Corrosion behaviour of hot-pressed austenitic stainless steel in H2SO4 solutions at room temperature

The corrosion behavior of hot-pressed stainless steel (HPSS) of Type 316 was investigated. Samples of HPSS with porosity of 10–30% were prepared. The influence of the porosity factor on corrosion behaviour was investigated by potentiodynamic polarization, open circuit potential, identification of corrosion products by EDAX and SEM observation.It was found that porosity of the HPSS is the main factor affecting corrosion resistance. High porosity results in low corrosion resistance. The open circuit potential of the HPSS is about ? 200 mV (VSCE) as compared to 200 mV for the wrought 316 stainless steel. The potentiodynamic measurements indicate that cathodic concentration polarization is achieved at a relatively low current density and secondary active-passive transition is observed at a relatively high current density in HPSS as compared to wrought 316 stainless steel.It is suggested that the main mechanism affecting the low corrosion resistance of HPSS in H₂SO₄ is the evolution of hydrogen concentration cells due to electrolytic stagnation in the interconnected open pores. As a result the surfaces of the interconnected open pores act as an active anode and the engineering sample surface acts as an active cathode.     

The corrosion behaviour of AISI 304L stainless steel in 0.1 M HCl at room temperature—I.

A consideration of the critical potential and the protection potential of localized corrosion is given. From a hypothesis about when a fully developed localized attack can occur a definition of the field of protection potential has been attempted. The potentiostatic method was used to define this field relative to solution heat treated AISI 304L stainless steel in 0.1 M HCl at 20°C, with test times of ? 150 h. The results obtained differ significantly from what can be deduced from the potentiodynamic technique, and they confirm the formulated hypothesis and definitions. In the active loop of potentiodynamic curves, the nucleation and development of pitting, together with general corrosion, is documented by SEM. The hypothesis can be advanced that such pitting corrosion is a direct consequence of inhibition phenomena resulting from products formed during overall corrosion.     

Acoustic emission during the electrochemical corrosion of 304 stainless steel in H2SO4 solutions

Acoustic emission (AE) behaviour during the electrochemical corrosion of 304 stainless steel (304SS) in H₂SO₄ solutions was studied. AE signals which related to transpassive dissolution are detected in solutions with low pH, and are very slightly influenced by current density and pre-strain. During hydrogen bubble evolution, a weak correlation exists between the AE signal amplitude and the hydrogen bubble diameter. The concept of potential – pH – AE diagram is proposed and such a diagram is drawn based on AE activity and b-values. The main mechanisms of AE sources which are transpassive dissolution and hydrogen bubble evolution, are also discussed.     

The corrosion behaviour of AISI 304 stainless steel in 0.1 M HCl at room temperature—III. The effect of sensitization

This work describes the results of a study concerning the influence of sensitisation upon the corrosion behavior of an AISI 304 in 0.1 M HCl at room temperature. Electrochemical tests show that sensitized steel requires long periods of time in order to reach quasi-stationary conditions, and that there is no potential field that guarantees a negligible propagation of the corrosive attack. Behavior in the passive state can depend upon behavior in the active region, due to the formation of corrosion products which are capable of inhibiting the anodic process, and of preventing the formation or facilitating the local destruction of passivity films. The metallurgical heterogeneity resulting from steel sensitization promotes the formation of inhibiting products in the active region, thus preventing a state of stable passivity to exist. The improvement in resistance to localized corrosion when molybdenum is added as an alloying element, is attributed, at least in part, to a reduction in the corrosion rate in the active region.     

Influence of Cu and Sn content in the corrosion of AISI 304 and 316 stainless steels in H2SO4

This paper addresses the influence of Cu and Sn addition on the corrosion resistance of AISI 304 and 316 stainless steels in 30 wt% H₂SO₄ at 25 and 50 °C. The corrosion process was evaluated by gravimetric tests, DC measurements and electrochemical impedance spectroscopy (EIS). The corrosion products were analysed by SEM, X-ray mapping and XPS before and after accelerated tests. The behaviour of both AISI 304 and 316 stainless steels in sulphuric acid solution was greatly improved by increasing Cu concentration and the synergic effect of Cu and Sn. Addition of Sn increased corrosion resistance, but less than addition of copper.     

The corrosion behavior of AISI 304L stainless steel in 0.1 M HCl at room temperature—II. The effect of cold working

This paper describes the results of a study concerning the influence of cold working upon the corrosion behaviour of an AISI 304L in HCl 0.1 M at room temperature. Potentiostatic tests, with test times of ≥ 150 h, followed by SEM observations, revealed that even though cold working lowers the critical pitting potential, it does not impair the susceptibility to localized corrosion. Evidence is provided for (1) pitting activity below the primary passivation potential, and (2) preferential attack on either the austenitic matrix or the martensitic phase, depending upon the corrosion potential below the protection field. It can be hypothesized that the above-mentioned behaviour is a consequence of the formation of corrosion products favoured by the presence of two metallic phases. Such products have inhibiting properties which determine pitting corrosion below the primary passivation potential and, in addition, they hinder the formation of passivity films and facilitate their local destruction.     

