Path Corrosion Research Articles

Enhanced corrosion resistance of a novel periodic multilayered Si/(Si, N)-DLC coating against simulated coal mine water

In this study, a novel periodic multilayered DLC coating, which was composed of a Si interlayer and a Si/N co-incorporated DLC layer (Si/(Si, N)-DLC) per period, was deposited; the corrosion behavior under the neutral, acidic, or alkaline coal mine water environment and its periodic number dependence, especially the fundamental corrosion mechanism, were systemically explored. Results suggest that compare to the substrate, the introduction of multilayered Si/(Si, N)-DLC coating presents a dramatic enhancement in the corrosion resistance under coal mine water environment. However, with increasing the periodic number, the corrosion resistance of the multilayered coating strongly depends on the working environment, which exhibits an enhancement in neutral and alkaline environments while a degeneration in acidic environment. This is attributed to not only the prolongation of the corrosion path caused by the multilayered structure but also the formation of an insulating silicon oxide layer in neutral and alkaline environments. However, in acidic environments, the strong permeability of H+ with the smallest ionic radius easily infiltrates the inherent defects of the coating. This not only weakens the protective properties of the multilayer structure but also leads to hydrogen-induced cracking, ultimately diminishing corrosion resistance. These findings theoretically guide the development of the DLC coatings with excellent corrosion resistance for coal mine applications.

Superior corrosion- and wear-resistance of graphene oxide with the aid of composite silanes

The practical application of magnesium alloy was limited greatly by the inherent poor corrosion- and wear-resistance. Herein, a composite coating composed of graphene oxide (GO), bis[3-(triethoxysilyl)propyl]tetrasulfide and octadecyltrimethoxysilane was prepared by spin-coating. Due to the cross-linking between silanes and GO, the so-obtained composite coating was more compact and less porous as compared with the coating of GO. The hydrophobicity was enhanced by the -S-S-S-S- moiety and high-density CH2 group in the silane chain; consequently, the so-obtained composite coating having the contact angle of about 140° was more hydrophobic as compared with the coating of GO (about 10°). Such a composite coating with higher hydrophobicity, denser siloxane networks and more compacter layered GO could slow down the permeation of corrosion medium and prolong the corrosion path. It was found that, compared to that of the Mg alloy substrate, the Ecorr of the composite coating increased by 713 mV and the icorr value decreased by nearly three orders of magnitude. Moreover, the composite coating possessed excellent wear resistance due to the intrinsic layered structure of GO and the good lubricity of silane.

In-situ rolling friction stir welding of aluminum alloys towards corrosion resistance

In-situ rolling friction stir welding (IRFSW) was proposed to improve corrosion resistance of 7075-T6 aluminum alloy joint via microstructural design and residual stress regulation. The residual stress at the weld edge was changed from +58.3 MPa to –25.7 MPa. The dissolution of precipitates and narrowing of precipitate-free zones reduced corrosion potential difference between the precipitates and the matrices. The active corrosion path was cut off by discontinuous distribution of fine precipitates in grain boundary. The ultimate tensile strength and elongation of IRFSW joints were increased by 24.1 % and 100.0 % compared to conventional FSW joints after constant load stress corrosion.

Pulse electrodeposition of a duplex-layer structured composite nickel-based coating with improved corrosion and abrasion resistance

