Potentiodynamic Polarization Tests Research Articles

Pitting behavior of austenitic stainless-steel welded joints with dense inclusions and methods to enhance pitting resistance

Purpose This study aims to assess the pitting resistance of austenitic stainless steel welded joints fusion zone (FZ) with high density of inclusions before and after surface treatment, including potentiostatic pulse technique (PPT) and pickling. Design/methodology/approach The potentiodynamic polarization tests and critical pitting temperature tests were carried out for estimating pitting resistance. The PPT and pickling were performed as surface treatment. Scanning electron microscope (SEM) and energy dispersive spectrometer were used for characterize the microstructure and elemental distribution. Electron back-scattered diffraction (EBSD) was used to assess the portion of phases and morphology of grains. Findings The weld metal exhibits a higher degree of alloying compared to the base metal, and it contains d-phase and sulfur-containing inclusions. Sulfur-containing inclusions serve as initiation sites for pitting, and they diminish the pitting resistance of weld metal. Both PPT and pickling can remove sulfur-containing inclusions, but PPT causes localized dissolution of the weld metal matrix around the inclusions, while pickling does not. Because of the high density of inclusions, certain pits initiated by PPT are significantly deeper, which makes the formation of stable pitting easier. Because of the high density of inclusions, certain pits initiated by the PPT are deeper. This characteristic facilitates the progression of these initial defects into fully developed, stable pits. Originality/value Analysis of pitting initiation in shielded metal arc welding FZ with PPT and ex situ SEM tracking observation. Explanation of why the PPT surface treatment is not able to enhance the pitting resistance of stainless steel with a high inclusion density.

In vitro degradation behavior of grain refined WE43 magnesium alloy for biodegradable temporary implant applications

AbstractIn the present work, grain‐refined WE43 magnesium alloy was produced by friction stir processing to investigate the in vitro degradation behavior targeted for temporary bone implant applications. Friction stir processing resulted in significant grain refinement (from 46±4.2 μm to 16.1±5.4 μm) as observed from microstructural studies. Increased wettability was observed from the contact angle measurements in grain‐refined WE43 alloy. The corrosion behavior of the base alloy and the grain refined alloy assessed by potentiodynamic polarization tests demonstrated the influence of the smaller grain size and decreased intermetallics on enhancing corrosion resistance. Immersion studies carried out in simulated body fluids for one week indicated a quick development of the protective magnesium hydroxide on the surface of grain‐refined WE43 alloy compared with the base alloy. The deposition of the mineral phases from the immersed solution on the surface of the samples was studied by scanning electron microscopy and x‐ray diffraction analysis to assess the effect of microstructure on the biomineralization. Promisingly, grain refined WE43 exhibited relatively excellent mineral deposition which further helped to control the degradation of the alloy. The weight loss measurements of the samples from the immersion tests were also in good agreement with the electrochemical test results. Hence, the results demonstrate the promising role of grain refinement by friction stir processing in tailoring WE43 magnesium alloy with better degradation behavior for temporary bone implant applications.

Formation of heterogeneous microstructure and its effect on corrosion properties of high-silicon stainless steel S38815 weldment

This study aims to clarify the formation of heterogeneous microstructure and its effect on corrosion properties of high-silicon stainless steel (high-Si SS) S38815 weldment. A series of tests about microstructure and electrochemical characteristics were performed, including the electron backscatter diffraction (EBSD) analysis, Mott-Schottky tests, electrochemical impedance spectroscopy (EIS) tests, potentiodynamic and potentiostatic polarization tests. The formation mechanism of heterogeneous microstructure related to high-silicon and its correlation on corrosion was discussed extensively. The results show that the significantly deformed and recrystallised grains were observed at the low temperature heat affected zone (LT-HAZ) and high temperature heat affected zone (HT-HAZ) respectively. The metastable pitting and low impedance values were formed in the above region, despite their low donor density. The deterioration in corrosion resistance of S38815 weldment as a result of high-angle grain boundaries (HAGBs) and carbides is more pronounced than the beneficial impact of Cr and Si oxidation. This study provides valuable references to the manufacturing and enhancing the anti-corrosion properties of this high-Si SS.

