Salt Immersion Test Research Articles

Effect of pH on the controlled release of benzotriazole from halloysite clay nanotubes for corrosion protection of mild steel

Due to the increase in severe consequences of mild steel corrosion, the development of coatings with improvement in corrosion-resistant properties has become very essential. In this work, benzotriazole (BTA) was encapsulated into halloysite nanotubes (HNTs) for inhibiting the corrosion of mild steel surface. The BTA-encapsulated HNT exhibits pH-responsive properties over a wide range of pH. It was found that a large amount of BTA was released at pH 3 (48 %), followed by pH 7 (30 %) and least in the case of pH 10 (20 %). At neutral pH, a rapid release of BTA was observed during initial exposure, reaching a steady-state later, with no significant release further. A salt immersion test was carried out after immersing mild steel (MS) substrates in BTA-HNT nanopowder dispersion in 3.5 wt% NaCl at different pH. SEM images and EDS maps confirmed that corrosion product formation on MS surface at pH 3 was significantly more with corrosion pits along with HNTs throughout the surface. At pH 7 and 10, corrosion pits were observed with very few halloysite nanotubes on the surface. An optimum amount of BTA is required to inhibit corrosion, excessive release may cause more Cl− ions to penetrate, leading to more corrosion. Electrochemical data also reveals the same trend, where the icorr value was maximum for pH 3 (1.09 × 10−5 A/cm2) > pH 7 (4.74 × 10−6 A/cm2) > pH 10 (3.43 × 10−6 A/cm2). Therefore, results suggest that BTA-encapsulated HNT can be efficiently incorporated into the coating matrix for their controlled release to provide corrosion protection under varying neutral and alkaline marine environments.

Time-depth dependent chloride diffusion coefficients of self-compacting concrete

Chloride attack severely impacts the performance of reinforced concrete. The total and free chloride ion concentrations (CICs) of self-compacting concrete (SCC) prepared with three supplementary cementitious materials (SCMs) - fly ash (FA), blast furnace slag (BS), and silica fume (SF) – were measured through the accelerated salt immersion tests. The apparent chloride diffusion coefficients (CDCs) at any exposure time and erosion depth were calculated using the Boltzmann-Matano method. The influence of the type and content of SCMs, the water-binder ratio (W/B), and the type of salt solution on CICs and CDCs were investigated. Both introducing SCMs and reducing W/B effectively reduced the CIC. The SCM that most effectively reduced CIC was SF, followed by BS and then FA. Free CICs were reduced to a greater degree than total CICs in FA and BS concrete, but the opposite was true for SF concrete. Presence of calcium chloride in salt solution increased total CICs while reducing free CICs. Apparent free CDC dropped over exposure time and initially increased with erosion depth but eventually stabilized. A model of apparent free CDC considering the time-depth dependence was created, which shows that time reduction factors of CDC is larger in SCM-containing SCC than in control SCC.

Self-repairing functionality and corrosion resistance of in-situ Mg-Al LDH film on Al-alloyed AZ31 surface

A novel Mg-Al LDH film was in-situ prepared hydrothermally in an alkaline aqueous solution on an Al-alloyed AZ31 substrate. The structural, chemical and functional characteristics of the film were explored by means of scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS), polarization curve, AC impedance and salt immersion tests, respectively. The anti-corrosion results indicated that the Mg-Al LDH film on the Al-alloyed AZ31 surface could effectively protect the AZ31 from corrosion attack even after 90 days of immersion in 3.5 wt.% NaCl solution. The protection performance is surprisingly better than most of the reported coatings on Mg alloys. More interestingly, when the Mg-Al LDH film was scratched, the exposed Al-alloyed surface might gradually release metal ions and re-generate dense LDH nano-sheets in the corrosive environment to inhibit the further corrosion there, exhibiting a self-repairing behavior. The combination of the benign long-term protection and desirable self-repairing performance in this new process of surface-alloying and LDH-formation may significantly extend the practical application of magnesium alloys.

