to simulations with a barren Sahara as it is today. The northward shift of monsoonal precipitation is caused by land surface–atmosphere interaction, i.e., the coupling of soil moisture and precipitation, as well as interactions of the land surface with the large-scale monsoon circulation (e.g., the African easterly jet). The response of the monsoon circulation to an increased vegetation cover is qualitatively similar but more pronounced in parameterized convection simulations. We attribute the differences in monsoonal precipitation to differences in soil moisture that are strongly controlled by runoff and precipitation characteristics. If precipitation is intense and falls over a spatially small region, as in our storm-resolving simulations, about 35 % of all precipitation water goes into runoff instead of filling soil moisture storage. In contrast, in light and spatially more homogeneous precipitation, as produced in our parameterized convection simulations, only some 20 % leaves the grid cell as runoff. Therefore, much more water is available to maintain high soil moisture content. We confirm the significant role of soil moisture and runoff by performing simulations with the same constant soil moisture field in both storm-resolving and parameterized convection simulations. These constant soil moisture simulations cancel the effect of lower soil moisture on the land–atmosphere feedback cycle in our storm-resolving simulations. We show that precipitation strongly increases in the storm-resolving simulations, especially in moisture-controlled regions, such as the northern Sahel and Sahara, and reaches equally high values as in parameterized convection simulations. Our study highlights how the type of rainfall (e.g., local and intense or widespread and light) impacts soil moisture and thus land–atmosphere feedbacks. This is contrary to many studies that focus mainly on the amount of rainfall and how it modifies land–atmosphere feedbacks. Moreover, this study suggests that comprehensive land-surface schemes, which appropriately respond to varying precipitation characteristics, are needed for studying land surface–atmosphere interaction.

An appraisal of the NEX-GDDP precipitation dataset across homogeneous precipitation sub-regions of Iran

An appraisal of the NEX-GDDP precipitation dataset across homogeneous precipitation sub-regions of Iran

A Quick and Convenient Route to Prepare Hydroxyapatite Porous Microspheres

Due to the big specific surface area, good flowability and absorption ability, porous spherical HA materials have received extensive attention of the researchers. However, the facile and convenient synthesis of well-rounded HA microspheres with a porous structure is rarely reported. What’s more, the size of HA microspheres was usually less than 10 μm. In this study, by employing hexamethylenetetramine (HMT) as the pH regulator, hydroxyapatite (HA) microspheres with good uniformity and a diameter of 30-150 μm are successfully fabricated by a one-step hydrothermal homogeneous precipitation method. To our knowledge, the synthesis of such HA microspheres by using HMT has not been reported yet. Results show that the initial pH value plays a key role in regulating the morphology of the final products and the optimal initial pH value to obtain well-rounded HA microspheres with a porous structure is 3.0-4.0, especially around 4.0. The obtained HA microspheres can be utilized as effective drug carriers for biomedical field.

Lychee-like TiO2@Fe2O3 Core-Shell Nanostructures with Improved Lithium Storage Properties as Anode Materials for Lithium-Ion Batteries.

In this study, lychee-like TiO2@Fe2O3 microspheres with a core-shell structure have been prepared by coating Fe2O3 on the surface of TiO2 mesoporous microspheres using the homogeneous precipitation method. The structural and micromorphological characterization of TiO2@Fe2O3 microspheres has been carried out using XRD, FE-SEM, and Raman, and the results show that hematite Fe2O3 particles (7.05% of the total mass) are uniformly coated on the surface of anatase TiO2 microspheres, and the specific surface area of this material is 14.72 m2 g-1. The electrochemical performance test results show that after 200 cycles at 0.2 C current density, the specific capacity of TiO2@Fe2O3 anode material increases by 219.3% compared with anatase TiO2, reaching 591.5 mAh g-1; after 500 cycles at 2 C current density, the discharge specific capacity of TiO2@Fe2O3 reaches 273.1 mAh g-1, and its discharge specific capacity, cycle stability, and multiplicity performance are superior to those of commercial graphite. In comparison with anatase TiO2 and hematite Fe2O3, TiO2@Fe2O3 has higher conductivity and lithium-ion diffusion rate, thereby enhancing its rate performance. The electron density of states (DOS) of TiO2@Fe2O3 shows its metallic nature by DFT calculations, revealing the essential reason for the high electronic conductivity of TiO2@Fe2O3. This study presents a novel strategy for identifying suitable anode materials for commercial lithium-ion batteries.

