Conductivity of crosslinked low surface energy epoxy coatings

A new and straightforward method has been studied to prepare crosslinked low surface energy semiconductive epoxy coatings. The low surface energy is obtained by adding a small amount of partially fluorinated bifunctional primary amine Jeffamine D230 crosslinker and the conductivity is achieved by adding a small amount of semiconductive nanosized Cobalt(III) phthalocyanine particles. The use of partially fluorinated crosslinker strongly influences the conductivity, the conductive particle network structure, and the network distribution in the coatings. Compared to coatings that are free of fluorine, variations in fractal dimension, percolation threshold, particle‐containing layer thickness, and conductivity level are observed as the amount of fluorinated species is varied. These differences can be explained by (local) differences in effective Hamaker constant, viscosity, curing rate, evaporation of the solvent, and presence or absence of polymer matrix between the particles in the network. Our results suggest that other crosslinked semiconductive low surface energy epoxy coatings can be realized in a similar manner, but careful optimization of processing conditions is required to obtain the desired conductivity levels at low filler concentration. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Chem 47: 366–380, 2009     

Potential of zinc based-graphene oxide composite coatings on mild steel in acidic solution

This study introduces varying concentrations of graphene oxide (GO) as a filler into zinc chromate in forming composite coatings to improve the corrosion protection of mild steel. The purity of synthesized GO was inferred through the application of complementary characterization techniques, including FT-IR, XRD, Raman, SEM-EDX, and TEM analyses. GO doped zinc chromate coatings were deposited on the surface of mild steel through the brushing method. Electrochemical studies, i.e., electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PD) were conducted to elucidate the anticorrosion properties of the coated mild steel exposed to 0.5 ​M HCl solution. It was revealed that the highest anticorrosion protection was attained at low doping amount of 0.5% of GO with a corrosion rate of 0.036 mpy. Surface analyses revealed that incorporating GO into zinc chromate coating can effectively improve the anticorrosion properties and adhesion strength.     

Cerium hybrid silica coatings on stainless steel AISI 304 substrate

AISI 304 Stainless Steel is widely used in different industrial fields because of its mechanical and corrosion properties. However, its tendency to corrosion in presence of halide ions limits the applications. One strategy to improve the corrosion resistance is the use of coatings barriers containing corrosion inhibitors in their formulation. The lanthanides present attractive green and corrosion properties for the substitution of chromates, which are the most common substances used as corrosion protection. However, these compounds are highly toxic, and an intense effort is being undertaken to replace them. Cerium is a good alternative because of its relatively low cost and abundance. It fulfils the basics requirements for being considered an alternative inhibitor: the ions form insoluble hydroxides and they present low toxicity. Inorganic and hybrid sol-gel coatings have been developed to increase the corrosion resistance of metals and they provide an excellent vehicle for the incorporation of secondary phases including particles and metal ions as cerium ions. The aim of this work was to study the influence of the incorporation of cerium ions in hybrid silica sol-gel coatings deposited on AISI 304 stainless steel as substrate as a potential replacement of chromate treatments. This system should combine the barrier protection effect of silica coating with the corrosion inhibitor effect of the cerium ions inside the coatings. After 7 days of immersion in NaCl, coated substrates showed lower current densities than the bare steel, although the coatings produced from Ce (III) salts experience a slight weakening in time and those obtained from Ce (IV) chemicals evidence an enhance in the coating performance, probably due to the plugging of corrosion products in the defective areas of the film.     

