Function Of Chloride Concentration Research Articles

Chloride Ion Sensing Using Fiber Brag Grating

Objective of our work is to demonstrate a new approach to chemical sensing. It is based on an optical probe using optical fiber with Brag Grating (FBG) coated with specific metal whose surface is modified to enhance selective adsorption of chemical species (Figure 1A). The goal is to demonstrate a chemical sensor whose transducing mechanism combines two phenomena: First, a light propagation/reflection through an optical fiber with Brag grating having strain dependent dialectic constants. Second, the electrocapillarity of a metal coating which exerts a pressure/strain on the grating dependent on the coverage of adsorbed species. The model system we investigate is sensing of Cl- in aqueous environment. The interest is driven by the critical need for a sensor capable of detecting low levels of chloride ion in the context of dialysis application. Chloride/chlorine is a primary agent used to purify water due to its cost-effectiveness, high reactivity with contaminants, and prolonged decay rate within distribution systems. However, while chlorine is effective at disinfection, its presence in dialysis water can have severe health implications, necessitating its careful monitoring and control. Our data demonstrate path towards the optimum sensor design with specific FBG materials, fiber dimeters and metal coatings selective to Cl- adsorbates(Figure 1B). This sensor provides an ultra-fast, real-time chemical sensing. Experimental data are also supported with full theoretical model i.e. transducer equation. Potential application our work should be of interest for many areas of biomedical engineering and medicine, nuclear reactor technology, high-pressure heat exchangers and turbines, oil and gas sector and military applications. Figure 1. (A) Schematics of FBG sensor coated with metal layer discussed in the text. Alternating dielectric layers with different refractive indexes n1 and n2 are indicated and represent the Bragg grating with radius of the fiber R. (B) Shift in the wavelength of Bragg light as a function of chloride concentration in solution of 0.1 M HClO4. Data sets are for two different potentials of the Au coating. Corresponding different slopes in data sets show dependence of the adsorption constant on the potential of the Au surface . Figure 1

Stainless steel selection tool for water application: pitting engineering diagrams

Introduction: This work systematically investigates the effect of chloride level, temperature, and the water system’s oxidative power on the pitting corrosion performance of stainless steels in pH-neutral environments.Methods: Two test programs were set to a) develop a robust method for constructing the pitting engineering diagrams and b) construct the pitting engineering diagrams based on the obtained method from the first test program. The various electrochemical techniques were selected to assess and understand factors that affect the corrosion behavior of stainless steel. Extensive testing was performed with short-term electrochemical measurements and long-term immersion tests.Results and Discussion: The obtained results demonstrate that the electrochemical methods are sufficient to define pitting diagrams showing the boundaries between pitting and no pitting as a function of chloride concentration, temperature, and the water system’s oxidation potential. The laboratory long-term electrochemical test results correspond the best to real applications and clearly underline the importance of an induction time for pit initiation. Accordingly, two sets of pitting engineering diagrams were constructed based on the water system’s oxidation potential. Measurements at the applied potential of 150 mV vs. saturated calomel electrode (SCE) correspond to applications in sterile tap water, whereas the applied potential of 400 mV vs. SCE corresponds to slightly chlorinated water or water with some biological activity. Pitting engineering diagrams were proved to be very useful tools to aid material selection in water application. However, it is important to realize that additional factors, such as different surface conditions and the presence of other environmental species, crevice design, or weld will affect the exact position of the boundaries between pitting and no pitting.

Time-dependent nonuniform numerical model of corrosion process and consequent corrosion-induced concrete cracking under chloride attack

Corrosion of steel bars and consequent concrete cracking are complicated processes and they mutually affect one another. In this study, a 3D time-dependent numerical model was developed to simulate localised corrosion in both circumferential and longitudinal directions, incorporating effects of nonuniform corrosion-induced cracks. Time-dependent evolution of corroded area in the circumferential direction around the steel bar was calculated as a function of chloride concentration, while two configurations of corroded length along the steel bar axis were simulated: (1) the entire length of steel bar was corroded at the same time and (2) the corroded length progressively developed from the middle of the bar towards its two ends. Microcell and macrocell mechanisms were applied to determine the total corrosion rate. Consequently, a finite element model was developed to simulate nonuniform corrosion-induced concrete cracking. It was found that once a vertical crack propagated through the concrete cover, not only did the corroded area spread faster, microcell and macrocell current densities also substantially increased, and the shape of corroded depth became more rounded.

