Surface Dissolution Research Articles

Dissolved Organic Radiocarbon in the West Indian Ocean

AbstractWe report marine dissolved organic carbon (DOC) concentrations, and DOC Δ14C and δ13C in seawater collected from the West Indian Ocean during the GO‐SHIP I07N cruise in 2018. We find bomb 14C in DOC from the upper 1,000 m of the water column. There is no significant change in ∆14C of DOC in deep water northward, unlike that of dissolved inorganic carbon (DIC), suggesting that transport of deep water northward is not controlling the 14C age of DOC. Variability of DOC ∆14C, including high values in the deep waters, is more pronounced than in other oceans, suggesting that dissolution of surface derived particulate organic carbon is a source of modern carbon to deep DOC in the West Indian Ocean. Low δ13C are present at two of the five stations studied, suggesting a source of low δ13C DOC, or additional microbial utilization of deep DOC.

Effect of dissolved oxygen on surface oxidation and dissolution of InGaAs and its impact on AsGa, AsIn, and VAs defect generation

Effect of dissolved oxygen on surface oxidation and dissolution of InGaAs and its impact on AsGa, AsIn, and VAs defect generation

Probability distributions of mineral dissolution rates: the role of lattice defects

The correct quantification of mineral dissolution rates is a critical task for macroscopic reactive transport modeling. Previous studies showed a substantial rate variability of about two orders of magnitude, which cannot be explained by variance of external environmental parameters alone. If the rate cannot be predicted as a constant parameter, then the critical question is whether it can be predicted as a stable reproducible probability distribution. Although a large variety of factors may contribute to the overall variance across the scales, the effect of defect density and defect spatial distribution can be considered as one of the key variance sources. Here, we tested the reproducibility of probability distributions for Kossel crystals with a different amount and spatial configurations of lattice dislocations. We ran several tests on systems with the same configurations and calculated the probabilities of material flux. Surprisingly, we discovered that the density of dislocations has minimal impact on the probability distributions. However, the spatial location of dislocations has a substantial influence on the rate distributions reproducibility. In cases where multiple etch pits operate simultaneously, reproducible rate distributions are found regardless of the number of dislocations. In cases where dislocations formed clusters, one large etch pit controlled the entire surface, and sets of reproducible probability distributions were detected. Then, more complex statistical behavior is expected, since the result is path-dependent. These results have serious consequences for the implementation of rate distributions in reactive transport models. Further studies, however, are needed to provide clear guidance on relating surface morphologies, dislocation distributions, and dissolution rate variance. The role of material-specific properties, such as crystallographic structure and bonding, in rate distributions, should be additionally addressed. The role of grain boundaries, crystal size and crystal habit, including nanoparticulate forms, in rate variance, also should be addressed for practical applications.

Numerical simulation and experimental study of optimized jet shape in electric arc electrochemical composite machining

A favorable flow field enhances the product transport capacity and also increases the electrochemical mass transfer rate. In this paper, an end-side connected electrode suitable for electric arc electrochemical composite milling was proposed based on the existing flushing form. The aim is to simultaneously enhance the machining of the groove surface and the side. The flushing form was optimized by the flow field, and it was shown that the internal flushing increased the area of the high flow rate zone of the bottom gap. In the experiments, it was found that the internal flushing reduced the secondary discharge probability, the accumulation of re-solidified material on the groove surface was decreased, and the surface dissolution was uniform with low oxidation. However, the central jet is lost along the course and a zero velocity zone exists at the corners of the groove. Therefore, the sidewall open flow field is proposed to reduce the sidewall recast layer. It was verified that the sidewall slots of the positive flow type improved both the surface quality of the groove surface and the side wall. It was also found that the increase in the number of open grooves facilitates the generation of uniform debris removal.

