A SECM assisted EQCM study of iron pitting

The local breakdown of the iron passive layer and the resulting pitting corrosion of iron were studied for massive material and for a thin film on an electrochemical quartz crystal microbalance (EQCM). The initiation and the propagation of a single pit on iron were controlled through the local production of chloride anion thanks to the silver chloride reduction at the tip of the scanning electrochemical microscope (SECM). Experiments were performed in borate buffer and in KOH solution, in order to investigate the influence of the solution pH. The influence of the iron potential and of the amount of chloride anion necessary for the breakdown of the passive layer were also investigated. The frequency response of the quartz was correlated to the pit evolution with respect to time. After the breakdown of the passive layer, the frequency changes were then directly linked to the generation of Fe(II) during the pit growth.     

Effects of coating thickness and surface treatment on the corrosion protection of diglycidyl ether bisphenol-A based epoxy coated carbon steel

The corrosion resistance of carbon steel specimens was compared, using different surface treatment methods such as blasting and zinc phosphate treatment on carbon steel followed by application of different coating thickness. Specimen surface morphology was observed by SEM. The corrosion performance of epoxy coated carbon steel was examined by electrochemical impedance spectroscopy (EIS), along with immersion test in 0.5N-NaCl solution and NORSOK M 501 cyclic test, respectively. EIS results showed that higher thickness of epoxy coating and zinc phosphate treatment on carbon steel showed better corrosion protection than rest of the specimens. Specimens with no treatment and blasting treatment followed by epoxy coating, showed poor corrosion protection. Results of NORSOK M 501 cyclic test showed similar trend as those of EIS results however degradation of specimens was more severe than those from immersion test.     

Self-healing of a high temperature cured epoxy using poly(dimethylsiloxane) chemistry

A high temperature cured self-healing epoxy is demonstrated by incorporating microcapsules of poly(dimethylsiloxane) (PDMS) resin and separate microcapsules containing an organotin catalyst. Healing is triggered by crack propagation through the embedded microcapsules in the epoxy matrix, which releases the healing agents into the crack plane initiating crosslinking reactions. A series of tapered double-cantilever beam (TDCB) fracture tests were conducted to measure virgin and healed fracture toughness. Healing efficiencies, based on fracture toughness recovery, ranged from 11 to 51% depending on the molecular weight of PDMS resin, quantity of healing agent delivered, and use of adhesion promoters.     

Fracture and fatigue response of a self-healing epoxy adhesive

A self-healing epoxy adhesive for bonding steel substrates is demonstrated using encapsulated dicyclopentadiene (DCPD) monomer and bis(tricyclohexylphosphine)benzylidine ruthenium (IV) dichloride (Grubbs’ first generation) catalyst particles dispersed in a thin epoxy matrix. Both quasi-static fracture and fatigue performance are evaluated using the width-tapered-double-cantilever-beam specimen geometry. Recovery of 56% of the original fracture toughness under quasi-static fracture conditions occurs after 24 h healing at room temperature conditions. Complete crack arrest is demonstrated for fatigue test conditions that render neat resin and control samples failed. Inspection of fracture surfaces by electron microscopy reveals evidence of polymerized DCPD after healing. These results are the first mechanical assessment of self-healing for thin (ca. 360 μm) films typical of adhesives applications.     

Investigation of corrosion protection properties of an epoxy nanocomposite loaded with polysiloxane surface modified nanosilica particles on the steel substrate

In this study, it has been aimed to investigate the corrosion protection properties of an epoxy/polyamide coating loaded with different concentrations (ranged from 3 to 6% (w/w)) of the polysiloxane surface modified silica nanoparticles (nano-SiO₂). The nanocomposites were applied on the steel substrates. Field emission scanning electron microscope (FE-SEM) and UV–vis techniques were utilized in order to investigate the nanoparticles dispersion in the coating matrix. The effects of addition of nanoparticles on the corrosion resistance of the coating were studied by an electrochemical impedance spectroscopy (EIS) and salt spray test. The coating surface degradation was studied by optical microscope and Fourier transform infrared radiation (FT-IR) spectroscopy. Results obtained from UV–vis and FE-SEM analyses revealed proper and uniform distribution of surface modified nanoparticles in the epoxy coating matrix. It was shown that the coating corrosion protection properties were significantly enhanced in the presence of 5 wt% silica nanoparticles. Less degradation occurred on the surface of the coatings loaded with 5 wt% nanoparticles.     

