An in situ Electrochemical Study of Electrodeposited Nickel and Nickel-Yttrium Oxide Composite Using Scanning Electrochemical Microscopy

Electrodeposited nickel and nickel-yttrium oxide composite samples were studied in situ using scanning electrochemical microscopy (SECM). The monitored probe currents in phosphate-citrate buffer (pH 4.2) in the presence or absence of Ru(NH3)63+ as an oxidizing mediator near the Ni surface show that the SECM is a useful tool for study of the electrochemical activity of heterogeneous metal surface at micrometer scales. The SECM ultramicroelectrode probe tip provides information about the shape, activity and location of particles, such as Y2O3 introduced (co-deposited) in the Ni-matrix of the composite. Experiments show that the Ni-matrix in the composite coating is more active than the pure Ni-coating. This fact is expected, because of texture changes in the Ni structure upon introduction (by co-deposition) of Y2O3 particles. In the absence of mediator in the solution, the electrochemical activity of heterogeneous metal surface at a micro-level is investigated by using O2 concentration changes. The rate of reaction for O2 reduction was found to locally vary at electrodes floating at the open-circuit potential (o.c.p) when compared to an electrode potentiostatically polarized at a more positive potential than the o.c.p. This behavior suggests that local anode and cathode regions are being observed at the o.c.p. sample

Comparison of soil properties measurements in pipeline corrosion estimation

Soil corrosion is a hazardous electrochemical process that affects buried metals in contact with soil. Corrosion in soils resembles atmospheric corrosion with corrosion rates usually higher and depending on the soil type. There are numerous properties of soil and thus soils can be classified in many different ways. Soil resistivity is one of the main indicators of soil corrosivity and thus of the hazardous impact the soil has on metal materials in soil environment, although it is not the only parameter affecting the risk of corrosion damage. In this work on-site measurements and laboratory measurements of soil characteristics are performed and compared. On- site measurements include measuring the redox potential and soil resistivity by Wenner 4-pin method, while the measurements in laboratory include measuring soil conductivity, as well as moisture content, pH, content of sulphates, chlorides and sulfides and polarization measurements, which give the most accurate results. The measurements have shown that if the Wenner 4- pin method is performed in a convenient way the obtained results are not precise but can give an indicative picture of the corrosivity of the observed soil

Effect of Laminar Flow on the Corrosion Activity of AA6061-T6 in Seawater

The electrochemical behaviour and surface changes on AA6061-T6 alloy exposed to Caribbean seawater from the Cozumel Channel for 30 days under laminar flow (0.1 ms−1) were studied, these contrasting then with stationary conditions. Open circuit potential monitoring and electrochemical current fluctuations, considered as electrochemical noise (EN), were employed as two nondestructive methods. The calculated corrosion current, based on Rn, was one order higher in laminar flow. The fluctuations of current were transformed in the frequency domain. Their power spectral density (PSD) plots were obtained in order to gain information concerning the dynamic of the spontaneous release of energy during the corrosion process. The value of the exponent β in PSD graphs suggested that the localised corrosion on AA6061-T6 surface occurs as a persistent stationary process, which dynamic is controlled by oxygen diffusion. The changes in the morphology and elemental composition of the formed layers revealed that the localised attacks occurred in the vicinity of intermetallic particles rich in Fe and Cu, which act as cathodes

Early stages of zinc corrosion and runoff process induced by Caribbean sea water

Flat samples of electrolytic zinc were immersed for periods of 8, 10, 30 and 90 days in Caribbean Sea water for further analysis of the corrosion behavior and runoff process using different techniques. The free corrosion potential (o.c.p.) were monitored and correlated with the runoff rate. The Zn2+ ions released from anodic sites interact with the OH- ions formed at the cathodic sites, giving origin to the slightly soluble Zn(OH)2 precipitated during the experiment. X-ray diffraction analysis revealed the formation of several zinc hydroxides. The main corrosion product was simonkolleite [Zn5(OH)8Cl2.H2O], and as minority phases two zinc carbonate hydroxides, [Zn5(CO3)2(OH)6] and [Zn4CO3(OH)6.H2O], and later stages Mg9Zn4(SO4)2(OH)22.8H2O and Zn(OH)2. The changes of pH in the interface zinc/substitute ocean water were monitored in situ with scanning electrochemical microscopy (SECM) technique and the local anodic and cathodic sites were mapped. Due to the corrosion reaction, the initial pH of sea water was diminished to 4.4 at the anodic sites as a consequence of metal ion hydrolysis. This fact leaded to the formation of a complex variety of zinc corrosion products, consuming at least a fraction of the produced OH- ions

The Activity of Silicon Carbide Particles in Al-Based Metal Matrix Composites Revealed by Scanning Electrochemical Microscopy

Scanning electrochemical microscopy (SECM) is used to image variations in electrochemical activity over the surface of an aluminum-based metal matrix composite (MMC) in contact with buffered or unbuffered neutral solutions. The composite consists of an Al - 13.5% Si - 9% Mg alloy matrix and reinforcing silicon carbide particles (SiCp). Feedback mode SECM imaging using ferrocenemethanol as a redox mediator in 0.1 M NaCl solution and in buffer solution (pH 6.8) revealed that the SiC particles are electrochemically active. The data suggest that the electronic conductivity at these sites is higher than that of the Al2O3 film covering the alloy matrix surface. The reduction of dissolved oxygen on the silicon carbide particles was investigated by in situ SECM images of samples and current vs. tip-substrate distance curves. The results with samples of SiCp/Al composites immersed in distilled water alone or in either 0.1 M NaCl or boric acid/borax buffer containing ferrocenemethanol as mediator demonstrate that the silicon carbide particles are conductive and act as local cathodes for the reduction of oxygen

