Monolayer and bilayer conducting polymer coatings for corrosion protection of steel in 1 M H2SO4 solution

In this study, monolayer polypyrrole (PPY), polyaniline (PANI), and bilayer PPY/PANI, PANI/PPY coatings were deposited onto steel electrodes by electropolymerization in 0.1 M monomer and 0.3 M oxalic acid solution. Such corrosion parameters of these electrodes, as corrosion potentials, anodic Tafel constants and corrosion current densities were determined by means of current–potential curves as a function of time in 1 M H₂SO₄ solution. These findings were compared to the corrosion parameters of a bare steel electrode in the same acid solution. The monolayer and bilayer polymer coatings were characterized by the Fourier transform infrared (FTIR) spectroscopy and SEM. Bilayer coatings displayed better corrosion inhibition efficiencies than monolayer coatings. Furthermore, the PPY/PANI coatings offered superior corrosion protection than the PANI/PPY coatings.     

Corrosion inhibition of pipeline steel grade API 5L X52 immersed in a 1 M H2SO4 aqueous solution using heterocyclic organic molecules

The effect of the concentration of four types of inhibiting heterocyclic molecules on the corrosion susceptibility of steel pipeline samples grade API 5L X52 in 1 M H₂SO₄ was studied by electrochemical testing and SEM analysis. The compounds used were: 2-mercaptobenzoimidazole (MBI), 5-mercapto-1-tetrazoleacetic sodium salt (MTAc), 1-hydroxybenzotriazole (HBT) and benzimidazole (BIA). The results showed that there was an optimum inhibitor concentration at which the maximum inhibiting efficiency, IE, was reached. Further, the MBI displayed the best inhibiting characteristics for this system, with a maximum IE of approximately 99% having added only 25 ppm. It is shown that this compound can affect both the anodic and cathodic processes, thus it can be classified as a mixed-type inhibitor for API 5L X52 steel corrosion in sulphuric acid. Moreover, this compound follows an adsorption mechanism, which can be adequately described by the Langmuir isotherm with an adsorption standard free energy difference (ΔG°) of −28.5 kJ mol⁻¹.     

New synthesised diamine derivatives as corrosion inhibitors of steel in 0.5 M H2SO4

The effect of addition of diamine derivatives on the corrosion of steel in 0.5 M H₂SO₄ solution is studied using weight loss measurements, electrochemical polarisation and impedance spectroscopy (EIS) methods. This study permits to follow the evolution of the inhibitive effect of diamine derivatives on steel in 0.5 M H₂SO₄. Polarisation measurements show that the diamines act as mixed inhibitors. The cathodic curves indicate that the reduction of proton at the steel surface happens within a pure activating mechanism. The inhibitors are adsorbed on the steel surface according to the Frumkin adsorption isotherm model. We note a good agreement between gravimetric, electrochemical polarisation and impedance spectroscopy methods.     

Hot corrosion and protection of Ti2AlC against Na2SO4 salt in air

The hot corrosion behavior of Na₂SO₄-coated Ti₂AlC was investigated by means of thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy/energy dispersive spectroscopy. This carbide displays good hot corrosion resistance below the melting point of Na₂SO₄ while the corrosion attacks become virulent when the salt is molten. A protectively continuous Al₂O₃ layer forms and imparts good corrosion resistance, and consequently, the corrosion kinetics is generally parabolic at 850 °C. However, porous oxide scales fail to protect the Ti₂AlC substrate at 900 and 1000 °C. The segregation of sulfur at the corrosion scale/substrate interface accelerates the corrosion of Ti₂AlC. Furthermore, a convenient and efficient pre-oxidation method is proposed to improve the high-temperature hot corrosion resistance of Ti₂AlC. An Al₂O₃ scale formed during pre-oxidation treatment can remarkably restrain the infiltration of the molten salt into the substrate and prevent the substrate from severe corrosion attacks.     

Corrosion of Si3N4-ceramics in aqueous solutions Part I: Characterisation of starting materials and corrosion in 1 N H2SO4

The corrosion behaviour of silicon nitride materials in acids strongly depends on the composition and amount of the grain boundary. But there exist no systematic investigations of the relation between the corrosion behaviour and the composition and amount of the grain-boundary phase. The aim of the series of these papers is the systematic investigation of these relations. In the first part the methods of determination of the amorphous grain-boundary phases are described in detail. Additionally, the correlation between the corrosion behaviour and the composition of the grain-boundary phases are given. The structural reasons and the mechanisms behind the observed changes in the corrosion behaviour will be given in part II of this paper.     

