Amount Of Dissolution Research Articles

Dissolution of Copper and Formation of IMC in Bulk Lead-Free Solders

Besides the popular reflow soldering practice, wave soldering is another established technique in the electronic packaging industry for obtaining the solder joints. In this study the dissolution behavior of copper and the growth of intermetallic compound (IMC) during wave soldering process have been investigated. The study involved two different solder compositions, viz. pure Sn and eutectic Sn–Ag solder. Dipping experiments were conducted for the temperature range of 221–300 °C and for dwell time starting form 5 s to 6 min. The average thickness of the intermetallic compound formed and the amount of copper dissolved was determined. Experimental results indicated that the amount and rate of copper dissolution were strongly affected by temperature of molten solder and dwell time. The initial rate of copper dissolution was very high but it decreased with time. Based on the experimental results, the kinetic parameters governing the dissolution of copper and growth of the IMC were determined for the two solders.

Study on leakage dissolution around the dam foundation of the Qingju Hydropower Station and its engineering influence on the dam

Leakage dissolution is one of the potential threats to the long-term operating safety of a dam. The aim of this paper is to analyze the characteristics of leakage dissolution around the dam foundation of Qingju Hydropower Station and evaluate its engineering influence based on laboratory testing and in situ monitoring. Comparative analysis of water samples in 20 representative positions shows that the bedrock of the dam foundation has been enduring obvious dissolution under the effects of the groundwater. In situ monitoring data of displacement and leakage during the period from 2005 to 2013 indicates that there has been no excessive deformation, obvious uneven settlement, or concentration leakage in these nine years, and; therefore, the leakage dissolution of the dam foundation has not resulted in critical danger to the safety of dam so far. However, with an annual amount of gypsum dissolution discharged by the drainpipes of about $$ 1.82 \times 10^{5}\,{\rm kg} $$ , long-term leakage dissolution may be hazardous, besides the higher content of SO4 2− than normal in the groundwater of the dam foundation caused by leakage dissolution may invoke some crystal corrosion and decrease the durability of the concrete structures. To guarantee the long-term safety of the dam, implementing grouting is proposed to prevent dissolution or slow down the dissolution rate on the basis of real-time monitoring and feedback.

Rock and mineral transformations in a fault zone leading to permanent creep: Interactions between brittle and viscous mechanisms in the San Andreas Fault

AbstractCreep processes may relax part of the tectonic stresses in active faults, either by continuous or episodic processes. The aim of this study is to obtain a better understanding of these creep mechanisms and the manner in which they change in time and space. Results are presented from microstructural studies of natural samples collected from San Andreas Fault Observatory at Depth borehole drilled through the San Andreas Fault, which reveal the chronology of the deformation within three domain types. (i) A relatively undeformed zone of the host rock reflects the first step of the deformation process with fracturing and grain indentations showing the coupling between fracturing and pressure solution. (ii) Shear deformation development that associates fracturing and solution cleavage processes leads to profound changes in rock composition and behavior with two types of development depending on the ratio between the amount of dissolution and deposition: abundant mineral precipitation strengthens some zones while pervasive dissolution weakens some others, (iii) zones with mainly dissolution trended toward the present‐day creeping zones thanks to both the passive concentration of phyllosilicates and their metamorphic transformation into soft minerals such as saponite. This study shows how interactions between brittle and viscous mechanisms lead to widespread transformation of the rocks and how a shear zone may evolve from a zone prone to earthquakes and postseismic creep to a zone of steady state creep. In parallel, the authors discuss how the creeping mechanism, mainly controlled by the very low friction of the saponite in the first 3–4 km depth, may evolve with depth.

Size-dependent reactivity of magnetite nanoparticles: a field-laboratory comparison.

