Corrosion Measurements of Reinforcing Steel by Different Electrochemical Techniques

Electrochemical techniques of the corrosion measurements of reinforcing steeI in concrete have been evaluated. These techniques include half-cell potential measurements, impressed voltage method, impressed current method and potentiostatic polarization technique. The results of corrosion behaviour of the steel in both 5%NaCl and 5%MgSO4 show that each electrochemical technique provides some information about the condition of the steel bar or the corrosivity of the environment being evaluated, yet none provides a complete data regarding the corrosion resistance of reinforcing steel in aggressive media

Crevice Corrosion Performance of 436 Ferritic Stainless Steel Studied by Different Electrochemical Techniques in Sodium Chloride Solutions with Sulfate Addition

The crevice corrosion behaviors of 436 stainless steels in chloride-containing solutions with sulfate addition were studied using potentiodynamic, galvanostatic and repassivation potential measurements. The results of these electrochemical tests were compared and discussed. Galvanostatic test was proved to be the most powerful technique in detecting the crevice corrosion of 436 stainless steels, while the repassivation potential measurement was the most time-saving method in this study. Sulfate ions have inhibited the crevice corrosion of 436 stainless steels in chloride-containing solution, which may result from the effects of competitive adsorption and the IR drop mechanism.

Electrochemical deposition of Mg(OH)_(2)/GO composite films for corrosion protection of magnesium alloys

Mg(OH)_(2)/graphene oxide(GO)composite film was electrochemical deposited on AZ91D magnesium alloys at constant potential.The characteristics of the Mg(OH)_(2)/GO composite film were investigated by scanning electron microscope(SEM),energy-dispersive X-ray spectrometry(EDS),X-ray diffractometer(XRD)and Raman spectroscopy.It was shown that the flaky GO randomly distributed in the composite film.Compared with the Mg(OH)_(2)film,the Mg(OH)_(2)/GO composite film exhibited more uniform and compact structure.Potentiodynamic polarization tests revealed that the Mg(OH)_(2)/GO composite film could significantly improve the corrosion resistance of Mg(OH)_(2)film with an obvious positive shift of corrosion potential by 0.19 V and a dramatic reduction of corrosion current density by more than one order of magnitude.

Electrochemical hydrogen storage performance of AB_(5-)CoB composites synthesized by a simple mixing method

AB5 （MlNi4.0Al0.3Cu0.5Zn0.2） alloy and CoB alloy were prepared by arc melting. AB5-CoB composites were synthesized by simple mixing of AB5 alloy powders and CoB alloy powders, and their electrochemical hydrogen storage properties were studied as negative electrodes in KOH aqueous solution. The maximum discharge capacity of the AB5-CoB（50%） composite （the content of CoB in the composite is 50 wt.%） reached 365.3 mAh.g^-1. After 100 charge-discharge cycles, the discharge capacity of the AB5-CoB（50%） composite was still much higher than that of the AB5 alloy. The high rate discharge capability （HRD） and potentiodynamic polarization were also tested.

Combined electronic/atomic level computational, surface(SEM/EDS),chemical and electrochemical studies of the mild steel surface by quinoxalines derivatives anti-corrosion properties in 1 mol·L^(-1) HCl solution

This work is devoted to the study of the inhibition of corrosion of mild steel(MS)in molar hydrochloric acid(1 mol·L-1 HCl)by two named quinoxaline derivatives namely,2-(2,4-dichlorophenyl)-1,4-dihydroquinoxaline(HQ)and 2-(2,4-dichlorophenyl)-6-methyl-1,4-dihydroquinoxaline(CQ).The inhibitory efficacy of HQ and CQ compounds is first evaluated using the gravimetric method and using electrochemical techniques(stationary and transient techniques).The results showed that our compounds are efficient corrosion inhibitors and the inhibition rates(ηEIS%)reached up to 91%and 94.2%at 10-3 mol·L-1 for HQ and CQ,respectively.The mentioned molecules are classified as mixed-type inhibitors.The adsorption of these inhibitors on the surface of steel in hydrochloric HCl 1 mol·L-1 medium obeys the Langmuir adsorption isotherm.The results of the scanning electron microscope(SEM)showed the formation of a protective film on the surface of the steel in the presence of the inhibitors studied.Elementary analysis is obtained by energy dispersive X-ray spectroscopy(EDS).The inhibition property was further elucidated by theoretical approaches such as:Density Functional Theory(DFT),quantum chemical descriptors(QCD),local reactive indices,solvent effect,theoretical complexation,Molecular Dynamic(MD)simulation,effect of temperature on adsorption energy(Eads),Radial Distribution Function(RDF),and Mean Square Displacement(MSD).The results of these approaches support the experimental results.