Interactions and corrosion mitigation prospective of pyrazole derivative on mild steel in HCl environment

The effectiveness of 1H?pyrazole?3,5?dicarboxylic acid 5?benzyl ester 3?phenyl ester (PCBPE) as a preventer for deterioration of IS 513 Gr. D steel in 1 M HCl medium is evaluated via weight loss, electrochemical impedance, and polarization techniques. Kinetic and thermodynamic parameters assessed the feasibility of the adsorption process at diverse temperatures. The inhibition action on mild steel has been enhanced with increasing PCBPE concentration. It is found from the polarization studies that PCBPE behaves as mixed type inhibitor in HCl medium. The adsorption process of PCBPE on mild steel surface from acid environment is favoured Langmuir adsorption isotherm. The shielding efficiency of PCBPE has been enhanced at elevated concentrations, and it has been diminished at amplified temperatures. The Atomic Force Microscope (AFM), Scanning Electron Microscope (SEM), and Energy Dispersive Spectrum (EDS) were used to establish a surface characterization of metal specimens. A quantum chemical analysis of electron density distributions in the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) demonstrated how the inhibitor undergoes adsorption on mild steel in 1 M HCl. All experimental findings substantiate the corrosion mitigation performance of PCBPE on mild steel in acidic environments.     

Improving the dispersion and flexural strength of multiwalled carbon nanotubes-stiff epoxy composites through β-hydroxyester surface functionalization coupled with the anionic homopolymerization of the epoxy matrix

Multiwalled carbon nanotubes (MWNTs) were functionalized in a two-step acid-epoxy functionalization process, in which suitable surface condition and reactivity compatible with the DGEBA epoxy resin was introduced. The use of (4-dimethylamino)-pyridine as an initiator for DGEBA homopolymerization produced covalent bonds between the functionalized MWNTs and the epoxy matrix through chain transfer reactions involving the secondary hydroxyls. This process yielded uniform MWNTs-stiff epoxy composites with significant enhancement in flexural strength without sacrificing the elastic modulus when compared to the neat resin.     

Adhesives and coatings based on phenolic/epoxy resins

Low molecular weight epoxy resin based on bis (4‐hydroxy phenyl) 1,1 cyclohexane was prepared and modified with various types of the prepared phenolic resins. Phenol–, cresol–, resorcinol–and salicylic acid–formaldehyde resins were used. The optimum conditions of formulation and curing process were studied to obtain modified wood adhesives characterized by high tensile shear strength values. This study indicated that the more suitable conditions are 1:2 weight ratio of phenol–or cresol–formaldehyde to epoxy resin in the presence of phthalic anhydride (20 wt%) of the resin content as a curing agent at 150°C for 80 min. Resorcinol–or salicylic acid–formaldehyde/epoxy resins formulated at 1:2 weight ratio were cured in the presence of paraformaldehyde (20 wt%) at 150°C for 60 min. The effect of the structure of phenolic resins on the tensile shear strength values of formulated resin samples, when mixed with the epoxy resins and cured under the previously mentioned optimum conditions for different times, was investigated. Metallic and glass coatings from the previous resins were also prepared and evaluated as varnishes or paints. Copyright © 1999 John Wiley & Sons, Ltd.     

Xanthione: A new and effective corrosion inhibitor for mild steel in sulphuric acid solution

The adsorption and inhibition effect of xanthione (XION) on mild steel in 0.5 M H₂SO₄ at 303–333 K were studied using gravimetric and UV–visible spectrophotometric methods. The results obtained show that XION acts as an effective corrosion inhibitor for mild steel in sulphuric acid and inhibition efficiency reaches 98.0% at a very low inhibitor concentration of 10 μM. Inhibition efficiency was found to increase with increase in XION concentration but decreased with temperature suggesting physical adsorption mechanism. Arrhenius law and its transition equation lead to estimate the activation parameters of the corrosion process. XION inhibits the corrosion of mild steel effectively at moderate temperature and adsorbs according to the Langmuir isotherm. Thermodynamic parameters governing the adsorption process have been calculated and discussed. The UV–visible absorption spectra of the solution containing the inhibitor after the immersion of mild steel specimen indicate the formation of a XEN–Fe complex. Attempt to correlate the molecular structure to quantum chemical indices was made using density functional theory (DFT).     