Corrosion protection of carbon steel by thin films of poly(3-alkyl thiophenes) in 0.5 M H2SO4

Poly(3-octyl thiophene) (P3OT) and poly(3-hexylthiophene) (P3HT) dissolved in toluene were deposited onto 1018 carbon steel and corroded in 0.5 M H₂SO₄. P3OT and P3HT films were chemically deposited by drop casting onto 1018-type carbon steel with two surface finishing, i.e. abraded with 600-emery paper and with alumina (Al₂O₃) particles of 1.0 μm in diameter (mirror finish). Their corrosion resistance was estimated by using potentiodynamic polarization curves, linear polarization resistance (LPR), and electrochemical impedance spectroscopy, EIS, techniques. In all cases, polymeric films protected the substrate against corrosion, but the protection was improved if the surface was polished with Al₂O₃ particles of 1.0 μm in diameter. The polymer which gave the best protection was P3HT because the amount of defects was much lower than that for the P3OT films. The polymers did not act only as a barrier layer against aggressive environment, but they improved the passive film properties by decreasing the critical current necessary to passivate the substrate, increasing the pitting potential and broadening the passive interval.     

The influence of gun transverse speed on electrochemical behaviour of thermally sprayed Cr3C2-NiCr coatings in 0.5 M H2SO4 solution

In the present study, different types of 75% Cr₃C₂-25% NiCr coatings were applied on a steel substrate by means of high velocity oxygen fuel spraying (HVOF), and studied using ac and dc electrochemical measurements in an aerated and unstirred 0.5 M H₂SO₄ solution. Structural characterization was determined before and after electrochemical tests. Differences between all sprayed systems are related to the gun transverse speed and number of deposited layers, which strongly affected the electrochemical characteristics of the coated steels. The coating obtained with a higher torch speed showed better resistance against corrosion. The electrochemical impedance results were analyzed using an equivalent circuit where porosity of the coatings and substrate oxidation were considered.     

The influence of steel microstructure on CO2 corrosion. EIS studies on the inhibition efficiency of benzimidazole

Electrochemical measurements employing a.c. and d.c. techniques were used to study CO₂ corrosion of carbon steel with two different microstructures: annealed, and quenched and tempered (Q&T), with and without inhibitors. The corrosive media was a deoxygenated 5% NaCl solution, saturated with CO₂ at 40 °C and pH 6. Benzimidazole was employed as inhibitor, with a concentration of 100 ppm. Electrochemical impedance spectroscopy (EIS) and linear polarization resistance (LRP) results showed that without inhibitor, Q&T samples have a better corrosion resistance than the annealed ones. On the other hand, the presence of inhibitor improves the corrosion resistance for the annealed samples whereas for the Q&T samples the opposite effect is observed. From the Bode phase angle plots it can be concluded that there is no evidence of inhibitor film formation in any microstructure condition. Based on the experimental findings in the present work, a mechanism of action for the inhibitor is proposed.     

Electrochemical study of effect of the concentration of azole derivatives on corrosion behavior of stainless steel in H2SO4

In order to improve corrosion resistance of the stainless steel structures exposed to acidic media, a variety of corrosion inhibitors particularly organic ones have been examined. In this work, the corrosion inhibition performance of two azole derivatives namely benzotriazole and benzothiazole on stainless steel in 1 M sulfuric acid was studied through taking advantage of electrochemical techniques as well as SEM surface analysis. Revealing effectiveness of the two inhibitors, the AC impedance spectra indicated no change in corrosion mechanism. The noise resistance and average current density as parameters extracted from electrochemical noise measurements revealed the direct proportion of inhibition function to the inhibitor concentration. In accordance with the polarization curves, benzotriazole and benzothiazole appeared to act as mixed type inhibitors. The adsorption of the two corrosion inhibitors was shown to obey Langmuir isotherm. Moreover, it was deduced from the isotherm that the type of adsorption can be physical and chemical in nature. The corrosion damage mitigation was also confirmed through SEM in the presence of benzothiazole.     