Electrochemical and Theoretical Studies of 1-Alkyl-2-substituted Benzimidazoles as Corrosion Inhibitors for Carbon Steel Surface in HCl Medium

The inhibition efficiencies of newly synthesized four 1-alkyl-2-substituted benzimidazole compounds（a^d） have been studied for the corrosion of carbon steel in 1.0 M HCl by using potentiodynamic polarization measurement. The four inhibitors act as mixed-type inhibitors,which mainly inhibit cathodes. The inhibition efficiency of these compounds enhanced when the concentration of the inhibitors increased. A theoretical study of the corrosion inhibition efficiency of these compounds was carried out by using the B3 LYP level with the 6-31＋G＊ basis set. Considering the solvent effect,the IEFPCM model was selected. Furthermore,the adsorption energies of the inhibitors with the iron（001） surface were studied by using molecular dynamic（MD） simulations. The theoretical results show that these inhibitors all exhibit several adsorption active-centers. Meanwhile,the MD simulations indicate that the adsorption occurs mostly through benzene ring and the lone pair electrons of the nitro atoms. These results demonstrated that the theoretical studies and MD simulations are reliable and promising methods for analyzing the inhibition efficiency of organic inhibitors.

Assembly and electrochemical testing of renewable carbon-based anodes in SIBs:A practical guide

Sodium-ion batteries(SIBs)are considered as a promising candidate to replace lithium-ion batteries(LIBs)in large-scale energy storage applications.Abundant sodium resources and similar working principles make this technology attractive to be implemented in the near future.However,the development of high-performance carbon anodes is a focal point to the upcoming success of SIBs in terms of power density,cycling stability,and lifespan.Fundamental knowledge in electrochemical and physicochemical techniques is required to properly evaluate the anode performance and move it in the right direction.This review aims at providing a comprehensive guideline to help researchers from different backgrounds(e.g.,nanomaterials and thermochemistry)to delve into this topic.The main components,lab configurations,procedures,and working principles of SIBs are summarized.Moreover,a detailed description of the most used electrochemical and physicochemical techniques to characterize electrochemically active materials is provided.

Coulometric determination of sulfur speciation in natural waters

A systematic analytical method for the species of trace sulfur in water has been developed by using electrochemically coulometric titration in combination with several separation and concentration techniques.Based on the reaction of iodine with sodium azide,the studies were carried out on the catalytically coulometric determination of ppb levels of ionic or molecular sulfides,thiosulfates and hydrogen sulfide in wateri constant current coulometric determination of sulfites;and indirect coulometric determination of sulfate salts and esters.Coupled with the determination of the content of total sulfur,the scope of distribution of the species of inorganic sulfur(including trace sulfur compounds in labile state)and organic sulfur in water was given.The method thus developed was found to be featured by being easy and reliable to operate with a higher sensitivity and reproducibility and to be applicable to the analysis of sulfur species in water.

Influence of surface modified mixed metal oxide nanoparticles on the electrochemical and mechanical properties of polyurethane matrix

