Open Circuit Potential Values Research Articles

Electrochemical Behavior of AZ31 Mg Alloy in Neutral Aqueous Solutions Containing Various Anions

<p>This work was performed to characterize the electrochemical behavior of AZ31 Mg alloy in neutral aqueous solutions where Cl<sup>−</sup>, SO<sub>4</sub><sup>2−</sup>, PO<sub>4</sub><sup>3−</sup>, and F<sup>−</sup> ions were present and pH was adjusted to 6 to exclude the contribution of H<sup>+</sup> and OH<sup>−</sup> ions. Open-circuit potential (OCP) transient, electrochemical impedance spectroscopy (EIS) and potnetiodynamic polarization curves were employed. The OCP value appeared to decrease in the order of F<sup>−</sup> > Cl<sup>−</sup> > SO<sub>4</sub><sup>2−</sup> > PO<sub>4</sub><sup>3−</sup> ions while corrosion current density increased in the same order. Electrochemical impedance spectroscopy (EIS) data showed two capacitive arcs in all the solutions and one more inductive arc appeared in PO<sub>4</sub><sup>3−</sup>-containing solution. By fitting of two capacitive arcs, capacitance of dense film (C<sub>df</sub>), resistance of porous film (R<sub>pf</sub>) and double layer capacitance (C<sub>dl</sub>) and charge transfer resistance (R<sub>ct</sub>) beneath the porous films were obtained. A simplified model in which various thicknesses and coverages of dense and porous films are assumed to be present on the AZ31 Mg alloy surface, is suggested to explain the effects of four different anions on the electrochemical behavior of AZ31 Mg alloy.</p>

A micro-alloyed Mg-Zn-Ge alloy as promising anode for primary Mg-air batteries

Alloying is one of the effective approaches to boost the discharge property of magnesium (Mg) anodes for primary Mg-air batteries and recently micro-alloying is highly recommended at the aim of developing advanced primary Mg system. In this study, micro-alloyed extruded Mg0.5Zn0.2Ge (in wt.%) alloy is evaluated as an anode candidate for primary Mg-air batteries in both half-cell and Mg-air full cell configurations, in comparison with commercially accepted Mg anodes, typified by as-cast HP Mg and extruded AZ31 alloy. The corrosion behavior at open circuit potential (OCP) condition of the three materials is also compared through electrochemical tests. Mg0.5Zn0.2Ge alloy displays the most negative OCP value and the highest corrosion resistance at OCP. During discharge, Mg0.5Zn0.2Ge anode exhibits low wasteful-discharge rate and homogeneous dissolution that gives rise to the absence of “chunk effect”. Consequently, the anodic efficiency and specific capacity of Mg0.5Zn0.2Ge anode are superior to those of HP Mg and AZ31 anodes, e.g. 57.3% and 1257 mAh g−1 at 1 mA cm−2. Additionally, Mg-air battery based on Mg0.5Zn0.2Ge anode offers higher cell voltage and specific energy than those assembled with HP Mg and AZ31 anodes, which can be further optimized by addition of electrolyte additives. Therefore, micro-alloyed Mg0.5Zn0.2Ge alloy can serve as a promising candidate for anode material of primary Mg-air batteries.

Electrochemical Characterisation of the Photoanode Containing TiO2 and SnS2 in the Presence of Various Pharmaceuticals

In this work, the behaviour of photoanodes made of TiO2, SnS2 and TiO2/SnS2 was examined in the presence and absence of pharmaceuticals diclofenac (DCF), memantine hydrochloride (MEM) and salicylic acid (SA). The focus of the current research is on the following photoelectrochemical (PEC) characterisation methods: linear polarisation, electrochemical impedance spectroscopy (EIS), and open circuit potential (OCP) monitoring. Linear polarisation and EIS provided useful information about the interaction between the pharmaceuticals and the photocatalytic materials. The presence of the selected pharmaceuticals affects the OCP value, mainly due to the pH change. The results obtained by PEC characterisation were compared to the photocatalytic (PC) efficiency of pharmaceutical degradation. In addition to the photocurrent response, the linear voltammogram indicates the electrochemical oxidation of DCF and SA. Geometry optimizations using density functional theory (DFT) showed that the HOMO orbitals’ position of DCF and SA are above the position of the TiO2 HOMO level and below the position of the SnS2 HOMO level. Due to this, the characteristic current peak for DCF and SA was registered, but only for TiO2 and TiO2/SnS2 photoanodes. The oxidation current peak was not registered for MEM, although h+ scavenging properties were noticed for TiO2 in the presence of MEM. Apparently, this is an interplay between the protonated and non-protonated forms of MEM and the differences in their HOMO positions.

