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.     

Corrosion properties of nickel free austenitic stainless steels in 0·5M H2SO4 and 0·5M H2SO4 plus 0·4M NaCl

Abstract

The corrosion behaviour of four nickel free austenitic stainless steels were investigated in 0·5M H₂SO₄ and 0·5M H₂SO₄ plus 0·4M NaCl solutions by means of potentiodynamic and potentiostatic anodic polarisation testing. The performances of the nickel free alloys are compared to those of an experimental intermediate nickel alloy (4%Ni) and a standard AISI 304 steel grade. Once passivity was reached all alloys displayed similar current densities i _p in 0·5M H₂SO₄, independent from alloying. Mo and Cu were shown to be beneficial in decreasing the active dissolution currents and i _crit values. The commercial AISI 304 steel displayed superior resistance to pit initiation during potentiodynamic testing, and AISI 304 steel displayed the highest E _pit value of all alloys tested. When tested potentiostatically the N and Mo alloyed nickel free alloys showed excellent resistance to pit initiation and growth. The dominant effect of N was associated with repassivation of incipient pits, while Mo appeared to act at an earlier stage, suppressing initiation.     

Dithizone and thiosemicarbazide as inhibitors of corrosion of type 304 stainless steel in 1·0M sulphuric acid solution

Abstract

Dithizone and thiosemicarbazide were investigated as inhibitors of the corrosion of type 304 stainless steel in 1·0M sulphuric acid solution by studying weight loss, polarisation curves, and polarisation resistance and using scanning electron microscopy and Auger electron spectroscopy. Various corrosion parameters such as Tafel slopes, corrosion rate, heat of adsorption, and activation energy were evaluated to understand the inhibition mechanism. Inhibition efficiency increased with an increase in concentration of both inhibitors and decreased with an increase in temperature. Both inhibitors seemed to obey the Langmuir adsorption isotherm equation. Dithizone was chemisorbed, whereas thiosemicarbazide was physisorbed on the surface of type 304 stainless steel. Dithizone acted as a mixed inhibitor, while thiosemicarbazide was cathodic in nature.     

Application of minielectrochemical cell to corrosion studies of welded joints of austenitic stainless steel

Abstract

A specific electrochemical cell for small scale electrochemical testing has been built. The electrochemical cell has been made bearing in mind the microstructural features of the stainless steel weldments and the performance of the design has been verified. Two polarisation methods (potentiodynamic anodic polarisation measurements and cyclic potentiodynamic polarisation measurements) and two reactivation electrochemical techniques (the electrochemical potentio-kinetic reactivation test, EPR, and electrochemical potentio-kinetic reactivation double loop test, EPRDL) have been applied to two austenitic stainless steels: AISI 304 and AISI 316L. The results are reliable and have been compared to large scale experiments. Scanning of the welding joints has been performed and the results have been correlated with their microstructural features. It, thus, makes it possible to study the intrinsic heterogeneous microstructures such as the heat affected zone of a welded joint.     

Effect of small additions of ruthenium on pitting corrosion resistance of LDX2101 duplex stainless steel

Four stainless steel alloys with ruthenium compositions of 0·16, 0·24, 0·32 and 0·64 wt-% were produced from pieces cut from commercial LDX2101 duplex stainless steel plate with the manufacturer’s composition of 0·03C–21·5Cr–1·5Ni–0·3Mo–5·0Mn plus pressed ruthenium powder with purity of 99·8%. After solution annealing the samples, the actual chemical composition was analysed using X-ray fluorescence analysis, and then, ASTM A923 (01·03) test method A – sodium hydroxide etch test for classification of etch structures of duplex stainless steel was used to analyse their microstructure. Corrosion potential and pitting potential of these samples were evaluated using a potentiodynamic polarisation technique, and the results were compared to corrosion and pitting potentials of the control alloy LDX2101. The tests for both produced and control alloys were performed in naturally aerated 3·56%NaCl aqueous solution at 25±2°C. The results indicated that small additions of ruthenium significantly improved the pitting potentials of the resulting alloys. The results also indicated that ruthenium additions have no detrimental effect to the microstructure of the resulting alloys. In addition, if such small additions of ruthenium will not improve the general corrosion of the resulting alloy, it will at least not have any detrimental effect on the resulting alloy. Ruthenium will also lower the current required to maintain the passive state of LDX2101 stainless steel. In addition to reduced current to maintain the passivity of LDX2101 stainless steel, ruthenium also increased the passive range of LDX2101 stainless steel.     