Inhibition of aluminium and mild steel corrosion in acidic medium using Gum Arabic

The corrosion behaviour of mild steel and aluminium exposed to H₂SO₄ solution and their inhibition in H₂SO₄ containing 0.1–0.5 g/L Gum Arabic (GA) used as inhibitor was studied at temperature range of 30–60 °C using weight loss and thermometric techniques. Corrosion rate increased both in the absence and presence of inhibitor with increase in temperature. Corrosion rate was also found to decrease in the presence of inhibitor compared to the free acid solution. Inhibition efficiency increases with increase in concentration of the inhibitor reaching a maximum of 37.88% at 60 °C for mild steel and 79.69% at 30 °C for aluminium at 0.5 g/L concentration of GA. The inhibitor, GA was found to obey Temkin and El-Awady et al. thermodynamic kinetic adsorption isotherm for mild steel and aluminium respectively from the fit of the experimental data at all concentrations and temperatures studied. The phenomenon of chemical adsorption is proposed for mild steel corrosion, while physical adsorption mechanism is proposed for aluminium corrosion. Results obtained for the kinetic/thermodynamic studies indicate that the adsorption of GA onto the metals surface was spontaneous. GA is a better corrosion inhibitor for aluminium than for mild steel.     

Inhibitive action of ethanol extracts from Nauclea latifolia on the corrosion of mild steel in H2SO4 solutions and their adsorption characteristics

The inhibitive action of ethanol extracts from leaves (LV), bark (BK) and roots (RT) of Nauclea latifolia on mild steel corrosion in H₂SO₄ solutions at 30–60 °C was studied using weight loss and gasometric techniques. The extracts were found to inhibit the corrosion of mild steel in H₂SO₄ solutions and the inhibition efficiencies of the extracts follow the trend: RT > LV > BK. The inhibition efficiency increased with the extracts concentration but decreased with temperature rise. Physical adsorption of the phytochemical components of the plant on the metal surface is proposed as the mechanism of inhibition. The adsorption characteristics of the inhibitor were approximated by the thermodynamic-kinetic model of El-Awady et al.     

Adsorption behavior and corrosion inhibitive potential of xanthene on mild steel/sulphuric acid interface

The inhibition of xanthene (XEN) on the corrosion of mild steel in 0.5 M H₂SO₄ was studied by gravimetric and UV–visible spectrophotometric methods at 303–333 K. Results obtained show that XEN act as inhibitor for mild steel in H₂SO₄ solution. The inhibition efficiency was found to increase with increase in XEN concentration but decreased with temperature. Activation parameters and Gibbs free energy for the adsorption process using Statistical Physics were calculated and discussed. The corrosion process in 0.5 M H₂SO₄ in the absence and presence of XEN follows zero-order kinetics. The UV–visible absorption spectra of the solution containing the inhibitor after the immersion of mild steel specimen indicate the formation of a XEN–Fe complex. Quantum chemical calculations using DFT were used to calculate some electronic properties of the molecule in order to ascertain any correlation between the inhibitive effect and molecular structure of xanthene.     

Growth feature of PTFE coatings on rubber substrate by low‐energy electron beam dispersion

Polytetrafluoroethylene (PTFE) coatings were prepared on Si and acrylonitrile‐butadiene rubber substrates by low‐energy electron beam dispersion. The effects of substrate nature, distance of target to substrate (d_ts) and coatings thickness on the surface morphology, structure, and tribological properties of the coatings were investigated. The results showed that substrate nature affects the shape and size distribution of surface conglomerations of PTFE coatings due to the interaction process of active dispersion particles with underlying polymer layer. Surface energy of PTFE coatings decreases first with the coatings thickness increases to 1.25 µm and then slowly increases with the thickness. Structure defects (pore, interstice, and so on) in the coatings increase with the thickness increases but reduce significantly with the d_ts increases. PTFE coating prepared at the d_ts of 20 cm had a higher intensity of the amorphous absorption bands. Friction experiment indicated that the destroyed area of the coatings in the friction region decreases with increases the coatings thickness but increases with the d_ts. The rubber modified by PTFE coatings with spherical structure possesses a higher stability in the friction process and a lower coefficient of friction. Copyright © 2015 John Wiley & Sons, Ltd.     

