Effect of thermal annealing on the corrosion protection of stainless steel by poly(3-octyl thiophene)

Poly(3-octyl thiophene) (P3OT) coatings have been chemically deposited by drop casting onto 304-type stainless steel. P3OT films were thermally annealed at 55, 80 and 100 °C in air during 30 h and their corrosion resistance was estimated by using polarization curves, linear polarization resistance (LPR), and electrochemical impedance spectroscopy measurements, EIS. P3OT films decreased the corrosion rate of the substrate by at least one order of magnitude, although the best corrosion protection was given by annealing it at 100 °C whereas the worst corrosion protection was given by annealing the coating at 80 °C.     

The examination of corrosion behaviors of hap coated Ti implant materials and 316L SS by sol-gel method

In this research, hydroxyapatite (HAP) coatings have been produced on Ti, Ti6Al4V alloy and 316L stainless steel substrates by sol-gel method. (NH₄) · H₂PO₄ is taken as P precursor and Ca(NO₃)₂ · 4H₂O is taken as Ca precursor to obtain HAP coating. Additionally, three different pretreatment processes (HNO₃, anodic polarization, base-acide (BA)) have been applied to Ti, Ti6Al4V alloy and 316L stainless steel substrates. The corrosion behaviors of bare and HAP coated samples are examined in Ringer and 0.9% NaCl. HAP coated Ti have showed over 87.85% inhibition. HAP coated Ti6Al4V alloys have showed over 87.33% inhibition. In Ringer solution, 99.24% inhibition has been showed in HAP coated anodic pretreatment for 316L stainless steel. All pretreatment processes are effective on clinging of HAP coating to the surface. It is seen that impedance values have increased in HAP coatings (Ti and Ti6Al4V). HAP coatings have raised the corrosion resistance of Ti and Ti6Al4V. The values of polarization resistance in HAP coated samples have increased for 316L stainless steel in 0.9% NaCl and Ringer solutions. It is seen in SEM images that open pores and attachments among pores have been observed in the coating, which increases osteointegration. It is noted in EDX analyses of the surfaces of the HAP coated samples that there is only Ca, O, and P on the surface. Ca/P ratio varies in 1.84–2.00 ranges. As Ca/P ratio increases, the inhibition increases too. It is seen in XRD images of HAP powder that there are HA ate structures. Additionally, it is seen in FTIR analysis, characteristic HA absorption bands have occurred in sintered powders.     

The protective effect of polypyrrole coating on the corrosion of steel electrode in acidic media

In this study, the corrosion parameters of stainless steel containing 12% Cr, have been determined by Tafel extrapolation method in 1 M HCl, H₂SO₄ and H₃PO₄ media. Later, steel was coated with polypyrrole in 0.1 M Pyrrole + 0.3 M Oxalic acid solution by cyclic voltametric method. The corrosion parameters and percentage inhibition efficiencies of coated electrodes were investigated according to immersion times in the same media. In all acidic media studied, increases in immersion time, produced increased corrosion densities and a decrease in percentage inhibition efficiencies were determined.     

A study on mechanism of corrosion protection of polyaniline coating and its failure

Polyaniline (PANI) coatings were electrochemically deposited on substrates of stainless steel and platinum in solutions of 0.2 M H₂SO₄ and 0.1 M aniline by cyclic voltammetry. The corrosion protection of the PANI coatings and their failure were investigated in 0.2 M H₂SO₄ solution. It was observed that the corrosion protection ability of the coating to steel substrate was increased with the increase of the coating thickness. The corrosion protection ability was mainly attributed to the passivating effect of PANI due to its oxidizing ability in its emeraldine state. During its operation, the PANI coating in emeraldine state tended to gradually lose its corrosion protection ability. This gradual failure of the PANI coating, but faster than expected, was confirmed to be related to a gradual reduction of the emeraldine PANI and a gradually increased resistance between the PANI coating and the stainless steel substrate. These findings lead to a new mechanism for the corrosion protection of PANI coating and its failure.     

