Dissolution Of Amorphous Silica Research Articles

Autogenous self-healing of ultra-high-performance fiber-reinforced concrete with varying silica fume dosages: Secondary hydration and structural regeneration

Secondary hydration is the main driving force of autogenous self-healing and directly impacts the closure of cracks in damaged cementitious materials. In fiber-reinforced cement composites, secondary hydration also dominates the regeneration of the fiber-matrix interface during the self-healing processes. As an important factor influencing the cement hydration, silica fume (SF) addition can be crucial to the self-healing performance of cementitious materials and composites. In this paper, the effect of SF on the autogenous self-healing of ultra-high-performance fiber-reinforced concrete was investigated. With a ≥20% SF addition, the secondary hydration the cement matrix adjacent to the cracks was accelerated. The dissolution of amorphous silica and the formation of Si-containing healing phases was observed. These effects predominated the closure of the mouth and the inner part of the cracks. SF addition also enhanced the regeneration of fiber-matrix interface by promoting the growth of self-healing products in these areas. The closure of cracks and the regeneration of fiber-matrix interface are both responsible for the restoration of flexural properties.

Amorphous silica dissolution kinetics in freshwater environments: Effects of Fe2+ and other solution compositional controls

The availability of dissolved silicon (DSi) exerts an important control on phytoplankton communities in freshwater environments: DSi limitation can shift species dominance to non-siliceous algae and increase the likelihood of harmful algal blooms. The availability of DSi in the water column in turn depends on the dissolution kinetics of amorphous silica (ASi), including diatoms frustules and phytoliths. Here, batch dissolution experiments conducted with diatom frustules from three diatom species and synthetic Aerosil OX 50 confirmed the previously reported non-linear dependence of ASi dissolution rate on the degree of undersaturation of the aqueous solution. At least two first-order dissolution rate constants are therefore required to describe the dissolution kinetics at high (typically, ≥0.55) and low (typically, <0.55) degrees of undersaturation. Our results further showed aqueous ferrous ion (Fe2+), which is ubiquitous in anoxic waters, strongly inhibited ASi dissolution. The inhibition is attributed to the preferential binding of Fe2+ to Q2 groups (i.e., surface silicate groups bonded to the silica lattice via two bridging oxygen) which stabilizes the silica surface. However, further increasing the aqueous Fe2+ concentration likely catalyzes the detachment of Q3 groups (i.e., silicate groups bonded to the silica lattice via three bridging oxygen) from the surface. Overall, our study illustrates the manyfold effects the aqueous solution composition, notably the inhibition effect of Fe2+ under anoxic conditions, has on ASi dissolution. The results help to explain the controversial redox dependence of DSi internal loading from sediments, which is vital to quantitatively understanding silicon (Si) cycling in freshwater systems.

Fluid-rock interaction during low-salinity water flooding of North Sea chalks

The injection of low-salinity water into carbonate oil-reservoirs has been the subject of much interest as a potential method to enhance oil recovery (EOR). Low salinity water injection has been shown to alter the geochemical equilibrium in the reservoir, and consequentially potentially change the surface wettability of the reservoir rocks. Nevertheless, the geochemical reaction pathways during low salinity water flooding in carbonates remain poorly understood.In order to provide a more comprehensive insight into the geochemical reaction pathways, a series of batch and core-flooding experiments have been performed at 70 °C. The experiments made use of analogous and authentic reservoir material from the Danish North Sea oil reservoirs, and brines with chemical composition similar to the formation water and injection water available in offshore flooding operations.Results show that both mineral dissolution and the precipitation of new secondary phases can accurately describe the geochemical changes observed in the experimental effluents during the course of a low-salinity water core-flooding scenario.The dissolution of amorphous silica (SiO2) present in the chalk, and the precipitation of a Mg–Si clay mineral, identified here as sepiolite, are key reactions that take place during low-salinity water core-flooding in chalks. The suggested geochemical pathway was successfully fitted by a simplified geochemical simulation which can accurately describe the experimental observations.Surface reactions which take place during modified-salinity water flooding were put into perspective by quantifying their contribution to the overall effluent composition.