Effect of Annealing after Casting and Cold Rolling on Microstructure and Electrochemical Behavior of High-Entropy Alloy, Cantor

High-entropy alloys (HEAs), a relatively new class of materials, have attracted significant attention in materials science owing to their unique properties and potential applications. High entropy stabilizes the phase of a solid solution over a wide range of chemical compositions, yielding unique properties superior to those of conventional alloys. Therefore, this study analyzed the microstructure and electrochemical behavior of HEAs (Cantor) to evaluate their corrosion resistance, according to their manufacturing process (casting, cold rolling, and annealing). The microstructural morphologies and sizes were analyzed using electron backscatter diffraction. The electrochemical behavior was examined using open circuit potential measurements, electrochemical impedance spectroscopy, potentiodynamic polarization tests, and critical pitting temperature measurements using a potentiostat. The casting process formed a nonuniform microstructure (average grain size = 19 μm). The cold rolling process caused the formation of fine grains (size = 4 μm). A uniform microstructure (grain size > 151 μm) was formed after heat treatment. The corrosion resistance of the HEAs was determined from the passivation layer formed by Cr oxidation. These microstructural differences resulted in variations in the electrochemical behavior. Microstructural and electrochemical analyses are crucial because HEAs have diverse potential applications. Therefore, this study contributes to future improvements in HEA manufacturing processes.

Tribological and electrochemical behaviour study of porous TiNiCu alloys manufactured by the powder metallurgy process

ABSTRACT The experimental work aims to study the effect of the Copper (Cu) addition on the tribological and electrochemical behaviour of porous Ti50Ni50-x-Cux alloys. In the first step pure metal powders of titanium (Ti), nickel (Ni), and Cu were ball-milled during 8 h in a planetary ball mill, and then compacted under a 4 ton load to obtain pre-alloyed powders. The final step is sintering at 950°C for 7 h in a tubular furnace under a controlled atmosphere. X-ray diffraction measurements (XRD), scanning electron microscopy (SEM) analyses, microhardness measurements, friction tests and electrochemical were carried out to characterise the tribological and electrochemical performances of the elaborated specimens. DRX results reveal the formation of four major phases: TiNi, Ti2Ni, TiNi3 and TiNi0.8Cu0.2. Potentiodynamic polarisation tests show the positive effect of adding Cu on corrosion resistance, where the 6% Cu sample exhibits the best corrosion behaviour. Tribological results show a decrease in the coefficient of friction and wear rate with the addition of Cu, compared to the initial state, without Cu addition. The minimum coefficient of friction (0.585) was recorded for the 2% Cu sample, while the minimum wear rate (Ws = 1.06. E−4mm3/N/m) was achieved for the 4% Cu sample.

A surface and corrosion characterisation of micro arc oxidation treated friction stir welded ZM21 and ZE41 magnesium alloy: a comparison study

Magnesium alloys have gained attention as promising materials in industrial applications, for their high specific strength and low density. Magnesium alloys have desirable mechanical properties, but their poor corrosion resistance prevents their safe implementation. Alloys such as ZM21 and ZE41, possess unique properties that provide improved machinability and increased red-hot strength, respectively, while remaining prone to corrosion. To improve corrosion resistance, surface treatments and coating processes are employed. Comparing the corrosion characteristics of ZM21 and ZE41 is vital for aerospace and automotive applications, directly affecting component durability, reliability, and performance against corrosion. Magnesium alloys are frequently joined through friction stir welding (FSW), hence, similar importance is provided to studying the corrosion performance of welds, since FSW introduces microstructural changes that alter corrosion performance of welded joints. The paper discusses electrochemical corrosion mechanisms and analyzes the effect of Micro Arc Oxidation (MAO) coating on electrode potential, passivity, and electrical resistance of ZM21 and ZE41 plates welded through FSW. MAO treatments were performed on both base material and FSW joints. The corrosion performance of MAO-coated FSWed ZM21 and ZE41 alloys was compared through the Electrochemical Impedance Spectroscopy (EIS) and Potentiodynamic Polarisation (PDP) tests. The PDP test revealed that MAO treatment enhanced the corrosion resistance of both base and FSWed ZM21 and ZE41 magnesium alloys. There was an improvement in potential polarization (Rp) values from 565 Ω cm2 to 11245 Ω cm2 for ZM21 and from 1184.4 Ω cm2 to 11435.69 Ω cm2 for ZE41 alloys. While exhibiting improvements in corrosion resistance, MAO-treated ZE41 performed better than MAO-treated ZM21. PDP results were verified through confirmatory EIS results. Therefore, MAO treatments are effective methods to improve the corrosion performance of Mg alloys. Evaluation of MAO coating performance on various FSW Mg alloys and studying their corrosion performance is crucial for engineering material selection.

