1,721,014 research outputs found
Role of Molybdenum on the Electronic Properties of Passive Films on Stainless Steels
No full textPotentiostatic polarization of different stainless steel grades with a mirror surface finishing was performed in order to investigate the role of Mo on stainless steels corrosion behaviour. In the attempt to gain more insight into transpassive dissolution mechanism, passive films were grown in neutral aqueous solution (pH ∼ 7) at different polarizing potentials ranging from passive to transpassive conditions. According to the photoelectrochemical characterization, Cr dissolution occurs even at low polarizing potentials in the case of AISI 304L, while higher band gap values were obtained for passive films grown on austenitic 316L and duplex SSs. Capacitance measurements suggest that the flat band potential values estimated for passive films grown on austenitic 316L and duplex SS are more noble if compared to that of AISI 304L at all polarizing potentials. This is rationalized by considering that passive films on 316L and duplex are doped with Mo during film growth, changing their electronics properties (band gap and flat band potential) with a consequent shift to more positive value of the potential for chromate formation and dissolution
Corrosion resistance of passive films on different stainless steel grades in food and beverage industry
No full textPassive films were grown on 304 L, 316 L and Duplex stainless steels by immersion at open circuit potential in solutions mimicking food and beverage industry environments. In acidic food stainless steel surfaces are covered by Cr rich passive films, and generalized dissolution occurs on their surface with consequent ions release into the electrolyte. In fatty food the concentration of released ions is significantly lower since generalized corrosion does not occur, but the loss on MnS inclusions strongly reduces the polarization resistance in this environment especially for 304 L due to its higher localized corrosion susceptibility with respect to the other grades
Semiconducting properties of passive films and corrosion layers on weathering steel
No full textAnodic films were grown on Weathering Steel by potentiostatic polarization in slightly alkaline solution. The photoelectrochemical results reveal that they are n-type iron oxide with Eg = 2.0 eV. Rust layer grown by atmospheric corrosion are n-type semiconductors with a band gap higher than that estimated for the anodic film attributed to the formation of γ-lepidocrocite. The electrochemical impedance spectra allow to evidence that rust layers have a higher conductivity with respect to anodic films due to the presence of highly doped iron oxide layers. The use of Mott-Schottky theory to model the dependence of oxide capacitance as function of potential is critically discussed
Sea Surface Temperatures and Paleoenvironmental Variability in the Central Mediterranean During Historical Times Reconstructed Using Planktonic Foraminifera
Full text linkThe ongoing anthropogenic‐induced warming assessment requires a robust background from
regional sea surface temperature (SST) reconstructions. Planktonic foraminifera have yielded valuable
insights into late Quaternary SST dynamics, but the techniques to estimate SST from fossil assemblages have only rarely been used in very recent sedimentary records (the last 2,000 years). Here we use two transfer function methods, modern analog technique and artificial neural networks, to reconstruct SST variability in two cores from the Central Mediterranean Sea that span the last five centuries. Both cores show similar and considerable changes in the planktonic foraminifera assemblages. However, the inferred mean annual SSTs only varied in a narrow range, in agreement with instrumental data that go back to 1850 CE. Our
reconstructions extend this time frame and indicate that SST variability did not exceed 1.5 °C over the past
three centuries. Rather than temperature, we suggest that the changes in the assemblages reflect switches
between sea surface winter/spring productivity and a deep winter mixed layer, due to the atmosphere/ocean
interplay that governs different productivity modes in neighboring mesoscale gyres
Studio della resistenza alla corrosione di acciai impiegati nell’industria alimentare e delle bevande
Full text linkIn the present study we performed the physico-chemical characterization of passive films grown on different stainless steel grades after long exposure time in hot purified water (HPW). In order to get more insight into dissolution phenomena that can induce rouging on equipment materials typically involved in food and beverage industries, 304L, 316L and a super duplex 2507 SS samples were passivated at the open circuit potential by different immersion times in HPW at 60°C. Photoelectrochemical and Electrochemical Impedance measurements were performed in the attempt to correlate the electronic properties of the passive films (band gap and conductivity type) to their corrosion resistance
The Effect of Anodizing Bath Composition on the Electronic Properties of Anodic Ta-Nb Mixed Oxides