Newly synthesized functional nanoparticles,3-amino-1,2,4-triazole(ATA)/SiO_(2)—TiO_(2)were introduced to the polyurethane(PU)matrix.Electrochemical techniques were used to investigate the barrier properties of the synthesized PU—ATA/SiO_(2)—TiO_(2)nanocomposite coated steel specimen.In natural seawater,electrochemical impedance spectroscopy experiments indicated outstanding protective behaviour for the PU—ATA/SiO_(2)—TiO_(2)coated steel.The coating resistance(Rcoat)of PU—ATA/SiO_(2)—TiO_(2)was determined to be 2956.90 kΩ·cm^(−2).The Rcoat of the PU—ATA/SiO_(2)—TiO_(2)nanocomposite coating was found to be over 50%higher than the PU coating.The current measured along the scratched surface of the PU—ATA/SiO_(2)—TiO_(2)coating was found to be very low(1.65 nA).The enhanced ATA/SiO_(2)—TiO_(2)nanoparticles inhibited the entry of electrolytes into the coating interface,as revealed by scanning electron microscopy/energy dispersive X-ray spectroscopy and X-ray diffraction analysis of the degradation products.Water contact angle testing validated the hydrophobic nature of the PU—ATA/SiO_(2)—TiO_(2)coating(θ=115.4°).When the concentration of ATA/SiO_(2)—TiO_(2)nanoparticles was 2 wt%,dynamic mechanical analysis revealed better mechanical properties.Therefore,the newly synthesised PU—ATA/SiO_(2)—TiO_(2)nanocomposite provided excellent barrier and mechanical properties due to the addition of ATA/SiO_(2)—TiO_(2)nanoparticles to the polyurethane,which inhibited material degradation and aided in the prolongation of the coated steel’s life.

A Study of Eruca vesicaria, Bromelia hemisphaerica and Erythrina americana as Green Corrosion Inhibitors for Carbon Steel in Sulfuric Acid

A study of Eruca vesicaria, Bromelia hemisphaerica and Erythrina americana as eco-friendly corrosion inhibitors for 1018 carbon steel in 0.5 M H2SO4 has been carried out by using weight loss tests, potentiodynamic polarization curves and electrochemical impedance spectroscopy measuremnts. Results have shown that the three extracts performed as good corrosion inhibitors, but the Eruca vesicaria exhibited the best performance followed by Erythrina americana. The three inhibitors formed a protective, passive film which protected the steel from corrosion. This was because they contain antioxidants present in their molecular structure with heteroatoms such as N, C and O like phenols, amino acids, etc., which react with metal and environment to form the protective film.

Corrosion Inhibition of Carbon Steel in Acidic Mediaby Using Actinidia deliciosa(Kiwifruit)Extract

The corrosion inhibition of 1018 carbon steel in 0.5 M H2SO4 by using Actinidia deliciosa (Kiwifruit) peel extract has been investigated by using potentiodynamic polarization curves and electro-chemical impedance spectroscopy. Two kinds of extracts are investigated, one from the tender, and another one from ripe Actinidia deliciosa. Concentrations include 0, 25, 50, 75, and 100 ppm at room temperature. Results indicate that both kind of extracts acted as good corrosion inhibitors, is more efficient in the ripe extract. Corrosion inhibition efficiency increases with increasing its concentration for ripe extract, whereas for the tender Actinidia deliciosa, the higest inhibitor efficiency is obtained by adding 25 ppm and decresaing with a further increase in its concentration. Both extracts improve the passive film properties by decreasing the passive current density values. It is found that the corrosion inhibition is due to the presence of heteroatoms present in Actinidia deliciosa, mainly quercitine, which is physically adsorbed in the steel following a Frumkin type of adsorption isotherm which forms a protective film.

MICROSCOPIC CORROSION STUDIES OF DUPLEX STAINLESS STEELS

Electrochemical scanning tunneling microscopy and scanning electrochemical microscopy have been used for in situ monitoring of localized corrosion processes of different Duplex stainless steels (DSS) in acidic chloride solutions. The techniques allow imaging of local dissolution events with micrometer resolution, as opposed to conventional electrochemical techniques, which only give an overall view of the corrosion behavior. In addition, combined scanning Kelvin probe force microscopy and magnetic force microscopy were used for mapping the Volta potential variation over the surface of DSSs. A significant difference in Volta potential between the austenite and ferrite phases suggests galvanic interaction between the phases. A compositional gradient appears within 2 micrometers across the phase boundary, as seen with scanning Auger microscopy (SAM). In all, the studies suggest that higher alloyed DSS exhibit a more homogeneous dissolution behavior than lower alloyed DSS, due to higher and more similar corrosion resistance of the two phases, and enhanced resistance of the ferrite/austenite phase boundary regions.