Influence of Deposition Temperature and WC Concentration on the Microstructure of Electroless Ni-P-WC Nanocomposite Coatings with Improved Hardness and Corrosion Resistance

This study aims to develop Ni-P coatings with high P content (≥11 wt.%) reinforced with WC nanoparticles on F22 steel substrates. The introduction of conductive WC in the plating solution dramatically increases reactivity of the plating solution, and consequently a tuning of deposition parameters, in terms of temperature and WC concentration, is required to obtain nanocomposite coatings with improved mechanical properties. The coatings’ porosity and incorporation and dispersion of the reinforcing phase as a function of temperature and WC concentration were analyzed by quantitative image analysis from Scanning Electron Microscopy (SEM) micrographs. Increasing the temperature and concentration of nanoparticles leads to a faster plating rate and a dramatic increase in both porosity and agglomeration of the reinforcing phase, with detrimental effects on the coatings’ microhardness. The best compromise between coating parameters was obtained by deposition at 70 °C and 6.5 g/L of WC, with a plating rate ≈ 12 μm/h, porosity lower than 1.5%, and a good combination between particle incorporation and agglomeration. In these conditions, a hardness increase by 34% is achieved in comparison to standard Ni-P. Coatings were then heat treated in air at 200 °C for 2 h, to induce growing stress relaxation, or 400 °C for 1 h, to study effects of crystallization and precipitation. X-Ray Diffraction (XRD) analysis demonstrated that WC introduction does not alter the microstructure of Ni-P coatings, but delays grain growth coarsening of precipitates. Hardness improvement by 6.5% and 45% is registered after treatment at 200 °C and 400 °C, respectively. An increase in elastic modulus, measured by instrumented indentation, was found in WC-reinforced coatings compared with Ni-P. Potentiodynamic polarization tests revealed that both introduction of WC nanoparticles and heat treatment also enhance corrosion resistance.

Enhancing wear resistance, anti-corrosion property and surface bioactivity of a beta-titanium alloy by adopting surface mechanical attrition treatment followed by phosphorus ion implantation

A two-step method of surface mechanical attrition treatment (SMAT) followed by phosphorous (P) ion-implantation was adopted to treat Ti-25Nb-3Mo-2Sn-3Zr (named as TLM) alloy. The initial SMAT process refined the grains from micrometer-scale to about 10–30 nm, and begot the TLM surface much rougher with apparently improved hydrophilicity. The subsequent P ion-implantation led to the formation of a hybrid structure of the TiP, β-Ti nanograins and P-interstitial amorphous in the surface layer of the TLM alloy, and resulted in a slight decrease of the surface roughness and wettability of the SMAT-processed alloy. The indentation, tribology and potentiodynamic polarization tests indicated that the SMAT procedure concurrently enhanced the microhardness, wear-resisting property and corrosion resistance of the TLM alloy, and the followed P-ion implantation could further improve these tested properties. Moreover, the P-ion implanted TLM alloy was verified to exhibit much better surface bioactivity (including biomineralization in the simulated body fluid (SBF) and in-vitro cell adhesion) as compared to the original TLM alloy. With the remarkable improvements of the wear resistance and anti-corrosion property as well as the surface bioactivity of the P ion-implanted TLM alloy, our study provides an alternative avenue to fabricating new-type Ti-based orthopedic implants with superior comprehensive performance

