Cerium salt activated nanoparticles as fillers for silane films: Evaluation of the corrosion inhibition performance on galvanised steel substrates

The present work investigates the electrochemical behaviour of galvanised steel substrates pre-treated with bis-[triethoxysilylpropyl] tetrasulfide silane (BTESPT) solutions modified with SiO₂ or CeO₂ nanoparticles activated with cerium ions. The electrochemical behaviour of the pre-treated substrates was evaluated via electrochemical impedance spectroscopy in order to assess the role of the nanoparticles in the silane film resistance and capacitance. The ability of the Ce-activated nanoparticles to mitigate corrosion activity at the microscale level in artificial induced defects was studied via scanning vibrating electrode technique (SVET). Complementary studies were performed using potentiodynamic polarisation. The results show that the presence of nanoparticles reinforces the barrier properties of the silane films and that a synergy seems to be created between the activated nanoparticles and the cerium ions, reducing the corrosion activity. The addition of CeO₂ nanoparticles was more effective than the addition of SiO₂ nanoparticles.     

Analytical characterization of silane films modified with cerium activated nanoparticles and its relation with the corrosion protection of galvanised steel substrates

Galvanised steel substrates were pre-treated in bis-1,2-[triethoxysilyilpropyl]tetrasulphide silane solutions containing SiO₂ or CeO₂ nanoparticles activated with cerium ions. The surface composition was investigated by infrared spectroscopy. The film thickness was determined by scanning electron microscopy. The results showed that the barrier properties of silane films modified with nanoparticles depend upon the concentration of nanoparticles. The results also showed that the silane film thickness increases when the nanoparticles are activated with cerium ions. The anti-corrosion behaviour of the cerium activated nanoparticles was also investigated at the microscale level, in artificial induced defects, using the scanning vibrating electrode technique (SVET). The substrates treated with the silane coating modified with CeO₂ nanoparticles revealed improved corrosion behaviour comparatively to the coatings modified with SiO₂ nanoparticles. X-ray photoelectron spectroscopy and Auger electron spectroscopy experiments carried out on the defects after immersion in NaCl solutions revealed the presence of a surface film containing zinc corrosion products and cerium/ceria compounds.     

Electrochemical behavior of organic and inorganic complexes of Zn(II) as corrosion inhibitors for mild steel: Solution phase study

This work intends to study inhibitive performance of organic and inorganic complexes of Zn(II) using electrochemical techniques along with surface analysis. In this regard, inorganic zinc aluminum polyphosphate pigment as modified zinc phosphate and zinc acetylacetonate and benzimidazole mixture representing organic replacement of zinc phosphate were employed. Through taking advantage of electrochemical impedance spectroscopy and DC polarization, two mentioned approaches were indicated to be efficient. Charge transfer resistance and corrosion current density values exhibited superiority of zinc aluminum polyphosphate and mixture of zinc acetylacetonate and benzimidazole compared to zinc phosphate and also zinc acetylacetonate and benzimidazole as individual inhibitors. Corrosion inhibition efficiencies calculated based on charge transfer resistance in consistent with those calculated from corrosion current density showed the following sequence; zinc aluminum polyphosphate > mixture of zinc acetylacetonate and benzimidazole > zinc acetylacetonate > zinc phosphate > benzimidazole. Showing film formation, surface analysis SEM/EDX confirmed the results obtained by electrochemical methods.     

Novel surfactant-free waterborne acrylic-silicone modified alkyd hybrid resin coatings containing nano-silica for the corrosion protection of carbon steel

We report a novel waterborne acrylic-silicone modified alkyd nanocomposite latex containing nano-silica prepared by the surfactant-free miniemulsion polymerization. The influences of γ-methacryloxy-propyltrimethoxysilane- (MPS-) modified nano-silica particle contents to the thermal, mechanical and anti-corrosion performance of hybrid latex coatings were studied. The results revealed that the incorporation of nano-silica particles into latex films could directly increase the thermal stability and mechanical properties. Electrochemical corrosion studies revealed that these nanocomposite coatings exhibited superior corrosion resistance performance (inhibition efficiency 99.36% and corrosion rate 1.09 × 10 ^?3 mm per year) than that of the control system (without SiO₂ NPs).     