Modeling and Predicting Reduction Reaction Kinetics for a Stainless-Steel in NaCl Solutions

A method for analyzing cathodic polarization curves on stainless steels is described and a framework for predicting the cathodic polarization response for UNS S13800 is developed, including a model for the diffusivity of dissolved oxygen as a function of chloride concentration and temperature. The cathodic polarization behavior of UNS S13800 in NaCl solutions, ranging from dilute to saturated, and across a range of temperature values was studied using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS). Analysis of the data indicated that the concentration of the solutions affected the ability of the oxide to catalyze reduction reactions. Dilute-to-low concentration solutions exhibited different Tafel slopes in the ORR-activation region while middle-to-high concentration solutions exhibited a single Tafel slope. The XPS and EIS results show a slightly thicker oxide formed in the low chloride concentration solutions over the course of the 18 hour open circuit duration along with a higher concentration of Fe3+ species.. The EIS data also showed the oxide formed in the low chloride solution had a higher charge-transfer resistance while the oxide formed in the high chloride solution had a higher oxide resistance.

In Situ EXAFS Study of Sr Adsorption on TiO2(110) under High Ionic Strength Wastewater Conditions

In order to provide important details concerning the adsorption reactions of Sr, batch reactions and a set of both ex situ and in situ Grazing Incidence X-ray Absorption Fine Structure (GIXAFS) adsorption experiments were completed on powdered TiO2 and on rutile(110), both reacted with either SrCl2 or SrCO3 solutions. TiO2 sorption capacity for strontium (Sr) ranges from 550 ppm (SrCl2 solutions, second order kinetics) to 1400 ppm (SrCO3 solutions, first order kinetics), respectively, and is rapid. Sr adsorption decreased as a function of chloride concentration but significantly increased as carbonate concentrations increased. In the presence of carbonate, the ability of TiO2 to remove Sr from the solution increases by a factor of ~4 due to rapid epitaxial surface precipitation of an SrCO3 thin film, which registers itself on the rutile(110) surface as a strontianite-like phase (d-spacing 2.8 Å). Extended X-ray Absorption Fine Structure (EXAFS) results suggest the initial attachment is via tetradental inner-sphere Sr adsorption. Moreover, adsorbates from concentrated SrCl2 solutions contain carbonate and hydroxyl species, which results in both inner- and outer-sphere adsorbates and explains the reduced Sr adsorption in these systems. These results not only provide new insights into Sr kinetics and adsorption on TiO2 but also provide valuable information concerning potential improvements in effluent water treatment models and are pertinent in developing treatment methods for rutile-coated structural materials within nuclear power plants.

Investigation of the Corrosion Electrochemistry of a Ni Based High Entropy Alloy in Chloride Containing Solutions

High entropy alloys (HEAs) contain five or more alloying elements typically in equimolar concentrations. In contrast, traditional solid solution alloys typically consist of one majority solvent element and several solute elements in comparatively low atomic proportions. HEAs are of interest for development of high performance materials particularly corrosion resistant alloys, because they can be engineered to form a single solid solution phase which reduces compositional and microstructural heterogeneity. Several hypotheses have been proposed to explain why HEAs form solid solutions, including a high entropy of mixing, and a near-zero enthalpy of mixing1 , 2. Many desired properties have been reported to arise in HEAs such as high hardness, superior wear resistance, high-temperature strength, and structural stability1 , 2. Excellent corrosion and oxidation resistance has been proposed but testing is limited1-3. HEAs are expected to perform superior to conventional alloys due to their unique combination of elements as well as an increase in the degrees of freedom in design which can be used to regulate the structure and properties of these alloys through alloying process control, and which cannot be achieved in typical binary and ternary systems3. This enhanced control over process variables in HEA design enables a systematic scientific examination of the effect alloy composition on corrosion properties, particularly passivity, metastable pitting, and repassivation. Characterization of the protective film formed on the HEA surface will provide an understanding of how alloy composition, microstructure, and oxide properties combine to improve passivity-based corrosion resistance and prevent film breakdown4. The focus of this talk will be to investigate alloy passivation as a function of chloride concentrations in an effort to elucidate the mechanism of aqueous corrosion in nickel-based HEAs, with the overarching goal of predictive corrosion-resistant alloy (CRA) design. In the present study a single HEA of composition 33.2Ni-16.85Cr-16.3Fe-8.57Mo-9.56Ru-5.48W, wt%, was designed and synthesized. The HEA demonstrated a stable FCC structure. The HEA was tested and compared to commercially pure Ni as well as the crystalline corrosion-resistant Ni-based alloy, C22 (Ni-21Cr-3.9Fe-13.3Mo-0.72Co-0.0035 C-0.23Mn-2.9W-0.026Si-0.011P-0.013V-0.0039S, wt%). Cyclic potentiodynamic polarization (CPP) scans were performed in solutions of increasing chloride concentration to assess the stability of the passive film. These tests enabled the identification of the passive current density, pitting, and repassivation potentials. A single frequency sinusoidal potential perturbation of 20 mV at 1 Hz was superimposed on the CPP scan to provide electrochemical impedance spectroscopy (EIS) data as a function of applied potential within the passive region. The electronic properties of the oxide film were also assessed using Mott-Schottky analysis of the EIS data. Ex-situ characterization was conducted to determine the corrosion morphology after electrochemical testing. The molecular identity of the oxide was determined using Raman and X-ray photoelectron (XPS) spectroscopies. Preliminary results indicated good corrosion resistance and a broad potential range for the passive region. Results were compared to pure Ni and C22. The passive range was compared to E-pH stability diagrams that were constructed using the CALPHAD approach and provided by Questek®. Acknowledgements This work was supported as part of the Center of Performance and Design of Nuclear Waste Forms and Containers, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0016584

