Precipitate Accumulation Research Articles

Phase-field chemo-mechanical modelling of corrosion-induced cracking in reinforced concrete subjected to non-uniform chloride-induced corrosion

A model for corrosion-induced cracking of reinforced concrete subjected to non-uniform chloride-induced corrosion is presented. The gradual corrosion initiation of the steel surface is investigated by simulating chloride transport considering binding. The transport of iron from the steel surface, its subsequent precipitation into rust, and the associated precipitation-induced pressure are explicitly modelled. Model results, obtained through finite element simulations, agree very well with experimental data, showing significantly improved accuracy over uniform corrosion modelling. The results obtained from case studies reveal that crack-facilitated transport of chlorides cannot be neglected, that the size of the anodic region must be considered, and that precipitate accumulation in pores can take years.

Visualizing the Effect of Temperature on Carbonate Salt Production in CO2 Electrolysis

Carbon dioxide (CO2) electrolysis is a novel and promising technology to tackle anthropogenic climate change by reducing our dependency on fossil fuels and creating a sustainable carbon cycle. However, current CO2 electrolysis suffers from low CO2 reduction reaction (CO2RR) selectivity and rapid gas diffusion electrode (GDE) degradation and flooding due to carbonate precipitation. As the hydrophilic precipitate accumulates in the porous structure of the cathode GDE, the liquid anolyte invades the pores, blocking the catholyte from reaching the catalyst layer. This effect promotes the adverse hydrogen evolution reaction and thus decreases the CO2RR selectivity (1). Current literature focuses on limiting carbonate precipitate formation as opposed to understanding the factors affecting its growth (2). While carbonate precipitation is dependent on the specific electrolyte in a flow cell, the impact of parameters, such as operating temperature and GDE porosity, on the nature of carbonate precipitation still need to be investigated (3).In this study, we examine the relationship between cell temperature with carbonate precipitate accumulation. A zero-gap alkaline membrane electrode assembly (MEA) was used with potassium carbonate as the anolyte and humidified CO2 as the catholyte. Electrochemical impedance spectroscopy was used to calculate the activation, ohmic, and mass transport losses of the cell before and after a constant current density phase where faradaic efficiency was measured to quantify the CO2RR selectivity degradation due to salt accumulation. Furthermore, to characterize precipitate growth, the cathode GDEs were imaged before and after electrochemical testing using scanning electron microscopy (SEM) and wavelength dispersive spectroscopy (WDS). To quantify precipitate-driven flooding over operation time, identical MEAs were imaged using operando X-ray synchrotron radiography over a range of temperatures. Through-plane images of the operating cell were processed to find the electrolyte thickness in the cathode GDE as a function of time. Radiography results revealed progressive, cyclical flooding as well as preferential gas pathways. Moreover, after four hours of constant current operation and at a cell temperature of 60℃, the catalyst layer exhibited large amounts of uniformly distributed precipitates, while the GDE contained large, localized precipitate crystals. This indicates that at high temperatures, carbonate precipitates significantly block the catalyst layer and cause flooding into the substrate layer. This work provides new insight into the effect of temperature on carbonate precipitate buildup, deepening the understanding of the mechanism responsible for precipitate degradation. M. E. Leonard, L. E. Clarke, A. Forner-Cuenca, S. M. Brown, and F. R. Brushett, ChemSusChem, 13 (2020).Y. Xu et al., ACS Energy Lett, 6, 809–815 (2021).E. R. Cofell, U. O. Nwabara, S. S. Bhargava, D. E. Henckel, and P. J. A. Kenis, ACS Appl Mater Interfaces, 13, 15132–15142 (2021).