Interaction of Hydrogen and Retained Austenite in Bainite/Martensite Dual-Phase High Strength Steel

The hydrogen trapping phenomena in two bainite/martensite dual-phase high strength steels(U20Si and U20DSi)were investigated by electrochemical permeation technique.The hydrogen diffusivity was calculated from data of permeation delay time,and the diffusion coefficient in U20 Si is far less than that in U20 DSi.Moreover,the hydrogen diffusivity decreases as the volume percent of retained austenite increases.The experiment results show that there are different hydrogen trappings and different volume percents of retained austenite in U20 Si and U20 DSi.The retained austenite is precipitated as films.The trap binding energy for the retained austenite and hydrogen is calculated to be 40.4kJ·mol-1.

Electrochemical co-reduction of Y(Ⅲ)and Al(Ⅲ)in a fluoride molten salt system and electrolytic preparation of Y-Al intermediate alloys

In this study,a molten salt co-reduction method was proposed for preparing Y-Al intermediate alloys and the electrochemical co-reduction behaviors of Y(Ⅲ)and Al(Ⅲ)and the reaction mechanism of intermetallic compound formation were investigated by transient electrochemical techniques.The results show that the reduction of Y(Ⅲ)at the Mo electrode is a reversible electrochemical process with a single-step transfer of three electrons,which is controlled by the mass transfer rate.The diffusion coefficient of Y(Ⅲ)in the fluoride salt at a temperature of 1323 K is 5.0238×10^(-3)cm^(2)/s.Moreover,the thermodynamic properties associated with the formation of Y-Al intermetallic compounds were estimated using a steady-state electrochemical method.Y-Al intermediate alloy containing 92 wt%yttrium was prepared by constant current electrolysis at 1323 K in the LiF-YF_(3)-AIF_(3)-Y_(2)O_(3)(6 wt%)-Al_(2)O_(3)(1 wt%)system at a cathodic current density of 8 A/cm^(2)for 2 h.The Y-Al intermediate alloy is mainly composed ofα-Y2Al and Y phases.The development and application of this innovative technology have solved major technical problems,such as a long production process,high energy consumption,and serious segregation of alloy elements at this stage.

Corrosion behavior of metallic alloys in molten chloride salts for thermal energy storage in concentrated solar power plants： A review

Recently, more and more attention is paid on applications of molten chlorides in concentrated solar power （CSP） plants as high-temperature thermal energy storage （TES） and heat transfer fluid （HTF） materials due to their high thermal stability limits and low prices, compared to the commercial TES/HTF materials in CSP- nitrate salt mixtures. A higher TES/HTF operating temperature leads to higher efficiency of thermal to electrical energy conversion of the power block in CSP, however causes additional challenges, particularly increased corrosiveness of metallic alloys used as contain- ers and structural materials. Thus, it is essential to study corrosion behaviors and mechanisms of metallic alloys in molten chlorides at operating temperatures （500-800℃） for realizing the commercial application of molten chlorides in CSE The results of studies on hot corrosion of metallic alloys in molten chlorides are reviewed to understand their corrosion behaviors and mechanisms under various conditions （e.g., temperature, atmosphere）. Emphasis has also been given on salt purification to reduce corrosive impurities in molten chlorides and development of electrochemical techniques to in-situ monitor corrosive impurities in molten chlorides, in order to efficiently control corrosion rates of metallic alloys in molten chlorides to meet the requirements of industrial applications.

Annealed microstructure dependent corrosion behavior of Ti-6Al-3Nb-2Zr-1Mo alloy

Corrosion resistance of titanium(Ti)alloys is closely connected with their microstructure which can be adjusted and controlled via different annealing schemes.Herein,we systematically investigate the specific effects of annealing on the corrosion performance of Ti-6 Al-3 Nb-2 Zr-1 Mo(Ti80)alloy in 3.5 wt.%NaCl and 5 M HCl solutions,respectively,based on open circuit potential(OCP),potentiodynamic polarization,electrochemical impedance spectroscopy(EIS),static immersion tests and surface analysis.Results indicate that increasing annealing tempe rature endows Ti80 alloy with a higher volume fraction ofβphase and finerαphase,which in turn improves its corrosion resistance.Surface characterization demonstrates thatβphase is more resistant to corrosion thanαphase owing to a higher content of Nb,Mo,and Zr in the former;additionally,the decreased thickness of a phase alleviates segregation of elements to further restrain the micro-galvanic couple effects betweenαandβphases.Meanwhile,the influential mechanisms of environmental conditions on corrosion of Ti80 alloy are discussed in detail.As the formation of a highly compact and stable oxide film on surface,annealed Ti80 alloys exhibit a low corrosion current density(10^(-6)A/cm^(2))and high polarization impedance(10^(6)Ω·cm^(2))in 3.5 wt.%NaCl solution.However,they suffer severe corrosion in 5 M HCl solution,resulting from the breakdown of native oxide films(the conversion of TiO_(2)to aqueous Ti^(3+)),active dissolution of substrate Ti to aqueous Ti^(3+)and existence of micro-galvanic couple effects.Those findings could provide new insights to designing Ti alloys with high-corrosion resistance through microstructural optimization.