Galvanic corrosion of bare and coated Al alloys coupled to stainless steel 304 or Ti-6Al-4V

The galvanic corrosion behavior of Al alloys 7075, 6061, 2024, bare or coated with the chemical conversion coating Alodine 600, coupled to stainless steel 304 or Ti-6Al-4V and immersed in aerated 3·5%NaCl solution, has been studied by continuous measurements of the galvanic current using a zero impedance ammeter and by weight loss measurements. Comparison of weight loss measurements for bare and coated uncoupled Al alloys shows that good corrosion protection is provided by the conversion coating. Data from weight loss and galvanic current measurements show that corrosion protection is also provided when coated Al alloys are coupled to stainless steel 304 or Ti-6Al-4V. Examination of potentiostatic polarization curves for the metals studied in 3·5%NaCl solution explains the protective action of the coating and also the higher dissolution rates of Al alloys coupled to stainless steel 304 instead of Ti-6Al-4V. Differences between dissolution rates calculated from galvanic current data and weight loss data are explained by theoretical considerations published recently by the authors taking into account the shapes of the individual polarization curves of the metals in the couple. After correction of galvanic current data, agreement between dissolution rates obtained by weight loss and galvanic current data is satisfactory. Continuous recording of the galvanic current reveals considerably more information than weight loss data.     

Cathodic electrolytic deposition of ZnO on mild steel

Abstract

The present paper deals with the deposition and characterisation of zinc oxide coatings on mild steel substrates by cathodic electrolytic deposition via a 0·1M zinc nitrate aqueous solution. The influence of the deposition parameters, such as applied cathodic potential and deposition time, on the growth of oxide coatings was also investigated. The protection efficiency of these coatings on the mild steel was examined by a potentiodynamic polarisation technique in 0·3M NaCl solution (pH?=?5·5, T?=?25°C). The obtained results showed that the ZnO coatings improve the anticorrosion performance of mild steel.     

Microstructural characterisation and corrosion behaviour of electroless Ni–W–P deposits of mixed nanocrystalline/amorphous structures

Abstract

An investigation has been undertaken of the influence of the mixed nanocrystalline and amorphous microstructure on the corrosion behaviour of electroless Ni–5·5W–6·5P (wt-%) deposits on steel substrates. The effects of annealing temperature on microstructure evolution were investigated. The corrosion behaviour of the deposits was evaluated by potentiodynamic polarisation in 0·5M H₂SO₄ solution and EIS measurements in 3·5%NaCl solution. Relationships between the microstructure and corrosion mechanisms of the as plated and the annealed deposits were considered by reference to microstructural information, including degree of crystallisation, grain sizes of both nickel and Ni₃P phases, porosity development, microstrains and residual stresses.     

