OCP Value Research Articles

High-efficiency dual protection of photoelectrochemical cathodic protection coating with In2O3/C3N4/CNT nanocomposites for 304 stainless steel in marine environment

A photoelectrochemical cathodic protection coating with EP/In2O3/C3N4/CNT composite was designed and its anti-corrosion mechanism was further investigated. It was found that the introduction of In2O3/C3N4 not only densified the microporous structure but also enhanced the hydrophobicity, tensile strength and UV aging resistance of epoxy resin (EP) coatings, improving the physical shielding effects of the coating. In addition, the photogenerated electrons produced by In2O3/C3N4 nanocomposites could transfer to surface of 304 SS through the electronic transmission network of CNT under illumination. Owing to its dual protection, the corrosion current (Icorr) of 304 SS/EP/In2O3/C3N4/CNT reduced by 95.8 % and 67.8 % of that of 304SS and 304 SS/EP in dark, respectively. Under illumination, the OCP values of EP/In2O3/C3N4 and EP/In2O3/C3N4/CNT composite coatings were rapidly shifted negatively to −170 mV and −274 mV, respectively, which were both lower than the self-corrosion potential of 304 SS. Therefore, the introduction of optoelectronic nanoparticles into coatings is believed to be an effective strategy for providing dual protection for metals, which not only improved the physical shielding effects of the coating but also enhanced the photocathodic protection performance at the dark state.

Experimental investigation on Nano-Al2O3 and hydroxypropyl methyl cellulose (HPMC) modified cement-based coatings for corrosion resistance

In this work, cementitious coatings doped with nano-Al2O3 (NA) and hydroxypropyl methyl cellulose (HPMC) were prepared in order to enhance corrosion resistance of steel bar. The electro-chemical behaviors and corrosion inhibition properties of coated steel bar and tensioned coated steel bars (subjected to 10 %, 30 % and 50 % yield load) were analyzed in 3.5 wt% NaCl solution for 840 h (35 days). At the end of electrochemical test, coating overall performance was evaluated by visual inspection. In addition, scanning electron microscopy (SEM), transmission electron microscopy (TEM) with energy dispersive spectroscopy (EDS) were used to examine microstructure and elemental composition of coatings. To comprehend the anti-corrosion mechanism of the coatings, X-ray diffraction (XRD) and infrared spectroscopy (FTIR) analysis to characterize products composition and chemical groups. Test results obtained by linear polarization resistance and electrochemical impedance spectroscopy indicated that both tensile and non-tensile coatings resistance show an increasing trend followed by a decrease with increasing NA content. Cementitious coatings incorporating 1 % NA and 0.12 % HPMC by weight of cement exhibited the best corrosion protection. The LPR fluctuates around 3700 Ω cm2, which is about twice as much as a single doped NA coating. Whether subjected to tensile loads or not, OCP values for all coated steel bar were below −0.273 V/SCE, indicating has a 90 % probability of being in active-corrosion. The corrosion resistance of tensioned coated bars decreased as time and increased load level. According to SEM and TEM image, HPMC forms a thin and continuous film on the substrate surface, which acts as a barrier to the penetration of moisture and corrosive agents. Coatings doped with 1 % NA and 0.12 % HPMC formed denser integrated polymer films at the microscopic. FTIR and XRD results showed that coating incorporated NA consumed the cement hydration product Ca(OH)2 to generate more nanofibers filling pores and microcracks. Coatings incorporating HPMC show better resistance to carbonization.

Photoelectrocatalytic efficiency of In2S3–In2O3 films as photoelectrodes/photocatalyst in hydrogen production reaction

In2S3–In2O3 films were used as photoelectrodes and photocatalysts for hydrogen production. The films were grown using a hydrothermal method for different reaction times (4, 6, 8, 12, 18 and 24h). The difference in the reaction time influences the presence of other crystalline phases, such as β-In2S3, In2O3, Ti3S4, and Ti5S8, on the film structure; the presence of these elements was verified by the XPS results. Furthermore, the mixture of phases generates different morphologies such as flowers, pyramids, and sheets. The best photoelectrochemical results were obtained from the films deposited at a reaction time of 6, 8, and 12 h, as these films have an OCP value of ∼0.3586, 0.3791 and 0.4771 VRHE and a photocurrent density of 3, 1.92, and 1.5 μA•cm−2 at 1.23 V vs. RHE, respectively. According to these results, the 12h/In2S3–In2O3 film has the highest donor density and the lowest Debye length, which enhances the efficiency of photogenerated electrons and electron-hole separation. Moreover, the highest photocatalytic hydrogen production was achieved with the 12h/In2S3–In2O3 film, which, in addition to presenting the most optimal photoelectrochemical properties, also has defects such as oxygen deficiencies, Ini and VIn, which could act as traps for electrons in the recombination process, increasing the reduction reactions at low energy and enhancing hydrogen production.