The corrosion behavior of Ti-6Al-3Nb-2Zr-1Mo alloy:Effects of HCl concentration and temperature

Investigation about the corrosion behavior of Ti alloys in different ambient environment is of great significance for their practical application.Herein,we systematically investigate the corrosion behavior of a newfound Ti-6 Al-3 Nb-2 Zr-1 Mo(Ti80)alloy in hydrochloric acid(HCl)ranging from 1.37 to 7 M,and temperature ranging from 25 to 55℃,by means of electrochemical measurements,static immersion tests and surface analysis.Results manifest that increasing either HCl concentration or temperature can accelerate the corrosion of Ti80 alloy via promoting the breakdown of native protective oxide film and then further facilitating the active dissolution of Ti80 matrix.According to potentiodynamic polarization curves,Ti80 alloy displays a spontaneous passive behavior in 1.37 M HCl at 25℃,compared to a typical active-passive behavior under the other conditions.As indicated by cathodic Tafel slope,the rate determining step for cathodic hydrogen evolution reaction is likely the discharge reaction step.The apparent activation energies obtained from corrosion current density and maximum anodic current density for Ti80 alloy in 5 M HCl solution are 62.4 and 55.6 kJ mol-1,respectively,which signifies that the rate determining step in the corrosion process of Ti80 alloy is mainly determined by surface-chemical reaction rather than diffusion.Besides,the electrochemical impedance spectroscopy tests demonstrate that a stable and compact oxide film exists in 1.37 M HCl at 25℃,whereas a porous corrosion product film forms under the other conditions.Overall,the critical HCl concentration at which Ti80 alloy can maintain passivation at 25℃can be determined as a value between 1.37 and 3 M.Furthermore,the corroded surface morphology characterization reveals that equiaxedαphase is more susceptible to corrosion compared to intergranularβphase due to a lower content of Nb,Mo,and Zr in the former.

Effect of Morinda Tinctoria Leaves Extract on the Corrosion Inhibition of Mild Steel in Acid Medium

The Morinda tinctoria (MT) plant leaves extract was prepared in aqueous and hydrochloric acid media and was used as corrosion inhibitor for mild steel in hydrochloric acid medium. MT is found to be an efficient inhibitor at room temperature and the efficiency decreases with increase in temperature. Results from colorimetric studies predict the amount of iron present in the test solution and the percentage inhibition efficiency values calculated from this data fit well with the weight loss experiments. The AC impedance studies reveal that the mild steel surface is positively charged and the process of inhibition is through charge transfer. Polarisation studies indicate the mixed nature of the inhibitor. Thermodynamic parameters obtained predict that the process of inhibition is a spontaneous one.

Influence of interface point defect on the dielectric properties of Y doped CaCu_(3)Ti_(4)O_(12) ceramics

CaCu_(3)Ti_(4-x)Y_(x)O_(12)(0≤x≤0.12)ceramics were fabricated with conventional solid-state reaction method.Phase structure and microstructure of prepared ceramics were characterized by X-ray diffraction(XRD)and scanning electron microscopy(SEM),respectively.The impedance and modulus tests both suggested the existence of two different relaxation behavior,which were attributed to bulk and grain boundary response.In addition,the conductivity and dielectric permittivity showed a step-like behavior under 405 K.Meanwhile,frequency independence of dc conduction became dominant when above 405 K.In CCTO ceramic,rare earth element Y^(3+)ions as an acceptor were used to substitute Ti sites,decreasing the concentration of oxygen vacancy around grainelectrode and grain boundary.The reason to the reduction of dielectric behavior in low frequencies range was associated with the Y doping in CCTO ceramic.