Enhanced control and stability of polypyrrole electromechanical actuators

The practical application of polypyrrole (PPy) actuators requires a stable strain response and a high degree of reproducibility from sample to sample. The use of symmetrical voltage cycling to control the actuation of polypyrrole is shown to lead to a slow net oxidation of the polymer after several tens of cycles. The result is a slow deterioration in the actuation strain. The use of current pulsing reduces this problem and gives a more stable strain response. Current pulsing in combination with an ionic-liquid (IL) electrolyte allowed a strain of 3% to be achieved repeatably for many different samples for at least 100 cycles.     

Polyaniline, polypyrrole and poly(3,4-ethylenedioxythiophene) as additives of organic coatings to prevent corrosion

The aim of this work is to compare the protection against corrosion imparted by different conducting polymers when these materials are used as anticorrosive additives in the formulation of conventional epoxy paints. Specifically, the polymers employed as anticorrosive additives are polyaniline emeraldine salt, polyaniline emeraldine base, polyaniline emeraldine salt composite with carbon black, polypyrrole composite with carbon black and poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulphonate). Initially, the structural, thermal and mechanical properties of the unmodified epoxy paint as well as the modified coatings, obtained by the addition of 0.3 wt.% of conducting polymers, have been characterized. After this, controlled accelerated corrosion assays in an aggressive solution medium were developed using coated steel panels. Results indicate that the protection against corrosion imparted by the formulations modified by the addition of poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulphonate), polyaniline emeraldine salt and, especially, polyaniline emeraldine base is significantly higher than that of the unmodified paint. In contrast, the use of conducting polymer composite with carbon black reduces the efficacy of the coating. Results indicate that some conducting polymer compositions should be considered as a suitable alternative to replace inorganic anticorrosive pigments currently used in paint formulations.     

On the development of polypyrrole coatings with self-healing properties for iron corrosion protection

This paper presents studies on the efficacy and on the limits of polypyrrole (Ppy) doped with either or [PMo₁₂O₄₀]³⁻ as self-healing corrosion protecting coatings. The kinetics of the cathodic delamination were studied by means of the Scanning Kelvin Probe (SKP). This method, in combination with cyclic voltammetry, UV–visible spectroscopy (UV–vis) and X-ray photoelectron spectroscopy (XPS), shows a potential driven anion release from the Ppy coating that results in an inhibition of the corrosion process taking place in the defect. Thus, an intelligent release of inhibitor occurs only when the potential at the interface decreases. Inhibitor anions are released only due to an active defect. However, the release mechanism can be easily negatively affected by the presence of small cations and/or by too high pH values at the buried interface. Hence, such a self-healing coating has to be carefully designed in order to ensure an effective performance.     

Corrosion protection of iron by polypyrrole coatings electrosynthesised from a surfactant solution

This work is a study of the electropolymerisation of pyrrole onto iron electrodes in the presence of sodium bis(2-ethylhexyl) sulfosuccinate in a wide pH interval. The characterisation of the films was done using electrochemical techniques, SEM/EDX and IR spectroscopy. We show that it is possible to synthesise homogeneous, adherent and very compact films in the pH range between 7 and 12 under potentiodynamic, galvanostatic and potentiostatic conditions without substrate dissolution. The effects of various parameters on electrodeposition were investigated. The new procedure for the electrochemical synthesis of polypyrrole results in improved anticorrosion properties. The inhibition is proposed to be due to the sum of a repulsion of chloride ions because AOT remains entrapped in the polymer matrix and the presence of the iron oxide. Advantages of the use of surfactants in the electropolymerisation solution are discussed.     

Thermal effects on the process of electropolymerization of pyrrole on mild steel

Polypyrrole films were electrosynthesized on mild steel with oxalic acid electrolyte at varying temperatures (25–65 °C), current density (0.5–6.0 mA/cm²) and pH (2.0, 4.0, 7.0 and 8.5). The concentrations of pyrrole and oxalic acid were maintained at 0.1 M each in galvanostatic experiments. The results show that lower temperatures favor the formation of polypyrrole on mild steel in acidic media. At higher temperature and lower current densities, oscillations in electrode potentials were observed. The film quality was poorest at pH 7.0, while very adherent and compact films were obtained in alkaline medium. Higher temperature in alkaline media favors the formation of better polypyrrole films in contrast with acidic media.     