In this study, a dual amorphous/crystalline nanocomposite coating of Ni–P/Ni–Mo–ZrO2 was designed and successfully deposited on pure copper substrates by pulse electrodeposition. The design of the Ni–P/Ni–Mo–ZrO2 dual coating takes advantage of the properties of the different structures and incorporates second phase reinforcing particles resulting in more comprehensive protective coatings. The surface morphology and microstructure were evaluated by SEM, EDS, WLI, XRD and TEM. The mechanical properties and electrochemical behaviors of the coating in a 3.5 wt% NaCl solution were investigated by wear tests, Tafel and EIS. The results show that the Ni–P/Ni–Mo and Ni–P/Ni–Mo–ZrO2 dual coatings are uniform, dense and crack-free, and the duplex interface is homogeneous. Compared with the Ni–Mo coating, the average friction coefficient and wear rate of the Ni–P/Ni–Mo duplex coating decreased to 0.18 and 5.433 × 10−4 mm3/N·m, respectively. The corrosion potential is positively shifted to −0.43 with a maximum impedance of 308 kΩ cm2. The mismatch of the interlayer defects causes a deviation in the corrosion path, resulting in a transformation from longitudinal pinhole corrosion into extended transverse corrosion, which effectively strengthens the capacity of the coating for corrosion resistance while maintaining the high hardness of its outer coating. Furthermore, the hardness of the dual Ni–P/Ni–Mo coating can be obviously reinforced by nanoparticles from 730 HV to 810 HV, the corrosion potential is shifted to −0.41 V, and the corrosion current density decrease to 7.7803 × 10−7 A/cm2. The improvement in the mechanical properties can be attributed to the ZrO2 nanoparticles, which could carry stress and transfer loads during the wear process. Meanwhile, the ZrO2 nanoparticles can reduce the nodule size by filling the binding boundary which is the main corrosion path, and reduce the number of surface defects, such as pinholes, which leads to a lower corrosion rate. In addition, the corrosion inhibition and nanoparticle codeposition mechanisms of the duplex coatings were further discussed.

Multifunctional hybrid T-PI-MPS composite coating: Corrosion resistance, low-wear/friction and heat-resistance

Despite methylphenylsiloxane (MPS) possesses heat-resistance and corrosion resistance, the brittleness hinders its widespread application. Herein, the polyimide (PI) and Ti3AlC2 were introduced for modifying MPS, thereby preparing the T-PI-MPS coating. The bilayer structure of surface-enriched MPS and internal-enriched PI was achieved by controlling the addition amount along with the density difference. The results indicate that the T-PI-MPS coating achieved a contact angle of 95.1° and exhibited corrosion resistance to salt spray for 28 days. Compared to PI-MPS, the wear rate of T-PI-MPS was reduced by 85 % and the friction coefficient declined from 0.75 to 0.58. As expected, T-PI-MPS exhibited exceptional excellent heat-resistance. The exceptional performance is attributed to the following three factors: I. the MPS-enriched layer is characterized by a stable SiO chain organization. This structure gives the corrosion resistance and water resistance, and prevents the hydrolytic swelling of PI. II. the PI-enriched layer is constructed from imide bonds, which give the coating superior friction performance due to its high load-bearing capacity. III. the incorporation of Ti3AlC2 plays a role in mitigating internal defects, prolonging the corrosion path, and inhibiting cracks due to its unique nanolayered structure, high temperature resistance, and hardness.

Corrosion behavior of N-containing low Ni deposited metal and Inconel 625 deposited metal in 40 mol% MgCl2 + 60 mol% KCl molten salt at 600 °C

The service environment of solar energy storage tube is faced with molten salt corrosion. After failure, Inconel 625 flux-cored wire is commonly used for repair welding. However, Ni is expensive and lacks resources. In this paper, a low-cost N-containing low Ni flux-cored wire was designed. It was used to replace the current Inconel 625 flux-cored wire. The corrosion behavior of two deposited metals in 40 mol % MgCl2 + 60 mol % KCl molten salt at 600 °C for 72 h was tested. The results showed that the corrosion rates of N-containing low Ni deposited metal and Inconel 625 deposited metal were 6.04 μm/year and 8.19 μm/year, respectively. The proportion of HAGBs was 83.9 % and 93.4 %, respectively. The hot corrosion path penetrates along the random HAGBs. The proportion of HAGBs of the N-containing low Ni deposited metal was small, and N element first combined with Cr element to inhibit the precipitation of Cr23C6. The N-containing low Ni deposited metal reduced the diffusion path of Cr element and improved its corrosion resistance.