十八胺改性环氧树脂研究

通过冲击试验机、热变性仪、硬度计、动态力学分析仪、热重分析仪等仪器研究了十八胺对环氧树脂固化物性能的影响,研究发现十八胺可以提高环氧树脂酸酐固化物的耐冲击性能、硬度改变较小、热变性温度降低。     

阻燃环氧树脂胶黏剂的研制

采用以KH-560硅烷偶联剂包覆三聚氰胺多聚磷酸酯（MPP）为阻燃剂,以环氧树脂E-44为基体,制备阻燃环氧树脂胶黏剂。通过对所制得胶黏剂进行剪切强度测试、热失重测试以及阻燃性能测试,研究了包覆阻燃剂对环氧树脂胶黏剂力学性能、热稳定性和阻燃性能的影响。结果表明,采用包覆处理MPP为阻燃剂制备的阻燃环氧树脂胶黏剂综合性能较好,其剪切强度为19．9MPa,氧指数为31．2。最佳配方为100份环氧树脂、30份阻燃剂、30份固化剂、温度为70℃。     

Electron spin resonance study of a cured epoxy resin exposed to high-energy radiation

Tetraglycidyl-4,4′-diaminodiphenyl methane cured with 4,4′-diaminodiphenyl sulphone was irradiated with varying dosages of 0.5 MeV electrons and 1.17 and 1.33 MeV gamma rays and was studied using electron spin resonance. The radical concentration increases with increasing radiation dose and decays, at ambient temperature, in a way consistent with a model that assumes two simultaneous second-order reactions occurring in different zones.     

Performance of self-healing epoxy with microencapsulated healing agent and shape memory alloy wires

We report the first measurements of a self-healing polymer that combines a microencapsulated liquid healing agent and shape memory alloy (SMA) wires. When a propagating crack ruptures the embedded microcapsules, the liquid healing agent is automatically released into the crack where it contacts a solid catalyst embedded in the matrix. The SMA wires are then activated to close the crack during the healing period. We show that dramatically improved healing performance is obtained by the activation of embedded SMA wires. We conclude that improved healing is due to a reduction of crack volume as a result of pulling the crack faces closed, and more complete polymerization of the healing agent due to the heat produced by the activated SMA wires.     

新型环氧树脂增韧剂的合成与研究

以聚醚和酸酐反应,再与环氧树脂反应,合成了一种新型的以环氧基封端的内增韧活性增韧剂,讨论了该增韧剂的固化特性和最佳掺合比例,在100份环氧树脂中加入10份这种增韧剂,环氧树脂固化物综合力学性能较好,剪切强度为23．6MPa,压缩强度达70．2Mpa。     

Corrosion protection mechanisms of carbon steel by an epoxy resin containing indole-3 butyric acid modified clay

This work is an extension of studies into the mechanisms of corrosion protection of mild steel by an epoxy resin containing organically modified clay (Hang et al. [1]; Truc et al. [2]). In a previous study (Truc et al. [2]), it was shown that indole-3 butyric acid (IBA)-modified clay improved the corrosion performance of epoxy. In the present study, it was shown that the IBA is an anodic inhibitor and its efficiency was about 93%. Exfoliation and dispersion of the IBA-modified clay in the epoxy coating were checked by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The improvement of the corrosion performance of the epoxy coating containing IBA-modified clay by comparison with pure epoxy coating was confirmed for a low film thickness (10 μm). Local electrochemical impedance measurements performed on scratched samples revealed the inhibitive action of IBA at the carbon steel/coating interface. It was shown that the inhibitor release from the IBA-modified clay was favoured for high pH values. Thus, in neutral media, the corrosion process which induces a local increase of pH will increase the self-healing performance.     

