Anodic Region Research Articles

Transformation of amorphous passive oxide film on Zr65Cu17.5Ni10Al7.5 metallic glass ribbons

Zr-based metallic glass with favorable properties and a stable surface oxide layer is foreseen as an alternative material for water/nuclear reactor pressure systems. The high stability of Zr65Cu17.5Ni10Al7.5 metallic glass (MG) in anodic and cathodic regions within 0.5 M H2SO4 solution is evidenced by the negligible shift in the corrosion potential upon linear sweep voltammetry cycles. The recorded passivation current density of 15 mA cm–2 is very similar to 430 stainless steel. The formation of an amorphous Zr-rich oxide phase and slight dissolution of the native ZrO2 layer are confirmed by scanning transmission electron microscopy – energy dispersive X-ray analysis, which result from the interaction of hydronium ions (H3O+) with the oxide layer during linear polarization. Furthermore, promising hydrogen absorption of the produced Zr-based MG ribbons (1.33 %wt, non-reversible) by Sieverts-type apparatus were recorded at 400 °C and under 6 MPa, which evidences that this alloy can minimize the hydrogen evolution within the chamber due to the coverage with an oxide film and thereby prevent accidents.

Fully organic electroactive monomers for electrochromic behaviors having high coloration efficiency and long cycle stability towards flexible Solid-State electrochromic device

• Design and synthesis of three donor–acceptor-donor type monomers and electro-polymerization. • Naphthalene diimide as acceptor core and triphenylamine Derivatives as the donor moiety. • Electrochromic behaviors of the polymer films. • Enhancement of colouration efficiency. Constructing an electrochromic material with high switching stability as well as energy-saving property is really challenging with respect to the practical application which mainly depends on the lower response time, higher switching stabilities and higher colouration efficiencies. Herein, we have reported the design and synthesis of electroactive triphenylamine end capped to central pyromellitic dianhydride, naphthalenetetracarboxylic dianhydride, perylenetetracarboxylic dianhydride based three donor - acceptor - donor type monomers which are subsequently electropolymerized on conductive glass surface to have polymers which are subsequently explored by extensive cyclic voltammetry studies. Density functional theory (DFT) studies disclose that HOMO is localized solely on triphenylamine unit which accounts for the electropolymerization process upon oxidation. Besides, TD-DFT calculations unveil the responsible electronic transitions for electrochromism in the polymers. Three polymers exhibit the reversible multiple colour changes of colourless to brown to deep blue in the anodic region by applying voltage 0 to 1 to 1.2 V and also colourless to deep pink in the cathodic region (voltage window of 0 to −2 V) with attractive response times, optical contrast, switching stabilities, and coloration efficiencies. These polymers can be switched upto 10,000 cycles with the colouration efficiency 800 cm 2 /C in the anodic process and 600 cycles for the cathodic process in a three electrodes configuration. These values, to the best of our knowledge, are not reported for triphenylamine based fully organic electrochromic material till now. Finally, Solid-state devices made of three polymers have demonstrated the electrochromism operated at a potential range of 0 to 2.5 V. Among them, the large area (5 × 5 cm 2 ) of device coated with naphthalenetetracarboxylic diimide is electrochemically stable for 4000 switching cycles, suggesting its suitability as a potential electrochromic material for next-generation flexible EC display application.

Flexible battery-less wireless glucose monitoring system

In this work, a low power microcontroller-based near field communication (NFC) interfaced with a flexible abiotic glucose hybrid fuel cell is designed to function as a battery-less glucose sensor. The abiotic glucose fuel cell is fabricated by depositing colloidal platinum (co–Pt) on the anodic region and silver oxide nanoparticles-multiwalled carbon nanotubes (Ag2O-MWCNTs) composite on the cathodic region. The electrochemical behavior is characterized using cyclic voltammetry and chronoamperometry. This glucose hybrid fuel cell generated an open circuit voltage of 0.46 V, short circuit current density of 0.444 mA/cm2, and maximum power density of 0.062 mW/cm2 at 0.26 V in the presence of 7 mM physiologic glucose. Upon device integration of the abiotic glucose hybrid fuel cell with the NFC module, the data from the glucose monitoring system is successfully transmitted to an android application for visualization at the user interface. The cell voltage correlated (r2 = 0.989) with glucose concentration (up to 19 mM) with a sensitivity of 13.9 mV/mM•cm2.