Three pyrazine derivatives as corrosion inhibitors for steel in 1.0 M H2SO4 solution

The inhibition effect of three pyrazine derivatives of 2-methylpyrazine (MP), 2-aminopyrazine (AP) and 2-amino-5-bromopyrazine (ABP) on the corrosion of cold rolled steel (CRS) in 1.0 M H₂SO₄ solution was studied by weight loss, potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) methods. The results show that all pyrazine compounds are good inhibitors, and inhibition efficiency follows the order: ABP > AP > MP. The adsorption of each inhibitor on CRS surface obeys Langmuir adsorption isotherm. For all these pyrazine derivatives, they act as mixed-type inhibitors. The probable inhibitive mechanism is proposed from the viewpoint of adsorption theory.     

N-Aminorhodanine as an effective corrosion inhibitor for mild steel in 0.5 M H2SO4

The corrosion inhibition effect of N-aminorhodanine (N-AR) on mild steel (MS) in 0.5 M H₂SO₄ was studied in both short and long immersion duration using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR), chronoamperometry and hydrogen gas evolution. The surface morphology of MS was examined with scanning electron microscopy (SEM) in absence and presence inhibitor. The inhibitor adsorption process on MS surfaces obeys the Langmuir adsorption isotherm. The results show that NAR is a good inhibitor for MS in the acidic medium. The inhibition efficiency obtained from potentiodynamic polarization, EIS and LPR up to 98% is determined.     

Effect of Mo and Mn additions on the corrosion behaviour of AISI 304 and 316 stainless steels in H2SO4

The work addresses the influence of Mn and Mo additions on corrosion resistance of AISI 304 and 316 stainless steels in 30 wt.% H₂SO₄ at 25 and 50 °C. Corrosion mechanism was determined by gravimetric tests, DC polarization measurements and electrochemical impedance spectroscopy (EIS). The morphology and nature of the reaction products formed on the material surface were analysed by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). Reduction of temperature from 50 to 25 °C drastically decreased the corrosion rate of AISI 304 and 316 stainless steels in sulphuric acid solution. Mn additions did not affect significantly the general corrosion resistance due to its low ability to form insoluble compounds in acid medium. Meanwhile, the formation of molybdenum insoluble oxides enhanced the corrosion performance.     

Inhibition of copper corrosion by isatin in aerated 0.5 M H2SO4

The corrosion inhibition of commercial copper by means of isatin was studied in aerated 0.5 M H₂SO₄ in the temperature range 25-55 °C using weight-loss, potentiodynamic and spectrophotometric tests, and determination of double layer capacitance. Inhibition efficiencies up to 94% in the concentration range of 1×10⁻⁴-7.5×10⁻³ M of isatin were obtained. The corrosion rates estimated with weight-loss measurements were higher than those correspondingly determined with the potentiodynamic test, especially at higher concentrations of inhibitor. This is in accord with other researches that have pointed out the limitation of the Tafel line extrapolation method in the determination of corrosion rates. The kinetics of cuprous and cupric ion formation and UV-visible spectra support the formation hypothesis of a complex between copper and isatin. The adsorptive behaviour of isatin on copper 0.5 M H₂SO₄ was also investigated.     

An anodic behaviour study of an analogical sintered system of austenitic stainless steel in H2SO4 solution

The anodic behaviour of sintered austenitic stainless steel was investigated on an analogical system using wrought plate stainless steel of Type 316. Potentiodynamic polarization measurements were carried out on wrought plate stainless steel of Type 316 in an analogical concentration cell using a special method. The effect of carbides precipitation on the anodic behaviour was investigated on carburized 316 wrought stainless steel containing an average carbon concentration of 0.06 and 0.15 (wt. %). The carburization treatment results in an increase in the critical current density although a clear active passive transition is observed. The anodic behaviour of sintered stainless steel in H₂SO₄ solution is mainly affected by the existence of interconnected open pores. The local intergranular sensitivity to the corrosive environment is increased due to carbide precipitation.     

