Studying the fine microstructure of the passive film on nanocrystalline 304 stainless steel by EIS,XPS, and AFM

The fine microstructure of the passive films on nanocrystalline (NC) and coarse crystalline (CC) 304 stainless steels (SSs) in 0.5 M H₂SO₄ were investigated by electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The results indicate that the passive film on both CC and NC SSs exhibits a two-layer microstructure consisting of a compact inner layer and a porous outer layer. Some hydrated compounds (HC) were present in the porous outer layer of NC SS but not CC SS in 0.5 M H₂SO₄ solution. The pores in the outer layer of the NC SS were observed to be in the nanoscale by AFM. HC filling of the pores in the passive film on NC SS may occur due to capillary forces endowed by the nanosize pores. XPS analysis of the passive films on both CC and NC SSs, however, does not show such a composition difference which is attributed to dehydration occurring in the XPS vacuum chamber. Both the inner and outer layers of the NC SS were determined by EIS analysis to be more compact and protective than the corresponding films on CC SS as evidenced by the lower Q value, higher n, and much higher R value in the corresponding layer.     

EIS monitoring study of the early microbiologically influenced corrosion of AISI 304L stainless steel condenser tubes in freshwater

This study examined the early stages of tarnishing of American Iron Steel Institute (AISI) 304L austenitic stainless steel (SS) condenser tubes in contact with running freshwater from the Tagus River in Spain. The immersion time of the tubes was 569 days. Tarnishing originated by biofouling was assessed using electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) analyses in conjunction with argon ion sputtering. The EIS diagrams showed a semicircle that was better defined as the experimental time increased, indicating the decreasing tarnishing resistance of the immersed specimens. The EIS results were validated using Kramers–Kronig relationships. SEM micrographs of biofouling indicated that the number of microorganisms on the SS surfaces increased with immersion time. According to the XPS spectra, the main elements deposited on the tarnished AISI 304L SS layer were calcium, phosphorus, and nitrogen. A mechanism of biofouling and microbiologically influenced corrosion behavior of AISI 304L SS condenser tubes in freshwater is proposed.     

XPS study of mechanically polished stainless steel surfaces

The surface of a commercial sheet of AISI type 304 stainless steel has been examined by XPS technique in order to determine the effects of its composition of different heat treatments and polishing procedures. Sheet specimens have been solution annealed or sensitised and mechanically polished in water with different SiC papers. The surface respects to be enriched in chromium, to a greater extent in the solution annealed condition, with little influence of polishing conditions. The passive film appears to consist of Fe and Cr oxides and hydroxides, while no Ni has been detected. Chromium appears always in the 3+ oxidation level, while different oxidation levels are present for iron.     

Surface characterization and electrochemical corrosion behaviour of 304 stainless steel in aqueous media

A formulation consisting 100 ppm of 3-phosphonopropionic acid, 50 ppm of Zn²⁺ and 150 ppm of Tween 80 (polyoxyethylene sorbitan monooleate) offered 97.4% inhibition to the corrosion of 304 austenitic stainless steel immersed in a groundwater environment. This formulation functioned as a mixed inhibitor. The protective film was analysed by luminescence, XRD and FTIR spectra and pit morphology and was also observed by scanning electron microscopy. Electronic Publication     

XPS depth profile study of porous zirconia films deposited on stainless steel by spray pyrolysis: the problem of substrate corrosion

Zirconia (ZrO₂) films of tissue‐like structure and narrow pore size distribution have been deposited by spray pyrolysis using aqueous zirconyl chloride octahydrate (ZrOCl₂·8H₂O) precursor solutions. Stainless‐steel sheets, protected or unprotected by a ZnO barrier layer, have been used as the substrate material held at 473 K. The ZnO barrier layers have been deposited on the stainless steel held at 523 K by spray pyrolysis using a zinc acetate precursor. Their property of corrosion protection to stainless steel has been proved by electrochemical polarization measurements in 0.5 M NaCl solution. A complementary study of XPS (depth profiling, mapping) and x‐ray diffraction has shown that the unprotected steel substrates were corroded during ZrO₂ film post‐annealing in air at T ≥ 773 K, whereas steel substrates protected with a compact barrier layer of crystalline ZnO before ZrO₂ film deposition did not show surface corrosion even after annealing up to 997 K. Copyright © 2004 John Wiley & Sons, Ltd.     

