Dissolution Precipitation Research Articles

Microstructure evolution, interface and mechanical properties of SiCp/2A14 joint during laser keyhole welding

Welding problems have restricted the applications of lightweight SiCp/Al composites in aerospace. In this work, the controllability of the keyhole mode, nucleation mechanism, and mechanical properties of the laser-welding process are studied in detail. The extrusion effect formed by the open keyhole pushes SiC particles to the bottom of the molten pool. To observe the nucleation and growth mechanism of the Al4C3 of keyhole laser-welded SiC/2A14Al composites, the dissolution–precipitation behavior of the SiC particles and growth behavior of the Al4C3 tip were observed. Owing to its high chemical properties, Al4C3 mainly begins nucleating from the open edges of the SiC particles and its formation is mainly distributed along the direction of Al grains. Al4C3 was the main crack source and propagation path while the small-sized SiC particles hindered the crack propagation. This work innovatively regulates the keyhole mode to achieve ‘small damage breakdown’ laser welding, greatly reducing the volume fraction of Al4C3. It also provides new insight into fusion welding of SiC particle-reinforced Al matrix composites.

Corrector estimates and numerical simulations of a system of diffusion–reaction–dissolution–precipitation model in a porous medium

A system of diffusion–reaction equations coupled with a dissolution–precipitation model is discussed in this paper. We start by introducing a microscale model together with its homogenized version. In the present paper, we first derive the corrector results to justify the obtained theoretical results. Furthermore, we perform the numerical simulations to compare the outcome of the effective (homogenized) model with the original heterogeneous microscale model.

Environmental impact of solution pH on the formation and migration of iron colloids in deep subsurface energy systems

Deep subsurface stimulation processes often promote fluid-rock interactions that can lead to the formation of small colloidal particles that are suspected to migrate through the rock matrix, partially or fully clog pores and microfractures, and promote the mobilization of contaminants. Thus, the goal of this work is to understand the geochemical changes of the host rock in response to reservoir stimulation that promote the formation and migration of colloids. Two different carbonate-rich shales were exposed to different solution pHs (pH = 2 and 7). Iron and other mineral transformations at the shale-fluid interface were first characterized by synchrotron-based XRF mapping. Then, colloids that were able to migrate from the shale into the bulk fluid were characterized by synchrotron-based extended X-ray absorption structure (EXAFS), scanning electron microscopy (SEM), and single-particle inductively coupled plasma time-of-flight mass spectrometry (sp-icpTOF-MS). When exposed to the pH = 2 solution, extensive mineral dissolution and secondary precipitation was observed; iron-(oxyhydr)oxide colloids colocated with silicates were observed by SEM at the fluid-shale interfaces, and the mobilization of chromium and nickel with these iron colloids into the bulk fluid was detected by sp-icpTOF-MS. Iron EXAFS spectra of the solution at the shale-fluid interface suggests the rapid (within minutes) formation of ferrihydrite-like nanoparticles. Thus, we demonstrate that the pH neutralization promotes the mobilization of existing silicate minerals and the rapid formation of new iron colloids. These Fe colloids have the potential to migrate through the shale matrix and mobilize other heavy metals (such as Cr and Ni, in this study) and impacting groundwater quality, as well produced waters from these hydraulic fracturing operations.

Extraction, characterization and biological activity of Galactomannan rich endosperm of Borassus flabellifer (Linn.) suitable for biofabrication of tissue scaffolds

The study deals with the isolation, purification and characterization of galactomannan from the endosperm of Borassus labellifer (Linn.) to be used for biomaterial fabrication in tissue engineering (TE) applications. The isolated Borassus flabellifer (Linn.) galactomannan (BFG) through a sequential aqueous dissolution, centrifugation and ethanol precipitation presented a total yield of 19.77 ± 1.05 % (w/w) with advantageous compositional and functional properties. BFG was found to have mannose to galactose (M/G) ratio of 1.4:1. The molecular weight of BFG was found to be 4.9 × 105 g/mol and the molecular structure analysis by FTIR and NMR spectroscopy revealed the presence of α–linked, d-galactopyranose units and β–linked, D-mannopyranose units. Further characterization by rheometer confirmed the non-Newtonian and pseudo-plastic behavior of different BFG concentrations and structural analysis by XRD and SEM confirmed the amorphous nature of BFG with the presence of pores and cervices on the rough surface. Finally, the favorable biological activity demonstrated in response to fibroblast cells against different BFG concentrations substantiates its relevance to be used in biofabrication of tissue scaffolds.