Comprehensive analysis of mechanical properties, wear, and corrosion behavior of AA7075-T6 alloy subjected to cryogenic treatment for aviation and defense applications

It is important that the parts to be used in the aviation and defense industry have high wear, fatigue and corrosion resistance. AA7075-T6 alloys are increasingly used in every field due to their advantageous physical and mechanical properties. However, some of the materials of this alloy types exhibit excellent fatigue strength and ductility, but their surface hardness and surface roughness after processing may be poor. For this reason, the wear resistance of AA7075-T6 aluminum alloy expected to be improved in order to increase their corrosion resistance properties. In this work, cryogenic treatment was applied to AA7075-T6 alloy and the mechanical characteristics, wear and corrosion behaviors of these samples were examined. As a result of the experiments, it was determined that cryogenic treatment improved the wear behavior of AA7075-T6 alloy. The untreated sample was found to have the highest wear rate, whereas the sample with deep cryogenic treatment (DCT) had the lowest wear rate. The hardness of the DCT process increased by 5.79 %, according to macro hardness measurements, making the AA7075-T6 alloy harder from 80.16 HRB to 84.8. The SEM images revealed that, the shallow cryogenic and deep cryogenic operations had substantial effects on the microstructure by modifying the size and distribution of precipitates in the AA7075-T6 alloy. In addition, tensile and hardness tests were carried out to assess the mechanical characteristics of the samples. Accordingly, the maximum tensile strength and hardness values were obtained in the deep cryogenically treated sample. The tensile strength of the DCT sample was approximately 544.18 MPa, a considerable 11.5 % increase above the untreated sample's 488.07 MPa strength. In potentiodynamic polarization testing, the DCT treated sample was determined to have the maximum corrosion resistance. Among the materials tested, the DCT sample showed the strongest corrosion resistance, with a corrosion potential of −0.689 V and a corrosion rate of 0.021 mm/year. Wear rate analysis revealed that DCT samples experienced the least material loss, demonstrating improved abrasion resistance. Enhanced hardness and the formation of stable oxide tribo-layers contributed to these superior wear characteristic.

Preparation and characterization of Ti5Al16O34 PEO ceramic coatings deposited on CP-Ti in mixed aluminate-phosphate electrolytes

Oxide ceramic layers of Ti5Al16O34 were fabricated on commercially pure titanium grade 2 substrates by plasma electrolytic oxidation in aqueous electrolyte media at a fixed 10 g/L concentration of trisodium phosphate and 25 g/L sodium aluminate. Lowering the sodium aluminate concentration to 15 g/L and 20 g/L, β-TiAl2O5 and Ti2Al6O13 components were produced under similar PEO processing conditions. The composition and structure of the PEO coatings were studied using XPS, XRD, SEM, EDS, mechanical (hardness, adhesion, and tribology), electrochemical impedance spectroscopy, and potentiodynamic polarization tests. The layers possess a polycrystalline character with minor amorphous phases, while their thicknesses varied slightly between samples with similar treatment times. The PEO coatings consist of a compact inner layer with an enriched phosphorus content of about 5–10 wt% and a porous outer layer in which phosphorus is found in less than 1 wt%. Ti5Al16O34 coatings showed better mechanical performance regarding microhardness and corrosion resistance compared to β-TiAl2O5 and Ti2Al6O13. At a longer applied PEO process duration of 10 min, Ti5Al16O34 layer thickness, microhardness, and corrosion current densities of 40.2 μm, 9.37 GPa, and 2.8 nA/cm2 were measured.