Effect of Organic Inhibitors on Chloride Corrosion of Steel Rebars in Alkaline Pore Solution

The inhibition properties of aspartic and lactic acid salts are compared with nitrite ions with regard to their effect on critical chloride concentration. The tests were carried out on carbon steel specimens in simulated pore solutions with initial pH in the range of 12.6 to 13.8. The critical chloride concentrations were estimated through multiple specimen potentiostatic tests at potentials in the usual range for passive rebar in noncarbonated concrete structures. During tests, chloride ions were progressively added until all specimens showed localized attack, obtaining cumulative distribution curves reporting the fraction of corroded specimens as a function of chloride concentration. The presence of the organic inhibitors on the passivity film was detected by IR spectra. The results confirm that 0.1 M aspartate exhibits an inhibiting effect comparable with nitrite ions of the same concentration. Calcium lactate does not increase critical chloride concentration; however it appears to promote the formation of a massive scale, reducing the corrosion propagation.

Electrochemical disinfection using boron-doped diamond electrode – The synergetic effects of in situ ozone and free chlorine generation

This work investigated the capability of using a boron-doped diamond (BDD) electrode for bacterial disinfection in different water matrices containing varying amounts of chloride. The feed water containing Pseudomonas aeruginosa was electrochemically treated while applying different electrode conditions. Depending on the applied current density and the exposure time, inactivation between 4- and 8-log of the targeted microorganisms could be achieved. The disinfection efficiency was driven by the generation of free chlorine as a function of chloride concentration in the water. A synergetic effect of generating both free chlorine and ozone in situ during the disinfection process resulted in an effective bactericidal impact. The formation of the undesired by-products chlorate and perchlorate depended on the water matrix, the applied current density and the desired target disinfection level. In case of synthetic water with a low chloride concentration (20mgL−1) and an applied current density of 167mAcm−2, a 6-log inactivation of Pseudomonas aeruginosa could be achieved after 5min of exposure. The overall energy consumption ranged between 0.3 and 0.6kWhm−3 depending on the applied current density and water chemistry. Electrochemical water disinfection represents a suitable and efficient process for producing pathogen-free water without the use of any chemicals.

THE EFFECT OF Fe-ENRICH PHASE ON THE PITTING CORROSION RESISTANCE OF Al ALLOY IN VARIOUS NEUTRAL SODIUM CHLORIDE SOLUTIONS

The pitting corrosion of 5052 alloy was investigated as function of chloride concentrations by using an electrochemical method, scanning electron microscope and energy dispersive X-Ray spectroscopy in neutral sodium chloride solutions at 293 K. The pitting corrosion of pure Al was also investigated under the same experimental condition for the comparison. The pitting potential obtained for 5052 alloy and pure Al decreased with increasing chloride concentration. The pitting potential of pure Al is higher than that of 5052 alloy where pitting resistance of pure Al is better than that 5052 alloy. The linear equation implies that certain pitting potential becomes a relevant parameter for predicting certain chloride ion concentration. The synergic role of chloride ion and a localized galvanic corrosion between aluminium metal and iron-containing constituent contribute the process of pitting for 5052 alloy.