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).     

Electrochemical performance of mechanically treated SnO<Subscript>2</Subscript> powders for OER in acid solution

Commercial tin dioxide powders have been subjected to mechanical treatment in order to modify their microstructure. Processed powders were then used to assembly thin film electrodes which worked as anodes in a three electrode cell to drive the oxygen evolution reaction from acid solution. Cyclic voltammetry and polarization experiments were carried out together with electrochemical impedance spectroscopy to highlight the effects of milling on the catalytic performance. The findings suggest that the mechanical processing is capable of generating a considerable amount of lattice defects. The grain boundary extension as well as the content of structural disorder increase with the processing time. The increase in both the reactive site density and extent of structural disorder results in an enhanced chemical reactivity of the assembled electrodes.     

Electrochemical study of carbon steel corrosion in buffered acetic acid solutions with chlorides and H2S

In this work, the corrosion behavior of SAE 1018 carbon steel in buffered acetic acid (HAc) solutions containing chlorides, with and without H₂S, was studied. Polarization curves obtained by different electrochemical techniques, indicate negligible modification of anodic slopes when adding H₂S; however, the cathodic branch is more sensitive showing an accelerated reduction reaction in the presence of H₂S. Interface characterization was performed by electrochemical impedance technique (EIS) in the absence and presence of H₂S and near to the corrosion potential (E_corr). Analysis of results shows no film of corrosion products, since the impedance spectra characteristics indicate a great activity of steel in the solutions studied, with differences only at low frequencies. The adsorbed complexes formed in the solution containing HAc, acetate and chlorides control the corrosion process and prevent passive film formation, even in the presence of H₂S.     

The effect of chromated and organic layers on corrosion resistance of galvanized steel sheets

Chromated zinc steel sheets have been used widely for corrosion resistance performance in various waters. The coating system includes a chromated layer and both a primer and topcoat, a commonly applied system for better corrosion performance. Electrochemical impedance spectroscopy results show that the corrosion resistance of chromated zinc is due to its passivity after water uptake during the exposure. In galvanized steel sheets with a primer, the electrolyte solution can only reach the metallic substrate through the coating pores; thus, a double layer could build up locally at the bottom of the pores, resulting in a good corrosion resistance for the sheet. On the other hand, the high-pore-resistance system of primer and topcoat provides no evidence of corrosion even after 8 weeks’ exposure.     

Electrochemical impedance characterization of FeSn2 electrodes for Li-ion batteries

This work reports the electrochemical characterization of a micro-scale FeSn₂ electrode in a lithium battery. The electrode is proposed as anode material for advanced lithium ion batteries due to its characteristics of high capacity (500 mAh g⁻¹) and low working voltage (0.6 V vs. Li). The electrochemical alloying process is studied by cyclic voltammetry and galvanostatic cycling while the interfacial properties are investigated by electrochemical impedance spectroscopy. The impedance measurements in combination with the galvanostatic cycling tests reveal relatively low overall impedance values and good electrochemical performance for the electrode, both in terms of delivered capacity and cycling stability, even at the higher C-rate regimes.     

Electrochemical impedance of two-phase Ni-Ti alloys during corrosion in eutectic (0.62Li, 0.38K)2CO3 at 650 °C

The corrosion of two-phase Ni-10Ti and Ni-15Ti in molten (0.62Li, 0.38K)₂CO₃ at 650 °C under the atmosphere of air has been studied by electrochemical impedance spectroscopy (EIS). The impedance spectra for both Ni-10Ti and Ni-15Ti are composed of a semi-circle at high-frequency port and a line at low-frequency port indicating a diffusion-controlled reaction. The corrosion of the alloys produces an external scale composed of NiO and TiO₂, and a wide internal oxidation region. An equivalent circuit representing the features of the corrosion of the alloys was proposed to fit the impedance spectra, and electrochemical parameters in the equivalent circuit were also calculated.     

