Constant Chloride Concentration Research Articles

Passive film alteration of reinforcing steel through [MoO42−]/[RCOO−] interfacial co-interaction for enhanced corrosion resistance in chloride contaminated concrete pore solution

Chloride-induced corrosion of carbon steel could be inhibited by molybdate (MO), while the MO/chloride ratio plays a vital role. This ratio has been reduced in constant chloride concentration using acetate (AC) as an organic corrosion inhibitor. Results showed that the MO-AC mixture, regardless of the concentration, possessed remarkable inhibition capability at the low concentration of MO. Electrochemical evaluations and surface analyses demonstrated the excellent behaviour of MO-AC, which promoted the formation of Fe2(MoO4)3, resulting in enhancing the properties of the passive-adsorbed layers. Based on the XPS results, more MO contributed to the formation of Fe2O3 in MO-AC as the Mo6+/Mo4+ ratio decreased and the value of Fe3+/Fe0 increased. Also, the low MO concentration assisted AC adsorption.

A MiniSandwich Experiment with Blended Ca-Bentonite and Pearson Water—Hydration, Swelling, Solute Transport and Cation Exchange

Shaft seals are geotechnical barriers in nuclear waste deposits and underground mines. The Sandwich sealing system consists of alternating sealing segments (DS) of bentonite and equipotential segments (ES). MiniSandwich experiments were performed with blended Ca-bentonite (90 mm diameter and 125 mm height) to study hydration, swelling, solute transport and cation exchange during hydration with A3 Pearson water, which resembles pore water of Opalinus Clay Formation at sandy facies. Two experiments were run in parallel with DS installed either in one-layer hydrate state (1W) or in air-dry two-layer hydrate (2W) state. Breakthrough at 0.3 MPa injection pressure occurred after 20 days and the fluid inlet was closed after 543 days, where 4289 mL and 2984 mL, respectively, passed both cells. Final hydraulic permeability was 2.0–2.7 × 10−17 m2. Cells were kept for another 142 days before dismantling. Swelling of DS resulted in slight compaction of ES. No changes in the mineralogy of the DS and ES material despite precipitated halite and sulfates occurred. Overall cation exchange capacity of the DS does not change, maintaining an overall value of 72 ± 2 cmol(+)/kg. Exchangeable Na+ strongly increased while exchangeable Ca2+ decreased. Exchangeable Mg2+ and K+ remained nearly constant. Sodium concentration in the outflow indicated two different exchange processes while the concentration of calcium and magnesium decreased potentially. Concentration of sulfate increased in the outflow, until it reached a constant value and chloride concentration decreased to a minimum before it slightly increased to a constant value. The available data set will be used to adapt numerical models for a mechanism-based description of the observed physical and geochemical processes.

Ionic Liquid-Based Dye for Highly Sensitive Optical Sensing Based on FRET and Ion Extraction System Using Plasticized PVC Membrane

Ionic Liquid-Based Dye for Highly Sensitive Optical Sensing Based on FRET and Ion Extraction System Using Plasticized PVC Membrane

Chloride penetration in concrete under marine atmospheric environment – analysis of the influencing factors

Marine atmospheric exposure conditions provide a severe environment for reinforced concrete structures, mainly due to the occurrence of chloride-induced reinforcement corrosion. This procedure was influenced by many parameters related to the concrete properties and to the environmental condition. In this paper, cubic concrete specimens with 150-mm edge, different types of cementitious material and different strengths, were arranged on a structure, which exposed them to a natural marine atmospheric environment. The purpose was to evaluate quantitatively the influence of different exposure conditions on the durability of concrete, measured in terms of chloride penetration into concrete. Both relative humidity (RH) and temperature were monitored in the experiment. The results indicated that the surface RH and temperature of the concrete were much different from that of the air. The diffusion coefficient and surface chloride concentration were time- and location-dependent, and were influenced by the RH, temperature, and the concrete strength. The results also indicate that error results would be made when using constant diffusion coefficient and surface chloride concentration with the air RH and temperature to predict long-term chloride penetration.