Corrosion Behavior of the AZ31 Mg Alloy in Neutral Aqueous Solutions Containing Various Anions

This work demonstrates the corrosion behavior of the AZ31 Mg alloy as a function of an immersion time of 48 h in 0.1 M HCl, H2SO4, H3PO4 and HF solutions, in which pH was adjusted to 6 to exclude the contribution of hydrogen ions (H+) and hydroxide ions (OH−). In situ observations, open circuit potential (OCP), weight changes and AC impedance measurements were performed with an immersion time of 48 h and the morphologies and chemical compositions of the surface products after 48 h of immersion were analyzed by SEM, EDS and XPS. In the chloride ion (Cl−)-containing solution, the corrosion of the AZ31 Mg alloy initiated locally and propagated discontinuously over the surface with immersion time. The OCP value of the AZ31 Mg alloy showed an initial increase from −1.51 VAg/AgCl to −1.47 VAg/AgCl after about 5 h of immersion and then a decrease to −1.51 VAg/AgCl due to corrosion initiation. In the F−-containing solution, after 48 h of immersion, the OCP showed an extremely large value of −0.6 VAg/AgCl, while the relatively lower values of −1.52 VAg/AgCl, −1.59 VAg/AgCl were seen in the solutions containing SO42− and PO43, respectively. In the sulfate ion (SO42−)-containing neutral aqueous solution, needle-like surface films were formed and there were no changes in the weight of the AZ31 Mg alloy with immersion time. In the phosphate ion (PO43−)-containing neutral aqueous solution, a vigorous gas evolution occurred, together with the formation of black surface films with cracks, and a high corrosion rate of −13.8018 × 10−3 g·cm−2·day−1 was obtained. In the fluoride ion (F−)-containing neutral aqueous solution, a surface film with crystalline grains of MgF2 was formed and the weight of the AZ31 Mg alloy increased continuously with immersion time. In conclusion, the corrosion of the AZ31 Mg alloy occurred uniformly in neutral phosphate solution but locally in chloride solution. No corrosion was observed in either the neutral sulfate or fluoride solutions.

Effect of Plasma Nitriding and Oxidation on the Corrosion Resistance of 304 Stainless Steel in LiBr/H2O and CaCl2-LiBr-LiNO3-H2O Mixtures

The effect of plasma nitriding and oxidation on the corrosion resistance of AISI 304 type stainless steel in LiBr/H2O and CaCl2-LiBr-LiNO3-H2O mixtures at 80 °C has been evaluated by using potentiodynamic polarization curves and electrochemical impedance spectroscopy techniques (EIS). Steel was plasma treated at 500 °C during 8 h under different atmospheres, nominally 20% N2 + 80% H2, 100% N2 and 100% O2. X-ray diffraction analysis (XRD) showed the presence of a CrN layer in nitrided specimens, whereas scanning electronic microscopy analysis revealed that specimen treated in the 20% N2 + 80% H2 atmosphere showed the thickest nitride layer. Specimens nitrided in the 20% N2 + 80% H2 atmosphere had the noblest open circuit potential value in both solutions, whereas potentiodynamic polarization curves indicated the formation of a passive layer. These specimens exhibited the lowest corrosion and passivation current density values. Corrosion process was under charge transfer control in both solutions regardless of the plasma treatment. The type of corrosion suffered by the steel under all treatments was the pitting type of corrosion. Pits density was the lowest for nitrides steels rather than that for untreated or pre-oxidized ones.