Seawater corrosion resistance of a novel Cu-Ni/γ-Al2O3&CeO2 composite coating on H64 brass

In this paper, γ-Al2O3&CeO2 composite powder (ACp) was prepared by a simple hydrothermal method, and γ-Al2O3 and ACp were deposited on the surface of H64 brass with copper and nickel from sulfate plating bath at a specific deposition current density. The phase composition and morphology of composite powder and coating were studied, and the electrochemical behavior of composite coating in simulated seawater (3.5 wt% NaCl) was evaluated. The results show that γ-Al2O3 and CeO2 are well combined, the corrosion potential and polarization resistance of Cu-Ni/γ-Al2O3&CeO2 composite coating (CNACc) are as high as 0.022 V and 21.107 kΩ•cm2, respectively, which is due to the fact that the composite coating can distort the Cl- corrosion path and play a good role in corrosion resistance.

Strengthening the mechanical properties and corrosion resistance of Ni[sbnd]W coatings by PDA-functionalized h-BN nanosheets

PDA-functionalized h-BN nanomaterials (Ph-BN) were used to reinforce the electrodeposited NiW coatings. Compared with the h-BN nanomaterial, Ph-BN has better dispersion in the plating solution, which can effectively improve the mechanical and corrosion resistance of the coating. Compared with the NiW coating, the microhardness value of the Ni-W/Ph-BN coating (662.8 Hv) was increased by 33.47 % and the friction coefficient (0.382) was reduced by 41.86 %. This is due to the special ceramic composite layered structure of Ph-BN namely the combination of flexible unit PDA structure and rigid unit h-BN structure, which will synergistically hinder the shedding of the coating during the friction process and help to improve the wear resistance of the coating. The Rct value of Ni-W/Ph-BN is 34,500 Ω•cm2, which is 105.36 % higher compared to NiW coating. Ni-W/Ph-BN also has the smallest corrosion rate (0.0465 mm•a−1), which is 45.74 % lower relative to NiW coating. The uniformly dispersed Ph-BN nanosheets in the coating prolong the corrosion path for corrosive ions. Besides, the PDA has the effect of anchoring Fe2+/ Fe3+, which will be beneficial for the composite coating corrosion resistance improvement.

Ti3C2Tx MXene@STPP novel waterborne long-term anti-corrosion coating with "3 + 1" multiple high-performance active-passive protection barrier mechanisms

Although environmentally friendly waterborne epoxy (WEP) coatings have the advantage of low volatile organic compounds (VOCs), their barrier performance is rather inferior to achieve long-term corrosion protection. Herein, we grafted the coupling agents KH560 and KH550 onto the etched Ti3C2Tx and sodium tripolyphosphate (STPP), respectively. On the one hand, Ti-O-Si covalent bonds can be formed to improve the water dispersion stability, and on the other hand, as a bridging agent, the functionalized modification yielded the interface-enhanced Ti3C2Tx@STPP filler. The Ti3C2Tx@STPP/WEP composite coating exhibits a high impedance value of 7.981 × 1010 Ω·cm2 after 120 days of saltwater immersion, which is at least two orders of magnitude higher than that of the pure WEP coating. Likewise, the chelating-passivation advantage of STPP with metal cations is fully exploited. The precipitation-oxidation self-healing corrosion inhibition mechanism was proposed and demonstrated by Tafel, EIS, XPS, and Raman experiments. The remarkable long-term corrosion protection performance can be concluded as (1) interface-enhanced two-dimensional Ti3C2Tx with extraordinary physical barrier to prolong the corrosion path; (2) due to high barrier properties, the further electrochemical reactions of steel surfaces can be effectively inhibited under low utilization of water and oxygen, and the Fe(OH)3 and Fe(OH)2 are converted into non-conductive Fe3O4 and/or Fe2O3 films after water loss, (3) and active protection by the chelation of STPP with iron ions to form iron tripolyphosphate passivation films, and (4) passive defense by the coating and resin itself. Therefore, a novel "3 + 1" high-performance protective coating, which integrates interface enhancement, physical barrier, and active-passive protection, is successfully prepared to achieve long-term corrosion protection of the coating.