1‐Methyl‐3‐pyridine‐2‐yl‐thiourea as inhibitor for acid corrosion of stainless steel

The inhibiting effect of 1‐methyl‐3‐pyridine‐2‐yl‐thiourea (MPT) on the corrosion of stainless steel in 0.5 M H₂SO₄ solution was investigated using weight loss and potentiostatic polarization techniques. The percentage inhibition efficiencies and surface coverage degrees increased with increasing additive concentration. Potentiostatic polarization studies revealed that MPT is of the mixed‐type inhibitor in 0.5 M H₂SO₄ solution. The adsorption of this inhibitor is also found to obey the Langmuir adsorption isotherm. From the adsorption isotherm, value of the ΔG_ads for the adsorption process was calculated. From the corrosion rate obtained at 25–55 °C E_a, ΔH_a and possible mechanism have been proposed. Scanning electron microscopy (SEM) was done from the surface of the exposed sample indicating uniform film on the surface.     

Poly(N-methylaniline) coatings on stainless steel by electropolymerization

Poly(N-methylaniline) (PNMA) coatings have been electropolymerized on 304 stainless steel alloy by potentiodynamic, galvanostatic and potentiostatic synthesis techniques from aqueous solutions of 0.1 M N-methylaniline (NMA) and 0.3 M oxalic acid. Characterization of PNMA coatings was carried out by cyclic voltammetry, UV-Vis and FTIR spectroscopy techniques. Corrosion behavior of PNMA coated stainless steel electrodes was investigated using linear anodic potentiodynamic polarization, Tafel test, chronoamperometry and electrochemical impedance spectroscopy (EIS) techniques in 0.5 M aqueous HCl solutions. Corrosion test results showed that PNMA coatings possessed protection to uncoated stainless steel against corrosion.     

Synthesis and passivation behavior of electroless Ni–P‐CNT composite coating

Carbon nanotubes (CNTs) have high chemical stability, unique hollow nanotube structure, and are believed to be ideal materials for fabricating composites. In this study, Ni–P and Ni–P‐CNT composite coatings were fabricated by electroless plating. Scanning electron microscopy was used to characterize the coatings. The corrosion behavior of Ni–P and Ni–P‐CNT coated samples were evaluated by polarization curves and electrochemical impedance spectroscopy in 3.5 wt% NaCl and 0.1 M H₂SO₄ aqueous solutions at room temperature. The results indicated that incorporation of CNTs in the coating significantly increased corrosion resistance. The role of CNTs in improvement of corrosion resistance of the coating was also discussed.     

Effect of substrate temperature and nitrogen concentration during sputtering on corrosion behaviour of AlN coatings

Aluminium nitride coatings were formed on stainless steel substrate by DC-reactive balanced magnetron sputtering at various nitrogen concentrations in the sputtering gas mixture, and different substrate temperatures. The electrochemical corrosion behaviour of the coatings obtained was studied in 0.5?M H₂SO₄. Continuous improvement in corrosion resistance of the coatings was observed with increasing coating deposition temperature up to 500?°C. The corrosion potential shifted from ?0.66 V_SCE at 100?°C to ?0.33?V_SCE at 500?°C. Accordingly, the corrosion current density decreased significantly with increase in the deposition temperature. However, no major difference in corrosion behaviour could be noticed for the coatings formed at various nitrogen concentrations.     

Polypyrrole coatings as a treatment for zinc-coated steel surfaces against corrosion

A single-step electropolymerization of pyrrole on zinc-coated steel electrodes in aqueous medium was investigated under several techniques (potentiodynamic, galvanostatic and potentiostatic modes) by using carboxylate salts, such as the citrate, the succinate, the oxalate, the malate and the tartrate. Adherent and homogeneous PPy coatings were obtained only with tartrate counter-ions.The corrosion behaviour of zinc-coated steel electrodes electrochemical modified by PPy films were estimated by open circuit potential and DC polarization in NaCl, HCl and H₂SO₄ aggressive solutions. The obtained results show that the PPy coatings increase the corrosion potential and reduce the corrosion current. The salt spray test results show that the PPy coating prepared under ultrasonic waves is more resistant than those obtained in normal conditions.     

