Permeability of paint films towards chloride ion

An apparatus for determining the permeability of paint films towards chloride ion is described. This set-up implements the time-lag, method and consists of a permeation cell made up of two chambers divided by a supported paint film. The upper chamber contains an aqueous sodium chloride solution and the lower one, water. The permeability is obtained from the conductivity history read at the lower chamber. Osmotic pressure issue is addressed and the reproducibility of the results reported. The time-lag, method is not described in any standard. The requirement concerning “surface protection systems for concrete” for chloride ion permeability is not quantified in prEN 1504-2. The standard establishes that this requirement is “subject to national standards and national regulations” but when the capillary adsorption of water is lower than 0.01 kg/(m²h^0.5) the diffusion of chloride ion is not to be expected. Some experimental results prove this is not correct and, in Portugal, the National Laboratory of Civil Engineering (LNEC) has proposed a threshold permeability value of 10⁻¹⁴ m²/sec for coatings claiming to be corrosion protective.     

Electrochemical repair techniques in carbonated concrete. Part II: cathodic protection

The role of several factors such as concrete composition, exposure condition and pre-corrosion of steel reinforcement in concrete on the effectiveness of the electrochemical realkalisation (ER) technique was discussed in Part I of this article (Bertolini and Redaelli in J Appl Electrochem, doi:, 2011). Here the same factors will be considered in the case of cathodic protection (CP). CP differs from ER since it is a permanent technique with much lower applied current density. It was originally introduced to protect steel from corrosion in chloride-contaminated concrete; however, it can be advantageous even in carbonated concrete, in particular compared to conventional repair. CP tests were carried out on reinforced specimens made with six different types of concrete, subjected to accelerated carbonation. CP was applied with a current density of 10 mA m⁻² of steel preceded by a start-up current density of 100 mA m⁻² for 3 weeks. Reference specimens in the same conditions were also considered.     

Elaboration and characterization of tubular macroporous ceramic support for membranes from kaolin and dolomite

A low cost macroporous support for ceramic membranes was prepared by in situ reaction sintering from local natural mineral kaolin with dolomite as sintering inhibitor. The characterization focused on the phase evolution, microstructure, pore structure, mechanical strength and water permeability at various compositions and sintering temperatures. The sintering of kaolin was improved with 5 wt% dolomite, but clearly inhibited with ≥10 wt% dolomite. For the 20 wt% dolomite samples, the crystalline phases were mainly composed of mullite, cordierite and anorthite after sintering between 1,150 and 1,300 °C. Moreover, both mean pore size and mechanical strength increased with increasing sintering temperature from 1,100 to 1,300 °C, but the water permeability and porosity decreased. The 1,250 °C sintered macroporous support with 20 wt% dolomite exhibited good performances such as porosity 44.6%, mean pore size 4.7 μm, bending strength 47.6 MPa, water permeability 10.76 m³ m⁻² h⁻¹ bar⁻¹, as well as good chemical resistance. This work provides opportunities to develop cost-effective ceramic supports with controllable pore size, porosity, and high strength for high performance membranes.     

The influence of nanocrystalline state of iron on the corrosion inhibitor behavior in aqueous solution

Effect of grain size reduction on the electrochemical and corrosion behavior of iron of different grain sizes (32–320 nm) produced by direct and pulsed current electrodeposition was characterized using Tafel polarization curves and electrochemical impedance spectroscopy (EIS). The grain size of deposits was determined by X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). The most intensive first-order peak (110) of the XRD patterns was taken for detailed analysis using a Gaussian fitting curve. The electrochemical tests were carried out in electrolyte 30 mg L⁻¹ NaCl + 70 mg L⁻¹ Na₂SO₄ + 250 mg L⁻¹ NaNO₂ aqueous solution. It was found that the corrosion potential and corrosion current density significantly changed as the microstructure morphology was changed. Results obtained from electrochemical tests suggested that the inhibition effect and corrosion protection of sodium nitrite inhibitor in near-neutral aqueous solutions increased as the grain size decreased from submicrocrystalline to nanocrystalline. This was attributed to the excess free energy, and concomitantly the increased number of the active sites caused by higher grain boundary and triple junction content in the nanocrystalline surface, which provides sites for electrochemical activity, and effect of sodium nitrite, was more pronounced.     