Machine learning assists in increasing the time resolution of X-ray computed tomography applied to mineral precipitation in porous media

Many subsurface engineering technologies or natural processes cause porous medium properties, such as porosity or permeability, to evolve in time. Studying and understanding such processes on the pore scale is strongly aided by visualizing the details of geometric and morphological changes in the pores. For realistic 3D porous media, X-Ray Computed Tomography (XRCT) is the method of choice for visualization. However, the necessary high spatial resolution requires either access to limited high-energy synchrotron facilities or data acquisition times which are considerably longer (e.g. hours) than the time scales of the processes causing the pore geometry change (e.g. minutes). Thus, so far, conventional benchtop XRCT technologies are often too slow to allow for studying dynamic processes. Interrupting experiments for performing XRCT scans is also in many instances no viable approach. We propose a novel workflow for investigating dynamic precipitation processes in porous media systems in 3D using a conventional XRCT technology. Our workflow is based on limiting the data acquisition time by reducing the number of projections and enhancing the lower-quality reconstructed images using machine-learning algorithms trained on images reconstructed from high-quality initial- and final-stage scans. We apply the proposed workflow to induced carbonate precipitation within a porous-media sample of sintered glass-beads. So we were able to increase the temporal resolution sufficiently to study the temporal evolution of the precipitate accumulation using an available benchtop XRCT device.

Effect of the static shoulder on microstructural, textural, and mechanical characteristics during friction stir welding of Al6061

In the present investigation, a novel static shoulder friction stir welding (SSFSW) tool has been designed and fabricated. The designed tool works both as rotating shoulder FSW (RS-FSW) and SSFSW. To evaluate the effectiveness of the developed tool, Al6061 plates have been subjected to both RS-FSW and SSFSW using the indigenously developed tool. The microstructure evolution, axial force, texture development, and mechanical properties were evaluated and compared for both RS-FSW and SSFSW. Adequate heat generation in SSFSW resulted in a homogeneous structure at the stir zone. Electron back scattered diffraction analysis demonstrated the presence of red-colored regions along the grain boundaries indicative of more dislocation density. These regions acted as preferable sites for precipitate (Mg2Si) accumulation, which greatly affected the mechanical properties of the joint. SSFSW joints contained a strong {111} texture of R-cube and S component with a maximum intensity of 6.85, while RS-FSW joints contained A and A* components with a maximum intensity of 4.85. The hardness plots showed a wide lower hardness region in RS-FSW with a maximum hardness of 101HV and 110HV (SSFSW). During the tensile test, both the joints failed in the lower hardness region after achieving 88% (SSFSW) and 75% (RS-FSW) strength of base material.

Enhanced detection sensitivity through enzyme-induced precipitate accumulation in LSPR-active nano-valleys.

Biomolecule detection based on the localized surface plasmon resonance (LSPR) phenomenon has advantages in label-free detection, good sensitivity, and measurement simplicity and reproducibility. However, in order to ultimately be used for actual diagnosis, the ability to detect trace amounts of biomarkers is necessary, which requires the development of signal enhancement strategies that enable ultrasensitive detection. In this paper, we provide a straightforward and efficient route to boost LSPR sensitivity based on multiple sample washings. We found that repeated washing and drying cycles lead to a shift in the LSPR peak in a concentration-dependent manner, where this process drives the accumulation of a precipitate, formed by an enzyme reaction with target specificity, in the sample's LSPR active plasmonic nano-valley structure. Results show that the washing and drying process leads to a signal enhancement of more 200 times compared to a sensor with only enzyme-based amplification. To maximize this effect, optimization of the plasmonic nanostructure was also carried out to finally achieve atto-molar detection of miRNA with a distinguishable LSPR peak shift.

The effect of the boiling process on the Oxalic acid content of some vegetables in the Syrian local market

Oxalic acid HOOC-COOH (OA) is the first in the homologous series of dicarboxylic acids. It is one of the most common acids present in vegetable world1, it is one of the abundant organic compound acts as an anti-nutrient present in most vegetables in various quantities. It is found as salts of insoluble complexes with divalent cations, minerals and trace elements. Oxalates react with calcium to precipitate calcium oxalate and accumulation of oxalates in the body prevents the absorption and utilization of calcium; which in turn causes calcium imbalance, rickets and osteomalacia. In the present study oxalate content of various vegetables commonly available in local market of Syria were determined and effect of boiling on oxalate content of selected vegetable were investigated. Most of the samples analyzed were contained more than 100mg/100g on dry weigh basis. The higher value of total oxalate content was found in Parsley (1466.82 mg/100g); spinach and Cabbage contain (478.7, 191.08 mg/100g). Boiling has shown reduction in total oxalate content and least reduction was obtained in Parsely leaves (28.33%) and highest reduction was obtained from Spinach (40.00%)

Pb(II)-mediated precipitate transformation promotes Cr(VI) immobilization by biogenic hydroxyapatite