Radioiodine-131 Therapy Used for Differentiated Thyroid Cancer Can Impair Titanium Dental Implants: An In Vitro Analysis.

The aim was to assess, in vitro, the effects of radioiodine-131 (I-131) on the structure of titanium implants. A total of 28 titanium implants were divided into 7 groups (n = 4) and irradiated at 0, 6, 12, 24, 48, 192 and 384 hours. At the end of the experiment, each sample was investigated via scanning electron microscopy (SEM) and electrochemical measures. The control sample revealed a smooth and compact surface. The small micro-sized porosity is slightly visible at the macroscopic level, but the precise details cannot be observed. A mild exposure to the radioactive solution for 6 to 24 h showed a good preservation of the macro-structural aspects such as thread details and surface quality. Significant changes occurred after 48 h of exposure. It was noticed that the open-circuit potential (OCP) value of the non-irradiated implants move toward more noble potentials during the first 40 min of exposure to the artificial saliva and then stabilizes at a constant value of -143 mV. A displacement of the OCP values toward more negative values was observed for all irradiated implants; these potential shifts are decreasing, as the irradiation period of the tested implants increased. After exposure to I-131, the structure of titanium implants is well preserved up to 12 h. The eroded particles start to appear in the microstructural details after 24 h of exposure and their numbers progressively increase up to 384 h after exposure.

Comparative Studies on Steel Corrosion Resistance of Different Inhibitors in Chloride Environment: The Effects of Multi-Functional Protective Film

A corrosion inhibitor was widely used to improve corrosion resistance of steel bar in reinforcement concrete structure. A kind of multi-component corrosion inhibitor, which is composed of organic and inorganic substances, was developed in this research. This corrosion inhibitor was comparatively studied with various other inhibitors by using open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) methods. The results show that the OCP values and charge transfer resistance (calculated by EIS curves) of the multi-component corrosion inhibitor remain, respectively, as high as −0.45 V and 932.19 kΩ·cm−2 after 60 days immersion, which are significantly better than other groups. Wide passivation interval and various peaks in cyclic voltammograms (CV) were applied to analyze the mechanism of adsorption (organic substance) and oxidation–reduction reactions (inorganic substance). The functional groups -OH in triethanolamine (TEA) and tri-isopropanolamine (TIPA) bond to the steel bar surface quickly, behaving as an adsorbent of organic substance in early age. An additional protective precipitate related to the reactions of Fe3+ was formed by inorganic substances (Fe2(MoO4)3 and FePO4), which is consistent with the EIS results and equivalent electrochemical circuits. As an eco-friendly substitute, multi-component corrosion inhibitors possess similar or even better protecting effects on steel bars in comparison to calcium nitrite. In addition, the concept of a “multi-functional protective film” was proposed, providing a new insight to achieve modified anti-corrosion capacity of inhibitors.

Efficacy of an organic–inorganic hybrid phosphorus compound in corrosion mitigation of reinforcement steel in concrete. I. Gravimetric and electrochemical analysis

Bis(hexamethylene)triamine-pentakis(methylphosphonic acid) (BTPMP) was investigated for its inhibiting action on corrosion of Fe500D reinforcement steel. Results of gravimetric studies inferred that 10 mM of BTPMP is effective in corrosion control of the steel in saturated calcium hydroxide solution tainted by chloride ions. According to the electrochemical studies, the interface of the metal/solution exhibits higher charger transfer resistance and lower constant phase element values in the presence of BTPMP. The open circuit potential (OCP) measurements indicate that the presence of BTPMP shifts OCP values of steel in concrete in positive direction. The nature of the film is protective as observed from prolonged time taken for failure of BTPMP-protected rebar compared with unprotected rebar during accelerated corrosion tests. Furthermore, it is observed that the bond strength between concrete and steel is unaffected by the inhibitor film.