Mass Transfer Analysis of CO2-Water-Rock Geochemical Reactions in Reservoirs

It is difficult to exploit low-permeability reservoirs, and CO2 flooding is an effective method to improve oil recovery from low permeability reservoirs. However, in the process of CO2 flooding, acidic fluids dissolved in formation water will react with rock to cause dissolution and precipitation, resulting in pores and precipitates, changing the evolution law of seepage channels, destroying formation integrity, and affecting the effect of CO2 oil displacement. The change in rock’s physical properties and the mass transfer law between CO2-water-rock are unclear. This paper considers the coupling effects of seepage, mechanics, and chemistry when CO2 is injected into the formation. The mass transfer model of CO2-water-rock in the geochemical reaction process is established on this basis. The physical properties of the reservoir after CO2 injection are quantitatively studied based on the microscopic mechanism of chemical reaction, and the migration law of solute in the reservoir rock during CO2 flooding under the coupling effects of multiple fields is clarified. The experimental results show that with the increase in reaction time, the initial dissolution reaction of formation rocks will be transformed into a precipitation reaction of calcite, magnesite, and clay minerals. The porosity and permeability of the rocks near the well first increase and then decrease. The far well end is still dominated by dissolution reactions, and the average values of formation porosity and permeability show an upward trend. Although the dissolution reaction of CO2-water-rock can improve the physical properties of reservoir rocks to a certain extent, the mutual transformation of the dissolution reaction and precipitation reaction further exacerbates the heterogeneity of formation pore structure, leading to the instability of CO2 migration, uneven displacement, and destruction of formation stability. The research results of this paper solve the problem of quantitative calculation of physical parameters under the coupling effect of multiple fields after CO2 injection into reservoirs and can predict the changes in formation physical properties, which can provide a certain theoretical basis for evaluating formation integrity and adjusting CO2 injection under the condition of CO2 flooding.

Microstructure and mechanical properties in additive manufacturing by friction surfacing of AA6061 alloy

This present study uses a novel solid-state additive manufacturing method based on friction surfacing as a mechanism for layer-upon-layer deposition. This utilizes severe plastic deformation to create a homogeneous fine-grain microstructure without melting to avoid solidification-related defects. The deposition of AA6061-T6 aluminum alloy was achieved by rotating a 20 mm diameter rod on top of a substrate at 1000 RPM and applying a 300 mm/min transverse speed with an axial feed rate of 50 mm/min. Advanced macro/microstructural techniques characterized the grain and precipitate structures in the deposited material, i.e., electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) analyses, along with micro-hardness and tensile testing of the mechanical properties. The multi-layer deposition contains a refined grain size in the range of 5–10 μm and sub-grains less than micron size, while a reasonable reduction in mechanical properties compared to the as-received rod was observed; in which hardness was reduced from 114 HV to 49 HV, and the tensile strength was reduced from 333 MPa to 161 MPa. These reductions are largely attributed to the dissolution of precipitates in the original rod due to the high temperatures imposed by friction and deformation. Achieving metallurgical bonding between the layers while suppressing porosity is critical to additive manufacturing, and this feasibility study of friction surfacing demonstrates this can be achieved along with superior isotropic mechanical properties. Based on the results, it was observed that additive manufacturing by friction surfacing is particularly suitable for metals that are sensitive to heat during deposition, though parameter optimization and secondary treatment may be required to enhance properties further.