Chloride induced mechanical degradation of ultra-high performance fiber-reinforced concrete: Insights from corrosion evolution paths

Chloride-induced corrosion of ultra-high-performance fiber-reinforced concrete (UHPFRC) inevitably affects structural durability. However, the process of multi-fiber corrosion and mechanical deterioration still lacks sufficient understanding. This work aims to reveal the fiber corrosion degradation mechanism from a microscopic to macroscopic view, applying multiple analytical analyses of atomic absorption spectrometry, SEM-EDS, nano-indentation, polarization, and macroscopic mechanical testing. Results show that the flexural strength of specimens decreases significantly with the increase of corrosion degree, and a clear reduction of up to 47% is found at a high corrosion degree. Elastic modulus and nano-hardness of corroded samples vary in a wide range of 30–189 GPa and 0.16–6.41 GPa. With the increase in fiber content, two distinctive corrosion mechanisms are proposed. The corrosion path deteriorates from fiber edge to inner by the invasion of erosive solution through the matrix at low contents (<2 vol%). Considering impurities, greater interfacial defects and macro-cell potential differences at high contents (≥2 vol%), another corrosion path originates from the fiber inner outward to the matrix. Fiber corrosion damages the fiber’s structural integrity and induces matrix deterioration, the micromechanics of the matrix along the fiber edge 20 μm decreases at least 10% more than the concrete matrix. This work firstly sheds light on the mechanical deterioration of UHPFRC from the perspective of fiber corrosion paths considering different initiation scenarios.

Effect of Na2SiO3 concentration on corrosion resistance and wear resistance of MAO ceramic film on the Al‐Mg‐Sc alloy

AbstractAlthough Al‐Mg‐Sc alloy was widely applied to aviation aerospace field, they were vulnerable to local corrosion and wear in the process of long‐term service in severe environmental conditions. In this paper, micro‐arc oxidation (MAO) ceramic films on Al‐Mg‐Sc alloy substrate were prepared in electrolyte solutions with different Na2SiO3 concentrations, and the corrosion resistance and wear resistance of the MAO samples were studied. The experimental results of potentiodynamic polarization (PDS) and long‐term immersion tests indicated that the MAO ceramic film prepared in 10 g/L Na2SiO3 electrolyte solution had the best corrosion resistance, as manifested by no obvious cracks, serious collapse and corrosion products on the sample surface and no deep cracks and corrosion paths in the cross‐sectional area. The increase of Na2SiO3 concentration in electrolyte solution also improved the wear resistance of MAO ceramic film, as manifested by low wear depth (10 μm)and width (1 mm) of the MAO ceramic film prepared in 10 g/L Na2SiO3 electrolyte solution against GCr15 steel ball. Studies in mechanisms suggested that as the Na2SiO3 concentration in the electrolyte increased, the MAO ceramic film became denser, which could prevent the penetration of corrosive medium, promote the generation of the anti‐wear layer with SiO2 as the main component to enhance the wear resistance. MAO ceramic film formed in Na2SiO3 electrolyte solution provided good protective performance for Al‐Mg‐Sc alloy in the corrosion and wear conditions, which had a broader application prospect.

Effect of Cu content on quenching sensitivity relative to exfoliation corrosion susceptibility of Al-Zn-Mg-(Cu) alloys

