The restoration of the passivity of stainless steel Weldments in pickling solutions observed using electrochemical and surface analytical methods

In this study, a solution containing ammonium fluoride (NH4F) and nitric acid (HNO3) was used as an alternative to the conventional highly toxic pickling solution HF/HNO3 for pickling weldments of selected stainless steels including Type 316 stainless steel (UNS S31600), duplex stainless steel 2205 (UNS S32205), and super duplex stainless steel 2507 (UNS S32750). Electrochemical and surface analytical methods were used to understand the effects of pickling on the stainless steel weldments. Cyclic potentiodynamic polarization (CPP) test results indicated that the restoration of passivity of stainless steel weldments could be achieved by pickling the weldments in both HF/HNO3 solution and NH4F/HNO3 solutions. Scanning electron microscopy observation of the UNS S32750 weldment surface revealed that both the HF/HNO3 solution and the NH4F/HNO3 solution could remove the heat tint on the weldment. X-ray photoelectron spectroscopy analysis indicated that treatment in these two pickling solutions produced passive films with similar characteristics. Thus, this work suggests that the NH4F/HNO3 solution is a promising alternative to HF/HNO3 solution for the pickling of stainless steel weldments, and that the CPP test approach can be used in conjunction with surface analytical methods for further development of safer and environmentally friendly picklingsolutions.

Iridium(III) N-heterocyclic carbene complexes: an experimental and theoretical study of structural, spectroscopic, electrochemical and electrogenerated chemiluminescence properties

Four cationic heteroleptic iridium(III) complexes have been prepared from methyl- or benzyl-substituted chelating imidazolylidene or benzimidazolylidene ligands using a Ag(I) transmetallation protocol. The synthesised iridium(III) complexes were characterised by elemental analysis, (1)H and (13)C NMR spectroscopy and the molecular structures for three complexes were determined by single crystal X-ray diffraction. A combined theoretical and experimental investigation into the spectroscopic and electrochemical properties of the series was performed in order to gain understanding into the factors influencing photoluminescence and electrochemiluminescence efficiency for these complexes, with the results compared with those of similar NHC complexes of iridium and ruthenium. The N^C coordination mode in these complexes is thought to stabilise thermally accessible non-emissive states relative to the case with analogous complexes with C^C coordinated NHC ligands, resulting in low quantum yields. As a result of this and the instability of the oxidised and reduced forms of the complexes, the electrogenerated chemiluminescence intensities for the compounds are also low, despite favourable energetics. These studies provide valuable insights into the factors that must be considered when designing new NHC-based luminescent complexes.

Electrochemical and DFT studies of quinoline derivatives on corrosion inhibition of AA5052 aluminium alloy in NaCl solution

Two quinoline derivatives, 8-aminoquinoline (8-AQ) and 8-nitroquinoline (8-NQ), have been used as inhibitors to examine their corrosion protection effect on AA5052 aluminium alloy in 3% NaCl solution. The weight-loss and electrochemical measurement have indicated that 8-AQ and 8-NQ play as anodic inhibitor to retard the anodic electrochemical process. SEM/EDS analysis clearly shows that 8-AQ and 8-NQ form a protective film on the AA5052 alloy surface. Density functional theory (DFT) calculation confirmed the formation of strong hybridization between the p-orbital of reactive sites in the inhibitor molecules and the sp-orbital of the Al atom. 8-aminoquinoline and 8-nitroquinoline may be useful as effective corrosion inhibitors for aluminium alloys.

Corrosion protection afforded by praseodymium conversion film on Mg alloy AZNd in simulated biological fluid studied by scanning electrochemical microscopy

Surface passivation of AZNd Mg alloy with Pr(NO3)3 is studied using scanning electrochemical microscopy (SECM) in surface generation/tip collection (SG/TC) and AC modes. Corrosion protection afforded by the Pr treatment and the degradation mechanism in a simulated biological environment was examined on a local scale and compared with non-treated AZNd. SG/TC mode results revealed a drastic decrease in H2 evolution due to the Pr treatment. Mapping the local insulating characteristics using AC-SECM showed higher conductivity of the surface where H2 evolution was most favorable.

Evaluation of corrosion behaviour of biodegradable base oils using electrochemical techniques

© 2015 Institute of Materials, Minerals and Mining. Published by Maney on behalf of the Institute. This paper describes an interesting attempt to quantitatively evaluate the corrosion behaviour of base oils using a novel approach based on electrochemical techniques. The present study evaluates the corrosion behaviour of biodegradable base oils with and without additives in an aqueous chloride solution using electrochemical measurements. Potentiodynamic polarisation and electrochemical impedance spectroscopy techniques were used to quantitatively determine the corrosion behaviour of these oils, and the results were compared to the conventional immersion tests. Both these electrochemical measurements were carried out in a three-electrode system where AS1020 mild steel alloy was used as a working electrode in a purpose made pipette cell. The results obtained from the electrochemical measurements help to evaluate the best biodegradable base oil for formulating eco-friendly industrial lubricants.