Performance of some thiophene derivatives as corrosion inhibitors for 304 stainless steel in aqueous solutions

The inhibitive effect of 2-cyano-3-hydroxy-4(Ar)-5-anilino thiophene derivatives on the corrosion of 304 stainless steel (SS) in 3 M HCl solution has been investigated by weight loss, galvanostatic polarization techniques, and potentiodynamic anodic polarization in 3.5 % NaCl. The results indicate that these compounds act as inhibitors retarding the anodic and cathodic corrosion reactions. The presence of inhibitors does not change the mechanism of either hydrogen evolution reaction or SS dissolution. The activation energy and some thermodynamic parameters are calculated and discussed. These compounds are mixed-type inhibitors in the acid solution, and their adsorption on the SS surface is found to obey the Temkin adsorption isotherm. The results suggest that the percentage inhibition of these thiophene derivatives increases with increasing inhibitor concentration and decreases with increasing temperature. The synergistic parameter (S) was calculated and found to have a value greater than unity, indicating that the enhanced inhibition efficiency caused by the addition of I^?, SCN^?, and Br^? is only due to a synergistic effect. The relationship between molecular structure and inhibition efficiency was elucidated by quantum-chemical calculations using semi-empirical self-consistent field (SCF) methods.     

Role of novel oxazocine derivative as corrosion inhibitor for 304 stainless steel in acidic chloride pickling solutions

Inhibition of 304 stainless steel corrosion in acidic chloride pickling (1.0 M HCl) solutions by newly synthesized oxazocine derivative 4 as a corrosion inhibitor have been studied using weight loss, potentiodynamic polarization, and atomic absorption spectroscopy investigations. Potentiodynamic polarization curves show that the inhibitor behaves as a mixed-type. The adsorption of the inhibitor on the metal surface in the acid solution was found to obey Langmuir’s adsorption isotherm. The inhibition mechanism of the investigated inhibitor was discussed in terms of its adsorption on the metal surface. The relationship between the molecular structure and the inhibition efficiency was elucidated by quantum chemical calculations.     

Positron annihilation study on interaction between hydrogen and defects in AISI 304 stainless steel

Interaction between hydrogen and defects in AISI 304 stainless steel was investigated by positron annihilation lifetime spectra (PALS) and coincidence Doppler broadening (CDB) measurements. PALS results show that long lifetime component τ₂ is about 260–270 ps, and does not change with current density, which is ascribed to the formation of three-dimensional vacancy cluster of 5–7 vacancies. Furthermore, the CDB ratio curves show that an obvious peak appears in the high-momentum region after hydrogen charging, and the peak site does not vary with current density. The mechanism of interaction between hydrogen with defects is discussed.     

Impact of sensitization on dissolution process of AISI 304 stainless steel during intergranular corrosion evaluated using DEIS technique

The paper presents the results of instantaneous impedance changes measurements vs. reactivation potential performed by means of dynamic electrochemical impedance spectroscopy (DEIS) technique for AISI 304 stainless steel (SS) dissolution process during intergranular corrosion (IG) in 0.5 M H₂SO₄ + 0.01 M KSCN solution. With the use of DEIS method, it was possible to estimate dynamic changes of the examined system’s impedance in conditions of proceeding IG process. Furthermore, the paper proposes an alternative way of evaluating AISI 304 stainless steel dissolution rate during intergranular corrosion based on approximation to theory of iron dissolution in sulfuric acid medium. Simultaneously, based on the DEIS measurements, information about the degree of sensitization of the examined material were obtained. Performed research revealed the advantages of the DEIS technique over the classical double-loop electrochemical potentiokinetic reactivation tests when investigating intergranular corrosion process.     

Poly(3-octylthiophene) and polystyrene blends thermally treated as coatings for corrosion protection of stainless steel 304

The effect of thermal annealing of poly(3-octylthiophene) (P3OT) and polystyrene (PS) blend coatings on the corrosion inhibition of stainless steel in a 0.5 M NaCl solution was investigated. P3OT was synthesized by direct oxidation of the 3-octylthiophene monomer with ferric chloride (FeCl₃) as oxidant. Stainless steel electrodes with mirror finish were coated with P3OT/PS blend by drop-casting technique. In order to study the temperature effect on the function like physical barrier against the corrosive species of P3OT/PS polymeric blend, the coatings were thermally annealed at three different temperatures (55?°C, 80?°C, and 100?°C). The corrosion behavior of P3OT/PS-coated stainless steel was investigated in 0.5 M NaCl at room temperature, by using potentiodynamic polarization curves, linear polarization resistance (LPR), and electrochemical impedance spectroscopy. The LPR values indicated that, at 100?°C, P3OT/PS coatings showed a better protection of the 304 stainless steel in 0.5 M NaCl; the corrosion rate diminished in two orders of magnitude with regard to the bare stainless steel. The superficial morphology of the coatings before and after the corrosive environment was researched by atomic force microscopy, optic microscopy, and scanning electronic microscopy. Morphological study showed that the increased temperature benefited the integration of the two polymeric phases, which improved the barrier properties of the coatings. The coating/metal adhesion and the coating thickness were evaluated. The temperature increases the adhesion degree coating/substrate; thus, the coating annealed at 100?°C showed the best adhesion.     