Logistic challenges make direct comparisons between laboratory- and field-based investigations into the size-dependent reactivity of nanomaterials difficult. This investigation sought to compare the size-dependent reactivity of nanoparticles in a field setting to a laboratory analog using the specific example of magnetite dissolution. Synthetic magnetite nanoparticles of three size intervals, ∼ 6 nm, ∼ 44 nm, and ∼ 90 nm were emplaced in the subsurface of the USGS research site at the Norman Landfill for up to 30 days using custom-made subsurface nanoparticle holders. Laboratory analog dissolution experiments were conducted using synthetic groundwater. Reaction products were analyzed via TEM and SEM and compared to initial particle characterizations. Field results indicated that an organic coating developed on the particle surfaces largely inhibiting reactivity. Limited dissolution occurred, with the amount of dissolution decreasing as particle size decreased. Conversely, the laboratory analogs without organics revealed greater dissolution of the smaller particles. These results showed that the presence of dissolved organics led to a nearly complete reversal in the size-dependent reactivity trends displayed between the field and laboratory experiments indicating that size-dependent trends observed in laboratory investigations may not be relevant in organic-rich natural systems.

Crystallographic controlled dissolution and surface faceting in disordered face-centered cubic FePd

Abstract

Dissolution of Platinum Single Crystal Surfaces under Potential Cycling in Sulfuric Acid Solution

Pt dissolution is one of the most important topics in Polymer Electrolyte Fuel Cell (PEFC) field because of the origin of the Pt nanoparticle growth, which results in a cell performance loss of PEFC.1 Recent reports showed a submonolayer of Pt dissolution occurs under potential cycling conditions simulating the PEFC operation in acidic environments.2Surface structural controls of Pt nanoparticles against Pt dissolution under potential cycling are a key point to improve the corrosion resistance of Pt surface. We investigated the effect of crystal orientations on the dissolution of Pt surface using Pt(100), Pt(110), and Pt(111) single crystal electrode. Commercial Pt(100), Pt(110) and Pt(111) single crystal electrodes were used as the specimen. The specimens were polished down to 0.25 mm diamond paste, annealed with an oxygen-hydrogen burner for 2 h, and cooled in a stream of Ar gas, prior to the electrochemical measurements. Cyclic voltammetry (CV) at single crystal surfaces was conducted for 100 cycles to examine Pt dissolution. The potential range of CV was from 0.5 to 1.0, 1.2, and 1.4 V. 0.5 M H2SO4solution at 298 K open to air was used as the electrolyte. After 100 cycles of CV, the solutions were analyzed with ICP-MS for the quantification of amount of dissolved Pt. The surface morphology of Pt single crystal electrodes was observed by electrochemical STM measurements. Figure 1 shows STM images of Pt(100), Pt(110), and Pt(111) single crystal surfaces after the anealing, and the cross section height profiles along the white arrows. The surfaces of Pt(100), Pt(110), and Pt(111) single crystal electrodes were composed of atomic height steps and smooth terraces. The saw-like step structures were observed at Pt(100) and Pt(110) surface. In addition, Pt(110) surface was relatively roughened. CVs at Pt(100), Pt(110), Pt(111) single crystal, and polycrystalline Pt surfaces were shown in Fig. 2. The voltammograms of single crystal electrodes exhibited characteristic hydrogen adsorption/desorption peaks between 0.05 and 0.4 V. These peaks were not sharp because of a exposure in air atmosphere during the setup of electrochemical measurements but similar to those reported in the literatures.3This demonstrates well-controlled surface structures of single crystal electrodes were obtained. Figure 3 shows the amount of Pt ions dissolved from single crystal surfaces under 100 cycles of CV in 0.5 M H2SO4solution. The horizontal axis means the upper potential limit of CV. The dissolved amount at Pt(100) and Pt(110) surfaces was almost the same, and increased with rising the upper potential limit. Pt(111) surface hardly dissolved at potentials below 1.2 V, and the amount of dissolution at this surface in the potential range of 0.5–1.4 V was about a half of that at Pt(100) and Pt(110) surfaces. This result indicates Pt(111) surface has the highest corrosion resistance among the three single crystal electrodes examined.1. Y. Shao-Horn, W. C. Sheng, S. Chen, P. J. Ferreira, E. F. Holby, and D. Morgan, Top Catal, 46, 285 (2007).2. Y. Sugawara, T. Okayasu, A. P. Yadav, A. Nishikata, and T. Tsuru, J. Electrochem. Soc., 159(11), F779 (2012).3. N. M. Marković, and P. N. Ross, Surf. Sci. Rep., 45, 117(2002).Caption list:Figure 1 STM images of Pt(100), Pt(110), and Pt(111) single crystal surfaces after the anealing treatment.Figure 2 CVs at Pt(100), Pt(110), Pt(111) single crystal, and polycrystalline Pt surfaces at 10 mVs-1 in 0.5 M H2SO4solution.Figure 3 Amount of Pt ions dissolved from single crystal surfaces as a function of the upper potential limit of CVs. The CVs were carried out for 100 cycles at 10 mVs-1 in 0.5 M H2SO4 solution.