Corrosion behaviour of as deposited and PMMA treated TiN coating systems deposited by cathodic arc technique

Abstract

Vapour deposited coatings usually contain microscopic defects, which can provide corrosive media with easy access to the substrate. Consequently, formation of galvanic cells between the coating and substrate can initiate localised corrosion at the defective sites. In this study, TiN coatings were deposited on mild steel (MS) and stainless steel (SS) substrates using a cathodic arc technique. A post-deposition treatment with polymethyl methacrylate (PMMA) was applied to both TiN/MS and TiN/SS systems to block access of corrosion media to the substrates through the coating defects. The as deposited and PMMA treated coating systems were subjected to electrochemical tests in 3·5%NaCl solution. Potentiodynamic polarisation testing results indicated that the PMMA treatment led to a higher corrosion potential and a lower anodic current density for both TiN/MS and TiN/SS systems when compared with their as deposited counterparts. Extended exposure in 3·5%NaCl caused severe localised corrosion in the as deposited TiN/MS due to the presence of coating defects and poor corrosion resistance of the substrate. Electrochemical impedance spectroscopic measurements demonstrated that the PMMA post-deposition treatment significantly improved corrosion resistance of both TiN/MS and TiN/SS systems by effectively sealing the open voids or pores associated with the coating defects.     

Inhibitory efficiency of oxalic N-phenylhydrazide-N′-phenylthiosemicarbazide on corrosion of carbon steel in 0·5M H2SO4

The inhibitory effect of an oxalic type organic compound oxalic N-phenylhydrazide-N′-phenylthiosemicarbazide on the corrosion of carbon steel in 0·5M H₂SO₄ aqueous solution was investigated by different experimental methods; gravimetry, voltammetry and electrochemical impedance spectroscopy. The surface state of the electrode after immersion of the steel coupons in corrosion test solutions, in absence and in presence of the inhibitor was characterised by scanning electron microscopy. The potentiodynamic polarisation measurements showed that the presence of the inhibitor in 0·5M H₂SO₄ decreased both cathodic and anodic processes. The action of this inhibitor is therefore of a mixed type. The electrochemical impedance measurements showed the adsorption of the inhibitor. The inhibitory efficiency reaches a value of 95% at an inhibitor concentration of 10^?3M.     

A study of zinc phosphate coatings on 12·5Cr–21·0Ni stainless steel

Abstract

12·5Cr–21·0Ni stainless steel was chemically treated with zinc phosphate in order to find the most suitable phosphate solution and its operating parameters. The phosphate coatings were tested for their corrosion protection of stainless steel using three methods: the salt spray test, the humidity cabinet test and the brine immersion test. The phosphate coatings were also mechanically tested using a tensile test for determining their mechanical properties. Results clearly show that phosphate coatings with a uniform appearance and full coverage can give high corrosion protection to 12·5Cr–21·0Ni stainless steel by forming a physical barrier against the corrosive environment. The 12·5Cr–21·0Ni stainless steel after coating with zinc phosphate still retains reliable mechanical properties, thereby providing valuable applications in the engineering field.     

Electrochemical behaviour of 254SMO stainless steel in comparison with 316L stainless steel and Hastelloy C276 in HCl media

Abstract

The electrochemical behaviour of 254SMO stainless steel in HCl solutions has been studied and compared with that observed for other alloys using open circuit potential measurements, potentiodynamic polarisation curves, and SEM analysis techniques. 254SMO does not display pitting corrosion at room temperature in HCl solutions having concentrations ≤5·0M. Its performance is comparable with that of Hastelloy C276 in HCl media in solutions of strength ≤1·0M. The critical pitting temperature for 254SMO exceeds 76°C in 3M HCl solutions.     

Effect of chloride ions on corrosion behaviour of austenitic nickel and nickel free stainless steels in phosphoric acid solutions

The effect of chloride ions' presence (0·005–1·0M NaCl) in phosphoric acid solutions (5, 40 and 75%) on the corrosion behaviour of three austenitic stainless steels (an experimental steel Fe–18Cr–12Mn–0·6N and two trade grades, Fe–18Cr–9Ni and Fe–14Cr–15Mn–0·2N) has been studied by potentiodynamic polarisation measurements. The surface examinations of the samples tested involved X-ray photoelectron spectroscopy as well as optical and scanning electron microscopy. It was established that chlorides added to phosphoric acid solutions deteriorate the general corrosion resistance, and under anodic polarisation, they provoke pitting corrosion. The composition of the stainless steels significantly influences its corrosion behaviour in the phosphoric acid solutions containing chloride ions. The replacement of nickel with manganese and nitrogen on top of lower chromium content has a strong negative effect on the corrosion resistance.     