Effect of Temperature on the Corrosion Behavior of a Al2Cr5Cu5Fe53Ni35 Multi-Principal Element Alloy (MPEA) in Simulated Soil Environments

The effect of varying temperatures (15, 35, and 45 °C) on the corrosion behavior of a new single-phase distorted face-centered cubic (fcc) Al2Cr5Cu5Fe53Ni35 multi-principal element alloy (MPEA) was studied in simulated soil environments (NS4 solution). X-ray diffraction and electron backscattered diffraction were used to confirm the presence of a single phase throughout the microstructure. Electrochemical tests such as electrochemical impedance spectroscopy and linear polarization resistance were performed to evaluate the interfacial behavior and corrosion rate at various test conditions. Additionally, cyclic potentiodynamic polarization (CPP) tests were also carried out at the selected temperatures to study the pitting behavior of the MPEA. Surface characterization techniques such as X-ray photoelectron spectroscopy and scanning electron microscopy were used to identify the nature of the passive film formed in such complex materials as well as study the pitting characteristics after CPP testing. A stable passive film was found to be present all tested temperatures with the absence of preferential sites for pitting due to homogenous element distribution.

Effect of solvent acids on the microstructure and corrosion resistance of chitosan films on MAO-treated AZ31B magnesium alloy

This study evaluated the effect of solvent acids on the structure and corrosion resistance performance of chitosan (CS) film on MAO-treated AZ31B magnesium (Mg) alloy. Initially, CS solutions were prepared in four solvent acids: acetic acid (HAc), lactic acid (LA), hydrochloric acid (HCl), and citric acid (CA). The CS films were subsequently deposited on MAO-treated AZ31B Mg alloy via a dip-coating technique. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction analysis (XRD), Fourier-transform infrared spectroscopy (FT-IR), contact angle measurement, and atomic force microscopy (AFM) were employed to characterize the surface and cross-sectional morphology as well as chemical composition. Furthermore, the samples were subjected to potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) tests to assess their resistance against corrosion in simulated body fluid (SBF). These results indicated that the CS film prepared with LA exhibited the lowest surface roughness (Ra = 31.2 nm), the largest contact angle (CA = 98.50°), and the thickest coating (36 μm). Additionally, it demonstrated superior corrosion protection performance, with the lowest corrosion current density (Icorr = 3.343 × 10−7 A/cm2), highest corrosion potential (Ecorr = −1.49 V), and highest polarization resistance (Rp = 5.914 × 104 Ω·cm2) in SBF. These results indicated that solvent acid types significantly influenced their interactions with CS. Thus, the structure and corrosion protection performance of CS films can be optimized by selecting an appropriate solvent acid.

Fabrication and characterization of hydroxyapatite coatings on anodized magnesium alloys by electrochemical and chemical methods intended for biodegradable implants

The fabrication of hydroxyapatite (HAP)/MgO composite coatings on Mg alloy is crucial for enhancing the corrosion resistance and biocompatibility of biomedical implants. In this study, we aimed to investigate the effects of two different surface modification methods, i.e., electrochemical (electrodeposition, ED) and chemical (solution treatment, ST), on the phase structure, degradation properties, and biocompatibility of the composite coatings in comparison to the anodized coating. The surface morphologies and crystalline structures of the coatings were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Subsequently, the degradation rate of the coatings in simulated body fluid were comprehensively evaluated by using electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and scanning electrochemical microscopy (SECM) tests. Additionally, in-vitro cell proliferation assays were employed to quantitatively assess the biocompatibilities of the coatings. The results showed that both ED and ST methods were effective in depositing HAP on anodized Mg alloy, resulting in different surface morphologies with hydroxyapatite layer thicknesses of 2.71 μm and 3.56 μm, respectively. In this way, the HAP-deposited coatings exhibited improved corrosion resistances and biocompatibilities compared with those of the anodized coating. Specifically, the ST-deposited composite film displayed superior degradability and biocompatibility which was attributed to its filiform surface morphology and thicker HAP layer. Overall, the present study demonstrates the potential of HAP/MgO composite coatings for biomedical applications, with implications for the development of advanced implant materials with improved performance and biocompatibility.