Performance evaluation of additive TiO2, MWCNT and GNP reinforced particles on Mg AZ31 based matrix composites by friction stir processing

Magnesium alloy-based matrix composites are extensively used in transportation industries because of their high specific strength and low weight. Several existing technologies were utilized for preparing these composites in any proportion of constituent elements. However, friction stir processing (FSP), which employs plastic deformation with high-energy input, has proven as the most successful with proper homogenization. This study examines the microstructure and mechanical characteristics evolved by FSP of a novel magnesium alloy grade (AZ31) with Titanium dioxide (TiO2), Multi-walled carbon nanotubes (MWCNT) and Research grade Graphene nanoplatelets (GNP) that have considerable electrical, thermal and mechanical performance. At a parametric combination, tool rotation of 1200 rpm, traverse speed of 80 mm per minute, plunge depth with 0.25 mm, AZ31 alloy was processed on a specifically engineered fixture with subzero coolant circulation through it. The average size of grains of the base alloy reduced from 52.96 µm to 2.07 µm (AZ31/TiO2), 3.19 µm (AZ31/MWCNT) and 2.54 µm (AZ31/GNP) composites at this combination. The hardness and tensile strength were enhanced from 115 to 130% and 25 to 38%, respectively. Micrographs shows that the shortened grain elongation occurred due to coolant circulation resulted in restricted strengthening precipitate dissolution, which usually occur at high temperature.

Effect of gradient temperature rolling process on precipitation behavior in Q690D steel

In this paper, the second phase precipitation model is incorporated into the finite element simulation system of hot rolling process through the secondary development subprogram VUSDFLD of ABAQUS, and the simulation analysis and calculation of nucleation rate, volume fraction and size of precipitates under different temperature fields and strain fields are realized. The size, morphology and distribution of the microalloyed carbonitride precipitates in Q690D steel under gradient temperature rolling (GTR) and uniform temperature rolling (UTR) were studied by laboratory rolling experiments. The results show that the nucleation sites of the microalloyed carbonitride precipitates in the matrix increase under GTR, which is conducive to the nucleation of new precipitates and promotes the re dissolution of large precipitates. Finally, after tempering, the precipitate particles are distributed randomly on the ferrite matrix, and the size is refined by 20 ∼ 35 nm, resulting in obvious precipitation strengthening and microstructure refining effects.

A study on the mechanical, electrochemical and microstructural behaviour of AA5052 welded sheets

Aluminium 5xxx series alloys are most robust non-heat-treatable aluminium alloy and mostly used in aerospace, automotive components and body structures due to its high corrosion resistance, good strength and light weight. The alloy used in this work is AA5052 H32 (cold rolled) of 1 mm thickness to highlight the precedence of friction stir welding (FSW) over fusion welding technique, i.e., Tungsten Inert Gas welding (TIG). In TIG, the selected input variable parameter is welding speed and the other parameters such as inert gas flow rate, welding speed and frequency were kept constant during the study. In FSW, the selected input variable is feed rate, and the parameters such as plunge depth and tool rotational speed were kept constant after conducting several trials. Mechanical, Electrochemical, and Microstructural behaviour of both welded samples were studied. It was found that Friction stir welding samples has better mechanical properties than TIG welding due to solidification cracks and porosity defects. The tensile and microhardness results of FSW were 7.3 % and 5.4% more than TIG due to solidification cracks, porosity defects and intermetallics formed. The corrosion behaviour of both FSW and TIG were less than the base material due to precipitate dissolution. In the present study a comparative study of FSW and TIG is studied and reported.

New insights to the metallurgical mechanism of niobium in high-carbon pearlitic steels

Two series of high-carbon pearlitic steels (68C-xNb and 75C-xNb) with different C and Nb contents were produced by hot-rolling. The effects of Nb on the microstructure and impact toughness of high-carbon pearlitic steels were investigated using scanning electron microscope, transmission electron microscope, electron backscattering diffraction and impact toughness tests. In particular, the nucleation and growth of pearlite were investigated through in-situ observations. It was found that the average pearlitic nodule was markedly refined from 10.2 μm to 6.0 μm with the addition of 0.026 wt% Nb in 68C steels, and it was refined from 13.7 μm to 6.7 μm with the addition of 0.014 wt% Nb in 75C steels. In situ observations determined that the refinement of the pearlitic nodule was due to the refinement of prior austenite grains and retardation of pearlite growth by Nb addition. The impact toughness of high-carbon steels was significantly improved by Nb addition without a decrease in strength because a finer pearlitic nodule was obtained. The maximum improvement ratios for 68C and 75C steels were 81% and 26%, respectively. In addition, according to the experimental results and theoretical calculations of the dissolution of Nb-containing precipitates, the refinement of prior austenite was mainly caused by the solute-dragging effect of Nb during isothermal holding at 1180 °C. Moreover, there was an optimum addition of Nb to 75C steels (less than 0.015 wt%); above this threshold, neither the prior austenite grains or pearlitic nodules were further refined, nor was the impact toughness further improved.