Mass transfer effects in the H2SO4 catalyzed pivalic acid synthesis

The synthesis of carboxylic acids from alkenes, carbon monoxide and water according to the Koch process is usually carried out in a stirred gas–liquid–liquid multiphase reactor. Due to the complex reaction system with fast, equilibrium reactions and fast, irreversible reactions the yield and product distribution depend on a number of process parameters. The effect of some of these parameters was studied for the production of pivalic acid, using sulfuric acid as a catalyst. For the 96 wt.% sulfuric acid catalyst solution used the main reactions are relatively fast with respect to mass transfer and mixing. Therefore, aspects like the position of the injection point, inlet concentration, agitation intensity and injection rate all influence the yield obtained. The presence of an inert organic liquid phase was found to be beneficial, due to a combined effect of enhanced gas–liquid mass transfer and a ‘local supply’ effect for carbon monoxide near the hydrocarbon reactant inlet.     

Protection of mild steel corrosion with Schiff bases in 0.5 M H2SO4 solution

Three new Schiff bases, viz., N,N′-ethylen-bis (salicylidenimine) [S₁], N,N′-isopropylien-bis (salicylidenimine) [S₂], and N-acetylacetone imine, N′-(2-hydroxybenzophenone imine) ortho-phenylen [S₃] have been investigated as corrosion inhibitors for mild steel in 0.5 M H₂SO₄ using Tafel polarization and electrochemical impedance spectroscopy (EIS). The three Schiff bases function as good inhibitors reaching inhibition efficiencies of ∼97-98% at 300 ppm concentration. The fraction <theta> of the metal surface covered by the inhibitor is found to increase with inhibitor concentration. Of the three Schiff bases, the S2 shows better efficiency than the other two Schiff bases. The adsorption of the inhibitor follows Langmuir isortherm. Thermodynamic calculations indicate the adsorption to be physical in nature.     

New degradation mechanism of Ti/IrO2 + MnO2 anode for oxygen evolution in 0.5 M H2SO4 solution

Degradation mechanism of Ti/IrO₂(0.7) + MnO₂(0.3) anode for oxygen evolution was studied in 0.5 M H₂SO₄ solution by field emission scanning electron microscopes (FESEM), Tafel slope, X-ray diffraction (XRD) and electrochemical impedance spectroscopic (EIS). The whole surface of the non-electrolyzed Ti/IrO₂(0.7) + MnO₂(0.3) anode consisted of nano-IrO₂ poles array. The anode surface had hardly discovered cracks and had compact morphology that can prevent the electrolyte from entering the Ti/oxide interface and an insulating TiO₂ film from growing on the Ti-based surface. An insulating TiO₂ phase had not been generated on the Ti/oxide interface during the process of O₂ evolution and the inactive anode surface still remained mass of the IrO₂ and MnO₂ oxides. The chemical dissolution of Ti/IrO₂(0.7) + MnO₂(0.3) anode coating was not the main reason for electrode degradation in 0.5 M H₂SO₄ solution. The degradation mechanism of Ti/IrO₂(0.7) + MnO₂(0.3) anode differed from other conventional oxide electrodes for O₂ evolution in acid medium. The platforms of Tafel slope and anode potential (900–1050 h) indicated that the change of the oxygen evolution reaction (OER) mechanism was the main reason for degradation of Ti/IrO₂(0.7) + MnO₂(0.3) anode due to the change of adsorption intermediate.     

H2SO4 as a passivating medium on the localised corrosion resistance of surgical 316L SS metallic implant and its effect on hydroxyapatite coatings

The localised corrosion resistance of 316L SS metallic implant due to H₂SO₄ treatment is being studied through electrochemical studies involving cyclic polarisation experiments and impedance studies. The efficiency of hydroxyapatite (HAP) coatings on H₂SO₄ treated 316L SS is also been investigated through electrochemical studies and the dissolution characteristics of the coatings. The study reveal that 15% H₂SO₄ treatment was found to be efficient in the corrosion resistance of 316L SS and dissolution of alloy is considerably reduced in the hydroxyapatite coatings on 15% H₂SO₄ treated 316L SS.     