Polypyrrole electropolymerized on aluminum alloy 1100 doped with oxalate and tungstate anions

Polypyrrole films doped with oxalic acid and tungstate were potentiostatically electropolymerized on aluminum alloy 1100. Two statistical factorial designs (fractional and complete) were used to study the influence of the synthesis variables on the film performance against corrosion. Corrosion protection of the polypyrrole films doped with oxalate and tungstate anions (PPy/OXA/W) on the aluminum alloy was evaluated by potentiometric and electrochemical impedance spectroscopy (EIS) measurements in a 0.05 mol L⁻¹ NaCl solution. The results obtained showed that the best performance against corrosion was detected with the PPy/OXA/W film synthesized at 1.0 V, 1.5 C in 0.2 mol L⁻¹ pyrrole, 0.1 mol L⁻¹ oxalic acid and 0.05 mol L⁻¹ sodium tungstate solutions provide a protective effect against corrosion.     

Synthesis and characterization of nanosized titanium dioxide and silicon dioxide for corrosion resistance applications

We are reporting the preparation and characterization of nano-titanium dioxide and silica. The corrosion resistance performance of these nanopigments in silicone as well as silicone–polypyrrole Interpenetrating Polymer Network has been evaluated by impedance spectroscopy. The capacitance and resistance exerted by this nanocomposite coating were compared with the microcomposite coating and found that the nanocomposite coatings has the resistance in the order of 10⁸ Ω cm² in 3% sodium chloride solution, which is more than the microcomposite coating. The comparison of heat resistance performance of these composite coatings indicates that nanocomposite coatings exhibit higher heat resistance property than the microcomposite coatings.     

Characterization and corrosion protection properties of polypyrrole / montmorillonite electropolymerized onto aluminium alloy 1100

Films of Polypyrrole/Montmorillonite (PPy/MT) clays were electropolymerized potentiostatically on aluminium alloy 1100, using sodium dodecylbenzenesulfonate (SDBS) as a dopant. Two clay species were used: Na⁺-Montmorillonite (MT-Na) and modified-Montmorillonite (MT-M). The characterization of the PPy/MT films performed by XRD and TEM shows that the exfoliation method employed, as well the electrochemical polymerization method used in this work, allow nanocomposite materials to be obtained. The PPy/MT films were found to have less electrical conductivity than pure PPy. The corrosion protection of aluminium alloy 1100 covering PPy/MT was evaluated by electrochemical techniques in 0.05 mol L⁻¹ NaCl medium. The electrochemical parameters derived from the polarization curves, together with the EIS data, revealed that the corrosion resistance of PPy/clay coatings depends on the type and concentration of Montmorillonite employed. The best performance in the corrosion protection of the aluminum was achieved with PPy/MT films containing 1% of clay.     

Development of Nanostructured Poly (<Emphasis Type="Italic">o</Emphasis>-toluidine) Reinforced Organic–Inorganic Hybrid Composites

The present work reports the synthesis and characterization of nanostructured poly (o-toluidine) (POT) reinforced epoxy-siloxane (ES) composite resins. The structural elucidation was carried out using FT-IR and UV–visible spectrometry. The FT-IR analysis confirmed the interaction between NH group of the POT and the OH group of ES via strong hydrogen bonding. The UV–visible spectra of POT/ES composites revealed a blue shift of 100 nm in the polaronic transition peak observed at 600 nm in pristine POT, which was attributed to the restriction in the delocalization of polarons in the POT chains due to electrostatic interaction via hydrogen bonding. The nanosize of POT and its dispersion in the ES matrix was confirmed by X-ray diffraction (XRD) and transmission electron microscopy studies. The particle size was found from 15–35 nm. The morphological studies confirmed the formation of a nanocomposite where POT appeared to act as reinforcing agent in the ES matrix. XRD showed the semi-crystalline nature of POT/ES nanocomposites. The conductivities of POT and its nanocomposites were 10⁻³–10⁻⁴ S/cm at 30 °C. The thermal stability increased with an increase in the loading of POT in ES. The nanocomposites revealed good physico-chemical and physico-mechanical characteristics, which suggests their potential application as corrosion protective coatings.     