Integrating bi-pH operation to enhance Ni2+ removal and recovery in fluidized-bed non-seeded granulation process

Anthropogenic activities and industrial processes generate large amounts of nickel in effluent, posing a threat to public and ecological health. Several processes have been developed to remove nickel and adhere to environmental limits. The fluidized-bed non-seeded granulation process has proven effective in removing and recovering metals including nickel. In this study, nickel was precipitated using phosphate while investigating bi-pH operation. The study compared single-pH and bi-pH and found that bi-pH was better. The effects of molar ratio ([Ni2+]:[PO43-]), initial nickel concentration, copper ion concentrations, and other co-existing chemical compounds were then investigated under bi-pH operation. The optimal conditions were observed at bi-pH 7.5 and 9.0, molar ratio of 1:1.3, and 300 mg/L initial nickel concentration. The results showed that bi-pH improved the granulation process by generating heterogeneous granulation through observed bi-layers. The effects of molar ratio and initial nickel concentrations were attributed to changes in the predominant saturation condition, dictating primary and secondary nucleation. Co-existing compounds had no significant effect on total nickel removal but reduced granulation efficiency due to nickel complexation, ionic competition, and precipitate dissolution.

Dissolution–precipitation kinetics during C[formula omitted]S hydration: A holographic interferometry study

Tricalcium silicate C3S has been widely employed in model systems to interpret the complex mechanisms of cement hydration. The present study aims at providing an accurate description of the dissolution rate of C3S by implementing a new approach based on holographic interferometry. We propose a protocol that allows the measurement of the pure dissolution rate constant of the C3S phase by experiments performed in supersaturated conditions with respect to C–S–H. In these experiments, a flat polycrystalline surface of C3S was monitored in a quiescent solution. The amount of calcium released within the holographic cell was measured and the aqueous solution composition was constrained to the C–S–H stoichiometry at the interface. An equilibrium approach was applied to assess interfacial pH, saturation indexes, and C–S–H precipitation at the experimental conditions. The rate law of the pure dissolution of C3S was assessed in conditions ranging from far to close-to-equilibrium.

Evaluation of rock-fluid interaction in a carbonate reservoir: Backflow test and reactive transport simulations

Water injection is one of the most used secondary oil recovery methods. However, when injected into a carbonate reservoir, it disturbs the equilibrium between the porous rock and the formation water, altering the geochemical system. The aim of this work is to evaluate the rock-fluid chemical interaction associated with seawater injection into a carbonate reservoir, based on field flow tests and flow simulations using COORES™ and ARXIM. Though previous studies were carried out under laboratory conditions, in this work, for the first time, rock-fluid interaction was observed and quantified during a field test in a high-temperature and high-pressure reservoir. Chemical analysis of produced water during the flow test showed that calcium and alkalis concentrations were higher than those calculated by the simple mixture of injected and formation waters, confirming the existence of chemical reactions under reservoir conditions. Reactive transport simulations were used to determine kinetic parameters related to calcite dissolution and dolomite precipitation in the reservoir. The results of this study enhance the understating of chemical interactions between injected fluids and carbonate reservoirs and provide data for more reliable simulations. These could lead to more accurate predictions regarding produced water composition and pH, anticipating the likelihood of reservoir collapse and scaling issues.

Fabrication of low-crystalline Mg-substituted β-tricalcium phosphate foam via dissolution–precipitation reaction

Fabrication of low-crystalline Mg-substituted β-tricalcium phosphate foam via dissolution–precipitation reaction

The enhanced separation effect of synthesized hydroxyapatite incorporated with ethylenediamine-tetramethylene phosphonic acid for Zn2+ and Co2+ ions and the deep insight into mechanism