Pitting corrosion of intermetallic compound Ni 3(Si,Ti) in sodium chloride solutions

The pitting corrosion of intermetallic compound Ni 3(Si,Ti) was investigated as functions of test temperature and chloride concentration in sodium chloride solutions by using a potential step method. In addition, the pitting corrosion of solution-annealed austenitic stainless steel type 304 and pure nickel was also studied under the same experimental condition for comparison. The pitting potential obtained for the intermetallic compound decreased with increasing chloride concentration and test temperature. A critical chloride concentration below which no pitting corrosion took place was found to exist and to decrease with increasing test temperature. The specific pitting potential at the critical chloride concentration also decreased with increasing test temperature. In addition, the pitting potential at various constant chloride concentrations above the critical chloride concentration decreased with increasing test temperature. The pitting potential of Ni 3(Si,Ti) was higher than pure nickel, but lower than that of type 304.

Anionic and Cationic Effects on the Crevice Corrosion Susceptibility of Alloy 22

AbstractAlloy 22 is highly resistant to all forms of corrosion; however, it may suffer crevice corrosion in presence of chloride ions especially at temperatures higher than ambient and at anodic potentials. The susceptibility of Alloy 22 to suffer crevice corrosion is highly dependent on the type of electrolyte solution that is in contact with the alloy including variety of species in solution and their relative concentration. Laboratory research has shown that at a constant chloride concentration, the susceptibility of Alloy 22 to crevice corrosion is not influenced by the nature of the cations present in solution. On the other hand, that nature of the anions is highly influential. Of the anions present in ground water, only chloride is detrimental and the others are inhibitors or innocuous for crevice corrosion susceptibility. That is, the presence of the other anions counter balances the negative effect of chloride. The inhibition effect is explained and the likelihood that Alloy 22 would suffer crevice corrosion in contact with ground water is discussed.

CORROSION INITIATION TIME FOR REINFORCED CONCRETE MEMBERS ALONG INDIAN COASTS: EFFECTS OF TEMPERATURE AND RELATIVE HUMIDITY — A PROBABILISTIC APPROACH

Corrosion initiation time of steel reinforcement for partially saturated concrete members subjected to chloride ingress is investigated at five places along Indian coasts using simplified probabilistic analysis and sensitivity of the parameters to reinforcement corrosion is studied. Previously proposed diffusion based chloride ingress model for constant surface chloride concentration and variable diffusion coefficient is used. Corrosion is initiated when the chloride concentration on steel reinforcement exceeds a threshold value. The various input parameters considered in the model are surface chloride concentration (Cs), chloride threshold value (Cth), Concrete cover (X), reference diffusion coefficient (Dref), age (t), reference age (tref), diffusion decay index (m) and monthly temperature and relative humidity correction factors f(T) and f(h) respectively; to reference diffusion coefficient. For prediction of corrosion initiation time temperature and relative humidity data collected by India metrological Department is used and all other parameters are assumed same. A large variation in corrosion initiation time is found and therefore it becomes necessary to consider the temperature and relative humidity data in a region. Life-365 considers fully saturated condition of concrete and thus underestimates the corrosion initiation time of a reinforced concrete member. The deterministic approach uses mean values of the parameters and provides a 50% probability of corrosion initiation but the probabilistic approach provides expected time of first corrosion for chosen risk of corrosion and also gives sensitivity of parameters to probability of corrosion. Corrosion initiation time in ascending order is found at Colaba, Kanyakumari, Santacruz, Chennai and Vishakhapatnam. Corrosion initiation time is useful for owner, designer, or to an organization to take decision in time of priority of repairs, repair strategy, corrosion protection in order to optimize maintenance planning and budgeting. Planned maintenance at the optimum time is the safest and most cost effective approach.

Oxidation of Tyrosine by Hexacyanoferrate(III) in Aqueous Ethanoic Acid Medium–A Kinetic and Mechanistic Study

The kinetics of oxidation of tyrosine by Fe(CN)63-have been studied in 40% AcOH-H2O containing 4.0 mol dm-3HCl. The oxidation is made possible by varying the difference in redox potential by adding HCl and AcOH to the reaction mixture. The reaction is first order with respect to [Fe(CN)63-and fractional (0.72) order with respect to [tyrosine]. Increasing the acid concentration at constant chloride concentration accelerates the reaction. The order with respect to acid concentration is nearly two and H2Fe(CN)6-is regarded as the active oxidant. The initially formed product, Fe(CN)64-retards the reaction. A suitable mechanism is proposed and the reaction constants of the different steps involved have been evaluated. Activation parameters have also been calculated with respect to the slow step of the mechanism and discussed.