Electrochemical Characteristics of Microbial Fuel Cells Operating with Various Food Industry Wastewaters

In the present work, four different wastewaters from the food industry were used in parallel, in four identical dual-chamber MFCs, with graphite granules as anodic electrodes. Specifically, a mixture of hydrogenogenic reactor effluents (effluents from a dark fermentation reactor fed with cheese whey (CW), for hydrogen production), CW, and a mixture of expired fruit juices and wastewater from the confectionery industry were simultaneously used in MFCs to evaluate the effect of the type of effluent/wastewater on their efficiency. An electrochemical characterization was performed using electrochemical impedance spectroscopy measurements under open- (OCP) and closed-circuit conditions, at the beginning and end of the operating cycle, and the internal resistances were determined and compared. The results showed that the highest OCP value, as well as the highest power density (Pmax) and Coulombic efficiency (εcb) at the beginning of the operating cycle, was exhibited by the MFC, using a sugar-rich wastewater from the confectionery industry as substrate (sugar accounts for almost 92% of the organic content). This can be correlated with the low internal resistance extracted from the Nyquist plot at OCP. In contrast, the use of CW resulted in a lower performance in terms of OCP, εcb and Pmax, which could be correlated to the high internal resistance and the composition of CW, a substrate rich in lactose (disaccharide), and which also contains other substances (sugars account for almost 72% of its organic content, while the remaining 28% is made up of other soluble compounds).

Electrodeposition of organic corrosion inhibitor prepared from eucalyptus robusta leaves

Eucalyptus Robusta leaves were used as raw material to develop a steel corrosion inhibitor. A straightforward approach was employed to extract organic molecules from Eucalyptus Robusta leaves, which were applied as a protective coating on steel surfaces to inhibit corrosion. The solution containing the organic inhibitor was electrodeposited onto the surfaces of ASTM A36 steel samples, and an investigation into the parameters of charge (positive or negative), voltage (5 or 20 V), and time (5 and 30 min) was conducted through a 23 factorial experiment. Electrodeposited wet and dry samples had their open circuit voltage (OCP) measured in an acid solution and compared with the OCP of samples in which the inhibitor was deposited by simple immersion (deposited samples) and samples without inhibitor (blank samples). All the samples that had contact with the inhibitor increased their OCP values, showing the effectiveness of the deposition of the inhibitor. Nevertheless, the electrodeposition process carried out for 30 min and with a positive charge (anodic) proved to be the most effective in increasing the OCP value. Optical and scanning electron microscopy analyses revealed that the inhibitor solution effectively formed a thin, uniform, compact film on the metal surface. However, occasional deposition anomalies resulted in the formation of protrusions with organic material accumulation. Electrochemical Impedance Spectroscopy and Tafel curves were used to evaluate the effectiveness of the organic inhibitors. Accelerated corrosion tests in an HCl solution indicated reduced corrosion and the formation of distinct corrosion products for samples with an inhibitor compared to a sample without an inhibitor.

Structural, mechanical and tribocorrosion behaviors of Mo-Ni-Si alloys

Mo-Ni-Si alloys were fabricated using arc melting, and their structural and tribocorrosion behaviors were investigated. The results revealed that the alloys have good comprehensive mechanical properties and tribocorrosion resistance with increasing Mo content. The alloys exhibit lower friction coefficients and wear rates owing to the creation of the MoO3-NiO-SiO2 passivation layer. The wear rates of the alloys were approximately one-tenth of that of 0Cr18Ni9. During the tribocorrosion tests, the OCP values of the alloys are inversely related to the friction coefficient, which is attributed to the synergistic effect of wear and corrosion. The main tribocorrosion mechanisms for Mo-Ni-Si alloys are pure wear and preferential tribocorrosion of the NiMo phase, whereas the wear loss of 0Cr18Ni9 is dominated by corrosion-induced wear.