Comprehensive investigation of a new pyrazole derivative Schiff base complex: Revealing its potent protection against carbon steel corrosion

A new pyrazole derivative from 4-Aminoantipyrine Schiff base complex, which has the potential for corrosion inhibition, have been successfully synthesized (HL). The objective of this research is to enhance the corrosion inhibition activities of the synthesized HL by coordinating it with Cobalt to form complex compound (Co-L) on mild steel. HL and Co-L molecules will be immobilized on the surface of mild steel, creating a protective layer against corrosion-causing species. The synthesized compounds underwent characterization using various techniques, including UV-Visible Spectrophotometer, Fourier Transform Infrared, Nuclear Magnetic Resonance, X-Ray Diffraction, Magnetic Susceptibility Balance, and Elemental Analysis, confirming the success of the synthesis. Corrosion tests were conducted using the Weight Loss method and Potentiodynamic Polarization (PDP). The results indicate that the complex forms of compounds exhibit higher corrosion inhibition efficiency compared to their ligands. In the Weight-Loss method test (in 1.0 M HCl solution), Co-L compounds demonstrated superior performance efficiency at a concentration of 1 ×10−4 M, reaching 92.96 %, while HL showed an efficiency of only 86.89 %. The PDP test revealed that the HL and Co-L exhibited inhibition efficiencies of 87.13 % and 93.97 %, respectively, at a specific concentration. Monte Carlo simulation further supported these findings, indicating that inhibitor molecules are adsorbed on the metal surface, with the energy of adsorption for the Co-L inhibitor surpassing that of HL. This simulation result correlates linearly with experimental observations.

Characterization of Electrochemical and Biocompatibility of Zinc Oxide Coating Electrodeposited on Commercial Pure Titanium Alloy

This study examines how the duration of electrodeposition affects the morphology and electrochemical characteristics of zinc oxide coatings applied to a pure titanium substrate. The morphology of the coating and the phases present within it are analyzed using a scanning electron microscope and the X‐ray diffraction technique. The coating's resistance to corrosion in a phosphate‐buffered saline solution is evaluated using two electrochemical methods: impedance spectroscopy and potentiodynamic polarization tests. The surface roughness of the coated samples is assessed using interferometry. The results demonstrate that an increase in electrodeposition time, ranging from 150 to 1200 s, leads to an enhanced texture intensity in the (0002) and (010) planes of the ZnO coating. Furthermore, the thickness of the ZnO crystals and surface roughness increases by factors of 3.25 and 2.79, respectively, as the deposition time is extended. This extended duration results in the formation of larger needle‐shaped and flower‐like ZnO crystals, leading to a significantly nonuniform structure. Correspondingly, the corrosion rate also increases as the electrodeposition time is extended from 150 to 1200 s, rising from 0.001951 to 9.117 μm year−1. The lowest corrosion rate (1.654 μm year−1) is achieved in coatings deposited for 300 s using a potential of 3 V.

Comprehensive Investigation of the Adsorption, Corrosion Inhibitory Properties, and Quantum Calculations for 2-(2,4,5-Trimethoxybenzylidene) Hydrazine Carbothioamide in Mitigating Corrosion of XC38 Carbon Steel under HCl Environment.

This study investigates the inhibitory effects of 2-(2,4,5-trimethoxy benzylidene) hydrazine carbothioamide (TMBHCA) on the corrosion of carbon steel in a 1 M HCl solution across various concentrations. The assessment employs a comprehensive approach, combining gravimetric analysis, potentiodynamic polarization tests, and electrochemical impedance spectroscopy (EIS). Additionally, scanning electron microscopy (SEM) and quantum chemical calculations are employed to provide a thorough understanding of the corrosion inhibition mechanism. The influence of exposure time on mild steel corrosion is systematically examined. Results reveal a remarkable reduction in the corrosion rate of steel, with TMBHCA demonstrating its highest inhibition efficiency of 97.8% at 200 ppm. Potentiodynamic polarization studies characterize TMBHCA as a mixed-type inhibitor, while Nyquist plots illustrate increased charge transfer resistance and decreased double-layer capacitance with escalating TMBHCA concentrations. Consistency between weight loss measurements and electrochemical findings further validates the efficacy of TMBHCA as a corrosion inhibitor. SEM images substantiate and visually support the obtained results. An immersion test conducted at 25 °C over 28 days showcases a notable enhancement in TMBHCA efficiency (IE%) from 45.16% to 92.43% at 200 ppm as the immersion period progresses from 1 day to 28 days. This improvement is attributed to the augmented adsorption of inhibitor molecules on the steel surface over time. These comprehensive findings significantly contribute to our understanding of TMBHCA's corrosion inhibition behavior, emphasizing its potential as a highly efficient corrosion inhibitor for diverse industrial applications.