Use of SECM to compare corrosion resistance of DIN W. Nr. 1·4460 high N and AISI 316L austenitic stainless steels in physiological solutions

Abstract

The pitting corrosion resistance of DIN W. Nr. 1·4460 stainless steel (SS) with high amounts of nitrogen (0·87%) was evaluated to be used for medical implants. The SS pitting corrosion resistance was tested in a minimum essential medium at 37°C by electrochemical impedance spectroscopy and potentiodynamic polarisation curves and in a 0·1 mol L^?1 NaCl solution at 25°C, by scanning electrochemical microscopy. This last technique measures the concentration of chemical species released by corrosion processes. The potential of an ultramicroelectrode was set to amperometrically detect the Fe²⁺ ions released at the anodic areas and also the depletion of oxygen due to the cathodic reactions in the vicinity of the cathodic areas. The AISI 316L stainless steel was also tested for comparison reasons. The results showed that the DIN W. Nr. 1·4460 with 0·87% nitrogen presents higher pitting corrosion resistance than the AISI 316L SS, being a potential candidate for biomaterial applications.     

Electrochemical and Weight Loss Measurements of Inhibition of the Acid Corrosion of Steel

Abstract

Stern-Geary and Tafel polarisation relationships have been obtained for steel in 0·5 M H₂SO₄ and 1 M HCl containing different concentrations of a wide range of n-alkylquaternary ammonium compounds and thiourea derivatives. The shape of the Stern-Geary polarisation relationship is found to depend on the difference between the anodic and cathodic Tafel slopes, b_a and b_c, in agreement with electrode kinetic theory.

For each solution the corrosion rate was derived from the electrochemical data in two different ways:

1. Substitution of the Stern–Geary gradient, ?I/?E, and the measured values of b_a and b_c in the Stern-Geary equation: II. Extrapolation of the Tafel lines to the point of intersection. The results from the two methods were in good agreement for all of the solutions tested.The corrosion inhibition values calculated from the Stern-Geary corrosion rates were also compared with those measured in separate experiments by weight loss. The agreement was good except for the n-alkylquaternary ammonium compounds in 0·5 M H₂SO₄, which gave considerable discrepancies at the lower levels of inhibition. This was shown to be due to differences in the pre-immersion treatment of the steel samples.     

Kinetic study of effect of amine based corrosion inhibitor in reducing corrosion rate of 1018 carbon steel in seawater solution

Abstract

The effect of an amine based inhibitor (CORTRON AR-505) on the corrosion of 1018 carbon steel in seawater was studied using weight loss, adsorption isotherm analysis, polarisation resistance and potentiodynamic polarisation techniques. AR-505 is adsorbed on the steel surface according to the Shawabkeh–Tutunji adsorption isotherm equation. A maximum adsorption capacity of 0·097 mg AR-505 was obtained to cover a monolayer of adsorption. Corrosion kinetics illustrated that inhibition efficiency has increased with increasing inhibitor concentration and solution pH, while it decreased with increasing solution temperature and stirring speed. Polarisation data fitted by the Butler–Volmer equation showed that the values of anodic and cathodic transfer coefficients are in the average of 0·84 and 0·15 respectively. Corrosion resistance measurements provided a rapid decrease in corrosion rate from 7 to 1 mm/year.     