AFM and FTIR studies of organic cation adsorption on carbon steel coupled with stainless steel

The electrochemical behavior of the anode of the galvanic couple and the adsorption behavior of the cationic inhibitor on it have been investigated by using electrochemical methods, atomic force microscopy (AFM) and infrared spectroscopy (FTIR) technology. A galvanic electrode was prepared by coupling N80 carbon steel (CS) and S31803 stainless steel. All experiments were performed in NaCl solution in the presence or absence of an inhibitor. The results show that, in aqueous NaCl solution, CS carries negative excess charge, for the couple, positive charge is carried on the CS side (anode). The adsorption behavior of the cationic inhibitor on CS is significantly affected by the excess charge carried on it. Owing to the charge interaction between electrodes and the cationic inhibitor, the inhibitor has a greater tendency to adsorb on the single CS and less tendency to adsorb on the CS of the couple. Because of this, the adsorption film on the anode (CS side) of the couple is thin and defective. The failure of inhibiting galvanic corrosion attributes to the defective protective layer formed on the anodic area. Copyright © 2006 John Wiley & Sons, Ltd.     

Inhibition effect of butan-1-ol on the corrosion behavior of austenitic stainless steel (Type 304) in dilute sulfuric acid

The electrochemical behavior of austenitic stainless steel (Type 304) in 3 M sulfuric acid with 3.5% recrystallized sodium chloride at specific concentrations of butan-1-ol was investigated with the aid of potentiodynamic polarization, open circuit measurement and weight loss technique. Butan-1-ol effectively inhibited the steel corrosion with a maximum inhibition efficiency of 78.7% from weight-loss analysis and 80.9% from potentiodynamic polarization test at highest concentration studied. Adsorption of the compound obeyed the Freundlich isotherm. Thermodynamic calculations reveal physiochemical interactions and spontaneous adsorption mechanism. Surface characterizations showed the absence of corrosion products and topographic modifications of the steel. Statistical analysis depicts the overwhelming influence and statistical significance of inhibitor concentration on the inhibition performance.     

Inhibition of cold rolled steel corrosion by Tween-20 in sulfuric acid: weight loss, electrochemical and AFM approaches

The inhibiting action of a nonionic surfactant of Tween-20 on the corrosion of cold rolled steel (CRS) in 0.5-7.0 M sulfuric acid (H(2)SO(4)) was studied by weight loss and potentiodynamic polarization methods. Atomic force microscope (AFM) provided the surface conditions. The results show that inhibition efficiency increases with the inhibitor concentration, while it decreases with the sulfuric acid concentration. The adsorption of inhibitor on the cold rolled steel surface obeys the Langmuir adsorption isotherm equation. Effect of immersion time was studied and discussed. The effect of temperature on the corrosion behavior of cold rolled steel was also studied at four temperatures ranging from 30 to 60 degrees C, the thermodynamic parameters such as adsorption heat, adsorption free energy, and adsorption entropy were calculated. The results revealed that the adsorption was physisorption mechanism. A kinetic study of cold rolled steel in uninhibited and inhibited acid was also discussed. The kinetic parameters such as apparent activation energy, pre-exponential factor, rate constant, and reaction constant were calculated for the reactions of corrosion. The inhibition effect is satisfactorily explained by both thermodynamic and kinetic models. Polarization curves show that Tween-20 is a cathodic-type inhibitor in sulfuric acid. The results obtained from weight loss and potentiodynamic polarization are in good agreement, and the Tween-20 inhibition action could also be evidenced by surface AFM images.     

XPS,AES, and AFM as tools for study of optimized plasma functionalization

The plasma-based surface modification of polymer materials with desirable bulk properties is a useful way to obtain polymers with tailor-made surface properties. This is necessary because the surface properties of most engineering polymers in use today are less then optimum for many applications. New functionalities such as biocompatibility, adhesion, special functional groups as well as lubricative, friction and wear-and-tear properties are demanded. By optimization of the process parameters during a low pressure plasma treatment, most of these requirements can be fulfilled. A specific functionalization with, e.g., carboxyl, amino, epoxy or hydroxyl groups as well as the generation of ultra thin layers with those functionalities is possible. The most challenging problem is not only to find parameters which do not lead to a fragmentation of the monomeric structure, but moreover the adhesion of the thin films to the substrates must overcome a stability test without delamination. To optimize plasma processes, with their great variety of parameters influencing the obtained surface properties, several surface analytical techniques are indispensable. XPS, AES as well as AFM are helpful tools to characterize the modified sample surfaces and consequently optimize the set of parameters for the glow discharge treatment. With XPS the retention of the monomer structure can be controlled. AES depth profiling clarifies the elemental composition of gradient layers, necessary for a good adhesion of scratch-resistant coatings. AFM visualizes the surface morphology which is important for, e.g., the friction properties of plasma-coated substrates.     