In-Situ Analysis of Scan Rate Effect on Pt Dissolution Under Potential Cycling

Introduction Degradation of a polymer electrolyte fuel cell (PEFC) caused by platinum (Pt) dissolution on the cathode remains a challenge for its durability in long-term applications. The cathode is repeatedly exposed to high potentials during ON-OFF cycles, which accelerates Pt dissolution. Sugawara et al. [1] reported that Pt dissolution was affected by the scan rate at which potential cycling was performed. The ex-situ analysis by ICP-MS[1]provided an average evaluation of the dissolution amount during one cycle or a given time period. It would be more helpful for specification of the dissolution mechanism in different potential regions, if the dissolution rate could be traced simultaneously with the dissolved species being identified. For this purpose, we employed a channel flow double electrode as an in-situ monitoring method, and investigated the dissolution behavior on a Pt electrode that underwent potential cycling at different scan rates. Experimental A channel flow double electrode (CFDE) consisted of a working electrode (WE) and a collector electrode (CE). The collection number (N) of the channel flow cell was 0.3, given the geometries shown in Figure 1.[2] In a prior work,[3] we proved that the submonolayer-level Pt dissolution on the WE under potential cycling could be detected on the CE. The current responses on the CE (collector current, I C) could be used as a detection parameter, from which the dissolution rate on the WE can be calculated.In this work, the WE was a thin film of Pt electroplated on a gold (Au) substrate. The solution was 0.5 M H2SO4 deaerated by argon gas. The average flow rate of the solution was 10 cm/s. The WE underwent potential cycling between 0.07 and 1.4 V (vs. SHE) at 1, 5, 20, 100, and 200 mV/s. A CE of Au was set at 0.3 V at which both Pt2+ and Pt4+ were reduced to Pt. Dissolution of Pt4+ was detected on a CE set at 0.7 V by reducing Pt4+ to Pt2+. All measurements were performed on a multi-channel potentiostat (PS-08, TOHO Technical Research, Japan) at room temperature. Results and discussion During a slow anodic scan (5 mV/s), both Pt2+ dissolution below 1.0 V and Pt4+ dissolution above 1.2 V are suppressed. This decline of Pt dissolution is due to surface passivation by Pt oxide, similar to that in potentiostatic conditions.[4] This result also suggests that surface passivation of Pt requires an excessive polarization such as a slow anodic scan.Interestingly, dissolution of Pt4+ is preponed as we slower the scan rate. Figure 2 shows the CVs of the WE (at 1 mV/s and 20 mV/s) and the I C recorded during an anodic scan on a CE set at 0.7 V. When the WE is scanned at 1 mV/s, the I C, representing detection of Pt4+, starts to increase at a lower potential. This shift of on-set potential of Pt4+ dissolution is only observed during a slow anodic scan. During a fast anodic scan (200 mV/s), the Pt4+ dissolution still starts around 1.2 V, though the dissolution rate tends to decrease. Thus, the place exchange between the O and Pt atoms[5] seems necessary for Pt4+dissolution above 1.2 V.However, the cathodic dissolution of Pt2+ from reduction of PtO2 is enhanced during a fast cathodic scan. The reduction rate of PtO2 is proportional to scan rate. As a result, more Pt2+ is produced when the PtO2 is being reduced at a faster cathodic potential shift. Therefore, in an operating PEFC, where the potential sweep on the cathode may be faster than 200 mV/s, cathodic dissolution is expected to be more severe. Interestingly, the ratio between cathodic dissolution of Pt2+ and reduction of PtO2in a cathodic scan decreases as we increase the scan rate. Reference Y. Sugawara, A.P. Yadav, A. Nishikata, T. Tsuru, ECS Trans., 16 (24), 117 (2009).H. Matsuda, J. Electroanal. Chem., 16, 153 (1968).Z. Wang, E. Tada, and A. Nishikata, J. Electrochem. Soc., 161(4), F380 (2014).X.P. Wang, R. Kumar, D.J. Myers, Electrochem. Solid-State Lett., 9, A225 (2006).G. Jerkiewicz, G. Vatankhah, J. Lessard, M.P. Soriaga, Y.S. Park, Electrochim. Acta., 49, 1451 (2004).

