Presence Of Sulfate Research Articles

Influence of Sulfate Ions on Chloride-Induced Reinforcement Corrosion in Portland and Blended Cement Concretes

AbstractReinforced concrete structures serving in marine environments and in soils contaminated with high concentrations of chloride and sulfate salts are prone to two problems, namely reinforcement corrosion and sulfate attack. While a substantial number of studies have been carried out on reinforcement corrosion in pure chloride environments, practically no data exist on the influence of sulfate ions on chloride-induced reinforcement corrosion in plain and blended cement concretes.In this study, the effect of chloride and sulfate ions, or both on reinforcement corrosion in plain and blended cement concretes was investigated. Reinforcement corrosion was evaluated by measuring corrosion potentials and corrosion current density at periodic intervals. The mechanisms of chloride-induced reinforcement corrosion in the presence of sulfate ions was elucidated by extracting and analyzing the pore solution.The time to initiation of reinforcement corrosion was observed to be strongly related to the mobility and diffusivity of the chloride ions. Once the chloride and sulfate ions reach the steel-concrete interface, the concomitant presence of sulfates and chlorides generally increases the corrosion rate of steel in both plain and blended cements. Despite the very aggressive internal chemical environment in silica fume cement concrete, the corrosion current density was the lowest and generally below the threshold level. The longer time to initiation of corrosion and lower corrosion current density observed in silica fume cement concrete, even in very aggressive environments marked by high chloride and sulfate concentrations, emphasizes its usefulness in aggressive media.

Preparation of Monodispersed Spherical Silica-Alumina Particles by Hydrolysis of Mixed Alkoxides

Spherical colloidal particles of mixed silica-alumina composition of narrow size distribution were prepared by cohydrolysis of mixed alkoxides in the presence of sulfate ions. The ratio of the constituents could be altered by the solution pH and the reactant concentrations. Analysis of the composition of growing particles showed that they were internally inhomogeneous, which was substantiated by microelectrophoresis. The solids as prepared were partially crystallized to mullite on calcination at 1100°C. During this process the powders retained the spherical shape, but underwent some sintering.

Formation mechanism of monodisperse peanut-type α-Fe 2O 3 particles from condensed ferric hydroxide gel

The formation mechanism of monodisperse peanut-type hematite particles obtained in large quantities from highly condensed ferric hydroxide gel in the presence of sulfate ions has been studied. It is disclosed that sulfate ions restrain the growth in all directions normal to the c axis. The anisotropy was elucidated in terms of the specific adsorption of sulfate ions onto the subcrystals of each hematite particle, retarding the surface reaction of ferric complexes such as Fe(OH) + 2 on the planes parallel to their c axes. From close observation of the surface structure of a growing anisometric particle with a transmission electron microscope and from X-ray diffraction (XRD) analysis of an oriented particulate monolayer of the anisometric particles, the formation mechanism of the peanut-like shape was explained by a characteristic growth mode of the subcrystals on both ends of an ellipsoidal particle. The fundamental growth process is otherwise the same as that of monodisperse pseudocubic hematite particles grown in the absence of sulfate ions through a two-step phase transformation from Fe(OH) 3 to β-FeOOH and from β-FeOOH to α-Fe 2O 3 via the solution phase.

X-ray absorption spectroscopic study of platinum supported on sulfate ion-treated zirconium oxide

Platinum particles supported on a sulfate ion-treated zirconium oxide (SO 4 2− -ZrO 2) were characterized by means of X-ray absorption near edge structure (XANES )/extended X-ray absorption fine structure (EXAFS) and temperature-programmed reduction (TPR) in order to elucidate the nature of the sulfar-aided metal-support interactions. X-ray edge shift and area calculation, which give the number of unoccupied d states of the platinum particles, are suggestive of electron transfer from the platinum particle to the support and/or existence of the platinum unreduced cations. Fourier transforms (FTs) of k 3-weighted EXAFS reveal that the Pt particles on the (SO 4 2− -ZrO 2 support after hydrogen treatment at 623 K are a mixture of Pt metal ( Pt-Pt bond length = 2.77A˚) and Pt oxides, whereas the Pt particles on ZrO 2 exist as metal (Pt-Pt bond length = 2.73A˚). TEM reveals that the presence of sulfate ion causes an increase of the Pt particle size (30A˚→50A˚). The low reducibility of the Pt particles on the (SO 2- 4-ZrO 2 support is evidenced by TPR results. The nature of the platinum-support interaction in the Pt/(SO 4 2− -ZrO 2 catalyst is understood in terms of a Redox (reduction-oxidation) metal-support interaction.