Quasi-In Situ Localized Corrosion of an Additively Manufactured FeCo Alloy in 5 Wt Pct NaCl Solution

FeCo alloys are important materials used in pumps and motors in the offshore oil and gas drilling industry. These alloys are subjected to marine environments with a high NaCl concentration, therefore, corrosion and catastrophic failure are anticipated. So, the surface dissolution of additively manufactured FeCo samples is investigated in a quasi-in situ manner, in particular, the pitting corrosion in 5.0 wt pct NaCl solution. The local dissolution of the same sample region is monitored after 24, 72, and 168 hours. Here, the formation of rectangular and circular pits of ultra-fine dimensions (less than 0.5 µm) is observed with increasing immersion time. In addition, the formation of a corrosion-inhibiting surface layer is detected on the sample surface. Surface dissolution leads to a change in the surface structure, however, no change in grain shape or grain size is noticed. The surface topography after local dissolution is correlated to the grain orientation. Quasi-in situ analysis shows the preferential dissolution of high-angle grain boundaries (HAGBs) leading to a change in the fraction of HAGBs and low-angle grain boundaries fraction (LAGBs). For the FeCo sample, a potentiodynamic polarisation test reveals a corrosion potential (Ecorr) of − 0.475 V referred to the standard hydrogen electrode (SHE) and a corrosion exchange current density (icorr) of 0.0848 A/m2. Furthermore, quasi-in situ experiments showed that grains oriented along certain crystallographic directions are corroding more compared to other grains leading to a significant decrease in the local surface height. Grains with a plane normal close to the langle {1}00rangle direction reveal lower surface dissolution and higher corrosion resistance, whereas planes normal close to the langle {11}0rangle direction and the langle {111}rangle direction exhibit a higher surface dissolution.

Seasonal dynamics of karst surface dissolution based on a limestone tables experiment (Slovak karst)

Chemical denudation in karst is the basic process of karst relief formation. However, it is influenced by many factors of varying intensity that depend on the climatic conditions and characteristics of each given location. Based on measurable results of weight loss of limestone tablets, we monitored the intensity of chemical denudation in two areas of the Slovak Karst, Silica Plateau and Jasov Plateau that are situated in the most developed karst plateau region of Slovakia. Both experimental sites are similar in terms of geographical conditions, thus comparable between them. In each locality, we placed three sets of standardized tablets at a depth of 50 cm, 20 cm, and on the soil surface. The research began in December 2016 and has continued up to the end of 2021, with drying and weighing of the samples taking place each three months. The lowest weight loss was recorded on samples placed on the surface (in both sites) and the highest at the depth of 20 cm. This is due to biological activity in the soil during the growing season (2.65 - 2.82 mg/cm 2/year). The highest weight losses over time are observed at the turn of winter and spring, where the effect of snowfall and snow melting water plays an important role. The average dissolution rate in the spring season is between 3.78 and 4.12 mg/cm 2/year, whereas in winter is from 3.24 to 4.06 mg/cm 2/year.

Cultivation and biogeochemical analyses reveal insights into biomineralization caused by piezotolerant iron-reducing bacteria from petroleum reservoirs and their application in MEOR

Interactions between minerals and iron-reducing bacteria under in-situ pressure and temperature conditions play important roles in oil extraction, residual oil methanation, and CO2 storage in petroleum reservoirs. However, the impacts of pressure on dissimilatory iron-reducing bacteria (DIRB) are poorly understood. Herein, the interactions between clay minerals and microbes under elevated hydrostatic pressure conditions were elucidated through enrichment experiments. Bioreduction experiments were performed under hydrostatic pressures of 0.1–40 MPa. Microbial diversity analysis revealed that high pressures significantly increased microbial diversity in petroleum reservoirs, which is helpful for restoring underground ecosystems in situ. The key piezotolerant iron-reducing bacteria in the samples were Shewanella and Flaviflexus. These two genera were isolated for the first time from petroleum reservoirs and identified as piezophiles. The SEM results clearly showed mineral surface dissolution. Moreover, nanoscale secondary minerals were produced during biomineralization. XRD analysis revealed that illite, albite, and clinoptilolite were present after bioreduction. The isolates showed the capacity to inhibit hydro-swelling and prevent plugging-related damage in reservoirs.