In this work, the mechanism of Pb(II)-mediated precipitation transformation to improve the removal of Cr(VI)-oxyanion on biogenic hydroxyapatite (BHAp) were investigated. The Pb(II)-preloading formed pyromorphite [Pb5(PO4)3Cl] precipitate on the BHAp surface (Pb@BHAp), thus causing an increase of 2.2 times in the uptake of Cr(VI) by Pb@BHAp at pH of 2.4. It was primarily due to the dissolution of Pb5(PO4)3Cl accompanied with the release of Pb(II), resulting in the rapid formation of crocoite (PbCrO4). Although the Ksp of Pb5(PO4)3Cl was approximately 23 orders of magnitude lower than that of PbCrO4, Pb(II)-mediated precipitation transformation could still occur. XRD and SEM-EDX analyses demonstrated that the process was a time-dependent that included rapid crystal precipitation in the initial 10 min and subsequent precipitate accumulation for several hours. The Pb(II) released from the dissolution of Pb5(PO4)3Cl was immediately immobilized by Cr(VI); therefore, it did not cause any retention risk of Pb(II) in the solution. Furthermore, a small quantity of Cr(VI) could be reduced to Cr(III) by BHAp, and Cr(III) could enter into the BHAp lattice for the exchange of Ca(II). This study provides a new insight into the resource utilization of Pb-bearing BHAp and a potential method for the successive removal of Pb(II) and Cr(VI).

Induction Infrared Thermography for Non-destructive Evaluation of Welding-Induced Sensitization in Stainless Steels

For medium- and high-carbon stainless steels, welding can induce sensitization in the heat affected zone (HAZ) adjacent to the weld, where chromium carbide $$(\hbox {Cr}_{23}\hbox {C}_{6})$$ precipitates out of the bulk metal and accumulates at the grain boundaries. This chromium depletion and precipitate accumulation at grain boundaries makes the alloy susceptible to intergranular corrosion, environmentally assisted cracking, and broader fracture. In this paper, we investigate the efficacy of using induction infrared thermography (IIRT) as a non-destructive method for detecting welding-induced sensitization, using the AISI 440C steel as an example. We start by presenting a laboratory experiment to demonstrate this approach, using a radio frequency function generator, an induction wand, and a FLIR SC8203 infrared camera. We use traditional metallography techniques and scanning electron microscopy (SEM) to identify the location of any sensitized regions and characterize the corresponding microstructure. The IIRT experimental results reveal a distinguishable heat signature, with higher temperature observed within the sensitized regions. Next, we present a computational study to simulate the IIRT experiment and investigate the underlying physics. We adopt a three-dimensional thermo-electro-magnetic model including Fourier’s law of heat conduction and Maxwell’s equations for predicting the electromagnetic field caused by a sinusoidal excitation current flowing through the induction coil. We solve the system of governing equations using the commercial solver COMSOL Multiphysics. To numerically investigate the possible causes of the disproportionate heating within the sensitized regions, we realistically vary the values of electrical resistivity and magnetic permeability therein. The simulated results indicate that the heat signature observed in the laboratory experiment may result from the increase of both electrical resistivity and magnetic permeability in the HAZ. The possible physical relationships between sensitization and the variation of these two properties are discussed.

Aluminum mobility in mildly acidic mine drainage: Interactions between hydrobasaluminite, silica and trace metals from the nano to the meso-scale

Aluminum precipitates control the hydrochemistry and mineralogy of a broad variety of environments on Earth (e.g., acid mine drainage, AMD, coastal wetlands, boreal and alpine streams, tropical acid sulfate soils, laterites and bauxites, …). However, the geochemical and mineralogical processes controlling Al (and other associated metals and metalloids) transport and removal in those environments are not fully understood. The geochemical system of Paradise Portal (Colorado, USA) comprises sulfate-rich mildly acidic waters, the hydrochemistry of which is directly controlled by the massive precipitation of hydrobasaluminite Al4(SO4)(OH)10·12-36H2O. Three connected but discernible aluminum precipitation stages were identified and described: 1) nanoparticle formation and size decrease along the creek, 2) hydrobasaluminite neoformation on the riverbed, and 3) precipitate accretion and accumulation on the riverbed leading to Al and Fe banded formations. The co-occurrence of Al and Si in the system was observed, recording significant amounts of Si accompanying the three different components of the system (i.e., nanoparticles and fresh and aged Al-precipitates). Also, abrupt and minor changes in the sedimentary record were described and proposed to be the response of the system to seasonal and interannual changes in AMD chemistry. Concerning the mobility of other metals and metalloids, P, Th, V, W, Ti and B showed a tendency to be preferentially incorporated into hydrobasaluminite, while others like Be, As, Se or Ba tend to remain dissolved in the water.