First Report of Organochlorine Pesticides and Heavy Metals in a Stranded Bottlenose Dolphin Off the Central Coast of Veracruz State: A Warning to Assess Pollution in a Reef Marine Ecosystem from the Gulf of Mexico

Live-strandings of cetaceans are uncommon in the southwestern Gulf of Mexico. However, an adult female bottlenose dolphin (Tursiops truncatus) with normal body condition was recorded at Pelicano’s Beach on the coast of Veracruz State. Health assessment showed multiple external injuries, possibly caused by the stranding event, as well as potential bacterial infection, and, thus, the individual was held in temporary facilities for rehabilitation. Blood samples were taken to assess the health status of the individual and were also analyzed for concentrations of 20 pollutants (14 organochlorine pesticides [OCPs] and six heavy metals [HMs]). The animal was released and found dead within a few days. The concentration of OCPs and HMs were close or above the government limits. Although these were lower than those reported in other living, free-ranging bottlenose dolphins, there are well-known negative effects for health. Low OCP values were attributed to an offloading process through lactation or mobility of the lipophilic OCPs that pass from blood to fat. Whereas HM concentrations (mainly non-essential metals: mercury [Hg], lead [Pb], and cadmium [Cd]—2.73, 21.13, and 12.67 µg L-1, respectively) were probably linked to the diet and the possible distribution of the specimen (possibly offshore). This is the first report on pollutants from anthropogenic origin in the area where uncontrolled activities are of major concern within a protected national reef park. Since marine ecosystems are under continuous pressure, several health issues for top predators are being noticed; therefore, this study underlines the relevance of studying health status of marine mammals in the Mexican waters of the Gulf of Mexico.

Tribocorrosion behavior of Ti-Nb-5Mo alloys designed for biomedical applications

This study investigated the tribocorrosion behavior of three alloys of the Ti-xNb-5Mo system. OCP and COF values were monitored, and the alloys' repassivation rate was calculated after sliding. The wear volume of the alloys was calculated by analyzing the profilometry results obtained by confocal microscopy. The alloy with the highest hardness (Ti-20Nb-5Mo) had the lowest wear volume (0.06 ± 0.02 mm³). Furthermore, OCP results during sliding showed that increasing Nb content increased the corrosion resistance of the alloys.

Polypyrrole zinc-doped film deposited on a plasma-treated surface improves the tribocorrosion behavior of titanium dental implant material

Polypyrrole (PPy) films have shown attractive electrochemical properties and promising implant applications when electrodeposited on plasma electrolytic oxidation (PEO) surfaces. Although the PEO + PPy surface demonstrates excellent mechanical and electrochemical performance, there are no reports on the effects of combined corrosion and mechanical interactions, which simulates the oral environment. In addition, since implant failures may be related to deficiencies in the osseointegration process, the electrodeposition of zinc (Zn) on the coating can promote an osteogenic substrate. Therefore, we aimed to investigate the tribocorrosion behavior of PEO-treated surfaces coated with PPy films with and without Zn and whether such PPy films affect the cellular response of MG-63 human osteoblast-like cells. Titanium discs with machined and PEO-modified surfaces were considered as controls. The experimental groups used PEO surfaces followed by electrodeposition of PPy (PEO + PPy) and PPy and Zn (PEO + PPy/Zn). The surfaces' physical-chemical properties were assessed. The tribocorrosion tests were run under free potential and potentiostatic (anodic and cathodic potentials) conditions using a pin-on-disk tribosystem simulating the oral environment (load = 1 N, stroke = 2 mm, number of cycles = 2000). Electrochemical impedance spectroscopy was performed before and after tribocorrosion to analyze the changes in corrosion kinetics. Worn areas were observed using white-light-interferometry and scanning electron microscopy. For in vitro cell experiments, the viability, number of live/dead cells, adhesion ability, and mineralization property of cells were evaluated. Our outcomes revealed that PPy films improved tribocorrosion performance by exhibiting more positive OCP values and slight fluctuation and variation of the current value during the sliding phases. In general, due to the films' morphology and “cushion effect”, PPy films enhanced the surface resistance against corrosion and wear, indicating a low total weight loss (Kwc) and wear-corrosion degradation mechanism. The PEO + PPy/Zn surface was cytocompatible, enhancing the cell adhesion and proliferation on the surface. Overall, PPy films represent a promising coating to improve the stability and lifetime of biomedical implants.