Influence of processing and microstructure on the corrosion behavior of ultrafine grained Al 5083 alloy

Ultrafine grained (UFG) material has received significant research interest due to its combination of strength and toughness when compared with its coarse-grained counterpart. In the present investigation, a distinct UFG microstructure of Al 5083 alloy fabricated through cryorolling (CR), CR followed by warm rolling (WR), and CR followed by short annealing (SA) have been subjected to salt immersion, polarization, and intergranular corrosion tests in 3.5% NaCl solution. A salt immersion test revealed that UFG structures have resistance to pitting corrosion for all conditions when compared to their coarse-grained counterpart. The presence of coarse intermetallic second phase particles leads to the formation of micro galvanic cells with matrix resulting in highly localized pitting corrosion in the solution treated (ST) material, whereas crystallographic pits along the lateral direction have been observed in deformed material. The lower values of corrosion current density ( icorr = 3.640 and 3.910 μA/cm2) were observed for CR and WR conditions, respectively, than ST samples ( icorr = 8.140 μA/cm2) were attributed to the presence of a higher volume fraction of low angle grain boundaries along with a high density of dislocations. SA after CR has slightly increased the corrosion current ( icorr = 3.8 μA/cm2) values thereby shifting the corrosion potentials to a noble direction.

Development of seismic resistant steel with high strength and corrosion resistance

Corrosion of reinforced steel inside concrete structures poses threat on designed life span of the buildings. This is more dangerous when used in seismic prone zones. Rebars with high strength and ductility can only provide better seismic resistance. Both strength and ductility can be obtained in steels produced through Quenched and Tempered (Q&T) process. Steels produced in this process acquire dual phases with tempered martensite at the case and ferrite plus pearlite at core. While, martensite is responsible for providing strength to the rebar and Ferrite plus pearlite provides the requisite ductility. Generally, corrosion starts from the surface of the steel bar in contact with concrete, because of the carbonation and chloride ion attack of the concrete. As the corrosion continues, both strength and ductility gets reduced substantially and ultimately results in failure of the structure during seismic activity. In view of this, a special steel was developed in this study and named as Earthquake, Corrosion Resistance, Fire Resistance (EQCRFR) steel. Corrosion studies were performed on 3 grades of steel such as Fe500D, DHSCRM and EQCRFR in carbonated and non-carbonated concrete pore solutions with varied chloride concentrations. Further, salt immersion tests were also carried out to supplement the results. This paper analyses the results to establish the corrosion characteristics of EQCRFR steel vis-à-vis two conventional steel grades Fe500D and DHSCRM. On the basis of experimental results, it is understood that EQCRFR grade steel possess improved corrosion resistance in comparison to other two grades considered in this study. In case of EQCRFR, the critical corrosion current density (icorr) did not exceed the limit of 0.1 µA/cm2 up to Chloride strength of 1.5 M in non-carbonated and carbonated solutions. However, the critical chloride concentration was very low at 0.05 M and 0.5 M for Fe500D and DHSCRM grades respectively.

Facile preparation of a multifunctional superhydrophilic PVDF membrane for highly efficient organic dyes and heavy metal ions adsorption and oil/water emulsions separation

At present, various water pollution problems have attracted extensive attention all over the world. Among them, a large amount of wastewater contains oil-water emulsions, heavy metal ions, organic dyes and other pollutants. Therefore, it is urgent to prepare multifunctional materials that can separate these pollutants. In this paper, superhydrophilicity/underwater superoleophobicity PVDF membrane and superhydrophilicity/underwater superoleophobicity polyester fiber were successfully prepared by deposition of suspension containing montmorillonite, β-cyclodextrin, tannic acid and sodium alginate on the substrate. The modified membrane showed good durability and stability under extreme environmental conditions such as different pH conditions, salt immersion test, ultraviolet irradiation and mechanical wear. he modified polyester fiber membrane can effectively separate oil-water mixture and various oil-in-water emulsions. More importantly, the modified PVDF membrane can effectively adsorb organic dyes and heavy metal ions, filter the mixture of oil, organic dyes and various heavy metal ion solutions, and the separation efficiency is very high. Based on all the advantages mentioned above, this study provides a new idea for the efficient adsorption of organic dyes and heavy metal ions and the efficient separation of oil-water mixtures.