Mapping of local corrosion behavior of zinc in substitute ocean water at its initial stages by SVET

The recent advent of a number of local probe techniques is greatly contributing to overcome some limitations when applied to the investigation of corrosion processes in situ. The scanning vibrating electrode technique is one of them, and it is based upon the measurement of potential field distributions in the electrolyte surrounding an electrochemically-active surface. The localized distributions of anodic and cathodic activities on zinc metal/electrolyte interface, exposed to substitute ocean water (diluted 1:1000), have been mapped in situ using SVET. The data provide in situ information on the local ionic fluxes produced in the electrolyte as result of the electrochemical corrosion reactions that occurred on the zinc surface, even in the first hours of the process. The maps demonstrated the evolution of the corrosion process, since the nucleation and propagation of corroding pits on the metal. The time evolution of the maps allows to more adequately characterize the complex chemical process involved in zinc corrosion in sea-water with high spatial resolutio

Challenges to Satellite Sensors of Ocean Winds: Addressing Precipitation Effects

Measurements of global ocean surface winds made by orbiting satellite radars have provided valuable information to the oceanographic and meteorological communities since the launch of the Seasat in 1978, by the National Aeronautics and Space Administration (NASA). When Quick Scatterometer (QuikSCAT) was launched in 1999, it ushered in a new era of dual-polarized, pencil-beam, higher-resolution scatterometers for measuring the global ocean surface winds from space. A constant limitation on the full utilization of scatterometer-derived winds is the presence of isolated rain events, which affect about 7% of the observations. The vector wind sensors, the Ku-band scatterometers [NASA\u27s SeaWinds on the QuikSCAT and Midori-II platforms and Indian Space Research Organisation\u27s (ISRO\u27s) Ocean Satellite (Oceansat)-2], and the current C-band scatterometer [Advanced Wind Scatterometer (ASCAT), on the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT)\u27s Meteorological Operation (MetOp) platform] all experience rain interference, but with different characteristics. Over this past decade, broad-based research studies have sought to better understand the physics of the rain interference problem, to search for methods to bypass the problem (using rain detection, flagging, and avoidance of affected areas), and to develop techniques to improve the quality of the derived wind vectors that are adversely affected by rain. This paper reviews the state of the art in rain flagging and rain correction and describes many of these approaches, methodologies, and summarizes the results

SVET study of the interaction of 2-Mercaptobenzothiazole corrosion inhibitor with Au, Cu and Au-Cu galvanic coupling

This study reports an electrochemical investigation of the interaction between 2-mercaptobenzothiazole (2MBT), a corrosion inhibitor, and two noble metals (Cu and Au), either isolated or under galvanical coupling. The surface reactivity of the inhibitor-modified metals in chloride-containing aqueous solution of 0.1 mM NaCl was studied using the Scanning Vibrating Electrode Technique (SVET). The potential gradients in the electrolyte were detected by the SVET and converted to local ionic currents distributed at different anodic and cathodic sites, where electrochemical redox reactions are taking place. No external polarization was applied during SVET measurements, leaving the samples at the spontaneous free corrosion potential (FCP). The values of FCP showed that the metals are not protected by 2MBT. SVET revealed a moderate electrochemical activity of Au and very low in the case of Cu

Investigating metal-inhibitor interaction with EQCM and SVET: 3-amino-1,2,4-triazole on Au, Cu and Au-Cu galvanic coupling

In this work, the scanning vibrating electrode technique (SVET) and the quartz crystal microbalance technique (EQCM) were used to characterize the electrochemical interaction of two corrosion inhibitors, 2-Mercaptobenzothiazole and 3-Amino-1,2,4-triazole (ATA), in Au and Cu samples individually and with both metals connected in order to form a galvanic pair Au-C

CSF concentrations of soluble TREM2 as a marker of microglial activation in HIV-1 infection

Objective: To explore changes in CSF sTREM2 concentrations in the evolving course of HIV-1 infection. Methods: In this retrospective cross-sectional study, we measured concentrations of the macrophage/microglial activation marker sTREM2 in CSF samples from 121 HIV-1–infected adults and 11 HIV-negative controls and examined their correlations with other CSF and blood biomarkers of infection, inflammation, and neuronal injury. Results: CSF sTREM2 increased with systemic and CNS HIV-1 disease severity, with the highest levels found in patients with HIV-associated dementia (HAD). In untreated HIV-1–infected patients without an HAD diagnosis, levels of CSF sTREM2 increased with decreasing CD4+ T-cell counts. CSF concentrations of both sTREM2 and the neuronal injury marker neurofilament light protein (NFL) were significantly associated with age. CSF sTREM2 levels were also independently correlated with CSF NFL. Notably, this association was also observed in HIV-negative controls with normal CSF NFL. HIV-infected patients on suppressive antiretroviral treatment had CSF sTREM2 levels comparable to healthy controls. Conclusions: Elevations in CSF sTREM2 levels, an indicator of macrophage/microglial activation, are a common feature of untreated HIV-1 infection that increases with CD4+ T-cell loss and reaches highest levels in HAD. The strong and independent association between CSF sTREM2 and CSF NFL suggests a linkage between microglial activation and neuronal injury in HIV-1 infection. CSF sTREM2 has the potential of being a useful biomarker of innate CNS immune activation in different stages of untreated and treated HIV-1 infection