Influence of plant extract on the homogeneous and heterogeneous green chemistry synthesis of nanostructured ZnO

In the present work, the influence of the nature of the plant extract on the synthesis of nanostructured ZnO via green chemistry was investigated. Two plant extracts were tested: Artemisia and Hibiscus. We noticed that Hibiscus plants prevented the growth of a film on the substrate, but resulted in nanoparticle formation. However, the Artemisia plant extract favours ZnO nanorod's growth on the substrate. We concluded that the low viscosity of Hibiscus favours homogeneous precipitation, whereas Artemisia, due to its larger viscosity, favours heterogeneous condensation on the substrate. Highlights The influence of the nature of the plant extract on the synthesis of nanostructured ZnO, that is, nanoparticles and nanorods, via green chemistry was investigated. Two plant extracts were tested: Artemisia and Hibiscus. Hibiscus plants prevented the growth of a film on the substrate but resulted in nanoparticle formation. Artemisia plant extract favoured ZnO nanorods growth on the substrate. This difference can be explained by the plant extract control of the condensation process in the solution.

Evaluation and projections of extreme precipitation using a spatial extremes framework

AbstractExtreme precipitation events are a major natural hazard and cause significant socio‐economic damages. Precipitation events are spatially extended and, thus, can cause large water accumulations, which can lead to flooding events. In order to help design flood protection infrastructure, a detailed investigation of the temporal and spatial dependencies of extreme precipitation is essential. Here, we use a statistical spatial extremes framework to systematically study the historical and projected spatial–temporal characteristics of extreme precipitation in Germany. For this purpose, we use data from 10 high‐resolution global climate model‐regional climate model (GCM‐RCM) combinations from the EURO‐CORDEX initiative and derive a statistical spatial extremes precipitation model. Our results show that there are large spreads in reproducing the temporal–spatial characters of extreme precipitation. Few climate simulations can well present the temporal clustering of observed extreme precipitation in both summer and winter. In reproducing the spatial dependencies of the observations, most GCM‐RCM combinations behave well in summer, while in winter most RCMs produce too many spatially localized extreme precipitation events. The derived statistical model, which accounts for both the spatial and temporal variability, performs well in representing the spatial dependency and intensity characteristics in summer. Furthermore, global warming will have a significant impact on the temporal and spatial dependencies of extreme precipitation in Germany. There will be more temporal‐dependent and homogeneous extreme precipitation in summer; and more temporal‐independent and localized extreme precipitation in winter. The intensity quantified by the 25‐year return level of the 10 GCM‐RCM combinations is increasing; with relative changes ranging from 5.33% to 53.24% in summer and from −15.38% to 32.33% in winter under RCP8.5. A future projection by our statistical spatial extremes model using projected temperature from GCM‐RCM combinations as a covariate shows that the 25‐year return level will increase by 3.02% under RCP2.6 and 4.16% under RCP8.5 in winter.

Facile Fabrication of ZnO Nanoparticles for efficient dye degradation: Effect of Adipic Acid in photocatalytic activity

AbstractPhotocatalysis is the most environmentally benign and efficient method for degrading organic dyes in water purification. Herein, the synthesis of ZnO nanoparticles was achieved by simple homogeneous chemical precipitation via the support of adipic acid and followed the calcination process at elevated temperatures. Based on the physical and morphological characterization analysis, the high crystallinity hexagonal structure with uniform granular shape morphology of the ZnO nanoparticles was formed with a band gap of 3.2 eV. The photocatalytic performance of the ZnO nanoparticles was investigated with the degradation of methylene blue (M.B.) dye as a model compound in an aqueous medium under UV light irradiation. The optimal ZnO‐700 nanoparticles demonstrated the highest photocatalytic activity thanks to their large surface area and numerous oxygen vacancies. More importantly, a small amount of photocatalyst (0.4 g/L) successfully degraded M.B. dye from an aqueous solution with 100 % efficiency within just 11 minutes of irradiation time under UV light with protective photocatalytic activity 4 sequential cycles. Besides, in‐depth photocatalysis experiments present that via a facile two‐step synthesis method, the as‐prepared ZnO photocatalysts depict enhanced chemical stability in a harsh environment and efficient photodegradation.