(Digital Presentation) A Mathematical Model for Localized Corrosion of Copper Under a Droplet

The Nuclear Waste Management Organization (NWMO) is responsible for the implementation of Adaptive Phased Management (APM), the federally-approved plan for the safe long-term management of Canada’s used nuclear fuel.1 Under APM, used nuclear fuel will ultimately be placed within a deep geological repository (DGR) in a suitable host rock formation. Part of evaluating the long-term performance and safety of the repository system is understanding the behavior of the copper coated container with respect to localized corrosion. Even though localized corrosion is not expected in the DGR design system, there is still a need to develop a mathematical model for localized corrosion of copper.The presentation will describe the development of a 2-D axisymmetric time-dependent model for the localized corrosion of copper under a drop of electrolyte using the concept of an Evans droplet.2 The model accounts for two reversible electrochemical reactions on the metal surface (copper dissolution/plating and hydrogen (H2) evolution/reduction) and two irreversible electrochemical reactions (cupric ion (Cu2+) reduction and oxygen (O2) reduction). Dissolved cuprous ion (Cu+) reacts in a second chemical step to form the cuprous chloride (CuCl) salt film treated as a diffusion barrier, or it reacts to form the cuprous oxide (Cu2O) film that partially blocks the active area on the metal surface. The model also accounts for a series of homogeneous reactions involving copper chloride complex, copper hydroxide complex, copper carbonate complex, and superoxide species. The associated equilibrium constants were obtained from PHREEQC thermodynamic software.3 The model includes a total of 23 dependent spatial-temporal variables.The mathematical model is developed using the finite-element method (COMSOL Multiphysics). The model includes coupled nonlinear conservation equations for ionic species, which include the contribution of diffusion, migration, local electroneutrality, and homogeneous reactions. The anodic and cathodic regions are not predefined but are rather determined by values of local concentration and potential from the simulation results. The surface coverage of film was calculated implicitly and expressed in terms of the thickness in units of monolayers. The model also accounted for the effect of porous CuCl film thickness on the surface oxygen concentration and potential applied on electrochemical reactions.In this preliminary study, two extreme conditions were chosen such that the droplet boundary could either have an infinite supply of oxygen or it could have no external supply of oxygen for an initially air-saturated droplet. The results show a 3-year time-dependent radial distribution of anodic and cathodic current density, surface coverage of CuCl film and Cu2O film, and localized corrosion rates and depths. The results include a distribution of pH, potential, and concentrations of dissolved gaseous and ionic species through the entire droplet. The potential change as the system transitions from aerobic to anaerobic conditions matches the expected equilibrium potential difference.4 The model could be used to explore the influence of different parameters on the localized corrosion rate and depth, film thickness and growth, and each individual current profiles. The parameters may be adjusted to conform to the DGR environment.References NWMO, “Choosing a Way Forward. The Future Management of Canada’s Used Nuclear Fuel. Final Study,” Nuclear Waste Management Organization, Toronto, Ontario, 2005.R. Evans, The Corrosion of Metals, E. Arnold & Company, London, 1926.PHREEQC Version 3, United States Geological Survey, 202, https://www.usgs.gov/software/phreeqc-version-3Cleveland, M. E. Orazem, and S. Moghaddam, “Response to “Comment on “Nanometer-scale corrosion of copper in de-aerated deionized water” [J. Electrochem. Soc., 161, C107 (2014)],” Journal of the Electrochemical Society, 163 (2016), Y5-Y11. AcknowledgementThis work was supported by the Nuclear Waste Management Organization, Canada, under project 2000904.

Proton-Coupled Electron Transfer in a Ruthenium(II) Bipyrimidine Complex in Its Ground and Excited Electronic States.