In-vitro biocompatibility, antibacterial activity, and corrosion resistance of HA-TiO2/ZnO coating fabricated by plasma electrolytic oxidation on Ti6Al4V

The hydroxyapatite/Zinc Oxide (HA-TiO2/ZnO) coatings were grown on the Ti6Al4V substrate by plasma electrolyte oxidation from the CaP-based electrolyte containing 1, 3, and 6 g/L ZnO nanoparticles. XRD results confirmed the presence of ZnO, HA, and rutile phases in all coatings. According to SEM observations, coatings presented the porous morphology as a result of micro-arc discharges during the PEO process, whereas some of the pores in the composite coatings were filled by ZnO proportional to its content. After 7 days of immersion in SBF solution, accumulations of bone-like clusters were visible on the surface, demonstrating a promising bio-mineralization ability for all coatings, although the higher amount of 6 g/L ZnO had partially an inhibitory effect on the apatite nucleation. In-vitro studies demonstrated a time and concentration-dependent impact of ZnO on the viability of MG-63 osteoblast-like cells so that the concentration of 3 and 6 g/L caused the death of some cells after 7 days. The antibacterial tests also showcased that the presence of ZnO decreased the activity of gram-negative bacteria (E. coli) and gram-positive bacteria (S. aureus), while the higher concentration of ZnO particles led to more antibacterial activity of the coating. Finally, evaluating the corrosion behavior of PEO coatings through a potentiodynamic polarization test in Ringer's solution manifested a better protection against corrosion by increasing the ZnO content in the coating, mainly owing to the blocking of the pores by the ZnO particles, and as a result, the greater difficulty of electrolyte to reach the titanium substrate.

Emerging Mo-doped MgAl-LDH lamellar/carbon nanotubes as 3D sustainable nanohybrid for designing a durable smart anti-corrosion composite

This paper focused on the utilization of 3D hybrid nanocomposites composed of layered double hydroxides (L) containing sodium molybdate (SM), which are chemically bonded with functionalized multi-walled carbon nanotubes (FCN), as nanocarriers for smart corrosion prevention. The SM molecules were loaded into the L, and L/FCN nanocarriers by an anion exchange process, and then the 3 synthesized nanoparticles (i.e., L, SM-L, and SM-L/FCN) were characterized. Following the electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PD) tests' outcomes, the maximum corrosion prevention efficiency (about 90.88 %) belongs to the SM-L/FCN nano reservoir containing saline extract. Additionally, for the epoxy phase, the EIS results (on the intact and scratched specimens) revealed a significant diminish in the chloride and water penetration into the epoxy coating during 63 days of immersion. EIS results indicated the enhancement of the charge transfer resistance (Rct) of the scratched coatings, from 17.42 kΩ.cm2 for the EP sample to 72.47 kΩ.cm2 for the SM-L/FCN/EP one in long immersion times, revealing the self-repairing behavior of the designed coating. The results of intact coating revealed that the Log (|Z|0.01 Hz) value reached 10.63 in long immersion time indicating a decreased occurrence of coating disbondment attributed to the electrolyte infiltration and corrosion of the underlying metal substratum. According to the pull-off and cathodic disbonding tests results, there was an enhancement in adhesion (51.5 % decrease in loss of adhesion strength, & a 52 % decline in diameter of cathodic disbondment), and a strong interaction between the interface of epoxy and substratum. According to the mechanical tests (Tensile and DMTA) results the incorporation of L and FCN nanoparticles into the SM-L/FCN sample enhanced the nanocomposite's mechanical properties. The tensile test showed an increase in ultimate tensile strength (σUTS) and elongation at break (Ɛb) of 130.61 % and 107.59 %, respectively, compared to the pure epoxy (EP) sample. Additionally, the dynamic mechanical thermal analysis (DMTA) test indicated a 144 % increase in crosslinking density for the SM L/FCN sample compared to the neat epoxy.