Pore-scale modeling of thermal-hydro-mechanical-chemical coupled rock dissolution and fracturing process

Acid fracturing can effectively improve the connectivity inside underground reservoirs, which is of significance for geothermal exploitation and geological carbon sequestration. It involves a complex thermal-hydro-mechanical-chemical (THMC) coupled process. This work first develops a pore-scale THMC coupled model combining the lattice Boltzmann method (LBM) and the discrete element method (DEM) to describe the acid fracturing process, particularly covering chemical damage, rock dissolution, and solute transport. A chemical damage variable based on the cohesive bond is proposed to characterize the alteration of mechanical parameters caused by local rock dissolution. The change of fluid pathway due to rock dissolution is handled by the lattice Boltzmann solute transport model combined with the volume of pixel method. Based on the proposed model, the influence of injection pressure and Damkohler number (Da) on the THMC coupled rock dissolution and fracturing process is analyzed. Results indicate three types according to dissolution morphologies, i.e., permeation, cavity, and permeation-cavity. The first and second types are related to the reaction-controlled and diffusion-controlled processes, respectively. Particularly, the permeation-cavity type occurs at conditions with high injection pressure and high Da and is the combination of the first two types, where the dissolution around the main fracture presents the cavity type but converts into the permeation type around secondary fractures. Additionally, the evolution patterns of reactive surface area and dissolution rate with time differ significantly with rock dissolution types. In particular, for the permeation type, the aperture of fracture far away from the injection hole could be larger than that near the injection hole under the THMC coupling, which is quite different from HM and THM coupling.

Stepwise dissolution of silica surface in alkaline solution revealed by molecular modeling

AbstractThe atomic scale solid–liquid interfacial process dominates the macro‐dissolution of silica, yet its direct experimental observation is challenging. Here we employed the reactive molecular dynamics to model this process in alkaline condition. An elevated temperature strategy under canonical ensemble (NVT) was applied to accelerate the process for sufficient sampling at temporal domain. A stepwise transformation from fully linked SiO4 network (Q3 and Q4) to reduced linkage and eventually aqueous species (Q0) was revealed. The simulated dissolution rate agrees well with the value predicted by empirical model. By tracing hydrogen atoms, we found that the dehydroxylated silica surfaces in alkaline electrolyte solutions underwent a transition from Si–O–Si bond cleavage‐dominated (mainly reacted with OH−) to hydroxylation‐dominated surface reactions. The free‐energy reconstruction of well‐tempered metadynamics reveals that 1500 K accelerates dissolution without altering the reaction pathways. These findings offer novel insights into the evolution of atomic‐scale surface configurations during the dissolution kinetics of silica.

Demonstrating the absence of metal ion contamination in operando PEM fuel cells utilizing unmodified stainless steel bipolar plates

Using stainless steel as material for bipolar plates (BPPs) in proton exchange membrane fuel cells (PEMFCs) carries a perceived risk of corrosion and subsequent metal ion contamination of the membrane electrode assembly (MEA). However, assessments in literature on this hazard to PEMFC systems have been based on ex-situ corrosion studies, where general assumptions made on the BPP environment might not be a correct simulation of real on-site conditions. In this contribution, uncoated BPPs from stainless steel grades 304 L, 316 L and 904 L were subjected to in-situ hybrid endurance/stress testing to simulate realistic conditions in operating fuel cell systems and re-evaluate the need of additional corrosion protection. A post analysis of the plates showed no signs of surface dissolution on any of the tested samples and the concentration of iron in the MEA averaged 7 to 10 ppm for uncoated samples and 7 to 11 ppm for coated and graphitic reference tests, displaying a negligible amount of trace metals compared to critical thresholds found in literature. Contact resistance values were stable for all samples and observable changes in cell performance and voltage degradation was confirmed to be unrelated to the presence of uncoated bipolar plates. The combined effects of decoupling of bipolar plate surface potentials from electrode potentials and operational control of stable gas flow compositions to sustain stainless steel surface passivation, were identified as explanation for the experimentally observed corrosion resistance of uncoated stainless steel plates in PEMFCs.