Simulation of rock salt dissolution and its impact on land subsidence

Abstract. Extensive land subsidence can occur due to subsurface dissolution of evaporites such as halite and gypsum. This paper explores techniques to simulate the salt dissolution forming an intrastratal karst, which is embedded in a sequence of carbonates, marls, anhydrite and gypsum. A numerical model is developed to simulate laminar flow in a subhorizontal void, which corresponds to an opening intrastratal karst. The numerical model is based on the laminar steady-state Stokes flow equation, and the advection dispersion transport equation coupled with the dissolution equation. The flow equation is solved using the nonconforming Crouzeix–Raviart (CR) finite element approximation for the Stokes equation. For the transport equation, a combination between discontinuous Galerkin method and multipoint flux approximation method is proposed. The numerical effect of the dissolution is considered by using a dynamic mesh variation that increases the size of the mesh based on the amount of dissolved salt. The numerical method is applied to a 2-D geological cross section representing a Horst and Graben structure in the Tabular Jura of northwestern Switzerland. The model simulates salt dissolution within the geological section and predicts the amount of vertical dissolution as an indicator of potential subsidence that could occur. Simulation results showed that the highest dissolution amount is observed near the normal fault zones, and, therefore, the highest subsidence rates are expected above normal fault zones.

Solution-Mediated Polymorphic Transformation of FV Sulphathiazole

The solution-mediated polymorphic transformation of FV sulphathiazole was investigated in ethanol at 10 °C. Powder X-ray diffraction (PXRD) identified the transformation product as a mixture of FII and FIV sulphathiazole. This mixture remained stable in solution at 10 °C with agitation for 24 h. In situ temperature controlled optical microscopy enabled visualization of the transformation in real time, allowing elucidation of the transformation mechanism. A modest amount of dissolution of FV sulphathiazole preceded the nucleation of FII and FIV crystals, which were detected simultaneously. Thereafter, these polymorphs grew rapidly. Experimental evidence is presented for a mechanism, whereby nucleation of FII and FIV was initiated on the roughened surface of the dissolving FV crystals, without any indication for a spatially extended structural relationship between the host form V and the nucleating phases. Subsequent growth of FII and FIV crystals consumed the remaining FV crystals completing the dissolution-recrystallization mechanism.

Seawater δ7Li: A direct proxy for global CO2 consumption by continental silicate weathering?

The fractionation of stable Li isotopes (6Li, 7Li) has become a promising proxy for assessing changes related to continental silicate weathering patterns. Recently, the first complete record of Cenozoic seawater Li isotopic composition (δ7Li) was reported (Misra and Froelich, 2012, Science 335, 818–821) showing a stepwise increase of +9‰ over the last 56Ma. This increase was attributed to a general change in continental silicate weathering behavior caused by tectonic uplift. In particular, the low global average riverine δ7Li inferred for the Paleocene–Eocene boundary was explained by congruent silicate weathering of primary silicate minerals, which is inconsistent with the stoichiometry of secondary minerals and the resultant water chemistry.In this study, we present a novel reactive transport modeling approach that explicitly includes Li isotopic fractionation to assess alternative geochemically-constrained interpretations that do not rely on congruent weathering. Simulations show that riverine δ7Li is mainly controlled by the subsurface residence time, the corresponding weathering intensity, and the concentration of a river's suspended load. Based on these factors, we suspect that the low δ7Li observed at the Paleocene–Eocene boundary was inherited from a high weathering intensity with predominant weathering of previously formed secondary mineral phases (e.g., clays, oxides) having low δ7Li values. Moreover, we conclude that the Cenozoic δ7Li increase was caused by an increasing amount of primary silicate mineral dissolution inherited from an increasing suspended river load concentration and a decreasing weathering intensity both likely induced by tectonic uplift. In contrast, Cenozoic cooling and corresponding pCO2 and precipitation variations do not seem to have a distinct control on the Cenozoic δ7Li record.Finally, our simulations revealed a close relation between δ7Li and CO2 consumption by silicate weathering implying that the Cenozoic seawater δ7Li record could be potentially used to quantify such CO2 consumption through time. However, more experimental and modeling work is required to quantify the correlation between seawater δ7Li and global CO2 consumption by silicate weathering. Key parameters are the temperature-dependent thermodynamic properties of specific Li-bearing primary and secondary minerals (e.g., crystallographic Li substitution reaction, maximum Li substitution, Li solubility, Li isotopic fractionation factor) as well as the determination of global average subsurface and river discharges through time.