Corrosion Behavior of a Laser-MIG Hybrid Welding-Brazing Joint of 6061 Aluminum Alloy to SUS304 Stainless Steel

Lightweight steel-aluminum structures have broad application prospects because of their lowering weight characteristics, however, the corrosion of welding-brazing joints in steel-aluminum structures is less concerned or studied. In this paper, the corrosion behavior of the laser-MIG (metal inert gas) hybrid welding-brazing joints of steel-aluminum is investigated through the tests and analysis of salt spray, immersion, and electrochemistry. The salt spray and immersion tests show that obvious galvanic corrosion occurs at the welded joints, in which the aluminum side is seriously corroded while the steel side is not corroded. The open-circuit potential (OCP) values of the aluminum alloy and the weld metal are similar (approximately −0.48 V), and the stainless steel has a higher OCP value of −0.33 V. The corrosion resistance of the weld metal is lower than aluminum- and steel-based materials. The corrosion resistance of the joints is controlled by the aluminum alloy part of the two metals based on the OCP and electrochemical impedance spectroscopy (EIS) analysis. A possible corrosion process schematic for the physical/chemical properties of a welding-brazing joint immersed in a sodium chloride solution is proposed according to EIS.

Fabrication of active corrosion protection waterborne polyurethane coatings using cerium modified palygorskite nanocontainers

AbstractThe development of eco‐efficient and environmental friendly active anti‐corrosion coatings for metallic substrates represents a fundamental milestone in many engineering applications. Herein, a new type of active corrosion protection coating was successfully synthesized simply based on waterborne polyurethane (WPU) and nanocontainer of Ce3+ modified palygorskite (Ce‐PAL). Particularly, the nanocontainer of Ce‐PAL was achieved via a facile and green process by cation exchange in water. Inductively coupled plasma atomic emission spectrometry (ICP) revealed that Ce3+ had successfully incorporated into PAL nanofibers with a loading amount of 10.334 g/kg. The salt immersion test, electrochemical potentiodynamic measurements and electrochemical impedance spectroscopy (EIS) demonstrated that the incorporation of Ce‐PAL only with 2 wt% into WPU led to a significant improvement of their corrosion protection properties. Finally, according to the results of scanning electron microscopy with energy dispersive X‐ray spectroscopy, the active anti‐corrosion mechanism of Ce‐PAL/WPU coating was proposed.

Development of chicken feather fiber filled epoxy protective coating for metals

Abstract The use of chicken feather short fiber (CFF) as filler for polymer offers an ecofriendly method for the development of composites and coatings. In the present study, CFF filled epoxy coating has been developed to protect carbon steel from corrosion. The morphology of the coating surfaces was investigated using optical microscopy (OM) and atomic force microscopy (AFM). The surface properties such as wettability and surface roughness were determined. The corrosion studies on the coatings were evaluated using an accelerated salt immersion test. This green approach for the development of epoxy/CFF coating offers protection of metal parts used in many modern industries from the corrosive environment, improve the performance and ensure safety.

Study on metal corrosion protection mechanism of graphene nano coating

Organic coating is considered to be one of the most effective methods to prevent metal corrosion. The corrosion resistance of the coating was tested by the improved copper accelerated acetic acid immersion test, and the quality change of the coating sample before and after immersion was tested. The appearance change of graphene was observed by SEM, and the anticorrosion mechanism of graphene was studied. The results showed that the copper salt accelerated acetic acid salt immersion test accelerated the corrosion process and shortened the determination time. There was no obvious change in the test sample after soaking for 400h. The main anticorrosion mechanism is that the conductive graphene in graphene nano anticorrosive coating can effectively protect the metal substrate by “conductive bridging”.