Additive manufacturing of Inconel 718—Copper alloy bimetallic structure using laser engineered net shaping (LENS™)

To understand processing ability and measure resultant interfacial and thermal properties of Inconel 718 and copper alloy GRCop-84, bimetallic structures were fabricated using laser engineering net shaping (LENS™), a commercially available additive manufacturing technique. It was hypothesized that additively combining the two aerospace alloys would form a unique bimetallic structure with improved thermophysical properties compared to the Inconel 718 alloy. Two approaches were used: the direct deposition of GRCop-84 on Inconel 718 and the compositional gradation of the two alloys. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray Diffraction (XRD), Vickers microhardness and flash thermal diffusivity were used to characterize these bimetallic structures to validate our hypothesis. The compositional gradation approach showed a gradual transition of Inconel 718 and GRCop-84 elements at the interface, which was also reflected in the cross-sectional hardness profile across the bimetallic interface. SEM images showed columnar grain structures at the interfaces with Cr2Nb precipitate accumulation along grain boundaries and the substrate-deposit interface. The average thermal diffusivity of the bimetallic structure was measured at 11.33 mm2/s for the temperature range of 50 °C–300 °C; a 250% increase in diffusivity when compared to the pure Inconel 718 alloy at 3.20 mm2/s. Conductivity of the bimetallic structures increased by almost 300% compared to Inconel 718 as well. Such structures with designed compositional gradation and tailored thermal properties opens up the possibilities of multi-material metal additive manufacturing for next generation of aerospace structures.

Experimental observations of boric acid precipitation scenarios

During a Loss of Coolant Accident (LOCA) in Light Water Reactors (LWR), borated water is injected into the core through the safety injection system. The continuous vaporization of the water from the core may increase the concentration of boric acid in the core that, under certain conditions may reach the solubility limit and precipitate. This includes scenarios where the liquid water supply to the core is affected by possible blockages due to debris accumulation. Questions have been raised on the effects of the precipitate in the core on the flow behavior, including the possibility of additional blockages produced by precipitate accumulation. A simple experimental facility was constructed to perform experimental observations of the behavior of borated water under the combined effects of the boiling and the boric acid precipitation (BAP). The facility consists of a transparent polycarbonate vertical pipe where forty-five heated rods have been installed to supply the power to the water to reach the saturation temperature, and maintain a desired boil-off rate. The layout and geometry of the experimental apparatus were conceived to emulate a simplified core of a Pressurized Water Reactor (PWR). Experimental observations have been conducted under two different conditions. Preliminary tests were conducted to observe the behavior of the water and the boric acid precipitate during a boil-off scenario without borated water addition (decreasing water level). During the main test runs, borated water was constantly injected from the top of the test section to maintain a constant mixture level in the test section. Both tests assumed no flow from the bottom of the test section which may be the case of PWR LOCA scenarios in presence of debris-generated core blockage. The observations performed with a set of cameras installed around the test section showed interesting effects of the vapor bubbles on the boric acid precipitate migration and accumulation in the test section. The results may help addressing some basic questions regarding the effect of the precipitation of boric acid during core blockage LOCA scenarios and, provide the basis for further experimental and computational analysis required to resolve the BAP issue as part of the Generic Safety Issue 191.