Improvement of corrosion protection offered to galvanized steel by incorporation of lanthanide modified nanoclays in silane layer

Silane sol–gel based films are very promising alternatives to the traditional chromate pre-treatments. However, the protection offered by the silane films strongly decreases when the coating is damaged. Some previous studies showed that the barrier properties of the silane layer can be improved by incorporation of clay nanoparticles. Moreover, inhibitive metallic cations can be incorporated in the nanoclays by ion exchange, providing a way to prepare cheap corrosion inhibitors nanoreservoirs offering self-healing properties. Rare earth (RE) metal salts have been shown to be effective corrosion inhibitors on a wide range of metals, including hot dip galvanized (HDG) steel. For this study, montmorillonite clay is modified to obtain a Ce(III) montmorillonite clay (Ce-MMT). The amount of incorporated Ce(III) is characterized by means of XRF measurements. X-ray diffraction showed that the Ce(III) is located in the interlayer space.     

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.     

Catalytic reduction of NO by propene in the presence of oxygen over mechanically mixed metal oxides and Ce-ZSM-5

The mechanical mixing of Mn₂O₃ or CeO₂ to Ce-ZSM-5 considerably enhanced the rate of the reduction of NO by propene in the low to medium temperature region, although Mn₂O₃ or CeO₂ itself was much less active for this reaction. In contrast, Mn₂O₃ was highly active and CeO₂ was moderately active for the oxidation of NO to NO₂. On the basis of the comparison of the rates of the C₃H₆ + O₂, NO + C₃H₆ + O₂ and NO₂ + C₃H₆ + O₂ reactions over these catalysts, a bifunctional mechanism is proposed, in which Mn₂O₃ and CeO₂ accelerate the oxidation of NO and the subsequent reaction steps between NO₂ and propene proceed on Ce-ZSM-5.     

Synthesis of poly-(BA-co-MMA) latexes filled with SiO2 for coating in construction applications

The synthesis of acrylic latexes filled with silica nanoparticles have been developed in the present work. Moreover, a exhaustive study of the influence of the synthesis conditions on the latex characteristics has been performed. The latex particles morphology has been observed using transmission electron microscopy (TEM) showing a raspberry morphology. Completely transparent coatings have been synthesized using these latexes and a high dispersion degree of the nanosize SiO₂ into the polymer matrix has been achieved. These characteristics of these latexes make especially suitable for construction applications (i.e., to protect natural stone). Nanoindentation tests have been carried out in order to measure the mechanical properties of the coating. These tests showed an increment of the elastic modulus and hardness, improving mechanical properties when SiO₂ is added to the polymer matrix.     

Copper oxide catalysts supported on ceria for low-temperature CO oxidation

Copper oxide catalysts supported on ceria were prepared by wet impregnation method using finely CeO₂ nanocrystals, which was derived from alcohothermal synthesis, and copper nitrate dissolved in the distilled water. The catalytic activity of the prepared CeO₂ and CuO/CeO₂ catalysts for low-temperature CO oxidation was investigated by means of a microreactor-GC system. The samples were characterized using BET, XRD, SEM, HRTEM and TPR.     

Photocatalytic degradation of toluene over doped and coupled (Ti,M)O2 (M = Sn or Zr) nanocrystalline oxides: Influence of the heteroatom distribution on deactivation

In this work, we have studied the photocatalytic oxidation (PCO) of toluene over Sn- and Zr-doped TiO₂, and coupled TiO₂/SnO₂ and TiO₂/ZrO₂ catalysts. The TiO₂ sample doped with Sn (8% of metal ions) is composed by the anatase and rutile phases of TiO₂, while the Zr-doped sample (same dopant content) contains only the anatase phase. The coupled photocatalysts are formed, in addition to the phases present in their doped counterparts, by a segregated MO₂ phase (M: Sn or Zr). For the photocatalytic degradation of toluene, higher rates in the stationary state are obtained with the coupled catalysts with respect to the doped ones and the TiO₂ references (both synthetic and Degussa P25). In the case of the coupled photocatalysts, these higher rates are due to the absence of the deactivation that does occur for the rest of samples. Fresh and used photocatalysts have been studied by FTIR and EPR spectroscopies and by solid/liquid extraction in methanol, followed by GC/MS analysis. The obtained results lead us to conclude that, while structural and electronic modifications, due to the guest cations, are responsible for the high activity of doped samples observed in previous studies for a reaction not causing catalyst deactivation (methylcyclohexane PCO), other factors are crucial for the PCO of toluene. For this reaction, there is a relationship between surface water, adsorbed intermediates and resistance to deactivation, and thus the modifications in the amount and arrangement of surface water molecules caused by the second oxide may be the cause of the high degradation rate obtained with the coupled TiO₂/SnO₂ and TiO₂/ZrO₂ photocatalysts.     