Proton-coupled electron transfer (PCET) was studied for the ground and excited electronic states of a [Ru(terpy)(bpm)(OH2)(PF6)2] complex, Ru-bpm. Cyclic voltammetry measurements show that the Ru(II)-aqua moiety undergoes PCET to form a Ru(IV)-oxo moiety in the anodic region, while the bpm ligand undergoes PCET to form bpmH2 in the cathodic region. The photophysical behavior of Ru-bpm was studied using steady-state and femtosecond transient UV-vis absorption spectroscopy, coupled with density functional theory (DFT) calculations. The lowest-lying excited state of Ru-bpm is described as a (Ru → bpm) metal-to-ligand charge-transfer (MLCT) state, while the metal-centered (MC) excited state was found computationally to be close in energy to the lowest-energy bright MLCT state (MC state was 0.16 eV above the MLCT state). The excited-state kinetics of Ru-bpm were found via transient absorption spectroscopy to be short-lived and were fit well to a biexponential function with lifetimes τ1 = 4 ps and τ2 = 65 ps in aqueous solution. Kinetic isotope effects of 1.75 (τ1) and 1.61 (τ2) were observed for both decay components, indicating that the solvent plays an important role in the excited-state dynamics of Ru-bpm. Based on the pH-dependent studies and the results from prior studies of similar Ru-complexes, we hypothesize that the 3MLCT state forms an excited-state hydrogen-bond adduct with the solvent molecules and that this process occurs with a 4 ps lifetime. The formation of such a hydrogen-bond complex is consistent with the electronic density accumulation at the peripheral N atoms of the bpm moiety in the 3MLCT state. The hydrogen-bonded state 3MLCT decays to the ground state with a 65 ps lifetime. Such a short lifetime is likely associated with the efficient vibrational energy transfer from the 3MLCT state to the solvent.

Ambipolar, multichromic metallopolymers of poly(3,4-ethylenedioxythiophene)

In this study, two novel bipyridine-based Ru(II) complexes (E1-Ru and E2-Ru) which contain different number of 3,4-ethylenedioxythiophene (EDOT) groups were synthesized and subjected to electrochemical polymerization both in absence and presence comonomer (EDOT). The resultant metallopolymers were examined in terms of their electrochemical and electrochromic properties. Cyclic voltammetry and spectroelectrochemistry studies revealed the ambipolar and multichromic nature of all the polymers where the reversible redox activity in the cathodic region was found to be mainly due to ligand centered reduction of the complex (Ru2+/1+ and Ru1+/0) and metal centered oxidation (Ru2+/3+) was found to be available along with redox activity of the conjugated backbone of the polymers in the anodic region. Contrary to pristine PEDOT all polymers displayed vibrantly multichromic behavior thanks to superimposed but independently functioning electrochromic/redox nature of the conjugated polymer backbone and the Ru complex. In general, increasing the number of polymerizable units in the monomer structure increased the quality of the films and brought color diversity to these metallopolymers. Copolymerization, on the other hand, not only contributed positively to the band gap and switching time but also widened the color pallet of these polymers which became even more remarkable upon changing the comonomer feed ratio.

Co-localizing Kelvin Probe Force Microscopy with Other Microscopies and Spectroscopies: Selected Applications in Corrosion Characterization of Alloys.

Kelvin probe force microscopy (KPFM), sometimes referred to as surface potential microscopy, is the nanoscale version of the venerable scanning Kelvin probe, both of which measure the Volta potential difference (VPD) between an oscillating probe tip and a sample surface by applying a nulling voltage equal in magnitude but opposite in sign to the tip-sample potential difference. By scanning a conductive KPFM probe over a sample surface, nanoscale variations in surface topography and potential can be mapped, identifying likely anodic and cathodic regions, as well as quantifying the inherent material driving force for galvanic corrosion. Subsequent co-localization of KPFM Volta potential maps with advanced scanning electron microscopy (SEM) techniques, including back scattered electron (BSE) images, energy dispersive spectroscopy (EDS) elemental composition maps, and electron backscattered diffraction (EBSD) inverse pole figures can provide further insight into structure-property-performance relationships. Here, the results of several studies co-localizing KPFM with SEM on a wide variety of alloys of technological interest are presented, demonstrating the utility of combining these techniques at the nanoscale to elucidate corrosion initiation and propagation. Important points to consider and potential pitfalls to avoid in such investigations are also highlighted: in particular, probe calibration and the potential confounding effects on the measured VPDs of the testing environment and sample surface, including ambient humidity (i.e., adsorbed water), surface reactions/oxidation, and polishing debris or other contaminants. Additionally, an example is provided of co-localizing a third technique, scanning confocal Raman microscopy, to demonstrate the general applicability and utility of the co-localization method to provide further structural insight beyond that afforded by electron microscopy-based techniques.