Mg-rich coatings: A new paradigm for Cr-free corrosion protection of Al aerospace alloys

Environmentally acceptable alternative coatings to chromate pigments and pretreatments for the corrosion control of Al alloy 2024 T-3, commonly used in aircraft, were designed, formulated, and tested as primer coatings to provide protection using particulate Mg-rich pigmentation. The system was designed by analogy to pigmented Zn-rich primer coatings used for the protection of steel. In the current study, four coating polymer systems were examined as possible candidates as polymer matrices for Mg-rich cathodic protect coatings. Mg-rich primers were formulated with ∼50-micron average particle size magnesium powder, near to the critical pigment volume concentration (CPVC) for this system. Top-coated scribed coatings systems have been subjected to Prohesion^™ exposure in dilute Harrison’s solution for up to 5000 hr. These coatings are the first nonchromated coatings to satisfy 3000 hr of such exposure and remain shiny and undamaged in the scribe area, only showing damage at about 4800 hr. The corrosion byproducts generated in the scribe areas during Prohesion exposure were examined by energy dispersive X-ray analysis (EDXA), and the local pH of the coating determined by the nature of the salt formed as a function of exposure conditions and time, did not cause Al corrosion. Presented at the 81 st Annual Meeting of the Federation of Societies for Coatings Technology, November 12–14, 2003, in Philadelphia, PA.     

Corrosion performance of the electroless Ni–P coatings prepared in different conditions and optimized by the Taguchi method

This paper presents an experimental study on the influence of anionic surfactant sodium dodecyl sulfate (SDS), pH, substrate finishing and annealing temperature on the corrosion resistance of electroless nickel phosphorus (Ni–P) coatings using electrochemical techniques and optimization of process parameters based on the Taguchi method. Parameters were selected in three levels and L9 from orthogonal robust array design was used. Corrosion performance of the electroless Ni–P coatings was evaluated by polarization and electrochemical impedance spectroscopy (EIS). Scanning electron microscope (SEM), Energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) analysis were used for studying surface morphology and chemical composition of the electroless Ni–P coatings. The results showed that SDS surfactant causes increasing of corrosion resistance and improves surface morphology. Finally, optimum conditions were achieved as, surfactant concentration: 1.5 g L⁻¹, pH: 5.5, substrate finishing provided with emery paper no, 2000, and annealing temperature of 200 °C.     

Corrosion tests of nickel coatings prepared from a Watts-type bath

This paper deals with the preparation and characterization of thin Ni layers. The electrodeposition was carried out galvanostatically from a Watts bath at different current densities in the range from 1 to 10 A dm⁻² and for deposition times between 900 and 7200 s. The structure and the morphology of the nickel coatings were investigated by SEM and XRD techniques. The microhardness of deposited layers, the electrochemical behavior and the corrosion properties of the deposits were investigated by means of Vickers microhardness, polarization measurements, and electrochemical impedance spectroscopy (EIS). The uniform deposits showed fine grains and good protection against corrosion.     

Electrochemical investigations on the corrosion behavior and corrosion natural inhibition of API-X100 pipeline steel in acetic acid and chloride-containing CO<Subscript>2</Subscript>-saturated media

The purpose of this experimental work was to investigate selected electrochemical aspects of the corrosion behavior of API-X100 in CO₂-saturated, multivariable-controlled corrosion media. Utilizing potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), the corrosion rates, anodic dissolution, cathodic regimes, and free interfacial interactions were discussed. The tests were performed with respect to the environmental factors of 10, 20, 30, 40, 50, and 60 g L⁻¹ chloride and of 10, 20, 30, 40, 50, and 60 mL L⁻¹ acetic acid at 20 and 90 °C in the absence and presence of 10 vol% crude oil. The corrosion rates exhibited a peak value with respect to the chloride content while they increased continuously with the acetic acid content irrespectively from temperature. The corrosion behavior was nearly independent from chloride in the presence of acetic acid and oil demonstrated an effective inhibition in all conditions. EIS results showed an agreement with the polarization findings and indicated adsorption-controlled mechanisms.     