Morphology and properties of polypyrrole electrosynthesized onto iron from a surfactant solution

The morphology of polypyrrole (PPy) deposits during electrosynthesis onto iron electrodes in sodium bis(2-ethylhexyl) sulfosuccinate (AOT) solutions have been investigated using Scanning Electron Microscopy (SEM). At the early stages of electrosynthesis, fibrillar, toroidal and globular forms are observed while polymerization at longer times leads to a closely packed deposit. The effects of electropolymerization parameters on the obtained morphology are discussed. It is proposed that electropolymerization rate and polymer stiffness are important factors in controlling the morphology. Electrochemical investigations demonstrate that toroid-shaped deposits present electrochemical activity. The experimental results indicate that a gelatinous product, formed as a result of iron dissolution, grows simultaneously with PPy.     

Corrosion protection of iron by polypyrrole modified by copper using the cementation process

Polypyrrole (PPy) coatings have been deposited on iron from aqueous oxalic acid solution at different current densities. The polymer deposit obtained at a current density of 2 mA cm⁻² yields strongly adherent and smooth PPy layers. The modification of the film by incorporation of copper microparticles using the cementation process was applied. The resulting PPy/Cu film electrodes were characterized by scanning electron microscopy and EDX analysis. The protective performance against corrosion of these films is evaluated by using open circuit potential monitoring in highly corrosive solution (3% NaCl + HCl, pH 1). The results obtained were promising in the protection against corrosion.     

Conducting polymers as free radical scavengers

The potential antioxidant activity of conducting polymers in biomedical applications has been evaluated by determining radical scavenging ability using the stable ,-diphenyl-β-picrylhydrazyl (DPPH) free radical and correlating this with the reducing strength of the polymer. Commercial soluble polyaniline grafted to lignin, poly(anilinesulfonic acid), and polypyrrole, were found to be very efficient scavengers of DPPH radicals, reacting with 2-4 DPPH radicals per aniline or pyrrole monomer unit. Shifts in IR bands in the case of a polyaniline powder pointed to polymer oxidation and methoxy-substitution as likely mechanisms. All of the conducting polymers had low formal potentials (ca. 150 mV (Ag/AgCl) at pH 7), similar to those of catechin-type polyphenol antioxidants. On the other hand, the formal potentials of pyrrole and aniline were quite high (ca. 700 mV), and the reaction of aniline with DPPH radicals was limited, while o-methoxyaniline with a lower formal potential (ca. 500 mV) neutralised DPPH radicals in a 1:1 ratio.     

CVD掺硅金刚石残余应力的X射线衍射和拉曼光谱分析(英文)

采用X射线衍射(XRD)和拉曼光谱2种方法测量了不同硅碳比的CVD掺硅金刚石薄膜的残余应力。采用偏压增强热丝化学气相沉积装置在硬质合金基底上制备了掺硅金刚石薄膜,将正硅酸乙酯以不同的体积比溶解在丙酮中以使得反应气体中的硅碳比从0.1%变化到1.4%,从而控制掺硅金刚石薄膜的掺杂浓度。SEM和XRD的表征结果显示,随着硅掺杂浓度的增加,金刚石薄膜的晶粒尺寸减小,而金刚石(110)的晶面则逐渐占优。XRD法是测量入射角从0°到45°变化时对应的金刚石(220)面XRD衍射峰,并采用sin2ψ方法计算掺硅金刚石薄膜的残余应力。拉曼谱法则是通过检测金刚石特征峰偏移1332cm1位置的偏移量来测量残余应力。2种方法测得的残余应力随着硅掺杂含量的升高显示出良好的一致性,所有的硅掺杂金刚石的残余应力均为压应力,Si/C摩尔比为0.1%的薄膜具有最高的残余应力,为~1.75GPa(拉曼谱法)或~2.3GPa(XRD法)。随着硅掺杂浓度的进一步升高,薄膜的残余应力则稳定在~1.3GPa左右。     

Corrosion and biofilm for a composite coated iron observed by FTIR-ATR and Raman spectroscopy

Corrosion of metallic materials occurs in various ways. Recently, many researchers have pointed out that biofilm formed by a biofouling process may be a main cause for the initial stage of corrosion. From this viewpoint, the control of biofilm would help lead to corrosion prevention. In this paper, the authors studied the composite film of silane compounds with dispersed organometallic compounds that showed anti-fouling effect on pure iron substrates. The specimens were immersed in a laboratory biofilm reactor for 7 days to form biofilms on them. The surfaces of the specimens were observed by optical and scanning electron microscopy, Raman spectroscopy and FTIR-ATR spectroscopy. Finally, the effect of the composite coating on biofilm formation and corrosion characteristics was studied and shown to inhibit both.     