Densification, Microstructure and Anisotropic Corrosion Behavior of Al-Mg-Mn-Sc-Er-Zr Alloy Processed by Selective Laser Melting

High-performance additives manufactured by Al alloys provide significant potential for lightweight applications and have attracted much attention nowadays. However, there is no research on Sc, Er and Zr microalloyed Al alloys, especially concerning corrosion behavior. Herein, crack-free and dense Al-Mg-Mn-Sc-Er-Zr alloys were processed by selective laser melting (SLM). After optimizing the process parameters of SLM, the anisotropic corrosion behavior of the sample (volume energy density of 127.95 J·mm−3) was investigated by intergranular corrosion (IGC) and electrochemical measurements. The results showed that the XY plane of the as-built sample is less prone to IGC, and it also has a higher open circuit potential value of −901.54 mV, a higher polarization resistance of 2.999 × 104 Ω·cm2, a lower corrosion current of 2.512 μA·cm−2 as well as passive film with superior corrosion resistance compared to the XZ plane. According to our findings, the XY plane has superior corrosion resistance compared to the XZ plane because it has fewer primary phases of Al3(Sc, Er, Zr) and Al2MgO4, which can induce localized corrosion. Additionally, a higher fraction of low-angle grain boundaries (LAGBs) and a stronger (001) texture index along the building direction are also associated with better corrosion resistance of the XY plane.

Effect of intermetallic compound on the corrosion behaviour of resistance spot welding joints between 5182 aluminium alloy and galvanized DP780 dual-phase steel

Interfacial intermetallic compound (IMC) layer is critical during realizing the galvanic corrosion mechanism and strength degradation of aluminium/steel resistance spot welding (RSW) joints. The effect of IMC layer on the corrosion behaviour of RSW joint between 5182 aluminium alloy and galvanized DP780 dual-phase steel was investigated by immersion corrosion method and electrochemical method. Results demonstrated localized corrosion around Fe-rich phase particles on aluminium nugget and preferential corrosion at the interface front near IMC layer. The IMC layer had the highest open circuit potential value of −0.569 V and low corrosion current density among the investigated nugget and substrates. The potential difference (0.184 V) between the cathodic IMC layer and large area of anodic aluminium nugget was responsible for the preferential initiation of localized corrosion at the interface front near the IMC layer.

Corrosion Behavior of Hastelloy C-276 in Hydrochloric and Sulfuric Acid

This research was conducted to determine the corrosion rate by varying the concentration of the solution against hydrochloric acid and sulfuric acid. The method used is open circuit potential (OCP) and Tafel plot. Based on the research conducted, Hastelloy C-276 was more prone to get oxidized in sulfuric acid rather than hydrochloric acid. It can be seen from the OCP value of sulfuric acid was much more negative than that of hydrochloric acid as of-1.5 V for 0.5 M sulfuric acid and-0.2 V for hydrochloric acid. The corrosion rate of Hastelloy C-276 in sulfuric acid was also higher compared to same alloy in hydrochloric acid. At the most concentrated solution, 0.5 M, the corrosion rate of sulfuric acid reached 0.39 mmpy and as for corrosion cate in hydrochloric acid, only at 0.16 mmpy. It is thought that there was a difference of passive film composition for both solutions. Keywords: Hastelloy C-276, Corrosion, Hydrochloric acid, Sulfuric acid.

Electrochemical Characterization of Biodiesel from Sunflower Oil Produced by Homogeneous Catalysis and Ultrasound

Biofuel production has increased significantly in several countries in recent decades. Different evaluation techniques are required for their characterization. The study measures the properties of the obtained biodiesel and a commercial diesel sample, using the techniques of open circuit potential, linear scanning voltammetry and electrochemical impedance spectroscopy. The transesterification reaction between sunflower oil and methanol was carried out with ultrasound as the energy source. The determination of triglyceride conversion to biodiesel is performed by high performance liquid chromatography (HPLC), obtaining up to 99.79% with a yield of 93.40% at a transesterification temperature of 50 ∘C for 60 min with a methanol/oil molar ratio of 6:1. The potassium hydroxide catalyst concentration was 1.0 g catalyst/100 g oil. The biodiesel samples generally showed open circuit potential (OCP) values less than 790 mV and stabilization time less than 120 s, Linear sweep voltammograms (LSV) show no reaction peaks with current densities on the order of NanoAmpere, Electrochemical impedance spectroscopy (EIS) showed a capacitive system with impedances on the order of MΩ cm2 at low frequency; This information could help characterize biofuels and other similar materials.