Development of permanganate assisted manganese phosphate coating on mild steel

Manganese phosphate coatings are widely used as pretreatment for corrosion and wear resistance of numerous automotive components. Manganese phosphating formulations are established with various additives to improve the coating weight besides achieving the required amount of iron dissolution in a shorter time. The aim of our investigation is to use permanganate as an additive to increase iron dissolution and to achieve subsequent improvement in the quality of manganese phosphate coating. Manganese carbonate, phosphoric acid, nitric acid are used to create a basic formulation in which permanganate concentration is varied. The composition of the final formulation is optimised by giving due consideration to higher iron dissolution and improved coating weight. The resultant coating is characterised with polarisation, electrochemical impedance spectroscopy (EIS), FT-IR, XRD, SEM and EDX. The kinetics of the coating formation is also followed using potential–time measurement for all the experimental baths. Kinetic studies showed earlier attainment of point of incipient precipitation of manganese phosphate coating in the optimised formulation when compared to other formulation under investigation. The study revealed that the addition of KMnO4 in the manganese phosphating bath enabled an increase in the rate of metal dissolution, and enrichment of ferrous ion concentration at the metal/solution interface thus, favoured precipitation of corrosion and wear resistant Hureaulite ((Mn,Fe)5H2(PO4)4.4H2O). For a given coating weight, addition of KMnO4 substantially reduced the processing time.

(Invited) Knitted Electrochemical Capacitors Via Natural Fiber Welded Electrode Yarns

This report presents a novel ionic liquid-based method for fabricating flexible double layer supercapacitor electrodes utilizing natural substrates. It also investigates the performance of these yarns knitted as fabrics, and with other cellulose-based fibers welded with carbon particles. Scanning electron microscopy, mechanical properties testing, conductivity and other electrochemical testing are performed to characterize both individual yarns and knitted devices. Natural fiber welding (NFW) is a process that uses controlled amounts of ionic liquids (ILs) and molecular co-solvents to selectively swell and mobilize biopolymers in fibrous, natural materials for functional (chemical and physical) modification.1-4 NFW processes control and minimize the amount of dissolution to fibrous natural substrates. By carefully regulating the ratio of solvent to substrate, solvent efficacy, time, temperature, pressure, location of solvent exposure, etc., hydrogen bonding networks are reconfigured and extended by only mobilizing the outer shell of individual fibers. The result is that fibers are essentially ‘welded’ together while the cores maintain their native states. In this work, the fiber welding process has been modified to incorporate carbon materials into the biopolymer matrix, delivering flexible carbon containing yarns for wearable supercapacitor applications. To determine whether the material is a viable candidate for wearable supercapacitors, the welded carbon-yarns are coated with polymer electrolyte, twisted with stainless steel yarn (current collector) and electrochemically tested in a symmetric configuration through cyclic voltammetry, galvanostatic cycling, and impedance spectroscopy. Electrochemical testing performed on samples randomly selected across the entire length of yarn electrodes (typically 10-20 ft in length) yielded 8-12 mF/cm, comparable with previously reported literature. However, when the cotton is twisted with steel prior to coating, the capacitance dramatically increased to 45 mF/cm. Fabrication can have a dramatic effect on the electrochemical performance. Because mechanical properties of the cellulose yarns play a crucial role when knitting these capacitive yarns into full fabrics, tensile testing of the yarns pre- and post- welding was conducted. With each yarn, an improved strength was observed at the expense of elasticity; viscose and linen showed the most notable increases in strength (107%, 78% respectively) and toughness (both 22%). Though many of the cotton yarn electrodes showed favorable electrochemical performance, none were machine-knittable. The linen, viscose, and bamboo yarn supercapacitors were successfully machine knitted at Drexel’s Shima Seiki Haute Tech Lab. We currently attribute this to the length of the fibers playing a role in flexibility and mechanical strength within the yarn. More work is currently underway to explain this process, and fabricate a welded cotton yarn that can be knitted. To date, we have demonstrated a coating process that is repeatable and scalable (coating hundreds of feet at a time), inexpensive, and delivers competitive performance to similar reports in the literature. Given that composites are constructed from a truly ‘green’ substrate (cotton, bamboo, etc.) and utilizing a nonfluorinated binder (cellulose from cotton), we believe this to be a major breakthrough for the prospects of wearable energy storage.5-7 Acknowledgements: Portions of this work were funded by the Air Force Office of Scientific Research. Any opinions, findings, conclusions or recommendations expressed in the material are those of the authors and do not necessarily reflect the views of the U.S Navy or U.S Air Force. K. Jost acknowledges support from the DoD National Defense Science and Engineering Graduate (NDSEG) Fellowship.