Oxygen reduction at Pt and Pt70Ni30 in H2SO4/CH3OH solution

The electrochemical oxygen reduction reaction (ORR) was studied at Pt and Pt alloyed with 30 atom% Ni in 1 M H₂SO₄ and in 1 M H₂SO₄/0.5 M CH₃OH by means of rotating disc electrode. In pure sulphuric acid, the overpotential of ORR at 1 mA cm⁻² is about 80 mV lower at Pt₇₀Ni₃₀ than at pure Pt. It was found that in methanol containing electrolyte solution the onset potential for oxygen reduction at PtNi is shifted to more positive potentials and the alloy catalyst has an 11 times higher limiting current density for oxygen reduction than Pt. Thus, PtNi as cathode catalyst should have a higher methanol tolerance for fuel cell applications. On the other hand, no significant differences in the methanol oxidation on both electrodes was found using cycling voltammetry, especially regarding the onset potential for methanol oxidation. During all the measurements no significant electrochemical activity loss was observed at Pt_0.7Ni_0.3. Ex-situ XPS investigations before and after the electrochemical experiments have revealed Pt enrichment in the first surface layers of the PtNi.     

以三氧化二锑为协效剂的复合阻燃剂对MVQ硫化胶阻燃性能的影响

分别研究硼酸锌／三氧化二锑、氢氧化铝／三氧化二锑和三氧化钼／三氧化二锑并用体系对甲基乙烯基硅橡胶(MVQ)硫化胶阻燃性能和物理性能的影响。结果表明，硼酸锌／三氧化二锑并用体系可有效提高MVQ硫化胶的阻燃性能，并能保持较好的物理性能；氢氧化铝／三氧化二锑并用体系的阻燃效果十分显著，但MVQ硫化胶的发烟量稍大；三氧化钼／三氧化二锑并用体系虽可减小MVQ硫化胶的发烟量，但阻燃效果不明显，且硫化胶的物理性能受损严重。     

Synthesis and H2 uptake of Cu2(OH)3Cl, Cu(OH)2 and CuO nanocrystal aggregate

Monodispersed Cu₂(OH)₃Cl nanoplatelets, Cu(OH)₂ nanowires, CuO nanoparticles and nanoribbons with a spherical morphology were synthesized using hydrothermal and heat-treatment reactions, and their H₂ storage characteristics were examined. The Cu₂(OH)₃Cl nanoplatelets particles formed immediately after mixing the reactant, which subsequently formed larger uniform spherical particles in the submicron range. This procedure highlights a practical strategy for producing spherical Cu(OH)₂ and CuO materials consisting of monodispersed nanocrystals. The spherical aggregates of Cu₂(OH)₃Cl nanoplatelets heat-treated at 473 K could reversibly store up to 2.35 wt.% H₂ at 38 bar and 293 K.     

Corrosion behavior of SM 80SS tube steel in stimulant solution containing H2S and CO2

Scanning electron microscopy, X-ray diffraction and electrochemical measurement technique were applied to investigate the corrosion of SM 80SS tube steel in stimulant solution with carbon dioxide (CO₂) and hydrogen sulfide (H₂S) at variable conditions of PCO₂/PH₂S and temperature. The results suggest that there exists a synergism of sweet corrosion and sour corrosion on the steel surface, corrosion attack increases in the initial stage and then decrease with the increase of PCO₂ or PH₂S; serious corrosion occurs in the PCO₂/PH₂S ranged from 31 to 520. In addition, the fitted parabola function equation Y = 0.47873 + 0.04014X - (3.23788E−5)X² is established, and the most serious corrosion is 600 for PCO₂/PH₂S. Under the moderate contents of PCO₂ and PH₂S, the corrosion scale consists of FeS_0.9 and FeCO₃; for relatively high PH₂S, additive product FeS comes into being at high temperature such as T = 150 °C, product FeO(OH) is found in the corrosion scale. The H₂S corrosion has a significant effect on the whole reaction process and iron sulfide is superior to precipitating on the steel surface compared with iron carbonate. In addition, the surface scales of iron sulfide almost act as a diffusion barrier and inhibit the corrosion by a coverage effect strongly depending on H₂S concentration by EIS measurement.     