Novel Na+ Ion diffusion mechanism in mixed organic-inorganic ionic liquid electrolyte leading to high Na+ transference number and stable, high rate electrochemical cycling of sodium cells

Ambient temperature sodium batteries hold the promise of a new generation of high energy density, low-cost energy storage technologies. Particularly challenging in sodium electrochemistry is achieving high stability at high charge/discharge rates. We report here mixtures of inorganic/organic cation fluorosulfonamide (FSI) ionic liquids that exhibit unexpectedly high Na+ transference numbers due to a structural diffusion mechanism not previously observed in this type of electrolyte. The electrolyte can therefore support high current density cycling of sodium. We investigate the effect of NaFSI salt concentration in methylpropylpyrrolidinium (C3mpyr) FSI ionic liquid (IL) on the reversible plating and dissolution of sodium metal, both on a copper electrode and in a symmetric Na/Na metal cell. NaFSI is highly soluble in the IL allowing the preparation of mixtures that contain very high Na contents, greater than 3.2 mol/kg (50 mol %) at room temperature. Despite the fact that overall ion diffusivity decreases substantially with increasing alkali salt concentration, we have found that these high Na+ content electrolytes can support higher current densities (1 mA/cm2) and greater stability upon continued cycling. EIS measurements indicate that the interfacial impedance is decreased in the high concentration systems, which provides for a particularly low-resistance solid-electrolyte interphase (SEI), resulting in faster charge transfer at the interface. Na+ transference numbers determined by the Bruce-Vincent method increased substantially with increasing NaFSI content, approaching >0.3 at the saturation concentration limit which may explain the improved performance. NMR spectroscopy, PFG diffusion measurements, and molecular dynamics simulations reveal a changeover to a facile structural diffusion mechanism for sodium ion transport at high concentrations in these electrolytes.

Electrochemical study of o-toluidine blue impregnated in mesoporous silica channels

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Studies on the electrochemical disinfection of water containing Escherichia coli using a Dimensionally Stable Anode

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Influence of spraying parameters on the electrochemical behaviour of HVOF thermally sprayed stainless steel coatings in 3.4% NaCl

Stainless steel coatings obtained by High Velocity Oxygen Fuel (HVOF) were characterized using optical (OM) and scanning electron microscopy (SEM), electron probe micro-analysis, X-ray diffraction (XRD), open-circuit potential (E-OC) measurements, electrochemical impedance spectroscopy (EIS) and polarisation tests. Differences among coated steels were mainly related with the gun-substrate distance parameter (310 nm for samples A and B and 260 min for C and D). The open-circuit potential values measured for all the samples after 18 h of immersion in aerated and unstirred 3.4% NaCl solution were: - 0.334, - 0.360, - 0.379 and - 0.412 V vs. Ag/AgCl,KClsat. for samples A to D, respectively. For EIS measurements, Nyquist plots showed higher capacitive semi-circle for samples sprayed at longer distance, indicating higher corrosion resistance in NaCl solution. (c) 2005 Elsevier B.V. All rights reserved.

Effects of thickness coating on the electrochemical behaviour of thermal spray Cr3C2-NiCr coatings

Thermally sprayed HVOF coatings are increasingly being used in industrial applications where high wear and corrosion resistance are needed [1,2]. In this paper, electrochemical ac and de experiments were used in order to obtain the corrosion resistance of coated steel with different numbers of Cr3C2-NiCr layers. This work has been performed in order to determine the role of coating thickness in the corrosion behaviour of a steel protected with cermet thermally sprayed coatings. It is known that a thicker layer protects better against corrosion when a metallic coating is evaluated. But cermet coatings, such as Cr3C2-NiCr, contain higher levels of porosity and residual stresses than metallic coatings, which really could influence the corrosion resistance of the deposited layer. Electrochemical measurements, such as Open-Circuit Potential (E-Osubset of), Polarisation Resistance (RP) and Cyclic Voltammetry (CV), were performed in an aerated 3.4 NaCI media (%wt.). Electrochemical Impedance Measurements (EIS) were also done in order to obtain a mechanism that explains the corrosion process. Structural Characterisation was carried out by means of Optical and Scanning Electron Microscopes (OM, SEM) with an Energy Dispersive Spectrometry analyser (EDS). Results show that the corrosion resistance of the complete system is mainly influenced by the substrate behaviour. The application of a higher number of deposited layers did not substantially increase their anticorrosive properties. Stress generation during the spraying deposition process plays an important role in the behaviour of the coated steel against corrosion phenomena. (C) 2002 Elsevier B.V. B.V All rights reserved.

Comparing label free electrochemical impedimetric and capacitive biosensing architectures

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Electrochemical method for quantitative determination of trace amounts of disperse dye in wastewater

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Impedance-derived electrochemical capacitance spectroscopy for the evaluation of lectin-glycoprotein binding affinity

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

A label-free electrochemical affisensor for cancer marker detection: the case of HER2

In this paper, we report the development of a sensitive label-free impedimetric biosensor based on the use of affibody as bioreceptor and gold nanostructured screen-printed graphite as a sensor platform for the detection of human epidermal growth factor receptor 2 (HER2). The affisensor is realized by immobilizing a terminal cysteine-modified affibody on gold nanoparticles. The sensor was characterized by electrochemical techniques and scanning electron microscopy (SEM). Furthermore, surface plasmon resonance (SPR) technology was also applied to explore the potential of affibodies as small-molecule discriminating tools. Using optimized experimental conditions, a single-use affisensor showed a good analytical performance for HER2 detection from 0 to 40μg/L. The estimated limit of detection was 6.0μg/L. Finally, the realized affisensor was applied to human serum samples.