Accurate computation of desalinated seawater re-mineralization processes using blending with surface water, chemicals dosing and minerals dissolution

Desalinated seawater often represents lack of merit nutrients, unstable and low buffer capacity owing to the fact that various aqueous ions are almost removed. The various re-mineralization processes, such as blending with surface water, chemicals dosing, and minerals dissolution, are commonly used for introduction of merit ions and carbonate alkalinity to desalinated seawater to meet health requirement and to protect water supply facilities from corrosion. This paper discusses the optimization of various re-mineralization processes based on accurate model computation with emphasis on carbonate system model, water stability index, blending model, and mineral surface dissolution model. The accurate model computation investigation justifies the efforts and costs through various re-mineralization processes for achieving narrow water quality criteria.

The surface dissolution process of smithsonite and its effect on flotation behaviour

Previous studies have shown that the dissolution alters the static intrinsic properties of mineral surfaces, such as changing the surface components or active sites, which in turn affects the floatability. In this work, the dissolution process of smithsonite with different particle sizes and its influence on the flotation behaviour were systematically investigated from a dynamic perspective of the dissolution of ions on the mineral surface. Micro-flotation experiments revealed the inhibition of the flotation of smithsonite during the early phases of dissolution, particularly in the case of the fine particle. Inductively coupled plasma optical emission spectroscopy (ICP-OES) tests, Inorganic carbon (IC) tests, and X-ray photoelectron spectroscopy (XPS) analysis indicated that the early phases of the dissolution process of smithsonite exhibited a more rapid rate of zinc ions. However, as the dissolution progressed and a state of saturation was reached, the further dissolution of carbonate inhibited that of zinc ions. Subsequent adsorption measurements and Fourier transform infrared (FTIR) analysis illuminated the transformation in flotation behaviour resulting from the surface dissolution of smithsonite, primarily by affecting the stability of the adsorption of agents. The rapid dissolution rate of ions on the surface of smithsonite led to decreased adsorption stability of (sodium oleate) NaOL and diminished floatability. This phenomenon was particularly discernible on the surface of fine particle smithsonite. This investigation advances a novel mechanism for comprehending the impact of the surface dissolution processes on the flotation behaviour of smithsonite of different particle sizes, providing a theoretical and practical reference for the flotation of fine particles and marginally soluble minerals.

Effects of dissolution by alkali treatment on anisotropic surface properties and flotation behavior of spodumene

The effect of dissolution pretreatment of spodumene using NaOH and Na2CO3 was investigated by micro-flotation test, contact angle measurement, XPS, ICP and AFM imaging. The results showed that NaOH treatment activated the spodumene flotation whilst Na2CO3 showed little depression effect. NaOH had more significant activating effect on the spodumene (001) surface than (110) surface. The surface dissolution was confirmed by AFM, showing that weak surface dissolution was observed in ultrapure water and Na2CO3 solution, while there was strong surface dissolution in NaOH solution. Some precipitates coated the surface at the very start in NaOH and Na2CO3 solution, and the precipitates redissolved rapidly in NaOH solution while redissolved very slowly in Na2CO3 solution. The ICP results verified the release of Si, Al and Li from spodumene surface. NaOH treatment gave larger relative contents of Al on spodumene surface than Na2CO3, and the relative contents of Al on the (001) surface increased to a greater extent than on the (110) surface, as revealed by XPS analysis. From the point of crystal structure, the dissolution made more dangling Al exposed on the (001) surface, making it more favor of NaOL adsorption.

Mass transfer enhancement and drying mechanism of high adhesion saturated impregnated Co-Al2O3 monolithic catalyst

The drying process significantly influences the dispersion of metals, physical properties, and performance of monolithic catalysts. In this research, a cordierite-based monolithic catalyst with Co/γ-Al2O3 was prepared using the slurry and impregnation method. The impact of ambient humidity on metal dispersion, mass transfer performance, and catalytic performance was investigated. The findings revealed distinct crystallization-deliquescence curves in the saturated impregnated monolithic catalysts, with alternating crystallization and deliquescence phenomena occurring as the ambient humidity changed. When the coating adhesion was high, the simultaneous occurrence of internal crystallization and surface dissolution resulted in concentrated internal stress, which facilitated the micro-stripping of the coating, leading to the formation of a cobweb-like microstructure. This process affected the distribution of pore sizes and enhanced mass transfer performance. The Co-based catalysts prepared in this study demonstrated a high selectivity for C5+ products (73.93%) when employed in the Fischer-Tropsch synthesis reaction. This research offers an optimization strategy for catalyst preparation, aiming to develop monolithic catalysts with low melting points, high crystallinity, and supersaturated supported transition metals.