The experiment research of corrosion behaviour about Ni-based alloys in simulant solution containing H2S/CO2

Aimed at the problem of tubing corrosion in environment that containing hydrogen sulfide (H₂S), carbon dioxide (CO₂), and chlorides (Cl⁻), the corrosion behaviour of two nickel based alloys (UNS 06985 and UNS 08825) in 15 wt%NaCl solution containing H₂S/CO₂ in high temperature and high pressure environment was investigated. The pitting corrosion behaviour of Ni-based alloys was studied in FeCl₃·6H₂O solution by means of polarisation curve and immersion tests. The scanning electron microscopy (SEM), energy disperse spectroscopy (EDS) was applied to analyse the microstructure and corrosion performance of the samples. The results showed that the pitting-resistant of nickel alloy UNS 06985 was superior to UNS 08825. With the rising of experimental temperature, the corrosion increased and some slight pitting attacks appeared on the surface of UNS 08825. The test temperature was the crucial factor that influenced not only the compactness and the growing rate of corrosion product scale, but also the corrosion rate of the alloys. Elemental sulfur is a strong oxidant, the presence of S0 leads to a serious localized corrosion. XRD showed that the corrosion films formed on nickel base alloys consisted of NiS, CrO₃, and the oxides of Ni and Fe. The polarisation curves showed a different corrosion behaviour of two alloys, anodic curve of UNS 06985 has a wider passivation area, and there has higher transpassive potential.     

A study on mechanism of charging/discharging at amorphous manganese oxide electrode in 0.1 M Na2SO4 solution

In the present work, the mechanism of charging/discharging at the amorphous manganese oxide electrode was investigated in 0.1 M Na₂SO₄ solution with respect to amount of hydrates and valence (oxidation) states of manganese using a.c.-impedance spectroscopy, anodic current transient technique and cyclic voltammetry. For this purpose, first the amorphous manganese oxide film was potentiostatically electrodeposited, followed by heat-treatment at 25–400 °C to prepare the electrode specimen with different amounts of hydrates and oxidation states of manganese. For as-electrodeposited electrode with the most hydrates, the anodic current transient clearly exhibited a linear relationship between the logarithm of current density and the logarithm of time, with a slope of −0.5, indicating that the charging/discharging is purely limited by Na⁺/H⁺ ion diffusion. From the analyses of the impedance spectra combined with anodic current transients measured on the hydrated electrode heat-treated at 25–150 °C, it was found that as the amount of hydrates decreases, the depth of cation diffusion in the electrode becomes shallower and the ratio of charge-transfer resistance to diffusion resistance also increases. This suggests that a transition occurs of pure diffusion control to a mixed diffusion and charge-transfer reaction control. For the dehydrated electrode heat-treated at 200–400 °C, the charging/discharging purely proceeds by the charge-transfer reaction. The reversibility of the redox reaction increases with increasing amount of hydrates and oxidation states of manganese, which provides us the higher power density. On the other hand, the pseudocapacitance decreases in value with increasing heat-treatment temperature, thus causing the lower energy density.     

Electrochemical performance of nanocrystalline Li3V2(PO4)3/carbon composite material synthesized by a novel sol–gel method

A novel sol–gel method based on V₂O₅·nH₂O hydro-gel was developed to synthesize nanocrystalline Li₃V₂(PO₄)₃/carbon composite material. In this route, V₂O₅·nH₂O hydro-gel, NH₄H₂PO₄, Li₂CO₃ and high-surface-area carbon were used as starting materials to prepare precursor, and the Li₃V₂(PO₄)₃/carbon was obtained by sintering precursor at 750 °C for 4 h in flowing argon. The sol–gel synthesis ensures homogeneity of the precursors and improved reactivity. The sample was characterized by XRD, SEM and TEM. X-ray diffraction results show Li₃V₂(PO₄)₃ sample is monoclinic structure with the space group of P2₁/n. The TEM image indicates that the Li₃V₂(PO₄)₃ particles modified by conductive carbon are about 70 nm in diameter. The Li₃V₂(PO₄)₃/carbon system showed that the discharge capacities in the first and 50th cycle are about 155.3 and 143.6 mAh/g, respectively, in the range of 3.0–4.8 V. The sol–gel method is fit for the preparation of Li₃V₂(PO₄)₃/carbon composite material which may offer some favorable properties for commercial application.