Corrosion Inhibition of 304 Stainless Steel by Nano-Sized Ti/Silicone Coatings in an Environment Containing NaCl and Water Vapor at 400–600°C

The corrosion behavior of 304 stainless steel (SS) and its corrosion inhibition by brushing nano-sized Ti/silicone coatings on its surface in an environment containing a solid NaCl deposit and water vapor at 400–600°C was studied. Results indicated that water vapor or NaCl, especially water vapor plus NaCl accelerated the corrosion of the steel markedly. The corrosion scales of the uncoated steel had a duplex structure at 400–500°C and internal oxidation occurred for the uncoated steel at 600°C in an environment containing NaCl and water vapor. The corrosion of the 304SS was inhibited efficiently by the coatings at 400–500°C, and the coated steel suffered corrosion to some extent and most of the coatings were destroyed at 600°C. X-ray diffraction (XRD) indicated that the corrosion products of the uncoated steel were mainly Fe₂O₃, Cr₂O₃, NiO or Na₂CrO₄, and the coatings consisted mainly of TiO₂ and SiO₂ after exposure at 400–500°C. The good corrosion resistance of the nano-sized Ti/silicon coatings was attributed to the formation of SiO₂, and TiO₂ that resulted from the decomposition of the organic components in the coating and fast oxidation of nano-Ti powder respectively during the experiments, TiO₂ mixed together with SiO₂ and formed a new coating on the steel surface that played an important role in the protection of the steel.     

Corrosion behaviour of single and double layer hydroxyapatite coatings on 316L stainless steel by plasma spray

AISI316L stainless steel is extensively used in orthopedic and dental applications. However, this alloy exhibits low integration behaviour when it comes in contact with surrounding bone tissue and implant healing duration can be as much as few months. The aim of this study is the fabrication of biocompatible hydroxyapatite (HA) coatings on stainless steel substrate in order to accelerate the process of osseointegration of implants. The biocompatible single layer of Titania (TiO₂), Hydroxyapatite and bi-layer TiO₂/HA coatings were deposited by atmospheric plasma spray on 316L stainless steel. Coated and uncoated stainless steel specimens were incubated in simulated body fluids and 0.9% NaCl solutions for 1h and 7 days. In vitro electrochemical-corrosion evaluation of coated and uncoated stainless steel specimens have been investigated by Tafel extrapolation and linear polarization methods. Results indicates that corrosion resistance of single layer HA coated stainless steel specimens are superior to single layer TiO₂ and bi-layer HA/TiO₂ coated stainless steel specimens.     

Electrochemical characteristics of 316l stainless steel processed with a thermally treated Ni- and Cr-rich surface coating

The influence of a thermally treated Ni-Cr rich protective coating on the corrosion behavior and contact resistance of stainless steel in a 0.1NH₂SO₄+ 2 ppmHF electrolyte at 80 °C was evaluated using electrochemicals, interfacial contact resistance (ICR) measurements and X-ray photoelectron spectroscopy. Through a low-cost, continuous production line, the Ni-rich coating film for stainless steels was developed by dipping steel samples in acrylic resin and CrO₃ solutions with different levels of NiSO₄·6H₂O added as a nickel source. Each sample was then heated at 800 for 10 min in a hydrogen-reducing environment. It was shown that an increase in residual Ni content in the surface coating noticeably lowered the interfacial contact resistance and raised the corrosion resistance, depending on the remaining nickel content and the thickness of the surface coatings. In support of the XPS depth profile, this was ascribed to the relative enrichment of the Ni element and the detectable reduction of oxygen content in the coating, which could be associated with the significant evaporation of acrylic resin that occurred during thermal treatment. The optimum Ni composition in the resultant coating film, achieved through the addition of 15 wt.% NiSO₄·6H₂O to the acrylic resin and CrO₃ solution, was estimated to be about 10 wt.%.     