A comparative study of epoxy and polyurethane based coatings containing polyaniline-DBSA pigments for corrosion protection on mild steel

Organic coatings based on epoxy and polyurethane matrices containing polyaniline doped with dodecyl benzene sulfonic acid (Pani-DBSA) were prepared and applied over steel plates (SAE 1020). The plates were submitted to salt spray chamber for up to 30 days in order to evaluate the corrosion protection of these coatings. The properties of the coated plates were analyzed as a function of time by electrochemical impedance spectroscopy, open circuit potential, optical microscopy, and Raman spectroscopy. In general, results indicate a decrease in the electrical resistance, increase in capacitance and decrease in open circuit potential. Epoxy based coatings have improved performance when Pani-DBSA is used as pigment, whereas for the polyurethane coatings, Pani-DBSA seems to play an adverse effect. Raman spectroscopy indicates a possible chlorination of the epoxy matrix after 30 days exposure to salt spray chamber.     

Comparison study of dicyandiamide-cured epoxy bonded steel joints and polyamidoamine-cured epoxy bonded steel joints

There are instances where efficiency and safety may be compromised as a result of deteriorating fluid transport systems. Thus, it is worth evaluating other methods that can repair the damage for a temporary period without shutting down the operation. The objective was to evaluate the durability of an epoxy-bonded steel in aqueous environments that would represent such a repair. EPON^® 828 was chosen as the epoxy resin, and dicyandiamide and polyamidoamine were two types of curing agents evaluated in this study. The epoxy-bonded steel joints were exposed in either distilled water or 3.4% NaCl solution for various times. The mechanical strength of the bonded joints was evaluated using a three-point flexure test. The interfacial shear strength of unaged samples ranged from 0.93 to 0.32 MPa. It was found that the interfacial shear strength decreased with aging time for both epoxy-bonded systems. Scanning electron microscopy (SEM), optical microscopy, and X-ray photoelectron spectroscopy (XPS) were used to determine the locus of failure of the bonded joints. It was concluded that failure occurred cohesively within the oxide layer if oxides were present on the substrate surface prior to the bonding procedure.     

The mode of action of chromate inhibitor in epoxy primer on galvanized steel

Investigations of the mechanism of the protective action of strontium chromate pigment in an epoxy primer were carried out with electrochemical impedance spectroscopy (EIS), atomic absorption spectroscopy (AAS), scanning reference electrode techniques (SRET) and water uptake measurements. Epoxy primers applied to galvanized steel were studied in a corrosion environment which models the atmospheric precipitation of European countries. Corrosion and electrochemical properties of samples of bare galvanized steel and coated galvanized steel were investigated. It was established that the protective function of the chromate in the primer is primarily due to a cathodic/mixed inhibition of the surface of galvanized steel in defect areas of the polymer coating. It is suggested that the process of leaching of chromate ions from epoxy primer into the environment takes place because the decrease in pH at anodic defect sites causes the destruction of the primer film and accelerates the dissolution of the chromate pigment.     

Electrochemical deposition and characterization of ZnCo alloys and corrosion protection by electrodeposited epoxy coating on ZnCo alloy

ZnCo alloys electrochemically deposited on steel under various deposition conditions were investigated. The influence of deposition current density, temperature and composition of deposition solution on the phase structure and corrosion properties of ZnCo alloys were studied. It was found that ZnCo alloy obtained from chloride solution at 5 A dm⁻² showed the best corrosion properties, so this alloy was chosen for further examination. Epoxy coating was electrodeposited on steel and steel modified by ZnCo alloy using constant voltage method. The effect of ZnCo alloy on the corrosion behavior of the protective system based on epoxy coating is interpreted in terms of electrochemical and transport properties, as well as of thermal stability.     

Corrosion behaviour of epoxy coatings electrodeposited on galvanized steel and steel modified by Zn–Ni alloys

The electrochemical and transport properties and thermal stability of epoxy coatings electrodeposited on hot-dip galvanized steel and steel modified by Zn–Ni alloys were investigated during exposure to 3% NaCl solution. Zn–Ni alloys were electrodeposited on steel by direct and pulse current. From the time dependence of pore resistance, coating capacitance and relative permittivity of epoxy coating, diffusion coefficient of water through epoxy coating, D(H₂O) and thermal stability, it was shown that Zn–Ni sublayers significantly improve the corrosion stability of the protective system based on epoxy coating. Almost unchanged values of pore resistance were obtained over the long period of investigated time for epoxy coatings on steel modified by Zn–Ni alloys, indicating the great stability of these protective systems, due to the existence of the inner oxide phase layer and the outer layer consisting of basic salts.     