Hydroxyapatite (HAP) incorporated with ethylenediaminetetramethylene phosphonic acid (EDTMP) was prepared and used for the separation of the toxic Zn2+ and Co2+ heavy metal ions in an aqueous solution. When the doping amount of EDTMP was 20%, the adsorption capacity of 20ED-HAP composite for Zn2+ and Co2+ reached 229.5 mg/g and 162.4 mg/g, which was 11.0 times and 11.8 times that of synthesized HAP in the absence of EDTMP. The effects of different concentrations of common coexisting ions such as Na+, K+, Ca2+, and Mg2+ were explored, and the removal rate of Co2+ or Zn2+ in a simulated actual water environment was also investigated. The removal of cobalt ions by EDTMP-HAP complex included ion exchange and surface complexation mechanisms. In addition to the above two mechanisms, the separation of zinc ions involved the dissolution precipitation mechanism with the formation of CaZn2(PO4)2·2H2O. Moreover, the affinity between EDTMP and HAP was revealed via Independent Gradient Model based on the Hirshfeld partition of molecular density (IGMH) and Hirshfeld surface analysis. Meanwhile, the interaction mechanism between EDTMP and Co2+ or Zn2+ was explored in depth through Multiwfn wavefunction analysis. The prepared adsorbent could be used as a low-cost potential adsorbent for toxic Zn2+ and Co2+ ions.

Effects of annealing temperature on microstructure and hardness of cold rolled high-purity V-4Cr-xTi alloys

The microstructural evolution and Vickers hardness variations upon annealing in the temperature range of 873 – 1273 K of cold rolled high-purity V-4Cr-(0∼4)Ti alloys are investigated. Results show that partial recrystallization occurs at 1073 K, recrystallization is complete at 1273 K, and Ti addition results in grain refinement. Grains become more isotropic after annealing at 1273 K. Besides, precipitates are observed after annealing at 973 K and above when Ti concentration is 1 wt% and higher. The size of precipitates increases with increasing Ti concentration and annealing temperature. Furthermore, Vickers hardness of cold rolled V-4Cr-xTi alloy drops to a minimum with increasing annealing temperature to 1173 K due to recovery of dislocations and recrystallization process. With annealing at 1273 K, hardness does not vary for V-4Cr-0Ti alloy, whereas it slightly increases for V-4Cr-(1∼4)Ti alloys, which is presumably attributed to partial dissolution of precipitates into the matrix. Additionally, purification by further reducing the high-activation impurities and interstitial impurities dose not evidently affect the recrystallization behavior and hardness of V-4Cr-4Ti alloy after recrystallization, however, the low-activation property is expected to be enhanced.

Two proteins prepared from defatted Antarctic krill (Euphausia superba) powder: Composition, structure and functional properties

Defatted krill powder, rich in protein, has emerged as a potential, novel food raw material. The present study aimed to prepare Antarctic krill protein from the supernatant (AKP-S) and precipitation (AKP-P) using the ultrasound-assisted alkali dissolution and acid precipitation method, and analyze their composition, structure, and functional properties were analyzed. The protein contents of AKP-P and AKP-S were more than 85% (dry weight), and their total amino acid content was 48.75 and 43.59 g/100 g of protein, respectively. The SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and surface morphology analysis (SEM) results showed that the AKP-S was degraded during acid treatment and had a smaller particle size than AKP-P. The α-helix and random curled structures of AKP-P and AKP-S were few or even disappeared. The solubility of AKP-S was more than 70% in the pH range of 3–13, and the change in AKP-P solubility with pH was consistent with the trend of β-sheets. Except for pH 7.0–9.0, the solubility of AKP-P and AKP-S with pH was positively correlated with surface-hydrophobicity (H0). The emulsifying activity of AKP-P and AKP-S at different pH was approximately positively correlated with the solubility. The minimum gel-forming concentration of AKP-P was 8%, while AKP-S could not form gel at 14%. The gel water holding capacity reached more than 90% when the AKP-P concentration was 12%. The rheological results showed that the storage modulus (G′) predominated over the loss modulus (G″) of AKP-P in the range of 8%–14% concentration.