Amorphous Silica Dissolution Kinetics in Freshwater Environments: Effects of Fe2+ and Other Solution Compositional Controls

Amorphous Silica Dissolution Kinetics in Freshwater Environments: Effects of Fe2+ and Other Solution Compositional Controls

Correction to: Enhancement of Amorphous Silica Dissolution by Interaction With Six-Membered Ring Heterocyclic Compounds

This article was updated to fix formatting errors in Eqs. 1, 2 and 3 introduced in the production process.

Geochemistry of vapor-dominated hydrothermal vent deposits in Yellowstone Lake, Wyoming

Yellowstone Lake hydrothermal vent systems have been studied using ROV assets to better understand the chemical and mineralogical evolution of the sublacustrine sediments through which the hot spring fluids discharge to the lake floor. Here we focus on the deposits/alteration and coexisting vent fluid chemistry associated with the Deep Hole on the lake floor, east of Stevenson Island. Remote in its location, at 120 m below the lake surface, this region in the northeast portion of Yellowstone Lake is associated with numerous hydrothermal vents and hot springs, providing evidence of high-temperature fluid-mineral interaction and phase separation phenomena. Vapor-dominated hydrothermal fluids issuing from Deep Hole vents attain temperatures in excess of 150 °C and are enriched in magmatically derived H2S and CO2. Upon mixing with lake water in the root zone of the hydrothermally active vents, the dissolved gases render the mixed fluid, both acidic and reducing, effectively transforming diatomaceous sediment, with detritally sourced Al and Fe components, to an alteration assemblage dominated by kaolinite, pyrite, and lesser boehmite. These alteration processes have been modeled by computer based simulations, coupling fluid flow and mineral dissolution kinetics, to provide insight on the temporal evolution of the vent system. Results predict rapid dissolution of amorphous silica. The magnitude and rate of silica loss, facilitated by the continuous influx of acidic source fluids, yields an increasingly silica poor alteration mineral sequence with time, characterized by quartz, followed by kaolinite and ultimately boehmite. These data are consistent with the observed decrease in SiO2/Al2O3 ratio of the vent deposits with increasing abundance of trace immobile elements, suggesting significant mass loss with reaction progress. Pyrite is predicted to form from sulfidation of magnetite, with noteworthy decrease in magnetic intensity, as measured for hydrothermally altered sediment in the near-field vent environment. Moreover, hydrogen isotope compositional data for kaolinite, together with δD vent fluid data, suggest temperatures in keeping with the high temperatures measured for the vent deposits and discharging fluid, while supporting the potential use of kaolinite as a geothermometer. The predicted and observed transformation of silica-rich protolith to kaolinite, boehmite, and pyrite underscores the large scale dissolution and removal of silica, with possible implications for the temporal evolution of vent deposits on the lake floor in the Stevenson Island Deep-Hole region.

Enhancement of Amorphous Silica Dissolution by Interaction with Six-Membered Ring Heterocyclic Compounds

AbstractSix-membered ring heterocyclic compounds are widely present in the Earth's surface environments as biological organic molecules composed of soil organic matter including plant and microbial residues, while little is known about their effect on the dissolution of silicate minerals including amorphous silica. To evaluate the effect of these biological molecules on amorphous silica dissolution, dissolution experiments were carried out by the flow-through method using 0.1 g of amorphous silica and 0.1 mM NaCl electrolyte solutions containing 0.0, 0.1, 1.0, or 10.0 mM of the heterocyclic compounds, piperidine (pK = 11.12), pyridine (pK = 5.25), or pyridazine (pK = 2.33), at a pH of 6, 5, or 4. Additionally, adsorption experiments of the compounds on the amorphous silica surface were performed to confirm the adsorption affinity for the amorphous silica surface. The results demonstrated that these heterocyclic compounds enhance the dissolution rate of amorphous silica in the following order: piperidine &gt; pyridine &gt; pyridazine. When 10.0 mM solutions were used, the heterocyclic compounds enhanced greatly the dissolution rate up to enhancement factors of 6.0 to ~14.8, 5.0 to ~14.0, and 1.0 to ~2.6 through an interaction of piperidine, pyridine, and pyridazine, respectively, in the pH range of approximately 6 to ~ 4. The adsorption experiments indicated that the heterocyclic compounds exhibited significant adsorption affinity for the amorphous silica surface as follows: piperidine &gt; pyridine &gt; pyridazine, which was consistent with the order of their effects on the dissolution enhancement. The geochemical calculation revealed that this order of enhancement was in good agreement with the concentrations of cationic species of heterocyclic compounds at corresponding pH conditions. Consequently, the enhancement of amorphous silica dissolution is likely to be influenced by the electrostatic complexation of the cationic species of the heterocyclic compounds with the negative &gt;SiO– sites on the amorphous silica surface.