Atomistic molecular modelling of crosslinked epoxy resin

In the present study, a new method was developed to construct atomistic molecular models of crosslinked polymers based on commercially important epoxy resin. This method employed molecular dynamics/molecular mechanics schemes and assumed close proximity. The generic Dreiding2.21 force-field and advanced compass force-field were used for the construction of models and prediction of properties, respectively. A polymer network with conversion up to 93.7% was successfully generated by this method. Density and elastic constants of the system were calculated from the equilibrated structure for the validation of the generated models. The simulated results compared reasonably with experimental data available. The developed method would hold great promise in further molecular simulations for structure and properties of epoxy resin or other cured systems.     

Integrated AFM and SECM for in situ studies of localized corrosion of Al alloys

Rolled 3xxx series Al alloys, e.g., EN AW-3003, are generally used as fin or tube material in heat exchangers for automobiles. With reducing fin thickness, maintaining fin material integrity is of increasing importance. This study aimed at exploring the differences in intrinsic corrosion properties between EN AW-3003 and a newly developed Al-Mn-Si-Zr fin alloy using state-of-the-art local probing techniques. Volta potential mapping of both alloys by scanning Kelvin probe force microscopy (SKPFM) indicates a cathodic behaviour of constituent intermetallic particles (>0.5 μm) relative to the alloy matrix. Compared to EN AW-3003, the Al-Mn-Si-Zr alloy has a smaller number of particles with large Volta potential difference relative to the matrix. In situ atomic force microscopy (AFM) measurements in slightly corrosive solutions showed extensive localized dissolution and deposition of corrosion products on EN AW-3003, and only a small number of corroding sites and “tunnel-like” pits on Al-Mn-Si-Zr. Probing the ongoing localized corrosion process by integrated AFM and scanning electrochemical microscopy (SECM) revealed more extensive local electrochemical activity on EN AW-3003 than on Al-Mn-Si-Zr. In all, the lower corrosion activity and smaller tunnel-like pits resulted in lower material loss of the Al-Mn-Si-Zr alloy, a beneficial property when striving towards thinner fin material.     

Adhesion characteristics and corrosion stability of epoxy coatings electrodeposited on phosphated hot-dip galvanized steel

The influence of hot-dip galvanized steel (HDG) surface pretreatment with phosphate coatings on the corrosion stability and adhesion characteristics of epoxy coatings electrodeposited on HDG steel was investigated. Phosphate coatings were deposited on hot-dip galvanized steel from baths with different concentrations of NaF (0.1, 0.5 and 1.0 g dm⁻³) and at different temperatures (50, 65 and 80 °C). The influence of fluoride ion concentration in the phosphating bath, as well as the deposition temperature of the bath, on the adhesion characteristics and corrosion stability of epoxy coatings on phosphated HDG steel was investigated. The dry and wet adhesions were measured by a direct pull-off standardized procedure, as well as indirectly by NMP test, while corrosion stability was investigated by electrochemical impedance spectroscopy (EIS).     

Performance evaluation of polyaniline pigmented epoxy coating for corrosion protection of steel in concrete environment

Corrosion protection of mild steel reinforcement offered by a newly developed epoxy based coating system containing inherently conducting polyaniline as one of the pigments has been studied. The synthesis of polyaniline and preparation of epoxy based coating system containing this polyaniline are described here. The corrosion resistant property of epoxy polyaniline system, coated on mild steel was evaluated by various techniques such as electrochemical impedance spectroscopy, potential time studies, cathodic disbondment test, anodic polarization study, salt spray test and chemical resistance test. The corrosion resistance of epoxy polyaniline coating system coated on reinforcement bars embedded in concrete was also studied by an accelerated time to cracking study. The formation of polyaniline was characterized using FTIR, UV, GPC, particle size analyzer and fineness studies. Electrochemical impedance studies reveal that the resistance of the coating decreased initially and then increased due to passivating ability of the polyaniline pigment. Based on the results of different techniques, it is found that epoxy coating with polyaniline pigment is effective in corrosion protection of steel in concrete environment.