An online method to measure mass transfer of slug flow in a microchannel

Physical absorption of CO2 bubbles under slug flow has been studied in a T-junction microchannel. Based on the absorption rate of gas bubbles, an online photographic method is proposed to determine the mass transfer coefficients. Validity of this method is verified by evaluating bubble expansion due to pressure drop and by comparing the results with literature. The effect of fluid properties on the mass transfer has also been studied with ethanol solutions, which shows that mass transfer coefficient increases with the increase of ethanol concentration. The amount of gas absorbed during the bubble formation process has been measured to be about 2–10% of the inlet gas phase, and is found to linearly scale with the maximum mass transfer rate. For each fluid system, the initial dissolution rates of bubbles differ very little for short contact distance, whereas, the final amount of dissolution only depends on the residence time.

The fluid mechanics of dissolution trapping in geologic storage of CO2

AbstractSequestration of carbon dioxide by injecting it into the deep subsurface is critical to successful mitigation of climate change by reducing anthropogenic emissions of greenhouse gases into the atmosphere. To achieve this we must understand how CO2 moves in the subsurface. Many interesting fluid mechanics problems emerge. Szulczewski, Hesse & Juanes (J. Fluid Mech., vol. 736, 2013, pp. 287–315) focus on one critical aspect, namely the dissolution of CO2 into the fluid resident in the subsurface and the flow dynamics that ensue. Even for this single problem, an elegant analysis identifies seven behavioural regimes that control the amount and timing of dissolution.

The Effect of Aquifer/Caprock Interface on Geological Storage of CO2

Abstract The migration of CO 2 stored in deep saline aquifers depends on the morphology of the top of the aquifer. Topographical highs, such as anticlines, may trap CO 2 and limit the distance migrated, or elevated ridges may provide pathways enabling CO 2 to migrate further from the injector. For example, seismic data of the Utsira formation at the Sleipner storage site indicates that a branch of the CO 2 plume is moving to the north [1] . It is therefore important to study the interface between the aquifer and the caprock when assessing risk as CO 2 storage sites. Undulations in the top surface of an aquifer may either be caused by sedimentary structures [2] , or by folding. In addition, irregularities may be generated by faulting [2] . Large-scale features are detected using seismic data (i.e. structures with amplitudes greater than 10 m), and such structures will generally be included in reservoir or aquifer models. However, smaller- scale features could also have an effect on a CO 2 plume migration, and this is the topic of our study. We have conducted simulations in models with a range of top-surface morphology, and have examined the distance migrated and the amount of dissolution. The results from this study suggest that the effects of sub-seismic variations in the topography of the aquifer/caprock interface are unlikely to have a significant impact on the migration and dissolution of CO 2 in a saline aquifer, compared with tilt or permeability anisotropy. The results were most sensitive to the kv/kh ratio during the injection period.