Corrosion-Erosion Effect on TiN/TiAlN Multilayers

The goal of this work is to study electrochemical behavior under corrosion-erosion conditions for [TiN/TiAlN] _n multilayer coatings with bilayer number (n) of 2, 6, 12, and 24 and/or bilayer period (??) of 1500, 500, 250, 150, and 125?nm deposited by a magnetron sputtering technique on Si (100) and AISI 1045 steel substrates. The Ti-N and Ti-Al-N structures for multilayer coatings were evaluated via x-ray diffraction analysis. Silica particles were used as the abrasive material in corrosion-erosion tests within the 0.5?M H₂SO₄ solution at impact angles of 30° and 90° over the surface. The electrochemical characterization was carried out using the polarization resistance technique (Tafel) to observe changes in corrosion rates as a function of the bilayer number (n) or bilayer period (??) and impact angle. Corrosion rate values of 359?mpy of uncoated steel substrate and 103?mpy for substrate coated with n?=?24 (???=?125?nm) under an impact angle of 30° were found. On the other hand, with an impact angle of 90° the corrosion rate exhibited 646?mpy on uncoated steel substrate and 210?mpy for substrate coated with n?=?24 (???=?125?nm). This behavior was related to the curves of mass loss for both coated samples and the surface damage was analyzed via SEM images for the two different impact angles. These results indicate that TiN/TiAlN multilayer coatings deposited on AISI 1045 steel are a practical solution for applications in erosive-corrosive environments.     

Corrosion of alloys and their diffusion aluminide coatings by KCl:K2SO4 deposits at 650 °C in air

P91 ferritic‐martensitic steel, 17Cr–13Ni and alloy 800 austenitic stainless steels and Inconel 617 alloy have been aluminised to form Fe₂Al₅, (Fe,Ni)Al and Ni₂Al₃ aluminide coatings. These alloys and their corresponding coatings were subjected to corrosion in air by 50:50 mol/mol K₂SO₄/KCl deposits at 650 °C for 300 h. With the exception of the Inconel 617 alloy, significant metal losses (>180 µm) were recorded. These losses were planar for P91 alloy but involved internal corrosion for the two austenitic steels. The (Fe,Ni)Al and NiAl coatings on the austenitic steels and the Inconel 617 alloy were significantly corroded via intergranular and internal chloridation–sulphidation–oxidation. In contrast, the Fe₂Al₅ coating on the P91 alloy coating was virtually unattacked. For the alloys, the relative extents of corrosion damage can be explained in terms of the stability and volatility of metal chlorides formed. For the coatings, STEM/EDS analyses enable clear linkages to be made between the presence and number of Cr‐rich particles on coating grain boundaries and the corrosion damage observed for the coatings.     

Comparative corrosion resistance of plasma-based low-energy nitrogen ion implanted austenitic stainless steel

A high nitrogen face-centered-cubic phase (γ_N) was obtained on the nitrided surface of 1Cr18Ni9Ti austenitic stainless steel by plasma-based low-energy nitrogen ion implantation. No pitting corrosion for the γ_N phase was confirmed by electrochemical polarization measurement in 3% NaCl solution. The protective passive film with a duplex character, iron hydroxide/oxides in the outer region and chromium hydroxide/oxides and iron oxides accompanying chromium and iron nitrides in the inner region, was by 2-3 times thicker than that of original stainless steel. The thick iron hydroxide/oxides region formed on the chromium hydroxide/oxides region due to the increase of alkalinity in the solution, leading to barrier against penetration of localized attack of the aggressive ions. The equivalent general corrosion resistance for the γ_N phase was observed in 0.5 mol/l H₂SO₄ solution relative to the original stainless steel. The passive film formed on the γ_N phase in 0.5 mol/l H₂SO₄ solution was similar to that of original stainless steel. The different role of nitrogen was proposed in pitting corrosion resistance and general corrosion resistance of austenitic stainless steel.     

The effects of a CeO2 coating on the corrosion parameters of type 304 stainless steel

Coatings of CeO₂ derived from inorganic sol-gel dispersions were applied to type 304 bright annealed stainless steel (British Standard 1449 type 304S31) coupons and subjected to heat treatments at 450 and 550 °C. The coatings, 0.5 μm thick, were transparent, adherent, and stable. The aqueous corrosion properties of the coated coupons in 1 molar NaCl were then studied by potentiodynamic polarization measurements and electrochemical impedance spectroscopy. The derived corrosion parameters were then compared with similarly heat-treated, uncoated 304SS coupons. The results indicate that the application of a CeO₂ coating, heat treated at 550 °C, improves the corrosion rate as compared to an uncoated heat-treated coupon. The polarization curve for the 450 °C heat-treated, coated coupon showed passive behavior compared to transpassive for the uncoated specimen. The impedance spectrum data for the uncoated, as-received coupon could be modeled using a resistor in series with a parallel capacitor resistor combination “Randles” equivalent circuit. A coated coupon, heat treated at 550 °C, could be modeled using a more complex equivalent circuit involving a constant phase element, due to the CeO₂ coating. Modeling of the impedance characteristics for the oxidized coupons required the addition of a second series element consisting of a parallel resistor capacitor combination to give a Chi square statistic fit of X² < 5 X 10^-4.     