The Tribocorrosion Behaviour of Ti-6Al-4 V Alloy: The Role of Both Normal Force and Electrochemical Potential

The tribocorrosion behaviour of Ti-6Al-4 V exposed to phosphate buffered saline was investigated under a range of normal forces in both cathodic and anodic regions to provide a basis for properly deriving the tribological constants of this alloy. To achieve this, a new customised tribotester was designed and manufactured to rub the Ti-6Al-4 V disks against zirconia balls. The tests were conducted at a sliding frequency of 1 Hz and a sliding distance of 4.8 mm under various normal forces and potentials as 17.5, 10.8, 6, 3.5 N, and − 1.2, − 0.6, 0, 0.4, 0.8 V/VAg/AgCl, respectively. The damaged surfaces were characterised by scanning electron microscopy and energy-dispersive X-ray spectroscopy, profilometer, and micro-hardness tester. The post analyses confirmed the appearance of some minor cracks together with third-body wear particles. No significant changes in the hardness were detected after the tribocorrosion tests. The results of profilometry and electrochemical current indicated that in the anodic region the chemical losses accounted for a significant proportion (up to 36%) of the total loss. The proportional chemical loss increased with the potential; however, neither direct nor reverse relationship was found with the normal force. Overall, in the anodic domain, the material loss increased with the potential level due to the formation of oxide layer which may induce more shear cutting. In the cathodic domain, hydrogen embrittlement changed the properties of the interface and thus, the amount of material loss. Both the mechanical and chemical wear were described by an existing tribocorrosion theory; thereby, the theory was equipped with its tribocorrosive constants for future analyses on the tribocorrosion of this alloy extensively used in various applications including biomedical implants.

Dynamic and localized microelectrochemical approaches to evaluate the corrosion resistance of newly developed lean duplex stainless steel alloys

AbstractA combination of scanning microelectrochemical techniques along with the conventional electrochemical approaches is explored to attain insight information on the localized corrosion on the newly developed lean duplex stainless steel (LDSS) alloys. The obtained results from dynamic electrochemical impedance spectroscopic (DEIS) tests explained the beneficial role of different alloying elements on the passive and transpassive regions of the investigated LDSS alloys in a 3.5% NaCl solution. The scanning vibrating electrode technique (SVET) was effective in examining the anodic and cathodic regions on the corroding LDSS, whereas the scanning electrochemical microscopy (SECM) technique was employed to explore the localized corrosion sites on LDSS in NaCl solution. The acquired SVET results revealed a reduction in the susceptibility of the newly developed alloys to localized corrosion concerning their composition, accounting for the enhanced corrosion resistance. The obtained result from conventional and scanning microelectrochemical techniques obviously revealed the LDSS alloy with the composition of Fe–16Cr–2Ni–2Mn–1Mo exhibited higher localized corrosion resistance in NaCl solution.

Multi-channel contactless conductivity detection device for online detection of free-flow electrophoresis separation

现有自由流电泳(FFE)装置因不具备在线检测功能,其实用性仍然存在明显不足。针对这一问题,该工作发展了一种多通道电容耦合式非接触电导检测(MC-C4D)装置并开发了自动测量软件。MC-C4D装置采用了并行分时的非接触电导检测技术,即由多个同样的非接触电导检测模块并行排列,而单个电导检测模块又由多个非接触电导检测池组成,采用模拟开关切换这些检测池,能够分时检测流经相应检测池溶液的电导率。多个电导检测模块的检测池总数等于FFE的组分数,它们分别串行接入到FFE各流路中,这样MC-C4D装置就可在线并行分时在线测量各组分溶液的电导率。为验证所设计MC-C4D装置的检测性能,采用配制的氯化钾标准溶液作为检测对象对MC-C4D装置进行了标定和测试。实验数据表明,MC-C4D装置电导率检测范围为0.015~2.5 mS/cm,检出限(LOD)为0.002 mS/cm,日内相对标准偏差(RSD, n=3)为2.31%,测量相对误差(RE)为3.03%和通道间测量相对偏差为1.60%,这些参数表明该装置检测范围较大,LOD低,重复性好,准确性高,通道间测量相对偏差小。另外,将MC-C 4D装置应用于往复式自由流等电聚焦电泳(RFFIEF)在蛋白质聚焦过程中对各组分溶液电导率进行实时在线检测,结果表明,所开发的MC-C4D装置不仅可实现对FFE各组分溶液电导率的实时在线检测,而且还可在RFFIEF实验中辅助掌握分离的实验进度,提高FFE装置的实用性。