Electrochemical study of three new morpholine-based inhibitors for P460N steel in 3.5 wt. % NaCl solution

BackgroundCorrosion of steel occurs due to the rough working environment in which it is used. It accelerates the deterioration of the steel components and results in substantial financial loss. Continuous research has been carried out to prevent or reduce the corrosion of steel and other metals because these materials have so many industrial applications. MethodsThe inhibition performance of three new organic substances, N1-(3-morpholinopropyl)-N1-((pyridine-2-yl)methyl)propane-1,3-diamine (I1), 2‑methoxy-6-(((3-((3-morpholinopropyl)(pyridin-2-ylmethyl)amino)propyl)imino)methyl)phenol (I2), and its reduced form, 2‑methoxy-6-(((3-((3-morpholinopropyl)(pyridin-2-ylmethyl)amino)propyl)imino) methyl) phenol (I3), on corrosion of the P460N in 3.5 wt.% NaCl solution was investigated by potentiodynamic polarization (PDP), EIS, immersion tests, and SEM techniques. Significant findingsA novel material exhibiting superior corrosion protection capabilities for steel was synthesized, and its efficacy was validated through both electrochemical and non-electrochemical testing methods. Comparing the OCP values in the blank and inhibitor-containing solutions shows a negative shift. According to PDP experiments, the highest value of icorr occurs with the P460N electrode in the inhibitor-free solution (79.4 μA.cm−2). Meanwhile, in the case of the highest concentration of I1, I2, and I3 inhibitors, a significant reduction in the corrosion rate was observed, with reductions of 6, 17, and 22 times, respectively. Notably, the reduced form (I3) exhibited exceptional protection against corrosion. PDP results confirmed that the inhibition efficiency reached the highest value of 84.1, 94.3, and 95.5% for I1, I2, and I3 at 2.0 mM concentration. From the EIS measurements, the inhibition performance of inhibitors follows the order I3 > I2 > I1 at equal concentration. Based on the immersion test results and SEM-EDS evaluation, the reduced sample (I3) demonstrated significantly lower corrosion over an extended period, indicating excellent long-term stability in the 3.5% NaCl solution. The electrochemical (PDP and EIS), and non-electrochemical (immersion tests) data confirmed that the inhibition efficiency of the inhibitor of I3 was better than the two other compounds. SEM and EDS analysis showed severe corrosion for the P460N surface without an inhibitor, and corrosion products such as iron oxide and trapped NaCl in porosity appeared very uneven, with different shapes. The study explored four absorption mechanisms: Langmuir, Temkin, Freundlich, and Frumkin. The three new inhibitors were found to adhere to the Langmuir adsorption isotherm with a high correlation coefficient of approximately 0.999. Moreover, these inhibitors demonstrated mixed inhibition behavior for P460N steel in a 3.5% NaCl solution.

Methane to Methanol Conversion Using Proton-Exchange Membrane Fuel Cells and PdAu/Antimony-Doped Tin Oxide Nanomaterials

This study investigates the use of Au-doped Pd anodic electrocatalysts on ATO support for the conversion of methane to methanol. The study uses cyclic voltammetry, in situ Raman spectra, polarization curves, and FTIR analysis to determine the optimal composition of gold and palladium for enhancing the conversion process. The results demonstrate the potential for utilizing methane as a feedstock for producing sustainable energy sources. The Pd75Au25/ATO electrode exhibited the highest OCP value, and Pd50Au50/ATO had the highest methanol production value at a potential of 0.05 V. Therefore, it can be concluded that an optimal composition of gold and palladium exists to enhance the conversion of methane to methanol. The findings contribute to the development of efficient and sustainable energy sources, highlighting the importance of exploring alternative ways to produce methanol.