The alkaline stability of phosphate coatings II: in situ Raman spectroscopy

In situ Raman spectroscopy was used to study the dissolution of phosphate layers on zinc coated steel in dilute sodium hydroxide solution. The Raman intensity of the symmetrical stretching vibration of the phosphate anion was used to quantify the relative amount of phosphate on the surface. During exposure to an alkaline electrolyte, the intensity was found to decrease in a near linear manner, indicative of the removal of the phosphate anion. Crystal layers containing secondary ions Mn²⁺ and Ni²⁺ showed an improved stability compared to monocation zinc phosphate layers. The formation of amorphous Mn-hydroxide was observed on phosphate layers containing manganese.     

Formation of poorly crystalline iron monosulfides: Surface redox reactions on high purity iron, spectroelectrochemical studies

In the use of iron for reductive dehalogenation of chlorinated solvents in ground water, due to presence of sulfate-reducing bacteria the formation of hydrogen sulfide is expected. To simulate those processes the interface between 99.99% pure iron and 0.1 M NaHCO₃ deoxygenated solution with 3.1 × 10⁻⁵-7.8 × 10⁻³ M Na₂S · 9H₂O added was studied. The surface processes were characterised by the in situ normal Raman spectroscopy (NRS) and ex situ techniques; X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive X-ray (EDX). The open circuit potential (OCP) was monitored during in situ NRS measurements, and potentiodynamic anodic polarization measurements were carried out to reveal electrochemical behaviour of iron electrode.Open circuit potential-time transients indicated that the native oxide is unstable in deaerated bicarbonate solution and undergoes reductive dissolution (i.e. autoreduction) leaving the metallic Fe covered by Fe(OH)₂, adsorbed OH⁻, and patches of ‘magnetite-like’ oxide. Immediately upon injection of the Na₂S-solution the iron interface undergoes complex redox surface processes and a poorly crystalline FeS film forms. Potentiodynamic anodic polarization measurements indicated a mechanical breakdown of the FeS film. The origin and initiation of this breakdown process is not clear but is probably a result of internal stress developed during film growth. Based on surface studies supported by electrochemical measurements, a conceptual model for the complex redox processes occurring at the iron interface is proposed. This model describes the structural development of a poorly crystalline FeS, which breaks down, allowing further dissolution of the Fe and formation of FeOOH at the interface. Simultaneously and despite the existence of thick layer of FeS the entrance of hydrogen was evident as the typical hydrogen cracks in bulk of the iron material. This work shed the light on the complexity of the iron/sulfide solution interface, this knowledge is important to understand the kinetic of reduction of organic groundwater contaminants.     

Electrochemical synthesis of polypyrrole films on copper from phytic solution for corrosion protection

Phytic acid (C₆H₁₈O₂₄P₆), the principal phosphorous storage form in many plant tissues, is a green material. A polypyrrole (PPy) doped with phytic acid (IP₆) was electrosynthesised on copper from an aqueous phytic acid solution. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and SEM were used to characterise the polymer. The polymer-covered copper was subjected to a corrosion test in NaCl solution. The dissolution of copper covered with PPy-IP₆ was found to be greatly inhibited in NaCl solution. The inhibition indicated protection of the PPy-IP₆ layer against copper corrosion.     

Electrochemical and quantum chemical studies on the formation of protective films by alkynols on iron

In order to find out the effect of cathodic and anodic polarisation on the formation of inhibitor films we measured the electrochemical impedance of an iron electrode in sulphuric acid and in hydrochloric acid solutions in the presence of oct-1-yn-3-ol or 2-〈2-(1,1-dimethyl-prop-2-ynyloxy)-ethoxy〉-ethanol inhibitors. We found that the anodic polarisation helped the initial binding of the inhibitor to the iron surface. Cathodic polarisation does not influence the initial formation but, if applied at a later stage, promotes the growth of the inhibitor film. The results support the assumption that film formation on iron surfaces from alkynols takes place in a two-step process: first chemisorption, then polymerisation. The binding of alkynols to iron was studied in model electronic structure calculations which indicate that a dative bond is formed between Fe and the triple bond. The calculated vibrational frequencies of the alkynol bound to iron can be used to successfully interpret the IR spectra found in the literature.     