All-solid-state miniaturised planar reference electrodes based on ionic liquids

The paper presents the design of all-solid-state miniaturised reference electrodes suitable for flow-through analysis. The sensors are based on Ag/AgCl planar microelectrodes covered with PVC membranes containing an ionic liquid (IL, 1-dodecyl-3-methylimidazolium chloride). The membrane with IL additive provides an internal solid electrolyte, maintaining constant chloride concentration in the layer and thus constant potential of the Ag/AgCl electrode in solution of different concentration of chloride and other interfering anions. The performance of the reference microelectrodes with different ionic liquid content in the membrane was determined. The electrodes exhibited good potential stability, reproducibility and long-term stability. The structures were applied as reference electrodes in flow-cell measurements with potassium-selective planar microelectrodes. Comparable calibration curves of K+-selective electrodes determined using the designed reference microelectrodes based on ionic liquid and a commercial Ag/AgCl reference electrode were obtained.

Kinetic investigation of the chlorine reduction reaction on electrochemically oxidised ruthenium

The rate and mechanism of the electroreduction of chlorine on electrooxidised ruthenium has been investigated with focus on the effect of solution pH. Current/potential curves for the reduction process in solutions with constant chloride concentration of 1.0 mol dm −3 and varying H + concentration have been obtained with the use of the rotating disk electrode technique (RDE). It was found that the chlorine reduction rate is highly inhibited in solutions with high H + concentrations and that it can be satisfactorily described by the Erenburg mechanism, previously suggested for the chlorine evolution on RuO 2 and RTO. The expression of the kinetic current as a function of chlorine and H + concentration was obtained by solving the elementary rate equations of the kinetic mechanism. The kinetic constants obtained from the correlation of the kinetic current expression to the experimental data were used to simulate the dependence of the surface coverages and elementary reaction rates on overpotential.

Obtaining progressive chloride profiles in cementitious materials

The ingress of chloride into concrete is controlled by its absorption and diffusion characteristics. The authors have carried out an investigation to monitor the rate of ingress of chlorides during a 48-week cyclic wetting and drying regime using a variety of cement blends, viz. pulverised fuel ash, ground granulated blast furnace slag, metakaolin and microsilica. Chloride profiles were obtained by analysing concrete dust samples extracted from different depths from the surface that was exposed to the chloride exposure regime. The resistivity of the concrete was determined by measuring conductance between pairs of electrodes, in order to assess if this could be used to determine the presence of chlorides. The water absorption (sorptivity) of the concrete was also measured in order to determine if any correlation existed with the chloride ingress. The chloride profiles depended on both the duration of exposure and the type of cementitious material. A linear relationship was established between the depths to a constant chloride concentration of 0.2% by weight of cementitious material and the square root of time, yielding a rate of chloride ingress coefficient. This coefficient was found to depend on the type of cementitious material. The lowest value was obtained for slag concrete and the highest value was found for the OPC concrete. This corresponded well with the results from the resistivity profiles which indicated slag cement was best at resisting chloride penetration and the OPC concrete the worst. The sorptivity decreased significantly after the testing regime, due to pore refinement caused by continued hydration and the binding of chloride ions, leading to a reduction in continuous porosity. No correlation was found between the sorptivity and the rate of chloride ingress, which indicates that the dominant mechanism responsible for the transport of the chloride ions was not absorption.

A kinetic and mechanistic study of oxidation of arsenic(III) by hexacyanoferrate(III) in aqueous ethanoic acid

The kinetics of oxidation of AsIIIby Fe(CN)63− has been studied spectrophotometrically in 60% AcOH–H2O containing 4.0 mol dm−3HCl. The oxidation is made possible by the difference in redox potentials. The reaction is first order each in [Fe(CN)63−] and [AsIII]. Amongst the initially added products, Fe(CN)64− retards the reaction and AsVdoes not. Increasing the acid concentration at constant chloride concentration accelerates the reaction. At constant acidity increasing chloride concentration increases the reaction rate, which reaches a maximum and then decreases. H2Fe(CN)6−, is the active species of Fe(CN)63−, while AsCl52− in an ascending portion and AsCl2+ in a descending portion are considered to be the active species of AsIII. A suitable reaction mechanism is proposed and the reaction constants of the different steps involved have been evaluated.