Cu-electrodeposited gold electrode for the sensitive electrokinetic investigations of nitrate reduction and detection of the nitrate ion in acidic medium

The electro-catalytic reduction of nitrate ion in acidic media was observed at the Cu-electrodeposited Au surface. The voltammetric analysis represented that the Cu/Au electrode has an enhanced catalytic activity towards nitrate reduction in acidic medium through by eight electrons transfer process. Ammonia (NH3) was produced from the reduction of nitrate (NO3–) which followed a concerted reaction pathway as the value of transfer coefficient was 0.45 at Cu/Au electrode in the acidic medium. The value of standard rate constant and open circuit potential was evaluated as 2.48 × 10−4 cms−1 and 0.10 V respectively. This Cu/Au electrode displayed a good sensitivity (5.9378 μAµM−1cm−2) and lower detection limit (LOD: 0.52 µM) towards the reduction of nitrate ion and exhibited excellent performance in real sample analysis.

Estimation of Corrosion Potential of Aluminium Brazing Fillets Using Area Method

<div class="section abstract"><div class="htmlview paragraph">Open Circuit Potential (OCP) is the potential established between the working electrode (the metallic surface to be studied) and the environment, with respect to a reference electrode, which will be placed in the electrolyte close to the working electrode. It is very important to measure the electric potentials of various metallic materials in order to know their corrosion behavior in various environments. But perhaps if there is brazing joint involved, as in the case of aluminium heat exchanger components, there are some challenges involved in knowing the potential of the fillet part which includes the selective masking of the areas within the same sample for testing. Firstly, getting reliable & accurate data due to masking process is one concern. Secondly, about the aluminium heat exchanger sample, the variation in OCP values within a single sample are possible due to various factors i.e. presence of cladding on the surface of the materials, presence of sacrificial Zn coating on the microtubes, variation in brazing parameters etc.</div><div class="htmlview paragraph">In this study analytical correlation is made to OCP values of individual postbrazed child part samples w.r.t the entire brazed joint sample. This is being done in order to calculate & estimate the electric potential of the brazing fillet part. The individual currents at various areas within the sample w.r.t total specimen area are calculated & evaluated in order to arrive at a correlation between the observed potential vs. the sample area. From the obtained results it was found that the predicted theoretical fillet potential was in close agreement with the measured value. However, there is a scope of improvement in refining the simulation methods used in this study, in order to obtain more repeatable & accurate measurement OCP values.</div></div>

Effects of Current Density and Deposition Time on Corrosion Behaviour of Nickel-based Alloy Coatings

Corrosion of fasteners is an on-going issue and stainless steel 304 (SS304) is prone to this destructive process. One method to mitigate corrosion is electrodeposition of Co-Ni-Fe nanoparticles. This paper studied the effects of deposition time and current density on corrosion behaviour of Co-Ni-Fe coated SS304 bolt. Co-Ni-Fe ternary alloys were electrodeposited onto SS304 bolt in 15, 30, or 45 minutes by using current density of 28, 35, 42 mA/cm2. Combinations of these parameters produced 9 samples. These samples were electrochemically tested by a potentiostat using open circuit potential (OCP) and potentiodynamic polarization (PDP). The samples were also characterised in terms of surface roughness and thickness of the coatings by using 3D surface metrology system. The OCP value decreased when deposition time was increased. All sample synthesised in 30 minutes had a more stable OCP curve. PDP curves exhibited active behaviour without passivation region. The corrosion potential (Ecorr) of T15 samples was more anodic than T30 and T45 samples. The corrosion current density (Icorr) of all samples fluctuated. Sample synthesised in 30 minutes using 42 mA/cm2 had the lowest corrosion rate. It was found that the surface roughness influences the corrosion behaviour in which a lower surface roughness tends to produce coating with better corrosion performance. Current density had small effect on the thickness of coating, whereas the tendency of a thickness to increase was obvious for deposition time.