Application of polyaniline to galvanic anodic protection on stainless steel in H2SO4 solutions

A stand-alone polyaniline (PANI) film electrode was made and then applied to protect 1Cr13 stainless steel (a type of stainless steel typically used in China, 0–15% C, 13% Cr) from corrosion in highly acidic solution, up to 5 M H₂SO₄. The stand-alone PANI electrode and 1Cr13 were coupled to study their galvanic interactions. PANI is a cathode while 1Cr13 is an anodic. The results indicate that PANI with a certain area can quickly passivate the stainless steel and effectively maintain the steady passive state for a long period of time. This specific method of PANI preventing 1Cr13 from corrosion is called galvanic anodic protection (GAP). Moreover, the efficiency, mechanism, and security of GAP were discussed. The results demonstrate that the stand-alone PANI electrode may have a potential application to galvanic anodic protection on stainless steel in highly corrosive H₂SO₄ solutions.     

Graphite intercalated polymer coatings on stainless steel

The use of graphite modified polymer films has been investigated, on stainless steel. Polythiophene and polypyrrole films have been synthesized electrochemically on stainless steel, and then very thin graphite layers were realized on polymer films. Since the graphite layer is not applicable as a top coat, polymeric top films were also electrosynthesized on graphite layers. Following this procedure, polypyrrole-graphite-polypyrrole and polythiophene-graphite-polythiophene coatings have been obtained on stainless steel. The corrosion behaviours of coated samples have been investigated in 0.1 M H₂SO₄ solution, by means of electrochemical impedance spectroscopy (EIS) and anodic polarization curves. The intercalation of graphite layer altered the performance and properties of coatings significantly. Especially, polypyrrole coating system was found to exhibit almost an excellent coating behaviour that hindered the attack of corrosive environment within 96 h exposure time. The EIS results of polypyrrole coating system were indicating to almost a perfect capacitive behaviour that the response was reflecting capacitive behaviour in a wide frequency region. This property was also examined with successive cyclic voltammograms in a potential range between 0.10 and 0.40 V (vs. Ag/AgCl). The charge densities involved in oxidation and reduction regions were determined for successive cycles and it was shown that coated sample was able to exhibit charge-discharge (i.e. oxidation and reduction) behaviour successfully, without any degradation.     

Electro-Synthesis of Nano-Colloidal PANI/ND Composite for Enhancement of Corrosion-Protection Effect of PANI Coatings

The polyaniline/nanodiamond (PANI/ND) nanocomposite coating was prepared on mild steel via electrochemical polymerization using cyclic voltammetry technique. The ultrasonic irradiation was used for effectively dispersing ND particles in electropolymerization solution. The prepared nanocomposite films were found to be nano-colloidal, and very adherent with low porosity. The corrosion performance of the coatings was investigated in 0.5 M H₂SO₄ solution by electrochemical impedance spectroscopy and polarization methods. The obtained results showed that the presence of ND particles significantly enhanced the corrosion protection performance of the PANI films in 0.5 M H₂SO₄ corrosive medium. X-ray diffraction and FT-IR techniques confirmed the intercalation of the nanoparticles in PANI matrix.     

Influence of tensile stress on corrosion behaviour of high‐strength galvanized steel bridge wires in simulated acid rain

Corrosion behaviour of the high‐strength galvanized steel wires under tensile stress was researched by electrochemical polarization and salt spray test (SST) using simulated acid rain as electrolyte. Electrochemical polarization and SST results showed corrosion rate rose significantly with increasing tensile stress; white grains were observed by SEM after polarization, while cellular and dendritic crystals appeared on the rust layer after SST. XRD and TG‐DTA results revealed (Zn(OH)₂)₃ · ZnSO₄ · 5H₂O was the main corrosion product, and traces of Fe₂(SO₄)₂O · 7H₂O, Fe₂(SO₄)₃, Fe₂O₃ · H₂O were also detected. A three‐stage corrosion process for the galvanized steel wires during SST was proposed.