Zinc complexation in chloride-rich hydrothermal fluids (25–600 °C): A thermodynamic model derived from ab initio molecular dynamics

The solubility of zinc minerals in hydrothermal fluids is enhanced by chloride complexation of Zn2+. Thermodynamic models of these complexation reactions are central to models of Zn transport and ore formation. However, existing thermodynamic models, derived from solubility measurements, are inconsistent with spectroscopic measurements of Zn speciation.Here, we used ab initio molecular dynamics simulations (with the PBE exchange–correlation functional) to predict the speciation of Zn–Cl complexes from 25 to 600°C. We also obtained in situ XAS measurements of Zn–Cl solutions at 30–600°C. Qualitatively, the simulations reproduced the main features derived from in situ XANES and EXAFS measurements: octahedral to tetrahedral transition with increasing temperature and salinity, stability of ZnCl42− at high chloride concentration up to ⩾500°C, and increasing stability of the trigonal planar [ZnCl3]− complex at high temperature. Having confirmed the dominant species, we directly determined the stability constants for the Zn–Cl complexes using thermodynamic integration along constrained Zn–Cl distances in a series of MD simulations. We corrected our stability constants to infinite dilution using the b-dot model for the activity coefficients of the solute species. In order to compare the ab initio results with experiments, we need to re-model the existing solubility data using the species we identified in our MD simulations. The stability constants derived from refitting published experimental data are in reasonable agreement with those we obtained using ab initio MD simulations. Our new thermodynamic model accurately predicts the experimentally observed changes in ZnO(s) and ZnCO3(s) solubility as a function of chloride concentration from 200 (Psat) to 600°C (2000bar). This study demonstrates that metal speciation and geologically useful stability constants can be derived for species in hydrothermal fluids from ab initio MD simulations even at the generalized gradient approximation for exchange–correlation. We caution, however, that simulations are mostly reliable at high T where ligand exchange is fast enough to yield thermodynamic averages over the timescales of the simulations.

Application of Two Different Methods for Determination of Water and Chloride Transport Parameters of Building Stones

The transport of 1M NaCl water solution in three different types of sandstones is studied For basic characterization of studied materials, their chemical composition, porosity, bulk density and matrix density are accessed. The chloride transport is analyzed using two different methods. In the first one, the chloride absorption coefficient is measured on the basis of a modified sorptivity concept. The second method consists in carrying out an inverse analysis of experimentally measured moisture and chloride concentration profiles, leading to the determination of chloride diffusion coefficient as a function of chloride concentration, and moisture diffusivity as a function of moisture content. The chloride transport properties obtained for the particular studied materials are compared and the observed differences are discussed.

Pitting Corrosion of Ni3(Si,Ti)+4Al Intermetallic Compound at Various Chloride Concentrations

The pitting corrosion of Ni 3 (Si,Ti) with 4 at% Al consisting of two regions of a Ni 3 (Si,Ti) single-phase of L1 2 structure and two phases of L1 2 and fcc Ni ss was investigated as function of chloride concentrations by using electrochemical method, scanning electron microscope and energy dispersive X-Ray spectroscopy in neutral sodium chloride solutions at 293 K. In addition, the pitting corrosion of Ni 3 (Si,Ti) and type C276 alloy were also studied under the same experimental condition for comparison. The pitting potential obtained for the Ni 3 (Si,Ti) with 4 at%Al decreased with increasing chloride concentration. The specific pitting potential and pitting potential of Ni 3 (Si,Ti) with 4at%, Ni 3 (Si,Ti) and C276 were the lowest, the moderate and the highest, respectively, which means that the pitting corrosion resistance of Ni 3 (Si,Ti) was higher than Ni 3 (Si,Ti) with 4at% Al, but lower than that of C276. A critical chloride concentration of Ni 3 (Si,Ti) with 4at% Al was found to be lower than that of Ni 3 (Si,Ti). The Pitting corrosion of Ni 3 (Si,Ti) with 4at% Al occurred in the two phase mixture (L1 2 + Ni ss ).