Corrosion behaviour of cermet-based coatings with a bond coat in 0.5 M H2SO4

The corrosion behaviour of an HVOF Ni–5Al/WC–17Co coating on Al-7075 is investigated in 0.5 M H₂SO₄. In the temperature range of 25–45 °C, the coating exhibits pseudopassivity that effectively protects from localized corrosion. At 25 °C, pseudopassivity proceeds via three stages: during the first stage, oxidation of W in the binder phase occurs. The second stage is characterized by oxidation of W in both the binder and the carbide particles. The third stage is characterized by intensive hydration of WO₃ and formation of Co₃O₄. During the second and third pseudopassive stages, the formation of a bi-layer surface film is postulated. The inner layer, consisting of anhydrous oxides, has a barrier character. The outer layer, composed of WO₃ · xH₂O, is unstable. In case of surface film disruption, the bond coat successfully hinders corrosion propagation into the Al-alloy. Higher electrolyte temperatures lead to faster corrosion kinetics and higher tendency for pitting.     

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.     

Tribocorrosion of 316L stainless steel and TA6V4 alloy in H2SO4 media

Tribocorrosion of stainless steel 316L and titanium alloy TA6V4 has been conducted in a sulphuric acid solution using an apparatus designed and built for evaluating the joint action of corrosion and wear. The material electrochemical and wear behaviours have been investigated during friction tests under electrochemical potential control. The specimens have been submitted to friction against an alumina ball under cathodic, free and anodic potentials. The friction coefficient, the wear rate and the current density were measured and the obtained results were discussed in terms of passivating film stability and repassivation kinetics.     

Tribocorrosion behaviour of low temperature plasma carburised 316L stainless steel in 0.5 M NaCl solution

Experiments have been carried out to study the tribocorrosion behaviour of low temperature plasma carburised 316L stainless steel under unidirectional sliding in 0.5 M NaCl solution, using a pin-on-disk tribometer integrated with a potentiostat for electrochemical control. It is found that the carburised layer exhibits much better resistance to material removal than the untreated specimen, particularly at anodic potentials. No corrosion pits are observed inside the wear track on the carburised specimen at anodic potentials as high as 750 mV (SCE). The results are discussed in terms of the relative contribution of wear and corrosion to overall material removal by tribocorrosion.     

XPS investigations of electrochemically formed passive layers on Fe/Cr-alloys in 0.5 M H2SO4

Passive layers on Fe20Cr and Fe15Cr were prepared by anodic oxidation in 0.5 M H₂SO₄ and were investigated by X-ray photoelectron spectroscopy. The preparation of the sputter-cleaned samples and their transfer to the ultrahigh vacuum was performed under protection of purified argon without any contact to the laboratory atmosphere. The prepassive layer consists of a homogeneous film with Cr(III)hydroxide and Cr(III)-sulphate with a low content of Fe(II). In the passive potential range a bilayer structure with enrichment of Cr(III)-oxides with an outer hydroxide and an inner oxide part is formed. Iron exists only in a bivalent oxidation state. In the transpassive potential range a pronounced change of the layer composition was observed: The outer part of the transpassive layer is formed predominantly by Fe(III) species whereas the inner part still contains a strong enrichment of Cr₂O₃.     

The electrochemical behavior of austenitic stainless steel with different degrees of sensitization in the transpassive potential region in 1 M H2SO4 containing chloride

This paper investigates electrochemical methods to estimate the degree of sensitization (DOS) for as-rolled and solution-treated austenitic stainless steels (AISI 304). The change in DOS was introduced by heat treatment of various time periods at 700 °C, and the electrochemical experiments were conducted at 27 °C in 1 M H₂SO₄ + 0.2 wt.% NaCl. The results show that there is no obvious difference in the anodic polarization curves of the specimens with the differences in DOS. However, the DOS of specimens can be clearly differentiated with AC impedance response in a particular transpassive potential region. In the transpassive potential region of the anodic polarization curve, as overpotential is increased beyond the breakdown potential, three types of anodic dissolution, passive dissolution, grain-boundary attack, and pitting can be characterized. The DOS can only be correctly evaluated with AC impedance response in the middle of the transpassive potential region, where anodic dissolution is of grain-boundary attack type, from 1.05 to 1.1 V. The chromium-depleted zone was preferentially attacked and an intergranular corrosion was found for the serious sensitized specimen after AC impedance test. The healing effect was observed in as-rolled specimens as the specimens were heated more than 72 h, but the effect was not found in the solution-treated specimens sensitized for up to 480 h at 700 °C.     

稀硫酸溶液清洗电镀铜晶种(英文)

采用稀硫酸溶液清洗以除去在铜晶种表面形成的氧化物。将通过溅射沉积在Ti/Si(100)薄片上生成的铜晶种暴露在空气中来生长原生铜氧化物。用稀硫酸溶液和TS-40A碱性清洗剂除去原生铜氧化物。先用TS-40A碱性清洗剂预处理以除去铜晶种表面的有机物,再用稀硫酸溶液除去铜氧化物(Cu2O和CuO)以及有机物和Cu(OH)2。