Cathodoluminescence as a tracing technique for quartz precipitation in low velocity shear experiments

Two simulated gouges (a pure quartz and a quartz-muscovite mixture) were experimentally deformed in a ring shear apparatus at a constant low velocity under hydrothermal conditions favourable for dissolution–precipitation processes. Microstructural analysis using scanning electron microscope cathodoluminescence imaging and cathodoluminescence spectroscopy combined with chemical analysis showed that quartz dissolution and precipitation occurred in both experiments. The starting materials and deformation conditions were chosen so that dissolution–precipitation microstructures could be unambiguously identified from their cathodoluminescence signal. Precipitated quartz was observed as blue luminescent fracture fills and overgrowths with increased Al content relative to the original quartz. In the pure quartz gouge, most of the shear deformation was localized on a boundary-parallel slip surface. Sealing of fractures in a pulverized zone directly adjacent to the slip surface may have helped keeping the deformation localized. In the quartz-muscovite mixture, some evidence was observed of shear-accommodating precipitation of quartz in strain shadows, but predominantly in fractures, elongating the original grains. Precipitation of quartz in fractures implies that the length scale of diffusive mass transfer in frictional-viscous flow is shorter than the length of the quartz domains. Additionally, fracturing might play a more important role than generally assumed. Our results show that cathodoluminescence, especially combined with chemical analysis, is a powerful tool in microstructural analyses of experimentally deformed quartz-bearing material and visualizing quartz precipitation.

Corrosion of glaze in the marine environment: study on the green-glazed pottery from the Southern Song “Nanhai I” shipwreck (1127–1279 A.D.)

The “Nanhai I” shipwreck is an important discovery in the underwater archaeology of China, and many ceramics have been unearthed. These ceramics are important material artifacts of China’s “Maritime Silk Road” and have considerable significance for the study of foreign trade in the Southern Song Dynasty (1127–1279 A.D.). However, these ceramics have been buried in a marine environment for approximately 800 years and have all been corroded to varying degrees, with green-glazed pottery being the most severely corroded. In this study, the chemical compositions of five samples of green-glazed pottery and the corrosion morphology and mechanism of a representative sample were analyzed by optical microscopy, scanning electron microscopy-energy dispersive X‐ray spectrometry (SEM–EDS), Raman spectroscopy, and X-ray diffraction (XRD). Results: The green glaze is a low-temperature silica-aluminum oxide-lead oxide (SiO2-Al2O3-PbO) glaze with copper ions (Cu2+) as the main colorant. The corrosion morphology is characterized by alternating silicon (Si)- and lead (Pb)-rich layers, a sharp reaction interface between the Si-rich layer and the pristine glaze, and a relatively high porosity of the Si-rich gel layer, which is formed by the accumulation of spherical hydrated silica colloidal particles. These features suggest that the glaze was corroded through an interface-coupled dissolution–precipitation mechanism and that the properties of the gel pores controlled the reaction kinetics. Fluctuations in the solution properties at the reaction interface produced the complex morphology of the gel layer, whereas changes in the dryness and humidity of the environment are not essential factors. The samples have been corroding in the marine environment for nearly a thousand years, and explorations of the corrosion morphology and mechanism could provide reference information on the corrosion of various ancient ceramics and glasses and a basis for scientific conservation of these objects.

Preparation of nanometer zirconia by hydrothermal method: Influence of temperature and mechanism

Monoclinic (m-ZrO2) and tetragonal zirconia (t-ZrO2) nanoparticles with average grain size of 22.8 nm were synthesized by hydrothermal method using zirconium oxychloride octahydrate (ZrOCl2·8H2O), urea (CO(NH2)2) and deionized water as zirconium source, precipitant, and solvent, respectively. The effects of CO(NH2)2 hydrolysis rate, hydrothermal temperature, and time on the crystal structure, morphology, and grain size were studied. The structure, morphology, grain size, and crystal phase of zirconium oxide (ZrO2) were characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Thermogravimetry (TG-DTA), and Fourier Transform Infrared spectroscopy (FT-IR). The results show that the formation mechanisms of different crystal forms can be controlled by the average pH value. The hydrolysis rate of CO(NH2)2 was relatively slow at 120 °C, resulting in a slower rate of OH− production. The lower average pH value favors the formation of m-ZrO2 through the dissolution precipitation mechanism. With the increase of crystallization temperature, the hydrolysis rate of CO(NH2)2 is accelerated, and the average pH value of the solution is increased, which is conducive to the structural rearrangement of [Zr(OH)8(H2O)16]8+ precursor to form tetragonal phase. In addition, the number of defect sites is directly proportional to the crystallization temperature. Extension of crystallization time helps the generation of ZrO2 crystals by polycondensation and directional growth.