Carbon/Pyropolymer-based Electrode Materials for Alkali Ion Storage

Carbon materials have large numbers of redox-active sites for alkali-ion storage, such as Stone-Wales, vacancy, edge, and pseudo-edge defect sites as well as extrinsic defects. The topological defects can be a redox host in anodic voltage regions, while the extrinsic defects can store alkali ions in a cathodic voltage range. Therefore, carbon materials can be a great candidate for both anode and cathode for alkali ion batteries. In this study, alkali ion storage behaviors of different carbon materials, highly defective graphene-based nanosheet (GNS), well-ordered graphite nanoplate (GNP), hard carbon series samples, and nanoporous pyropolymers which are a kind of carbon materials including numerous defects, are reviewed, and their potentials as both anode and cathode for alkali ion batteries are discussed.

An investigation of precipitation strengthened Inconel 718 superalloy after triode plasma nitriding

In this study, we investigated the microstructural evolution, surface hardening and general corrosion properties of a precipitation-strengthened Inconel 718 Ni-superalloy after triode-plasma nitriding (TPN) at low treatment temperatures of 400–450 °C (i.e. thermodynamic paraequilibrium conditions) and a high treatment temperature of 700 °C. At low treatment temperatures, apart from the formation of nitrogen-expanded austenite (γN) from the high-Cr γ matrix, the pre-existing γ′ and γ″ intermetallic nano-precipitates appear to exhibit different nitriding responses. The spheroidal N-modified γ′ (or γ′N) precipitates were ‘slightly-expanded’, leading to slightly shifted XRD peaks, i.e. 2-theta angles of ~0.2° from γsubstrate(111) and ~0.5° from γsubstrate(200). In contrast, N-modified γ″ (or γ″N) could experience substantial lattice expansion close to that of the γN matrix. With increasing treatment temperature, nitride formation started as additional nano-sized precipitates (e.g. ~3–6 nm diameter as observed at 450 °C) and grew into laths (e.g. ~5–10 nm thick and ~15–30 nm wide as observed at 700 °C).Without changing core microstructure/properties, surface nitrogen modification and hardening were obtained on alloy 718 after TPN (e.g. from ~486 HV0.025 to ~1212 HV0.025 after TPN at 400 °C). No degradation of corrosion performance was observed for the nitrogen-supersaturated surface after TPN at 400 °C. However, the 450 °C TPN-treated surface showed a slightly increased current density in the anodic region, which can be associated with early-stage nitride formation. The significantly deteriorated corrosion performance after TPN treatment at 700 °C is due to pronounced nitride formation and segregation of substitutional alloying elements.

Corrosion of Linear-Friction-Welded AZ91 and AZX912 Mg-Al Alloys

The corrosion performance of the AZ91 and AZ91 + 2%Ca (AZX912) magnesium alloys joined using linear friction welding was investigated. For similar and dissimilar metal combinations—namely AZ91/AZ91, AZX912/AZX912, and AZ91/AZX912, the performance was evaluated by mass loss analysis and the scanning vibrating electrode technique in 1 wt% NaCl solution. Galvanic behavior between AZ91 and AZX912 was examined by potentiostatic polarization and galvanic current measurements. Approximately 0.3–0.6 mm thick seamless weld zones were generated in all of the welds, which did not show any appreciable changes in the surface profiles acquired after the corrosion test. The corrosion-induced mass loss rate of the AZ91/AZX912 dissimilar weld was 10% higher than those of the AZ91/AZ91 and AZX912/AZX912 similar welds. The galvanic test indicated that AZ91 and AZX912 were the anodic and cathodic regions, respectively, with a difference in the corrosion potential of 20–30 mV. The corrosion of the AZ91/AZX912 weld was presumed to proceed via a macro-galvanic cell between the base alloys, whereas the weld acted as a bridge and did not influence the corrosion.