The effect of Cu content on quenching sensitivity relative to exfoliation corrosion susceptibility of Al-Zn-Mg-(Cu) alloys was investigated by electrochemical test, immersion test, optical microscopy, electron backscattered diffraction, scanning electron microscopy, scanning transmission electron microscopy and scanning Kelvin probe force microscopy. As quenching rate decreases from 400 °C/s to 4 °C/s, exfoliation corrosion (EXCO) susceptibility increases for Cu-containing alloys (0.5–2.6 wt%); while for the Cu-free alloy, EXCO susceptibility first increases and then decreases, reaching the lowest at the quenching rate of 70 °C/s, and then continues to increase. Quenching sensitivity of the Cu-free alloy is the lowest, and that of Cu-containing alloys is similar. The decrease of quenching rate or the increase of Cu content leads to a larger difference in the Volta potential between grain boundary precipitates (GBPs) and the matrix. Corrosion tends to propagate only along grain boundaries at high quenching rates, but along both grain boundaries and subgrain boundaries below a critical quenching rate, which increases with increasing Cu content. The corrosion behavior has been discussed primarily based on the features of GBPs and precipitates free zones, and the Volta potential difference between GBPs and the matrix. • Quenching sensitivity is the lowest for Al-Zn-Mg and similar for Al-Zn-Mg-Cu. • EXCO susceptibility of Al-Zn-Mg-Cu is higher at a lower quench rate. • EXCO susceptibility of Al-Zn-Mg is lowest at the quench rate of 70 °C/s. • Corrosion path is related to quench rate and Cu content. • Potential difference is larger at a lower quench rate or a higher Cu content.

Improved corrosion resistance of EP coating on Mg alloy through GO hybridization and silica-based superhydrophobic surface

Epoxy resin (EP) coating has high hydrophilicity and poor long-term corrosion resistance. In order to improve its protection ability, an EP-graphene oxide (GO)/SiO 2 multifunctional coating is fabricated on Mg-Zn-Ca alloy in this study, through a spin/spray assisted self-assembly technique. The morphologies and microstructures of the coated samples were observed using scanning electron microscopy (SEM), Fourier infrared spectrometer (FTIR) and atomic force microscope (AFM). Hydrophobicity and self-cleaning property of the composite coating were tested by an optical contact angle meter and black graphite powders. The stability of the superhydrophobic surface was tested by rubbing with sandpaper and immersing in corrosion solution. The corrosion resistance of coated samples was tested in 3.5 % NaCl solution using electrochemical impedance spectroscopy (EIS). The GO sheets are uniformly dispersed in EP coating. EP-GO acts as a dense bottom layer, effectively promoting its adhesion with the superhydrophobic SiO 2 coating, and the water contact angle (WCA) values range from 158° to 168°. After stability testing, the WCA value of the superhydrophobic coating remains at a high level (115°–155°). The R ct of this composite coating was remarkably increased to 1.0 × 10 22 Ω/cm 2 , implying that the corrosion resistance was improved by eighteen orders of magnitude compared to bare substrate. These results show that the combination of the labyrinth effect and the hydrophobic surface extend the corrosion path and reduce the contact area of the corrosion solution with the coating, which strengthens the barrier effect of the composite coating. The composite coating exhibits superior corrosion resistance durability and self-cleaning property. • EP-GO/SiO 2 coating exhibits superior anticorrosion/self-cleaning properties. • Labyrinth and superhydrophobic effects improve the barrier ability. • Superhydrophobic top layer possesses good stability.

An Opposite Tendency of Mechanical Properties and Corrosion Resistance of a High-Strength Al-5024 Alloy Processed by Laser Powder Bed Fusion

Abstract Laser Powder Bed Fusion (LPBF) manufactured Al-5024 alloy has gained worldwide interest due to its ability to fabricate high-performance complex components. This work focuses on quantitative characterization and synergic optimization of the microhardness, tensile strength, and corrosion resistance of an LPBF manufactured Al-5024 alloy by optimization of heat treatment parameters. The effect of the isothermal heat treatment (IHT) process on the microstructure evolution, mechanical properties, and electrochemical properties of an LPBF-processed Al–4.2Mg–0.4Sc-0.2Zr alloy was systematically revealed. Results showed that superior tensile strength of 506.7 ± 10.4 MPa combined with inferior corrosion resistance was simultaneously obtained at a peak-aging condition. Based on microstructure observations by electron microscopy in backscattered mode (BSE) and transmission electron microscopy (TEM), the enhanced mechanical properties were attributed to the generation of a high number density (3.8 × 109/mm2) of grain interior precipitates, while the reduced corrosion resistance was related to the massive Al3(Sc,Zr) precipitates generated along grain boundaries. As aging time further increased, the size and spacing of the precipitates were increased, which blocked the corrosion path along grain boundaries and led to a reduction of mechanical properties and an enhancement of corrosion resistance. Unlike the expected synergistic improvement in mechanical properties and corrosion resistance, an opposite evolution tendency of mechanical properties and corrosion resistance of LPBF-processed Al-5024 alloy during heat treatment was revealed in this paper, and its intrinsic mechanism is further analyzed based on microstructure characterization.