Physical characterizations and methane gas–sensing of AlxZn1-xO nanoparticles

The effects of the Al ratio on the morphological and structural parameters, thermal stability, surface area, optical band gap, and methane (CH4) gas–sensing of AlxZn1-xO nanoparticles were investigated. The homogeneous precipitation method was used to prepare AlxZn1-xO nanoparticles (x = 0, 0.5, 1, 2, and 4 at.%) and their compositions were revealed by EDX mapping. The hexagonal crystal structure of ZnO was obtained by annealing at 600 °C and wasn’t affected by the Al ratio. The crystallite/particle size was decreased while dislocation density and stacking fault were increased as Al content increased. The Al ratio controls the morphology of AlxZn1-xO e.g., rod-like, and nano-sheet shapes were observed for higher Al ratios. UV–visible absorption spectroscopy was utilized to investigate the optical absorbance and optical band gap (Eg), e.g., increasing the Al content increased Eg from 3.38 eV (for ZnO) up to 5.8 eV for Al0.04Zn0.96O. Al-doped ZnO has a considerable impact on both the surface area and the thermal stability of ZnO. The maximum surface area (189.72 m2/g) was achieved for the Al0.005Zn0.995O. The sensing parameters as a function of operating temperature and Al doping ratio have been thoroughly tested. The Al0.005Zn0.995O revealed the best sensing performance toward CH4 gas.

A facile homogeneous precipitation route synthesis of LiNi1/3Co1/3Mn1/3O2 cathode material for lithium-ion batteries

LiNi1/3Co1/3Mn1/3O2 (NCM111) cathode material has widen prospects due to its high thermal stability, long battery life and high safety. However, the electrochemical performance of NCM111 is affected by particle distribution microstructure. In this paper, NCM111 cathode material is prepared by urea-based homogeneous precipitation method. The obtained NCM111 has small particle and well distributed, which has good electrochemical performance. The as-synthesized NCM111 cathode material exhibits a good initial discharge specific capacity of 205 mAh/g at 0.2 C. The study manifested that homogeneous precipitation method is a simple way to prepare high property NCM111 cathode material.

乾式機械的処理を利用した無溶媒均一沈殿法によるヘマタイトナノ粒子の合成

Hematite (α-Fe2O3) nanoparticles were synthesized by a solvent-free homogeneous precipitation method using urea hydrolysis via dry mechanical treatment of urea and ferric nitrate nonahydrate for activation. This novel method consists of high-energy ball milling of the raw materials and subsequent heating of the activated liquid precursor, which can provide smaller-sized nanoparticles than conventional methods. The milling and heating conditions were systematically investigated in detail. It was found that the hematite formation can be promoted by milling ferric nitrate nonahydrate and urea simultaneously under dry conditions even when relatively gentle milling and heating treatments were employed. The hematite nanoparticles had a similar crystallite size and particle diameter regardless of the conditions. This method can contribute to large-scale environmentally-friendly synthesis of fine hematite nanoparticles.

Influence of overlap precipitate on the strength–ductility synergy of the Al–10.0Zn–3.0Mg–2.5Cu alloy with a new aging strategy

This paper proposes a new aging strategy in which natural aging, combined with pre-deformation, is embedded between the solid solution and artificial aging. The overlap precipitates (η′−ηd) were formed after this process, which included homogeneous (η′) and heterogeneous precipitates (ηd). The overlap precipitates exhibited a better dislocation storage ability than traditional single precipitates, contributing to their superior work hardening rate and strengthen effect. The ultimate tensile strength and elongation of the representative sample were 800.5 MPa and 7.4%, respectively. Compared to the traditional peak aging sample (770.8 MPa, 3.8%), the strength and ductility of Al–10.0Zn–3.0Mg–2.5Cu alloy were further improved synergistically through regulating overlap precipitates. Notably, the proposed novel aging strategy showed excellent engineering application potential.

Synthesis of Fe3O4/CuO/ZnO/RGO and its catalytic degradation of dye wastewater using dielectric barrier discharge plasma

The design of an efficient and green dye degradation technology is of great significance to mitigate water pollution as well as ecological damage. Fe3O4/CuO/ZnO/RGO was prepared by solvothermal synthesis and homogeneous precipitation. X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), and vibrating-sample magnetometry (VSM) were used to characterize the samples, to explore the morphology and structural composition of the composites. To enhance the degradation efficiency, a dielectric barrier discharge (DBD)–Fe3O4/CuO/ZnO/RGO co-catalytic system was created based on the DBD plasma technology. Response surface methodology analysis results demonstrate that the degradation effect of DBD–Fe3O4/CuO/ZnO/RGO is optimal and the decolorization rate is 95.06 % when the solution pH is 3, conductivity is 0.5 mS/cm, the input voltage is 90 V, and Fe3O4/CuO/ZnO/RGO concentration is 0.18 g/L. Therefore, this study offers a novel method for dye degradation and confirms the viability of a DBD–Fe3O4/CuO/ZnO/RGO synergistic catalytic system.