Microstructure, mechanical properties and tribocorrosion characteristics of (Mo1-xCrx)5Si3 alloys

(Mo1-xCrx)5Si3 alloys were prepared by vacuum arc melting technique. The microstructure and mechanical properties of (Mo1-xCrx)5Si3 alloys were characterized using a scanning electron microscope (SEM), X-ray diffraction (XRD) and nano-indentation tests. The tribocorrosion characteristics of the alloys were investigated using a tribocorrosion tester in 3.5 wt% NaCl solution. The results revealed that the thermal expansion anisotropy ((CTE(c)/CTE(a))) of the (Mo1-xCrx)5Si3 alloys decreased from 2.25 to 1.45 with increasing Cr content. The Cr-alloyed (Mo1-xCrx)5Si3 alloys exhibited a high hardness, and their fracture toughness, ratios of H3/E2 and H/E were improved. (Mo1-xCrx)5Si3 alloys showed a strong wear-corrosion combined effect, and an opposite trend between friction coefficient and OCP values was observed during the tribocorrosion tests. The tribocorrosion resistances of (Mo1-xCrx)5Si3 alloys were better than that of 0Cr18Ni9 stainless steel due to the formation of Cr2O3-MoO3-SiOx protective films. The (Mo0.8Cr0.2)5Si3 alloy exhibited the best tribocorrosion characteristics with a low friction coefficient and wear rate. For the 0Cr18Ni9 and Mo5Si3 alloy, pure wear (Vw) was dominant, nevertheless, corrosion-induced wear (Vcw) was the main tribocorrosion mechanism of (Mo0.8Cr0.2)5Si3 alloy.

High-efficiency photocathodic protection performance of novel MnIn2S4/TiO2 n-n heterojunction films for Q235 carbon steel in chloride-containing simulated concrete pore solution

In this work, the n-type TiO2 nanotube film was modified successfully by n-type MnIn2S4 nanoparticles with one-step hydrothermal method, and a novel MnIn2S4/TiO2 heterojunction material with excellent photoelectrochemical properties was constructed firstly. Owing to the modification, the light response range of MnIn2S4/TiO2 nanocomposites was extended to the visible light region. Benefiting from the presence of type II n-n heterojunction with built-in electric field effects in the nanocomposites, the photogenerated carriers recombination rate decreased significantly. In addition, the photocathodic protection effects of MnIn2S4/TiO2 (MIS/T) photoanodes on Q235 carbon steel (Q235 CS) immersed in simulated concrete pore solution containing chloride were investigated. Under visible light irradiation, the cathodic protection current density of MIS/T-2 photoanode was found to be more than 30 μA/cm2 and over 10 times that of T photoanode. The MIS/T-2 photoanode has good long-term photochemical stability and maintains excellent photocathodic protection effect on Q235 CS (OCP value are about - 870 mV (vs. SCE)) under visible light irradiation. The amount of MnIn2S4 nanoparticles deposited on the TiO2 film could affect the photoelectrochemical properties of MnIn2S4/TiO2 n-n heterojunctions and an appropriate number of the nanoparticles, corresponding to the best cathodic protection performance was revealed.

Selection of New Heat Treatment Conditions for Novel Electroless Nickel-Boron Deposits and Characterization of Heat-Treated Coatings

Electroless nickel-boron coatings were deposited from a novel deposition bath that was stabilizer-free. Those coatings were analyzed by DSC to determine the crystallization temperature of nickel-boride phases, and then the best heat treatment conditions for the new coatings were selected using the Knoop hardness test and XRD. The results of DSC analysis and XRD were coherent with the findings of previous studies, which shows that the new coating has a boron content lower than 4% wt. The maximum hardness was obtained after heat treatment at 300 °C for 4 h and reached 1196 ± 120 hk50, which is much higher than the as-deposited coating. The heat-treated coatings were then fully characterized using optical and scanning electron microscopy, as well tribological and corrosion tests. Various sliding tests (ball-on-disk and ball-on-flat configurations) were conducted to analyze the coefficient of friction (COF) and wear behavior of the coatings. The maximum von Mises stress was calculated, and values of 624 MPa and 728 MPa were obtained for the ball-on-disk and ball-on flat, respectively, at a depth close to 14 µm from the surface, confirming the suitability of the applied load. Abrasive, adhesive, and fatigue wear mechanisms were observed on the worn sample morphology using SEM. It has been determined that during the corrosion test the OCP and corrosion potential values for the heat-treated coating increase as compared with the as-deposited one, whereas its corrosion resistance decreases.