Development of electrophoresed anti-corrosion coating for copper from functionalized multi layered graphene nano-sheets synthesized through anionic acidic electrochemical exfoliation

Following the discovery of graphene, a two-dimensional carbonaceous substance, numerous possibilities in materials science domain have evolved, one being its function as a corrosion inhibitor. This investigation undertakes the synthesis of functionalized multi-layered graphene nanosheets (FMLGNs) from pyrolytic graphite sheets through electrochemical exfoliation involving four distinct acid-based solutions (H2SO4, HCLO4, HNO3 and combination of the above three in 1:1:1 ratio). Post-exfoliation analysis of FMLGNs included X-ray diffraction (XRD) wherein 2θ values were reported at 26° confirming graphene's presence. Raman spectroscopy reiterated the same observation along with an increase in ID/IG ratio to ≈ 1 hinting at the presence of functional groups and defects. UV–visible spectroscopy indicating π-π* transitions, Fourier transform infrared spectroscopy (FTIR) showing CO stretching and X-ray photoelectron spectroscopy (XPS) with a C/O ratio = 3.12 gave an idea about the functionalization in FMLGNs. Average particle sizes of FMLGNs was in the range of 400–500 nm and zeta potential measurements showed stable dispersion behaviour (≈−40 mV). Utilizing scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM), authors observed a layered (10–15 layers), overlapping shape of FMLGNs. Electrophoretic deposition (EPD) method was employed to coat FMLGNs onto copper substrates under various iterative conditions (number of layers and time of deposition) which produced depositions of ≈20–30 μm. SEM images displayed adequate coverage of graphene sheets on copper surfaces, backed by energy-dispersive x-ray spectroscopy (EDS). Crack propagation resistance (CPR) values of 34.03 N highlighted better adherence than other similar coatings. The coated copper samples were subjected to cyclic voltammetry (CV), potentio-dynamic polarization (PDP) and electrochemical impedance (EIS) tests in 3.5 wt% NaCl solution for analysing the inhibitory impacts of coatings. An inhibition efficiency of 85 % and charge transfer resistance of 5535 Ω.cm2 was observed, which highlighted better corrosion mitigation than reported literatures. The authors also identified that 1 layered coatings showed better reliability than two layered coatings.

A predictive model for corrosion of carbon steel exposed to organic acids: Theory and validation in formic, azelaic and citric acid

Organic acids can severely corrode metals, despite rarely reaching particularly low pH values. The mechanisms underlying the corrosion process in the presence of organic acids can be different and more complex with respect to the ones in the presence of strong acids. Since organic acids are commonly found in several industrial environments, they pose a serious threat that needs to be carefully addressed and investigated. Throughout the years, many research efforts have been put towards predictive modeling of corrosion. The Tafel-Piontelli model aims at becoming a universal and versatile model for acidic corrosion, able to adapt to different situations and predict corrosion rates of active metals exposed to all kinds of acidic environments. The model foundations are grounded in the principles of the corrosion process, regulated by the Tafel law. The efficacy of the model was tested on carbon steel samples immersed in solutions of weak acids with increasing proticity — formic, azelaic, and citric acid — at temperatures ranging from 20°C to 60°C and pH values from 3 to 4. The validation analysis was conducted using two primary tests: mass loss tests to assess corrosion rates and potentiodynamic polarization tests to determine the kinetic parameters of the cathodic and anodic reactions involved in the corrosion process. The results from the experiments are promising, confirming and extending the predictive capabilities of the model to the case of organic acids. These findings have broad implications for improving safety and durability in industrial applications where organic acids are prevalent, highlighting the model’s potential to significantly enhance preventive strategies and material selection.