Determination of chloride diffusion coefficient of concrete using open-circuit potential measurements

The rate of chloride ion ingress into concrete is of great importance for the performance of reinforced concrete structures exposed to chloride-contaminated environments. The service life of reinforced concrete structures subjected to such exposure conditions is closely related to the rate of chloride ion diffusion through the concrete. This paper presents the determination of the apparent chloride diffusion coefficient of concrete using open-circuit potential measurements. The chloride diffusion coefficients obtained are in the range of 6.4×10⁻⁸ to 12.4×10⁻⁸ cm²/s for a simulated seawater tidal condition, which is quite consistent with those reported in the literature. This indicates that open-circuit potential measurements can be considered as an approximate but simple method of assessing the diffusivity of chloride through concrete. Limited with the testing conditions and the characteristics of concrete used, results indicated that the time necessary for corrosion initiation of concrete with a cover depth of 7 cm ranges from 3 to 6 years for the seawater exposure, whereas it is only 1.5 years for a 3% sodium chloride exposure.     

Advances in the science and technology of paints, inks and related coatings: 2005

Summary  This review summarises the developments in adhesion, VOC emissions, coatings, transparent conductive coatings, hybrid organic-inorganic coatings, UV curing, biocidal coatings, paints, weathering, wood coatings, surface treatment of concrete, metal corrosion, pigments, film formation, printing, modelling fluid flow in printing, dot gain and inkjet printing reported inSurface Coatings International Part B: Coatings Transactions,88, 2005.     

The corrosion resistance of coated steel dowels determined by impedance spectroscopy

The corrosion resistance of coated smooth steel dowels in simulated pore solution with and without 3.5% sodium chloride solution is reported. The dowels are coated with a double-layer structure composed of a 180 μm of Nickel-Chromium-Boron (referred to as NiCrB) that is overlaid by a 20 μm inorganic layer made of silicon powder, silica fume, blast furnace slag, and combinations thereof. The composition of the synthetic pore solution is based on the composition of pore fluids expressed from Type I portland cement that is characterized by pH of about 13.4 and an ionic strength of 0.4.Alternating current impedance spectroscopy measurements conducted in the range of 10 mHz to 10 kHz were found to be instrumental in detecting any change in the resistance of the coatings. It was found that the NiCrB sub-layer provides a good corrosion resistance that outperforms that of the inorganic coating. Of the five inorganic compositions tested, the combination of slag and silica fume has the best performance. The protection against corrosion is attributed mostly to particle packing rather than densification of the matrix due to pozzolanic reaction.     

Preparation and characterization of tubular porous ceramics from natural zeolite

Tubular porous ceramics with more than 40% open porosity and about 6 μm mean pore size were fabricated from natural zeolite powder with starch as pore-forming agent. The optimized processing parameter was 1100–1150 °C with a holding time of 1 h. Permeability of nitrogen and water flux of the tubular specimens was measured and discussed, and the obtained optimized values are 2480 m³m⁻² h⁻¹bar⁻¹ and 26 m³m⁻² h⁻¹ bar⁻¹, respectively.     

Synthesis and characterization of nanoporous sodium-substituted hydrophilic titania ceramics coated on 316L SS for biomedical applications

Bioactive sodium-substituted titania coating on 316L SS substrate was prepared. XRD patterns exhibited the formation of a mixture of two phases (Na₂Ti₃O₇, Na₂Ti₆O₁₃) with monoclinic structure. FTIR spectra showed that the set of overlapping peaks in the range of 800–400 cm⁻¹ are related to Ti–O and Ti–O–Ti groups. SEM-EDAX, AFM, and TEM showed the surface morphology of the coated surface to be nanoporous and uniform. The influence of the bioactivity of the coating in a simulated body fluid (SBF) medium was examined. Excellent adhesion of the ceramic composites to the substrate was achieved. The hydrophilic nature of the sodium titanate coating induced the formation of hydroxyapatite layer on the metal surface. The corrosion protection performance of the coatings has been evaluated using potentiodynamic polarization and electrochemical impedance spectroscopy measurements, which proved increased corrosion resistance of nanosodium titanate-coated 316L SS. These results imply that the sodium titanate-coated 316L SS acts as a barrier layer to the metallic substrate.     