Sequence of steps in the pitting of aluminum by chloride ions

Corrosion pit initiation in chloride solutions is given by an electrode kinetic model which takes into account adsorption of chloride ions on the oxide surface, penetration of chloride ions through the oxide film, and localized dissolution of aluminum at the metal/oxide interface in consecutive one-electron transfer reactions. A previous model has been extended here to consider that penetration of chloride ions can occur by oxide film dissolution as well as by migration through oxygen vacancies. Pit initiation occurs by chloride-assisted localized dissolution at the oxide/metal interface. The electrode kinetic model leads to a mathematical expression which shows that the critical pitting potential is a linear function of the logarithm of the chloride concentration (at constant pH), in agreement with experiment. The model also predicts that the critical pitting potential is independent of pH (at constant chloride concentration), also in agreement with experiment. Corrosion pit propagation leads to formation of blisters beneath the oxide film due to localized reactions which produce an acidic localized environment. The blisters subsequently rupture due to the formation of hydrogen gas in the occluded corrosion cell. Calculation of the local pH within a blister from the calculated hydrogen pressure within the blister gives pH values in the range 0.85 to 2.3.

Desalting a process cooling water using nanofiltration

The cooling water system of a chemical plant of Akzo Nobel is a partly open system. The site is located at the North Sea. The air in contact with the cooling water contains seawater droplets dissolving and increasing the chloride concentration. The cooling water contains chromate to protect the installation for corrosion. Nevertheless, the chloride concentration in the cooling water may not exceed 50 ppm. To maintain a constant chloride concentration level, a part of the cooling water should be drained and replaced by de-mineralized water. However, the drainage of chromate is limited by governmental regulations. This paper describes a systematic approach from problem definition to the membrane process design encompassing membrane module pre-selection, lab-scale proof of principle and on-site pilot demonstration, the latter to characterize the fouling and scaling potential of the feed solution. Finally, the paper discusses various membrane process design options.

Chronocoulometric studies of chloride adsorption at the Pt(111) electrode surface

Abstract Chronocoulometry and a thermodynamic analysis of charge density data were used to describe chloride adsorption at the Pt(111) electrode surface. The Gibbs excess, the Gibbs energy of adsorption, the number of electrons flowing to the interface per adsorbed chloride ion at a constant potential (electrosorption valency) and at constant chloride concentration (reciprocal of the Esin–Markov coefficient) were determined. Chloride forms a chemisorption bond with platinum. The charge numbers at constant potential and at constant chloride concentration are close to unity. This result suggests that the polarity of the chemisorption bond is very small. The highest packing density of chloride determined by the thermodynamic method corresponds to 0.43 ML. This number agrees well with coverage determined in recent surface X-ray scattering experiments [1] . Adsorption of chloride at Pt(111) is potential and pH dependent. We have demonstrated that at negative potentials, co-adsorption of Cl and hydrogen atoms has a synergistic character. In contrast the adsorption of chloride and OH at positive potentials has a competitive nature.

SOLVENT EXTRACTION OF PALLADIUM FROM CHLORIDE SOLUTIONS BY ALKYLAMMONIUM DI(2-ETHYLHEXYL)DITHIOPHOSPHATES

ABSTRACT The extraction of palladium (II) from chloride solutions (over a wide region of aqueous acidity) by di(2-ethylhexyl)dithiophosphates of tetraoctylammonium, tri-n-octylammonium and di-n-octylammonium in toluene at the constant chloride concentration has been studied. A synergistic effect was shown to be observed in these systems and it is explained by the formation of unusual complexes with mixed ligands. It has been established the palladium complexes, such as (R3NH)[PdCl2A], (R3NH)[PdCl2A] and (R2NH2)[PdCl2A], involving both alkylammonium cation and dialkyldithiophosphate anion are extracted under conditions of the loaded organic phase using distribution methods depending on a composition of aqueous and organic phase. At the excess of R3NHA or R2NH·HA, PdA2 is extracted into the organic phase. Table 8 reports the results obtained and indicates the domains of existence of the various species of palladium (II) extracted into the organic phase in the binary ex-tractant systems in comparison with the initial systems

Evidence for several mechanisms of volume regulation in neuroblastoma×glioma hybrid NG108-15 cells