Long time corrosion test of AZ31B Mg alloy via micro-arc oxidation (MAO) technology

Micro-arc oxidation (MAO) ceramic coatings of AZ31B Mg alloy were formed in phosphate-silicate based electrolyte with the addition of K2ZrF6. The effect of treatment time on physical and chemical properties of the coatings were thoroughly investigated. The results showed that the micropores on the surface of the coatings increased on size and decreased on porosity with the increasing MAO treatment time. The ZrO2 was inclined to absorbed into the outer porous layer than that of the inner dense layer. The corrosion study presents that the corrosion resistance increased with the increasing treatment time, which was proved directly proved by 150 h salt immersion test. The potentiodynamic polarization test proved that the coating with the MAO treatment time of 40 min is of the most superior corrosion resistance. In addition, the long time electrochemical impedance spectroscopy (EIS) test of the coating formed in the electrolyte with the treatment time of 40 min showed that, the corrosion resistance of the coating decreases in the initial immersion stage (64 h) little by little is because of the MgO decomposition in the outer porous layer. With the immersion time increased, the blocking effect of the outer porous layer postpone the deterioration of the inner dense layer.

Self-Repairing Composites for Corrosion Protection: A Review on Recent Strategies and Evaluation Methods.

The use of self-healing coatings to protect metal substrates, such as aluminum alloys, stainless steel, carbon steel, and Mg alloys from corrosion is an important aspect for protecting metals and for the economy. During the past decade, extensive transformations on self-healing strategies were introduced in protective coatings, including the use of green components. Scientists used extracts of henna leaves, aloe vera, tobacco, etc. as corrosion inhibitors, and cellulose nanofibers, hallyosite nanotubes, etc. as healing agent containers. This review gives a concise description on the need for self-healing protective coatings for metal parts, the latest extrinsic self-healing strategies, and the techniques used to follow-up the self-healing process to control the corrosion of metal substrates. Common techniques, such as accelerated salt immersion test and electrochemical impedance spectroscopy (EIS), for evaluating the self-healing process in protective coatings are explained. We also show recent advancements procedures, such as scanning vibrating electrode technique (SVET) and scanning electrochemical microscopy (SECM), as successful techniques in evaluating the self-healing process in protective coatings.

Promoting the effect of zinc‐rich epoxy via poly(aniline‐co‐anisidine)/iron waste composite on corrosion protection of steel

AbstractThe purpose of this article was to evaluate the performance of a poly(aniline‐co‐anisidine)/iron waste composite (COIW) as an anticorrosive pigment for primer coatings. A procedure was outlined to prepare COIW and evaluate its anticorrosive properties following the electrochemical behavior and corrosion test of the coated steel. Various zinc‐rich epoxy primers were formulated by replacing part of the zinc powder (ZP) pigment with COIW. In all formulas, the ratio of pigment to epoxy resin was fixed at 2. In the pigment mix, the percentage of COIW was ranged from 5% to 60% by weight to the ZP. The performance of the formulated primers was estimated by the salt immersion test and potentiodynamic polarization measurement (corrosion potential, polarization resistance, and corrosion rate essays). It was demonstrated that COIW is effective in protecting steel from corrosion when it is used in combination with ZP.