Corrosion, ion release, and surface hardness of Ti-6Al-4V and cobalt-chromium alloys produced by CAD-CAM milling and laser sintering

Statement of problemHow the corrosion properties of cobalt-chromium (Co-Cr) and Ti (Ti-6Al-4V) alloys, frequently used in dental prostheses, are affected by different production methods is unclear. PurposeThe purpose of this in vitro study was to compare Co-Cr and Ti-6Al-4V alloys produced by computer-aided design and computer-aided manufacturing (CAD-CAM) milling or laser sintering in terms of corrosion, ion release, and surface hardness. Material and methodsCo-Cr and Ti-6Al-4V specimens were produced by CAD-CAM milling and direct metal laser sintering/selective laser sintering techniques. Testing included Vickers hardness and then open circuit potential (OCP), Tafel extrapolation, and static immersion to determine the corrosion behavior. The study used an inductively coupled plasma mass spectrometer to measure ion release. The data were analyzed by using the Kruskal-Wallis and Mann-Whitney U tests, with Bonferroni correction (α=.05). ResultsThe Ti-6Al-4V laser-sintered group showed the highest Vickers hardness value (P<.008), the lowest OCP value (P<.008), and the lowest corrosion potential (Vcorr) value (P<.008). The corrosion current density (Icorr) level of the Co-Cr CAD-CAM milling group was statistically significantly lower than that of the Ti-6Al-4V CAD-CAM milling and the Ti-6Al-4V laser-sintered groups (P<.008). The highest weight change was observed in the Ti-6Al-4V laser-sintered group. The Co, Cr, and Ti ion emissions were higher in specimens produced by laser sintering (P<.05), and no statistically significant difference in terms of Al and V oscillations was found among the groups (P>.05). ConclusionsTi-6Al-4V alloys may be a good alternative for patients with Co-Cr allergies, but as per the results of this study, Co-Cr still seems more suitable for clinical use.

An Innovative Approach to Produce Magnetite Nanoparticles Synthesized by a Combined Electrochemical and Chemical Coprecipitation Method and their Electrochemical Monitoring

The synthesis of magnetite nanoparticles ( NPs) remains an interesting topic for the electrochemistry community. However, currently, there is still some lack of information related to their production. For instance, the basic reaction stages involved in electrochemical synthesis and their dependence on the oxygen concentration, the optimal polarization potential and the current density applied are parameters that should be agreed upon. In this work, a simple and innovative approach is presented not only to efficiently produce NPs but also their side products in a selective manner by controlling the dissolved oxygen in the reaction media. The approach includes a two-step methodology. First, is electrochemically produced. As a second step, the production of magnetite nanoparticles is carried out through a purely chemical method with different amounts of atmospheric oxygen, as oxidizing agent. Thus, it is demonstrated that the NPs are produced by chemical reactions rather than by an electrochemical process. Furthermore, through the acquisition of both open circuit potential and pH values as a function of time, it is possible to determine the optimal parameters, i.e., dissolved atmospheric oxygen and pH of the media, to selectively obtain not only NP but also byside products such as hematite, maghemite, akageneite and lepidocrocite.

Development of biofuel cell based on anode modified by glucose oxidase, Spirulina platensis-based lysate and multi-walled carbon nanotubes