Effect of Temperature on Gold Dissolution in Acidic Media

Temperature has a tremendous effect on the rate and amount of gold dissolution. In potentiodynamic experiments the total amount of dissolved gold increases by a factor of 4.5 when the temperature is increased from 25 to 75°C. Moreover, the previously reported correlation between the onset of oxide formation and the commencement of the dissolution process is found to be correct for all studied temperatures. Negative shift in the advent of oxidation is accompanied by a similar shift in the dissolution onset potential. Similarly, the dissolution rate rises significantly with temperature during potentiostatic and galvanostatic polarization steps. A correlation between the temperature-dependent oxygen evolution reaction (OER) and gold dissolution is found. Arrhenius plots for the OER and gold dissolution are used to obtain information on the apparent activation energy EA for both processes. It is found that for OER and Au dissolution EA = 57 kJ mol−1. The later finding suggests that there is a common intermediate for both reactions, the formation of which constitutes the rate-determining step.

Theoretical and Experimental Study of Controls on CO2 Dissolution and CH4 Outgassing Rates

Abstract Understanding CO 2 dissolution is significant to the development of CO 2 geological storage. It allows us to more accurately predict the extent of the CO 2 plume. It also provides a better estimate of the trapping mechanisms to assist in interpreting the monitoring observations and to assess the risk of CO 2 leakage. When CO 2 is injected into methane-saturated brine aquifers, the dissolution process has been observed to be accompanied by CH4 outgassing from the pore water, which affects the properties of the gas phase and in turn CO 2 migration. Currently available commercial and academic multiphase flow simulators (such as CMG-GEM and TOUGH2) assume instantaneous equilibrium of CO 2 dissolution within a single grid cell, which introduces the maximum amount of dissolution and methane outgassing. The incomplete mixing due to the presence of a porous media and subsurface heterogeneity reduces CO 2 dissolution rates by orders of magnitude compared to the well-mixed case. In this study, we investigate the effects of mixing-controlled CO 2 dissolution and of methane outgassing on CO 2 migration in the subsurface with the help of numerical simulations and laboratory experiments. We first developed numerical pore-scale models to demonstrate that the mass transfer rate of CO 2 depends on the gas saturation and the aqueous CO 2 concentration and that the mass transfer rate can be written as a power-law function of the CO 2 saturation. Based on the mass transfer rate obtained from the pore-scale models, we then simulated the two-phase Darcy's flow in a column test considering the dynamic dissolution process. Results show that the CO 2 migration is affected by the mass transfer rate into the aqueous phase. Even within a small scale of several meters, which is the typical grid size used in simulation of carbon storage in the field, the assumption of instantaneous equilibrium may not be valid. When the mass transfer time scale is much larger than the advection time scale, the CO 2 -water flow acts as an immiscible flow, and the amount of CO 2 dissolved within the advection time scale is negligible. As the mass transfer rate increases, the flow approaches the scenario with instantaneous equilibrium. Modeling and experiment presented here confirm the well-known observations that CO 2 dissolution into pore water introduces a retardation effect on CO 2 breakthrough. When the mass transfer rate of CO 2 into pore water increases, the CO 2 breakthrough is delayed, decreasing the extent of the CO 2 plume.

Combination of CO2 geological storage with deep saline water recovery in western China: Insights from numerical analyses