Surface analysis of corrosion inhibitor films by XPS and ToFSIMS

In recent years developments in the capabilities of techniques such as XPS and static SIMS have led to wider application of these methods for the characterisation of industrial materials. After a brief discussion of recent key developments of these techniques, this paper presents a selection of results from research work at our laboratory in the characterisation of organic film-forming corrosion inhibitors on a range of metal substrates which illustrate the nature of the information available. The inherent advantage ofsurface sensitivity and the advantages of a multi-technique approach for the evaluation of surface molecular structure from complex organic compounds is discussed. The additional benefits for analysis offered by the latest developments in technique are also demonstrated.     

Characterization of surface modifications of stainless steel samples after electron and ion bombardment by SEM, AES, and XPS

The interaction of inert or reactive gas plasmas with the surface of stainless steel has been investigated with the aim, to modify the surface and hence to reduce the outgassing rate of the material, an important factor for the production of an ultrahigh vacuum. The plasma treatments investigated may be an alternative to the common used in situ baking. The samples have been exposed to electrons, argon and oxygen ions either in a DC glow discharge or in a microwave discharge. The DC glow discharge in Ar/O₂, the most effective plasma treatment reduces the outgassing rate by a factor of 10. After this treatment the surfaces of the samples have been investigated with respect to the topography and the chemical composition (depth profile) by Secondary Electron Microscopy (SEM), Auger Electron Spectroscopy (AES) and X-ray Photoelectron Spectroscopy (XPS), respectively. The surface modifications resulting from the different treatments of the samples have been correlated to the outgassing rate.     

Adsorption and Bioactivity of Protein A on Silicon Surfaces Studied by AFM and XPS

The adsorption of protein A on silicon surfaces was studied by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy. The deposition was made statically from various concentrations of protein A in water solution. The biological activity was checked by the immobilization of rabbit immunoglobulin G. The protein adsorption occurs in least two different phases and leads to a multilayer film. The first monolayer of proteins is rapidly adsorbed on the surface. The adsorption of the second layer of proteins occurs much more slowly (a thousand times slower) and also involves the third monolayer. The protein A of the first monolayer is denaturated and biologically inactive. On the contrary, the proteins of the second monolayer keep their natural diameter and remain biologically active. AFM artifacts such as the convolution with small objects and the resulting estimation of the coverage ratio are discussed. Copyright 2001 Academic Press.     

Divalent Cd and Pb uptake on calcite {1014} cleavage faces: an XPS and AFM study

The interaction of divalent Cd and Pb with the {101 4} cleavage faces of calcite has been investigated with X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Analysis of the {101 4} cleavage planes of calcite was carried out with X-ray photoelectron spectroscopy (XPS) after exposure to divalent metal-bearing solutions in the 0.1-100 microM concentration range for times ranging from 1 to 24 h. The uptake of Cd2+ by calcite was determined to be greater than that of Pb2+ under similar experimental conditions (1 microM, pH 8.2, 24 h exposure time). In both cases, the majority of the divalent metal was postulated to exist in a surface precipitate. AFM results showed that the exposure of calcite to a 1 microM Pb2+ solution resulted in ellipsoidal surface growths that were attributed to the nucleation of a PbCO3 bulk phase. In the Cd circumstance, AFM showed comparatively flat growth features forming on the calcite surface even at concentrations down to 0.1 microM, where the solution would be expected to be undersaturated with respect to Cd bulk phases. These features were attributed to a (Ca,Cd)CO3 solid solution. The individual exposure of these Cd/CaCO3 and Pb/CaCO3 samples to water pre-equilibrated with calcite (metal free) for 1 h led to the removal of no more than 20% of the divalent metal, suggesting that if there was an adsorbed Pb or Cd complex initially on the calcite surface, it was an minority species compared to the precipitate phase. Exposure of calcite to 100 microM Cd and Pb resulted in the accumulation of precipitate on the calcite surface presumably due to the divalent metal initial solution concentrations exceeding the solubility products of CdCO3 and PbCO3, respectively.     

Atmospheric corrosion of copper and silver influenced by particulate matter

The atmospheric corrosion of copper and silver influenced by graphite and alumina as particulate matter (PM) in an environment containing 200 μg m^?3 SO₂ + 150 μg m^?3 NO₂ at 85% RH and 25 °C was analyzed. Different proportions of PM mixture conditions were used, and the corrosion rate was followed using gravimetric analysis. Results of linear sweep voltammetry (LSV) and coulometric reduction (CR) indicated that larger corrosion rates were obtained in the presence of deposited PM. Under present exposure conditions, copper corrosion rate was larger than silver corrosion rate. X-ray diffraction (XRD) shows the presence of cuprite (Cu₂O) and brochantite (Cu₄SO₄(OH)₆) in the case of copper and achantite (Ag₂S) in the case of silver.