Numerical simulation of the initial particle parking structure of cement/geopolymer paste and the dissolution of amorphous silica using real-shape particles

Many particle-based numerical models have been used to simulate the hydration process of cementitious materials. Most of those models employ regular shape particles, like the commonly used spheres, to represent cement, slag, or fly ash, which neglects the influence of particle shape. To deal with this issue, this study extended the Anm material model and used irregular shape particles to simulate the initial particle parking structures of cement/geopolymer pastes. The irregular shapes of cement, slag and fly ash particles were characterized by spherical harmonic series. Compared to the initial particle structures simulated using spherical particles, those using irregular shape particles had total surface areas and bulk specific surface areas with up to 37.40% and 36.84% larger, respectively. However, the pore size distributions of the simulated initial particle structures did not show significant influence of particle shape. As a demonstration to illustrate the influence of particle shape on dissolution, the initial particle parking structure of amorphous silica in alkaline solution was generated using irregular shape particles, and was used as input to simulate the dissolution of silica particles. The Lattice Boltzmann method was used to simulate the transport process of aqueous ions and thermodynamics was employed to consider the rate of dissolution of silica. The dissolved fractions of silica at different temperatures in the simulations agreed well with experimental measurements. The influences of continuous stirring, concentration of alkali and particle shape on the dissolution kinetics of silica were investigated numerically.

Secondary structure and dynamics study of the intrinsically disordered silica-mineralizing peptide P5 S3 during silicic acid condensation and silica decondensation.

The silica forming repeat R5 of sil1 from Cylindrotheca fusiformis was the blueprint for the design of P5 S3 , a 50-residue peptide which can be produced in large amounts by recombinant bacterial expression. It contains 5 protein kinase A target sites and is highly cationic due to 10 lysine and 10 arginine residues. In the presence of supersaturated orthosilicic acid P5 S3 enhances silica-formation whereas it retards the dissolution of amorphous silica (SiO2 ) at globally undersaturated concentrations. The secondary structure of P5 S3 during these 2 processes was studied by circular dichroism (CD) spectroscopy, complemented by nuclear magnetic resonance (NMR) spectroscopy of the peptide in the absence of silicate. The NMR studies of dual-labeled (13 C, 15 N) P5 S3 revealed a disordered structure at pH 2.8 and 4.5. Within the pH range of 4.5-9.5 in the absence of silicic acid, the CD data showed a disordered structure with the suggestion of some polyproline II character. Upon silicic acid polymerization and during dissolution of preformed silica, the CD spectrum of P5 S3 indicated partial transition into an α-helical conformation which was transient during silica-dissolution. The secondary structural changes observed for P5 S3 correlate with the presence of oligomeric/polymeric silicic acid, presumably due to P5 S3 -silica interactions. These P5 S3 -silica interactions appear, at least in part, ionic in nature since negatively charged dodecylsulfate caused similar perturbations to the P5 S3 CD spectrum as observed with silica, while uncharged ß-d-dodecyl maltoside did not affect the CD spectrum of P5 S3 . Thus, with an associated increase in α-helical character, P5 S3 influences both the condensation of silicic acid into silica and its decondensation back to silicic acid.