Corrosion resistance of Pb–Sn composite coatings reinforced by carbon nanotubes

Carbon nanotubes/Pb–Sn composite coatings were prepared by electrodeposition technology. The polarization curves and electrochemical impedance of the Pb–Sn coatings and carbon nanotube/Pb–Sn composite coatings were studied in 3.0 wt% HCl, 10 wt% NaOH, and 3.5 wt% NaCl electrolyte solutions, respectively. The results show that the corrosion potential of carbon nanotubes/Pb–Sn composite coatings were improved in the three kinds of corrosive medium, especially in 3.5 wt% NaCl electrolyte solution, where it increased significantly from −0.592 V (vs SCE) to −0.535 V (vs SCE). In addition, composite coatings have higher electrochemical impedance. Carbon nanotubes can improve the corrosion resistance of lead–tin electroplated coatings.     

Corrosion inhibition of steel in sodium chloride solution by undoped polyaniline epoxy blend coating

In this study an undoped polyaniline (PAni) was synthesized by chemical oxidative polymerization with ammonium persulfate as an oxidizing reagent. The synthesized PAni was used as a corrosion inhibitive pigment in an epoxy matrix. The corrosion protection performance of steel coated panels in 3.5% sodium chloride solution was evaluated via determination of open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS). It was found that after 300 days of immersing the resistance of coating was about 4 × 10⁵ Ω cm². The OCP was shifted to the noble region due to the passivation effect of PAni pigment. Besides, the phase angle (theta) at 10 kHz was stable around 87 ± 1° during immersion period. Results revealed that PAni pigmented paint showed acceptable protection against the corrosion of carbon steel in 3.5% sodium chloride solution.     

Corrosion protection with zinc-rich epoxy paint coatings embedded with various amounts of highly dispersed polypyrrole-deposited alumina monohydrate particles

Active anodic zinc content below 90 wt.% does not support sufficient electrical contacts but higher contents cause high porosity of traditional liquid zinc-rich paints (ZRPs). To resolve this problem, our proposal is the application of highly dispersed polypyrrole (PPy) coated alumina inhibitor particles (PCAIPs) in zinc-rich paint compositions. Using these nano-size inhibitor particles at concentrations from 4.55 to 0.85 wt.%, hybrid paints were formulated with zinc contents ranging from 60 to 85 wt.% at the same time. Submicron morphology and nano-scale structure, spectroscopy characteristics and electrochemical properties of the PCAIPs were studied by transmission electron microscopy (TEM) and rheology, Fourier-transform infrared spectroscopy (FT-IR) and cyclic voltammetry (CV) in first part of the work. In the second part, electrolytic corrosion resistivity of two sets of paint coatings were salt-spray chamber and immersion tested with 5 wt.% aqueous solution of sodium chloride. Active corrosion prevention ability of the salt-spray tested coatings was evaluated in compliance with ISO recommendations. Dielectric properties of the coatings during the immersion tests were monitored by electrochemical impedance spectroscopy (EIS). Corrosion tested area of the coatings was investigated by glow-discharge optical emission spectroscopy (GD-OES) to disclose infiltration of corrosive analytes and oxygen enrichment in the cross-section of the primers in comparison with their pristine states. Morphology of the zinc pigments was examined by scanning electron microscopy (SEM), and quality of steel specimens and the interfacial binder residues by X-ray photoelectron spectroscopy (XPS) as well as FT-Raman and Mössbauer spectroscopy. The results of both types of corrosion tests evidenced efficient utilisation of sacrificial anodic current for galvanic protection and improved barrier profile of the hybrid coatings, along with the PCAIP inhibited moderate self-corrosion of zinc. As a result of well balanced active/passive function, the hybrid coating containing zinc at 80 wt.% and PCAIPs at 1.75 wt.% embedding PPy at 0.056 wt.% indicated the most advanced corrosion prevention. Galvanic function of the hybrid paints is interpreted on the basis of size-range effect and spatial distribution of the alumina supported PPy inhibitor particles and basic electrical percolation model considerations.