The effect of counter anions on corrosion resistance of steel covered by bi-layered polypyrrole film

The bi-layered polypyrrole (PPy) coatings were investigated for corrosion prevention of a carbon steel. The inner layer was doped with the Keggin structure anions of (PMo₁₂) and anions for stabilization of the passive oxide film at the metal-polymer interface, and the outer layer was doped with four organic anions of dihydroxynaphthalenedisulfonate (DHNDS), naphthalenedisulfonate (NDS), anthraquinonedisulfonate (AnqDS) or dodecylsulfate (DoS) for inhibition of the decomposition and release of PMo₁₂. The corrosion tests were performed in 3.5 wt.% NaCl aqueous solution. The corrosion resistance of the steels covered by the bi-layered PPy films was found in the following order: PPy-PMo₁₂/PPy-DHNDS < PPy-PMo₁₂/PPy-NDS < PPy-PMo₁₂/AnqDS < PPy-PMo₁₂/PPy-DoS. The performance of corrosion protection related to the oxidized state of the polymer was discussed.     

Corrosion protection of molybdate doped polypyrrole film prepared in succinic acid solution

ABSTRACT

Polypyrrole (PPy) was prepared on the mild steel substrate by electrochemical polymerisation in the solution containing pyrrole monomer and succinic acid. The mild steel surface could be passivated before and during electropolymerisation by molybdate. The morphology and structure of the PPy film were studied with SEM. The typical cauliflower structure of PPy was observed. Raman and IR spectroscopy showed that the obtained PPy was in an oxidised state. The thermal stability of PPy was investigated by the thermal gravimetric analysis, showing that PPy was stable at higher than 480°C. The electrochemical property of the PPy film was performed by open circuit potential, polarisation curves (I/E), and electrochemical impedance spectroscopy. The corrosion behaviour of mild steel (CT3) with PPy film in solution NaCl 3% was studied.

This paper is part of a supplementary issue from the 17th Asia-Pacific Corrosion Control Conference (APCCC-17).     

The effect of ultrasonic irradiation during electropolymerization of polypyrrole on corrosion prevention of the coated steel

Ultrasonic irradiation was imposed during electropolymerization of polypyrrole (PPy) in acid phosphate solution containing molybdophosphate () ions and pyrrole monomer. Corrosion of the steel coated by the PPy film prepared under ultrasonic irradiation was tested in 3.5 wt.% NaCl solution and compared with corrosion of the steel coated by the PPy film without ultrasonic irradiation. The PPy film prepared under ultrasonic irradiation kept the steel in the passive state one and a half times as long as that prepared without ultrasonic irradiation. Imposition of ultrasound enhanced the doping of and decreased the doping of . The surface morphology of the PPy film was changed with imposition of ultrasound in electropolymerization process. Under imposition of ultrasound, a dense and compact PPy layer was formed. The structure of the PPy film obtained under ultrasonic irradiation was assumed to result from change in nucleation-growth mechanism.     

Corrosion monitoring of galvanised coatings through electrochemical impedance spectroscopy

In this work, corrosion of industrial galvanised coatings is monitored through potentiodynamic and electrochemical impedance spectroscopy (EIS) methods and supported by real-time immersion tests. For such purpose, the corrosion behaviour is studied in different media (NaCl, NaOH and rain water), at different concentrations and varying immersion times. The results show that EIS allows to establish the interfacial reactions and the dissolution mechanisms occurring in three corrosive media, hence to foresee the protection conferred by these coatings. The impedance diagrams of the coated steel do not provide information on the slowest reactions, which only occur in natural rain water. Finally, each Zn/medium interface is characterised by a specific equivalent circuit giving a similar impedance response.     

A study on transition of iron from active into passive state

An investigation was carried out on the transition of an iron electrode from active to passive state in a sulphuric acid solution. It was found that the active-passive transition was an auto-catalytic process in which a pre-passive film grew on the electrode surface. The growing pre-passive film had a fractal edge whose dimension was affected by the applied passivating potential and the presence of chlorides in the solution. Applying a more positive passivating potential led to a faster active-passive transition and resulted in a more irregular pre-passive film. If chlorides were introduced into the sulphuric acid solution, the active-passive transition became more rapid and the pre-passive film more irregular. Apart from the influence on the growth of the pre-passive film, the presence of chlorides in the passivating solution was found to deteriorate the stability of the final passive film. All these phenomena can be understood if the passivating iron electrode is regarded as a dissipative system. To explain these results, a fractal pre-film model is proposed in this paper.     

A comparative study of magnetron co-sputtered nanocrystalline titanium aluminium and chromium aluminium nitride coatings

A comparative study of magnetron co-sputtered (Ti,Al)N and (Cr,Al)N coatings was made. It was found that while both coatings followed similar development pattern with increasing nitrogen pressure, the (Cr,Al)N coatings achieved much higher deposition rate and hardness, suggesting the coatings had a great potential for many industrial applications.