Volumes of neuroblastoma×glioma hybrid NG 108-15 cells were electronically measured in order to characterize the mechanisms involved in volume regulation in isosmotic and anisosmotic conditions. The cells behave as perfect osmometers when tonicity was changed at constant chloride concentration by adding sucrose or replacing NaCl with CaCl 2 or MgCl 2. In contrast, the cell volume was poorly dependent on tonicity when the Cl − concentration was changed by adding NaCl or H 2O. Cell shrinkage was induced by cell stirring or after a hypotonicity-induced swelling. These volume decreases were abolished by caffeine but not by ryanodine or EGTA. Shrinkage was also induced by the Ca 2+ ionophore ionomycin. The ionomycin-induced volume decrease was abolished by EGTA. Cell swelling induced an outwardly rectifying Cl − current which was blocked by 5-nitro-2-(3-phenylpropylamino)benzoic acid, 4,4′-diisothiocyanatostilbene-2,2′-disulphonic acid and dihydroindenyl-oxy-alkanoic acid. When the tonicity was reduced at constant Cl − concentration by replacing NaCl with CaCl 2 or MgCl 2, the volume increased and then slowly decreased towards its control value. This regulatory volume decrease was blocked by 5-nitro-2-(3-phenylpropylamino)benzoic acid, 4,4′-diisothiocyanatostilbene-2,2′-disulphonic acid and dihydroindenyl-oxy-alkanoic acid. Long-term (hours–days) cell shrinkage was induced by a reduction of the culture medium osmolarity. Long-term cell swelling was induced by an increase of the culture medium osmolarity. These volume changes were abolished by the protein translation inhibitor cycloheximide. The results suggest that NG 108-15 cell volume is regulated by at least four interacting mechanisms controlled, respectively, by intracellular Ca 2+, extracellular NaCl, cell volume and intracellular ionic strength. The speculative nature of ionic systems responsible for these volume regulating mechanisms is discussed.

Copper electrodissolution in 1M HCl at low current densities. I. General steady-state study

Anodic oxidation of a copper rotating disk in hydrochloric acid is studied under steady-state conditions. At low current densities, a pseudo-Tafel behaviour varying with the speed of the rotating disk is observed. At potentials higher than −0.15 V/SCE, the value of the high frequency resistance, obtained from EIS measurements, increases and does not correspond to the sole resistance of the electrolytic solution. This behaviour is explained by the occurrence of the electroadsorption process. A two step mechanism for copper oxidation is studied with the only assumption of a constant chloride concentration at the interface. Kinetic zone diagrams are plotted and all the possible limiting kinetic behaviours of the model are pointed out. Interpretation of the experimental results reveals the limiting form taken by the current density vs potential curves.

Evaluation of miniaturised solid state reference electrodes on a silicon based component

A study of two different types of micro reference electrodes with respect to preparation and performance is described. The first, Type 1 Ag/AgCl, consists of a silver/silver chloride ink screen printed onto platinum on silicon. The second, Type 2 Ag/AgCl, uses the screen printed reference electrode just described, Type 1 Ag/AgCl, covered with a chloride doped vinyl ester resin. The latter eliminates some of the difficulties and drawbacks associated with Type 1 Ag/AgCl because the requirement for a constant chloride concentration in the analyte solution is removed when using Type 2 Ag/AgCl. Type 1 Ag/AgCl acted as a chloride selective electrode with a slope of 55.83 mV per decade for chloride activity and Type 2 Ag/AgCl potential versus SCE varied from −40.1 to −20.3 mV for KCl concentrations of 10 −7 and 1 M, respectively. The performance of a commercially available macro solid state reference electrode (called MacroRefex in this work), fabricated from the same materials as Type 2 Ag/AgCl, was also investigated.

Whys and wherefores of juxtaglomerular apparatus function

The juxtaglomerular apparatus is an anatomic structure which links the distal end of the thick ascending limb at the macula densa with the glomerular vascular pole. Specialized interstital cells and renin containing granular cells are located in the vascular hilum at this site. Evidence has accumulated that this connection is critical for local regulation of renin secretion and glomerular vascular tone via the tubuloglomerular feedback mechanism. The tubuloglomerular feedback mechanism maintains a constant chloride concentration at the macula densa at a set point determined by the volume state of the animal, a effect probably important for adjustment of renin secretion to changing salt balance. Evidence supporting these two regulatory roles is reviewed here.