Turning on Lithium-Sulfur Full Batteries at -10 °C.

Lithium-sulfur (Li-S) batteries using Li2S and Li-free anodes have emerged as a potential high-energy and safe battery technology. Although the operation of Li-S full batteries based on Li2S has been demonstrated at room temperature, their effective use at a subzero temperature has not been realized due to the low electrochemical utilization of Li2S. Here, ammonium nitrate (NH4NO3) is introduced as a functional additive that allows Li-S full batteries to operate at -10 °C. The polar N-H bonds in the additive alter the activation pathway of Li2S by inducing the dissolution of the Li2S surface. Then, Li2S with an amorphized surface layer undergoes the modified activation process, which consists of the disproportionation and direct conversion reaction, through which Li2S is efficiently converted into S8. The Li-S full battery using NH4NO3 delivers a reversible capacity and cycling stability over 400 cycles at -10 °C.

Size-Dependent Corrosion of Al-Fe Intermetallic Particles at Al-Mg Alloy Surfaces Investigated by In-Liquid Nanoscale Potential Measurement Technique.

Corrosion of Al alloy often starts from the nanoscale corrosion around the surface-exposed Al-Fe intermetallic particles (IMPs) and leads to a serious damage limiting its application range in the automobile industry. To solve this issue, understanding of the nanoscale corrosion mechanism around the IMP is essential, yet it is impeded by the difficulties in directly visualizing nanoscale distribution of reaction activity. Here, this difficulty is overcomed by open-loop electric potential microscopy (OL-EPM) and investigate nanoscale corrosion behavior around the IMPs in H2 SO4 solution. The OL-EPM results reveal that the corrosion around a small IMP settles down in a short time (<30min) after transient dissolution of the IMP surface while that around a large IMP lasts for a long time especially at its edges and results in a severe damage of the IMP and matrix. This result suggests that an Al alloy with many small IMPs gives a better corrosion resistance than that with few large IMPs if the total Fe content is the same. This difference is confirmed by corrosion weight loss test using Al alloys with different IMP sizes. This finding should give an important guideline to improve the corrosion resistance of Al alloy.

Electrochemical dissolution behavior of TNM intermetallic in sodium nitrate solution

TNM alloy is a new kind of lightweight and high temperature resistant material. Electrochemical machining (ECM) is an ideal manufacturing method for TNM alloy because of its high machining efficiency and good machining quality. In this work, the dissolution properties and surface passive film of TNM in NaNO3 solution are studied comprehensively. The passivation properties of the samples are tested using potentiodynamic, potentiostatic and CV curves. The results show that there are obvious passive and transpassive areas on the surface of TNM alloy, and the corrosion resistance of the passive film gradually increased with the test time from 0 to 7200 s. XPS and EIS indicate that the passive film mainly consists of Al2O3, TiO2, Nb2O5 and MoO3. Its structure is a bi-layer consisting of an inner layer with few pores and an outer layer with many pores. A corresponding schematic model is also proposed to characterize the interface structure between TNM alloy matrix and passive film. TNM alloy has a very high material removal rate according to the ηω-j curve. The dissolution morphology of TNM alloy is observed at various current densities. It is found that the surface dissolution morphology is very different under low and high current densities. The sample exhibits a loose lamellar microstructure with some isolated lamellar colonies at low current density, while the surface is quite smooth (about Ra 0.55 μm) when current density (j) > 20 A/cm2. Finally, the material dissolution process of TNM alloy at 2 and 25 A/cm2 is also presented.