Effect of current density on the corrosion protection performance of polyaniline coated AISI 4140 steel

The present work reports on electropolymerisation of aniline onto AISI 4140 steel substrate at room temperature in oxalic acid media by the potentiodynamic electrodeposition method. The effect of coating current density on the morphology of conductive polymer films and their corrosion behaviour has been investigated. The electrolyte solution comprised 0.1 M aniline?+?0.3 M oxalic acid. The effects of deposition current density changes (0.1, 0.2, 0.3, 0.4 and 0.5?mA cm^?2) on the films were investigated. The PANI film was characterised using cyclic voltammetry and optical microscopy; it was covered with a dark green-yellow homopolymer film of strongly adherent homogeneous characteristic. The corrosion behaviour of steel electrodes with and without polyaniline (PANI) film in 3.5 wt-% NaCl solution was investigated through anodic polarisation curves. The results indicated that the PANI coating obtained under 0.2?mA cm^?2 was the most corrosion protective.     

Role of thickness on electrochemical behaviour of Ni2Si coatings in NaCl solution

Abstract

Ni₂Si intermetallic coatings were deposited on a substrate of 420 stainless steel using a high velocity oxy-fuel (HVOF) process. The electrochemical corrosion behaviour of the coatings in 3.5% NaCl solution was investigated by means of Tafel polarisation tests and electrochemical impedance spectroscopy (EIS) measurements. Two coatings with different thicknesses, 55 and 115?μm, were investigated. The results showed that the corrosion rate of the thicker coating was lower than that of stainless steel by one order of magnitude. Local attack of the substrate was observed after the polarisation test of this coating, while the coating was still intact. The thinner coating and the stainless steel substrate showed similar corrosion rates. In this case, the substrate was severely attacked after the polarisation test. Two time constants were observed in the EIS spectra of both coatings which were related to charge transfer processes and pore resistance, respectively.     

Corrosion resistance of laser cladded 304L stainless steel enriched with Ru in hydrochloric acid

The corrosion behaviour of laser surface cladding made from 304L stainless steel alloyed with varying concentrations of ruthenium in 1M HCl at 25°C was evaluated, fresh and after 12 hours, by electrochemical tests including open circuit potential and potentiodynamic polarisation scans. The ruthenium concentration in the 800?µm cladded layer varied from 0.82?wt-% to 4.67?wt-% ruthenium. The ruthenium doped samples were compared against a 304L stainless steel laser surface cladding with no ruthenium, 304L stainless steel samples with no laser cladding, 316L stainless steel, SAF2205 duplex stainless steel and Hastelloy C276®. Initial passivation was not observed in the 1M HCl but after 12 hours the addition of ruthenium led to reduced corrosion rates and improved passivation characteristics compared to the surface cladding without ruthenium. An optimum ruthenium range was observed between 3?wt-% and 5?wt-%. It was shown that at this optimum concentration, the ruthenium containing stainless steel clad on 304L stainless steel can compete commercially with the SAF2205 and Hastelloy C276® as long as the clad is 200?µm or less.     

Anticorrosive properties with catalytic behaviour of primer PANI film and top PPy coating synthesised in presence of novel norephedrine based amino alcohol compound

Polyaniline film as primer coating was deposited on stainless steel (SS) in aniline containing aqueous oxalic acid solution, and subsequent synthesis of top PPy film with 2-((5-ethylthiophen-2-yl) methylamino)-1-phenylpropan-1-ol (AAN) compound of different concentrations was achieved in acetonitrile-LiClO₄ successfully. The corrosion performances of coated and uncoated electrodes in 3·5%NaCl solution were evaluated with the help of AC impedance spectroscopy, anodic polarisation plots and open circuit potential time curves. The protective effect of bilayer coatings with AAN compound on SS electrode grew in parallel with extended exposure time. The regular increase in the charge transfer resistance of SS/PANI/PPy-AAN17 electrode was attributed to allowing the limited ion diffusion of top PPy coating with AAN17 compound. The high 21764 Ω s^?1/2 value of the Warburg coefficient showed that PPy-AAN17 film on the SS/PANI coating led to the formation of protective oxide layers due to the catalytic behaviour of PANI film.