Electrochemical behaviour of SiO2 sol-gel coatings on stainless steel

SiO₂ coatings onto stainless steel substrates have been prepared by sol-gel in order to study the performance and mechanism of attack in different corrosive solutions. The electrochemical behaviour of the samples has been evaluated by Electrochemical Impedance Spectroscopy using NaCl and HCl as electrolytes. Comparative tests have been performed on samples with one and two silica layers as well as on uncoated ones. SiO₂ coatings produce no important protection of stainless steels subjected to electrochemical corrosion. This behaviour may be explained by micropores and microcracks produced during the coating sintering.     

Adsorption and inhibitive properties of aminobiphenyl and its Schiff base on mild steel corrosion in 0.5 M HCl medium

Electrochemical measurements were performed to investigate the effectiveness and adsorption behaviour of aminobiphenyl (Aph) and 2-(3-hydroxybenzylideneamino)biphenyl (Aph-S), as corrosion inhibitors for mild steel (MS) in 0.5 M HCl solution. Potentiodynamic polarization, linear polarization resistance (LP) and electrochemical impedance spectroscopy (EIS) techniques were applied to study the metal corrosion behaviour in the absence and presence of different concentrations of Aph and Aph-S. In order to gain more information about adsorption mechanism the AC impedance technique was used to evaluate the potential of zero charge (PZC) from polarization resistance (R_p) versus voltage (E) plot. Potentiodynamic polarization measurements showed that Aph act as cathodic type inhibitor where as Aph-S act mixed type. The inhibition efficiency (IE%) increases with increasing concentration of compounds and reached 92.6% for Aph and 97.2% for Aph-S at 5 × 10⁻³ M. Double layer capacitance (C_dl) and polarization resistance (R_p) values are derived from Nyquist plots obtained from AC impedance studies. The experimental data fit Langmuir isotherm for both Aph and Aph-S, and from the adsorption isotherm some thermodynamic data for the adsorption processes are calculated and discussed. The effect of exposure time on the corrosion behaviour of mild steel in the absence and presence of inhibitor over 168 h was also studied.     

Corrosion prevention of mild steel in acidic medium by 2-Pyrrolidin-1-yl-1,3-thiazole-5-carboxylic acid: Theoretical and experimental approach

The inhibition efficiency of 2-Pyrrolidin-1-yl-1,3-thiazole-5-carboxylic acid (PTCA) against mild steel (MS) corrosion was investigated in acidic solution by using quantum chemical calculations based on Density Functional Theory (DFT) method and electrochemical measurements. The electrochemical impedance spectroscopy (EIS), potentiodynamic, potential zero charge (pzc) analysis and electrochemical noise (EN) measurements at various concentrations (from 0.1 to 10 mM) and immersion times were utilized in experimental part. The surface analysis was achieved scanning electron microscope (SEM) and contact angle measurements in the absence and presence of 10 mM PTCA. According to DFT results, PTCA exhibited 3.737 eV band gap and 8.130 Debye dipole moment which were a signal of potentially convenient corrosion inhibitor properties. PTCA has a remarkable corrosion inhibition capability to mild steel, which inhibited both anodic and cathodic corrosion rates, relying on it's physically adsorption on the metal solution interface and protection ability was increased with increasing PTCA concentration. The obtained adsorption equilibrium constant was 11.11 × 10³ M^-1 and calculated standard free energy of adsorption was ?33.03 kJ mol^?1. The determined activation energy values were 55.58 kJ mol^?1 and 96.86 kJ mol^?1 in 0.5 M HCl in the absence and presence of 10 mM PTCA, respectively. PTCA demonstrated a strong inhibition efficiency of 98.3%, after 168 h immersion, according to the EIS results. As a consequently, we recommend that PTCA is a convenient inhibitor in 0.1 M HCl for mild steel protection against corrosion.     