Rate equations for sodium catalyzed amorphous silica dissolution

Newly measured amorphous silica dissolution rate data were combined with data from the literature to produce an equation that predicts the dissolution flux (J, mol/m2s) of amorphous silica as a function of temperature (T, K), sodium concentration (mNa+, molal), and hydrogen ion activity (aH+).J=14.6210-774002.303R1T+8.9510-777002.303R1TmNa+0.490aH+0.377The same data fit equally well to an equation that expresses the dissolution flux as a function of temperature, sodium concentration, and hydroxide ion activity (aOH−).J=14.6210-774002.303R1T+1.73×10610-777002.303R1TmNa+0.490aOH-0.377These equations have the same form as those for quartz (Rimstidt, 2015) and show that sodium ions have the same catalytic effect on amorphous silica dissolution as they do for quartz.

Pozzolanic reaction of glass powder and its role in controlling alkali–silica reaction

It is well recognized that finely ground soda-lime glass exhibits high pozzolanic reactivity. Fine glass grains will not undergo an Alkali-silica reaction (ASR) in the presence of alkali, and can even mitigate the ASR between alkali and reactive aggregates. Influences of the pozzolanic reaction of glass powder on solid phases, pore solution in cement paste, and the ASR mitigating effect are investigated in the study. The pozzolanic reaction of glass not only consumes portlandite to form in-situ C-S-H, which appears as reaction rim around glass grains, and precipitated C-S-H, but also reduces monosulfate level. The impacts of the pozzolanic reaction on species in pore solution are characterized by increased aluminum, sulfate, sodium, and silicon concentrations and decreased calcium concentration. The increase in aluminum and sulfate concentrations results from the decrease in solid monosulfate. Glass powder controls ASR by increasing aluminum concentration in pore solution to reduce the dissolution of amorphous silica from reactive aggregates.

Thermochemical and kinetic investigations of amorphous silica dissolution in NaOH solutions

Dissolution of amorphous silica in 4, 8 and 11 mass% of sodium hydroxide solutions was followed by microcalorimetry at temperature between 353.15 and 403.15 K. Decreasing the Na2O/SiO2 molar ratio leads to the successive formation of the following dissolved entities Si4O11Na6, Si2O5Na2, Si3O7Na2 and Si5O11Na2. Their formation enthalpies were determined at 393.15 K as −5640.8, −2492.2, −3401.8 and −5214.7 kJ mol−1, respectively. A kinetic investigation showed that dissolution cannot be described by one-step controlled process. Isoconversional model allows determining a complex variation in the activation energy of dissolution in the range 6–21 kJ mol−1.

Successive stages of calcitization and silicification of Cenomanian spicule-bearing turbidites based on microfacies analysis, Polish Outer Carpathians

Mid-Cretaceous turbidites with large proportions of sponge spicules are widely distributed in the Silesian Nappe of the Outer Carpathians, giving rise to diversified types of sediments, from spiculites to spicule-bearing siliciclastics and calcarenites. Part of this succession, Middle–Late Cenomanian in age, was transformed into cherts. A microfacies study showed that these turbidite sediments underwent several stages of calcitization and silicification, which took place during Mid-Cretaceous times in different sedimentary environments, i.e., on a northern shelf bordering the Silesian Basin and on a deep sea floor. The first diagenetic changes were related to changes to the biotic components of the turbidite layers, dominated by siliceous sponge spicules. This process, which took place in the spiculitic carbonate mud on the shelves, was related to the calcitization of sponge spicules. Calcareous clasts and calcified skeletal elements also were corroded by bacteria. After transportation down the slope, the biogenic and siliciclastic particles were deposited below the carbonate compensation depth. Taphonomic processes on the basin floor and alternating phases of carbonate and silica cementations, recrystallization and dissolution occurred in these sediments and were related to the diversification in composition of successive turbidite layers. Silicification was related to the formation of quartz precipitates as fibrous chalcedony or microcrystalline quartz, which were derived from the earlier dissolution of amorphous silica, originating mostly from siliceous sponge spicules and radiolarian skeletons. However, a source of silica from hydrothermal vents was also possible. The initial silica precipitation could have taken place in a slightly acidic environment, where calcite was simultaneously dissolved. A number of silicification stages, visible as different forms of silica precipitate inside moulds after bioclasts, occur in the particular turbidite layers. They were related to changes in various elements of the pore-water profile after descending turbidity-current flows. A very low sedimentation rate during the Middle–Late Cenomanian in the Silesian Basin may have favoured the sequence of initial calcitization and silicification stages of the turbidite sediments.