Effect of gamma radiolysis on pit initiation of zircaloy-2 in water containing sea salt

In spent fuel pools at the Fukushima Daiichi Nuclear Power Station (1F), seawater was injected for cooling purposes after the tsunami disaster in March 2011. It is well known that the chloride in the seawater has the potential to cause localized corrosion (e.g., pitting corrosion) in metals. In this study, we evaluated the pitting potentials of zircaloy-2, the material used in the fuel cladding tubes in 1F, as a function of chloride concentration. To accomplish this, we used artificial seawater under gamma-ray irradiation and investigated the effect of radiolysis on pit initiation of zircaloy-2 in water containing sea salt. Changes in the composition of water containing sea salt were analyzed as well, both before and after gamma-ray irradiation. The characteristics of the resultant oxide films formed on zircaloy-2 were evaluated by X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy. The experimental results showed that the pitting potential under irradiation was slightly higher than that under conditions in which no radiation was present, and that the pitting potential decreased with increasing chloride concentration in the presence as well as the absence of radiation. Solution analyses for water containing sea salt showed that hydrogen peroxide was generated by irradiation. The oxide film was composed of zirconium oxide and was made thicker during the irradiation. The higher pitting potential could thus be explained by the capacity of hydrogen peroxide to oxidize the surface and enhance oxide film formation. Under gamma-ray irradiation, the zircaloy-2 surface with an oxide film formed by radiolysis products was found to be resistant to pitting in the presence of chloride.

Role of β/δ101Gln in Regulating the Effect of Temperature and Allosteric Effectors on Oxygen Affinity in Woolly Mammoth Hemoglobin

The oxygen affinity of woolly mammoth hemoglobin (rHb WM) is less affected by temperature change than that of Asian elephant hemoglobin (rHb AE) or human normal adult hemoglobin (Hb A). We report here a biochemical-biophysical study of Hb A, rHb AE, rHb WM, and three rHb WM mutants with amino acid substitutions at β/δ101 (β/δ101Gln→Glu, Lys, or Asp) plus a double and a triple mutant, designed to clarify the role of the β/δ101 residue. The β/δ101Gln residue is important for responding to allosteric effectors, such as phosphate, inositol hexaphosphate (IHP), and chloride. The rHb WM mutants studied generally have higher affinity for oxygen under various conditions of pH, temperature, and salt concentration, and in the presence or absence of organic phosphate, than do rHb WM, rHb AE, and Hb A. Titrations for the O2 affinity of these mutant rHbs as a function of chloride concentration indicate a lower heterotopic effect of this anion due to the replacement of β/δ101Gln in rHb WM. The alkaline Bohr effect of rHb WM and its mutants is reduced by 20-50% compared to that of Hb A and is independent of changes in temperature, in contrast to what has been observed in the hemoglobins of most mammalian species, including human. The results of our study on the temperature dependence of the O2 affinity of rHb WM and its mutant rHbs illustrate the important role of β/δ101Gln in regulating the functional properties of these hemoglobins.

Pitting Corrosion of Ni3(Si,Ti) Intermetallic Compound at Various Chloride Concentrations

The pitting corrosion of Ni 3 (Si,Ti) intermetallic compound was investigated as function of chloride concentration by using electrochemical method and scanning electron microscope in sodium chloride solutions at 293 K. In addition, the pitting corrosion of type C276 alloy was also studied under the same experimental condition for comparison. The pitting potential obtained for the intermetallic compound decreased with increasing chloride concentration. The specific pitting potential and pitting potential of Ni 3 (Si,Ti) were lower than those of C276 alloy, which means that the pitting corrosion resistance of C276 alloy was higher than that of Ni 3 (Si,Ti).

Pitting Potential of Zircaloy-2 in Artificial Seawater under Gamma-Ray Irradiation

Pitting potentials of zircaloy-2 in artificial seawater were measured as a function of chloride concentration or solution temperature with and without gamma-ray irradiation. The corrosion potentials of zircaloy-2 were also measured over 720 h. The pitting potential with gamma-ray irradiation was slightly greater than that without the irradiation. In both cases with and without the irradiation, the corrosion potentials of zircaloy-2 did not exceed the pitting potential. The pitting potential under irradiation was decreased with increasing chloride concentration and/or solution temperature.