Effect of acetone on mechanical properties of epoxy used for surface treatment before adhesive bonding

A thin layer of un-cured resin over metal substrates applied by using an acetone-diluted resin solution (without hardener) has been found to be beneficial to strong adhesive bonding. The resin pre-coating (RPC) solution can effectively seal sub-surface micro-cavities and increase the substrate wettability. This study examines possible aftermath effects of the acetone dilution on mechanical properties of epoxy through comparison of samples made from as-received resin and resins diluted once and twice by acetone. RPC can be accepted with confidence in substrate pre-treatments for strong adhesive bonding if no detrimental effect on epoxy properties is observed. Fourier transform infrared spectrum (FTIR) was conducted, showing the spectrogram of the resin previously diluted by acetone was the same as that of as-received resin, i.e. no change in epoxy molecular structures after complete evaporation of acetone. Strength and modulus of elasticity measured by flexural and compressive tests were compared using samples made from as-received resin, and resins diluted once and twice by acetone. Variations among results from the three groups were less than 2%, or negligible, affirming the RPC method can be used for substrate pre-treatments and stronger adhesive bonding.     

Influence of surface energy distribution on neuritogenesis

PC12 cells are a useful model to study neuronal differentiation, as they can undergo terminal differentiation, typically when treated with nerve growth factor (NGF). In this study we investigated the influence of surface energy distribution on PC12 cell differentiation, by atomic force microscopy (AFM) and immunofluorescence. Glass surfaces were modified by chemisorption: an aminosilane, n-[3-(trimethoxysilyl)propyl]ethylendiamine (C₈H₂₂N₂O₃Si; EDA), was grafted by polycondensation. AFM analysis of substrate topography showed the presence of aggregates suggesting that the adsorption is heterogeneous, and generates local gradients in energy of adhesion. PC12 cells cultured on these modified glass surfaces developed neurites in absence of NGF treatment. In contrast, PC12 cells did not grow neurites when cultured in the absence of NGF on a relatively smooth surface such as poly-l-lysine substrate, where amine distribution is rather homogeneous. These results suggest that surface energy distribution, through cell–substrate interactions, triggers mechanisms that will drive PC12 cells to differentiate and to initiate neuritogenesis. We were able to create a controlled physical nano-structuration with local variations in surface energy that allowed the study of these parameters on neuritogenesis.     

Improvement of hardness and anti-corrosion behavior of mild steel by plasma sprayed coating of Al2O3/GO composite

A robust and fast non-transferred plasma torch method was employed for developing coating of alumina (A₂O₃) and alumina/graphene oxide (A₂O₃/GO) on mild steel. Micro Raman analysis of GO confirms its spectroscopic behavior. The energy band gap of GO was determined as 3.44 eV. The successful coating formation of A₂O₃ and A₂O₃/GO (0.5 wt%) on mild steel was confirmed by X-ray diffraction analysis. Microhardness of mild steel was found to increase about 43.75% after coating with A₂O₃/GO (0.5 wt%) composite. The microstructure of A₂O₃/GO (0.5 wt%) coated mild steel represents better quality of coating and improved structural behavior. Mild steel becomes more corrosive resistance by reduction of corrosion potential (less negative than −0.05 V) after A₂O₃/GO (0.5 wt%) coating on it.     

Corrosion inhibition studies on mild steel in HCl by a newly synthesized benzil monohydrazone based Schiff base

The corrosion inhibition effect of newly formulated Schiff base 2-((E)-((E)-2-hydrazone-1, 2-diphenylethylidene) amino phenol) (HDAP) ligand L derived from Benzil monohydrazone and 2-Aminophenol on mild steel in 1 ​M HCl was examined. Electrochemical (Tafel and EIS) and mass loss techniques were employed to evaluate its corrosion protection efficiency. The inhibition efficiency (η %) was elevated with raise in concentration of compound L.Maximum inhibition efficiency of 94.18% was obtained at 0.01 ​M concentration of HDAP from Tafel polarisation curve. From electrochemical impedance (EIS) studies, it was confirmed that increase in concentration of HDAP led to enhancement of the charge transfer resistance. Both physical and chemical types of adsorptions were observed for the Schiff base via π-bonding electrons which obey Langmuir adsorption isotherm. The SEM picture revealed development of a thin layer on metallic surface. Quantum chemical evaluations were conducted to find out the mechanism of corrosion retardation power of HDAP.