Kinetic study of silica dissolution in aqueous solutions of aromatic organic electrolytes

To evaluate the effect of organic compounds on the dissolution rate of amorphous silica, the dissolution of amorphous silica in pure water and in organic electrolyte solutions were investigated at room temperature at pH 6. Based on the kinetic analyses, the dissolution rate constants of amorphous silica in the organic electrolyte solutions were 18–30 times larger than in pure water but less than those in the NaCl solution, which contained the same Na+ concentration as the organic electrolyte solution. The order of dissolution rate constants was NNaCl>Ntiron>Nphthalate>Nsalicylate>Nwater. In these experiments, the dried samples were analyzed by FT-IR, and the results indicated that all of the organic composition was adsorbed on the surface of the silica. Compared with pure water, the cations in the organic electrolyte solution were a dominant factor in increasing the dissolution rate of silica. However, compared with NaCl, the dissolution rate of silica decreased in the aromatic organic electrolyte solution due to the adsorption of the organic electrolytes on the surface of the silica as well as to a decrease in the exposed surface. In fact, organic anions containing in the organic electrolytes are retarding the dissolution rate of silica.

The Dissolution of Amorphous Silica in the Presence of Tropolone Under Acidic Conditions

AbstractDissolution of amorphous silica or silicate is an important reaction to release silicic acid in natural water and this reaction is affected by several factors. The existence of a natural organic compound, tropolone, because of its abundance, is of particular importance. In the present study, the dissolution of amorphous silica in the presence of tropolone (HL) was investigated in an aqueous solution under acidic conditions. The dissolution is controlled by the reaction between silicic acid and tropolone (Si(OH)4 + 3HL + H+ ⇌ SiL3+ + 4H2O), where the conditional formation constant K = [SiL3+]/[Si(OH)4][HL]3[H+]). The solubility of amorphous silica in the presence of tropolone was significantly greater than that in pure water due to the formation of the Si-tropolonate complex in the solution. The acceleration of silica dissolution by tropolone depends on the reaction pH and tropolone concentration. The solubility of the amorphous silica in the tropolone solution at pH 1 was approximately ten times greater than in the 0.1 mol/dm3 HCl used as a reference. This increase in the solubility correlates to a K value of the Si-tropolone complex at each pH. From the solubility experiments, the conditional formation constants (log K) of the Si-tropolonate complex at each reaction pH 1, 2, and 3 were 6.39, 5.88, and 5.77, respectively. The significant acceleration of the dissolution of amorphous silica by tropolone at pH 1 can be attributed to the large formation constant of the Si-tropolonate complex.

Correction: Reactive simulations of the activation barrier to dissolution of amorphous silica in water

Download options Please wait... Associated articles Reactive simulations of the activation barrier to dissolution of amorphous silic… Article information DOI https://doi.org/10.1039/C4CP90161D Article type Correction Submitted 15 Oct 2014 Accepted 15 Oct 2014 First published 22 Oct 2014 This article is Open Access Download Citation Phys. Chem. Chem. Phys., 2014,16, 25649-25649 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Correction: Reactive simulations of the activation barrier to dissolution of amorphous silica in water M. Kagan, G. K. Lockwood and S. H. Garofalini, Phys. Chem. Chem. Phys., 2014, 16, 25649 DOI: 10.1039/C4CP90161D This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given. Read more about how to correctly acknowledge RSC content. Social activity Tweet Share Search articles by author Michael Kagan Glenn K. Lockwood Stephen H. Garofalini

Reactive simulations of the activation barrier to dissolution of amorphous silica in water