Polyaniline for corrosion prevention of mild steel coupled with copper

Polyaniline emeraldine base/epoxy resin (EB/ER) coating was investigated for corrosion protection of mild steel coupled with copper in 3.5% NaCl solution. EB/ER coating with 5-10 wt% EB had long-term corrosion resistance on both uncoupled steel and copper due to the passivation effect of EB on the metal surfaces. During the 150 immersion days, the impedance at 0.1 Hz for the coating increased in the first 1-40 days and subsequently remained constant above 10⁹ Ω cm², whereas that for pure ER coating fell below 10⁶ Ω cm² after only 30 or 40 days. Immersion tests on coated steel-copper galvanic couple showed that EB/ER coating offered 100 times more protection than ER coating against steel dissolution and coating delamination on copper, which was mainly attributed to the passive metal oxide films formed by EB blocking both the anodic and cathodic reactions. Salt spray tests showed that 100 μm EB/ER coating protected steel-copper couple for at least 2000 h.     

Room temperature ammonia sensing based on graphene oxide integrated flexible polyvinylidenefluoride/cerium oxide nanocomposite films

ABSTRACT

In this work, novel room temperature (RT) ammonia (NH₃) sensors comprising graphene oxide (GO) integrated polyvinylidenefluoride (PVDF)/cerium oxide (CeO₂) nanocomposite films have been prepared via simple solution casting technique. The structural and morphological characteristics of flexible tertiary PVDF/CeO₂/GO nanocomposite films have been investigated using various analytical techniques and their NH₃ gas-sensing performance was evaluated at RT and the relevant sensing mechanism was established. The flexible PVDF/CeO₂/GO nanocomposite films responded strongly to NH₃ gas with enhanced gas sensing properties at RT as compared with various other volatile organic compounds (VOCs) such as acetone, ethanol, formaldehyde and toluene.     

Acidity studies of titania-silica mixed oxides

A series of titania-silica mixed oxides were prepared by co-precipitation and sol-gel methods. The mole fraction of titanium was varied from 0 to 1. The effects of preparation method and chemical composition on the physical properties and acidity profiles of mixed oxides were examined. While pure silica was non-acidic and titania contained only Lewis acid sites, Brønsted acidity was created by the Ti-O-Si interaction in the binary oxides. Samples containing a titania: silica mole ratio of 9 1 possessed the largest amount of Brønsted acidity. The generation of acid sites and the stability of the oxide was a strong function of preparation method. With all preparation methods, higher calcination temperatures increased crystallinity and decreased the total number of acid sites.     

Kinetic behavior of LiFePO4/C cathode material for lithium-ion batteries

The composite cathode materials of LiFePO₄/C were synthesized by spray-drying and post-annealing method. The crystalline structure and morphology of products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The charge-discharge kinetics of LiFePO₄/C electrode was investigated using electrochemical impedance spectroscopy (EIS). The results show that the increment of the resistance has a close relation to the appearance of the FePO₄ phase during charge-discharge course, and that the ohmic resistance, charge transfer resistance and lithium-ion diffusion coefficients of the LiFePO₄/C electrode do not change much by extended cycling tests, implying a relatively superior cyclability of the battery. The effect of cell temperature on the electrochemical reaction behaviors of LiFePO₄/C electrode was also investigated using the EIS. It is confirmed that the effect of the cell temperature on the impedance results mainly from the enhancement of the lithium-ion diffusion at elevated temperatures.