Roles of Amino Acid Residues in Woolly Mammoth Hemoglobin on the Temperature Effect of Oxygen Binding

The O2 affinity of hemoglobin (Hb) is affected by allosteric effectors (e.g. H+, chloride, and organic phosphate) and temperature. Hb oxygenation is exothermic, i.e., the oxygen-binding affinity increases significantly with decreasing temperature. This makes it difficult for the Hb molecule in blood to deliver oxygen to the tissues under conditions of hypothermia during major surgical operations. We constructed plasmids to express recombinant woolly mammoth Hb (rHb WM) and Asian elephant Hb (rHb AE). Our biochemical-biophysical studies show that the apparent heat of oxygenation (ΔH) of rHb WM is less negative than that of rHb AE and human normal adult Hb (Hb A), suggesting that the O2 affinity of rHb WM is much less dependent on temperature. In order to investigate the key residues of the Hb molecule responsible for the temperature effect on O2 affinity, mutants with β/δ101 substitutions (β/δ101Gln→Glu, Lys, and Asp) in rHb WM have been expressed.Compared to rHb WM,these mutants exhibit a higher affinity for oxygen, and a more negative ΔH value under various conditions of pH, temperature, and salt concentration, with and without organic phosphates. Titrations for the O2 affinity of those mutant rHbs as a function of chloride concentrations indicate a lower heterotropic effect of this anion due to the replacement of β/δ101Gln, suggesting that the β/δ101Gln residue in rHb WM is important for its stronger response to chloride ions, and also responsible for its lower temperature effect of O2 affinity. NMR measurements for rHb WM and its mutants have been used to correlate their structural and functional properties. These findings could provide new insights into designing hemoglobin-based oxygen carriers (HBOCs) for treating patients undergoing therapeutic hypothermia (e.g. cardiac arrest, traumatic brain injury, stroke, etc.).

Factors Controlling the Location of Crevice Attack in Austenitic Stainless Steels

Microfabrication techniques and computational modeling were employed to examine the factors controlling the spatial distribution of crevice corrosion of 316L stainless steel in ferric chloride environments. Crevice fabrication consisted of a structural material surrounding a sacrificial material, the latter of which was selectively etched to form a rigorously defined hollow structure over the 316L substrate. For crevice gaps below 3 microns, the site of greatest attack down the crevice length was independent of gap size. A multivariable surface was used to model the variations in the electrochemical boundary condition as a function of chloride concentration. Modeling results predicted the location of greatest attack and that neither ohmic drop nor chemistry change models are suitable for austenitic stainless in acidic chloride environments. Instead, results showed that a chemistry dependent potential-current behavior is the factor that controls the spatial distribution of crevice corrosion attack in this system.

Coupled effect of ambient high relative humidity and varying temperature marine environment on corrosion of reinforced concrete

Chloride induced corrosion under coupled environmental effects of high humidity and high temperature often found in gulf marine environment is a very serious threat for durability of reinforced concrete structures. There exist different schools of thought between various researchers and the data in high relative humidity and high temperature range is also limited. This has been investigated by laboratory controlled experimentation under three different temperature conditions (30, 40 and 50 °C) and 85% R.H. A non-uniform and non-linear corrosion reaction was observed even after the breaking of passive layer. Furthermore, a decrease in corrosion potential and corrosion mass loss at 50 °C in comparison to 40 °C temperature conditions was seen. This may be due to the reduction of oxygen solubility in the pore solution at high temperature and blockage of concrete pores at high relative humidity. Thus, producing a reversing trend in corrosion mass loss as a function of chloride concentration at high temperature condition of 50 °C and high relative humidity of 85%. It is expected that a stable oxide layer may have developed under limiting oxygen controlled corrosion reaction. This can form basis for the development of a new technique to passivate steel bar embedded in chloride contaminated concrete. The paper also presents qualitative analysis of the microstructure of corrosion products under coupled varying temperature-chloride conditions and identifies the dividing line and turning point chloride concentration.

Effectiveness of pretreatment method to hinder rebar corrosion in concrete

This paper aims to evaluate the ability of phosphate pretreatments applied on steel rebars to hinder the corrosion reinforcements using synthetic pore electrolyte and mortar contaminated by chloride ions. The electrochemical behaviour of the pretreated substrate was assessed by corrosion potential, polarisation resistance and electrochemical impedance spectroscopy measurements. The results have demonstrated that the treatment of the rebar by immersion in the Na3PO4 (0·5M) solution favours the formation of a passive layer on the steel rebar surface, which increases the resistance to corrosion initiation up to 0·3M Cl– instead of 0·1M Cl– without treatment. The pretreatment also provides enhancement of corrosion protection of the steel rebar in mortar. The evolution of the impedance spectra in function of chloride concentration is in a fairly good agreement with the results obtained from RP measurements.