Application of ginger and grapefruit essential oil extracts on the corrosion inhibition of mild steel in dilute 0.5 M H2SO4 electrolyte

Admixture of ginger and grapefruit essential oils (GPP) were studied for their corrosion inhibition properties on mild steel (MS) in 0.5 M H2SO4 solution by potentiodynamic polarization, open circuit potential measurement, electrochemical impedance spectroscopy, weight loss analysis and ATF-FTIR spectroscopy. Results from potentiodynamic polarization shows GPP significantly reduced the corrosion of MS from 8.430 mm/y at 0% GPP concentration to values between 1.979 mm/y and 0.565 mm/y. The corresponding inhibition efficiency values ranged from 76.52% to 93.5% and corrosion current density from 1.88 × 10−4 A/cm2 to 5.36 × 10−5 A/cm2. GPP displayed mixed-type inhibition at all GPP concentrations studied. The OCP plot at 0% GPP initiated at -0.495V compared to -0.443V and -0.451V at 1% and 3.5% GPP. At 9000s, the corresponding OCP values are -0.442V, -0.410V and -0.424V due to electropositive plot shift and passivation of MS surface at 1% and 3.5% GPP, though significant potential transients were present on the OCP plot at 1% GPP. The electrochemical impedance results indicate that the corrosion resistance of MS increased from 4.402 Ω cm2 to 99.318 Ω cm2 upon the addition of 3.5% GPP resulting in inhibition efficiency of 96%. Data from weight loss analysis shows decrease in corrosion rate from 184.48 mm/y to values between 8.94 mm/y and 6.25 mm/y. The corresponding inhibition efficiency values varies from 95.16% at 1% GPP to 96.61% at 3.5% GPP concentration. The ATF-FTIR results confirm the adsorption of GPP molecules on the surface of the carbon steel electrode.

Electrochemical and XPS investigations on the galvanic interaction between pentlandite and pyrrhotite in collectorless flotation system

Pentlandite and pyrrhotite are ubiquitously symbiotically aggregated with each other, and the galvanic interaction between them inevitably occurs in flotation process. However, there were few detailed researches regarding this galvanic interaction and its effect on the surface oxidation of pentlandite and pyrrhotite that has been reported. In this work, the galvanic interactions and its influence on the surface oxidation and collectorless flotation behaviors of pentlandite and pyrrhotite were systematically researched at pH 8.5. Results of electrochemical measurements showed that pentlandite had a higher OCP value than pyrrhotite, indicating that pentlandite would act as the cathode, while pyrrhotite acted as the anode in the galvanic couple. Compared to the minerals oxidized solely, a more passivated surface was found for both pentlandite and pyrrhotite. ICP-OES and XPS analyses demonstrated that in the presence of pyrrhotite, a thicker iron oxide/hydroxide film was obtained with a decrease in the species of sulfate and nickel oxide/hydroxide on pentlandite surface. For pyrrhotite, within the galvanic interaction, the oxidation and metal dissolution of pyrrhotite was accelerated. However, the hydrogen ion generated in the anodic reaction would hinder the precipitation of iron oxide/hydroxide and sulfate on pyrrhotite surface. Micro-flotation results further confirmed that the galvanic interaction between pentlandite and pyrrhotite significantly affected their collectorless flotation behaviors, which was also affected by the relative content ratio between them. This work systematically studied the galvanic interaction and its role in the surface oxidation in pentlandite/pyrrhotite collectorless flotation system, which could also provide reference for the further study on complex Ni-bearing sulfide minerals flotation.

Corrosion resistance of NiCr(Ti) coatings for metallic bipolar plates

In the present work, the electrochemical behavior of various NiCr(Ti) protective coatings manufactured using laser cladding were studied. The coatings were obtained by adding Ti in different wt% to the NiCr-based feedstock material. Thus, the coatings are investigated as new materials with potential applications for metallic bipolar plates used in polymer electrolyte membrane fuel cell (PEMFC) applications. The electrochemical tests were carried out at room temperature in a solution of H2SO4 0.5 M (pH = 0.3) + 2 ppm F- used as electrolyte. Chronoamperometry measurements were first employed in simulated anodic and cathodic conditions for 6 h. Afterward, electrochemical impedance spectroscopy (EIS) studies were performed in the frequency range of 100 mHz − 100 kHz with an alternative voltage amplitude of 10 mV. The recorded EIS data were fitted with an equivalent electrical circuit (EEC). Furthermore, the potentiodynamic polarization curves were recorded at a scan rate of 1 mV/s in the potential range of −250 mV to + 250 mV versus to the OCP values. Finally, the obtained data were analysed and compared. The studies showed that the corrosion behavior of the studied materials increase with the content of Ti addition.