In this study, the GC/PEI/CNT/S.p./GOx bioanode was successfully designed using the chemical oxidized multi-walled carbon nanotubes (CNT) and Spirulina platensis-based lysates that facilitate the electron transfer and reduce the open circuit potential (OCP) drop along the electron transfer pathway. Composition, morphology and chemical modification efficiency of CNT was examined using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and simultaneous thermal analysis (STA) coupled with mass spectrometric (MS) analysis of evolving gaseous species (TG/DTA–MS). The power density generated by GC/PEI/CNT/S.p./GOx bioelectrode was 21.8 times higher if S. platensis-based lysates were applied in bioanode design (than GC/PEI/CNT/GOx bioelectrode). The magnitude of maximal power density evaluated by linear sweep voltammetry (LSV) measurements was estimated to be 3.2 µW cm−2 at 213 mV voltage, whereas the bioelectrode act as a bioanode and bare glassy carbon as a cathode in a single-compartment biofuel cell design. Furthermore, the GC/PEI/CNT/S.p./GOx bioanode shows high long-term stability, while the magnitude of power density after seven days achieved approximately 89.6 % (2.87 µW cm−2) of its initial value. The initial OCP value of bioanode with S. platensis-based lysates was found to be -156 mV, which was reduced after the addition of 12.5 mM glucose. The equilibrated average value of OCP (-259 mV vs Ag/AgCl (3 M KCl)) indicates that glucose oxidase (GOx) immobilized on CNT functionalized with S. platensis-based lysates possess superior electron transfer and reduce the OCP drop along the electron transfer pathway.

The role of the electrical percolation threshold on the anticorrosion performance of an aqueous polyurethane dispersion containing polyaniline

In this study, the anticorrosion properties of a waterborne polyurethane dispersion (WPU) containing polyaniline (PAni) were investigated and discussed considering the electrical percolation threshold (EPT) of this mixture. For that, easily dispersible poly(styrene sulfonic acid)-doped PAni (PAni:PSS) was incorporated into an anionic WPU at contents ranging from 1 to 8 wt%. Free-standing films of PAni:PSS/WPU reached the EPT at 6 wt% (4.8 v.%) of PAni:PSS. The mixtures remained stable and without signs of PAni dedoping. Based on the electrical behavior curve, PAni:PSS/WPU coatings were prepared below (1, 2, 3 wt%), close to (5 wt%), at (6 wt%) and above the EPT (8 wt%). The coatings were applied on ground low-carbon steel panels and evaluated regarding their contact angle, adhesion, and anticorrosion performance in electrochemical tests. The coatings prepared below the EPT presented higher hydrophobicity, good wet adhesion, and higher open circuit potential (OCP) and impedance modulus in the low frequency range (|Z|10 mHz). The best overall performance was achieved at 3 wt% of PAni:PSS which presented OCP values in the range of 34 ± 11 mV for 144 h and initial |Z|10 mHz of 108 Ω.cm2. These coatings also presented a colorimetric feature of changing color as the corrosion progressed. Meanwhile, the coatings containing PAni:PSS quantities close, at and above the EPT, i.e., at 5, 6 and 8 wt% presented high porosity, poor wet adhesion, and intense blistering. They also presented OCP values in the region of active corrosion and impedance spectra typical of coatings with poor barrier properties. These results indicate that, the formation of conducting networks within the insulating matrix is not necessarily a condition that must be met for a coating containing PAni achieve an optimal anticorrosion performance.

Electrochemical Behavior of Co-Cr Alloy in Hygienic Tablets Solution

Objective The aim of this study was to evaluate the electrochemical behavior of a cobalt-chromium (Co-Cr) dental alloy after immersion in denture cleansers. Method: Twenty-four specimens (Ø13x2mm) of Co-Cr were produced and divided into three groups (n=8) according to their experimental condition. The group 1 (control group) was composed only of distilled water, group 2 received a hygienic tablet (Corega Tabs™) at the moment that electrochemical test started, while the group 3 received the hygienic tablet (Corega Tabs™) 1h after immersion. The electrochemical tests recorded the open circuit potential (OCP) and current density (icorr). The surfaces of specimens were examined using a SEM. Data were statistically analyzed using analysis of variance (ANOVA) and Duncan test’ multiple comparisons post hoc analysis (α=0.05). Results: The values of OCP and icorr revealed statistically differences between the groups. The highest results were recorded for group 2 (-26.87±48.48mV; 0.29±0.22μA), which were similar to group 3 (-47.37±35.36mV; 0.26±0.10μA), and these values were difference to group 1 (-314.87±24.22mV; 0.50±0.17μA). SEM image show high corrosion with Corega Tabs™. Conclusion: The immersion in denture cleanser solution was not detrimental to the Co-Cr dental alloy and presented a lower tendency to corrosion process development than the control group.