Experimental and theoretical investigation of corrosion inhibition effect of two piperazine-based ligands on carbon steel in acidic media

In this study, the corrosion of carbon steel in 1.0 M HCl solutions containing either 1,4-bis(2-(2-hydroxyethyliminomethyl)phenyl)piperazine (1) or its reduced form, 1,4-bis(2-(2-hydroxyethylaminomethyl)phenyl)piperazine(2), as possible corrosion inhibitors, were compared to a solution containing no (1) or (2). The various concentrations of inhibitors, 0.2, 1.0, and 2.0 mM, were used to explore the inhibition ability of the synthesized materials against carbon steel corrosion. The morphology and chemical analysis of the as-received and corroded samples were investigated by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). By assessing potentiodynamic data, the icorr of carbon steel electrode is the highest value among the other inhibitor-containing solutions, demonstrating a minimum corrosion resistance in 1.0 M HCl solution. While, the protection of carbon steel (1) and (2)-containing solution increased by raising the concentration of (1) and (2) from 0.2 to 2.0 mM. The reduced form of (1) showed a superior corrosion resistance for carbon steel compared to inhibitor (1). The corrosion efficiency of carbon steel in 1.0 M HCl attained a maximum value of 66.08% for inhibitor (1) and 88.51% for inhibitor (2) when the concentration of inhibitor reached the highest value. The results obtained from electrochemical impedance spectroscopy, EIS, illustrated that the capacitance of the double layer, Cdl, decreased with an increment of inhibitor (1) and (2) concentration, while the charge transfer resistance of carbon steel enhanced as the inhibitor increased. SEM images reveals that the carbon steel had a sever corrosion inhibitor-free solution, while the surface in inhibitor (1) and (2)-containing solution looks more smooth and uniform. The obtained results in EIS and Tafel measurements were clearly consistent with our observation in the SEM images. According proposed inhibition mechanism, the inhibitor adsorption on the carbon steel prevents the hydrogen evolution from the cathodic sites and dissolution of iron in the anodic regions. Adsorption of both inhibitors, (1) and its reduced form (2), was found to obey the Temkin adsorption isotherm. The inhibitory properties of inhibitor molecules have also been studied by theoretical calculations, using Gaussian 09 software program, enabling a comparison of the properties of (1) and (2).

Performance of Reduced Titanium Oxide and Boron Doped Diamond as anodes in hyperthermophilic bioelectrochemical systems

This work investigates Reduced Titanium Oxide (RTO) in comparison with Carbon Cloth (CC) and commercial Boron Doped Diamond (BDD) as anodes in hyperthermophilic bioelectrochemical systems operating at 80°C by Thermotoga neapolitana. Two samples of RTO were synthesized by plasma electrolytic oxidation (PEO) of titanium plates and subsequent electrochemical reduction. Electrochemical performance of CC, BDD, and RTO are tested by performing cyclic voltammetry in the anodic region (0-1V, 50 mV/s), in abiotic and biotic conditions. The surface of colonized materials is observed by SEM microscopy. Results show that bacteria fast settle on all tested material, significantly affecting their electrochemical conductivity. The integration of voltammetric cycles reveals that biofilm generates capacitive effects on the anodic surfaces, particularly evident in RTO, less in CC and absent in BDD. Charge densities provided by capacitive response of RTO and CC are of the order of 5.58 and 0.77 mC/cm2, respectively.

Efficiency of xylenol orange as corrosion inhibitor for aluminium in trichloroacetic acid

The corrosion of aluminium in trichloroacetic acid (TCA) containing xylenol orange has been studied. In TCA, the corrosion rate increases with the increase in acid concentration. At constant acid concentration, the inhibition efficiency of xylenol orange increases with the inhibitor concentration. At constant inhibitor concentration, the inhibition efficiency decreases with the increase in the acid concentration. As temperature increases, percentage of inhibition decreases. Plot of log (θ/1-θ) versus log C results in a straight line, suggesting that the inhibitor cover both the anodic and cathodic regions through general adsorption following Langmuir isotherm. The polarization curves show very little anodic but significant cathodic polarization.