Phosphate sealing improvement of the corrosion resistance of thin cerium oxides coatings electroless deposited on aluminium

The corrosion-protective ability was investigated of electroless deposited ceria conversion coatings on substrate(s) of technically pure aluminium. By applying different electrochemical methods, a comparative study of the investigated samples was conducted regarding the effect of pre-treatment of the Al substrate and the type of phosphate post-treatment on the change of: E OCP values, monitored EOCP vs. time plot; course of i a transients at the Epit of Al, i.e., ia vs. time plot; Rp vs. time of exposure of the samples in a corrosion medium and connected with this change in the CR of the systems studied. The juxtaposition of the obtained results showed the order of stabilities of the investigated systems towards the appearance and development of pitting corrosion. The presented results can be connected with and explain the data obtained earlier about the calculated stoichiometry of the elements in the so-formed compounds in the surface layers ascertaining that they are built of phosphate and oxide compounds of Ce3+, Ce4+ and Al3+, as well as with the influence of the concentrations of Cu and Fe around them.

Transient potentiometry based d-serine sensor using engineered d-amino acid oxidase showing quasi-direct electron transfer property

d-Serine biosensing has been extensively reported based on enzyme sensors using flavin adenine dinucleotide (FAD) -dependent d-amino acid oxidase (DAAOx), based on the monitoring of hydrogen peroxide generated by the enzymatic reaction, which is affected by dissolved oxygen concentration in the measurement environment in in vivo use. Here we report a novel sensing principle for d-serine, transient potentiometry based d-serine sensor using engineered DAAOx showing quasi-direct electron transfer (DET) property. DAAOx Gly52Val mutant, revealed to possess dye-mediated dehydrogenase activity using artificial synthetic electron acceptors, while its oxidase activity was negligible. The enzyme was immobilized on electrode and was modified with amine-reactive phenazine ethosulfate, resulted an enzyme electrode showing quasi-DET type response. Although OCP based monitoring took more than several minutes to obtain steady state OCP value, the time dependent OCP change monitoring, transient potentiometry, provided rapid and sensitive sensor signals. While dOCP/dt based monitoring was suitable for sensing with longer than 5 s time resolution with d-serine concentration range between 0.5 mM and 5 mM, dOCP/d t based monitoring is suitable for d-serine monitoring with much shorter time resolution (less than 1 s) with high sensitivity with wider dynamic range (20 μM–30 mM). The maximum dOCP/d t was −39.2 ± 2.0 mV/s1/2, the Km(app) was 1.9 mM, and the lower limit of detection was 20 μM. In addition, d-serine monitoring was also possible in the artificial cerebrospinal fluid. The transient potentiometry based sensing reported in this study will be further utilized to realize miniaturized, continuous, real-time, in vivo sensor for d-serine monitoring.

Tribological properties of Ti3C2Tx MXene reinforced interpenetrating polymers network coating

Multiple advantages of Ti3C2Tx MXene are of significance to enhance the mechanical properties of organic coating. Herein, few-layer amino-functionalized Ti3C2Tx nanosheets (k-Ti3C2) were introduced into interpenetrating polymers network (IPN) for constructing k-Ti3C2/IPN composite coatings, and their tribological properties were investigated in depth. The composite coating with 0.75 wt% k-Ti3C2 nanosheets displays excellent tribological behaviors under extremely operating conditions, like the lowest COF (0.18) and the highest OCP value (−0.28 V) under tribocorrosion condition. Such excellent tribological properties mainly depend on good dispersion and interfacial compatibility of k-Ti3C2 nanosheets in IPN matrix, as well as amino functionalized Ti3C2Tx nanosheets as barrier to external damage. This work highlights a pathway to solve the wear/corrosion problem of organic coatings under extreme conditions.