Arrangement of substrates at the active site of yeast phosphoglycerate kinase. Effect of sulfate ion.

beta, gamma-Bidentate CrATP, a stable exchange-inert metal-nucleotide analog, was used as a probe of the conformation of the substrates at the active site of yeast phosphoglycerate kinase (PGK). The paramagnetic effects of Cr3+ on the longitudinal relaxation rates (1/T1p) of the 1H, 31P, and 13C nuclei of 3-phospho-D-glycerate (3PGA) were examined to determine the distances between enzyme-bound CrATP and the nuclei of 3PGA in the ternary PGK.CrATP.3PGA complex. Kinetic studies indicated that Ki(CrATP) was dependent on the concentration of 3PGA that was abolished in the presence of activator sulfate ion. Similarly, NMR studies showed that the environment of CrATP bound at the active site was altered by the presence of sulfate ion. The determined metal-to-nucleus distances show the close proximity of the substrates at the active site of PGK, which is consistent with a hinge-bending mechanism of the enzyme for bringing the two substrates together. Additionally, the presence of an activating concentration of sulfate was observed to cause significant changes in both the relative Cr(3+)-to-3PGA distances and the overall conformation of 3PGA when compared to the findings in the absence of sulfate. This is consistent with the active site being in a "less closed" configuration when sulfate is present. Under both conditions, models can be constructed that allow for direct transfer of a phosphoryl group between the bound substrates.

Preparation and Properties of Uniform Coated Colloidal Particles: VII. Hafnium Oxide on Indium Oxide

A coating procedure using preformed indium (hydrous) oxide particles dispersed in aqueous solutions of hafnium oxychloride in the presence of sulfate ions is described. The concentration of the latter controls the thickness of the hafnium (hydrous) oxide shell produced. Above a certain concentration of Na 2SO 4 a mixed dispersion is obtained. On calcination at 800°C the core and the coating of the composite particles are converted to the corresponding oxides.

Competing ion effect on chromium adsorption with fresh and starved subsurface bacterial consortium

The sorption of chromium (Cr+6) was investigated for 50 day starved and fresh cells in the presence of sulfate ion as a competing ion at three pH values (pH 6.0, 7.5 and 9.0). The chromium distribution in the subcellular components was also determined by conducting cell fractionation. Although a previous study showed that cells which had been starved for 50 days prior to being exposed to a chromium containing solution sorbed 10–15% more chromium than did fresh cells (Kong et al., 1992a), this study demonstrated that such cells did not sorb more chromium in the presence of sulfate ion.

硫酸イオン存在下でのアルミニウム塩水溶液からのアルミナ水和物の析出挙動と粒子の合体

硫酸イオン存在下でのアルミニウム塩水溶液からのアルミナ水和物の析出挙動と粒子の合体

硫酸イオン存在下でのアルミニウム塩水溶液からの水酸化アルミニウムの初期析出挙動

硫酸イオン存在下でのアルミニウム塩水溶液からの水酸化アルミニウムの初期析出挙動

Effects of sulfate ions on Alzheimer beta/A4 peptide assemblies: implications for amyloid fibril-proteoglycan interactions.

To model the possible involvement of sulfated proteoglycans in amyloidogenesis, we examined the influence of sulfate ions, heparan, and Congo red on the conformation and morphology of peptides derived from the Alzheimer beta/A4 amyloid protein. The peptides included residues 11-28, 13-28, 15-28, and 11-25 of beta/A4. Negative-stain electron microscopy revealed a sulfate-specific tendency of the preformed peptide fibrillar assemblies of beta(11-28), beta(13-28), and beta(11-25), but not beta(15-28), to undergo extensive lateral aggregation and axial growth into "macrofibers" that were approximately 0.1-0.2 micron wide by approximately 20-30 microns long. Such effects were observed at low sulfate concentrations (e.g., 5-50 mM) and could not be reproduced under comparable conditions with Na2HPO4, Na2SeO4, or NaCl. Macrofibers in NaCl were only observed at 1,000 mM. At physiological ionic strength of NaCl, fibril aggregation was observed only with addition of sulfate ions at 5-50 mM. Selenate ions, by contrast with sulfate ions, induced only axial and not substantial lateral aggregation of fibrils. X-ray diffraction indicated that the original cross-beta peptide conformation remained unchanged; however, sulfate binding did produce an intense approximately 65 A meridional reflection not recorded with control peptides. This new reflection probably arises from the periodic deposition of the electron-dense sulfate along the (long) axis of the fibril. The sulfate binding could provide sites for the binding of additional fibrils that generate the observed lateral and axial aggregation. The binding of heparan to beta(11-28) also produced extensive aggregation, suggesting that in vivo sulfated compounds can promote macrofibers. The amyloid-specific, sulfonated dye Congo red, even in the presence of sulfate ions, produced limited aggregation and reduced axial growth of the fibrils. Therefore, electrostatic interactions are important in the binding of exogenous compounds to amyloid fibrils. Our findings suggest that the sulfate moieties of certain molecules, such as glycosaminoglycans, may affect the aggregation and deposition of amyloid fibrils that are observed as extensive deposits in senile plaques and cerebrovascular amyloid.