Preparation of graphene/polyaniline nanocomposite by in situ intercalation polymerization and their application in anti-corrosion coatings

This study reports a strategy for further simplifying the synthesis process of polyaniline-modified graphene (An/G) nanocomposite. For this purpose, the An/G nanocomposite was prepared by expanded graphite (EG) and aniline (An) via in situ polymerization. The structures and morphologies of the An/G nanocomposite were examined by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, ultraviolet–visible spectroscopy and atomic force microscopy. The results show that the An/G nanocomposite was synthesized successfully. The coatings were prepared using polyaniline (PANI) and An/G as the fillers and epoxy resin as the matrix. The anti-corrosion performance was evaluated by electrochemical impedance spectroscopy, Tafel polarization curve and salt immersion test. When An/G100 nanocomposite with a mass ratio of An to EG of 100:1 as a filler is used, the coating on the steel exhibited superior anti-corrosion effect. In particular, the impedance at 0.01 Hz of the coating with the An/G100 nanocomposite at a low loading of 2 wt% (An/G100-2) remained constant above 1 × 1010 Ω·cm2 for up to 35 days in 3.5 wt% sodium chloride solution. The Tafel plots reveal that the undamaged zone of the An/G100-2 coating possessed a high corrosion potential of −0.16 V, and the corrosion current density was only 1.5 × 10−11 A cm−2. The protective mechanism of graphene and PANI is discussed.

Microcapsules of multilayered shell structure synthesized via one-part strategy and their application in self-healing coatings

Abstract The microcapsules of multilayered shells structure loaded with dicyclopentadiene (DCPD) were prepared via one-part strategy in Pickering emulsions stabilized by hydrolyzed poly(glycidyl methacrylate) (PGMA) nanoparticle. The target microcapsules had polyurethane (PU) inner shell layer, phenol-formaldehyde (PF) outer shell layer, and PGMA outermost layer. Meanwhile, in order to compare with the target microcapsules, the microcapsules of double layered shells (Sample 1) were both acquired. Size distribution, morphology, chemical structure and reaction heat of the capsules were studied by particle size analysis, scanning electron microscopy (SEM), fourier transform infrared spectra (FTIR), nuclear magnetic resonance (NMR), and differential scanning calorimetry (DSC). It was found that the ingredients of PF, PU and PGMA were contained in the target microcapsules of multilayered shells, and the encapsulated core materials still kept high chemical reactivity. The resistant properties against thermal and solvent were evaluated by thermogravimetric analysis (TGA) and the solvent immersion test. When the IPDI content was suitable, the multilayered shells microcapsules (Sample 2, 3) possessed excellent thermal and solvent resistances comparing with Sample 1. In addition, the coatings embedded Sample 3 have displayed good self-healing performance by SEM, electrochemical impedance spectroscopy (EIS), salt immersion test and the tensile analysis of tapered double cantilever beam (TDCB) fracture specimens.

Feasibility tests of nickel as a containment material of molten Li2O-LiCl salt containing Li metal at 650 °C during electrolytic reduction

In this study, we investigated the feasibility of nickel (Ni) as a material to contain molten Li2O-LiCl salt containing lithium (Li) metal at 650 °C as an electrolyte during the electrolytic reduction process of pyroprocessing (also known as oxide reduction, OR). First, the behaviors of Ni in four different LiCl salts (0.1 wt% Li-LiCl, 1 and 8 wt% Li2O-LiCl, and 8 wt% Li2O-0.1 wt% Li-LiCl) in an argon atmosphere were examined through immersion tests. Then, Ni was used as a vessel material for five consecutive OR runs of simulated oxide fuel using 1.0 wt% Li2O-LiCl salt. The tested Ni was analyzed by microbalance, X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Concentrations of Ni in the salt were measured using inductively coupled plasma atomic emission spectroscopy. No corrosion product of Ni, except Cr2Ni3, was observed on the Ni used for both the salt-immersion tests and the OR runs because the Ni was not exposed to oxygen gas. However, leaching of Ni in the OR salt containing excessive Li metal was observed. Therefore, Ni can be used as the salt containment material in the OR process when excessive Li metal and oxygen gas in the salt are maintained at low levels.