Phase engineering and surface reconstruction of CrxMnFeNi high entropy alloys for electrocatalytic water splitting

The quest for cost-effective and efficient catalysts for oxygen and hydrogen evolution reactions is vital for a carbon-neutral future. High entropy alloys (HEAs), known for their exceptional thermodynamic stability and performance, have recently emerged as promising candidates in this field. Yet, the relationship between the phase and catalytic performance in HEAs remains understudied. Commonly, metallic catalysts undergo surface reconstruction under high oxidizing potentials under the oxygen evolution reaction (OER), making the identification of the truly active species essential for designing efficient catalysts. Nonetheless, characterization of surface reconstruction of nanoscale HEAs is challenging due to low content of each metal, exacerbated by the use of nonmetal support during synthesis. In this study, we unveil the phase-performance relationship in HEAs and identify that the body-centered cubic (BCC) phase CrMnFeNi outperforms its face-center cubic (FCC) phase counterparts in catalyzing both OER and the hydrogen evolution reaction (HER) due to its superior electrical conductivity and optimized electronic structures. Particularly, Cr1.5MnFeNi with the most prominent BCC phase demonstrates superior OER activity (η10 of 255 mV and Tafel slope of 28.7 mV dec−1), surpassing other Cr, Mn, Fe, Ni-based catalysts, and even state-of-the-art RuO2. X-ray photoelectron spectroscopy (XPS) analysis a transition of Mn, Fe, and Ni elements from metallic states to oxidation states, with surface dissolution of Cr after OER durability tests. This research elucidates the phase-dependent electrocatalytic performance and surface reconstruction in HEAs, providing valuable insights for designing and optimizing HEA materials for electrocatalytic applications.

Effect of chromium on corrosion resistance of Ni-Cr-Mo-Gd alloys in seawater

Neutron absorbing materials are being considered within commercial spent nuclear fuel disposal canisters to maintain nuclear subcriticality. To select candidate alloys for the canisters, both neutron absorption and corrosion resistance must be considered for this application. This work examines corrosion resistance of Ni-Cr-Mo-Gd alloys developed specifically for neutron absorption. The addition of Gd results in a secondary gadolinide phase (Ni5Gd) that significantly changes the corrosion properties. Testing was performed primarily in seawater at 30 °C. Seawater was selected as the most prevalent terrestrial brine and is characterized by a high chloride concentration. Various electrochemical corrosion techniques were carried out to evaluate Ni-Cr-Mo-Gd alloys with different Cr compositions and investigate the role of Ni5Gd phase on corrosion behavior. C22 was included as a benchmark material, due to the similarity in composition and the significant corrosion data available. Test results showed a tendency to passivate over time which is attributed primarily to dissolution of surface exposed Ni5Gd phase particles leaving primary phase exposed. Cross-sectional analysis indicated that dissolution could penetrate up to hundreds of micrometers deep under aggressive conditions. It was found that higher Cr variant (21.01%) showed much shallower impact, suggesting Cr prevented primary phase corrosion and thus reduced deeper Ni5Gd phase dissolution. Acid pickling of the specimens showed much less dissolution for the higher Cr material and suggested some primary phase dissolution for the low Cr specimen. Acid pickled specimens showed positive shifts in the repassivation potential, suggesting increased surface passivation.

Ultrasound application in alkaline pretreatment process of spodumene to improve particle floatability

Selective surface dissolution was found to be important in spodumene flotation. In this study, we proposed to introduce ultrasound into the pretreatment process to accelerate particle vibration and cavitation, as well as the migration of mineral surface components to solution. Micro-flotation results showed that the flotation recovery of spodumene can be 86.08% by ultrasound pretreatment, but only 39.30% by traditional mechanical agitation pretreatment. Compared with traditional mechanical agitation, ultrasonic pretreatment can shorten the pretreatment process, reduce the dosage of agents, reduce the mechanical agitation speed, and improve the efficiency of the pretreating process. Inductively coupled plasma analysis showed that, in the ultrasonic system, the amount of Li, Al, and Si species in the solution was twice as much as those in the traditional preprocessing system. Moreover, the scanning electron microscope results demonstrated a larger surface dissolution area in the ultrasonic system. X-Ray photoelectron spectroscopy results showed that the atomic concentration of Si species on the spodumene surface decreased, whereas the relative atomic concentrations of Li and Al species increased, indicating that the ultrasound effect strengthened the selective dissolution of elements on the mineral surface. The high-resolution spectra of O 1s showed that more collectors are adsorbed on the mineral surface treated by ultrasonic pretreatment.