Synthesis and characterization of primary alumina, titania and binary membranes

The synthesis and characterization of supported and non-supported membranes of γ-Al2O3, TiO2 and their binary combinations are described. Non-supported γ-Al2O3 and TiO2 membranes were prepared from colloidal dispersions (sols) of boehmite and titania, respectively. Stable binary sols were also prepared by mixing boehmite and titania sols under appropriate pH conditions, and these were used to prepare binary (γ-Al2O3/TiO2) membranes. Supported γ-Al2O3, TiO2 and binary membranes were made by the slip-casting process using the same sols. The membrane layers had, after calcination, a thickness of 3–6 μm depending on the dipping conditions, and an average pore diameter of ∼-3–4 nm with a narrow pore-size distribution. The structural transformation of titania from the anatase to the rutile phase was retarded by performing the hydrolysis in the presence of sulphate ions. Polyvinyl alcohol was added to the sols to strengthen the gel network during the drying and calcination process. This resulted in a less critical and more controllable membrane formation process. Multiple dipping (e.g. to repeat the dipping, drying and calcination steps) appeared to be a technique by which (i) defected layers could be repaired; (ii) thick membrane layers could be prepared; and (iii) multilayer membranes consisting of layers of different components could be prepared.

Effect of sulphate and chloride ions on the crevice chemistry and stress corrosion cracking of alloy 600 in high temperature aqueous solutions

Concentration-pH diagrams for Alloy 600 which may suffer from crevice corrosion at 316°C in sulphate or chloride aqueous solutions have been constructed. The steam generator made of Alloy 600 is one of the key components in a PWR nuclear power plant. If steam generator degradation occurs, the nuclear power plant will be forced to shutdown or derate. Crevice corrosion of samples was studied under [SO 4 2−] ≥ 15,000 ppm, pH 25 ≤ 4 and [Cl −] ≥ 10 ppm, pH 25 ≤ 4 conditions and easily occurred in acidic media. Heavily etched surfaces resulted from the coalescence of creviced regions on the specimen. With the decrease of pH value, the critical chloride concentration for generating crevice corrosion was lowered. However, the presence of sulphate ions (8000 ppm) suppressed the anodic dissolution reactions, perhaps through the formation of sulphate salts. Their presence also increased the endurance of chloride attack on Alloy 600 by two orders of magnitude. Only in extremely acidic conditions (pH 25 ≥ 1.5) was the stress corrosion cracking of Alloy 600 observed.

A model for sequential first-order phase transitions occurring in the underpotential deposition of metals

A model for the underpotential deposition of metals that occurs in stages is introduced. In this model the deposition takes place as a sequence of first order phase transitions of the adsorbate. In this application we study the underpotential deposition of Cu on a Au(111) surface in the presence of sulfate ions. The voltammogram of the deposition shows two sharp spikes which are reproduced by our model.

Changes in the iron(III)/iron(II) redox process at a gold microelectrode in liquid and frozen low temperature perchloric and sulfuric acid electrolyte media

Voltammetric studies of the Fe 3+ + e − ⇌ Fe 2+ electrode process have been undertaken at a 2.5 μm radius gold disk microelectrode in liquid and frozen perchloric and sulfuric acid electrolyte. Studies when the electrolyte contains Fe 3+, Fe 2+ or mixtures of Fe 3+and Fe 3+ reveal that the redox mechanism changes from diffusion control in the liquid state at ambient temperatures to a surface confined pathway in frozen media at low temperatures with the reversible potential for both electron transfer pathways being essentially the same. In perchloric acid electrolyte, over the temperature range 0 to −60°C, where ice is present, both mass transport pathways are observed simultaneously. The rate of electron transfer in the low temperature studies in acidic electrolyte is considerably enhanced by the presence of sulfate ions, as is the case in the liquid state at ambient temperatures.