Gallbladder sludge associated with ceftriaxone therapy for typhoid fever in Nigerian children: A case series

Ceftriaxone is a third-generation cephalosporin with a wide spectrum of activity against both gram-negative and gram-positive organisms. Ceftriaxone has proven efficacy against severe and difficult-to-treat community-acquired infections including typhoid fever and other sepsis syndromes caused by multi-drug resistant organisms. Several studies including prospective studies exist in the literature that described the accumulation of sonographically demonstrable sludge (or precipitates) in the gallbladder and sometimes in the urinary tract. The accumulation of sludge occurs during therapy for severe infections in some children identified with certain predisposing factors. The condition is often asymptomatic but might be associated with clinical features that could mimic disease progression in patients with intra-abdominal manifestations of infection such as typhoid fever. Five Nigerian children aged between 4 and 11 years developed demonstrable gallbladder sludge (precipitate) while on treatment for typhoid fever with ceftriaxone. Three of the children manifested clinical features suggestive of gallbladder precipitate accumulation following commencement of the antibiotic, while the other two did not. Ceftriaxone therapy was continued to completion in all the cases along with conservative management. Four of the children recovered and had resolution of the sludge, while the fifth died of multi-organ failure after surgery for intestinal perforation. Although several studies exist in the literature regarding this condition, our search using Medline and Google Scholar did not identify such reports from children in Nigeria or sub-Saharan Africa. The cases are presented to create awareness on the possibility of occurrence of a drug-induced biliary precipitate formation in children.

Passive System for Bio-Recovery of Copper from Acid Mine Drainage

In Central Chile, acid mine drainages (AMDs) are characterized by high concentrations of copper, which can be recovered. Passive biochemical reactors are eco-friendly technologies for the treatment of AMD. They use organic substrate mixtures to drive microbial sulfate reduction and metal sulfide precipitate formation. The performance of conventional biochemical reactors, however, is limited by metal toxicity, and metal recovery is difficult. Diffusive exchange systems on the other hand can be tailored to resist metal toxicity. This is achieved by having separate zones for AMD movement and for sulfate reduction, and by allowing the diffusive exchange of solutes between these zones. Also, higher reaction rates are possible, because much finer organic materials can be utilized as substrates. A key innovation of this research is the use of vertical tubular screens to convey the AMD through the reactor while simultaneously allowing transverse diffusive exchange of dissolved species with the substrate. The tubular screens act as reactors for precipitate formation, settling and accumulation, from where precipitates can be periodically recovered. This design promotes higher reaction rates, eliminates clogging and facilitates the recovery of valuable metals. This work studied the performance of a 2-m long vertical diffusive exchange column. Detailed insight was gained into reactions and transport processes within the tubular screen by the use of several sampling points along the column. During the first two months the reactor was fed with increasing concentrations of sulfate only, to determine its sulfate reduction potential. Then the reactor was fed with AMD for three additional months. During the operation with AMD, significant metal removal occurred, and copper precipitates accumulated, and were recovered.

Mineral Transformation and Biomass Accumulation Associated With Uranium Bioremediation at Rifle, Colorado

Injection of organic carbon into the subsurface as an electron donor for bioremediation of redox-sensitive contaminants like uranium often leads to mineral transformation and biomass accumulation, both of which can alter the flow field and potentially bioremediation efficacy. This work combines reactive transport modeling with a column experiment and field measurements to understand the biogeochemical processes and to quantify the biomass and mineral transformation/accumulation during a bioremediation experiment at a uranium contaminated site near Rifle, Colorado. We use the reactive transport model CrunchFlow to explicitly simulate microbial community dynamics of iron and sulfate reducers, and their impacts on reaction rates. The column experiment shows clear evidence of mineral precipitation, primarily in the form of calcite and iron monosulfide. At the field scale, reactive transport simulations suggest that the biogeochemical reactions occur mostly close to the injection wells where acetate concentrations are highest, with mineral precipitate and biomass accumulation reaching as high as 1.5% of the pore space. This work shows that reactive transport modeling coupled with field data can bean effective tool for quantitative estimation of mineral transformation and biomass accumulation, thus improving the design of bioremediation strategies.

Modelling species fate and porous media effects for landfill leachate flow

A numerical, multiple-species, reactive transport model, coupled to models of kinetic biodegradation, precipitation, and particle attachment and detachment for predicting landfill leachate-induced clogging in porous media for one-dimensional flow systems, is described. The finite-element method is used for transport modelling, with reactions incorporated into point-source or sink terms. The species modelled include three volatile fatty acids, active and inert suspended biomass, dissolved calcium, and inorganic particles. The clog matter consists of active biofilm, inert biofilm, and inorganic solids. A biofilm model is used to simulate the growth and decay of active biomass and removal of substrate. Precipitate accumulation and calcium removal are simulated by a model of calcium carbonate precipitation. Interphase movement between clog matter and fluid includes the processes of attachment and detachment. A geometric representation of the porous media allows porosity and specific surface to be estimated from the thickness of the accumulated clog matter. The porosity of the media can thus change spatially and temporally. The behaviour of the model is demonstrated with a hypothetical example.Key words: clogging, landfills, leachate collection systems, modelling, biofilms, mineral precipitation.