Molecular dynamics simulations employing reactive potentials were used to determine the activation barriers to the dissolution of the amorphous SiO2 surface in the presence of a 2 nm overlayer of water. The potential of mean force calculations of the reactions of water molecules with 15 different starting Q4 sites (Qi is the Si site with i bridging oxygen neighbors) to eventually form the dissolved Q0 site were used to obtain the barriers. Activation barriers for each step in the dissolution process, from the Q4 to Q3 to Q2 to Q1 to Q0 were obtained. Relaxation runs between each reaction step enabled redistribution of the water above the surface in response to the new Qi site configuration. The rate-limiting step observed in the simulations was in both the Q32 reaction (a Q3 site changing to a Q2 site) and the Q21 reaction, each with an average barrier of ∼14.1 kcal mol(-1). However, the barrier for the overall reaction from the Q4 site to a Q0 site, averaged over the maximum barrier for each of the 15 samples, was 15.1 kcal mol(-1). This result is within the lower end of the experimental data, which varies from 14-24 kcal mol(-1), while ab initio calculations using small cluster models obtain values that vary from 18-39 kcal mol(-1). Constraints between the oxygen bridges from the Si site and the connecting silica structure, the presence of pre-reaction strained siloxane bonds, and the location of the reacting Si site within slight concave surface contours all affected the overall activation barriers.

The Effect of Aluminum in Solution on the Dissolution of Amorphous Silica and its Relation to Cementitious Systems

One of the most serious causes of degradation of concrete is the alkali–silica reaction. Amorphous silicates present in certain aggregates react with the alkaline pore solution of the concrete to form a gel, which absorbs water and swells, leading to the expansion of the concrete. It is known that the deleterious effects of ASR can be suppressed by the incorporation of supplementary cementitious materials in the concrete, but the mechanisms operating are not clear. In this article, we study a model system of amorphous silica plates in simulated pore solutions by X‐ray photoelectron spectroscopy (XPS), to demonstrate that aluminum in solution can directly suppress the dissolution of amorphous silica under the highly alkaline conditions found in concrete. XPS shows that aluminum species are incorporated into the framework of the silica structure. Scanning electron microscope (SEM) and atomic force microscope (AFM) images confirmed the reduction in dissolution of silica in solutions containing aluminum.

The influence of aluminium on the dissolution of amorphous silica and its relation to alkali silica reaction

It is known that the addition of supplementary cementitious materials (SCMs) in concretes reduces or even stops expansion due to alkali silica reaction (ASR). It has been widely shown that the main mechanism controlling ASR in blends is the alkali fixation capacity of silica rich C–S–H, which lowers the pH of the pore solution. The role of alumina additions is less clear. It was shown in a previous paper [1] that the alumina present in certain SCMs does not further reduce the alkalinity of the paste pore solution. It is proposed here that aluminium acts directly on the reactive phases of the aggregates. Aluminium species, present in the pore solution, are absorbed on the silica surface and limit the dissolution of amorphous silica of the aggregates, restricting ASR. The effect of aluminium was demonstrated through a study of mortar expansion and SEM image analysis of reactive aggregates in simulated pore solutions.

Additive-Driven Dissolution Enhancement of Colloidal Silica. 2. Environmentally Friendly Additives and Natural Products

The effect of various environmentally friendly chemical additives and natural products on the dissolution of amorphous silica (Aerosil 200 and laboratory-synthesized, SSD) is studied. The silica scale dissolvers tested include the following: ascorbic acid (vitamin C, ASC), citric acid (CITR), carboxymethyl inulin (CMI), 3,4-dihydroxybenzoic acid (catechuic acid, DHBA), 3,4,5-trihydroxybenzoic acid (gallic acid, GA), dopamine hydrochloride (DOPA), iminodiacetic acid (IDA), histidine (HIST), phenylalanine (PHALA), and malic acid (MAL). The chemical structures of these chemical additives contain potentially dissolution-active moieties, such as 1,2-dihydroxyethylene (ASC), α-hydroxycarboxylate (MAL and CITR), catecholate (DHBA, GA, and DOPA), α-aminocarboxylate (HIST and PHALA, both aminoacids), and finally carboxy-modified fructofuranose units (CMI). It was found that all studied molecules showed variable dissolution efficiency, with MAL, CMI, HIST, and PHALA being the slowest/least effective dissolvers, and...