Full text linkAnodic oxides were grown to 50 V on Ta-Nb sputtering deposited alloys, with high Nb content, in acetate ions containing an aqueous solution to study the effect of the anodizing bath composition on anodic layers' dielectric properties. Photoelectrochemical measurements proved the presence of a photocurrent in the band gap of photon energy lower than oxides, due to optical transitions involving localized electronic states as a consequence of acetate ions incorporation. Flat band potential value estimates assessed the insulating nature of the anodic oxides grown in the acetate buffer solution. Differential capacitance measurements showed that the highest capacitance value was measured for the sample grown on Ta-66%Nb. This capacitance value was higher with respect to those estimated for pure Ta and pure Nb anodic layers and with respect to the same alloy anodized in NaOH solution, i.e., acetate-free anodizing bath
YTTRIUM AND REE SIGNATURE RECOGNIZED IN CENTRAL MEDITERRANEAN SEA (ODP SITE 963) DURING THE MIS 6 – MIS 5 TRANSITION
No full textThe Mediterranean Sea acts as a miniature ocean with the development of its own conveyor belt. It constitutes an ideal location to study and forecast how the marine environment responds to rapid climatic change. Here we present a palaeoenvironmental study carried out on the sediments of ODP Site 963, recovered in the Sicily Channel, the sill which divides the western from the eastern Mediterranean basin. We focused on the transition between the penultimate glacial (MIS 6) and the last interglacial (MIS 5), between approximately 130 and 115 kyr BP. A novel approach is proposed, taking into account centennial-scale geochemical data on major elements, selected trace elements, and yttrium and REE (YREE). This approach was demonstrated to be suitable to recognize both environmental conditions existing during deposition of the studied sequences and to establish whether diagenetic modifications of the original geochemical signature occurred. Our results highlight the delivery of Fe-rich material to the basin, probably from the arid continental environment of southern Sicily. This phenomenon seems to be interrupted in coincidence with the development of Eemian forests at about 126–127 kyr BP in southern Europe. The deposition of weathered products suggests increate humidity in Sicily between 127 and 124 kyr BP. Less oxidizing/more productive conditions characterized the Sicily Channel sea floor between 124 and 119 kyr BP, while sapropel S5 was depositing in the eastern Mediterranean. They are evidenced by the enrichment of heavy REE, the decrease in positive Ce anomaly, and a slight increase in excess barium. This implies that oceanographic processes which led to bottom anoxia in the eastern Mediterranean might have had an impact even on the Sicily
Channel environment
Effect of NaClO disinfection/cleaning on passive films on AISI 316L
Full text link316 L stainless steel samples were passivated in NaClO containing solutions in order to simulate disinfection processes. Passive films were grown at the open circuit potential by immersion in NaClO aqueous solutions at different concentrations and temperature in order to understand how exposure to aggressive environments could affect subsequent corrosion resistance of SSs. In the attempt to study the passive film growth mechanism, in-situ Open Circuit Potential measurements were performed in the same growth solutions. Photoelectrochemical and impedance investigation of passive films was carried out in order to link their solid state properties with their corrosion behaviour
Effect of citrate anion incorporation on dielectric properties of anodic oxide grown on Ti-Si alloy
Full text linkAnodic oxides were galvanostatically grown on sputtered Ti-12at%Si alloy at 5 mA cm-2 up to 50 V in phosphoric acid and sodium citrate aqueous electrolytes in order to investigate the effect of anions incorporation (if any) on dielectric properties of the grown oxides. Photoelectrochemical measurements supported the occurrence of incorporation of citrate anions when anodizing is carried out in a citrate-containing solution. Indeed, two different absorption thresholds were estimated due to energy transitions involving localized states in the mobility gap. Differential capacitance measurements showed higher capacitance values for anodic oxide grown in the citrate-containing solution, with a beneficial effect on the dielectric constant. The increased capacitance can be explained considering the synergistic effect of a more favourable anodizing ratio provided by the presence of Si cations from the bare alloy as well as the incorporation of foreign species due to the inward migration of citrate anions from the electrolyte during the anodizing process
Highly Active and Stable NiCuMo Electrocatalyst Supported on 304 Stainless Steel Porous Transport Layer for Hydrogen Evolution in Alkaline Water Electrolyzer
Full text linkSeveral functionalized porous transport layers with Pt-free electrocatalysts for hydrogen evolution reaction in alkaline conditions, based on Ni, Cu, and Mo, are prepared through electrodeposition onto a 304 stainless steel mesh. Morphological characterization confirms the fabrication of electrodes with high electrochemical surface active area due to the formation of hierarchical nanostructures. Mo presence into the electrocatalysts increases the activity toward the hydrogen evolution reaction. The optimization of electrodeposition process leads to the preparation of highly active NiCuMo electrocatalyst that exhibits near zero onset overpotential and overpotentials of 15 and 113 mV at 10 and 100 mA cm(-2), respectively, in 1 m KOH electrolyte. Moreover, this electrocatalyst shows superior stability with respect to other Pt-free electrocatalysts, reaching 100 h of durability with low overpotentials value demonstrating the successful preparation of very promising functionalized porous transport layers for future-generation alkaline electrolyzers
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