Chemical Analysis of Cores Obtained from a Vertical Flow Pond

The vertical flow pond at Jennings Environmental Education Center, Butler County, PA, was constructed in 1997. After five years of operation, the system continued to produce alkalinity and remove iron and aluminum, but the flow rate through the system has continuous declined. To determine the type and pattern of chemical distribution throughout the system, 9 cores were obtained and analyzed for iron, manganese, aluminum, silica, sulfate, calcium and trace metal concentrations. Iron precipitates accumulated in the upper 7-10 cm of the spent mushroom compost and limestone mixture with the majority of aluminum precipitate accumulation occurring between 10 and 20 cm below the surface of the media. Although there was sufficient CaCO3 in the substrate to continue to provide alkaline addition, the accumulation of metals in the upper 10 cm of the substrate has reduced the permeability of the substrate.

Control of As Precipitation in Low-Temperature GaAs by Electronic and Isoelectronic Delta Doping

A systematic study of electronic (Si and Be) and isoelectronic (In and Al) delta-doping effects on the formation of arsenic precipitates in GaAs grown by molecular beam epitaxy (MBE) at low substrate temperature is presented. Both electronic dopant Si and isoelectronic dopant In are found to accumulate As precipitates in postgrowth-annealed samples, while the precipitate accumulation effect is more prominent for Si than In. As precipitate is depleted from regions doped with Be or Al. The results suggest that the electronic property of impurity does not have a direct correlation with the As precipitation process. The effects of doping concentration and postgrowth annealing temperatures are also reported. The ability to control the As precipitates in low-temperature materials should lead to a wide variety of device applications.

Arsenic precipitate accumulation and depletion zones at AlGaAs/GaAs heterojunctions grown at low substrate temperature by molecular beam epitaxy

AlxGa1−xAs/GaAs heterojunctions were grown by molecular beam epitaxy under normal growth conditions except that the substrate temperature was 250 °C. After a 1 h anneal at 600 °C, a narrow precipitate depletion (PD) zone was observed on the AlxGa1−xAs sides of the heterojunctions, while a high density precipitate accumulation (PA) zone was observed on the GaAs sides. The formation of these PD and PA zones is explained as a result of diffusion of excess As atoms across the interface from the AlxGa1−xAs layer to the GaAs layer. No significant difference in PD and PA zones was found at interfaces between AlxGa1−xAs grown on GaAs and GaAs grown on AlxGa1−xAs, indicating a negligible effect due to the growth sequence. Widths of PDs were about 250 Å, exhibiting a weak dependence on the Al concentration of the AlxGa1−xAs layers.

Effect of concentrated hydrogen peroxide solution on the surface morphology of cut human dentin.

Abstract The effect of concentrated hydrogen peroxide solution, alone and in combination with acid‐etching with 37% phosphoric acid for 60 s, on the surface morphology of cut human dentin was investigated by SEM and compared to controls in which saline solution rather than hydrogen peroxide solution was used. Examination of the specimens revealed that the smear layer on the surface of cut dentin was not removed by hydrogen peroxide alone, and that a dense amorphous precipitate was formed on the surface of the smear layer after extended exposure. The precipitate accumulation was first noted after 20 min of exposure. Examination of the dentin after hydrogen peroxide exposure followed by acid‐etching revealed the presence of a fine granular deposit on an otherwise clean dentin surface. A modest amount of amorphous precipitate was seen over the entire dentin surface after 60 min of hydrogen peroxide exposure. Examination of specimens that were acid‐etched before being exposed to hydrogen peroxide indicated that the smear layer was effectively removed and the orifices of the dentinal tubules were enlarged to permit more effective penetration of the peroxide solution. It also resulted in less accumulation of precipitate on the dentin surface than the other methods.