Preparation and Characterization of a Novel Hydrogel-Based Fouling Release Coating

With the rapid development of marine transportation industry, biological fouling not only affects the speed of navigation but also highly increases fuel consumption. In the paper, a novel hydrogel-based fouling release coating is developed to address the issue by a combination of non-stick property with a low surface tension of the coating. A hydrogel-based silicone fouling release coating was synthesized and two kinds of different intermediate coatings were studied to give a proper match as the tie layer between the substrate coated with primer and the hydrogel silicone on the surface. The adhesion strength, surface tension as well as surface topography of the fouling release coating were studied. The corrosion resistance and anti-fouling performance of the substrates sprayed with the coating were characterized by salt spray test and immersion test in a simulated marine system. The results show that the adhesion between the substrate and the fouling release coating is grade two measured by grid test. The water contact angle of the coating is 104.8o and Rz of the coating is 10.71μm. The specimen is intact after 1000 hours under salt spray test. No diatom was found settled on the specimens in a simulated static marine system while a little diatom was observed on the specimens in a simulated dynamic marine system. It has been found that the intermediate coating comprising of epoxy resin gives proper match between the primer and the fouling release coating consisting of PDMS resin. The coating exhibits superior anti-fouling performance under stationary state.

Studies on surface treatment of electrodeposited Ni–Zn alloy coatings using saccharin additive

Ni–Zn alloy coatings were electrodeposited galvanostatically at room temperature. Saccharin (0 to 1.8 g L−1) was added in the deposition bath as an additive agent. The effects of varied saccharin content addition on the physical properties of Ni–Zn alloy coatings were studied. The Ni–Zn alloy coatings were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic absorption spectroscopy (AAS), atomic force microscopy (AFM), contact angle, electrochemical impedance study (EIS), salt immersion test, friction coefficient, and wear resistance tribology techniques. The XRD study confirmed the formation of Ni–Zn alloys with mixed phases of Ni–Zn alloy depending upon the saccharin content addition. The AAS analyses based on varied saccharin addition confirmed Ni–Zn alloy composition between 64:36 and 22:78 at.%. The effects of varied saccharin addition on physical properties like stress, strain, microstructure, topography, wettability, wear, and corrosion resistance were studied. The optimized 1.6 g L−1 saccharin addition in the deposition bath with Ni–Zn composition as 25:75 at.% possesses highly enhanced surface properties like compact, smooth microstructure, and increased corrosion resistance with reduced friction coefficient value.

Corrosion Behavior of Tungsten Copper Alloy Produced by Infiltration Sintering

In this paper, W80CuNi0.3 alloy was prepared by cold isostatic pressing (CIP) and infiltration sintering, and its corrosion behavior was investigated by neutral salt spray accelerated test, immersion test and electrochemical measurement. It turned out that in the neutral salt spray and immersion test,the mass loss and corrosion rate of W80CuNi0.3 were far lower than those of 45 steel. The corrosion mainly occurs in the bonding phase of Cu, and the initial corrosion form of W80CuNi0.3 was pitting, the main reason of W80CuNi0.3 corrosion was Cl- erosion. The polarization curves analysis showed that compared with 45 steel, W80CuNi0.3 alloy had higher corrosion potential and lower corrosion current. Therefore, W80CuNi0.3 alloy are prone to stable passivation, so it has superior corrosion resistance.

Corrosion Behavior of Anodized 2195 Al-Li Alloys with Different Sealing Methods

The influence of post-sealing treatment on corrosion behavior of anodized 2195 Al-Li alloys was studied by potentiodynamic polarization, Electrochemical Impedance Spectroscopy(EIS),salt spray test and immersion test in solution of phosphoric acid/chromic acid. The anodic films were post- treated with boiling water, potassium dichromate, nickel sulfate and cerium nitrate, respectively. The results show that the post- sealing can greatly enhance the corrosion resistance of the anodized 2195 Al- Li alloy. The corrosion resistance of the anodic oxide film after post- treatment with cerium nitrate is far better than that with boiling water, but slightly inferior to those with potassium dichromate and nickel sulfate. Finally long term spray test results reveal that the anodized 2195 Al-Li alloy after sealing treatment with potassium dichromate exhibits the highest corrosion resistance among the four post-sealing treatments.