Investigation of the corrosion resistance of graphene-nickel composite micro-parts

Nickel-based microparts possess a short lifetime owing to their rapid dissolution in corrosive environments. To mitigate this phenomenon, composite microparts of graphene/Ni were prepared using UV-LIGA technology; their corrosion behavior was examined in acid, alkali, and salt solutions as well as after subjecting them to heat-treatment processes. The microstructures were investigated with scanning electron microscopy (SEM), x-ray diffraction (XRD), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). Corrosion resistances were characterized through various electrochemical tests and compared with those of pure Ni microparts. The results demonstrate that the surface oxidation layer (i.e.,the protective layer) of the microparts was readily destroyed in NaCl and H2SO4 solutions without the formation of a passivation film; however, a passivation film was formed in the NaOH solution. The corrosion rates of graphene/Ni in NaCl, NaOH, and H2SO4 corrosion solutions were reduced by 73%, 22%, and 84%, respectively, relative to those of pure Ni microparts. This can be primarily attributed to the homogeneous dispersion of graphene in the Ni matrix, which refined the grain size, and the impermeability and chemical stability of graphene, which lengthened the diffusion path of the corrosive medium. In addition, heat treatment of the graphene/Ni microparts at 200 °C increased the corrosion resistance by a factor of nearly one with little change in microhardness, which can be attributed to the removal of internal stress and the increased proportion of CSL grain boundares. Corrosion occurred at the interface between nickel and graphene, lengthening the corrosion path.

A versatile thin polysiloxane composite coating targeting for threads endowed with properties of anti-corrosion and friction reduction

Threads play an essential role of connecting pipes, but they are still faced with an enormous challenge of corrosion and gluing. Herein, the thin polysiloxane composite coating filled with MoS2 modified by γ-(2, 3-epoxypropoxy) propytrimethoxysilane (MK) and nano-SiO2 was prepared. MK prolongs the corrosion path and possesses lubrication property while nano-SiO2 fills the micropores during the solvent evaporation and provides rolling friction simultaneously. The synergistic effect of MK and nano-SiO2 endows coatings with unique properties of anti-corrosion and friction reduction, catering for the demands of thread coatings. Specifically, electrochemical impedance spectroscopy (EIS) manifested that the impedance at 0.01 Hz of the optimal ~30-μm-thick coating still maintained at 3.16 × 1010 Ω·cm2 after the immersion in 3.5 wt% NaCl solution for 30 days. The average coefficient of friction (COF) of the final product was 0.2769, decreasing by 27.69 % compared with that of the pure 818C coating, which could lower the risk of thread gluing. The composite coating prepared in this work could become a potential candidate of protecting threads.

Effect of special grain boundary on hot corrosion path in Incoloy825 alloy

Effect of special grain boundary on hot corrosion path in Incoloy825 alloy

The Corrosion Susceptibility of 304L Stainless Steel Exposed to Crevice Environments.

The present study focuses on the corrosion behavior of 304L stainless steel in crevice corrosion environments. The specimen with a salt deposit of 0.1 g/m2 was assembled with a crevice former made of Poly-tetra fluoroethylene (PTFE) to make a test device. The assembled test devices were kept at the ambient temperature of 45 °C in combination with a relative humidity of 45%, 55%, and 70%. After testing for 5000 h, the corroded area of the specimen exposed to 70% humidity was three times larger than that subjected to 45% humidity. For the specimen sustaining a tensile force, the crack growth rate was approximately 1.4 mm/year at the stress level of 300 MPa in a crevice corrosion environment with 0.1 g/m2 of sea salt deposited on the surface. The small portion of intergranular cracking occurred at the surface due to the existed strain on the surface. As cracks propagate in a grain, the grain undergoes a greater localized deformation, and some secondary cracks would develop inside the grain; transgranular cracking was vigorous due to the path corrosion that nucleated at the slip steps.