Effect of norcholine fluid derivative on the resilience of mild steel to electrochemical degradation in weak HCl media

The resilience of mild steel to electrochemical degeneration in weak electrolyte corrosion (0.5 M HCl) was assessed at discrete concentrations of Norcholine derivatives by potentiodynamic polarization and open circuit potential analysis. Degradation rate of the steel substantially declined with augmentation of Norcholine concentration from 9.49 mm/y in control HCl (no Norcholine) to 0.27 mm/y at highest Norcholine value of 15%. The degradation rate at this inhibitor concentration correlates of 97.1% protection performance. Norcholine demonstrated cathodic inhibition effect from observation of the negative deviation in corrosion potential. Norcholine was also observed to indicate substantial passive reaction mechanism on the anodic polarization regions of the polarization graphs. This translates to evolution of non-porous layer on the steel exterior. Open circuit potential graphs indicate substantial variation between the inhibited and acid degraded graphs of the steel. Mathematical computations through analysis of variance demonstrates Norcholine concentration and potential tracking time are statistically important variation sources influencing the protection performance of Norcholine at values of 68.03% and 26.4%.

Stable Diarylamine-Substituted Tris(2,4,6-trichlorophenyl)methyl Radicals: One-Step Synthesis, Near-Infrared Emission, and Redox Chemistry

Stable Diarylamine-Substituted Tris(2,4,6-trichlorophenyl)methyl Radicals: One-Step Synthesis, Near-Infrared Emission, and Redox Chemistry

Synthesis and evaluation of photophysical and electrochemical properties of vinyl chalcogenide derivatives of phenothiazines

The Wittig-Horner mediated syntheses of phenothiazines carrying vinylsulfide and vinylselenide motifs attached to the aromatic ring(s) or connected to the central nitrogen atom of the heterocycle, and the subsequent study of their photophysical and electrochemical properties, are reported. These compounds were obtained as mixtures of geometric isomers, in good to excellent yields. To complete the study, a small set of vinylsulfoxide and vinylsulfone derivatives was also prepared from the corresponding oxidized phosphinoxides. The photophysical properties of the compounds were examined in solvents of varying polarity, in which they presented absorption maxima in the UV region, with molar absorptivity coefficients compatible with symmetry-allowed π–π* electronic transitions. The heterocyclic derivatives were fluorescent. Compounds bearing vinylsulfide moieties associated to the nitrogen atom of the heterocycle displayed less intense fluorescence than the phenothiazine derivatives carrying vinylchalcogenides bonded to the aromatic ring; the latter also exhibited more red-shifted absorption spectra, and Stokes shifts in the range 6115–8170 cm−1 with weak dependence of solvent polarity. The sulfoxide and sulfones displayed more red-shifted spectra than the corresponding sulfides. The cyclic voltammograms of all derivatives exhibited a common pattern of reversible or quasi-reversible processes in the anodic region, related to the phenothiazine unit.

Scientific insights of electrochemical replacement approach to describe the origin of Pre-Columbian Peruvian gilded copper-based objects

Pre-Columbian Peruvian goldsmiths developed gilded copper-based objects by ancient techniques that require identification to propose conservation strategies. Lechtman H, conducted experiments to suggest that the electrochemical replacement was the gilding technique used by the Moche and Vicus cultural groups. Despite her remarkable achievement, the quantitative data provided by her is still open to discussion. This work focused on obtaining experimental data to recreate her protocol by introducing less gold precursor. Polished copper pieces were plated with an adherent gold film of up to 7.5 µm after immersing them into an electrolytic solution for 3 min and 6 min at 80 °C. Our results demonstrated that the electrochemical replacement technique gives rise to anodic regions in the plated objects. Further studies around the corrosion process that undergoes these heritage objects in burial and environmental conditions are suggested to determine their deterioration rate. Moreover, electroless and galvanic techniques should be explored in order to improve current approaches.