CO2 geological storage, when combined with deep saline water recovery (CO2-EWR), not only achieves the relatively secure storage of CO2 that was captured from the coal chemical industry, due to lower pressure, but also enhances saline water for drinking and industrial or agricultural utilization. This storage will undoubtedly become a win–win choice for the enhancement of energy security and for the promotion of regional development in China, particularly for western regions with a relative shortage of water resources and a more fragile ecological environment. In this paper, a three-dimensional injection–extraction model is established that uses the TOUGH2/ECO2N program according to typical formation parameters of a coal chemical industry in the Xinjiang Uyghur Autonomous Region. Numerical results showed that under the guarantee of sufficient water conditions, 1.73×108tons of saline water could be produced when the CO2-EWR is adopted. Well arrangements and formation parameters are also analyzed, and the following conclusions can be drawn: arrangements of pumping wells, such as pumping well number, pumping rate and distance, have considerable influences on the reservoir pressure, and in addition, the sensitivity of pressure on the distance and pumping rate decreases as their values increase. In view of these features, it is necessary to find an optimal point to achieve the best combination of pressure, the leakage time and the amount of dissolution. Formation parameters primarily control the mechanism of CO2 migration and dissolution. Salinity in the salt water has the greatest impact on CO2 dissolution trapping followed by permeability and porosity. The arrival time that is allowable for saline water production primarily depends on porosity followed by the permeability ratio and the arrangements of pumping wells. The reservoir pressure change that is caused by parameters is not obvious compared with setting pumping wells. Overall, CO2-EWR technology is a potential strategic choice for China, particularly in western regions. Additionally, the analysis results provide a reliable guide and reference for CO2 storage site selection, as well as the practical arrangements of wells.

Biological Control on Acid Generation at the Conduit-Bedrock Boundary in Submerged Caves: Quantification through Geochemical Modeling

No-mount Cave, located in Wekiwa Springs State Park in central Florida, USA, is an aphotic, submerged, freshwater cave in which large colonies of sulfur-oxidizing bacteria live in filamentous microbial mats. Upwardly discharging groundwater enters the cave from the Upper Floridan aquifer, specifically the Eocene-aged Ocala Limestone. We undertook a combined field, laboratory, and modeling study in which we sought to determine the amount of calcite dissolution attributable to the generation of protons by microbially mediated sulfide oxidation. The chemical compositions of groundwater within the limestone formation collected through a newly designed sampling device and of water in the cave conduit were used in geochemical modeling. We used the reaction-path model PHREEQCI to quantify the amount of calcite dissolution expected under various plausible scenarios for mixing of formation water with conduit water and extent of bacterial sulfide oxidation. Laboratory experiments were conducted using flow-through columns packed with crushed limestone from the study site. Replicate columns were eluted with artificial groundwater containing dissolved HS- in the absence of microbial growth. Without biologically mediated sulfide oxidation, no measurable calcite dissolution occurred in laboratory experiments and no additional amount of speleogenesis is expected as formation water mixes with conduit water in the field. In contrast, significant calcite dissolution is driven by the protons released in the biological transformation of the aqueous sulfur species. Although a range of results were calculated, a plausible amount of 158 mg Ca2+ released to conduit water per liter of groundwater crossing the formation-conduit boundary and mixing with an equal volume of conduit water was predicted. Our modeling results indicate that significant cave development can be driven by microbially mediated sulfide oxidation under these hydrogeochemical conditions.ž Keywords: calcite dissolution, microbial sulfide oxidation, geochemical model. DOI: 10.3986/ac.v42i2-3.663

Enhancement of solubility, dissolution release profile and reduction in ulcerogenicity of piroxicam by inclusion complex with skimmed milk

Context: Piroxicam (PXM), a non-steroidal anti-inflammatory drug which is poorly soluble in water and ulcerogenic. Milk has been used against the gastric disturbances caused by non-steroidal anti-inflammatory drugs. In this study, skimmed milk (SKM) is used as the carrier for inclusion complex (IC) due to its surface active agent and amino acid content.Purpose: To enhance the solubility, dissolution rate and prevent ulcerogenicity of PXM though IC with SKM.Methods: IC of PXM were prepared with SKM by solvent evaporation method using rota evaporator and were evaluated for solubility, dissolution, solid state characterization, drug excipient interaction, rat intestinal permeation, ulcerogenicity and histopathological studies.Results: Solubility of PXM was enhanced 2.5 times with IC. The dissolution release and amount of PXM permeated through rat small intestine was enhanced significantly with IC. Decreases in the gastric lesion index values of IC were observed than physical mixture (PM) and free PXM. The histopathological studies revealed significant reduction in ulceration in rat stomach after treatment with IC.Conclusion: It is concluded that SKM is a good carrier to prepare IC of PXM for oral administration.