Sulfide Stress Cracking (SSC) of Low Alloy Linepipe Steels in Low H&lt;sub&gt;2&lt;/sub&gt;S Content Sour Environment

Resistance to Sulfide Stress Cracking (SSC) caused by local hard zones of pipe inner surface has been required in low alloy linepipe steel. In this study, using two samples with different surface hardness, the detailed SSC initiation behavior was clarified by four-point bend (4PB) SSC tests in which immersion time and applied stress were changed in a sour environment containing 0.15 bar hydrogen sulfide (H2S) gas. SSC cracks occurred when the applied stress was higher than 90% actual yield strength (AYS) in higher surface hardness samples over 270 HV0.1. From the fracture surface observation of SSC crack sample, it was found that the mechanism gradually shifted from active path corrosion (APC) to hydrogen embrittlement (HE), and that the influence of APC mechanism remained partially in the process of SSC initiation at the tip of corrosion pit or groove. The polarization measurement in the 4PB SSC test showed that the anodic and cathodic reactions (especially cathodic reactions) were activated when the applied stress was 90% AYS or higher. The FEM coupled analysis simulating the stress and strain concentration at the bottom tip of the corrosion groove and the hydrogen diffusion and accumulation was carried out. The principal stress in the tensile direction showed the maximum value at 0.04-0.06 mm away from the tip of the corrosion groove, and the hydrogen accumulation became the maximum. It was analytically found that the SSC crack initiated and propagated with HE mechanism dominated type when the threshold value of about 0.82 ppm is exceeded.

Influence of silane functionalized nanoclay on the barrier, mechanical and hydrophobic properties by clay nanocomposite films in an aggressive chloride medium

The surface alteration of silica clay by a silane coupling agent was done to improve the compatibility with epoxy polymer matrix. It can be attained with ethoxy based silanes namely (3-mercaptopropyl) triethoxysilane (MPTES), propyltriethoxysilane (PTES) and 3-aminopropyl(diethoxy)methylsilane (APDES) in order to enhance the anticorrosion potential of epoxy coatings on mild steel. The structural and thermal properties of the functionalized clay nanoparticles are studied by X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The morphological features of the functional nanoclay were also described by employing field emission scanning electron microscopy with energy dispersive x-ray analysis (FE-SEM/ EDX) and TEM (Transmission electron microscopy) analysis. These analyses showed the well functionalization of nanoclay by silanes. The well dispersion of functionalized nanoclay in the epoxy resin produces better nanocomposites which are coated on the mild steel. The coated steel samples were analyzed in terms of microstructure and corrosion resistant properties in 3.5% NaCl solution. Electrochemical impedance spectroscopy (EIS), scanning electrochemical microscopy (SECM), salt spray analysis, and analysis of oxygen and water permeability were applied to assess the barrier properties against water permeation, oxygen penetration and protectiveness of silane-modified epoxy coatings. It was found that all the modified coatings showed higher barrier resistance and superior corrosion resistance than pure epoxy coating, which were described by higher charge transfer resistance (Rct) 6815.36 kΩcm2 and lower double-layer capacitance (Cdl) 405.51 µF at the electrolyte/metal interface. The tensile strength was found to be 113 MPa for EP-MPTES/clay nanocomposite while the value of pure epoxy coated specimen was 41 MPa. Therefore, the silane grafted clay nanoparticles results in slower diffusion processes, which specifically slow down the anodic reaction, thus blocking the overall corrosion path. Modified clay-epoxy nanocomposite displays good thermostability, better dispersion, outstanding mechanical property and superior water resistance property. Among the examined silanes, MPTES shows an effective functionalization of nanoclay, followed by the APDES and PTES. A possible mechanism has also been proposed.