Purification and properties of aldose reductase and aldehyde reductase from EHS tumor cells

Engelbreth-Holm-Swarm (EHS) tumor cells were utilized as a model for investigating the production of basement membrane components. These cells contain two immunologically distinct NADPH-dependent reductases, aldose reductase (EC 1.1.1.21) and aldehyde reductase (EC 1.1.1.2), which were purified to apparent homogeneity by a combination of procedures which included ammonium sulfate fractionation, Sephadex G-75 gel filtration, Matrex Gel Orange A affinity chromatography, and chromatofocusing on Phannacia Mono P. The molecular weights of aldose and aldehyde reductases were estimated to be 38K and 40K, respectively, by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Substrate specificity studies showed that both enzymes were capable of reducing a variety of aldehydes to their respective alcohols; however, only aldehyde reductase oxidized l-gulonic acid. Surprisingly, both enzymes showed similar reactivities with d-glucose and d-galactose, suggesting that both aldose and aldehyde reductases may contribute to sorbitol production in the EHS tumor cell. The activities of both enzymes were increased by the presence of sulfate ion, but chloride ion decreased the activity of aldose reductase. Both aldose and aldehyde reductases were inhibited by a series of structurally diverse aldose reductase inhibitors.

An electrochemical investigation of the behaviour of aluminum alloys in different electrolytes

The anodic behaviour of aluminum alloys, mainly Al 5083-H321 and Al 6061-T651, in aqueous chloride solution in the presence of sulphate ions has been investigated at room temperature by the linear sweep polarization technique and potential step method. For both electrodes the i- E curves were characterized by a minor peak prior to the major dissolution region, but with the high current density for Al 5083-H321 due probably to a monolayer(s) formation of Al 2O 3 and/or MgO. The detection of Mg was shown by SIMS analyses. Significant pitting was observed for Al 5083-H321, as a result of the combined effects of the electrochemically active Mg in the matrix of the electrode, its subsequent influence on hydrogen evolution, and the chloride attack on the aluminum electrode surface.

Preparation and properties of uniform colloidal indium compounds of different morphologies

Colloidal indium compounds, consisting of uniform particles of narrow size distribution of different morphologies were prepared by precipitation from homogeneous solutions at elevated temperatures. The forced hydrolysis of indium nitrate and chloride solutions yielded prismatic In(OH) 3 crystals. In the presence of sulfate ions, aging of solutions resulted in dispersions of different particle shapes, which depended on the reaction time, temperature and the pH. These solids contained sulfate ion which could not be removed by washing. A mechanism for the formation of such dispersions is suggested. All powders, so prepared, were transformed by calcination to In 2O 3, while the particle shape was preserved.

Heterogeneous nucleation of ice at the liquid-liquid interface

Aerosol particles containing liquid terpenes do not act as cloud condensation nuclei; they do not initiate formation of cloud droplets in clouds. They do, however, act as ice-forming nuclei initiating formation of ice particles. Presence of sulfate ions in cloud droplets appears to make them susceptible to freezing at higher temperatures when in contact with some of the terpenes. Heterogeneous nucleation of ice at a liquid-liquid interface was found to take place at higher temperatures in aqueous ammonium sulfate solutions than in pure water. The averaged temperatures of the phase transition were −3.6, −4.7, −4.4 and −4.8°C for pine needle oil, α-pinene oxide, eucalyptol and linalool, respectively; the corresponding temperature increases were 4.7, 7.8, 3.6 and 6.7°C. Separation of terpene molecules by dilution in carbon tetrachloride produced a marked decrease in ice nucleation temperatures. It was suggested that the arrangements of dipoles at the interface have decisive influences on the phase transition. Temperature of ice nucleation in the presence of solutions of hexadecanol in carbon tetrachloride generally decreases with a decrease of its concentration; the highest temperature of −5.0°C was found at 10 −3 M of hexadecanol and 10 −1 M of ammonium sulfate.

An XPS and FTIR spectroscopic investigation of surface adsorbates on a Pt/TiO 2 catalyst in the reaction of methanol, formaldehyde and formic acid with vanadyl sulfate

Platinum/titanium dioxide catalysts were used for the oxidation of methanol, formaldehyde and formic acid by oxovanadium(IV) ions in aqueous sulphuric acid medium. After use the catalysts were investigated by XPS and Diffuse Reflectance Infrared Fourier Transform spectroscopy (DRIFT). In all cases a set of five bands appeared in the mid-infrared region (1492±1 cm −1, 1410 ± 10 cm −1,1310 ± 10 cm −1 1270 ± 15 cm −1 and 1220 ± 7 cm −1). Furthermore, bands due to adsorbed sulphate ions and hydroxyl groups from hydrolysis of the carrier were detected. The XPS data also indicate the presence of sulphate ions and the absence of formate groups. The interpretation of the spectra indicates an equilibrium system on the platinum surface of multi-site bonded species related to the dioxymethylene acetal.

Metal complexes as indicators of solvent structures. Part IV. The effect of solvation on the interaction between tris-1,2-diaminoethanecobalt(III) and anions in aqueous solution

Changes in the circular dichroism of (+)tris-1,2-diaminoethanecobalt(III) in the presence of sulphate ion can be attributed to changes in the cybotactic solvation of the complex ion as well as to the formation of discrete ion-pairs.